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Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

VAR

See volt-ampere-reactive
varactor
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.