Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

one or more cells connected so as to produce energy.

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
(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.

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
See basic input–output system
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.
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.
total loss of power to the entire power system.

an insulating rubber mat which is fitted temporarily over energized conductors to protect nearby workers.

blocked-rotor current
See locked-rotor current
blocked-rotor test
an induction motor test conducted with the shaft held so it cannot rotate. Typically about 25% of rated voltage is applied, often at reduced frequency and the current is measured. The results are used to determine the winding impedances referred to the stator.
boiling water reactor
a nuclear reactor from which heat is transferred in the form of high-pressure steam.

bolted fault
a bolted fault is a short circuit fault with no fault resistance. Bolted faults deliver the highest possible fault current for a given location and system configuration, and are used in selecting equipment withstand and interrupting ratings and in the setting of protective relays.
a curve that separates two sets of points.