Glossary of Electrical Engineering Terms
- Professor J R Lucas
You are Visitor No to this site at the Department of Electrical Engineering,University of Moratuwa, since its inauguration on 11 December 2001.
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
I would be grateful for any amendments, suggestions or additions to the glossary, so as to benefit the users. email: firstname.lastname@example.org
*absolute value Value of an expression without regard to sign or phase angle.
*absolute zero The temperature where thermal energy is at minimum. -273.15°C or 0 Kelvin.
*ac [see alternating current]
*accessory A device, other than current using equipment, associated with such equipment or with the wiring of an installation.
*acceleration Rate of change of velocity. [Unit: m/s2]
*acceleration due to gravity g Acceleration of a body falling freely in a vacuum as a result of the gravitational pull of the earth. g = 9.807 m/s2
*accumulator Storage battery or secondary cell for storing electricity.
*accuracy Specifies the nearness of the measured value from the true value.
*acid Containing an excess of hydrogen ions over hydroxyl ions.
*acoustics Study of sound.
*a c potentiometer An apparatus for the comparison of a.c. voltages. Balance requires both the magnitude and the phase angle of the unknown voltage to be balanced with the known voltage. This may be done either in cartesian form or in polar form.
*acre Unit of area in the Imperial system. 1 acre = 4047 m2 = 0.4047 hectares
*active element An element capable of generating electrical energy.
*active filter Any filter using an op amp is called an active filter.
*actuator Mechanical part of a limit switch that uses mechanical force to actuate the switch contacts.
*acute angle An angle of less than 90o.
*address The number that uniquely identifies the location of a word in memory.
*adiabatic process taking place without heat entering or leaving the system.
*admittance Reciprocal of impedance. Ratio of the electric current to the voltage. [Unit: siemens or S]
*aerodynamics Study of air moving around solid objects, or air flowing around a stationary structure.
*air conditioning The control of temperature, humidity and the purity of the air. In tropical countries like Sri Lanka, air conditioning only cools the air and not heats it, but in cold countries both modes are available.
*algebraic sum Total of a number of quantities of the same kind, with due regard to sign.
*algorithm A systematic mathematical procedure which enables a problem to be solved in a definite number of steps.
*alkaline Containing an excess of hydroxyl ions over hydrogen ions.
*alloy A composition of two or more metals.
*alphanumeric The collection of numbers, alphabetic characters and symbols.
*alternate sweep A vertical mode of operation for a dual-trace oscilloscope. The signal from the second channel is displayed after the signal from the first channel. Each trace has a complete trace, and the display continues to alternate.
*alternating current, *ac A current whose instantaneous values reverses in regularly recurring intervals of time and which has alternative positive and negative values, the cycle being repeated continuously. The term is commonly used to refer to sinusoidal waveforms.
*alternator A machine (generator) for producing alternating currents or voltages.
*ALU [see arithmetic logic unit]
*ambient temperature The temperature of the surroundings in which the equipment is used or operated.
*ammeter An instrument for measuring electric current.
*ampacity The current-carrying capacity of conductors or equipment, expressed in ampere.
*ampere (A) The ampere is the SI unit of current. It is a fundamental unit. It is defined as that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 meter apart in vacuum, would produce between these conductors a force equal to 2 x 10-7 newton per meter of length .
*ampere hour capacity The quantity of electricity measured in ampere-hour which may be delivered by a cell or battery under specified conditions.
*ampere-turn (AT) Formerly used as the unit of magnetomotive force (mmf). It is the product of the number of turns in a coil and the current in amperes which flows through it. [Note: Since turns is not a unit, the SI Unit of mmf is the ampere]
*amplification Procedure of expanding the strength of a signal.
*amplifier A device or circuit used to increase the power current, and voltage level of a signal.
*amplitude Maximum or peak value of a quantity or wave varying in an oscillatory manner, measured with respect to the reference.
*amplitude modulation, *AM A process whereby the amplitude of the carrier is controlled by the modulating signal.
*analog The branch of electronics dealing with continuously varying quantities.
*analog to digital converter, *A/D converter, *A to D converter A device or circuit used to convert an analog signal to a digital signal across a pair of terminals.
*analogue meter Show a particular (continuous variable) deflection for a given input quantity.
*analogy A likeness in some ways between dissimilar things that are otherwise unlike. Because of the similarity, many of the equations are identical except for a change of variables or subscripts.
*AND gate A digital logic circuit used to implement the AND operation. The output of this circuit is 1 only when each one of its inputs is a 1.
*angstrom A unit used to measure very small lengths, such as wave length. Equal to 10-10 m
*angular velocity w Rate of rotation about an axis. It is the rate of change of angle with time. It is measured either in revolutions per second, revolutions per minute (r.p.m.) or radians per second (rad/s).
*annealing Very slow regulated cooling, especially of metals, to relieve strains set up during heating or other treatment.
*anode positive electrode. The element of an electronic device that receives the flow of electrons.
*antenna A device consisting of spaced elements that are used to receive broadcast signals.
antenna A system of conductors that radiates and or receives electromagnetic waves (radio waves).
*aperture Opening. In optical instruments, it is the size of the opening admitting light.
*apparent power The apparent power of an alternating current circuit is the product of the rms values of the voltage and the current. [Unit: volt-ampere or VA]
*appliance An Item of current using equipment other than a luminaire or an independent motor. These are generally not industrial and normally built in standardized sizes or types, which are installed or connected as a unit to perform one or more functions.
*arc Highly luminous discharge at a very high temperature (around 3000oC). An electric arc is produced when an electric current flows between two electrodes.
*are A metric unit of area, especially with land. Equal to 100 square meter.
*argand diagram A plot of the cartesian co-ordinates (real and imaginary components) or the polar co-ordinates of a complex number on the x-y plane.
*arithmetic logic unit *ALU A digital circuit used in computers to perform arithmetic and logic operations.
*arithmetic progression A series of quantities in which each term differs from the preceding term by a constant difference.
*armature The coil or coils of an electric motor or generator or of an electric apparatus in which a voltage is induced by a magnetic field.
*armoured cable Cable with a metal protective covering.
*arm's reach A zone of accessibility to touch, extending from any point on a surface where persons usually stand or move about to the limits which a person can reach with a hand in any direction without assistance.
*arrester A device placed from phase to ground, or phase to phase, whose nonlinear impedance characteristics provide a path for high-amplitude transients.
*asymmetric Not possessing symmetry. Unequal distribution about one or more axes.
*asynchronous Not synchronous. Especially used with electric machines to denote that the magnetic field and the rotation are not exactly the same.
*atmosphere Unit of pressure corresponding to standard atmospheric pressure. It is taken as the pressure that will support a column of mercury 760 mm high. It is also equal to 1.013 * 105 pa
*atomic mass unit *amu Unit used for expressing masses of isotopes of elements. 1 a.m.u. = 1.661 x 10-27 kg
*attenuation Loss of signal power or amplitude suffered during its transmission through a medium.
*attenuator A passive device used to reduce signal strength.
*atto (a) Decimal sub-multiple prefix corresponding to 10-18
*audio amplifier An amplifier designed to be used in the audio range of frequencies.
*audio frequency A frequency corresponding to audible sound waves, and thus corresponds to a frequency between 20 Hz and 20 kHz.
*automatic transfer switch A switch that automatically transfers electrical loads to alternate or emergency-standby power sources.
*automation The application of mechanical or electronic techniques to minimise the use of manpower in any process.
*autoreclose A feature of certain circuit breakers where they close automatically after a predetermined time after an automatic opening due to a transient fault.
*autotransformer A transformer in which both the primary and the secondary windings share common turns. It provides no isolation.
*autotransformer starter A starter that includes an auto-transformer to furnish reduced voltage for starting an alternating current motor.
*auxiliary contacts The contacts of a switching device, in addition to the main current contacts, that operate with the movement of the latter. They can be normally open (NO) or normally closed (NC) and change state when operated.
*avalanche A build up of particles caused by the collision of a high energy particle with any other form of matter. [Note: The term is derived from the avalanches occurring in a mountain]
*average value The average value of a periodic waveform is defined by taking the mean value of the full-wave rectified waveform.
*avoided capacity cost Avoided capacity cost of constructing new power plants.
*avoided cost Cost that a utility avoids by purchasing power from an independent power producer(IPP), rather than generating power themselves, or constructing new power plants.
A Public Utility calculates avoided costs for each utility, which are the basis upon which IPPs are paid for the electricity they produce. There are two parts to an avoided cost calculation: the avoided capacity cost and the avoided energy cost.
*avoided energy cost Avoided energy cost of fuel and operating and maintaining utility power plants.
*AWG, *American Wire Gage . This term refers to the U.S. standard for wire size.
*axis Line about which a given body or system is considered to rotate.
*axis of symmetry Line about which a given figure is symmetrical.
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*back emf The emf set up in the coil of an electric motor, opposing the current flowing through the coil, when the armature rotates.
*back flashover Flash-over occurring from an object usually at earth potential (such as a tower) to a line conductor due to the potential of the earthed object rising due to lightning.
*balanced three phase A three phase voltage or current is said to be balanced when the magnitude of each phase is the same, and the phase angles of the three phases differ from each other by 120o. A star-connected load or a delta-connected load is said to be balanced when the three arms of the star or the delta have equal impedances in magnitude and phase.
*ballast A Ballast is an electrical device which is required for all discharge lamps. It limits the current through the lamp, preventing damage to both the lamp and the electrical supply.
*ballistic galvanometer Instrument for measuring the total quantity of electricity passing through a circuit due to a momentary current. The period of oscillation of the galvanometer must be long compared with the time during which the current flows.
*ballistics The study of the flight path of projectiles.
*bandpass filter A filter designed to pass all frequencies within a band of frequencies.
*bandstop filter A filter designed to eliminate all frequencies within a band of frequencies.
*bandwidth Commonly defined as the difference between the upper and lower frequencies of the half power points of the response relative to the reference frequency.
*bandwidth The difference between the two dominant critical frequencies of an amplifier. It is also equal to the upper critical frequency when there is no lower critical frequency.
*bandwidth The data a cable can carry measured in bits per second (bps).
*bar Unit of pressure equivalent to 105 pa.
*barometer Instrument for measuring atmospheric pressure.
*barrier A part providing a defined degree of protection against contact with live parts from any usual direction of access.
*base The part of a transistor which separates the emitter from the collector. The middle part of the transistor. permits electrons from emitter to pass through to the collector.
*base The reference quantity in a per-unit or percentage calculation.
*baseline forecast A prediction of future energy needs which does not take into account the likely effects of new conservation programs that have not yet been started.
*base load The minimum load experienced by an electric utility system over a given period of time, which must be supplied at all times.
*base load capacity Capacity of generating equipment operated to serve loads 24-hours per day.
*base load plant A power plant built to operate around-the-clock. Such plants tend to have low operating costs and high capital costs and are best utilized by running continuously. Coal fired and nuclear fuelled plants are typical base load plants.
*basic insulation Insulation applied to live parts to provide basic protection against electric shock and other hazards, which do not necessarily include insulation used exclusively for functional purposes.
*basic insulation level *BIL It defines the insulation level of power system equipment. It is a statement of the impulse (lightning or switching as appropriate) withstand voltage and the short duration power frequency withstand voltage.
*battery A number of primary or secondary cells arranged in series or parallel. A device for turning chemical energy into electrical energy.
*battery backup A battery or a set of batteries in a UPS system. Its purpose is to provide an alternate source of power if the main source is interrupted.
*battery charger A device or a system which provides the electrical power needed to keep the battery backup fully charged.
*BCD *Binary coded decimal . A digital code based on 0 and 1.
*beckmann thermometer Sensitive thermometer for measuring small differences or changes in temperature.
*bel Ten decibels. (see decibel)
*bewley lattice diagram This is a convenient diagram devised by Bewley, which shows at a glance the position and direction of motion of every incident, reflected, and transmitted surge on the system at every instant of time. The diagram overcomes the difficulty of otherwise keeping track of the multiplicity of successive reflections at the various junctions.
*bhp, *BHP [see brake horse power].
*BIL [see basic insulation level]
*bilateral contract A direct contract between the power producer and user or broker outside of a centralized power pool.
*billion A thousand million or 109 (US). Also a million million (British)
*bimetallic strip A strip composed of two different metals welded together in such a way that a rise of temperature will cause it to deform as a result of the unequal expansion. It is used in switches for control of temperature.
*binary cell An element in a computer which can store information by virtue of its ability to remain stable in one of two possible states.
*binary coded decimal [see BCD]
*binary notation A system of numbers which has only two different integer values 0 and 1.
*biomass Any plant-derived organic matter available on a renewable basis, including dedicated energy crops and trees, agricultural food and feed crops, agricultural crop wastes and residues, wood wastes and residues, aquatic plants, animal wastes, municipal wastes, and other waste materials.
*bipolar transistor A transistor where both free electrons and holes are necessary for normal operation.
*bisection Division into two equal parts.
*bit The unit of information in information theory. The amount of information required to specify one of two alternatives 0 and 1.
*bitumen A term covering numerous "tarry" mixtures of hydrocarbons.
*black body Thermal radiator that absorbs completely all incident radiation, whatever the wavelength, the direction of incidence or the polarization.
*blackout A total loss of the commercial electrical power lasting for more than one cycle. Blackouts can result from any of a number of problems, ranging from Acts of God (high winds, storms, lightning, falling trees, floods, etc.) to situations such as cables being cut during excavation, equipment failures at the utility, vandalism, corrosion, etc. Used synonymously with Outage.
*blackout A power loss affecting many electricity consumers over a large geographical area for a significant period of time.
*blanking process of making the trace, or parts of a trace, invisible.
*bleaching Removing the colour from coloured materials by chemical transformation.
*board of trade unit or *BOT unit. Unit of electrical energy (British) supplied to the consumer. Equal to 1 kWh. Energy obtained when a power of 1 kW of power is maintained for 1 hour.
*bode plot Semi-log plots of the magnitude (in decibel) and phase angle of a transfer function (or performance) against frequency.
*boiling The state of a liquid at its boiling point when the maximum vapour pressure of the liquid is equal to the external pressure to which the liquid is subject, and the liquid is freely converted into vapour.
*boiling point The temperature at which the maximum vapour pressure of the liquid is equal to the external pressure. The temperature at which the liquid boils freely under that pressure.
*boiling water reactor or *BWR A nuclear reactor in which water is used as coolant and moderator. Steam is thus produced in the reactor under pressure and can be used to drive a turbine.
*bonding A complete and permanent electrical connection. The permanent joining of metallic parts to form an electrically conductive path that ensures electrical continuity and the capacity to conduct safely any current likely to be imposed.
*bonding conductor A protective conductor providing equipotential bonding.
*boolean algebra A branch of symbolic logic used in computers. Logical operations are performed by operators such as "and", "or", in a way analogous to mathematical signs.
*brake horse power *bhp, *BHP Horse power of an engine measured by the degree of resistance offered by a brake. Represents the useful power that the machine can develop.
*branch An element in a circuit connecting two nodes.
*breakdown The occurrence of a large current between electrodes separated by a dielectric at a critical voltage.
*breaker Short for circuit breaker.
*breeder reactor A nuclear reactor which produces the same kind of fissile material as it burns. For example, a reactor using plutonium as a fuel can produce more plutonium than it uses by conversion of Uranium-238.
*bridge rectifier A full-wave rectifier where the diodes are connected in a bridge circuit (two of them are always conducting at any given time). This allows the current to the load during both the positive and negative alternation of the supply voltage. This is the most common type of rectifier circuit to produce a unidirectional voltage for an alternating input.
*brightness Brightness is the quotient of the luminous intensity of a small element of the source and the area of the element projected on to a plane perpendicular to the given direction. [Unit: candela per unit area or Cd/m2]
*british thermal unit *BTU Quantity of heat required to raise the temperature of 1 pound of water through 1 oF. It is equal to 1054 joule or 251.98 calories.
*broadband communications The result of utilities forming partnerships to offer consumers "one-stop-shopping " for energy-related and high-tech telecommunications services.
*broker A retail agent who buys and sells power. The agent may also aggregate consumers and arrange for transmission and other ancillary services as needed.
*brownout A long duration reduction in the voltage of the ac supply without complete loss of power. Brownouts are usually caused by heavy usage during peak hours and sometimes may even be planned as an energy conservation strategy.
*brownout A controlled power reduction in which the utility decreases the voltage on the power lines, so consumers receive lower quality electricity. Brownouts can be used if total power demand exceeds the maximum available supply.
*buffer registerThe register that holds digital data temporarily.
*building service entryThe point where commercial power enters the building.
*bulk power market Wholesale purchases and sales of electricity.
*bulk power supply Commonly used interchangeably with wholesale power supply. In broader terms, it refers to the aggregate of electric generating plants, transmission lines, and related equipment.
*burning (see combustion)
*busbar A rigid conductor used for connecting together distributors or feeders.
*bushing Bushings are insulators which are used to take high voltage conductors through earthed barriers such as walls, floors, metal, and tanks.
*butterworth filter A filter designed to produce a flat response up to the cut-off frequency.
*bypass capacitor A capacitor placed from a dc signal to ground to remove any ac component of the signal by creating an ac short circuit to ground.
*byte A group of 8 bits.
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*cable Conducting wire or wires separated and surrounded by a dielectric substance or insulation.
*cable channel An enclosure situated above or in the ground, ventilated or closed, and having dimensions which do not permit the access of persons but allow access to the conduits and/or cables throughout their length during and after installation. A cable channel may or may not form part of the building construction.
*cable coupler A means of enabling the connection or disconnection, at will, of two flexible cables. It consists of a connector and a plug.
*cable ducting An enclosure of metal or insulating material, other than conduit or cable trunking, intended for the protection of cables which are drawn in after erection of the ducting.
*cable ladder A cable support consisting of a series of transverse supporting elements rigidly fixed to main longitudinal supporting members.
*cable tray A rigid structure use to support cables. A raceway consisting of a continuous base with raised edges and no covering. A cable tray may or may not be perforated.
*cable trunking A closed enclosure normally of rectangular cross section, of which one side is removable or hinged, used for the protection of cables and for the accommodation of other electrical equipment.
*cable tunnel A corridor containing supporting structures for cables and joints and/or other elements of wiring systems and whose dimensions allow persons to pass freely throughout the entire length.
*calibration The graduation or confirmation of the graduation of an instrument to enable measurements in definite units to be made with it. Thus for example the deflection of a meter can be calibrated to read the current causing the deflection.
*calorie (cal) Unit of quantity of heat. The amount of heat required to raise the temperature of 1 gram of water through 1o C. 1 calorie = 4.184 joule.
*calorific value The calorific value of a fuel is the quantity of heat produced by a given weight of the fuel on complete combustion.
*candela (Cd) The candela is the SI unit of luminous intensity. It is defined as the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 x 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian 
*candle power The candle power of a light source, in a given direction, is the luminous intensity of the source in that direction expressed in terms of the candela.
*capability Maximum load that a generating unit can carry without exceeding ratings.
*capacitance The ability of a system of electrical conductors and insulators to store electric charge when a potential difference exists between the conductors. It is expressed as a ratio of the electrical charge stored to the voltage across the conductors. [Unit: farad or F]
*capacitor A device consisting of two conducting surfaces separated by a layer of insulating material (dielectric)and having the ability of storing electric energy. Also called a condenser, the principal characteristics of which is the capacitance.
*capacity The maximum load a generating unit, generating station, or other electrical apparatus is rated to carry by the manufacturer or can actually carry under existing service conditions.
*capacity charge An charge or assessment based on the amount of capacity being purchased.
*capacity factor The ratio of the electric energy produced by a generating unit to the electrical energy that could have been produced at continuous full-power operations.
*captive consumer A consumer who does not have realistic alternatives to buying power from the local utility, even if that consumer had the legal right to buy from competitors.
*captive generation Generating plant available at CEB customer facilities, but not connected in parallel with the CEB network.
*captive load Load which may be supplied by an Embedded Generator, in addition to the generator auxiliaries, which is within the Generating Company premises.
*carnot's cycle An ideal reversible four step cycle of operations for the working substance of a heat engine.
*carrier In a semiconductor, the mobile electrons or holes which carry charges are called carriers.
*carrier wave A continuous electromagnetic radiation, of constant amplitude and frequency, emitted by a transmitter. By modulation of the carrier wave, oscillations caused at the transmitting end are conveyed to the receiving end.
*cartesian co-ordinates The (x,y) co-ordinates of a point in the plane.
*cartridge fuse It is a fuse inside a cartridge. The fuse wire is usually enclosed in an evacuated glass tube with metal end caps.
*cartridge fuse link A device comprising a fuse element or several fuse elements connected in parallel enclosed in a cartridge usually filled with arc extinguishing medium and connected to terminations (see fuse link).
*cascade connection An arrangement of two or more components or circuits such that the output of one is the input to the next.
*catenary Curve formed by a chain or string hanging from two fixed points.
*cathode Negative electrode. The element of an electronic device that provides the flow of electrons.
*cathode ray oscilloscope *CRO An instrument based upon the cathode ray tube, which provides a visible image of one or more rapidly varying electrical quantities.
*cathode ray tube *CRT An electron-beam tube in which the beam can be focused to a small cross-section on a luminescent screen and varied in both position and intensity to produce a visible pattern. Electric potentials applied to the deflection plates are used to control the position of the beam, and its movement across the screen, in a desired manner.
*celsius (oC) Degrees celsius is an international thermometric scale on which the interval between the triple point of water and the boiling point of water is divided into 99.99 degrees with 0.01° representing the triple point and 100° the boiling point. Celsius degrees are the same size as kelvin but the zero point is shifted to the triple point of water, minus 0.01 K. (0 °C = 273.15 K). Note: The thermodynamic temperature of the triple point of water is 273.16 K
*centi (c) Decimal sub-multiple prefix corresponding to one-hundredth or 10-2. This is not a preferred suffix.
*centigrade Older name for celsius. (see celsius)
*central processing unit [see CPU]
*centre of gravity The centre of gravity of a body is the fixed point through which the resultant force due to the Earth's attraction upon it always passes, irrespective of the position of the body.
*centrifugal force The outward force acting on a body rotating in a circle round a central point.
*centripetal force The radial force imposed by the restraining system, necessary to keep the body moving in a circular path. [Note: the centrifugal force and the centripetal force are equal and opposite].
*ceramic pertaining to products involving the use of clay or other silicates.
*ceylon electricity board *CEB A body corporte duly constituted by Act No. 17 of 1969 of the Democratic Socialist Republic of Sri Lanka.
*CFL [see compact fluorescent lamp]
*cgs system, *centimetre-gram-second system A decimal system which is an earlier form of the metric system.
*chain reaction Any self-sustaining molecular or nuclear reaction, the products of which contribute to the propagation of the reaction.
