Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

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.

apparent power
(1) in an AC system, the product of voltage, Eand current, I. Apparent power (or total power) is composed of two mutually independent components -- an active component (real power), and a reactive component (imaginary power). Apparent power is denoted by S, and has the unit of voltamperes.
(2) the scalar product of the voltage and current delivered to the load. It can also be expressed as the vector S = P + jQ, where P = real power and Q = reactive power.
average power
the average value, taken over an interval in time, of the instantaneous power. The time interval is usually one period of the signal.
bulk power
a term inclusive of the generation and transmission portions of the power system.
candle power

See candela
candlepower distribution
a curve, generally polar, representing the variation of luminous intensity of a lamp or luminaire in a plane through the light center.
reactive power Q
The region of allowable operation is determined by factors such as rotor thermal limit, stator thermal limit, rated power of prime mover (alternator operation), and stability torque limit.
constant-horse power drive
a variable speed drive that is operating in a speed region where it is capable of delivering rated power. For DC machines, this region is above base speed and is achieved by field weakening. For AC induction motors, this region is above rated speed and is achieved by increasing the frequency of the applied voltage.
DC input power
the total DC or bias power dissipated in a circuit, which is usually dependent on signal amplitudes, expressed in watts. This may include input bias, bias filtering, regulators, control circuits, switching power supplies and any other circuitry required by the actual circuit. These considerations should be explicitly specified, as they will affect how efficiency calculations are performed.
directional power relay
a protective relay that operates for power flow in a given direction. Applications are in cases where normal power flow is in one direction, including anti-motoring protection on a turbine-generator and fault backfeed protection on parallel step-down transformers.
dissipation power
(1) ratio of real power (in phase power) to reaction power (shifted 90. out of phase).
(2) the ratio of the imaginary to real parts of the complex permittivity, expressed as a dimensionless ratio.
firm power
an amount of electric power intended to be available at all times to a commercial customer, regardless of system conditions.
fractional horsepower
National Electrical Manufacturers Association (NEMA) classification describing any "motor built in a frame smaller than that having a continuous rating of 1 horsepower, open type, at 1700 to 1800 rpm."
governor power flow
the inherent response of prime movers or governors to a change in the operating condition of the power system in an attempt to balance the power equation. All generators participate at some level in the change, with larger generators picking up relatively larger amounts.
half-power point
The two-sided half-power bandwidth is twice the half-power point.
horsepower-rated switch
a manually operated switching device designed for motor circuit applications. It is designed to interrupt the rated overload current at rated voltage of a motor with a horsepower rating that is less than or equal to the horsepower rating of the switch.
hydropower
conversion of potential energy of water into electricity using generators coupled to impulse or reaction water turbines.
imaginary power

See reactive power
incident power
power in an electromagnetic wave that is traveling in an incident direction.
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