PEC电气工程专业英语证书考试-ElectricityGlossary.doc

PEC电气工程专业英语证书考试-Electricity Glossary

A

ac - abbreviation for alternating current

active power - see real power

alternating current - an electrical current which reverses direction repeatedly due to a change in voltage which occurs at the same frequency. Often abbreviated AC or ac.

alternator - an electric generator designed to produce alternating current. Usually consists of rotating parts which created the changing magnetic field to produce the alternating current.

American National Standards Institute - a private organization that coordinates and/or approves some US standards, particularly those related to the electrical industry. Abbreviated ANSI.

American Wire Gauge - A standard measure which represents the size of wire. The larger the number, the smaller the wire. Abbreviated AWG.

ampacity - the maximum continuous current that a conductor can carry without overheating above its temperature rating.

Ampere - electric current produced by one volt applied across a resistance of one ohm. It is also equal to the flow of one coulomb per second. Named after French physicist Andre M. Ampère 1836.

ambient temperature - the surrounding temperature.

Ampere-hour - the flow of electricity equal to one ampere for one hour. Commonly used to rate the capacity of batteries.

analog - a measuring or display methodology which uses continuously varying physical parameters. In contrast, digital represents information in discrete binary form using only zeros and ones.

apparent power - the mathematical product of voltage and current on ac systems. Since voltage and current may not be in phase on ac systems, the apparent power thus calculated may not equal the real power, but may actually exceed it. Reactive loads (inductance and/or capacitance) on ac systems will cause the apparent power to be larger than the real power.

AWG - abbreviation for American Wire Gauge.

B

battery - a group of two or more cells connected together to provide electrical current. Sometimes also used to describe a single cell which converts chemical energy to electrical current.

battery cycle life - the number of discharge and recharge cycles that a battery can undergo before degrading below its capacity rating.

battery self-discharge - the gradual loss of chemical energy in a battery that is not connected to any electrical load.

black start - refers to certain electric utility generating units that can start upon demand without any outside source of electric power. These are often combustion turbines that have stationary battery banks to provide backup power to energize all the controls and auxiliaries necessary to get the unit up and running. In the event of an large area-wide blackout, these units are critical to restoring the utility grid. Most utility generating units do not have black start capability.

bonding - an electrical conducting path formed by the permanent joining of metallic parts. Intended to assure electrical continuity and the capability to safely conduct any likely current. Similar to bonding jumper or bonding conductor.

branch circuit - the conductors between the last overcurrent protective device and the outlets or loads.

C

capacitor - a device that stores electrical charge usually by means conducting plates or foil separated by a thin insulating layer of dielectric material. The effectiveness of the device, or its capacitance, is measured in Farads.

cell - a single device which converts chemical energy into electrical current. Sometimes also referred to as a battery.

charge rate - the rate at which a battery or cell is recharged. Can be expressed as a ratio of battery capacity to current flow.

circuit breaker - a device designed to open a circuit either by manual action or by automatic action when current exceeds a value longer than permitted. A circuit breaker can provide overcurrent protection.

conductor - usually a metallic substance capable of transmitting electricity with little resistance. The best conductor at normal temperature ranges is silver. The most common is copper. Some other recently discovered substances called super conductors actually have zero resistance at extremely low temperatures.

continuous load - a sustained electrical load current for three hours or more.

Coulomb - the practical unit of electric charge transmitted by a current of one ampere for one second. It is the charge carried by 6.2418 x 1018 electrons. Named for the French physicist Charles A. de Coulomb 1806.

current - the flow of electricity commonly measured in amperes.

cycles-per-second - a measure of the frequency in an ac electric system. Abbreviated cps or cycles. Now replaced with the unit Hertz.

D

dc - abbreviation for direct current.

decibel - a logarithmic measure of the ratio of two quantities. Abbreviated dB. For electrical power, 1 dB = 10 x log10 P1/P2. For electric voltage or current, 1 dB = 20 x log10 E1/E2.

depth of discharge - the percent of rated capacity of a battery that has been discharged from the battery.

diode - an electronic semiconductor device that predominantly allows current to flow in only one direction.

direct current - electrical current that normally flows in one direction only. Abbreviated dc.

