Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

power follow transformer
a rugged, high-current power transformer used in tests of lightning arresters to test the arrester's power follow arc suppression capability.
power flux density
a vector that gives both the magnitude and direction of an electromagnetic field's power flow. The units are watts per square meter.
power fuse
a protective device that consists of a fusible element and an arc quenching medium. An overload or fault current in the fuse melts the fusible element, which creates an arc. The quenching medium then interrupts the current at a current zero, and prevents the arc from restriking.
power quality
(1) the concept of maintaining appropriate voltage and current waveforms and frequency in transmission, distribution, and generation systems, and usually taken to mean undistorted and balanced waveforms.

(2) a measure of an electric supply to meet the needs of a given electrical equipment application. As delivered by the utility, power quality is the faithfulness of the line voltage to maintain a sinusoidal waveform at rated voltage and frequency.
power supply
an electronic module that converts power from some power source to a form which is needed by the equipment to which power is being supplied.
power system stabilizer
a control device that provides an additional input signal to the AVR to damp power system oscillations.
power transformer
a transformer that is used to transmit power from one voltage level to another. Power transformers can be of either single phase or three phase design, and include either two or three windings.
predictive control
control policy (scheme), realized at a given control layer, involving repetitive usage of a decision mechanism based upon considering, at each intervention instant, the future operation of the controlled process (or the control system as a whole) over specified period of time (prediction interval). Usually, predictive control involves the use of optimization-based decision tools and of the free input forecasting; predictive control is the term describing a variety of possible control schemes, in particular open-loop-feedback control and limited-look-ahead-control.
primary
(1) the source-side winding.

(2) refers to the portion of a nuclear power plant containing the reactor and its equipment. primary coolant the medium used to remove energy, in the form of heat, from a nuclear reactor core, e.g., water, helium, or liquid metal.
primary voltage
in power distribution the voltage at the primary winding of the distribution transformer.
primary winding
the transformer winding connected to the energy source.
prime mover
the system that provides the mechanical power input for a mechanical-to-electrical energy conversion system (generator), e.g., the diesel engine of an engine-generator set.
PSC motor

See permanent split-capacitor motor
PT
potential transformer
See voltage transformer
pull-in torque
the amount of torque needed to change a synchronous motor's operation from induction to synchronous when self-started.
pull-out torque
the maximum value of torque that an AC motor can deliver. An induction motor operating at the pull-out torque will operate at maximum slip, and loading it beyond the pull-out torque will cause the motor to stall. Synchronous motors remain at synchronous speed up to the pull-out torque. Exceeding the pull-out torque for a synchronous machine will lead to pole slipping and destruction of the machine.
pull-up torque
the minimum torque generated by an AC motor as the rotor accelerates from rest to the speed of breakdown torque. For an induction motor, this value usually is less than the locked-rotor torque, and thus establishes the maximum load that can be started.
pulse
a sudden change of an electrical value of short duration with a quick return to the original value. A pulse injects a short sharp burst of energy into a system and is usually quantified by its area rather than its amplitude or its duration. In the limit as the amplitude tends to infinity and the duration to zero, it approaches the Dirac delta function whose Laplace transform is unity.
rare-earth permanent magnet
magnet made of compounds of iron, nickel, and cobalt with one or more of the rare-earth elements such as samarium. These materials combine the high residual flux density of the alnico-type materials with greater coercivity than ferrites.
reactive compensation
process of counteracting the reactive component of a device by means of capacitors and inductors. Both series and shunt compensation are prevalent.
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