Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

power factor correction
the addition of reactive load to bring the combined power factor nearer unity. Since most industrial loads are inductive, capacitors are often employed as passive devices for power factor correction.
power fault arc
an arc through soil extending from a power lines's lightning ground to a buried, grounded structure. These may form when lightning strikes an energized overhead electric power line.
power flow studies
solutions of transmission line active and reactive power flow and bus voltages giving system load.
power flow study
the circuit solution of an electric power system which yields the voltage of each bus and thus the power flows throughout the system.
power follow
a fault condition, especially through a lightning arrester, in which power line current flows along a path through air or other insulation broken down by a high voltage impulse such as a lightning stroke to a conductor. See power fault arc.
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.
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