*channel In television, a portion of the RF spectrum 6 MHz wide which carries the audio and video carriers of the television signal.
*charge (see electric charge)
*chemical reaction The interaction of two or more substances resulting in chemical changes in them.
*chip The finished IC (integrated circuit) is commonly known as a chip.
*choke A coil of low resistance and high inductance used in electrical circuits to pass low frequency or direct components while suppressing (or choking) the higher frequency undesirable alternating currents.
*chopped waveform The standard surge waveform applied is suddenly made zero (chopped) at a predefined time to simulate the surge waveform with flashover.
*chop mode A vertical mode of operation for dual-trace oscilloscopes in which the display is switched between the two channels at some fixed rate much less than the sweep time.
*circuit An electrical circuit is the complete path traversed by an electric current.
*circuit An assembly of electrical equipment supplied from the same origin and protected against overcurrent by the same protective device(s).
*circuit breaker A mechanical switching device capable of making, carrying, and breaking currents under normal conditions. Also making, carrying for a specific time, and automatically breaking currents under specified abnormal circuit conditions, such as those of short circuit. It is usually required to operate infrequently although some types are suitable for frequent operation.
*circuit protective conductor *cpc A protective conductor connecting exposed conductive parts of equipment to the main earthing terminal.
*circular mil A unit of area used in measuring the cross section of fine wire. 1 circular mil corresponds to the area of a circle whose diameter is equal to one-thousandth of an inch. 1 circular mil = 0.5067*10-9 m2
*circularly polarised light Light which can be resolved into two vibrations lying in planes at right angles, of equal amplitude and frequency and differing in phase by 90o.
*clamping level The voltage point at which a surge protector begins to limit surges.
*class I equipment Equipment in which protection against electric shock does not rely on basic insulation only, but which includes an additional safety precaution in that means are provided for the connection of the equipment to the protective earth conductor in the fixed wiring of the installation in such a way that accessible metal parts cannot become live in the event of a failure of basic insulation.
*class II equipment Equipment in which protection against electric shock does not rely on basic insulation only, but which additional safety precautions such as double insulation or reinforced insulation are provided, there being no provision for protective earthing or reliance upon installation conditions.
*class III equipment Equipment in which protection against electric shock relies on supply at SELV and in which voltages higher than those of SELV are not generated.
*clean power Electrical power which has been conditioned and/or regulated to remove electrical noise from the output power.
*clock The basic timing signal in a digital system.
*CMOSA circuit with complementary MOS transistors.
*coal A material occurring in large underground deposits consisting of carbon and various carbon compounds. Formed by the decomposition of vegetable matter over many millions of years.
*coaxial cable A popular transmission medium usually consisting of one central wire surrounded by an insulator and encased in either a wire mesh or an extruded metal sheathing.
*coefficient A number or other known factor or multiplier which measures some specified property of a given substance or algebraic expression.
*coercive force The strength of the magnetic field to which a ferromagnetic material undergoing a hysteresis cycle must be subjected in order to demagnetise the material completely.
*coercivity The coercive force when the material is magnetised to saturation during the cycle.
*cogeneration The production of electricity and the utilization of waste heat, which could be used to produce steam for additional power generation (as in a combined cycle facility).
*coincidence factor The ratio of the coincident maximum demand of two or more loads to the sum of their non-coincident maximum demands for a given period.
The coincidence factor is the reciprocal of the diversity factor and is always less than or equal to one.
*coincidental demand Two or more demands that occur at the same time.
*coincidental peak load Two or more peak loads that occur at the same time.
*collector The electrode in a transistor through which a primary flow of carriers leaves the inter-electrode region. It is called a collected because it collects or gathers the carriers sent into the base by the emitter.
*colour The sensation of colour is the result of the interpretation by the human central nervous system of the effect produced upon the eye by electromagnetic radiation of a particular wave length.
*colour rendering General expression for the effect of an illuminant on the color appearance of objects in conscious or subconscious comparison with their color appearance under a reference illuminant.
*colour temperature The temperature of a full radiator (radiation of all frequencies) which would emit visible radiation of the same spectral distribution as the radiation from the light source under consideration. [Unit kelvin, K]
*combined cycle Combines the gas turbine cycle together with a heat recovery steam cycle that extracts heat from the gas turbine exhaust flow to produce steam.
*combined cycle unit An electricity generating unit consisting of one or more gas (combustion) turbines combined with a steam turbine. The steam turbine utilises the waste exhaust heat from the combustion turbines. This process increases the efficiency of the electric generating unit.
*combined heat and power *CHP A plant that generates electricity and supplies thermal energy, typically steam, to an industrial or other heating requirement.
*combustion or Burning. A chemical reaction or complex chemical reaction, in which a substance combines with oxygen producing heat, light and flame.
*combustion turbine A type of generating unit normally fired by oil or natural gas. The combustion of the fuel produces expanding gases, which are forced through a turbine, thereby generating electricity.
*commercial operation Commercial operation occurs when control of the generator is turned over to the system dispatcher.
*common mode noiseElectrical noise or interference between each of the conductors and ground
*common mode signal A signal that is applied with equal strength to both inputs of a differential amplifier or an operational amplifier.
*common mode tripping Automatic removal of two or more generating plant from the system owing to a cause that is common to both or all the generators.
*commutation angle, *overlap angle The commutation period between two thyristors on the same side of the bridge is the angle by which one thyristor commutates to the next.
*commutator Device for altering the direction of an electric current.
*compact fluorescent lamp, *CFL A fluorescent lamp in compact form that may be conveniently used, in normal holders, in place of the lesser efficient incandescent lamps. The lamp life is significantly longer than incandescent lamps.
*compass The magnetic compass is used to obtain the direction of the earth's magnetic field at a point. In its simplest form consists of a magnetised needle pivoted at its centre so that it is free to move in a horizontal plane.
*competitive bidding This is a procedure that utilities use to select suppliers of new electric capacity and energy. Under competitive bidding, an electric utility solicits bids from prospective power generators to meet current or future power demands. Competitive bidding systems to select more fairly among numerous supply alternatives.
*complex number Consists of two parts, real and imaginary. They obey the ordinary laws of algebra except that their real and imaginary parts must be equated separately.
*complementary MOS,*CMOS A method of reducing the current drain of a digital circuit by combining n-channel and p-channel MOSFETs.
*compound motor A d.c. motor with both a series connected winding as well as a shunt connected winding. Depending on whether the fields of the series winding and the shunt winding aid each other or oppose each other, they are called cumulative compound or differential compound.
*concentric Circles having the same centre.
*condenser (see capacitor)
*conductance The conductance is the reciprocal of the resistance in a resistive circuit, or the real part of the admittance in a complex circuit. It is also the ability of an element to conduct electric current [Unit: siemens or S]
*conductivity Electrical conductivity is the reciprocal of electrical resistivity.
*conductor A wire, cable, rod, tube or bus bar designed for the passage of electrical current.
*conductor An object or substance which conducts electric current.
*conductor loss Loss occurring in a conductor due to the flow of current. Also known as the I2 R loss and copper loss.
*conduit A tubular raceway for power or data cables. Both metallic conduit and non-metallic forms may be used.
*connector The part of a cable coupler or of an appliance coupler which is provided with female contacts and is intended to be attached to the end of the flexible cable remote from the supply.
*conservation Reducing energy consumption and energy waste using a strategy to attain higher efficiency in energy production and utilization, to accommodate behaviour to maximize personal welfare in response to changing prices, and shifting from scarce to more plentiful energy resources.
*conservation of energy The law of conservation of energy states that in any system energy cannot be created or destroyed.
*conservation of mass The law of conservation of mass states that in any system matter cannot be created or destroyed.
*conservation of mass and energy A principle resulting from Einstein's special theory of relativity, which combines the separate laws of conservation of mass and energy. It states that in any system the sum of the mass and energy remains constant.
*conservation of momentum The law of conservation of momentum states that for a perfectly elastic collision, the total momentum of two bodies before impact is equal to their total momentum of two bodies before impact is equal to their total momentum after impact.
*consumer A person or organisation that purchases a product, usually electricity.
*consumer education Efforts to provide consumers with skills and knowledge to use their resources wisely in the marketplace.
*consumer service charge Portion of the consumer's bill which remains the same from month to month. The charge is determined separately from the amount of energy used based on the costs associated with connecting a consumer to the utility's distribution system, including the service connection and metering equipment. This charge also recovers expenses such as meter reading, billing costs, consumer accounting expenses records and collections, and a portion of general plant items such as office space for consumer service personnel.
*consumer unit (may also be known as a consumer control unit or electricity control unit) A particular type of distribution board comprising a co-ordinated assembly for the control and distribution of electrical energy, principally in domestic premises, incorporating manual means of double pole isolation on the incoming circuit(s) and an assembly of one or more fuses, circuit breakers, residual current operated devices or signalling and other devices purposely manufactured for such use.
*contactor An electro-mechanical device that is operated by an electric coil and allows automatic or remote operation to repeatedly establish or interrupt an electrical power circuit. A contactor provides no overload protection as required for motor loads.
*continuity Continuous, without a break.
*contract price Price marketed on a contract basis for one or more years.
*convection Transference of heat through a liquid or gas by the actual movement of the fluid.
*converter A device which changes electrical energy from one form to another, such as from alternating current to direct current.
*convolution The convolution of two signals consists of time-reversing one of the signals, shifting it, and multiplying it point by point with the second signal,and integrating the product. It is used to characterise physical systems.
*copper loss Same as conductor loss. Conductors were traditionally made of copper, hence the name.
*co-ordinated Usually refers to characteristics which are co-ordinated to give optimum performance.
*cooperative electric utility A utility established to be owned by and operated for the benefit of those using its services.
*core loss The Loss occurring in a magnetic core due to alternating magnetisation. It is the sum of the hysteresis loss and the eddy current loss.
*corona discharge Bluish white luminous discharge which appears surrounding a conductor surface at a field exceeding corona inception, but not being sufficient to cause sparking or flash over.
*corona inception Inception of the ionisation of the air on the surface of a conductor, caused by the voltage gradient exceeding a critical value, but not being sufficient to cause sparking or flash over.
*corona loss power loss due to corona.
*corrosion Surface chemical action, especially on metals, by the action of moisture, air or chemicals.
*co-tree of network Complement of the tree of the network.
*coulomb (C) SI unit of electric charge. One coulomb is equal to the amount of charge accumulated in one second by a current of one ampere.
*coulomb's law The force of attraction or repulsion between two point charges is proportional to the magnitude of the charges and inversely proportional to the square of the distance between them.
*coupling coefficient The coupling coefficient of a pair of coils is a measure of the magnetic coupling between two coils.
*coupling capacitorA capacitor used to transmit an ac signal from one node to another.
*CPU An acronym used for the central processing unit of a computer.
*creepage distance Shortest path along the surface of insulating material between two conductive parts.
*crest factor The ratio of the peak or maximum value of a wave, to the r.m.s. value.
*CRO [see cathode ray oscilloscope]
*cross-subsidization The transfer of assets or services from the regulated portion of an electric utility to its unregulated affiliates to produce an unfair competitive advantage.
Cross-subsidy can refer to one rate class (such as industrial consumers) subsidizing the rates of another class (such as residential consumers).
*critical damping Critical damping of a measuring instrument causes the equilibrium deflection to be reached in the shortest possible time, with the oscillations of the needle being quickly damped out. [Note: Under damped instruments have their needles oscillating for some time, while over damped instruments take a long time to reach the final equilibrium deflection]
*critical mass The minimum amount of fissile material required in a nuclear reactor to sustain a chain reaction.
*cross-bonding A method of connecting the sheaths of single core cables in a three phase system in order to reduce the circulating currents flowing in the sheaths.
*CRT [see cathode ray tube]
*cumulo-nimbus cloud Thunder cloud from which lightning strikes originate.
*curie Measure of the activity of a radioactive substance. It is defined in terms of the rate of decay of a quantity of a radioactive isotope.
*current [see electric current]
*current carrying capacity of a conductor The maximum current which can be carried by a conductor under specified conditions without its steady state temperature exceeding a specified value.
*current balance Instrument for the determination of an electric current in absolute electromagnetic units.
*current rating This is the maximum current, which the fuse will carry for an indefinite period without undue deterioration of the fuse element.
*current source A source which essentially maintains the source current at a predefined value almost independent of the load conditions.
*current transformer An instrument transformer specifically designed to give an accurate current ratio for measurement and/or control purposes. They are always connected in series with the circuit (like an ammeter) and hence should never be allowed to have their secondary to be on open circuit to avoid saturation
*cycle One complete set of values through which an alternating voltage or current passes successively.
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*daily peak The maximum amount of power or energy or service demanded in one day from a company or utility service.
*damping Decrease in the amplitude of an oscillation or wave motion with time.
*danger Risk of injury to persons (and livestock where expected to be present) from: (i) fire, electric shock and bums arising from the use of electrical energy, and (ii) mechanical movement of electrically controlled equipment, in. so far as such danger is intended to he prevented by electrical emergency switching or by electrical switching for mechanical maintenance, of non electrical parts of such equipment.
*data Information in numeric, alphanumeric, or other form.
*data processing equipment Electrically operated machine units which, separately or assembled in systems, accumulate, process and store data. Acceptance and divulgence of data may or may not be by electronic means.
*dc [see direct current]
*dc potentiometerA potentiometer in which the supply is a battery and the balance is under d.c. conditions.
*decade A factor of 10.
*deci (d) Decimal sub-multiple prefix corresponding to one-tenth or 10-1. This is not a preferred suffix.
*decibel One tenth of a bel. A unit which compares levels of power in logarithmic form. Two power levels p1 and p2 are said to differ by n decibels given by n = 10 log10 p2/p1
*decibel In the case of sound, the intensity is often measured in decibel with reference to the lowest audible note of the same frequency.
*defibrillation The use of electric shock to stop abnormally fast heart rhythms. Electrical current is used to restore the heart's natural pacemaker function which resumes a normal heartbeat. The shock is administered through electrodes placed on the chest wall (external defibrillation) or in the heart (internal defibrillation).
*defibrillator The machine or device that produces the electric shock current for defibrillation
*deflection Movement of an indicating needle.
*degree celsius(oC) - see celsius
*deka (da) Decimal multiple prefix corresponding to ten or 10. This is not a preferred suffix.
*delay angle or *control angle The control angle for rectification (also known as the ignition angle) is the angle by which firing is delayed beyond the natural take over for the next thyristor.
*delta connection A method of connecting three elements of a three-phase electrical system in a closed triangle or delta, and with the three phases being taken from the corners of the triangle.
*demand The rate at which electric energy is delivered to or by a system, part of a system, or a piece of equipment. It is expressed in kilowatts, kilovoltamperes or other suitable unit at a given instant or averaged over any designated period of time. The primary source of "Demand" is the power-consuming equipment of the customers.
*demand charge The sum to be paid by a large electricity consumer for its peak usage level.
*demand factor The ratio of the maximum demand of a system, or part of a system, to the total connected load of a system or the part of the system under consideration.
*demand-side management (DSM)The planning, implementation, and monitoring of utility activities designed to influence customer use of electricity in ways that will produce desired changes in a utility's load shape. Utility programs falling under the umbrella of DSM include: load management, customer generation, and innovative rates. These changes must produce benefits to both the utility and its customers.
*demagnetisation The process of removing the magnetic properties from a material.
*demodulation The process or separating information from a modulated carrier wave.
*density The mass of unit volume of a substance. [Unit: kg/m3].
*dependable capacity The system's ability to carry the electric power for the time interval and period specified.
Dependable capacity is determined by such factors as capability, operating power factor and portion of the load the station is to supply.
*depreciation, straight-line Straight-line depreciation takes the cost of the asset less the estimated salvage value and allocates the cost in equal amounts over the asset's estimated useful life.
*derating factor A value that tells how much to reduce the power rating of a device for each degree above the reference temperature.
*deregulation The elimination of regulation from a previously regulated industry or sector of an industry.
*derived units Units of physical measurement, other than the fundamental units, but derived from these.
*designated agent An agent that acts on behalf of a transmission provider, consumer or transmission consumer as required under the tariff.
*design current (of a circuit) The magnitude of the current (rms value for a.c.) to be carried by the circuit in normal service.
*detector An instrument to detect the unbalance in a bridge circuit.
*device A unit of an electrical system that is intended to carry but not utilize electric energy.
*diacA silicon bilateral device used to gate other devices such as triacs.
*dielectric Non-conductor of electricity. An insulator. Substance in which an electric field gives rise to no net flow of electric charge but only to a displacement of charge.
*dielectric constant Relative permittivity. It is the ratio of the capacitance of a capacitor with the given material as dielectric, to the capacitance of the same capacitor with vacuum (or air) as the dielectric.
*dielectric heating A form of heating in which electrically insulating material is heated by being subjected to an alternating electric field. Results from energy being lost by the field to electrons within the atoms and molecules of the material.
*dielectric loss Loss occurring in the leakage resistance of the dielectric.
*dielectric strength The ability of a dielectric material of specified thickness to withstand high voltages without breaking down.
*diesel oil The oil left after petrol and kerosene have been distilled from crude petroleum. Used as a fuel in diesel engines.
*difference amplifier A device that amplifies the difference between two inputs. It rejects any signals common to the two input.
*differentiator An op amp whose output is proportional to the rate of change of the input signal.
*diffuse reflection Diffusion by reflection in which, on the macroscopic scale, there is no regular reflection.
*diffuse transmission Transmission in which, on the macroscopic scale, there is no regular transmission.
*diffused lighting Lighting in which the light on the working plane or on an object is not incident predominantly from a particular direction.
*digital meter Show a discrete reading, in the form of a decimal number, for a given input quantity.
*digital to analog converter or *D/A converter or *D to A converter A device or circuit used to convert a digital signal to an analog signal across a pair of terminals.
*dimensions of unit The dimensions of a physical quantity are the powers to which the fundamental units expressing that quantity are raised.
*diode Simplest and most fundamental non-linear circuit element. It is a two terminal device which only allows current to flow in one direction.
*direct current, *dc An electric current flowing always in the same direction from positive to negative poles.
*direct contact Contact of persons or livestock with live parts.
*direct energy conversion Production of electricity from an energy source without transferring the energy to a working fluid or steam.
For example, photovoltaic cells transform light directly into electricity. Direct conversion systems have no moving parts and usually produce direct current.
*direct lighting Lighting by means of luminaires with a light distribution such that 90 to 100 per cent of the emitted luminous flux reaches the working plane direct, assuming that this plane is unbounded
*disaggregation The functional separation of the vertically integrated utility into smaller, individually owned business units (i.e. generation, dispatch/control, transmission, distribution).
*discharge Electrical discharge can occur by the release of the electric charge stored in a capacitor through an external circuit. It can also occur by the breakdown of gaseous dielectrics within solid dielectrics on the application of a field.
*discharge current The surge current that flows through the surge diverter during spark over or operation.
*discharge lamp Lamp in which the light is produced, directly or indirectly, by an electric discharge through a gas, a metal vapor, or a mixture of several gases and vapors.
*discharge voltage [see residual voltage]
*disconnecting means A device or group of devices, or other means whereby all the ungrounded conductors of a circuit can be disconnected simultaneously from their source of supply.
*disconnector A mechanical switching device which, in the open position, complies with the requirements specified for isolation. A disconnector is otherwise known as an isolator.
*discount/interest Rate The discount rate is used to determine the present value of future or past cash flows.
The rate accounts for inflation and the potential earning power of money.
*discrimination The ability to discriminate. The characteristics of protective devices must be such that a fault on one circuit will not disconnect another circuit.
*disk A memory device which uses a magnetic media for the storage of information. Disk, as a term, has expanded into other areas often used to describe the shape of the storage media, that is: floppy disk, compact disk, laser disk, or hard disk.
*display The visual representation of a signal on a screen.
*distortion An undesired change in waveform. Distortion is a term that describes abnormal wave shapes.
*distributed generation A distributed generation system involves small amounts of generation located on a utility's distribution system for the purpose of meeting local peak loads and/or displacing the need to build additional local distribution lines.
*distribution Outside a building distribution refers to the process of delivering power from the transmission system to the premises. Inside the building, distribution is the process of using feeders and circuits to provide power to devices.
*distribution board An assembly containing switching or protective devices (e.g. fuses, circuit breakers, residual current operated devices) associated with one or more outgoing circuits fed from one or more incoming circuits, together with terminals for the neutral and protective circuit conductors. It may also include signalling and other control devices. Means of isolation may be included in the board or may be provided separately.
*distribution company *Disco The regulated electric utility entity that constructs and maintains the distribution wires connecting the transmission grid to the final consumer.
The Disco can also perform other services such as aggregating consumers, purchasing power supply and transmission services for consumers, billing consumers and reimbursing suppliers, and offering other regulated or non-regulated energy services to retail consumers. The "wires" and "consumer service" functions provided by a distribution utility could be split so that two totally separate entities are used to supply these two types of distribution services.
*distribution system The portion of an electric system (after the transmission system) that is dedicated to delivering electric energy to an end user.
*distribution line This is a line or system for distributing power from a transmission system to a consumer. It is any line operating at less than 69,000 volt.
*distributor A person who distributes electricity to consumers using electrical lines and equipment that he owns or operates.
*diversity exchange Exchange of capacity or energy between systems that have peak loads occurring at different times.
*diversity factor The ratio of the sum of the non-coincident maximum demands of two or more loads to their coincident maximum demand for the same period.
*diversity factor The ratio of the sum of the maximum power demands of the subdivisions, or parts of a system, to the maximum demand of the whole system or of part of the system under consideration.
*donor A type of impurity that adds electrons to the atoms of a semiconductor substance.
*dot notation A notation used to denote similar ends of mutually coupled coils.
*double exponential waveform A waveform obtained by taking the difference of two exponential waveforms. Usually they have time constants which are highly different to give a waveform with fast rise time and relatively slow overall decay.
*double insulation Insulation comprising both basic insulation and supplementary insulation.
*DRAM, *Dynamic RAM A type of semiconductor memory that stores data as capacitor charges that need to be refreshed periodically.
*drive A machine used to drive or cause rotation in a piece of apparatus.
*dry location A location not normally subject to dampness or wetness. A location classified as dry may be temporarily subject to dampness or wetness, as in the case of a building under construction.
*DSM [see demand side management]
*duality principle The duality principle establishes an analogy between similar variables when governed by analogous differential equations. For example, series circuits and parallel circuits are analogous if resistance is replaced by conductance, conductance by resistance, inductance by capacitance or vice versa, current by voltage or vice versa. There is also an analogy between electrical and magnetic circuits.
*dual channel oscilloscope An oscilloscope that has two independent input connectors and vertical sections and can display them simultaneously.
*duct A closed passageway formed underground or in a structure and intended to receive one or more cables which may be drawn in.
