Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

boundary bus
one of a set of buses which define the boundary between the portion of a power system to be analyzed and the rest of the system. Boundary buses are connected to both the internal and external systems.
braking
operating condition in an electric motor in which the torque developed between the stator and rotor coils opposes the direction of rotation of the rotor. Typical braking methods in DC machines include "plugging" in which the polarity of either the field or the armature coil, but not both, is reversed while the rotor is turning, "dynamic braking" in which generator action in the armature is used to dissipate rotor energy through a braking resistor, and "regenerative braking" in which generator action in the rotor is used to dissipate rotor energy by returning electric power to the power source as the rotor slows. Typical braking methods in AC machines include switching of the phase sequence of the supply voltage, dynamic braking through the armature coils, and varying the frequency of the AC supply voltage.
See phase sequence
braking resistor
resistive elements which can be switched into the electrical system to create additional load in the event of a transient disturbance, thus limiting the generator rotor acceleration such that the system can more readily return to synchronism.
branch circuit
the three components of an electrical circuit are source, load, and interconnecting circuit conductors. A branch circuit is an electrical circuit designed to deliver power to the lowest-order load(s) served on a facility. It includes the overcurrent device, circuit conductors, and the load itself.
branch current
the current in a branch of a circuit.
branch line coupler
coupler comprised of four transmission lines, each of 90. electrical length, arranged in a cascaded configuration with the end of the last transmission line section connected to the beginning of the first transmission line to form a closed path. The input, coupled, direct, and isolated ports are located at the connection point of one transmission line with the next one.
branch voltage
the voltage across a branch of a circuit.
breakaway torque
minimum torque needed to begin rotating a stationary load. Breakaway torque represents the absolute
minimum starting torque specification for a motor used to drive the load.
breakdown
as applied to insulation (including air), the failure of an insulator or insulating region to prevent conduction, typically because of high voltage.
breakdown strength
voltage gradient at which the molecules of medium break down to allow passage of damaging levels of electric current.
breakdown torque
maximum torque that can be developed by a motor operating at rated voltage and frequency without experiencing a significant and abrupt change in speed. Sometimes also called the stall torque or pull-out torque.
broadband
a service or system requiring transmission channels capable of supporting bit rates greater than 2 Mbit/s.
broadband integrated services digital network (B-ISDN)
a generic term that generally refers to the future network infrastructure that will provide ubiquitous availability of integrated voice, data, imagery, and video services.
Brown book

See IEEE Color Books
brownout
an intentional lowering of utility voltage to reduce loading on the system.
brush
a conductor, usually carbon or a carbon-copper mixture, that makes sliding electrical contact to the rotor of an electrical machine. Brushes are used with sliprings on a synchronous machine to supply the DC field and are used with a commutator on a DC machine.
brush rigging
the components used to hold the brushes of a rotating machine in place, and to insure proper brush tension is applied.
brush tension
the force required on the brushes of a rotating machine to insure proper contact between the brush and the commutator or slipring. Proper brush tension is usually provided by springs, and is specified in the manufacturer's technical manual of the machine.
brushless DC motor

See electronically commutated machine
brushless exciter

See rotating-rectifier exciter