Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

high phase order (HPO)
polyphase systems that contain 6, 9, or more phases ather than the standard three-phase system.

HPO systems may be used to provide a means of transmitting more electrical power down existing right-of-ways than three-phase systems, without an increase in transmission voltage, and without an increase in EMF levels at the edge of the right-of-way.
phase
(1) a notion used extensively in interpreting complex quantities such as Fourier series, Fourier transforms etc. Given a complex number c = x+iy = r cos θ + ir sin θ, then r represents the magnitude of c and  the phase.

(2) a horizontal translation parameter of the signal. Given a sinusoidal signal s(t) = Asin(2πft + θ), then f represents the frequency (in Hz) of s and θ the phase.

phase angle meter
meter used to measure the phase angle difference between two AC quantities. In power systems, typical meters use perpendicular moving coils to measure the phase angle between an AC current and an AC voltage. More accurate devices typically measure the time interval between zero crossings of the two input signals.
phase comparator
often referred to as a phase detector; a three-port device that produces an analog output proportional to the phase difference between its two inputs.

Since both inputs are periodic, the relative output voltage (or current) as a function of input phase difference (i.e., the transfer function) is also periodic; the shape of the transfer function (sometimes called the "output characteristic" of the phase detector) depends upon the particular technique used to accomplish the phase detection. These include sinusoidal, triangula, and sawtooth shape factors. Analog/digital implementation, required linearity, and range of input phase difference are primary factors in determining a suitable output characteristic for a specific phase comparator application.
phase comparison relay
a phase comparison relay is a protective relay used on transmission lines which operates by comparing phase angles of signals generated at opposite ends of the line. They employ a dedicated communications channel to make the comparison. The signals compared are typically corresponding phase currents or sequence currents.
phase constant
a constant, which is generally complex, that is important in the study of electromagnetic waves. The phase constant is equal to the frequency of excitation of the wave times 2 times pi times the square root of the product of the permeability and the permittivity of the medium that the wave is traveling in. Also called propagation constant or wavenumber.
phase control
a method for controlling the amount of power delivered to a load by varying the delay angle. This controls the delay between the instant when the voltage across the power semiconductor goes positive and the actual start in conduction of the device.
phase delay
the difference in the absolute angles between a point on a wavefront at the device output and the corresponding point on the incident input wavefront, expressed in seconds or degrees. The delay can exceed 360 degrees.
phase detector gain
the ratio of the DC output voltage of the phase detector to the input phase difference. This is usually expressed in units of volts per radian.
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.
polyphase system
electrical system that has more than one phase, which are separated by angles of 360=n, where n is the number of phases. For example, three phase systems are polyphase systems where the three phases are separated by 120 electrical degrees from each other. A six-phase system is a polyphase system where each successive phase is separated by 60 electrical degrees from the other.
single phase to ground fault

See single line to ground fault
single-phase inverter
an inverter with a single-phase AC voltage output. Half-bridge and full-bridge configurations are commonly used.
single-phase rectifier
a rectifier with a single-phase AC voltage input. See also half-wave rectifier and full-wave rectifier.
three phase fault
a fault on a three phase power line in which all three conductors have become connected to each other and possibly the ground as well.
three-phase inverter
an inverter with a three-phase AC voltage output.
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