Substation1
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.
AC motor
an electromechanical system that converts alternating current electrical power into mechanical power.
AC/AC converter
a power electronics device in which an AC input voltage of some magnitude, frequency, and number of phases is changed to an AC output with changes to any of the previously mentioned parameters.

AC/AC converters usually rectify the input source to a DC voltage and then invert the DC voltage to the desired AC voltage.
AC/DC converter

See rectifier
AC-DC integrated system
a power system containing both AC and DC transmission lines.
active device
a device that can convert energy from a DC bias source to a signal at an RF frequency. Active devices are required in oscillators and amplifiers.
active filter
(1) a filter that has an energy gain greater than one, that is, a filter that outputs more energy than it absorbs.
(2) a form of power electronic converter designed to effectively cancel harmonic currents by injecting currents that are equal and opposite to, or 180. out of phase with, the target harmonics. Active filters allow the output current to be controlled and provide stable operation against AC source impedance variations without interfering with the system impedance.
The main type of active filter is the series type in which a voltage is added in series with an existing bus voltage. The other type is the parallel type in which a current is injected into the bus and cancels the line current harmonics.
active power

See real power
active power line conditioner

a device which senses disturbances on a power line and injects compensating voltages or currents to restore the line's proper waveform.

active RC filter
an electronic circuit made up of resistors, capacitors, and operational amplifiers that provide well-controlled linear frequency-dependent functions, e.g., low-, high-, and bandpass filters.
adaptive control
a control methodology in which control parameters are continuously and automatically adjusted in response to be measured/estimated process variables to achieve near-optimum system performance.
additive polarity
polarity designation of a transformer in which terminals of the same polarity on the low-and high-voltage coils are physically adjacent to each other on the transformer casing. With additive polarity, a short between two adjacent terminals results in the sum of the two coil voltages appearing between the remaining terminals. Additive polarity is generally used for transformers up to 500kVA and 34.5kV. Larger units use subtractive polarity.
See subtractive polarity
adjustable-speed drive

See variable speed drive
admittance
the reciprocal of the impedance of an electric circuit.
air capacitor

a fixed or variable capacitor in which air is the dielectric material between the capacitor's plates.

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 core transformer
two or more coils placed so that they are linked by the same flux with an air core. With an air core the flux is not confined.
air terminal
a lightning rod; any device which extends upward into the air from a structure for purposes of lightning protection.
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.
air-gap voltage
the internal voltage of a synchronous machine that is generated by the air gap flux. Also referred to as the voltage behind leakage reactance.