Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

circuit
a physical device consisting of an interconnection of elements, or a topological model of such a device. For example, an electric circuit may be constructed by interconnecting a resistor and a capacitor to a voltage source.
circuit breaker
a circuit breaker is a device that makes and breaks the electrical contact between its input and output terminals. The circuit breaker is capable of clearing fault currents (tripping) as well as load currents. The circuit breaker consists of power contacts with arc clearing capability and associated control and auxiliary circuits for closing and tripping the breaker under the required conditions.
circuit protection
devices or control measures used to safeguard electrical circuits from unsafe operating regions, such as over-currents and over-voltages.
circular polarization
a polarization state of a radiated electromagnetic field in which the tip of the electric field vector traces a circle as a function of time for a fixed position. The sense of rotation of the electric field vector is either right-hand or left-hand (clockwise or counter-clockwise).
code letter

See NEMA code letter
coefficient of thermal expansion (CTE) mismatch
the difference between the coefficients of thermal expansion of two components, i.e., the difference in linear thermal expansion per unit change in temperature. (This term is not to be confused with thermal expansion mismatch).
coefficient of utilization (CU)
the ratio of the lumens reaching the working plane to the total lumens generated by the lamp. This factor takes into account the efficiency and distribution of the luminaire, its mounting height, the room proportions, and the reflectances of the walls, ceiling, and floor.
cogeneration
(1) any of a number of energy generation systems in which two (or more) forms of energy are produced in forms practical for use or purchase by an end user. Typical systems produce electrical energy for sale to a utility and process steam for local space heating or other process uses. Cogeneration designs are generally adopted to increase the overall efficiency of a power generation process.
(2) typically, the production of heat energy, e.g. to heat buildings, as an adjunct to the production of electric power.
coherent illumination
a type of illumination resulting from a point source of light that illuminates the mask with light from only one direction. This is more correctly called "spatially coherent illumination."
coherent light
light having a relatively long coherence length; laser light.
coil pitch

See coil span
color temperature
the color a black object becomes when it is heated. The standard color "white" occurs when a tungsten filament is heated to a temperature of 6800 degrees Kelvin. The temperature of 6800 K corresponds to a standard white raster as defined by the NTSC. The color temperature for white is useful for comparing color matching and color decoding among different displays that use different color phosphors. The standard "white" is obtained by mixing the 30% red, 59% green, and 11% blue color signals. Differences in the color saturation for the different phosphors found in television CRTs will modify the required proportions of red, green, and blue to produce the standard "white."
combined cycle plant
a gas-turbine power plant in which the exhaust gases are used to heat water in a boiler to provide steam to run a turbogenerator.
commutating inductance
in switched circuits (converters, inverters, etc.), the inductance that is in series with the switching elements during the process of commutation from one topological state to another. This inductance results in noninstantaneous commutation due to the fact that current in an inductor cannot change instantaneously.
commutating pole

See interpole
commutating winding

See interpole
commutation
the process by which alternating current in the rotating coil of a DC machine is converted to unidirectional current. Commutation is accomplished via a set of stationary electrical contacts (brushes) sliding over multiple, shaft-mounted electrical contacts that turn with the machine rotor. The contacts are the connection points in a series-connected loop of the coils that make up the rotor winding. The brushes, sliding over these contacts, continually divide the loop into two parallel electrical paths between the brushes.
The brushes are positioned such that they make contact with those commutator segments that are connected to coils that are
moving through a magnetic neutral point between poles of the machine's field flux. As a result, all coils making up one parallel path are always moving under a north magnetic pole, and the others are always moving under
a south magnetic pole. The movement of the commutator contacts underneath the brushes automatically switches a coil from one path to the other as it moves from a north pole region to a south pole region. Since the coils in both paths move in the same direction, but through opposite flux regions, the voltages induced in the two paths are opposite. Consequently, the positive and negative ends of each path occur at the same points in the series loop, which are at the points where the
brushes contact the commutator. The brush positions, thus, represent a unidirectional (or DC) connection to the rotating coil.
See commutator
commutation angle
time in electrical degrees from the start to the completion of the commutation process.

See overlap angle
commutator
a cylindrical assembly of copper segments, insulated from each another, that make electrical contact with stationary brushes, to allow current to flow from the rotating armature windings of a DC machine to the external terminals of the machine. It also, enables reversal of current in the armature winding.
See commutation
commutator film
an oxide layer on the commutator surface, indicated by a dark color or a "film," that is required for proper commutator action and full loading of the machine. On a new DC machine commutator, or on a commutator that has just been stoned, there is no "film" on the commutator. It is advisable to refer to the manufacturer's technical manual for the proper procedure to "break in" the commutator and develop the film so the machine can be operated at rated conditions.
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