*dustproof Constructed or protected so that dust will not interfere with its successful operation.
*dynamo Device for converting mechanical energy into electrical energy. The mechanical energy of rotation is converted into electrical energy in the form of a current in the armature.
*dynamometer instrument This instrument is also a moving coil instrument except that in this case, the permanent magnet is replaced by a pair of fixed coils to give the fixed field.
*dyne Unit of force in the c.g.s. system. 1 dyne = 10-5 N
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*earth The conductive mass of the Earth, whose electric potential at any point is conventionally taken as zero.
*earthing Connecting a conductor, or exposed conductive parts of an installation, to the Earth to maintain earth potential.. The Earth is taken as the reference.
*earth electrode A conductor or group of conductors in intimate contact with, and providing an electrical connection to, Earth.
*earth electrode resistance The resistance of an earth electrode to Earth.
*earth fault current A fault current which flows to Earth.
*earth fault loop impedance The impedance of the earth fault current loop starting and ending at the point of earth fault. The earth fault loop comprises the following, starting at the point of fault: the circuit protective conductor, and the consumer's earthing terminal and earthing conductor, and for TN systems, the metallic return path, and for TT and IT systems, the earth return path, and the path through the earthed neutral point of the transformer, and the transformer winding, and the phase conductor from the transformer to the point of fault.
*earth leakage Flow of current from a live conductor to earth in an unintended path through the insulation.
*earth leakage current (see Protective conductor current).
*earth leakage circuit breaker, *elcb The elcb is designed to protect both equipment and users from fault currents between the live and earth conductors by detecting the rise in voltage of the frame earth connection with respect to a reference earth.
*earthed concentric wiring A wiring system in which one or more insulated conductors are completely surrounded throughout their length by a conductor, for example a metallic sheath, which acts as a PEN conductor.
*earthed equipotential zone A zone within which exposed conductive parts and extraneous conductive parts are maintained at substantially the same potential by bonding, such that, under fault conditions, the differences in potential between simultaneously accessible exposed and extraneous conductive parts will not cause electric shock.
*earthing Connection of the exposed conductive p" of an installation to the main earthing terminal of that installation. Earthing conductor. A protective conductor connecting the main earthing terminal of an installation to an earth electrode or to other means of earthing.
*echo Effect produced when sound is reflected from a surface sufficiently far away for the reflected sound to be separately distinguishable.
*economic dispatch The distribution of total generation requirements among alternative sources for optimum system economy with consideration to both incremental generating costs and incremental transmission losses.
*economic efficiency A term that refers to the optimal production and consumption of goods and services. This generally occurs when prices of products and services reflect their marginal costs. Economic efficiency gains can be achieved through cost reduction, but it is better to think of the concept as actions that promote an increase in overall net value (which includes, but is not limited to, cost reductions).
*economic energy Energy produced and substituted for the traditional but less economical source of energy. Economic energy is usually sold without capacity and is priced at variable costs plus administration costs.
*eddy currentsLocalized induced circulating electric currents set up in metal parts not normally meant to carry currents due to changes in electromagnetic fields. Also known as Foucault currents.
*eddy current loss power loss in magnetic materials due to eddy currents. This loss is proportional to the square of the thickness and hence can be reduced by the use of laminations.
*effective earthing Effective earthing avoids having dangerous potentials on the equipment even during electrical faults and also ensures the proper operation of electrical protection equipment during fault conditions. A system is said to be effectively earthed if the factor of earthing does not exceed 80%, and non-effectively earthed if it does.
*effective value The effective value of a periodic waveform (current or voltage) is the equivalent constant waveform that delivers the same average power to a resistor as the periodic waveform.
*efficacy Relative ability to produce a desired effect.
The amount of energy service delivered per unit of energy input. [often used in reference to lighting systems - see luminous efficacy]
*efficiency Means of getting the same or better service while using fewer resources.
*efficiency of a machine The ratio of the output energy to the input energy, usually expressed as a percentage. The efficiency of a machine can never exceed unity or 100%.
*EF protection: *earth fault protection
*elasticity of demand The ratio of the percentage change in the quantity demanded of a good to the percentage change in price.
*elastic modulus or modulus of elasticity The ratio of the stress to the strain in a given material.
*electrical degree One cycle in a rotating electric machine is accomplished when the rotating field moves from one pole to the next pole of the same polarity. There are 360 electrical degrees in this time period. [i.e. for each pair of poles there are 360 electrical degrees. In a machine with more than one pair of poles, one electrical cycle is completed for each pair of poles in the mechanical cycle; or the electrical degrees per revolution is obtained by multiplying the number of pairs of poles by 360.]
*electrical heating The heating characteristic of an electric current is used extensively in industrial and domestic heating applications. Electric heating can be obtained from (a) resistance heating, (b) induction heating, (c) eddy current heating (d) dielectric heating, and (e) electric arc heating.
*electric capacity The ability of a power plant to produce a given output of electric energy at an instant in time.
*electrical equipment Any item for such purposes as generation, conversion, transmission, distribution or utilisation of electrical energy, such as machines, transformers, apparatus_ measuring instruments, protective devices, wiring systems, accessories, appliances and luminaires.
*electric charge Charge is an electrical property of the atomic particles of which matter is made. The elementary particle called the electron is negatively charged while the proton is equally positively charged so that normal matter is electrically neutral. [Unit: coulomb or C]
*electric circuit An interconnection of electrical elements.
*electric current An electric current flows through a conductor when there is an overall movement of charge through it and is measured as the time rate of change of charge. [Unit: ampere or A]
*electric distribution company The company that owns the power lines and equipment necessary to deliver purchased electricity to the consumer.
*electric field The electric field is a region in which a force is exerted on a charged particle. It is defined as the force acting on a unit positive charge placed at that point.
*electric fluxA measure of the electricity coming out from a charged surface. [Unit: coulomb]
*electric flux density Electric flux passing through unit area perpendicular to the direction of the flux. [Unit: C/m2]
*electricity A form of energy produced by the flow of particles of matter and consists of commonly attractive positively (protons [+]) and negatively (electrons [-]) charged atomic particles. A stream of electrons, or an electric current.
*electric light Illumination produced by the use of electricity. The light sources may be of the incandescent, fluorescent, gas discharge or LED type.
*electric plant (physical) A facility that contains all necessary equipment for converting energy into electricity.
*electric power Electric power is given by the product of the potential difference and the current.
*electric power supplier Non-utility provider of electricity to a competitive marketplace.
*electric motor Device for converting electrical energy into mechanical energy in the form of rotation.
*electric polarizationA type of polarisation occurring in a dielectric.
*electric shock A dangerous physiological effect resulting from the passing of an electric current through a human body or livestock.
Injury to the skin or internal organs that results from exposure to an electrical current. Electric shock occurs when the body becomes a part of an electric circuit. The electrical current must enter the body at one point and leave at another. The human body is a good conductor of electricity. Direct contact with electrical current can be potentially fatal. While some electrical shocks may appear not to be serious, there still may be serious internal damage, especially to the heart and brain.
*electric system All of the elements needed to distribute electrical power. It includes overhead and underground lines, poles, transformers, and other equipment.
*electric utility An enterprise engaged in the production and/or distribution of electricity for use by the public.
*electrical installation (abbr: Installation) An assembly of associated electrical equipment supplied from a common origin to fulfil a specific purpose and having certain co-ordinated characteristics.
*electrically independent earth electrodes Earth electrodes located at such a distance from one another that the maximum current likely to flow through one of them does not significantly affect the potential of the other(s).
*electric welding In electrical welding, a very high electric current produces the heat needed to melt the material and join two metals together.
*electrochemical breakdown In a practical insulation ions may arise from dissociation of impurities or from slight ionisations of the insulating material itself. When these ions reach the electrodes, reactions occur in accordance with Faraday's law of electrolysis, but on a much smaller scale. The products of the electrode reaction may be chemically or electrically harmful and in some cases can lead to rapid failure of the insulation.
*electrodynamic The interaction of magnetism and electrical current.
*electrodynamometer An instrument dependant on the interaction of the electromagnetic fields of fixed and movable coils. It can measure current, voltage or power in both d.c. and a.c.
*electrolytic capacitor (condenser) An electrical capacitor in which one electrode is a metal foil coated with a thin layer of the metal oxide, and the other electrode is a non-corrosive salt paste. The metal foil is maintained positive to prevent the removal of the oxide film by the hydrogen liberated.
*electrolysis Electric current passing through an electrolyte which produces chemical changes in it.
*electrolyte An electrically conductive fused salt or a solution where the charge is carried by ionic movement.
*electromagnet Temporary magnet formed by winding a coil of wire round a piece of soft iron, when an electric current flows through the wire, the iron becomes a magnet.
*electromagnetic Relating to a magnetic field created by an electric current.
*electromagnetic damping Electromagnetic damping is produced by the induced effects when the coil moves in the magnetic field and a closed path is provided for the currents to flow.
*electromagnetic field Electric and magnetic force field that surrounds a moving electric charge.
*electromagnetic interference EMI A term that describes electrically induced noise or transients, usually at frequencies above 1 MHz.
*electromagnetic relay A relay controlled by electromagnetic means, to open and close electric contacts.
*electromagnetic spectrum The range of frequencies over which electromagnetic radiations are propagated.
*electromotive force emf The source of electrical energy required to produce an electric current in a circuit. Defined as the rate at which electrical energy is drawn from the source and dissipated in a circuit when unit current is flowing in the circuit. [Unit: volt or V]
*electron An elementary particle having a negative charge and a constituent of all atoms. It has a rest mass of 9.1095x10-31 kg and a charge of 1.60219x10-19 C
*electron affinity The tendency of an atom or molecule to accept an electron and form a negative ion. The halogens have high electron affinities.
*electron emission The escape of electrons from certain materials.
*electronic ballast A ballast which uses semi-conductor components to increase the frequency and control the operation of a fluorescent lamp. Fluorescent system efficiency is increased due to the higher frequency.
*electron gun The source of electrons in a cathode ray tube. Consists of a cathode emitter of electrons, an anode with an aperture through which the beam of electrons can pass, and one or more focussing and control electrodes.
*electron lens A system of electric or magnetic fields used to focus a beam of electrons in a manner analogous to an optical lens.
*electron volt Unit of energy used in dealing with subatomic particles. It is the increase in energy or the work done on an electron when passing through a potential rise of 1 volt. 1 eV = 1.602 x 10-19 J
*electrostatic Relating to an electric field created by an electric charge.
*electrostatic generator A machine designed for the continuous separation of electric charge. An example is the Van de Graaf Generator.
*electrostatic meter These basically work on the principle that the force (or torque) of attraction is proportional to the product of the charges and the force is proportional to the square of the voltage. Thus this meter reads the mean square value and hence is calibrated to read the root mean square value. The electrostatic meter is basically a voltmeter.
*ellipsoid A solid figure traced out by an ellipse rotating about one of its axes.
*embedded generator A single generator, or a group of generators, connected to the distribution network of the CEB, at voltages between 400 V and 33 kV.
*embedded generation (*dispersed generation or *distributed generation) Plant which is connected directly to (embedded within) the utility's distribution network rather than to the high voltage transmission system (or nation grid). They are generally considered to be less than 10-100 MW in capacity and are not centrally planned or dispatched.
They are commonly found on industrial sites and in areas of high renewable energy source such as wind, hydro and solar.
*emergency lightingLighting provided for use when the supply to the normal lighting fails.
*emergency power An independent reserve source of electric power which, upon failure or outage of the normal power source, provides stand-by electric power.
*emergency stopping Emergency switching intended to stop an operation.
*emergency switching An operation intended to remove, as quickly as possible, danger, which may have occurred unexpectedly.
*emf [see electromotive force]
*emitter The part of the transistor that is the source of carriers. For npn transistors, the emitter sends free electrons into the base, whereas for pnp transistors, the emitter sends holes into the base.
*empirical Based upon the results of experiment and observation only.
*enclosure The cabinet or specially designed box or fence or walls in which electrical controls and apparatus are housed, to prevent personnel from accidentally contacting energized parts or to protect the equipment from physical damage.
A part providing protection of equipment against certain external influences and in any direction protection against direct contact.
*encoderA digital circuit that converts information into coded form.
*end-use The specific purpose for which electric is consumed (i.e. heating, cooling, cooking, etc.).
*energized Electrically connected to a source of voltage
*energy Capacity to do work. [Unit: joule or J]
In the electric power industry, energy is more narrowly defined as electricity supplied over time, expressed in kilowatt-hours.
*energy audit A review of the customer's electricity and/or gas usage often including recommendations to alter the customer's electric demand or reduce energy usage. An audit usually includes a visit to the customer's facility.
*energy charge The amount of money owed by an electric consumer for kilowatt-hours consumed.
*energy consumption The amount of energy consumed in the form in which it is acquired by the user. The term excludes electrical generation and distribution losses outside his point of entry of supply.
*energy costs Costs, such as for fuel, that are related to and vary with energy production or consumption.
*energy efficiency programs Programs that reduce consumption.
*energy meter Instrument to measure energy, usually a house service meter.
*energy source A source that provides the power to be converted to electricity.
*energy use Energy consumed during a specified time period for a specific purpose (usually expressed in kWh).
*engine A device for converting one form of energy into another, especially for converting other forms of energy into mechanical (kinetic) energy.
*entrance cable/service entrance conductor Cable running outside of a consumer's house into the meter. This cable is owned by the consumer and its maintenance is the consumer's responsibility.
*environmental attributes Environmental attributes quantity the impact of various options on the environment. These attributes include particulate emissions, SO2 or Nox, and thermal discharge (air and water).
*EPROM Erasable programmable read only memory.
*equilateral Having all the sides equal in length. Equilateral triangle is one which has all three sides equal.
*equilibrium State of balance between opposing forces or effects.
*equipment A general term including material, fittings, devices, appliances, luminaires (fixtures), apparatus, and the like used as a part of, or in connection with, an electrical installation.
*equipotential bonding Electrical connection maintaining various exposed conductive parts and extraneous conductive parts at substantially the same potential.
*equipotential lines and surfaces Lines and surfaces having the same electric potential.
*erg Unit of work or energy in the c.g.s. system of units. 1 erg = 10-7 J
*erosion In a surface discharge, if the products of decomposition are volatile and there is no residual conducting carbon on the surface, the process is simply one of pitting and is known as erosion. Erosion occurs in organic materials.
*error An error is a deviation from the true value of the measured variable.
*evaporation Conversion of a liquid into vapour, without necessarily reaching the boiling point.
*even symmetry or *even function A function has even symmetry when its plot is symmetrical about the vertical axis. f(t) = f(-t)
*exa (E) Decimal multiple prefix corresponding to 1018
*exbi (Ei)Binary multiple prefix corresponding to gigabinary or 260 or (210)6 or 10246. [IEC 1998]
*excitation The addition of energy to a nucleus, an atom or a molecule transferring it from its ground state to a higher energy level. The excitation is the difference in energy between the ground state and the excited state.
*export of electrical energy - Supply of Electrical Energy by a Generator to the CEB system.
*exponent The number indicating the power of a quantity.
*exposed conductive part A conductive part of equipment which can be touched and which is not a live part but which may become live under fault conditions.
*extraneous conductive part A conductive part liable to introduce a potential, generally earth potential, and not forming part of the electrical installation.
*extrapolation Filling in values or terms of a series on either side of the known values thus extending the range of values.
*extrinsic semiconductor A semiconductor in which the carrier density results mainly from the presence of impurities or other imperfections, as opposed to an intrinsic semiconductor in which the electrical properties are characteristics of the ideal crystal.
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*factor of earthing This is the ratio of the highest r.m.s. phase-to-earth power frequency voltage on a sound phase during an earth fault to the r.m.s. phase-to-phase power frequency voltage which would be obtained at the selected location without the fault. This ratio characterises, in general terms, the earthing conditions of a system as viewed from the selected fault location.
*fahrenheitTemperature scale in which the melting point of ice is taken as 32 oF and the boiling point of water under standard atmospheric pressure (760 torr) as 212 oF. A Fahrenheit degree is 1/180 of the difference between these two temperatures.
*farad (F) SI unit of electric capacitance. One farad is defined as the ability to store one coulomb of charge per volt of potential difference between the two conductors.
*faraday Quantity of electricity required to liberate or deposit 1 gram-equivalent of an ion. 1 Faraday = 96,490 coulomb.
*fast neutrons Neutrons resulting from nuclear fission that have lost little of their energy by collision and therefore travel at high speeds. It is usual to define neutrons with energies in excessof 0.1 MeV as fast.
*fatigue of metals Deterioration of metals owing to repeated stresses above a certain critical value, accompanied by changes in the crystalline structure of the metal.
*fault A circuit condition in which current flows through an abnormal or unintended path.
This may result from ah insulation failure or a bridging of insulation. Conventionally the impedance between live conductors or between live conductors and exposed or extraneous conductive parts at the fault position is considered negligible.
*fault current A current resulting from a fault.
*feedback The term is generally applied to electronic amplifiers to which a portion of the output energy is used to reduce or increase the amplification, by reacting on an earlier stage according to the relative phase of the return.
*feeder All circuit conductors between the service equipment, the source of a separately derived system, or other power supply source and the final branch-circuit overcurrent device.
*field The region in which an electrically charged body (electric field), or a magnetised body (magnetic field) exerts its influence.
*field coil A coil of wire used for magnetising an electromagnet.
*field emission The emission of electrons from an unheated surface as a result of a strong electric field existing at that surface.
*field-effect transistor *FET A three terminal semiconductor device that depends on the action of an electric field to control its conductivity. In a "FET" the current is from source to drain because a conducting channel is formed by a voltage field between the gate and the source.
*femto (f) Decimal sub-multiple prefix corresponding to 10-15.
*fermi A unit of length used in nuclear physics. 1 fermi = 10-15 meter.
*fermi-dirac statistics The branch of statistical mechanics used with systems of identical particles which have the property that their wave function changes sign if any two particles are interchanged.
*ferrimagnetism The type of magnetism occurring in materials in which the magnetic moments of adjacent atoms are anti-parallel, but of unequal strength, or in which the number of magnetic moments oriented in one direction outnumber those in the reverse direction. Typical ferrimagnetic materials are the ferrites.
*ferrites A group of ceramic materials which exhibit the property of ferrimagnetism. As they are basically electrical insulators, they do not suffer from the effects of eddy currents.
*ferroelectrics Dielectric materials which exhibit properties such as hysteresis which are usually properties of ferromagnetic materials.
*ferromagnetism Ferromagnetism is due to unbalanced electron spin in the inner electron orbits of the elements concerned giving the atoms a resultant magnetic moment. Ferromagnetic materials have very large magnetic permeabilities which vary with the strength of the applied field.
*ferroresonance Resonance resulting when the iron core of an inductive component of an LC circuit is saturated, increasing the inductive reactance with respect to the capacitance reactance.
*fertile material Isotopes which can be transformed into fissile material by the absorption of neutrons.
*FET [see field effect transistor].
*financial attributes Attributes that measure the financial health of the company. Key financial attributes include capital requirements, earnings per share of common equity, capitalization ratios, and interest coverage ratios.
*firm energy Power or power-producing capacity covered by a commitment to be available at all times during the period.
*fixed cost The annual (or sometimes monthly) costs associated with the ownership of property such as depreciation, taxes, insurance, and the cost of capital.
*filament A thin thread. A wire of high melting point heated by the passage of current inside a vacuum tube, incandescent lamp or other similar device.
*filter A circuit that is designed to pass signals with desired frequencies and reject or attenuate other frequencies.
*final circuit The final circuits in an electrical wiring system.
A circuit connected directly to current using equipment, or to a socket outlet or socket outlets or other outlet points for the connection of such equipment.
*fissile material Isotopes which are capable of undergoing nuclear fission. Sometimes the term is restricted to apply only to isotopes which are capable of undergoing fission upon impact with a slow neutron.
*fission products Both stable and unstable isotopes produced as a result of nuclear fission.
*fixed equipment Equipment designed to be fastened to a support or otherwise secured in a specific location.
*flame Glowing mass of gas produced during combustion.
*flashover Arcing that is caused by the high voltage breakdown of insulation between two conductors, resulting in high current.
*flash point The lowest temperature at which a substance gives off sufficient inflammable vapour to produce a momentary flash when a small flame is applied.
*flat rate A fixed charge for goods and services that does not vary with changes in the amount used, volume consumed, or units purchased.
*fleming's rules If the forefinger, second finger, and thumb of the right hand are extended at right angles to each other, the forefinger indicates the direction of flux, the second finger the direction of the emf and the thumb the direction of the motion in an electric generator. If the left hand is used, the fingers indicate the conditions for an electric motor.
*flexible cable A cable whose structure and materials make it suitable to be flexed while in service.
*flexible cord A flexible cable in which the cross sectional area of each conductor does not exceed 4 mm2.
*flexible load shape The ability to modify the utility's load shape on short notice. When resources are insufficient to meet load requirements, load shifting or peak clipping may be appropriate.
*flexible retail pool a model for the restructured electric industry that features an Independent System Operator (ISO) operating in parallel with a commercial Power Exchange, which allows end-use consumers to buy from a spot market or "pool" or to contract directly with a particular supplier.
*flexible wiring system A wiring system designed to provide mechanical flexibility in use without degradation of the electrical components.
*flip flop A memory device capable of storing a logic level.
*floppy disk Flexible magnetic disk used for mass storage.
*fluctuation A surge or sag in voltage amplitude, often caused by load switching or fault clearing.
*fluorescence property of many substances, of absorbing light of one wavelength (or colour) and emitting light of another wavelength (or colour).
*fluorescent lamp Discharge lamp of the low-pressure mercury type in which most of the light is emitted by a layer of fluorescent material excited by the ultraviolet radiation from the discharge.
*flux linkage The linking of the magnetic flux with the conductors of a coil. The value obtained by multiplying the number of turns in the coil by the flux passing through the coil.
*fluxmeter An instrument for the measurement of magnetic flux.
*focus A control that converges beams to produce a sharp display.
*foot ( ft)Imperial unit of length. 1 foot = 12 inches = 304.8 mm exactly
*foot candle Unit of illumination at a point one foot distance from a one candela source. (in the imperial system of units) 1 foot candle = 1 lumen per square foot.
*foot lambert Unit of luminance. It is the luminance of a uniform diffuser emitting a foot candle.
*foot pound (ft. lb.) Unit of energy. 1 ft.lb. = 1.356 J
*force External agency capable of altering the state of rest or motion of a body. [Unit: newton or N]
*form factor Ratio of the rms value to the average value in a periodic waveform.
*forced outage An outage that results from emergency conditions that requires a component to be taken out of service automatically or as soon as switching operations can be performed.
The forced outage can be caused by improper operation of equipment or by human error. If it is possible to defer the outage, the outage becomes a scheduled outage.
