Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

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.
alternator-rectifier exciter
a source of field current of a synchronous machine derived from the rectified output voltage of an alternator. The components of the exciter consist of the alternator and the power rectifier (including possible gate circuitry), exclusive of all input control elements. The rectifier circuits may be stationary, or rotate with the alternator, which may be driven by a motor, prime mover, or by the shaft of the synchronous machine.
American National Standards Institute (ANSI)
The U.S. organization that recommends standards for metrology, drawing
symbology and numerous other facets for products and industries.
ampacity
the maximum current which can be safely carried by a conductor under specified conditions.
angular frequency
the rate of change of the phase of a wave in radians per second.
antiparticle
a particle having the same mass as a given fundamental particle, but whose other properties, while having the same magnitude, may be of opposite sign. Each particle has a partner called an antiparticle. For example, electrical charge in the case of the electron and positron, magnetic moment in the case of the neutron and antineutron. On collision a particle and its antiparticle may mutually annihilate with the emission of radiation. Some properties of the antiparticle will be identical in magnitude but opposite in sign to the particle it is paired with.
antireflection coating

See antireflective coating
antireflective coating (ARC)
a coating placed on top or below the layer of photoresist to reduce the reflection of light, and hence reduce the detrimental effects of standing waves or thin film interference.
aperiodic waveform
a phrase is used to describe a waveform that does not repeat itself in a uniform, periodic manner. Compare with periodic waveform.
arc fault interrupter
the mechanism that breaks the fault current arc in a power circuit breaker.
arc lamp
lamp made by driving a high current across a gap between two electrodes. Some types operate in air consuming the electrode, for example, a carbon arc in which the electrode material is made as a rod and fed into the discharge to replace what is consumed. Others operate in a vacuum envelop that reduces the electrode consumption.
arc resistance
period of time that the surface of an insulating material can be submitted to the action of an electrical arc without becoming conductive.
arcing fault

See arcing ground
arcing ground
a ground fault on a power line which alternately clears and restrikes, causing high, repetitive voltage surges.
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.
armature reaction
(1) in DC machines, a distortion of the field flux caused by the flux created by the armature current. Armature reaction in a DC machine causes lower flux at one pole-tip and higher flux at the other, which may lead to magnetic saturation. It also shifts the neutral axis, causing sparking on the commutator.

(2) in AC synchronous machines, a voltage drop caused by the armature current. In the steady state model of the synchronous machine, the armature reaction is accounted for by a component of the synchronous reactance. armature voltage control a method of controlling the speed of a DC motor by varying the voltage applied to the armature while keeping the voltage applied to the field circuit constant.
armless construction
a method of distribution line construction, often used for aesthetic purposes, in which pin insulators are mounted on steel brackets bolted directly to a utility pole without the use of a crossarm.
arrester discharge current
the current in an arrester during a surge.
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