Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

automatic generation control (AGC)
phrase describing the computer-based process by which electric utilities control individual generating stations to maintain system frequency and net interchange of power on a highly interconnected transmission grid. Automatic generation control (AGC) systems monitor grid frequency, actual and scheduled power flows, and individual plant output to maintain balance between actual and scheduled power production, both within transmission control areas and at individual generating stations. Control is generally accomplished by adjusting the speed control (or droop) characteristics of individual generating units. Control actions are determined by planned production schedules and power exchange agreements among participating utilities.
automatic transfer switch
a self-acting switch which transfers one or more load conductor connections from one power source to another.
automatic voltage regulator (AVR)
an automatic feedback control system that is responsible for maintaining a scheduled voltage either at the terminals of a synchronous generator or at the high-side bus of the generator step-up transformer. The control is brought about by changing the level of excitation.
B coefficient

See loss coefficient
back EMF

See counter-EMF
backfeed
in power distribution work, power which flows from the secondary lines into the primary lines through the distribution transformer, e.g.,from an emergency generator connected to customer load.
backflash
an arc which forms along a tower during a lightning strike due to high tower or footing impedance.
background noise
the noise that typically affects a system but is produced independent of the system. This noise is typically due to thermal effects in materials, interpreted as the random motion of electrons, and the intensity depends on the temperature of the material. In radio channels, background noise is typically due to radiation that is inherent to the
universe and due mainly to radiation from astronomical bodies. There is a fundamental lower bound on the intensity of such noise which is solely dependent on the universe and independent of antenna and receiver design.

See thermal noise
balanced line
symmetric multiconductor transmission line in which the voltage on each conductor along the transmission line
has the same magnitude, but the phases are such that the voltage would sum to zero. In a two conductor transmission line, the voltages would be equal and 180 degrees out of phase. This is the equivalent of a virtual ground plane or zero E-field plane at the geometric center plane of the transmission line cross section, or balanced with respect to virtual ground. Balanced wiring configurations are often used to prevent noise problems such as ground loops. Contrast with unbalanced line.
balanced load
a load on a multi-phase power line in which each line conductor sees the same impedance.
base vector
a unit vector in a coordinate direction.
basic impulse insulation level (BIL)
a measurement of the impulse withstand capability of a piece of electric power equipment based on its ability to withstand 50% of impulses applied at the BIL voltage.
basic input-output system (BIOS)
part of a low-level operating system that directly controls input and output devices.
basic lightning impulse level (BIL)
the strength of insulation in terms of the withstand voltage crest value using a standard voltage level impulse.
bearing currents
current flow in the bearings of electrical machines, because of electromagnetic unbalance in the machine
or from using high dv inverters. The latter is able to charge up the stray capacitance present between the stator and rotor and between the rotor and shaft and thus allows motor bearing currents to flow, with resulting bearing damage.
beta particle
an electron or positron emitted from a radioactive source.
bimetal overload device
an overload device that employs a bimetal strip as the actuating element. The bimetal strip consists of two metals bonded together. When heated, the bimetal strip will bend due to the different coefficients of linear expansion of the two metals. The bending operates a set of contacts that automatically removes the affected
load from the source of electrical power.
See overload relay
black start
the task of re-starting an isolated power system which is completely de-energized. Most generating plants require substantial external electric power to start. Thus a black start may be initiated by hand-starting gas turbine generators or by opening the gates of a hydroelectric generator somewhere in the system.
blackbody
theoretically contrived object that gives rise to the so-called "black body radiation." One might imagine a closed surface object (say of metal) possessing one opening that connects the interior surface with the outside world. When the object is heated, the opening becomes a perfect "black" radiator. Such radiation depends on temperature only.
blackout
total loss of power to the entire power system.
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