Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

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
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.
boiling water reactor
a nuclear reactor from which heat is transferred in the form of high-pressure steam.
bundle spacer
a rigid structure which is used to maintain the spacing of wires in a bundled conductor on an overhead electric power transmission line.

See bundle
reactive power Q
The region of allowable operation is determined by factors such as rotor thermal limit, stator thermal limit, rated power of prime mover (alternator operation), and stability torque limit.
capacitance
the measure of the electrical size of a capacitor, in units of farads. Thus a capacitor with a large capacitance stores more electrons (coulombs of charge) at a given voltage than one with a smaller capacitance.
In a multiconductor system separated by nonconductive mediums, capacitance (C) is the proportionality constant between the charge (q) on each conductor and the voltage (V ) between each conductor. The total equilibrium system charge is zero. Capacitance is dependent on conductor geometry, conductor spatial relationships, and the material properties surrounding the conductors.
Capacitors are constructed as two metal surfaces separated by a nonconducting electrolytic material. When a voltage is applied to the capacitor the electrical charge accumulates in the metals on either side of the nonconducting material, negative charge on one side and positive on the other. If this material is a fluid then the capacitor is electrolytic; otherwise, it is nonelectrolytic.
capacitive reactance
the opposition offered to the flow of an alternating or pulsating current by capacitance measured in ohms.
capacitor bank
(1) an assembly at one location of capacitors and all necessary accessories, such as switching equipment, protective equipment, and controls, required for a complete operating installation.
(2) a group of (typically 3) capacitors mounted on an electric power line for voltage boosting or power factor correction.
capacitor-start induction motor (CSIM)
a single-phase induction motor with a capacitor in series with its auxiliary winding, producing nearly a 90. phase difference between the main winding and the auxiliary winding currents at starting. This results in a high starting torque, so this motor is used for hard-to-start loads. The auxiliary winding and capacitor are removed from the circuit by a centrifugal switch as the machine approaches operating speed.
chain reaction
a process in which high-energy neutrons emitted from fissile radioactive material are directed into more fissile material such that more neutrons are emitted. The process creates heat which is used to power thermal power plants.
compound-connected DC machine
a direct current machine with two field windings in which one field winding is connected
in series and one field winding is connected in parallel (shunt) with the armature winding. The shunt winding may be connected ahead of the series winding (long-shunt connection), or behind the series winding (short-shunt connection).
crest factor
the ratio of the peak value of a signal to its RMS value.
crossarm brace
a brace, often insulated, which keeps a crossarm from rotating on its attachment bolts.
current distribution factor
in economic dispatch studies, the proportion of a power line's total current which is contributed by a particular generating plant.
cylndrical-rotor machine
a synchronous machine with a cylindrical rotor containing a distributed field winding and an essentially uniform air-gap. This design is limited to two and four pole machines (3600 and 1800 rpm at 60 Hz) and is usually used in large generators.
See salient-pole rotor machine
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