Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

three-phase inverter
an inverter with a three-phase AC voltage output.
three-point starter
a manual DC motor starter in which a handle is pulled to start the motor. The motion of the handle causes a contact to move across a variable resistance in the armature circuit to limit the starting current. When the handle is moved to its fullest extent, the resistance is out of the armature circuit and an electromagnet holds the handle in place. With a three-point starter, the electromagnet is in series with the shunt field and loss of the field will shut down the motor. The disadvantage is that if it is desired to weaken the field for speed control, the motor starter may drop out. Also, the three-point starter cannot be used on a series DC motor.
total harmonic distortion
disturbance level an electromagnetic disturbance level due to all emissions from equipment in a system.

This is expressed as a ratio of the RMS value of the harmonic content to the RMS of the fundamental and is calculated as a percentage of the fundamental component.
transient short-circuit
time constant pass and stop bands are critical. A longer filter length generally implies that the filter can have a steeper transition band to a similarly shaped shorter length filter.
twelve-pulse converter
the combination of two 6-pulse converters connected through a Y-Y and a delta-Y transformer in order to cancel the characteristic 5th and 7th harmonics of the 6-pulse converters. The lowest characteristic harmonics with twelve-pulse converters under balanced conditions are the 11th and 13th harmonics. The converters are connected in parallel on the AC side and in either series or parallel on the DC side, depending on the required DC output voltage.
up-down converter

See buck-boost transformer
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.
voltage distortion
a change from a nominal clean sinusoidal waveform
voltage fed inverter

See voltage source inverter
voltage source inverter
a power converter that takes a DC voltage from a battery or the output of a rectifier and supplies a voltage of controllable and variable frequency and magnitude to a single or multiphase load.
See current source inverter
volts/hertz control
a method of speed control of induction machines, used below rated speed. When the volts/hertz ratio is kept constant, the current through the stator windings remains almost the same, except for very low speeds; hence, the available torque remains constant, but the speed changes due to change in frequency.
warm start
(1) reassumption, without loss, of some processes of the system from the point of detected fault.

(2) the restart of a computer operating system without going through the power-on (cold) boot process.
wye-delta starter
a motor starter that starts a three-phase AC motor in wye or star configuration so that the motor starts on approximately 58% of normal voltage, with a two-thirds reduction in starting current. As the motor approaches operating speed, the windings are reconfigured in delta configuration so that full voltage is applied for normal operation. The transition from star to delta is performed with the help of timer settings and contactors.
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