*fortin barometer A mercury in glass barometer, which used in conjunction with correction tables enables accurate measurement of atmospheric pressure to be made.
*forward biasA dc voltage applied to a pN junction semiconductor so that the positive terminal of the voltage source connects to the p-type material and the negative terminal to the N-type material. It produces forward current in the circuit.
*forward current Current in a circuit of a semiconductor device due to conduction by majority carriers across the pN junction.
*fossil fuel Any naturally occurring organic fuel, such as petroleum, coal, and natural gas. Remains of organisms embedded in the surface of the Earth, with high carbon and/or hydrogen content, used as fuels.
*fossil fuel plant A plant using coal, oil, gas and other fossil fuel as its source of energy.
*fourier analysis The expansion of a mathematical function or an experimentally obtained waveform in the form of a trigonometric series.
*fourier series Resolution of a periodic function into its direct component, its fundamental sinusoidal component and an infinite series of harmonic sinusoidal components.
*fourier transform An integral transformation from the time domain to the frequency domain.
*fps system The foot pound second system of units is an imperial set of units derived from the fundamental units of the foot, the pound mass and the second.
*free electron An electron which is not attached to an atom, molecule or ion, but is free to move under the influence of an electric field.
*freezing point The temperature of equilibrium between solid and liquid substance at a pressure of one standard atmosphere.
*frequencyThe number of complete cycles of an alternating voltage or current per unit of time. [Unit: hertz or Hz]
*frequency counter A circuit that can measure and display the frequency of a signal.
*frequency modulation FM A process whereby the frequency of the carrier is controlled by the modulating signal.
*frequency response The frequency response of a circuit is the variation of its behaviour (voltage or current) with change in frequency.
*frequency spectrum The frequency spectrum of a signal consists of the plots of the amplitude and phases of the harmonics against frequency.
*fuel Any substance which is used for producing heat energy, either by means of the release of its chemical energy by combustion or its nuclear energy by nuclear fission.
*fuel adjustment charge A clause in the rate schedule that provides for adjustment of the amount of a bill as the cost of fuel varies from a specified base amount per unit. The specified base amount is determined when rates are approved. This item is shown on all consumer bills and indicates the current rate for any adjustment in the cost of fuel used by the utility. It can be a credit or a debit. The fuel adjustment lags usually lags one or two months behind the actual price of the fuel.
For example, the cost of oil in January will be reflected in March's fuel adjustment.
*fuel cell A electrochemical energy conversion device for producing electricity converting hydrogen and oxygen into electricity. These cells convert chemical energy directly into electrical energy.
*fuel diversity A utility or power supplier that has power stations using several different types of fuel.
Avoiding over-reliance on one fuel helps avoid the risk of supply interruption and price spikes.
*fuel element An element of nuclear fuel for use in a nuclear reactor, usually uranium encased in a case.
*fuel escalation The annual rate of increase of the cost of fuel, including inflation and real escalation, resulting from resource depletion, increased demand, etc.
*fuel expenses Costs associated with the generation of electricity.
*full load current The largest current that a motor or other device is designed to carry under specific conditions. Also current at rated conditions.
*full wave rectifier A rectifier with a centre tapped secondary windings and two diodes, or a bridge rectifier circuit.
*functional earth conductor Conductor to be connected to a functional earth terminal.
*functional earthing Connection to Earth necessary for proper functioning of electrical equipment.
*functional earth terminal Terminal directly connected to a point of a measuring supply or control circuit or to a screening part which is intended to be earthed for functional purposes.
*function generatorA circuit that produces a variety of waveforms.
*functional extra low voltage (FELV) An extra low voltage system in which not all of the protective measures required for SELV or PELV have been applied.
*functional switching An operation intended to switch 'on' or 'off' or vary the supply of electrical energy to all or part of an installation for normal operating purposes.
*fundamental displacement factor *FDF Cosine of the phase difference between the fundamental components of voltage and current. For non distorted sinusoids, it is also equal to the power factor.
*fundamental units The units in which physical quantities are measured which are independent from each other.
*fuse An over-current protective device for opening a circuit by means of a conductor designed to melt and break when an excessive current flows along it for a sufficient time. The fuse comprises all the parts that form the complete device.
*fuse carrier The movable part of a fuse designed to carry a fuse link.
*fuse element A part of a fuse, which is designed to melt and thus open a circuit
*fuse linkA part of a fuse, which comprises a fuse element and a cartridge (or other container) and is capable of being attached to the fuse contacts
*fusing current This is the minimum current that will cause the fuse element to heat up melt or blow
*fusing factor This is the ratio of the fusing current to current rating
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*gain A measure of amplification of a device, usually expressed in dB.
*gallon (gal) Imperial gallon. A measure of volume. 1 gal = 4.54596 litre
*gallon (US) A measure of volume. 1 US gallon = 3.785 litre
*galvanised iron Iron coated with a layer of zinc to prevent corrosion, usually by hot dipping into the molten metal.
*galvanometer An instrument for detecting, comparing, or measuring small electric currents, but not usually calibrated. Usually depends on the magnetic effect produced by an electric current.
*gas A substance whose physical state (gaseous state) is such that it always occupies the whole of the space in which it is contained.
*gas turbine Consists typically of an axial-flow air compressor, one or more combustion chambers (where liquid or gaseous fuel is burned). The hot gases are passed to the turbine and expanded to drive the generator and run the compressor.
*gas turbine plant A plant in which the prime mover is a gas turbine.
*gate The terminal of a FET that controls drain current. Also the terminal of a thyristor used to turn on the device.
*gauss G An old unit for measuring magnetic flux density (or magnetic induction). 1 G = 10-4 T
*generating station, *generating plant The location of prime movers, electric generators, and auxiliary equipment used for converting mechanical, chemical, and nuclear energy into electric energy.
*generating unit Any combination of physically connected generators, reactors, boilers, combustion turbines, or other prime movers operated together to produce electric power.
*generation The process of producing electrical energy by transforming non electrical forms of energy.
*generation company *genco A regulated or non-regulated entity (depending upon the industry structure) that operates and maintains existing generating plants. The Genco may own the generation plants or interact with the short term market on behalf of plant owners.
In the context of restructuring the market for electricity, Genco is sometimes used to describe a specialized "marketer" for the generating plants formerly owned by a vertically-integrated utility.
A company, group or individual who plan to connect or has already connected an Embedded Generator to the CEB distribution network.
*generation dispatch and control Aggregation and dispatching (sending off to some location) generation from various generating facilities, providing backup and reliability of services.
*generator A machine for converting mechanical energy into electrical energy.
*geothermal plantA plant in which the prime mover is a steam turbine driven by steam that derives its energy from heat found in rocks or fluids beneath the surface of the earth. The energy is extracted from naturally occurring geothermal fields or by drilling and/or pumping.
*gibi (Gi)Binary multiple prefix corresponding to gigabinary or 230 or (210)3 or 10243. [IEC 1998]
*giga (G) Decimal multiple prefix corresponding to a billion(US) or 109.
*gigawatt Unit of electric power equal to one billion watt, or one thousand megawatt.
*gilbertThe c.g.s. unit of magnetomotive force in electrostatic units. 1 gilbert = 10 A.
*glare Condition of vision in which there is discomfort or a reduction in the ability to see significant objects, or both, due to an unsuitable distribution or range of luminance or to extreme contrasts in space or time.
*glow discharge Electric discharge in which the secondary emission from the cathode is much greater than the thermionic emission.
*good utility practice Methods and practices that are approved by a significant portion of the utility industry.
*graticule The CRT grid lines that facilitate the location and measurement of oscilloscope traces.
*graph of network The geometric structure of the interconnection of the network elements which completely characterises the number of independent loop currents or the number of independent node-pair voltages necessary to study the network.
*greenhouse effect The greenhouse effect allows solar radiation to penetrate but absorbs the infrared radiation returning to space. It thus increases the mean global surface temperature of the earth caused by gases in the atmosphere (including carbon dioxide, methane, nitrous oxide, ozone, and chlorofluorocarbon).
*greenhouse gases Greenhouse gases include carbon dioxide, methane, nitrous oxide, hydrocarbons, and chlorofluorocarbons. These provide the greenhouse effect.
*grid The layout of an electrical transmission and distribution system.
*grid interconnection: A link between CEB Electricity system and Embedded Generator's Electricity System, made for the purpose of Exporting or Importing Electrical Energy.
*gross generation Amount of electric energy produced by generating units as measured at the generator terminals.
*ground A conducting connection, either intentional or accidental, between an electric circuit or equipment and the Earth or some conducting body serving in place of the Earth.
*grounded neutral The common neutral conductor of an electrical system which is intentionally connected to earth to provide a current carrying path for the line to neutral load devices.
*ground fault An undesired path that allows current to flow from a line to ground.
*ground fault interruption A unit or combination of units which provides protection against ground fault currents below the trip levels of the breakers of a circuit.
*ground loopThe condition of having two or more ground references in a common system. When two or more grounds have a potential difference between them, current can flow. This flow of current is a new circuit or loop which can interfere with the normal operation of the system.
*ground state The most stable energy state of a nucleus, atom or molecule.
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*half-life The time taken for the activity of a radioactive isotope to decay to half of its original value. In other words the time taken for half the atoms present to disintegrate.
*half wave rectifierA rectifier with only one diode in series with the load. The output is a half-wave rectified voltage with the other half wave being at zero voltage.
*half wave symmetry A function has half-wave symmetry when one half of its waveform is exactly the negation of the previous half of the waveform.
*halide Binary compound of one of the halogen elements (fluorine, chlorine, bromine or iodine).
*hall effect If an electric current flows in a wire placed in a strong transverse magnetic field, a potential difference is developed across the wire, at right angles to both the magnetic field and the wire.
*halogen lamp Gas-filled lamp containing a tungsten filament and a small proportion of halogens.
*hard diskA rigid metal magnetic disk used for mass storage.
*harmonic A frequency that is a multiple of the fundamental frequency. For example, 100 Hz is the second harmonic of 50 Hz, 150 Hz is the third harmonic, and so forth.
*harmonic distortion The presence of harmonics that change the AC voltage waveform from a simple sinusoidal to complex waveform. Harmonic distortion can be generated by a load and fed back to the AC utility line, causing power problems to other equipment on the same circuit.
*harmonized standard A standard which has been drawn up by common agreement between national standards bodies notified to the European Commission by all member states and published under national procedures.
*heat rate A measure of generating station thermal efficiency and generally expressed as BTU per net kWh. The heat rate is computed by dividing the total BTU content of the fuel burned (or of heat released from a nuclear reactor) by the resulting net kWh generated.
*heat sink A mass of metal attached to the case of a transistor or other device to allow the heat to escape more easily and prevent overheating of the transistor or device.
*heavy oilThe fuel oils remaining after the lighter oils have been distilled off during the refining process. Except for start-up and flame stabilization, virtually all petroleum used in steam plants is heavy oil.
*hectare A measure of large area. 1 hectare = 100 are = 104 m2
*hecto (h) Decimal multiple prefix corresponding to a hundred or 102. This is not a preferred suffix.
*henry (H) SI unit of electric inductance. One henry is equal to the inductance of a closed circuit in which an electromotive force of 1 volt is produced when the electric current in the circuit varies uniformly at the rate of 1 ampere per second.
*hertz (Hz) SI unit of frequency. One hertz is equal to one cycle per second.
*hexadecimal A number system consisting of 16 symbols, namely 0 to 9 and A to E.
*heuristic A method of solving mathematical problems for which no algorithm exists. Involves the narrowing down of the field of search for a solution by inductive reasoning from past experience of similar problems.
*high intensity discharge *HID lamp A type of lamp that may consist of mercury vapor, metal halide, high pressure sodium, or low pressure sodium.
*high pass filter A filter designed to pass all frequencies above its cut-off frequency.
*high-pressure mercury (vapor) lamp Mercury vapor lamp, with or without a coating of phosphor, in which during operation the partial pressure of the vapor is of the order of 105 pa.
*high-pressure sodium (vapour) lamp Sodium vapour lamp in which the partial pressure of the vapour during operation is of the order of 104 pa.
*high rupturing capacity fuses, *HRC fuses The HRC fuse is usually a high-grade ceramic barrel containing the fuse element. The barrel is usually filled with sand, which helps to quench the resultant arc produced when the element melts. They are used for high current applications.
*high tension , *HT High voltage.
*high voltage direct current transmission, *hvdc transmission power transmission carried out at high voltage direct current.
*high voltage test A test which consists of the application of a specified voltage higher than the rated voltage between windings and frame, or between two or more windings, for the purpose of determining the adequacy of insulating materials and spacing against breakdown under normal conditions. [It is not the test of the conductor insulation of any one winding.
*histogram A type of graphical representation, used in statistics, in which the frequency distribution is expressed by rectangles.
*hole In a crystal lattice, a point which has been vacated by an electron.
*horsepower (hp) A method of rating motors. 1 hp = 0.746 kW
*hot wire instrument An electrical instrument which depends upon the expansion (or change of resistance) of a wire which is heated by the passage of an electric current.
*hooke's law Within the elastic limit, a strain is proportional to the stress producing it.
*house service meter Energy meter at a consumer's premises, measuring power in kWh.
*HRC fuse [see high rupturing capacity fuse]
*hub A wiring concentrator used in local area networks.
*humidity The humidity of the atmosphere is a measure of the water vapour present in the air.
*hv: *high voltage exceeding 1000 V between conductors and 600 V between conductors and earth.
*hydrocarbon Organic compounds which contain only carbon and hydrogen.
*hydroelectric plant A plant in which the turbine/generators are driven by the kinetic energy of water. One common type of hydropower plant involves using a dam to store water in a reservoir and when released spins a turbine, creating electricity.
*hysteresis A physical phenomena wherein the path followed during relieving an applied stress lags that during applying the stress, so that on complete removal of the applied stress a strain remains. This particularly occurs in magnetic materials - the lagging of induced magnetism behind the magnetizing force.
*hysteresis loss power loss in the magnetic core due to hysteresis.
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*IC engine [see internal combustion engine]
*IC *integrated circuit A type of circuit in which all the components are integrated on a single silicon chip of very small size.
*ideal current source A source which maintains the source current at a predefined value independent of the load conditions.
*ideal dependent source An active element in which the source voltage or current is controlled precisely by another voltage or current.
*ideal op amp An operational amplifier with infinite open-loop gain, infinite input impedance and zero output impedance.
*ideal source An ideal independent source is an active element that provides a specified voltage or current that is completely independent of the remaining circuit elements.
*ideal voltage source A source which maintains the source voltage at a predefined value independent of the load conditions. In other words the terminal voltage is maintained equal to the internal emf.
*IEE Institution of Electrical Engineers. Based in Savoy Place, London, UK.
*IEEE Institute of Electrical and Electronic Engineers. Based in New York, USA.
*IESL Institution of Engineers, Sri Lanka. Based in Wijerama Mawatha, Colombo.
*IEE wiring regulations Regulations framed for wiring installations for the protection of persons, property and livestock from electric shock, fire, burns and injury from mechanical movement of electrically actuated equipment. It is a joint publication of the IEE and the British Standards Institute.
It is a legal requirement in Sri Lanka.
*illuminance The quantity of light at one point on a surface. It is the quotient of the luminous flux incident on an element of the surface containing the point, and the area of that element. [Unit lux, lx]
*illumination Emission of optical radiation by the process of thermal radiation.
*imaginary Numbers with negative squares. S-1 is the base of such numbers.
*imaginary axis The y-axis in the complex plane.
*imaginary operator j An multiplier or operator with a magnitude of unity and an anticlockwise rotation of 90o. It also has the value S-1 in the complex domain.
*impedance The total opposition a circuit offers to the flow of alternating or other current in an electrical circuit. It is the ratio of the voltage to the current. [Unit: ohm , W]
*impregnation The process of filling the pores of paper and similar material in order to improve its insulation properties.
*impulse A disturbance of the voltage waveform that is less than about one millisecond. Voltages can rise to hundreds or even thousands of volt in a very short period of time. An impulse may be additive or subtractive.
*impulse function A mathematical function with zero magnitude other than at zero time, where it has an infinite magnitude. The magnitude of an impulse function is defined as its time integral.
*impulse generator In most impulse generators, certain capacitors are charged in parallel through high series resistances, and then discharged through a combination of resistors and capacitors, giving rise to the required surge waveform (usually double exponential) across the test device.
*impulse response Behaviour of a circuit when the excitation is the unit impulse function. The excitation function may be a voltage or a current.
*incandescent (electric) lamp Lamp in which light is produced by means of an element heated to incandescence by the passage of an electric current.
*incentive A rebate or some form of payment used to encourage consumers to implement a given demand-side management (DSM) technology.
The incentive is usually calculated as the amount of the technology costs that must be paid by the utility to achieve the desired benefit/cost ratio to drive the market.
*inch A measure of length in the imperial system. It is now defined as follows. 1 inch = 25.400 mm
*incidence matrix A connection matrix having elements 1, -1 or 0 dependent on whether a particular connection is present and having the same sign as the reference, has the opposite sign to the reference or not connected at all.
*independent power producer *IPP Private entrepreneurs who develop, own or operate electric power plants fueled by alternative energy sources such as biomass, cogeneration, small hydro, waste-energy and wind facilities.
Organisations with generating capacity that are not associated with traditional electricity utilities.
*independent system operator *ISO An entity responsible for the reliable operation of the grid and provision of open transmission access to all market participants on a non-discriminatory basis.
*index The number indicating the power to which the quantity is raised.
*indirect contact Contact of persons or livestock with exposed conductive parts which have become live under fault conditions.
*indirect lighting Lighting by means of luminaires with a light distribution such that not more than 10 per cent of the emitted luminous flux reaches the working plane direct, assuming that this plane is unbounded.
*indicating instrumentA piece of equipment in which the output is given as the deflection of a needle or the reading of a counter.
*indirect utility cost Any cost that is not identified with a specific DSM category such as Administration, Marketing, etc.
*inductance The property of a circuit or coil that causes an emf to be set up due to a rate of change of current in the circuit or coil. The constant of proportionality is the inductance.
*induction heating A form of heating in which electrically conducting material is heated as a result of the electric currents induced in it by an alternating magnetic field.
*induction machine Induction machines run at a speed slightly different to synchronous speed as the difference speed, known as slip, is required to generate torque. Induction motors run at sub-synchronous speed where as induction generators run at super-synchronous speed.
*induction meter The induction meter depends on the torque produced by the reaction between a flux (whose value depends on the value of the current in one coil) and the eddy currents which are induced in a non-magnetic disc (usually aluminium) by another flux (produced by current in a second coil). Since the action depends on induction, they can be used to measure alternating quantities only. The meter would have a deflection proportional to the product of the two currents.
*inductor A circuit element which is a wire wound into a coil to create a magnetic field.
*inertia Tendency of a body to preserve its state of rest or uniform motion.
*infinitesimal A very small quantity tending to zero, without actually being zero.
*infinity A very large quantity greater than any assignable quantity and tending to the inverse of zero.
*infrared The form of radiation in the electromagnetic spectrum beyond red light from 760 nanometers to 1000 microns.
*infrared radiation Optical radiation for which the wavelengths are longer than those for visible radiation and shorter than those for radio waves. It corresponds to invisible heat radiation.
*inorganic Not belonging to the large class of carbon compounds which are termed organic.
*installed capacity The total generating units' capacities in a power plant or on a total utility system.
The capacity can be based on the nameplate rating or the net dependable capacity.
*insertion loss This is the loss that occurs as signals pass through a passive device. Insertion loss occurs in all devices which do not amplify the signal. Also called "feed through loss".
*installation An electrical installation is a combination of electrical equipment installed to fulfil a specific purpose and having coordinated characteristics.
*instantaneous frequency The rate of change of phase angle (in rad/s) or additionally divided by 2p (in Hz).
*instantaneous value The value of an alternating current or voltage at any specified instant in a cycle.
*instructed person A person adequately advised or supervised by skilled persons to enable him/her to avoid dangers which electricity may create.
*instrument transformer A transformer specifically designed to be used with instruments. Their design ensures high accuracy for the quantity to be measured.
*insulation Suitable non conductive material enclosing, surrounding or supporting a conductor.
*insulation co-ordination Insulation co-ordination now comprises the selection of the electric strength of the various equipment in relation to the voltages which can appear on the system for which the equipment is intended. The overall aim is to reduce to an economically and operationally acceptable level the cost and disturbance caused by insulation failure and resulting system outages.
*insulation failure Fault between the phase conductor and non-current carrying metallic parts of an electrical equipment, as a result of which high voltages may appear on the frames of equipment and may be dangerous to a person coming in contact with it.
*insulation level It defines the level of insulation with regard to power frequency and with regard to surges. For equipment rated at less than 300 kV, it is a statement of the Lightning impulse withstand voltage and the short duration power frequency withstand voltage. For equipment rated at greater than 300 kV, it is a statement of the Switching impulse withstand voltage and the power frequency withstand voltage.
*insulator A non-conductor of electricity (or heat)
*integer A whole number.
*integrated circuit A device that contains its own transistors, resistors, and diodes within itself.
*integrating meter A meter whose output is proportional to the integrated value of a quantity over time. They are usually with rotating discs where the revolutions correspond to the time of integration.
*integrator An op amp whose output is proportional to the integral of the input signal.
*interconnection (electric utility) The linkage of transmission lines between two utilities, enabling power to be moved in either direction.
Interconnections allow the utilities to help contain costs while enhancing system reliability.
*interconnection voltage: - The nominal voltage at which the grid interconnection is made.
*interlock A device connected in such a way that the motion of one part is held back by another part.
*internal combustion engine IC engine An engine in which energy supplied by a burning fuel is directly transformed into mechanical energy by the controlled combustion of the fuel in an enclosed cylinder behind a piston. Usually used in petrol and diesel engines.
*internal discharge A discharge occurring within a material.
*international candle [An old unit of luminous intensity, now replaced by the candela.] A point source emitting light uniformly in all directions at one-tenth the rate of the Harcourt pentane lamp burning under specific conditions.
*intermediate load (electric systems) A load in the range from base load to peak load.
*intermittent resources Resources whose output depends on some other factor that cannot be controlled by the utility, such as wind or sun. Thus, the capacity varies by the hour.
*interpolation A process of filling in intermediate values or terms between known values or terms.
*interruptible loads Loads that can be interrupted in the event of capacity or energy deficiencies on the supplying system.
*interruptible power Power whose delivery can be curtailed by the supplier, usually under some sort of agreement by the parties involved.
*interruptible rate Tariff rate for the provision of power at a lower rate to large industrial and commercial consumers who agree to reduce their electricity use in times of peak demand.
*intrinsically safe A term used to define a level of safety associated with the electrical controls or circuits.
*intrinsically safe device A device, instrument or component that will not produce any spark or thermal effects under any conditions that are normal or abnormal that will ignite a specified gas mixture.