E

electrolyte - a nonmetallic conductor of electricity usually consisting of a liquid or paste in which the flow of electricity is by ions.

energy - the capacity for, or the ability to do, mechanical work. Electrical energy is measured in kilowatt-hours for billing purposes.

F

Farad - a unit of capacitance. One coulomb of charge will produce a potential difference of one volt across a capacitance of one Farad. Named for the English physicist Michael Faraday 1867.

fault - a short circuit.

feeder - circuit conductors between the service equipment and the last downstream branch circuit overcurrent protective device.

filter - a device made up of circuit elements designed to pass desirable frequencies and block all others. It typically consists of capacitors and inductors.

FLA - Full load amperes, also sometimes abbreviated RLA for full load amperes. This is the current in amperes that a motor requires to produce rated nameplate horsepower output when rated nameplate voltage and frequency is provided to it's terminals.

float charge - charging current supplied to a battery which overcomes the battery self-discharge rate. This current, under otherwise normal conditions, will maintain the battery in a fully charged state.

frequency - the number of complete alternations or cycles per second of an alternating current. It is measured in Hertz. The standard frequency in the US is 60 Hz. However, in some other countries the standard is 50 Hz.

G

gassing - gas by-products produced by the chemical reactions that occur when charging a battery. Since one of these gasses is often hydrogen, safety precautions must be taken to ensure proper ventilation to avoid the danger of explosion.

generator - a rotating machine which converts mechanical energy into electrical energy. In the automotive industry traditional terminology uses generator to refer to only those machines designed to produce dc current through brushes and a commutator (as opposed to alternator).

grid - in the electrical arena, a term used to refer to the electrical utility distribution network.

ground - a conducting connection between an electrical circuit or device and the earth. A ground may be intentional, such as in the case of a safety ground, or accidental which may result in high overcurrents.

H

harmonic - a sine wave which is an integral multiple of a base frequency. For example, the third harmonic on a 60 Hz system is a frequency of 180 Hz. Certain types of electrical equipment generate harmonics which interfere with the proper functioning of other devices connected to the same system.

Henry - the practical unit of inductance. One Henry is equal to the inductance in which the change of one ampere per second results in an induced voltage of one volt. Abbreviated H. Named for the American physicist Joseph Henry 1878.

Hertz - unit of frequency. One Hertz equals one complete cycle per second of an ac source. Abbreviated Hz. Named after the German physicist Heinrich R. Hertz 1894. This unit replaces the former "cycles-per-second."

horsepower - a unit of power equal to 746 watts.

Hz - abbreviation for Hertz.

I

IEEE - abbreviation for Institute of Electrical and Electronics Engineers.

impedance - the total effects of a circuit that oppose the flow of an ac current consisting of inductance, capacitance, and resistance. It can be quantified in the units of ohms.

inductance - the characteristic of an electric circuit by which a voltage is induced in it by a variation of current. This can be a variation of the current in the circuit itself (self-inductance) or in a nearby circuit (mutual inductance). The magnitude of the characteristic is measured in the units of Henries.

Institute of Electrical and Electronics Engineers - an independent organization which develops electrical standards and furthers the profession of electrical and electronics engineers.

inverter - an electrical device which is designed to convert direct current into alternating current. This was originally done with rotating machines which produced true sine wave ac output. More recently this conversion has been performed more economically and efficiently using solid state electronics. However, except for the most expensive models, these devices usually do not produce perfect sine wave output. This sometimes can result in electromagnetic interference with other sensitive electronic devices.

ion - a positively or negatively charged atom or molecule.

J

Joule - a unit of work or energy equal to one watt for one second. One kilowatt hour equals 3,600,000 Joules. Named after James P. Joule, an English physicist 1889.

