Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

power
(1) a measurable quantity that is the time rate of increase or decrease in energy. Units are in watts.

(2) ratio of energy transferred from one form to another (i.e., heat, radio waves, light, etc.) to the time required for the transfer, expressed in watts.
power angle
the angular displacement of the rotor from the stator rotating magnetic field while the machine is on load. The power angle is also the angle between the terminal voltage Vt of a synchronous machine and the generated voltage Eg or Em, respectively, for a generator or motor. This angle denoted by δ is also referenced as power angle or torque angle or the load angle in a synchronous machine. It signifies the limits of the machine to remain in synchronism.
See torque angle
power angle curve
a curve shown the relationship between the active power output of a generator and its power angle.
power conditioner
a device designed to suppress some or all electrical disturbances including overvoltages, undervoltages, voltage spikes, harmonics, and electromagnetic interference (EMI). Example power conditioners are active filters for the reduction of harmonics, metal-oxide varistors (MOVs) and isolation transformers for the protection against voltage spikes, and EMI filters.
power disturbance
a variation of the nominal value of the voltage or current.
power divider
passive electronic circuit consisting of one input and two or more outputs. A signal applied to the input is divided into equiphase output signals, generally of equal amplitude.
power factor
in an AC system, the ratio of the (active component) real power P to the apparent power S; it is given by the cosine of the angle subtended by S on the real, P axis. See also apparent power, real power, reactive power.
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 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 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 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.
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