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Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

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.
bandwidth
(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
base
(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.

base quantity
See per-unit system
base speed
corresponds to speed at rated torque, rated current, and rated voltage conditions at the temperature rise specified in the rating. It is the maximum speed at which a motor can operate under constant torque characteristics or the minimum speed to operate at rated power.
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.

battery
one or more cells connected so as to produce energy.

baud
the signaling rate, or rate of state transitions, on a communications medium. One baud corresponds to one transition per second. It is often confused with the data transmission rate, measured in bits per second.
Numerically, it is the reciprocal of the length (in seconds) of the shortest element in a signaling code. For very low-speed modems (up to 1200 bit/s) the baud rate and bit rate are usually identical. For example, at 9600 baud, each bit has a duration of 1/9600 seconds, or about 0.104 milliseconds.
Modems operating over analog telephone circuits are bandwidth limited to about 2500 baud; for higher user data speeds each transition must establish one or more decodable states according to amplitude or phase changes. Thus, if there are 16 possible states, each can encode 4 bits of user data and the bit rate is 4 times the baud rate.
At high speeds, the reverse is true, with run-length controlled codes needed to ensure reliable reception and clock recovery. For example FDDI uses a 4B/5B coding in which a "nibble" of 4 data bits is encoded into 5 bits for transmission. A user data rate of 100 Mbit/s corresponds to transmission at 125 Mbaud.
baud rate
See baud
beam
(1) transverse spatial localization of the power in a wave field.
(2) a slender unidirectional stream of particles or radiation.

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.

bell insulator
a type of strain insulator, shaped like saucer with ribs on its lower side and frequently used in insulator strings.
beryllium oxide
a compound commonly used in the production of ceramics for electrical applications and whose dust or fumes are toxic.

beta particle
an electron or positron emitted from a radioactive source.

BIL
basic lightning impulse level

See basic impulse insulation level
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