Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

V-V transformer

See open-delta transformer
vacuum capacitor
a capacitor with a vacuum between its plates.
vacuum circuit breaker
a power circuit breaker where a vacuum chamber is used as an insulating and arc clearing medium.
vacuum insulation
any insulation scheme which depends upon the dielectric capabilities of a high vacuum.
vapor cooling
a cooling technique for power vacuum tubes utilizing the conversion of hot water to steam as a means of safely conducting heat from the device and to a heat sink.

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.
a quantity having both magnitude and direction.
vector controlled induction motor
a variable speed controller and motor in which the magnetizing and torque producing components of current are controlled separately. Some vector drives requires rotor position sensors. Vector controlled induction motors can operate over a wider speed range, and may produce rated torque even at zero speed, much like a DC motor. Thus, vector controlled induction motors are often used for applications that might otherwise require a DC motor drive.
velocity of light
in vacuum, a constant equal to 2.997928 x 108 meters/second. In other media, equal to the vacuum value divided by the refractive index of the medium.
very small aperture terminal (VSAT)
a small earth station suitable for installation at a customer's premises. A VSAT typically consists of an antenna less than 2.4 m, an outdoor unit to receive and transmit signals, and an indoor unit containing the satellite and terrestrial interface units.
vibration damper
any of a number of devices mounted on a power line to reduce vibrations caused by wind.
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.
Volta, Alessando (Corte) (1745-1827) Born: Como, Italy

is best known for the invention of a number of practical devices including the first battery (voltaic pile), a simple electrometer for measuring current and electrophorus. Volta was not a theoretical physicist, but a good researcher. He was able to follow up Benjamin Franklin's early work and that of Luigi Galvani by devising devices and experiments that allowed him to explore the physics. Volta is honored by having his name used as the unit of electromotive force, the volt.