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.
alternating current (AC)
a periodic current the average value of which over a period is zero.
alternating current machine
an electromechanical system that either converts alternating current electrical power into mechanical power (AC motor), or converts mechanical power into alternating current electrical power (AC generator, or alternator). Some AC machines are designed to perform either of these functions, depending on the energy source to the dynamo.
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.
armature current limiting
a condition wherein the stator currents are clamped at the maximum allowable limit due to excessive heating of the stator.
arrester discharge current
the current in an arrester during a surge.
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
bearing currents
current flow in the bearings of electrical machines, because of electromagnetic unbalance in the machine
or from using high dv inverters. The latter is able to charge up the stray capacitance present between the stator and rotor and between the rotor and shaft and thus allows motor bearing currents to flow, with resulting bearing damage.
blocked-rotor current

See locked-rotor current
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.
branch current
the current in a branch of a circuit.
charging current
that portion of an electric power line's current which goes to charge the capacitance of the line. The charging current is not available for power transmission.
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.
circular mil
the area of a circle which measures 0.001 inch in diameter. Used to specify the cross-sectional area of a wire.
circular polarization
a polarization state of a radiated electromagnetic field in which the tip of the electric field vector traces a circle as a function of time for a fixed position. The sense of rotation of the electric field vector is either right-hand or left-hand (clockwise or counter-clockwise).
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