电气英语证书考试(PEC)-电气工程专有名词2.doc

电气英语证书考试(PEC)-Glossary of Electrical Engineering Terms2
A
*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 [1948].
*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.

B
*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