*inverse square law A law which states that the intensity of an effect due to a source varies inversely as the square of the distance between.
*inverter An electric or electronic device for producing alternating current from direct current.
*inverting amplifier Reverses the polarity of the input signal while amplifying it.
*ionisation Ionisation is the process by which an electron is removed or added to an atom, leaving the atom with a nett negative charge (negative ion) or a nett positive charge (positive ion). A process of formation of ions.
*irradiation Exposure to radiation of any kind.
*irreversible process A process that is not fully reversible.
*islanding: The process whereby a power system is separated into two or more parts, with generators supplying loads connected to some of the separated systems.
*islanded operation: - The situation that arises when a part of the electrical system is disconnected from the main grid and is energised by one or more generators connected to it.
*isokeraunic level Contours of constant keraunic level or thunder days.
*isolation The degree to which a device can separate the electrical environment of its input from its output, while allowing the desired transmission to pass across the separation.
A function intended to cut off for reasons of safety the supply from all, or a discrete section, of the installation by separating the installation or section from every source of electrical energy.
*isolation transformer A transformer with physically separate primary and secondary windings. An isolation transformer does not transfer unwanted noise and transients from the input circuit to the output windings.
*isolator A mechanical switching device which, in the open position, complies with the requirements specified for isolation. An isolator is otherwise known as a disconnector.
*isothermal A process that is kept at a constant temperature.
*isotropic Substances exhibiting uniform properties throughout, in all directions.
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*J-K flip flop A type of flip-flop that can operate in the 'no change', 'set', 'reset' and 'toggle' modes.
*joule (J) SI unit of work or energy. One joule is defined to be the work done by a force of one newton acting to move an object through a distance of one meter in the direction in which the force is applied.
*joule's equivalentMechanical equivalent of heat. 4.185 J/cal
*junction box An enclosure where conductors or wires an spliced or terminated.
*junction diodeA diode consisting of a pN junction and suitable connecting leads.
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*karnaugh map An arrangement of cells representing the combinations of variables in a Boolean expression and used for a systematic simplification of the expression.
*kelvin (K) The kelvin is unit of thermodynamic temperature. It is a fundamental unit. It is defined as the fraction 1/273.16 of the thermodynamic temperature of the triple point of water 
*kelvin double bridge It is a double bridge arrangement, which is an extension of the Wheatstone bridge, for the precise measurement of low resistance. The errors due to contact and lead resistances are eliminated by the additional bridge incorporated.
*keraunic level Number of days in the year in which thunder is heard.
*kibi (Ki) Binary multiple prefix corresponding to kilobinary or 210 or (210)1 or 1024. [IEC 1998]
*kilo(k) Decimal multiple prefix corresponding to a thousand or 103.
*kilogram (kg) The kilogram is the SI unit of mass. It is a fundamental unit. It is equal to the mass of the international prototype of the kilogram preserved in France 
*kilovolt ampere *kVA The practical unit of apparent power, which is 1,000 volt-ampere.
*kilowatt-hour (kWh) The standard unit of electricity supplied to the consumer. Equal to 1 kilowatt acting for 1 hour. 1 kWh = 3.60 x 106 J
*kinetic energy The energy which a body posses by virtue of its motion.
*kirchoff's current law *KCL States that the algebraic sum of the currents entering a node (or a closed boundary) is zero.
*kirchoff's voltage law *KVL States that the algebraic sum of the voltages around a closed loop is zero.
*klydonograph An instrument for the detection and recording of the occurrence of lightning in transmission lines.
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*lag The time delay between the output signal and the response time of the receiver of the signal.
*lag The angle delay between voltage signal and the corresponding current signal.
*lagging load An inductive load with current lagging voltage.
*lambert An old unit of luminance. The luminance of a uniform diffuser of light which emits one lumen per square centimetre. 1 lambert = 10-4 lux
*laminations Thin layers or sheets. The term usually refers to the thin sheets of iron used to build up the core of a transformer.
*LAN *Local Area Network A data communications system confined to a certain area. The area served may consist of a single building, or a cluster of buildings.
*laplace transform An integral transformation of a function from the time domain to the complex frequency domain. Used to analyse transients in circuits.
*laser Acronym for Light Amplification by Stimulated Emission of Radiation. The laser produces a powerful, highly directional, monochromatic, and coherent beam of light.
*latch A non-clocked flip-flop.
*latent heat Quantity of heat required to effect a change of state of a unit mass of a substance from solid to liquid (latent heat of fusion) or from liquid to vapour (latent heat of vaporisation) without change of temperature.
*lattice A regular network of fixed points arranged in a geometrical pattern of straight lines.
*LCD see Liquid crystal diode.
*leaching Washing out of a soluble constituent of a material.
*lead The angle advance between voltage signal and the corresponding current signal.
*leading load A capacitive load with current leading voltage.
*leakage current Electric current in an unwanted conductive path under normal operating conditions.
Current flowing from the enclosure, or parts thereof, accessible to the operator in normal use, through an external conductive connection other than the protective earth conductor to earth or to another part of the enclosure.
*leakage factor Ratio of the total flux to the useful flux is defined as the leakage factor. It has a value of around 1.2 for electrical machines.
*leakage inductance A small inductance associated with the flux of a transformer winding which are not magnetically coupled to the other windings of the transformer.
*leased line A dedicated circuit, typically supplied by the telephone company, that permanently connects two or more user locations. These lines are used to transmit data.
*least cost alternatives The lowest cost option for providing for incremental demands. In least cost planning to serve electric demands, the least cost alternatives are often construed broadly to include demand-side management as well as various generation and purchased power options.
*LED *light emitting diode: emits light when current is passed through it. A semiconductor light source that radiates light such as red, green, yellow and white, or invisible light such as infra red.
*lens Any device which causes a beam of rays to converge or diverge on passing through it.
*lenz's law When a coil and a magnetic field move relative to each other, the electric current is induced in the coil will have a magnetic field opposing the motion.
*light Any radiation capable of causing a visual sensation direct i.e. Visible electromagnetic radiation in the wavelength range 400 to 700 nano meter.
*lightning Any form of visible electric discharge between thunder clouds or between a thunder cloud and the earth. Ninety percent of all lightning never touches the ground - it occurs inside the thunder cloud or jumps from cloud to cloud.
*lightning arrester A device used to pass large impulses to ground. It is vital that this device be placed upstream from the equipment to be protected.
*lightning rod A grounded metallic rod set up on a structure (like a building) to protect it from lightning.
*light oil Lighter fuel oils distilled off during the refining process. Virtually all petroleum used in internal combustion and gas turbine engines use light oil.
*light year A measure of astronomical distances. 1 light year = 9.461 x 1015 m
*line A line is a system of poles, conduits, wires, cables, transformers, fixtures, and accessory equipment used for the distribution of electricity to the public.
*line A designation of one or more power-carrying conductors for power distribution. The brown (or red) wire is the line conductor, the blue (or black) wire is the neutral, and the green-yellow (or green) wire is the ground. The voltage difference between the line conductor and the neutral is the supply voltage.
*linear circuit One whose output is linearly related to the input. A circuit which obey's Ohm's law.
*linear motor A form of motor (normally induction motor) in which the stator and rotor are linear instead of cylindrical and parallel instead of coaxial.
*line conditioner A line conditioner contains multiple protection devices in one package to provide, for example, electrical noise isolation and voltage regulation.
*line to line A term used to describe a given condition between conductors of a multiphase feeder.
*line to neutral A term used to describe a given condition between a phase conductor and a neutral conductor.
*line voltage The voltage between two lines (or phases) of a three phase system is defined as the line-to-line voltage or more commonly as the line voltage. For a balanced three phase system, the line voltage is Ö3 times the phase-to-neutral voltage.
*liquid crystal display, *LCD Displays made from liquid crystals which usually change from transparent to opaque in the presence of electric or magnetic fields. They are commonly used in digital displays.
*liquid A state of matter between a solid and a gap. Liquids assume the shape of the vessel containing them, other than the top surface which will assume a horizontal position when free to air. They are only slightly compressible.
*lissajous pattern The pattern appearing on an oscilloscope when harmonically related signals are applied to the horizontal and vertical inputs of an oscilloscope.
*live part A conductor or conductive part intended to be energised in normal use, including a neutral conductor but, by convention, not a PEN conductor.
*load Any passive electrical device connected to a power source may be called by the general term of "load". It is the amount of electric power delivered or required at any specific point or points on a system. The requirement originates at the energy consuming equipment of the consumers. [Unit: kW or MW]
*load center A limited geographical area where large amounts of power are used by consumers.
*load diversity The load condition that exists when the peak demands of a variety of electric consumers occur at different times.
*load duration curve *LDC A curve that displays load values on the horizontal axis in descending order of magnitude against percent of time (on the vertical axis) the load values are exceeded.
*load factor The ratio of the average load supplied (kW) during a designated period to the peak or maximum load (kW) occurring during that period.
*load forecast Estimate of electrical demand or energy consumption at some future time.
*loading effect Connection of a meter (an ammeter in series or a voltmeter in shunt) to a circuit to make a measurement alters the original circuit in that it draws some energy from the circuit. The error caused is known as the loading effect.
*load management Techniques used by utilities to manage daily and/or seasonal fluctuations in customer demand.
Managing the level and shape of demand for electrical energy so that demand conforms to present supply situations and long-run objectives and constraints.
*load profile Information on a consumer's usage over a period of time, sometimes shown as a graph.
*load shape A curve showing power (kW) supplied (on the horizontal axis) plotted against time of occurrence (on the vertical axis), and illustrating the varying magnitude of the load during the period covered.
*load shifting A load shape objective that involves moving loads from peak periods to off-peak periods.
If a utility does not expect to meet its demand during peak periods but has excess capacity in the off-peak periods, this strategy can be considered.
*local lighting Lighting for a specific visual task, additional to and controlled separately from the general lighting.
*load line Locus of instantaneous operating points used to find the exact operating values of voltage and current.
*lockout A mechanical device which may be set to prevent the operation of a push-button or other device.
*locus The line that can be drawn through adjacent positions satisfying a given criteria.
*logic circuit A circuit that behaves according to a set of logic rules.
*logic level State of a voltage variable. States HIGH and LOW correspond to the two usable voltage levels of a digital device.
*letter of intent *LOI: - Issued by CEB to a Generating Company to signify CE13's intent to purchase power from a Generating Company at a particular location.
*LOM protection: *loss of mains protection
*loop or mesh A closed path of elements in a circuit.
*loop current A component of current common to the complete loop.
*loss angle Angle of deviation of the current from the ideal current for a dielectric for a sinusoidal input.
*loss factor A factor which defines the loss component of a dielectric.
*loss tangent The loss factor, which also corresponds to the tangent of the loss angle.
*loss of load probability *LOLP A measure of the probability that system demand will exceed capacity during a given period; this period is often expressed as the expected number of days per year over a long period, frequently taken as ten consecutive years.
An example of LOLP is one day in ten years.
*losses The general term applied to energy (kWh) and capacity (kW) lost in the operation of an electric system. Losses occur principally as energy transformations from kWh to waste-heat in electrical conductors and apparatus. This power expended without accomplishing useful work occurs primarily on the transmission and distribution systems.
*low pass filter A filter designed to pass only frequencies from d.c. up to the cut-off frequency.
*low noise earth An earth connection in which the level of conducted or induced interference from external sources does not produce an unacceptable incidence of malfunction in the data processing or similar equipment to which it is connected. The susceptibility in terms of amplitude/frequency characteristics varies depending on the type of equipment.
*low-pressure mercury (vapor) lamp Mercury vapor lamp, with or without a coating of phosphor, in which during operation the partial pressure of the vapor does not exceed 100 pa.
*low-pressure sodium (vapor) lamp Sodium vapor lamp in which the partial pressure of the vapor during operation does not exceed 5 pa.
*lumen (lm) SI unit for measuring the flux of light. One lumen is equal to the luminous flux emitted in unit solid angle (steradian) by uniform point source having a luminous intensity of 1 candela.
*luminaire Apparatus that distributes, filters or transforms the light given by a lamp or lamps and which includes all the items necessary for fixing and protecting these lamps and for connecting them to the supply circuit.
*luminaire efficiency The ratio of total lumen output of a luminaire to the lumen output of the lamps, expressed as a percentage.
*luminous efficacy Quotient of the luminous flux emitted by a source and the power consumed. [Unit lumen per watt, lm/W]
Visible light output of a luminary measured relative to power input.
*luminous flux The quantity derived from radiant flux by evaluating the radiation according to its action upon the standard photometric observer. [Unit lumen, lm].
*luminous intensity distribution Distribution of the luminous intensities of a lamp or luminaire in all spatial directions.
*lux (lx) SI unit for measuring the illumination of a surface. One lux is defined as an illumination of one lumen per square meter.
*lv *low voltage - not exceeding 1000 V between conductors and 600 V between conductors and earth.
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*magnetic shield A piece of magnetic material used to carry the magnetic flux around an object to prevent the object from being affected by the magnetic field.
*magnetic field A region of space that surrounds a moving electrical charge or a magnetic pole, in which the electrical charge or magnetic pole experiences a force that is above the electrostatic ones associated with particles at rest.
*magnetic flux A measure of quantity of magnetism, taking account of the strength and the extent of a magnetic field. [Unit: weber]
*magnetic mechanism The magnetic mechanism uses a solenoid with an iron piece to operate the circuit breaker in the event of an overcurrent.
*magnetisation curve The relationship between the magnetic flux density and the applied magnetic field (or the magnetic flux and the applied mmf) is called the magnetisation curve.
*magnetism The property of certain materials to attract iron and other magnetic materials.
*magneto-hydrodynamics *MHD A method of generating electricity by subjecting the free electrons in a high velocity flame or plasma to a strong magnetic field. The free electron concentration in the flame is increased by the thermal ionisation of added substances of low ionisation potential.
*magnetomotive force The force that sets up a magnetic field within and around an object.
*magnetostriction A change in the dimensions of ferromagnetic substances on magnetisation.
*main earthing terminal The terminal or bar provided for the connection of protective conductors, including equipotential bonding conductors, and conductors for functional earthing, if any, to the means of earthing.
*main switch The principal (or main) switch in an electrical installation.
*maintenance factor Ratio of the average illuminance on the working plane after a specified period of use of a lighting installation to the average illuminance obtained under the same conditions for a new installation.
*malleability Capacity of being hammered out into thin sheets.
*manual transfer switch A switch designed so that it will disconnect the load from one power source and reconnect it to another source while at no time allowing both sources to be connected to the load simultaneously.
*marginal cost The sum that has to be paid for the next increment of product of service. The marginal cost of electricity is the price to be paid for kilowatt-hour above and beyond those supplied by presently available generating capacity irrespective of sunk costs.
*market-based-price A price set by the mutual decisions of many buyers and sellers in a competitive market.
*matching transformer A device used to convert impedance between two levels. A common use is between a 75 ohm impedance and a 300 ohm impedance.
*maximum demand The largest of all demands of the load (usually expressed in kVA or MVA) that has occurred within a specified period of time.
*maxwell Mx An old unit of magnetic flux. 1 Mx = 10-8 Wb
*mcb [see miniature circuit breaker]
*mccb [see moulded case circuit breaker]
*mean time between failure A statistical estimate of the time a component, subassembly, or operating unit will operate before failure will occur.
*mebi (Mi) Binary multiple prefix corresponding to megabinary or 220 or (210)2 or 10242. [IEC 1998]
*medical electrical equipment Electrical equipment, provided with no more than one connection to a particular supply mains, and intended to diagnose, treat or monitor the patient under medical supervision and which makes physical or electrical contact with the patient and/or transfers energy to or from the patient and/or detects such energy transfer to or from the patient. The equipment includes those accessories as defined by the manufacturer which are necessary to enable the normal use of the equipment.
*mega (M) Decimal multiple prefix corresponding to a million or 106.
*megawatt One million watts.
*megawatt-hour *MWh One thousand kilowatt-hours or one million-watt hours.
*megger or *megohmeter A high resistance range specially designed ohmmeter for measuring insulation resistance of conductors and other electrical equipment.
*melting point The constant temperature at which the solid and liquid phase of a substance are in equilibrium at a given pressure.
*mercury vapour lamp Lamp emitting a strong bluish-white light by the passage of an electric current through mercury vapour in a bulb.
*mesh (see loop)
*mesh analysis A method of analysis of circuits based on defining mesh currents as the variables.
*metal oxide varistor [see MOV]
*metal halide lamp Discharge lamp in which the major portion of the light is produced by the radiation from a mixture of a metallic vapor (for example, mercury) and the products of the dissociation of halides (for example, halides of thallium, indium or sodium).
*metal oxide semiconductor FET [see MOSFET]
*metal vapor lamp Discharge lamp such as the 'mercury (vapor) lamp' and the 'sodium (vapor) lamp' in which the light is mainly produced in a metallic vapor.
*meter (m) The meter is the SI unit of length. It is a fundamental unit. It is defined as the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second 
*metering Monitoring of energy or water consumption or other data over a period of time.
*micro (m) Decimal sub-multiple prefix corresponding to one-millionth or 10-6.
*microphone An electromechanical transducer that converts sound pressure into an electrical signal.
*microprocessor A large scale integrated circuit that can be programmed to perform arithmetic and logic functions and to manipulate data.
*microwave Electromagnetic radiation with wavelengths ranging from very short radio waves to almost infra-red region. Wavelengths from 300 mm to 1 mm.
*mil A unit of small length in the imperial system equal to one-thousandth of an inch. 1 mil = 2.54 x 10-5 m
*mile Unit of distance in the imperial system. 1 mile = 1.609 km
*miles per hour (mph) Unit of speed in the imperial system. 1 mph = 0.44704 m/s
*milli (m) Decimal sub-multiple prefix corresponding to one-thousandth or 10-3.
*mineral Substance occurring naturally in the Earth.
*mineral oil General name given to the various mixtures of natural hydrocarbons.
*miniature circuit breaker *mcb A device designed to perform the same function as a fuse but resettable. When the circuit breaker activates, or trips out, it disconnects the circuit. The fault condition must be found and rectified before the mcb can be reset. Usually for ratings less than 63 A.
*mks system The metric system in which the meter, kilogram and the second are the fundamental units.
*mobile substation A movable substation which is used when a substation is not working or additional power is needed.
*moderator A substance used in nuclear reactors to reduce the speed of fast neutrons produced by nuclear fission.
*modem A hardware device that converts digital computer data into analog tones that can be transmitted over dial-up telephone circuits.
*modulator The process of varying some characteristic of one wave (carrier wave) in accordance with some characteristic of another wave.
*mole (mol) The mole is the SI unit of the amount of substance. It is defined as the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12; 
*momentary overvoltage or swell An increase in voltage outside the normal tolerance for a few seconds or less. Voltage swells are often caused by sudden load decreases or turn-off of heavy equipment.
*monochromatic radiation Radiation characterized by a single frequency. In practice, radiation of a very small range of frequencies that can be described by stating a single frequency.
*monopoly The only seller with control over market sales.
*mortality rate The number of operating hours elapsed before a certain percentage of the lamps fail.
*MOSFET Metal oxide semiconductor FET often used in switching amplifier applications. This transistor provides extremely low power dissipation even with high currents.
*motor A rotating device which converts electrical power into mechanical power.
*motor generator set A motor generator set consists of an ac motor coupled to a generator. The utility power energizes the motor to drive the generator, which powers the critical load. Motor generator sets provide protection against noise and spikes, and, if equipped with a heavy flywheel, they may also protect against sags and swells.
*moulded case circuit breaker *mccb A circuit breaker with a moulded case originally designed for currents exceeding 100 A.
*MOV ,*metal oxide varistor A solid state device which becomes conductive when the voltage across it exceeds a certain level. When the voltage exceeds the MOV's threshold, a heavy current flows through the MOV instead of the load.
*moving coil meter In this instrument, a moving coil is suspended between the poles of a permanent magnet. When a current is passed through the coil, the coil becomes an electromagnet and tries to align with the permanent magnet. The deflecting becomes proportional to the current.
*moving iron meter An instrument working on the principle of a moving iron placed within an electromagnet getting an induced emf and with the deflection being proportional to the square of the current. The meter is calibrated with the square root of the deflection and hence has basically a non-linear scale.
*multiplex To put information from several sources on to a single line or transmission path.
*municipal electric utility A power utility system owned and operated by a local jurisdiction or local authority.
*municipal solid waste A Biomass resource that can be used to produce energy by the process of incineration.
*mutual inductance The ability of one conductor to induce an emf in a nearby conductor when the current in the first conductor changes. It is the constant of proportionality between the induced voltage in the second inductor and the rate of change of current in the first inductor.
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*NAND gate The logic gate that outputs a 0 only when all its inputs are 1s. It gives the complement of the AND gate.
*nano (n) Decimal sub-multiple prefix corresponding to one-trillionth (US) or 10-9.
*natural gas A naturally occurring mixture of hydrocarbon and non-hydrocarbon gases found in porous geological formations beneath the earth's surface, often in association with petroleum. The principal constituent is methane.
*natural response The natural response of a circuit refers to be behaviour of the circuit (in terms of voltage and current), in the absence of external excitation.
*NEC, *national electrical code A set of rules and regulations that are put out by the National Fire protection Association. Generally accepted as the building wiring standard in the US.
*negative feedback Feeding a signal back to the input of an amplifier, or other circuit, that is proportional to the output signal, but having a phase that opposes the input signal.
*negative sequence A balanced set of three phase components which have the same magnitude, opposite sequence to the original unbalanced set, and phase angle diferring from each other by 120o. The frequency is of course the same as the original unbalanced three phase system.
*NEMA *National Electrical Manufacturers Association A non-profit trade association supported by the manufacturers of electrical apparatus and supplies in the US. NEMA promulgates standards to facilitate understanding between the manufacturers and users of electrical products.
*net capability Maximum load carrying ability of the equipment, excluding station use.
*net generation Gross generation minus the energy consumed at the generating station for its use.
*network A system of transmission and distribution lines cross-connected and operated to permit multiple power supply to any principal point on it.
*network synthesis Finding a network that represents a given transfer function.
*neutral point displacement voltage: The voltage between the real or virtual neutral point and the earth.
*neutral The point common to all phases of a polyphase circuit, a conductor to that point, or the return conductor in a single phase circuit.
*neutral conductor A conductor connected to the neutral point of a system and contributing to the transmission of electrical energy. The term also means the equivalent conductor of an IT or d.c. system unless otherwise specified in the Regulations and also identifies either the mid wire of a three wire d.c. circuit or the earthed conductor of a two wire earthed d.c. circuit.
*newton (N) SI unit of force. One newton is equal to the force required to accelerate a body with the mass one kilogram by one metre per second per second.
*nodal analysis A method of analysis of circuits based on defining node voltages as the variables.
