Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

phase sequence
describes the rotational orientation of the voltage phasors in a 3phase electrical power system.
A positive phase sequence, designated by the nomenclature ABC, indicates a 3-phase connection in which the B phase voltage lags the A phase voltage by 120 degrees, and the C phase voltage leads the A phase voltage by 120 degrees.
A negative phase sequence, designated by ACB, reverses this relationship so that the B phase leads the A phase, and the C phase lags the A phase.
See phase sequence indicator
phase sequence indicator
device used to detect the phase sequence of a 3-phase electrical power system.
See phase sequence
phase shift
a time displacement of a waveform with respect to another waveform of the same frequency.
phase shifter
a device that changes the phase angle between two buses in a power system. Conventional phase shifters are special autotransformers in with each phase voltage in connected in series with a variable component of voltage from another phase.

By adjusting the variable component, the phase angle can be changed. Newer phase shifters are built with power electronic devices. Phase shifters are often used in antenna arrays.
phase-to-phase fault
a fault with two transmission lines being short circuited.
phonon
a quantized packet of energy associated with material lattice vibrations that have been excited by an incident photon.
photodetector
device capable of producing or modifying an electrical signal in proportion to the amount of light falling on the active area of the device.
photoelectric effect
the phenomenon whereby light of sufficiently short wavelength falls on the emitter electrode of a photocell and causes electrons to be emitted from the electrode.
photogalvanic effect

See photovoltaic effect
photoluminescence
the process by which light is emitted from solids, atoms, gases, after excitation by an additional light source. The input light excites electrons to higher energy states, and as they relax they emit light (through electron-hole recombination) whose frequency is characteristic of the statistical properties of the carriers.
photovoltaic
effect a photoelectric phenomenon in certain photorefractive crystals, for example, LiNbO3, BaTiO3, LiTaO3,in which the illumination of light leads to the generation of electric current along certain direction in the crystals. This leads to the accumulation of charges on the surfaces of the crystals, causing an open circuit voltage.
photovoltaics
conversion of insolation into DC electricity by means of solid state p-n junction diodes.
pickup current
the specified value that, if exceeded, causes the relay to act on its contact and cause a circuit breaker action. It is the threshold current for system protection, and a magnitude above this is considered a fault or abnormal condition.
pickup voltage

See pickup current
pig tail
a type of hot stick that can slide over an overhead conductor.
pigtail
short electrical conductor used to connect the brushes of an electrical motor or generator to the external electrical connections of the machine.
pilot carrier
a means of providing a carrier at the receiver, which matches the received carrier in phase and frequency. In this method, which is employed in suppressed carrier modulation systems, a carrier of very small amplitude is inserted into the modulated signal prior to transmission, extracted and amplified in the receiver, and then employed as a matching carrier for coherent detection.
pin insulator
an electric insulator which is concentric with a hollow, threaded hole so that it can be screwed onto a steel pin mounted on a utility pole or crossarm.
pipe cable
a paper-insulated high-voltage electric power transmission cable laid within a rigid steel pipe containing pressurized insulating oil.
pitch factor
in an electric machine, the ratio of the fractional pitch in electrical degrees to the full pitch, also in electrical degrees.