Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

auxiliary relay
a relay employed in power system protection schemes that does not directly sense fault presence and location. Typical auxiliary relays include lockout relays, reclosing relays, and circuit breaker anti-pump relays.
auxiliary winding
a winding designed to be energized occasionally for a specific purpose, such as starting a single-phase motor. The power to the winding may be controlled by various means including a timer, centrifugal switch, current sensing relay, or voltage (counter EMF) sensing relay.
average power
the average value, taken over an interval in time, of the instantaneous power. The time interval is usually one period of the signal.
average-value model
a mathematical representation in which the average value of variables are used to model a system. In electric machines and drives, system variables are typically averaged over various switching intervals. This eliminates the high-frequency dynamics, but preserves the slower dynamics of the system.

See automatic voltage regulator
American Wire Gauge, a system of wire sizing used in the USA especially in smaller conductors used in residential and
commercial wiring.
B coefficient

See loss coefficient
broadband integrated services digital network.
back EMF

See counter-EMF
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.
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.
a starting and control mechanism for fluorescent and other types of gas-discharge lamps. Initially a ballast supplies the necessary starting (or striking) voltage in order to ionize the gas to establish an arc between the two filaments in the lamp. Once the gas is ionized, the ballast controls the input power and thus the light output to maximize the efficiency and life of the lamp.
a network for the transformation from an unbalanced transmission line, system or device to a balanced line, system or
device. Baluns are also used for impedance transformation. Derived from "balanced to unbalanced".
In antenna systems, baluns are used to connect dipole-type antennas to coaxial cable, to balance the current on dipole armatures, and to prevent currents from exciting the external surface of the coaxial shield.
band stop filter
filter that exhibits frequency selective characteristic such that frequency components of an input signals pass through unattenuated from input to output except for those frequency components coincident with the filter stop-band region, which are attenuated. The stop-band region of the filter is defined as a frequency interval over which frequency components of the input signal are attenuated.
band-pass network
a configuration of solely passive components or combination of active and passive components that will attenuate all signals outside of the desired range of frequency.
(1) the frequency range of a message or information processing system measured in hertz.
(2) width of the spectral region over which an amplifier (or absorber) has substantial gain (or loss); sometimes represented more specifically as, for example, full width at half maximum.
(3) the property of a control system or component describing the limits of sinusoidal input frequencies to which the system/component will respond. It is usually measured at the half-power points, which are the upper and lower frequencies at which the output power is reduced by one half. Bandwidth is one measure of the frequency response of a system, i.e., the manner in which it performs when sine waves are applied to the input.
(4) the lowest frequency at which the ratio of the output power to the input power of an optical fiber transmission system decreases by one half (3 dB) compared to the ratio measured at approximately zero modulation frequency of the input optical power source. Since signal distortion in an optical fiber increases with distance in an optical fiber, the bandwidth is also a function of length and is usually given as the bandwidth-distance product for the optical fiber in megahertz per kilometer.
See bandwidth-distance product
(1) the number of digits in a number system (10 for decimal, 2 for binary).
(2) one of the three terminals of a bipolar transistor.
(3) a register's value that is added to an immediate value or to the value in an index register in order to form the effective address for an instruction such as LOAD or STORE.