*node point of connection between two or more elements or branches in a network.
*noise An unwanted random signal (in the form of a voltage or current) in an electrical circuit making the information more difficult to identify.
*nominal voltage A nominal value assigned to a circuit or system for the purpose of conveniently designating its voltage rating. The actual voltage at which a circuit operates can vary from the nominal within a range that permits satisfactory operation of equipment.
A suitable approximate value of voltage used to designate or identify a System.
*non-coincidental peak load The sum of two or more peak loads on individual systems, not occurring in the same time period.
*non-firm power Power supplied or available under terms with limited or no assured availability.
*non-inductive load A non-inductive load is a load in which the current is in phase with the voltage across the load. (See Inductive Load)
*non-linear A characteristic which does not follow a straight line.
*non-utility generator Independent power producers, exempt wholesale generators and other companies in the power generation business that have been exempted from traditional utility regulation.
*non-utility power producer A legal entity that owns electric generating capacity, but it not an electric utility.
*NOR gate A logic circuit that outputs a 1 only when each one of its inputs is a 0.
*normally open and *normally closed The terms "Normally Open" and "Normally Closed" are applied to a magnetically operated switching device (such as a contactor or relay, or to the contacts thereof) to signify the position taken when the operating magnet is de-energized.
*normal-mode noise noise signal which appears between a set of phase conductors.
*norton's theorem States that a linear two-terminal circuit can be replaced by an equivalent circuit consisting of an equivalent current source and a shunt equivalent admittance.
*NOT circuit A logic circuit that inverts its only input.
*NTP, *Normal temperature and pressure condition. Normal temperature may be taken as 0oC (physics) or 20oC (engineering) while normal pressure is taken as 760 torr.
*nuclear energy Energy produced in the form of heat during the fission process in a nuclear reactor. When released in sufficient and controlled quantity, this heat energy may be used to produce steam to drive a turbine-generator and thus be converted to electrical energy.
*nuclear fission A nuclear reaction in which a heavy atomic nucleus splits into two parts, and at the same time emitting neutrons and releasing very large amounts of nuclear energy.
*nuclear fuel Fissionable materials that have been enriched to such a composition that, when placed in a nuclear reactor, will support a self-sustaining fission chain reaction, producing heat in a controlled manner for process use.
*nuclear fusionA nuclear reaction between light atomic nuclei as a result of which a heavier nucleus is formed and a large quantity of nuclear energy is released.
*nuclear power power released in exothermic (a reaction which gives off heat) nuclear reactions which can be converted to electric power by means of heat transformation equipment and a turbine-generator unit.
*nuclear power plant A facility in which heat produced in a reactor by the fissioning of nuclear fuel is used to drive a steam turbine.
*NVD: *neutral voltage displacement.- A technique to measure the displacement of the neutral voltage with respect to earth.
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*obligation to serve The obligation of a utility to provide electric service to any consumer who seeks that service, and is willing to pay the rates set for that service.
Traditionally, utilities have assumed the obligation to serve in return for an exclusive monopoly franchise.
*octal A group of 8 symbols from 0 to 7.
*odd symmetry or *odd function A function has odd symmetry when its plot is anti-symmetrical about the vertical axis. f(t) = - f(-t)
*oerstead Oe An old unit of magnetic field in the c.g.s. system. 1 Oe = 7.958 x 10-1 A/m
*ohm, W SI unit of electric resistance. One ohm is equal to the electric resistance between two points of a conductor when a constant potential difference of 1 V, applied to these points, produces in the conductor a current of 1 A, the conductor not being the seat of any electromotive force.
*ohmmeter A device for measuring electrical resistance directly in ohm.
*ohm's law States that the voltage across a resistor is directly proportional to the current flowing through the resistance.
*off-line UPS An uninterruptible power supply (UPS) which feeds power to the load directly from the utility and then transfers to battery power via an inverter after utility drops below a specified voltage. The delay between utility power loss and inverter startup can be long enough to disrupt the operation of some sensitive loads.
*off-peak Periods of relatively low system demands.
*online UPS A UPS in which the inverter is on during normal operating conditions supplying conditioned power to the load through an inverter or converter that constantly controls the AC output of the UPS regardless of the utility line input. In the event of a utility power failure, there is no delay or transfer time to backup power.
*on-peak energy Energy supplied during periods of relatively high system demand as specified by the supplier.
*op amp, *operational amplifier An electronic circuit element that behaves like a voltage-controlled voltage source. It is designed to perform mathematical operations of addition, subtraction, multiplication, division, differentiation and integration.
*open circuit A circuit element which has an impedance approaching zero.
*operating temperature The range of temperature over which a device may be safely used. The temperature range which the device has been designed to operate.
*operating voltage The value of the voltage under normal conditions at a given instant and at a given point in the system.
*operational amplifier [see op amp]
*operation and maintenance (*O & M , *O and M) expenses Costs that relate to the normal operating, maintenance and administrative activities of a business.
*operator person handling equipment.
*optical radiation Electromagnetic radiation at wavelengths between the region of transition to Xrays (l » 1 nm) and the region of transition to radio waves (l » 1 mm).
*optocoupler A combination of an LED and a photodiode to give high isolation between the input and the output.
*optoelectronics A technology that combines optics and electronics, including many devices based on the action of a pn junction. Examples are LEDs, photodiodes, and optocouplers.
*OR gate A logic circuit that outputs a HIGH whenever one of its inputs is a HIGH.
*origin of an installation The position at which electrical energy is delivered to an electrical installation.
*options Options are potential decisions over which a utility has a reasonable degree of control.
*oscillator A circuit that produces an alternating waveform as output when the primarily powered by a direct input.
*oscilloscope An instrument for making visible the instantaneous values of one or more rapidly varying electrical quantities as a function of time or of another electrical or mechanical quantity.
*outage The period during which a generating unit, transmission line, or other facility is out of service.
*outlet A point on the wiring system at which current is taken to supply utilization equipment.
*overcurrent Any current in excess of the rated current of equipment or the ampacity of a conductor. It may result from overload, short circuit, or ground fault.
*overcurrent detection A method of establishing that the value of current in a circuit exceeds a predetermined value for a specified length of time.
*overload Over-loading occurs when extra power is taken from the supply. The increased current due to over-loading will have an immediate effect on the cables; they will begin to heat up. If the over-loading is sustained the result could be an accelerated deterioration of the cable insulation and its eventual breakdown to cause an electrical fault.
*overload current An overcurrent occurring in a circuit which is electrically sound.
*overload protection Effect of a device operating on excessive current, but not necessarily on short circuit, to cause and maintain the interruption of current flow to the device being managed.
*overload relay A relay that responds to electric load and operates at a pre-set value of overload.
*overvoltage Similar to a surge but for a longer period of time, over 2.5 second.
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*panelboard A single panel or group of panel units designed for assembly in the form of a single panel, including buses and automatic overcurrent devices, and equipped with or without switches for the control of light, heat, or power circuits; designed to be placed in a cabinet or cutout box placed in or against a wall, partition, or other support; and accessible only from the front.
*paper Normally consists of sheets of cellulose, mainly obtained from wood pulp from which lignin and other non-cellulosic materials have been removed.
*parallel Two or more elements are connected in parallel if they are connected to the same pair of nodes. parallel elements have the same voltage across them.
*parallel resonance A resonance condition usually occurring in parallel RLC circuits, where the voltage becomes a maximum for a given current.
*parity bit An additional bit that is attached to each code group so that the total number of 1s being transmitted is either odd or even.
*partial discharge Discharges which are partial and are not flash overs across electrodes.
*pascal (pa) SI unit of pressure. One pascal is equal to the force of one newton exerted on one square meter.
*passive element An element which does not generate electricity but either consumes it or stores it.
*payback period The length of time it takes for the savings received to cover the cost of implementing the technology.
*peak Period of relatively high system demand.
*peak Maximum value of an alternating or other waveform.
*peak clipping Peak clipping is used to reduce a utility's system peak, reducing the need to operate peaking units with relatively high fuel costs. Peak clipping is pursued only when the resources are not expected to be able to meet the impending load requirements.
*peak day The day of highest customer demand for electricity during a year.
*peak demand The maximum load during a specified period of time.
*peak factor Ratio of the peak value to the r.m.s. value of an alternating waveform.
*peaking capacity Capacity of generating plants normally reserved for operation during the hours of highest daily, weekly, or seasonal loads.
This equipment is usually designed to meet the portion of load that is above base load.
*peaking plants power plants that operate for a relatively small number of hours, usually during peak demand periods. Such plants usually have high operating costs and low capital costs.
*peak inverse voltage In an electron tube, the maximum negative voltage that can be applied to the plate without danger of arc-over. In a semiconductor diode, the maximum reverse bias voltage that can be applied without reaching the zener (or breakdown) voltage.
*peak shaving Techniques used by electric utilities to lower the peak demand on the system.
*peak-to-peak value The maximum voltage change occurring during one cycle of alternating voltage or current. The total amount of voltage between the positive peak and the negative peak of one cycle or twice the peak value.
*peak value The highest or maximum value of an alternation of alternating current or voltage. This peak value occurs twice during each cycle.
*pebi(pi) Binary multiple prefix corresponding to petabinary or 250 or (210)5 or 10245. [IEC 1998]
*PEN conductor A conductor combining the functions of both protective conductor and neutral conductor.
*period Duration between repetitions of a waveform cycle. It is also equal to the inverse of frequency).
*periodic function A function which repeats itself after a definite period.
*performance attributes Performance attributes measure the quality of service and operating efficiency. Loss of load probability, expected energy curtailment, and reserve margin are some of the performance attributes.
*permanent magnet moving coil meter or *pmmc [see moving coil meter]
*permeability A measure of how easily magnetic lines of force can pass through a material. The permeability of a material is defined as the constant of proportionality between the magnetic flux density and the magnetic field. It is a constant for a given magnetic material in the linear region.
*permeability of free space (eo) = 8.854 x 10-12 F/m
*permeance Inverse of reluctance. [Unit: H]
*permittivity The permittivity of a material is defined as the constant of proportionality between the electric flux density and the electric field. It is a constant for a given dielectric.
*permittivity of free space (µo) = 4 x 10-7 H/m
*per unit *pu per unit is a method of expressing the value of a quantity in terms of a reference or base quantity. It is very similar to percentage, except that there is no multiplying constant of 100.
*peta (P) Decimal multiple prefix corresponding to 1015.
*petroleum A mixture of hydrocarbons existing in the liquid state found in natural underground reservoirs often associated with gas. petroleum includes crude oil, fuel oil, kerosene and jet fuel.
*petroleum (crude oil) A naturally occurring, oily, flammable liquid composed principally of hydrocarbons. Crude oil is occasionally found in springs or pools but usually is drilled from wells beneath the earth's surface.
*phase conductor A conductor of an a.c. system for the transmission of electrical energy other than a neutral conductor, a protective conductor or a PEN conductor. The term also means the equivalent conductor of a d.c. system unless otherwise specified in the Regulations.
*phase difference Difference in phase angle between two sinusoids or phasors.
*phase modulation Modulation of the phase angle of a sinusoidal carrier by an amount proportional to the instantaneous value of the modulating wave.
*phase sequence or *phase rotation The time order in which the voltages (or currents) pass through their respective maximum values (or any other definable position).
*phase voltage The voltage between the phase and neutral of a three phase system is defined as the phase-to-neutral voltage or more commonly as the phase voltage. For a balanced three phase system, the phase voltage is 1/S3 times the line-to-line voltage. The voltage across one arm of either a star-connected load or a delta-connected load is also sometimes referred to as the voltage across a phase or phase voltage. This latter quantity is the same as the phase-to-neutral voltage for a star-connected load, and the line-to-line voltage for a delta-connected load.
*phasor Representation of a sinusoid on the Argand diagram in the form of the magnitude (usually r.m.s.) and phase angle. It may be represented as a complex number in either cartesian co-ordinates or polar co-ordinates.
*phosphor A substance which is capable of luminescence. That is storing energy and later releasing it in the form of light.
*photocell or *photo-electric cell Device used for the detection and measurement of light.
*photodiode A reverse biased diode that is sensitive to incoming light.
*photon A quantum of electromagnetic radiation which has zero rest mass and energy equal to the product of the frequency of radiation and planck's constant.
*photovoltaic A technology that directly converts light into electricity. The process uses modules, which are usually made up of many cells (thin layers of semiconductors).
*PID A three mode control consisting of time Proportioning, Integral and Derivative rate action.
*piecewise continuous waveforms Waveforms which are essentially continuous but in which multi-values occur over finite bounds. The waveform is single-valued and continuous in pieces.
*piezo electric effect Vibrtion that occurs when a crystal is excited by an ac signal across its plates.
*pico (p) Decimal sub-multiple prefix corresponding to one trillionth (US) or 10-12.
*pilot program A utility program offering a limited group of consumers their choice of certified or licensed energy suppliers on a one year minimum trial basis.
*planned generator Proposal to install generating equipment at an existing or planned facility or site.
*Plant A facility containing prime movers, electric generators, and other equipment for producing electric energy.
*plasma An ionized gas containing about equal numbers of positive and negative charges, which is a good conductor of electricity, and is affected by a magnetic field.
*planck's constant (h) = 6.6262x10-34 Js = 4.1357x10-15 eVs,
*planck's constant (h/2p) = 1.05459x10-34 Js
*plug A device, provided with contact pins, which is intended to be attached to a flexible cable, and which can be engaged with a socket outlet or with a connector.
*pN junction A junction between an N-type semiconductor and a p-type semiconductor made by some method of diffusing, fusing or melting.
*point (in wiring) A termination of the fixed wiring intended for the connection of current using equipment.
*point of common coupling Power supplier-consumer metering point at which power is supplied to the electrical equipment of the consumer.
*point of common coupling *PCC: The location of the connection between the CEB network and the Embedded Generator, beyond which other customer loads may be connected on the CEB side. The PCC may be separate from the Point of Supply where a line is dedicated to the connection of an Embedded Generator.
*point of delivery Point for interconnection on the Transmission Provider's System where capacity and/or energy are made available to the end user.
*point of supply *POS: - The location of the connection between the CEB network and the Embedded Generator.
*polar co-ordinates The (r,q) co-ordinates of a point in the plane.
*polarity Magnetically, opposite poles, north and south. In electricity, oppositely charged poles, positive and negative.
*polarisationChange in the potential of an electrode as the result flow.
*polyphase A general term applied to any system of more than a single phase. This term is ordinarily applied to symmetrical systems.
*polygon of forces If the forces acting on an object can be represented by the sides of a polygon taken in order, the forces will be in equilibrium.
*polythene Tough thermoplastic material, made by the polymerisation of ethylene. It is flexible, transparent, chemically resistance and a good electrical insulator.
*polyvinyl chloride *PVC A white thermoplastic material, produced by the polymerisation of vinylidene chloride.
*porcelain Hard, white material made by the firing of a mixture of pure kaolin (china clay) with felspar and quartz, or with other materials containing silica.
*port A pair of terminals through which a single current may enter or leave a network.
*portable equipment Electrical equipment which is moved while in operation or which can easily be moved from one place to another while connected to the supply.
*positive feedback Feedback where the returning signal aids the effect of the input signal.
*positive sequence A balanced set of three phase components which have the same magnitude, same sequence as the original unbalanced set, and phase angle diferring from each other by 120o. The frequency is of course the same as the original unbalanced three phase system.
*potential difference potential difference is the work done in moving a unit positive electric charge from one point to another. [Unit: volt or V]
*potential divider A combination of impedances which allows a fraction of the input voltage to be taken as output.
*potential energy Energy which a body possesses by virtue of its position. The potential energy of water in a reservoir is usually measured with respect to sea level.
*potential equalization conductor Conductor providing a connection between equipment and the potential equalization busbar of the electrical installation.
*potential transformer An instrument transformer specifically designed to give an accurate voltage ratio for measurement and/or control purposes. They are always connected in parallel with the circuit (like a voltmeter).
*potentiometer A three terminal device with a wiper that is positioned along a resistive element, making it a voltage divider.
*potentiometer It is essentially a piece of apparatus by means of which emfs are compared using null deflection.
*pound lb The imperial unit of weight. 1 lb = 0.453,592 kg
*poundal The imperial unit of force. It is that force which acting on a mass of 1 lb will impart to it an acceleration of 1 ft/s2.
*power Is the time rate of consuming or absorbing energy. [Unit: watt or W]
*power The active component of power in an alternating circuit is usually referred to as power or active power. [Unit: watt or W]
*power conditioning systems A broad class of equipment that includes filters, isolation transformers, and voltage regulators. Generally, these types of equipment offer no protection against power outages.
*power dissipation The amount of power that is consumed and converted to heat.
*power distribution unit A portable electrical distribution unit that provides an easily expandable and flexible electrical environment for an equipment and its associated peripherals.
*power exchange This is a commercial entity responsible for facilitating the development of transparent spot prices for energy capacity, and/or ancillary services.
*power factor *PF Ratio of the active power consumed by a component or circuit to the apparent power. For purely sinusoidal waveforms, this is also equal to the cosine of the phase angle between the voltage and the current.
*power factor correction process of increasing the power factor to near unity without altering the original load.
*power factor correction capacitor This is a device that helps improve the efficiency of the flow of electricity through distribution lines by reducing energy losses. It is installed in substations and on poles. Usually it is installed to correct an unwanted condition in an electrical system.
*power grid (*National Grid) A network of power lines and associated equipment used to transmit and distribute electricity over a geographic area (or country).
*power marketers Entities engaged in buying and selling electricity.
*power plant A generating station where electricity is produced.
*power pool An association of two or more interconnected electric systems having an agreement to coordinate operations and planning for improved reliability and efficiencies.
*power purchase agreement A contract entered into by an independent power producer and an electric utility. The power purchase agreement specifies the terms and conditions under which electric power will be generated and purchased.
Power purchase agreements generally include: specification of the size and operating parameters of the generation facility; contract terms; price mechanisms; service and performance obligations; dispatchability options; and conditions of termination or default.
*power purchase agreement *PPA An agreement between the CEB and the Generating Company for the purchase of electricity by the CEB.
*power supply The part of a circuit that supplies power to the entire circuit or part of the circuit. Usually a separate unit that supplies power to a specific part of the circuit in a system.
*precision Degree of agreement within a group of measurements or instruments.
*present value The amount of money required to secure a specified cash flow on a future date at a given rate of return.
*present worth factor The adjustment factor that discounts a sum of future dollars back to the current year.
*pressure The force per unit area acting on a surface.
*price cap Situation where a price has been determined and fixed.
*primary That winding of a transformer which is connected to and receives energy from an external source of electrons.
*primary circuit Distribution circuit (less than 69,000 volts) on the high voltage side of the transformer.
*prime moverThe engine, turbine, water wheel, or similar machine that drives an electric generator; or, for reporting purposes, a device that converts energy to electricity directly (e.g., photovoltaic solar and fuel cells).
*printed circuit A method of manufacturing parts of electronic equipment in which the wiring between components, and certain fixed components themselves, are printed on to an insulating board.
*probe An oscilloscope input device, usually having a pointed metal tip for making electrical contact with a circuit element and a flexible cable for transmitting the signal to the oscilloscope.
*production The act or process of generating electric energy.
*production costing A method used to determine the most economical way to operate a given system of power resources under given load conditions.
*project financing Most commonly used method to finance the construction of independent power facilities. Typically, the developer pledges the value of the plant and part or all of its expected revenues as collateral to secure financing from private lenders.
*pROMA ROM that can be programmed by the user. It cannot be reprogrammed.
*prorated bills The computation of a bill based upon proportionate distribution of the applicable billing schedule.
*prospective fault current The value of overcurrent at a given point in a circuit resulting from a fault of negligible impedance between live conductors having a difference of potential under normal operating conditions, or between a live conductor and an exposed conductive part.
*protective conductor A conductor used for some measures of protection against electric shock and intended for connecting together any of the following parts:
- exposed conductive parts
- extraneous conductive parts
- the main earthing terminal
- earth electrode(s)
- the earthed point of the source, or an artificial neutral.
*protective conductor current Electric current which flows in a prospective conductor under normal operating conditions:
*protective multiple earthing (PME) An earthing arrangement, found in TN C S systems, in which the supply neutral conductor is used to connect the earthing conductor of an installation with Earth, in accordance with the Electricity Safety, Quality and Continuity Regulations 2002.
*protective earth conductor Conductor to be connected between the protective earth terminal and an external protective earthing system.
*protective earth terminal Terminal connected to conductive parts of Class I equipment for safety purposes. This terminal is intended to be connected to an external earthing system by a protective earth conductor.
*protective extra low voltage *PELV An extra low voltage system which is not electrically separated from earth, but which otherwise satisfies all the requirements for SELV.
*psi lb/in2 Unit of pressure in the imperial system.1 psi = 6895 pa
*proximity sensor or proximity switch A sensor or switch with the ability to detect it's relationship to a metal target without making physical contact.
*public utility A utility operated by a non-profit governmental or quasi-governmental entity. Public utilities include municipal utilities, cooperatives, and power marketing authorities.
*public utility commission State regulatory agencies that provide oversight, policy guidelines and direction to public utilities including electricity.
*publicly owned utilities Municipal utilities (utilities owned by branches of local government) and/or co-operatives (utilities owned cooperatively by consumers).
*pulse width modulation *PWM Control of the width of pulses for the purpose of information transmission.
*pumped storage hydroelectric plant A plant that usually generates electric energy during peak-load periods by using water previously pumped into an elevated storage reservoir during off-peak periods when excess generating capacity is available.
*pumped storage A facility designed to generate electric power during peak load periods with a hydroelectric plant using water pumped into a storage reservoir during off-peak periods.
*purchased power adjustment A clause in a rate schedule that provides for adjustments to a bill when energy from another system is acquired.
*pushbutton part of an electrical device, consisting of a button that must be pressed to effect an operation.
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*quadrant Quarter circle. Sector of a circle bounded by an arc and two radii at right angles.
*quadratic equation An equation involving terms up to the second power of the unknown quantity. It has two roots which satisfy the equation.
*quadrature Two quantities which are at right angle to each other.
*quality factor Q The quality factor of a resonant circuit is the ratio of its resonant frequency to its bandwidth. The higher the quality factor, the lower the losses in the circuit and higher the resonant peak.
*quality control Inspection, analysis and action required to ensure quality of output.
*quantisation error The error caused by non-zero resolution of an analog to digital converter. It is an inherent error of the device.
*quantum One of the very small discrete packets into which many forms of energy are subdivided.
*quantum electronics Applying molecular physics to electronics.
*quark A hypothetical basic subatomic nuclear particle believed to be the basic component of protons, neutrons, etc.
*quartz A form of silicone dioxide. Commonly used in the making of radio transmitters and heat resistant products.