Joule’s law - defines the relationship between current in a wire and the thermal energy produced. In 1841an English physicist James P. Joule experimentally showed that W = I2 x R x t where I is the current in the wire in amperes, R is the resistance of the wire in Ohms, t is the length of time that the current flows in seconds, and W is the energy produced in Joules.

K

kilovar - unit of ac reactive power equal to 1000 vars. Abbreviated kVAr or KVAR.

kilovolt - unit of electrical potential equal to 1000 volts. Abbreviated kV or KV.

kilovolt amperes - a unit of apparent power equal to 1000 volt amperes. Here, apparent power is in contrast to real power. On ac systems the voltage and current will not be in phase if reactive power is being transmitted. Usually abbreviated kVA or KVA.

kilowatt - unit of power equal to 1000 watts. Abbreviated kW or KW.

kilowatt-hour - unit of energy or work equal to one kilowatt for one hour. Abbreviated as kwh or KWH. This is the normal quantity used for metering and billing electricity customers. The price for a kwh varies from approximately 4 cents to 15 cents. At a 100% conversion efficiency, one kwh is equivalent to about 4 fluid ounces of gasoline, 3/16 pound LP, 3 cubic feet natural gas, or 1/4 pound coal.

kV - abbreviation for kilovolt and equal to 1000 volts.

kVA - abbreviation for kilovolt amperes.

kVAr - abbreviation for kilovar. A unit of ac reactive power equal to 1000 vars.

kW - abbreviation for kilowatt. A unit of power equal to 1000 watts.

L

listed - an electrical device or material that has been tested by a recognized organization and shown to meet appropriate standards. Many local governmental authorities require that installed electrical products be listed. A well-known listing organization is Underwriters Laboratories (UL).

load - a device which consumes electrical power and is connected to a source of electricity.

LRA - Locked rotor amperes. This is the current that a motor would require if the rotor were locked in place and prevented from rotating and rated nameplate voltage and frequency were applied to its terminals. This is also the current that could appear briefly during motor starting. While the motor comes up to speed this current gradually drops off and when the speed approaches running rpm this current rapidly falls to the RLA value. Often the starting current is less than the LRA value because the voltage at the motor terminals dips during starting. This LRA value is important when sizing a generator because the generator's surge rating must be large enough to handle it.

M

MCA - Minimum circuit amperes. This is the minimum current rating allowed for the wiring and circuit breaker or fuse protection for the equipment. It is used by the installer and electrician to size the branch circuit to feed the equipment.

N

National Electrical Code - a code for the safeguarding of people and property from hazards related to the use of electricity. Compliance with this code along with proper maintenance will result in an installation essentially free from hazard. Abbreviated NEC. The NEC was first developed in 1897 as a result of the efforts of various insurance, electrical, architectural, and allied interests. It is sponsored and regularly updated by the National Fire Protection Association.

NEC - abbreviation for the National Electrical Code.

neutral - a conductor of an electrical system which usually operates with minimal voltage to ground. Depending on the type of system, it may carry little current or only unbalance current. Systems that have one conductor grounded use the neutral for this purpose.

O

Ohm - a unit of electrical resistance. A circuit resistance of one ohm will pass a current of one ampere with a potential difference of one volt. Abbreviated using the Greek letter omega (W ). Named for the German physicist George Simon Ohm 1854.

Ohm’s Law - defines the relationship between voltage, resistance, and current. In 1828 the German physicist George Simon Ohm showed by experiment that the current in a conductor is equal to the difference of potential between any two points divided by the resistance between them. This may be written as I = E / R where E is the potential difference in volts, R is the resistance in Ohms, and I is the current in amperes.

open circuit voltage - the maximum voltage produced by a power source with no load connected.

overcurrent - any current beyond the continuous rated current of the conductor or equipment. This may be value slightly above the rating as in the case of an overload, or may be far above the rating as in the case of a short circuit.

overload - operation of electrical equipment above its normal full-load rating or of a conductor above its rated ampacity. An overload condition will eventually cause dangerous overheating and damage.

P

power - the rate