Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

frequency variation
a change in the electric supply frequency.

static var compensator
a device for fast reactive compensation, either inductive or capacitive, brought about by thyristor-based control of an effective shunt susceptance. It is typically used to regulate voltage at a bus on the high voltage transmission system.
static VAR regulator
also called a static VAR compensator. A nonrotating electrical device designed to adjust the reactive power flow of an AC power system. It typically consists of a reactive load (either inductive or capacitive) and a series electronic switch (thyristor) that controls the reactive power.

See volt-ampere-reactive
a reverse biased PN or Schottky diode that uses the voltage variable depletion region as a tuning element or as a nonlinear frequency multiplier.
varactor diode
a diode designed to have a repeatable and high capacitance vs. reverse voltage characteristic. A two terminal semiconductor device in which the electrical characteristic of primary interest is the voltage dependent capacitance.
varactor tuner
a tuning circuit at the input of a television receiver that uses a varactor diode. The tuning capability comes from the characteristic of a varactor, or varicap, to function as a voltage-sensitive capacitance.
variable frequency drive
electric drive system in which the speed of the motor can be varied by varying the frequency of the input power.
variable speed AC drive
an AC motor drive that is capable of delivering variable frequency AC power to a motor to cause it to operate at variable speeds. Induction motors and synchronous motors are limited to operation at or near synchronous speed when a particular frequency is applied. Variable speed drives rectify the incoming AC source voltage to create a DC voltage that is then inverted to the desired frequency and number of phases.
variable speed DC drive
a DC motor controller that allows the DC motor to operate over a wide speed range. A common type of variable speed DC drive uses a separately excited DC motor. Armature voltage control is used to provide operation below base speed, and field weakening is used to provide operation above base speed.
variable speed drive (VSD)
See variable speed AC drive or variable speed DC drive.
volt-ampere-reactive (VAR)
a unit of power equal to the reactive power in a circuit carrying a sinusoidal current when the product of the root-mean-square value of the voltage (expressed in volts), the root-meansquare value of the current expressed in amperes), and the cosine of the phase angle between the voltage and the current, equals one; the unit of reactive power in the International System. Also expressed as megavars and kilovars.
voltage variation
long duration a change of voltage RMS value from nominal for a time period greater than 1 minute, and can be used with the words showing a magnitude change such as overvoltage, or under-voltage.
voltage variation
in short duration a change of the voltage RMS value from nominal for a time period from 0.5 cycles to 1 minute, and can be used with the words sag, swell, and interruption for magnitude changes, and the words instantaneous, momentary, of temporary for showing duration.
watt-VAR meter
meter capable of simultaneously measuring the real and reactive power delivered to an AC load.