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*raceway An enclosed channel of metal or nonmetallic materials designed expressly for holding wires, cables, or busbars. Raceways include, but are not limited to, rigid metal conduit, rigid nonmetallic conduit, intermediate metal conduit, liquidtight flexible conduit, flexible metallic tubing, flexible metal conduit, electrical nonmetallic tubing, electrical metallic tubing, underfloor raceways, cellular concrete floor raceways, cellular metal floor raceways, surface raceways, wireways, and busways.
*rad The unit of absorbed dose of ionising radiation. One rad is equal to the energy absorption of 100 ergs per gram of irradiated material.
*radar An acronym for RAdio Detection And Ranging. A general term now used to include any system employing microwaves for the purpose of locating, identifying, navigating, or guiding such moving objects as ships, aircraft, etc.
*radial circuits Each circuit commences from the consumer unit/distribution board through an MCB/fuse of specific rating (e.g. 20A), loop into each socket outlet but ends at a socket outlet (does not return to the original fuse/mcb). No loops are formed.
*radian (rad) The radian is SI unit of the plane angle. It is a supplementary unit. It is defined as the plane angle between two radii of a circle that cut off on the circumference an arc equal in length to the radius.
*radiant efficiency Ratio of the radiant flux (power) emitted from a source to the power consumed.
*radiation RF energy which is emitted or leaks from a distribution system and travels through space. These signals often cause interference with other communication services.
*radio The use of electromagnetic radiation to communicate electrical signals without wires. In the widest sense the term incorporates sound broadcasting, television and radar.
*radio-activity The property of spontaneous disintegration possessed by certain unstable types of atomic nucleii.
*radio-frequency interference *RFI Electromagnetic signals of a frequency associated with electromagnetic radiation which are coupled to a conductor either directly or as with an antenna.
*RAM, *Random access memory . A memory in which the access time is the same for all locations.
*rankine oR scale of temperature It is the absolute Fahrenheit scale, starting from absolute zero at - 459.69 oF. Can be converted to degree Fahrenheit by the addition of 459.69 oF.
*rated voltage The voltage of electrical apparatus at which it is designed to operate.
*ratepayer A retail consumer of the electricity distributed by an electric utility. This includes residential, commercial and industrial users of electricity.
*rating The rating of an electrical device includes (1) the normal r.m.s. current which it is designed to carry, (2) the normal r.m.s. voltage of the circuit in which it is intended to operate, (3) the normal frequency of the current and the interruption (or withstand) rating of the device.
*RCCB [see residual current circuit breaker]
*RCD [see residual current device]
*reactance That part of the impedance that does not consume active power. It is the imaginary part of the impedance.
*reactive power That component of complex power which corresponds to storage and retrieval of energy rather than consumption.
*read The process of retrieving information from a memory.
*real-time pricing The instantaneous pricing of electricity based on the cost of the electricity available for use at the time the electricity is demanded by the consumer.
*receiver The part of a communications system which converts electrical waves into visible or audible form.
*recovered energy Reused heat or energy that otherwise would be lost.
For example, a combined cycle power plant recaptures some of its own waste heat and reuses it to make extra electric power.
*rectification The conversion of ac to pulsating dc.
*rectifier A device which converts ac to pulsating dc.
*rectifier type meter A moving coil meter used together with a bridge rectifier to measure the average value of the waveform. They are usually calibrated to read the rms value of a sinusoidal waveform by multiplication by the form factor 1.1107 during calibration.
*redundancy Duplication of elements in a system or installation to enhance the reliability or continuity of operation.
*reduced low voltage system A system in which the nominal phase to phase voltage does not exceed 110 volts and the nominal phase to earth voltage does not exceed 63.5 volts.
*refresh The process of renewing the contents of a dynamic memory.
*register A group of flip-flops capable of storing data.
*regulation A term used to describe the action of holding a constant electrical value in the face of fluctuations.
*regulation An activity of government to control or direct economic entities by rulemaking and adjudication.
*reinforced insulation Single insulation system applied to live parts which provide a degree of protection against electric shock equivalent to double insulation under the conditions specified in the relevant standard. The term 'single insulation' does not imply that the insulation must be one homogeneous piece. It may comprise several layers which cannot be tested singly as supplementary or basic insulation.
*reflection process of sending back that occurs when a surge meets a discontinuity in transmission.
*relative humidity The ratio of the pressure of water vapour actually present in the atmosphere to the pressure of the vapour which would be present if the vapour were saturated at the same temperature. [This is also sometimes expressed in terms of masses rather than pressure].
*relative permeability Ratio of the permeability of the magnetic material to that of free space. The permeability of free space is 4p´10-7 H/m. The permeability of air is very nearly equal to the permeability of free space.
*relative permittivity Ratio of the permittivity of the dielectric material to that of free space. The permittivity of free space is 8.854´10-12 F/m. The permittivity of air is very nearly equal to the permittivity of free space.
*relay An electric device that is designed to interpret input conditions in a prescribed manner and, after specified conditions are met, to respond and cause contact operation or similar abrupt changes in associated electric control circuits.
*reliability The guarantee of system performance at all times and under all reasonable conditions to assure constancy, quality, adequacy and economy of electricity. It is also the assurance of a continuous supply of electricity for customers at the proper voltage and frequency.
*reliability Electric system reliability has two components - adequacy and security.
Adequacy is the ability of the electric system to supply the aggregate electric demand and energy requirements of the consumers at all times, taking into account scheduled and unscheduled outages of system facilities.
Security is the ability of the electric system to withstand sudden disturbances such as electric short circuits or unanticipated loss of system facilities.
*reluctance The reluctance of a magnetic material is the ability to oppose the flow of magnetic flux. It is the constant of proportionality between the applied mmf and the flux produced. [Unit: henry-1]
*remanence The residual magnetisation of a ferromagnetic substance subjected to a hysteresis cycle when the magnetising field is reduced to zero.
*remote control The Control of an electrical device from a remote point.
*renewable energyEnergy sources that are derived from the sun or other natural processes and which can be naturally replenished. Examples include wind, solar, geothermal, hydro, photovoltaic, wood and waste. [Non-renewable energy sources include coal, oil, and gas which all exist in finite amounts.]
*repowered plant An existing power facility that has been substantially rebuilt to extend its useful life.
*reregulation The design and implementation of regulatory practices to be applied to the remaining regulated entities after restructuring of the vertically-integrated electric utility.
Reregulation could employ the same or different regulatory practices as those used before restructuring.
*resellers Companies that purchase utility service from a wholesaler and resell it to consumers.
*reserve capacity Capacity in excess of that required to carry peak load.
*reserve margin The percentage of installed capacity exceeding the expected peak demand during a specified period.
*residential The residential sector is defined as private household establishments which consume energy primarily for lighting, refrigeration, cooking, heating and air conditioning.
*residual fuel oil The topped crude oil remaining after the refining operation. Residual fuel oil is used for the production of electric power and various industrial purposes.
*residual current Algebraic sum of the currents in the live conductors of a circuit at a point in the electrical installation.
*residual current circuit breaker *rccb [see residual current device]
*residual current device *rcd Devices are designed to protect both equipment and users from fault currents between the live and earth conductors. An RCD detects the residual current between the live and neutral conductors and prevents fatal electric shocks by disconnecting the supply if the detected current exceeds a safe limit (typically 30mA).
*residual voltage or *discharge voltage The voltage that appears between the line and earth terminals of the surge diverter during the passage of discharge currents.
*resinNatural resins are amorphous organic compounds which are secreted by certain plants and insects. They are usually insoluble in water but soluble in various organic solvents.
*resistance The resistance of an element denotes its ability to resist the current flow through it. [Unit: ohm or W].
*resistance area (for an earth electrode only) The surface area of ground (around an earth electrode) on which a significant voltage gradient may exist.
*resistance thermometer A device to measure temperature using the temperature coefficient of the material of the device (usually platinum wire).
*resolution The smallest change that can occur in the output for a change in the input.
*resonance A condition in which a quantity reaches maximum value. In electrical circuits, it is a condition in an RLC circuit in which the magnitude of the voltage or the current becomes a maximum or the circuit becomes purely resistive.
*response time The amount of time it takes for a device to react to an input signal.
*rest mass The mass of a body when at rest relative to the observer.
*restructuring The reconfiguration of the vertically-integrated electric utility.
Restructuring usually refers to separation of the various utility functions into individually-operated and-owned entities.
*retail Sales covering electrical energy supplied for residential, commercial, and industrial end-use purposes.
*retail company A company that is authorized to sell electricity directly to industrial, commercial and residential end-users.
*retail competition A system under which more than one electric provider can offer to sell to retail consumers, and retail consumers are allowed to choose more than one provider from whom to purchase their electricity.
*retail transaction The sale of electric power from a generating company or wholesale entity to the consumer.
*return stroke The neutralising and main stroke in a lightning strike.
*revenue The total amount of money received by an organisation from sales of its products and/or services, gains from the sales or exchange of assets, interest and dividends earned on investments, and other increases in the owner's equity except those arising from capital adjustments.
*reverse bias A dc voltage applied to a pN junction so that the positive terminal of the voltage source connects to the N-type material and the negative terminal to the p-type material. It produces reverse current in the circuit.
*rewirable fuse It is a semi-enclosed simple fuse which can be re-wired. It consists of a short length of wire, generally of tinned copper.
*rheostat An adjustable resistor constructed so that its resistance may be changed without opening the circuit.
*ring circuit Each circuit commences from consumer unit (or distribution board) through an MCB (or fuse) of specific rating usually 30 A, loops into each socket outlet and returns to the same MCB (or fuse) in the consumer unit (distribution board). Looping must be done for the live conductor, neutral conductor and the protective conductor in separate rings. The ring method of connection is done only for the 13 A socket outlets, as the individual 13A plugs are separately having fuses (fuses may be usually rated at 13 A or 3 A depending on the type of load).
*ripple A fluctuation in the intensity of a steady current or voltage.
*rise timeUsually defined as the time taken for the leading edge of a pulse or waveform to rise from 10% to 90% of its final value.
*rms value or root-mean-square value The rms value of a periodic waveform is obtained by taking the square root of the mean of the squared waveform. It is also the same as the effective value of the waveform. For a.c. waveforms, unless otherwise specified, it is always the rms value that is specified.
*ROM Read only memory.
*room index K Code number, representative of the geometry of a room, used in calculation of the utilization factor or the utilance. The room index is usually given by the formula K = (l x b)/h(l + b) where: l is the length of the room, b is the width and h is the distance of the luminaires above the working plane.
*root mean square value [see rms value]
*rotor The rotating cylindrical member of a machine, placed inside the stator with a narrow intervening air gap to allow for smooth rotation.
*routine tests Routine tests are conducted on each and every single equipment to ensure that each equipment meets a minimum standard of quality.
*rpm Speed of rotation of a machine expressed in revolutions per minute.
*RS-232 port This is a serial port. A method of communicating digital information in which the data bits are transmitted sequentially over one line.
*running and quick-start capability Generating units that can be made available to carry load within a 30-minute period.
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*sag A voltage sag is a momentary (less than 2 seconds and more than 1 cycle) decrease in voltage outside the normal tolerance. Voltage sags are often caused by starting heavy loads, such as motors or welding equipment, and by power system faults.
*sample tests This is done only on a few samples of the equipment. In these the sample is tested fully, up to and including the point of breakdown.
*saponification The chemical process of forming a soap. More particularly a deterioration by softening of caused by the action of aqueous alkali on fatty-acid constituents.
*scheduled outage The shutdown of a generating unit, transmission line, or other facility, for inspection or maintenance, in accordance with an advance schedule.
*SCR Silicone Controlled Rectifier.
*second(s) The second is the SI unit of time. It is a fundamental unit. It is defined as the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom 
*secondary That winding of a transformer which receives its energy by electromagnetic induction from the primary. A transformer may have one or more secondaries.
*selector switch A multi-position switch which can be set to the desired mode of operation.
*self-generation A generation facility dedicated to serving a particular retail consumer, usually located on the consumer's premises.
The facility may either be owned directly by the retail consumer or owned by a third party with a contractual arrangement to provide electricity to meet some or all of the consumer's load.
*semiconductor An electrical conductor whose resistance decreases with rising temperature and the presence of impurities, in contrast to normal metallic conductors for which the reverse is true. Semiconductors which may be elements or compounds include germanium, silicon and selenium.
*semi-enclosed fuse [see rewirable fuse]
*sensitivity Ratio of the output signal or response of the instrument to a change of input or measured variable.
*sequence components [see symmetrical components]
*separated extra low voltage (SELV) An extra low voltage system which is electrically separated from Earth and from other systems in such a way that a single fault cannot give rise to the risk of electric shock.
*series Two or more elements are connected in series if they are connected sequentially. Series elements have the same current through them.
*series resonance A resonance condition usually occurring in series RLC circuits, where the current becomes a maximum for a given voltage.
*series motor d.c. motor with a series connected field.
*seven segment display A display consisting of 7 linear segments arranged in such a way as to be able to produce all the 10 digits from 0 to 9 by proper excitation.
*service agreement An agreement entered into by the transmission customer and transmission provider.
*service life The length of time a piece of equipment can be expected to perform at its full capacity.
*sheath The covering around the insulation of a cable.
*sheet lightning Lightning in diffused or sheet form due to reflection and diffusion by the clouds and sky. A single bolt within a cloud or between clouds can illuminate an entire cloud from the inside. This is called sheet lightning.
*shellac A yellowish natural resin secreted by the lac insect which is parasitic on certain trees.
*shielding The process of shielding pieces of apparatus from the effect of electrostatic fields which are external to the apparatus itself.
*shielding protective coating that helps eliminate electromagnetic and radio frequency interference.
*short circuit A circuit element which has an impedance approaching zero.
*shift register A digital circuit capable of storing and shifting binary data.
*shock current A current passing through the body of a person or livestock such as to cause electric shock and having characteristics likely to cause dangerous effects.
*short circuit current An overcurrent resulting from a fault of negligible impedance between live conductors having a difference in potential under normal operating conditions.
*shunt A component connected in parallel. A current shunt is a device for altering the amount of electric current flowing through a piece of apparatus, such as a galvanometer.
*shunt motor d.c. motor with a shunt connected field.
*side band The band of frequencies lying on either side of a modulated carrier wave.
*SI units The International System of Units.
*siemens (S) SI unit of electric conductance. One siemens is equal to the conductance between two points of a conductor having a resistance of 1 W. siemens is the reciprocal of the ohm.
*signal A visual, audible, electrical or other indication used to convey information.
*signal-to-noise ratio *S/N ratio The ratio of desired signal level to the undesired noise level, expressed in dB.
*silicon controlled rectifier or SCR A thyristor.
*simultaneously accessible parts Conductors or conductive parts which can be touched simultaneously by a person or, in locations specifically intended for them, by livestock. Simultaneously accessible parts may be: live parts, exposed conductive parts, extraneous conductive parts, protective conductors or earth electrodes.
*sine wave A sinusoidal periodic oscillation. The fundamental waveform from which other waveforms may be generated by combinations of various group of harmonics. The voltage and current waveforms produced from the power company generators (alternators) are basic sine waves.
*single phase A circuit having two conductor, one of which is the live conductor and the other the neutral conductor.
*single phase line Carries electrical loads capable of serving the needs of residential consumers, small commercial consumers, and streetlights. It carries a relatively light load as compared to heavy duty three phrase constructions.
*single-point ground The practice of tying the power neutral ground and safety ground together at the same point, thus avoiding a differential ground potential between points in a system.
*single sweep The ability of an oscilloscope to display just one window of time, thus preventing unwanted multiple displays. Necessary in the display of transient waveforms.
*sine wave A fundamental waveform produced by periodic oscillation that expresses the sine or cosine of a linear function of time or space, or both.
*sinusoid A signal which is having a sinusoidal waveform.
*Skilled person A person with technical knowledge or sufficient experience to enable him/her to avoid dangers which electricity may create.
*skin effect The tendency of current to stick to the outer layers of a conductor due to the presence of internal flux. The skin effect is more prominent at higher frequencies.
*slip per unit speed by which the rotor falls behind the stator field. Slip is positive for induction motors and negative for induction generators.
*slip rings The rotating contacts which are connected to the loops of a generator.
*small power producer Refers to a producer that generates at least 75% of its energy from renewable sources.
*socket outlet A device, provided with female contacts, which is intended to be installed with the fixed wiring, and intended to receive a plug. A luminaire track system is not regarded as a socket outlet system.
*solar cell An device which converts energy from the sun directly into electrical energy.
*solar thermal electric A process that generates electricity by converting incoming solar radiation to thermal energy.
*solenoid A coil of wire wound uniformly on a cylindrical former, having a length which is large compared with its radius.
*solid state relayA completely electronic switching device with no moving parts or contacts.
*solid angle The angle subtended at the center of a sphere by an area on its surface numerically equal to the square of the radius. [Unit steradian, sr].
*space charge In an electrode assembly, a cloud of free electrons surrounding the cathode.
*specific heat The quantity of heat required to raise the temperature of unit mass through 1oC.
*spectrum The plot of amplitude against frequency.
*speed of light speed of light in vacuum (co) = 2.997 925 x 108 m s-1
*sphere gap A gap between two spherical electrodes. The sphere gap method of measuring high voltage is the most reliable and is used as the standard for calibration purposes.
*spheroid Solid figure generated by an ellipse rotating about one of its axes.
*spike (or impulse, switching surge, lightning surge) These terms refer to a voltage increase of very short duration (microsecond to millisecond). Spikes can range in amplitude from 200 V to 6,000 V and are caused by lightning, switching of heavy loads, and short circuits or power system faults.
*spike A spike involves a sudden marked jump in voltage, which can damage electronics and corrupt or destroy data.
*spike suppressor A device that provides protection against short duration (microsecond to millisecond) voltage increases known as spikes, impulses, transients, or high-frequency surges.
*spinning reserve The generating capacity running at no load and synchronized to the electric system and kept as a reserve to meet sudden increases in demand.
*spinning reserve: The difference between the total available capacity of all generating sets already coupled to the system and their total actual loading.
*spotlight A (small) projector giving concentrated light of usually not more than 20° divergence.
*spot price The price at which the commodity electricity is selling at for immediate delivery at a given time and place.
*spot pricing Determination every half-hour a new price for electricity in a given region of the network. The spot market essentially schedules the cheapest generators tha are able to supply the load.
*sprites Massive but weak luminous flashes that appear directly above an active thunderstorm system and are coincident with cloud-to-ground or intra-cloud lightning strokes. Sprites are immense. They can shoot up from the top of a 8 km thundercloud to heights of 40 km or more.
*spur A branch from a ring final circuit.
*square wave A periodic wave which alternates between two fixed amplitudes for equal lengths of time, with the time of transition between the amplitudes being negligibly small.
*squirrel cage rotor This type of rotor has the simplest and most rugged construction and is almost indestructible. The rotor consists of a cylindrical core with parallel slots for carrying the rotor conductors which are not wires but heavy bars of copper, aluminium or alloys. The rotor bars are permanently short-circuited at the ends to form the winding or cage. About 90% of induction motors are squirrel cage type.
*SRAM Static RAM. A RAM that stores information in flip flop cells which do not have to be refreshed unlike those of the DRAM.
*stability The property of a system or element by virtue of which its output will ultimately attain a steady state. The stability of a power system is its ability to develop restoring forces equal to or greater than the disturbing forces so as to maintain a state of equilibrium.
*stable system A system is stable when all the poles (roots of the denominator) of its transfer function H(s) lie in the left half of the s plane.
*standard cell A specially prepared primary cell which is characterised by a highly constant emf over long periods of time.
*standby power supply The power supply that is available to furnish electric power when the normal power supply is not available.
*star connection A method of connecting three elements of a three-phase electrical system at a common node, and with the three phases being taken from the remaining nodes of the elements. This is also known as “wye” connection.
*starter A device to assist in the starting process.
*stationary equipment Electrical equipment which is either fixed, or equipment having a mass exceeding 18 kg and not provided with a carrying handle.
*statistical impulse voltage This is the switching or lightning overvoltage applied to equipment as a result of an event of one specific type on the system (line energising, reclosing, fault occurrence, lightning discharge, etc), the peak value of which has a 2% probability of being exceeded.
*statistical impulse withstand voltage This is the peak value of a switching or lightning impulse test voltage at which insulation exhibits, under the specified conditions, a 90% probability of withstand. In practice, there is no 100% probability of withstand voltage. Thus the value chosen is that which has a 10% probability of breakdown.
*stator The stationary member of a machine in the form of an hollow cylinder inside which the rotor will be placed with a narrow intervening air gap.
*steady state response Behaviour of a circuit after a long time when steady conditions have been reached after an external excitation.
*steam plant (conventional) A plant in which the prime mover is a steam turbine. The steam used to drive the turbine is produced in a boiler where fossil fuels are burned.
*step leaders Thin, luminous feelers, caused by electrical breakdown in a cloud, that move in short bursts, or steps, and precede lightning strikes. Lightning begins in the negatively charged region at the base of a cloud. Here, thin, barely luminous feelers called step leaders zigzag through the cloud and can travel to the earth.
*step response Behaviour of a circuit when the excitation is the unit step function. The excitation function may be a voltage or a current.
*step voltage: The difference in surface potential experienced by a person bridging a distance of 1 m with his feet without contacting any other grounded structure.
*step waveform A waveform which has one level (usually zero) prior to zero time and another level after time zero.
*steradian (sr) The steradian is SI unit of the solid angle. It is a supplementary unit. It is defined as the solid angle that, having its vertex in the centre of a sphere, cuts off an area of the surface of the sphere equal to that of a square with sides of length equal to the radius of the sphere.
*streamer A ribbon like discharge.
*streamer mechanism The development of a spark discharge directly from a single avalanche.
*strategic conservation Strategic conservation results from load reductions occurring in all or nearly all time periods. This strategy can be induced by price of electricity, energy-efficient equipment, or decreasing usage of equipment.
*strategic load growth A form of load building designed to increase efficiency in a power system. This load shape objective can be induced by the price of electricity and by the switching of fuel technologies (from gas to electric).
*stray coupling Capacitive coupling that may occur between adjacent arms, sources, detector, leads etc.
*stroboscope Any device used to study, measure, balance, or otherwise alter the motion of a moving, rotating, or vibrating body by making it appear to slow down or stop with the use of pulsed bursts of light or by viewing it through intermittent openings in a revolving disk.
*substation A facility used for switching and/or changing or regulating the voltage of electricity. Service equipment, line transformer installations, or minor distribution or transmission equipment are not classified as substations.
*sulphur (in coal) One of the elements present in varying quantities in coal which contributes to environmental degradation when coal is burned. In terms of sulphur content by weight, coal is generally classified as low (less than or equal to 1 percent), medium (greater than 1 percent and less than or equal to 3 percent), and high (greater than 3 percent).
