Electrical definitions - Electrical Engineering Gate

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Sunday, November 29, 2015

Electrical definitions

Electrical definitions

(alternating current (AC

electrical current which reverses direction repeatedly, usually several times per second, due to a change in voltage which occurs at the same frequency. Often abbreviated AC or ac

ambient temperature 

the surrounding temperature


the magnitude of change in a varying quantity from it's zero value. Usually measured in Voltage, or deciBels, can denote volume


the measurement unit for electrical current. 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).


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

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


a group of two or more cells connected together to provide electrical current


a complete loss of power lasting for more than one cycle. A black-out can damage electronics, corrupt or destroy data, or cause a system shutdown. Blackouts can result from several problems, ranging from atmospherical events (hurricanes or other high winds, ice storms, lightning, trees falling on power lines, floods, geomagnetic storms triggering by sunspots and solar flares, etc.) to situations such as cables being cut during excavation, equipment failures at the utility, vandalism, corrosion, etc. Also known as power outage


a prolonged sag, occurring when incoming power is reduced for an extended period. Usually caused when demand is at its peak and the line becomes overloaded.


a device that stores electrical charge usually by means of 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


the maximum load that a generating unit, generating station, or other electrical apparatus can carry under specified conditions for a given period of time without exceeding approved limits of temperature and stress


the amount of electric power delivered or required for which a generator, turbine, transformer, transmission circuit, station, or system is rated by the manufacturer


a conductor or a system of conductors through which electric current flows

circuit breaker

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

circuit diagram 

a circuit diagram shows the arrangement of electrical components and wires by using symbols. It is an electrician's map


a physical assembly of one or more electrical coil sections generally surrounded by common insulation


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

continuous load 

a sustained electrical load current for three hours or more

critical load 

equipment that must have an uninterrupted power input to prevent damage or loss to a facility or to itself, or to prevent danger of injury to operating personnel


a flow of electrons in an electrical conductor. The strength or rate of movement of the electricity is measured in amperes. Current may be either direct or alternating. Direct current refers to current whose voltage causes it to flow in only one direction. Common direct current sources are batteries. Alternating current refers to current whose voltage causes it to flow first in one direction, then the other, reversing direction periodically, usually several times a second. A common alternating current source is commercial/household power. This current reverses direction 100 times each second, thus passing through 50 complete cycles each second for a frequency of 50 Hertz


one complete revolution of e.g. a generator, from 0° to 360°. One cycle is said to be one wavelength long and takes one period in time to produce. All cycles can be measured in frequency and amplitude


a measure of the frequency in an AC electric system. Abbreviated cps or cycles. Now replaced with the unit Hertz


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

(direct current (DC

electrical current that normally flows in one direction only. Abbreviated DC

(earth-leakage crcuit breaker (ELCB

a device used to prevent electrical shock hazards in mains voltage power systems, including independent power systems. Also known as residual current devices (RCDs

(earth (wire

a wire connected to the metal parts of some appliances to provide a safe route for electricity to flow in the event of a live wire accidentally touching the metal


Electromagnetic/Radio Frequency Interference. These high frequency signals are generally low level (<1V) and range from 1MHz up. EMI/RFI filters are generally not suitable for large amplitude surge suppression


the capacity for doing work as measured by the capability of doing work (potential energy) or the conversion of this capability to motion (kinetic energy). Energy has several forms, some of which are easily convertible and can be changed to another form useful for work. Electrical energy is usually measured in kilowatt-hours


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


the number of complete alternations or cycles per second of alternating current. It is measured in Hertz.


a rotating machine which converts mechanical energy into electrical energy


a term used to refer to the electrical utility distribution network


a sine wave which is an integral multiple of a base frequency. Certain types of electrical equipment generate harmonics which interfere with the proper functioning of other devices connected to the same system

harmonic distortion 

a measure of the degree to which the impedance of a protection equipment affects the shape of the output voltage waveform. Distortion is stated as a percentage and may refer to any single harmonic or to the total waveform, in which case it is referred to as "total harmonic distortion" (THD

(Hertz (Hz

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

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