Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

AC circuit
electrical network in which the voltage polarity and directions of current flow change continuously, and often periodically.

Thus, such networks contain alternating currents as opposed to direct currents, thereby giving rise to the term.
air circuit breaker
a power circuit breaker where the power contacts operate in air. Some versions employ an air blast to extend and clear the arc on contact opening, while others employ arc chutes with magnetic or thermal assists.
air-blast circuit breaker
a circuit breaker in which the arc which forms between the contacts on opening is extinguished with a blast of high-pressure air.
armature circuit
components of the machine that carry armature current. For example, in a DC machine the armature circuit could consist of the armature windings, brushes, series field winding, compensating windings, interpoles, starting resistor(s), main-line contacts, and overload sensor.
asynchronous circuit
(1) a sequential logic circuit without a system clock.
(2) a circuit implementing an asynchronous system. asynchronous demodulation a technique for extracting the information-carrying waveform from a modulated signal without requiring a phase-synchronized carrier for demodulation.
See synchronous demodulation
automatic circuit recloser

See recloser
branch circuit
the three components of an electrical circuit are source, load, and interconnecting circuit conductors. A branch circuit is an electrical circuit designed to deliver power to the lowest-order load(s) served on a facility. It includes the overcurrent device, circuit conductors, and the load itself.
circuit
a physical device consisting of an interconnection of elements, or a topological model of such a device. For example, an electric circuit may be constructed by interconnecting a resistor and a capacitor to a voltage source.
circuit breaker
a circuit breaker is a device that makes and breaks the electrical contact between its input and output terminals. The circuit breaker is capable of clearing fault currents (tripping) as well as load currents. The circuit breaker consists of power contacts with arc clearing capability and associated control and auxiliary circuits for closing and tripping the breaker under the required conditions.
circuit protection
devices or control measures used to safeguard electrical circuits from unsafe operating regions, such as over-currents and over-voltages.
DC circuit
electrical networks in which the voltage polarity and directions of current flow remain fixed. Thus such networks contain direct currents as opposed to alternating currents, thereby giving rise to the term.
direct-axis subtransient open-circuit time constant
a constant that characterizes the initial decay of transients in the d-axis variables of the synchronous machine with the stator windings open-circuited. The interval characterized is that immediately following a disturbance, during which the effects of all amortisseur windings are considered. A detailed (derived) closed-form expression for the subtransient open-circuit time constant of a machine with a single d-axis amortisseur windings is obtained by taking the reciprocal of the smallest root of the denominator of the d-axis operational impedance. An approximate (standard) value is often used, in which it is assumed the field winding resistance is very small and the detailed expression simplified.
direct-axis subtransient short-circuit time constant
a constant that characterizes the initial decay of transients in the d-axis variables of the synchronous machine with the stator windings short-circuited. The interval characterized is that immediately following a disturbance, during which the effects of amortisseur windings are considered. A detailed (derived) closed-form expression for the subtransient short-circuit time constant of a machine with a single d-axis amortisseur winding is obtained by taking the reciprocal of the largest root of the numerator of the d-axis operational impedance. An approximate (standard) value is often used, in which it is assumed the field winding resistance is small and the detailed expression simplified.
direct-axis transient open-circuit time constant
a constant that characterizes the decay of transients in the d-axis variables of the synchronous machine with the stator windings open-circuited. The interval characterized is that following the subtransient interval, but prior to steady-state, during which the effects of the amortisseur windings are small (possibly negligible). A detailed (derived) closed-form expression for the transient open-circuit time constant of a machine with a single d-axis amortisseur winding is obtained by taking the reciprocal of the smallest root of the denominator of the d-axis operational impedance. An approximate (standard) value is often used, in which it is assumed the amortisseur winding resistance is infinite and the detailed expression simplified.
direct-axis transient short-circuit time constant
a constant that characterizes the decay of transients in the d-axis variables of the synchronous machine with the stator windings short-circuited. The interval characterized is that following the subtransient interval, but prior to steady-state, in which the effects of the amortisseur windings are small (possibly negligible). A detailed (derived) closed-form expression for the short-circuit transient time constant is obtained by taking the reciprocal of the smallest root of the numerator of the d-axis operational impedance. An approximate (standard) value is often used, in which it is assumed the amortisseur winding resistance is infinite and the detailed expression simplified.
equivalent circuit
a combination of electric circuit elements chosen to represent the performance of a machine or device by establishing the same relationships for voltage, current, and power.
feeder circuit
an electrical circuit designed to deliver power from the service equipment or separately derived system to the branch circuit panelboard(s) on a facility. For large systems, there may be more than one level of feeder circuits. See also branch circuit.
field circuit
a set of windings that produces a magnetic field so that the electromagnetics induction can take place in electric machines.
gas circuit breaker
a circuit breaker in which the arc between the contacts is extinguished by immersion in or a blast of an electronegative gas.
ground-fault circuit interrupter (GFCI)
a device designed to detect ground-fault current above a threshold value (several milliamperes) and then interrupt the source of electrical power by opening a circuit breaker or a set of contacts. GFCIs are designed for personnel protection and are generally available in the form of circuit breakers and receptacles.
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