*summing amplifier An op amp that combines several inputs and produces an output that is the weighted sum of the inputs.
*super-conductivity The electrical resistance of a metal or alloy which decreases with decrease in temperature and becoming vanishingly small at a finite temperature.
*superposition The superposition principle states that the results in a circuit due to independent sources can be superposed to give the resultant quantity.
*supplementary insulation In dependent insulation applied in addition to basic insulation in order to provide protection against electric shock in the event of a failure of basic insulation.
*supplier A person or corporation, generator, broker, marketer, aggregator or any other entity, that sells electricity to consumers, using the transmission or distribution facilities of an electric distribution company.
*supply mains permanently installed power source which may also be used to supply electrical apparatus
*supply-side Technologies that pertain to the generation of electricity.
*supply-side management Steps utilities take to manage their generating and transmission facilities for maximum efficiency.
*surge A transient (or momentary) wave of current, potential, or power in an electric circuit.
The word "surge" has different meanings to different engineering communities. To the protection engineer a "surge" is a transient overvoltage with a duration of a few microseconds, i.e., a spike. To others a "surge" is a momentary overvoltage lasting up to a few seconds, a swell.
*surge arrester A protective device for limiting surge voltages on equipment by discharging or bypassing surge current. It prevents continued flow of follow through current to earth, and is capable of repeating these functions as specified.
*surface flashover Surface flashover is a breakdown of the medium in which the solid is immersed. The role of the solid dielectric is only to distort the field so that the electric strength of the medium is exceeded.
*surplus energy Excess firm energy available from a utility or region for which there is no market at the established rates.
*susceptance That part of the admittance that does not consume active power. The imaginary part of admittance. For a pure reactance, it is also the inverse of the reactance.
*swell A momentary overvoltage lasting up to a few seconds.
*switch A mechanical device capable of making, carrying and breaking current under normal circuit conditions, which may include specified operating overload conditions, and also of carrying for a specified time currents under specified abnormal circuit conditions such as those of short circuit. It may also be capable of making, but not breaking, short circuit currents.
*switchboard A large single panel, frame, or assembly of panels on which are mounted on the face, back, or both, switches, overcurrent and other protective devices, buses, and usually instruments. Switchboards are generally accessible from the rear as well as from the front and are not intended to be installed in cabinets.
An assembly of switchgear with or without instruments, but the term does not apply to groups of local switches in final circuits.
*Switchgear An assembly of main and auxiliary switching apparatus for operation, regulation, protection or other. control of an electrical installation.
*switching station Facility equipment used to tie together two or more electric circuits through switches. The switches are selectively arranged to permit a circuit to be disconnected, or to change the electric connection between the circuits.
*Switch, linked A switch the contacts of which are so arranged as to make or break all poles simultaneously or in a definite sequence.
*sweep Movement of the electron beam across a CRT screen.
*symmetrical components The analysis of an unbalanced three phase system into three balanced components, namely the positive sequence, negative sequence and zero sequence.
*synchronous machine A machine which runs at a fixed speed, dependant on the frequency, called the synchronous speed. The machine speed is thus independent of the load.
*synchronous speed A mechanical speed related to the electrical frequency by number of pairs of poles. n = f/p rps = 60f/p rpm
*synthetic oil Oil produced by artificial means and having similar properties to mineral oil.
*system (electric) physically connected generation, transmission, and distribution facilities operated as an integrated unit under one central management.
*system An electrical system consisting of a single source of electrical energy and an installation. For certain purposes of the Regulations, types of system are identified as follows, depending upon the relationship of the source, and of exposed conductive parts of the installation, to Earth:
- *TN system, a system having one or more points of the source of energy directly earthed, the exposed conductive parts of the installation being connected to that point by protective conductors,
- *TN C system, a system in which neutral and protective functions are combined in a single conductor throughout the system,
- * TN S system, a system having separate neutral and protective conductors throughout the system,
- *TN C S system, a system in which neutral and protective functions are combined in a single conductor in part of the system,
- *TT system, a system having one point of the source of energy directly earthed, the exposed conductive parts of the installation being connected to earth electrodes electrically independent of the earth electrodes of the source,
- *IT system, a system having no direct connection between live parts and Earth, the exposed conductive parts of the electrical installation being earthed.
*system peak demand The highest demand value that has occurred during a specified period for the utility system.
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*tachometer An instrument for measuring speed (rpm) of a rotating shaft.
*target market A specific group of people or geographical area that has been identified as the primary buyers of a product or service.
*tariff A document, approved by the responsible regulatory agency, listing the terms and conditions, including a schedule or prices, under which utility services will be provided.
*tebi (Ti) Binary multiple prefix corresponding to terabinary or 240 or (210)4 or 10244. [IEC 1998]
*telecommunications The communication of signals, data, sounds or images over a distance by wire and wireless transmission.
*telegraph A method of transmitting messages over a distance using electrical impulses sent through wires, using the morse code.
*telemetering The transmission of measuring, alarm and control signals to and from remote station controls and a central monitoring location.
*tera (T) Decimal multiple prefix corresponding to Trillion (US) or 1012.
*terminal block An insulating base equipped with terminals for connecting wires.
*tesla (T) SI unit of magnetic flux density. One tesla is defined as the field intensity generating one newton of force per ampere of current per meter of conductor.
*testing The process of verifying the properties of an equipment by a process of application and measurement.
*thermal overload protector Device which protects motor windings from excessive temperature by opening a set of contacts.
*thermal breakdown Heat is generated continuously in electrically stressed insulation by dielectric losses, which is transferred to the surrounding medium by conduction through the solid dielectric and by radiation from its outer surfaces. If the heat generated exceeds the heat lost to the surroundings, the temperature of the insulation increases leading ultimately to thermal breakdown if a stable temperature is not reached.
*thermal mechanism The thermal mechanism uses a heat sensitive bimetal element to operate the circuit breaker in the event of an overcurrent.
*thermal ohm The thermal ohm is the resistance of a path through which a temperature difference of 1 0C produces a heat flow of 1 watt.
*thermal resistance Opposition to the flow of heat.
*thermal resistivity The thermal resistivity is the temperature drop in degree celsius produced by the flow of 1 watt between the opposite faces of a metre cube of the material.
*thermistor An electrical resistor composed of semiconductor material, the electrical resistance of which varies rapidly with increase of temperature.
*thermocouple A device for the measurement of temperature using a bimetallic strip.
*thermoplastic Substance which becomes plastic on being heated. A plastic material which can be repeatedly melted or softened by heat without change of properties.
*thermosetting plastics plastics which, having once been subjected to heat and pressure lose their plasticity.
*thevenin's Theorem States that a linear two-terminal circuit can be replaced by an equivalent circuit consisting of an equivalent voltage source and a series equivalent impedance.
*three phase circuit A combination of circuits energized by three alternating sources which differ in phase usually by one third of a cycle (120o). A three phase circuit may be three wire or four wire with the fourth wire being the neutral wire.
*thunder The sound that follows a flash of lightning and is caused by the sudden expansion of the air in the path of the electrical discharge. This explosive heat produces a massive, deafening shock wave - thunder.
*thyristor A solid-state switching device for semiconductors to convert AC current in one of two directions controlled by an electrode.
A four-layer semiconductor device that acts as a latch.
*time base Circuitry that controls the time dependence for the sweep. The saw tooth waveform is commonly used to give a repetitive linear time base.
*time constant The time constant of a circuit is the time required for the state of the circuit to change from the initial state to the final state at the initial rate of change.
*time-of-day rate Electricity prices that vary depending on the time periods in which the energy is consumed. In a time-of-day rate structure, higher prices are charged during utility peak-load times. Such rates can provide an incentive for consumers to curb power use during peak times.
*TN system A system having one or more points of the source of energy directly earthed, the exposed conductive parts of the installation being connected to that point by protective conductors.
*ton An imperial unit of weight. 1 ton = 1.016 tonnes = 1016 kg
*tonne Metric tonne. An unit of weight. 1 tonne = 1000 kg
*tool Object (e.g. screwdriver) which may be used to secure or release fasteners or to make adjustments.
*topology A branch of geometry concerned with the way in which figures are connected, rather than their shape or size. These geometric factors are unaffected by deformation.
*toroid A circular, donut shaped core used in transformers.
*torque product of a force and the perpendicular distance between the force and the axis of action.
*torr Unit of pressure. 1 torr = 1 mm of Hg = 133.3 pa
*total harmonic distortion *THD The effective value of all the harmonics taken together expressed as a ratio of the effective value of the fundamental.
*touch voltage: The potential difference between the ground potential rise (GPR) and the surface potential at the point where a person is standing where at the same time having his hands in contact with a grounded structure. GPR defined as the maximum voltage that a station grounding grid may attain relative to a distant grounding point assumed to be at the potential of remote earth. The touch voltage could be from hand to hand also.
*tower A structure (usually steel) found along transmission lines which is used to support conductors.
*trace The visual representation of an individual signal on a CRT.
*tracking Tracking is the formation of a permanent conducting path across a surface of the insulation, and in most cases the conduction (carbon path) results from degradation of the insulation itself leading to a bridge between the electrodes. Tracking occurs in organic materials.
*transducer A device to condition and transform a specific physical quantity to a specific variable output electrical signal proportional to the input signal. Typical inputs include variable pressure, level, voltage or current. A transducer must be specifically designed to be compatible with the input/output requirements of the total system.
*transfer function The transfer function of a circuit is the ratio of the response to the input.
*transformation Change of one form variable or substance into another.
*transformer A static electric device consisting of a single winding, or two or more coupled windings, used to transfer power by electromagnetic induction between circuits at the same frequency, usually with transformed values of voltage and current.
*transferred voltage: This is a special case of the touch voltage where the voltage is transferred into or out of the station by a conductor grounded at a remote point or at the station ground, respectively.
*TNS system of earthing: In this earthing system, the supplier provides separate Neutral and Protective conductors throughout the system. The Protective Conductor is connected to the neutral of the source. All exposed conductive parts of a consumer's installation are connected to the Protective Conductor provided by the supplier via. the main earthing terminal of the consumer's installation.
*transient A phenomenon of a non-repetitive nature caused by a sudden change in conditions that persist for a relatively short time after the change.
*transient response The temporary behaviour of a circuit due to an external excitation, which will die out with time.
*transistor A semi-conductor device capable of amplification.
*transmission The movement of large quantities of electric energy.
*transmission and distribution *T & D The process of delivering electricity from generation plants to homes and businesses. Transmission is considered to end when the energy is transformed for distribution to the consumer.
*transmission and distribution losses, *T & D losses Losses that result from the friction that energy must overcome as it moves through wires to travel from the generation facility to the consumer. Because of losses, the demand produced by the utility is greater than the demand that shows up on the consumer bills.
*transmission and distribution system, *T & D system An interconnected group of electric transmission lines and associated equipment for the movement or transfer or electric energy in bulk between points of supply and points at which it is transformed for delivery to the ultimate consumers.
*transmission lines Heavy wires that carry large amounts of electricity over long distances from a generating station to places where electricity is needed. Transmission lines are held high above the ground on transmission towers.
*transmission system (Electric) An interconnected group of electric transmission lines and associated equipment for moving or transferring electric energy in bulk between points of supply and points at which it is transformed for delivery over the distribution system lines to consumers, or is delivered to other electric systems.
*transmitting utility A regulated entity which owns, and may construct and maintain, wire used to transmit wholesale power. It is regulated to provide non-discriminatory connections, comparable service and cost recovery. Any electric utility, qualifying cogeneration facility, qualifying small power production facility, or Federal power marketing agency which owns or operates electric power transmission facilities which are used for the sale of electric energy at wholesale.
*travelling waves Voltage waveforms which effectively travel along a line without a significant change in waveshape.
*traverse-mode noise Often used as a synonym for normal-mode noise, it more clearly relates to noise that is the result of the conversion of common-mode noise to normal-mode noise after it passes through a transformer.
*tree of a network A graph of the network with some of the links removed in such a way so as to leave all the nodes connected together by the graph, but so as not to have any loop left in the network.
*triac A thyristor that can conductor in both directions. Because of this, it is useful for controlling alternating current. It is the equivalent of two SCRs in parallel with opposite polarities.
*triangle of forces If three forces acting at the same point can be represented in magnitude and direction by the three sides of a triangle, taken in order, they will be in equilibrium.
*trickle charge With the trickle charging process, the battery receives a constant voltage feeding a low current. Constant use of this method dries the electrolyte and corrodes the plate, reducing potential battery service life by up to 50 percent.
*trigger The signal used to initiate a sweep on an oscilloscope and determine the beginning point of the trace.
*trigger level The instantaneous level that a trigger source signal must reach before a sweep is initiated by the trigger circuit.
*true value Average value of the infinite number of measurements, when the average deviation tends to become zero.
*TT system A system having one point of the source of energy directly earthed, the exposed conductive parts of the installation being connected to earth electrodes electrically independent of the earth electrodes of the source.
*TT system of earthing: An earthing system where all exposed conductive parts of an installation are connected to an earth electrode provided by the consumer which is electrically independent of the Source earth.
*tunnel effect The passage of an electron through a narrow potential barrier in a semiconductor, despite the fact that, according to classical theory, the electron does not possess sufficient energy to surmount the barrier.
*turbine A machine for generating rotary mechanical power from the energy of a stream of fluid (such as air, water, steam, or hot gas). Turbines convert the kinetic energy of fluids to mechanical energy. It generally consists of a series of curved vanes emanating from an axis that is turned by forcing the fluid past the vanes.
*TVSS *Transient voltage Surge SuppressorA device designed to protect connected devices from transient voltages.
*two-port network An electrical network with two separate ports for input and output.
*two-way switch A two-way switch is one which enables operation of a lamp from two positions, such as at the top and bottom of a staircase and at the ends of a long corridor.
*type tests These tests are done to ensure that the particular design is suitable for a specific purpose. They are normally done either at design stage, or when a purchaser (of large orders) requires them to be done.
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*ultra high frequency *UHF Radio frequencies in the range 300 MHz to 3000 MHz.
*ultrahigh voltage transmission, *UHV transmission Transporting electricity over bulk-power lines at voltage greater than 800 kilovolt.
*ultra-violet radiation, *UV radiation Electromagnetic radiation in the wavelength range of approximately 400 nm to 500 nm. These fall between the visible light and the X-rays.
*unbalanced three phase system A three phase system in which either the supply or the load or both are not fully balanced.
*unbundling Disaggregating electric utility service into its basic components and offering each component separately for sale with separate rates for each component.
For example, generation, transmission and distribution could be unbundled and offered as discrete services.
*uncertainties Uncertainties are factors over which the utility has little or no foreknowledge, and include load growth, fuel prices, or regulatory changes. Uncertainties are modeled in a probabilistic manner. However, in the Detailed Workbook, you may find it is more convenient to treat uncertainties as "unknown but bounded" variables without assuming a probabilistic structure. A specified uncertainty is a specific value taken on by an uncertainty factor (e.g. 3 percent per year for load growth). A future uncertainty is a combination of specified uncertainties (e.g. 3 percent per year load growth, 1 percent per year real coal and oil price escalation, and 2.5 percent increase in housing starts).
*under-voltage Like a sag, but for a longer period of time: over 2.5 second.
*unijunction transistor *UJT This low power transistor is useful in electronic timing, waveshaping and control applications.
*uninterruptible power supply *UPS A system designed to automatically provide power, without delay or transients, when the normal power supply is incapable of supplying acceptable power. Some UPSs also filter and/or regulate utility power.
*unit impulse A function with unit integral area, which is zero everywhere except at zero time where it is infinite.
*unit ramp A function which is zero for negative time, and unit slope for positive time.
*unit step A function with zero magnitude for negative time and unit magnitude for positive time.
*universal resource locator *url This is the method of addressing on the web. They include the file transfer protocol (ftp) and the hyper text transfer protocol (http).
*user Authority responsible for the use and maintenance of equipment.
*utilisation The process of exploiting (using) electrical energy for various purposes.
*ultra high frequency *UHF Radio frequencies in the range 300 MHz to 3000 MHz.
*ultra-violet radiation or *UV radiation Electromagnetic radiation in the wavelength range of approximately 400 nm to 500 nm. These fall between the visible light and the X-rays.
*unbalanced three phase system A three phase system in which either the supply or the load or both are not fully balanced.
*under-voltage Like a sag, but for a longer period of time: over 2.5 seconds.
*uninterruptible power supply *UPS A system designed to automatically provide power, without delay or transients, when the normal power supply is incapable of supplying acceptable power. Some UPSs also filter and/or regulate utility power.
*unserved energy The average energy that will be demanded but not served during a specified period due to inadequate available generating capacity.
*utility A regulated entity which exhibits the characteristics of a natural monopoly. For the purposes of electric industry restructuring "utility" refers to the regulated, vertically-integrated electric company.
"*Transmission utility" refers to the regulated owner/operator of the transmission system only.
"*Distribution utility" refers to the regulated owner/operator of the distribution system which serves retail consumers.
*utilization factor The ratio of the maximum demand of a system or part of a system to the rated capacity of the system or part of the system.
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*valley filling A form of load management that increases or builds, off-peak loads. This load shape objective is desirable if a utility has surplus capacity in the off-peak hours. If this strategy is combined with time-of-day rates, the average rate for electricity can be lowered.
*variable cost Costs, such as fuel costs, that depend upon the amount of electric energy supplied.
*vertical integration An arrangement whereby the same company owns all the different aspects of making, selling, and delivering a product or service.
In the electric industry, it refers to the historically common arrangement whereby a utility would own its own generating plants, transmission system, and distribution lines to provide all aspects of electric service.
*visual corona Visible signs (usually a bluish glow) of the presence of corona, which occurs at a higher electric field than is necessary for the inception of corona.
*very high frequency *VHF Radio frequencies in the range 30 MHz to 300 MHz.
*VLSI *very large scale integration. (10,000 to 99,999 gates per chip)
*volatile memory Memory requiring electrical power to keep information stored.
*volt(V) SI unit of electric potential. One volt is equal to the potential difference between two points of a conducting wire carrying a constant current of 1 A, when the power dissipated between these points is equal to 1 W.
*voltage(see potential difference)
*Band I - Band I covers:
o installations where protection against electric shock is provided under certain conditions by the value of voltage;
o installations where the voltage is limited for operational reasons (e.g. telecommunications, signalling, bell, control and alarm installations).
Extra low voltage (ELV) will normally fall within voltage band I.
*Band II - Band II contains the voltages for supplies to household, and most commercial and industrial installations.
Low voltage (LV) will normally fall within voltage band II. Band II voltages do not exceed 1000 V a.c. rms or 1500 V d.c.
*voltage drop The loss of voltage between the input to a device and the output from a device due to the internal impedance or resistance of the device.
*voltage, nominal Voltage by which an installation (or part of an installation) is designated. The following ranges of nominal voltage (rms values for a.c.) are defined:
o Extra low. Normally not exceeding 50 V a.c. or 120 V ripple free d.c., whether between conductors or to Earth,
o Low. Normally exceeding extra low voltage but not exceeding 1000 V a.c. or 1500 V d.c. between conductors, or 600 V a.c. or 900 V d.c. between conductors and Earth.
The actual voltage of the installation may differ from the nominal value by a quantity within normal tolerances.
*voltage, reduced (see Reduced low voltage system).
*voltage source A source which essentially maintains the source voltage at a predefined value almost independent of the load conditions. In other words the terminal voltage is maintained close to the internal emf.
*voltampere (VA) The basic unit of Apparent power. The voltamperes of an electric circuit is the mathematical product of the volt and ampere of the circuit. The practical unit of Apparent power is kilovoltampere (kVA).
*voltmeter An instrument for measuring voltage.
*voltage regulator Voltage regulators control the output voltage, eliminating voltage sags and swells in the input voltage that last from 15 milliseconds to one-half second. They are typically relatively inexpensive feedback controlled transformers and the more expensive ferroresonant transformer.
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*wagner earthing A null-balance method of keeping the arms of a bridge at earth potential without directly earthing any part of the bridge.
*watt(W) SI unit of power. One watt is equal to a power rate of one joule of work per second of time.
*wattmeter An instrument for measuring the average power.
*waveform The graphic representation of the variation of a quantity (such as voltage) as a function of some variable, usually time.
*wavefrontportion of the wave from zero to peak value. Wavefront is sometimes defined as the extrapolated time based on 30% and 90% of peak value.
*weber (Wb) SI unit of magnetic flux. One weber is equal to the magnetic flux which, linking a circuit of one turn, would produce in it an electromotive force of 1 V if it were reduced to zero at a uniform rate of 1 s.
*wheastone bridge A four arm resistance bridge where the balance is obtained by null deflection when the ratio of the adjacent arms are equal.
*wholesale bulk power Very large electric sales for resale from generation sources to wholesale market participants and electricity marketers and brokers.
*wholesale competition A system whereby a distributor of power would have the option to buy its power from a variety of power producers, and the power producers would be able to compete to sell their power to a variety of distribution companies.
*wholesale power market The purchase and sale of electricity from generators to resellers (who sell to retail consumers) along with the ancillary services needed to maintain reliability and power quality at the transmission level.
*wind energy conversion A process that uses energy from the wind and converts it into mechanical energy and then electricity.
*wiring system An assembly made up of cable or busbars and parts which secure and, if necessary, enclose the cable or busbars.
*word A group of bits representing a complete piece of digital information.
*wound rotor Rotor of an induction motor provided with a three-phase winding in the rotor.
*write The process of storing information in a memory.
*wye connection [see star connection]
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*x-rays An electromagnetic radiation produced when the inner satellite electrons of heavy atoms have been excited by collision with a stream of fast electrons return to their ground state, giving up the energy previously imparted to them. Electromagnetic radiations of the same type as light, but of much shorter wave-length, in the range of 5 nm to 6 nm produced when cathode rays strike a material object.
*x-y plot A graphic representation of the relationship of the X signal, which controls the horizontal position of the beam in time, and the Y signal, which controls the vertical position of the beam in time.
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*yocto (y) Decimal sub-multiple prefix corresponding to 10-24
*yotta (Y) Decimal multiple prefix corresponding to 1024
*Young's modulus Elastic modulus applied to a stretched wire or to a rod under tension or compression. The ratio of the stress to the strain.
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*zener diode- A junction diode designed to operate in the reverse bias region.
*zepto (z) Decimal sub-multiple prefix corresponding to 10-21
*zero sequence A balanced set of three phase components which have the same magnitude and the same phase angle, and hence hence no sequence. The frequency is of course the same as the original unbalanced three phase system.
*zetta (Z) Decimal multiple prefix corresponding to 1021
*The signal in an oscilloscope that controls the electron-beam brightness as the trace is formed.
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© Copyright reserved by the author professor J R Lucas. December 2001.(updated October 2004)