Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

coil pitch

See coil span
coil side
that portion of a motor or generator winding that cuts (or is cut by) lines of magnetic flux and, thus, contributes to the production of torque and Faraday EMF in the winding.
coil span
the distance, measured either in number of coil slots or in spatial (mechanical) degrees, between opposite sides of a winding of an electric machine. A full-span (full-pitch) winding is one in which the winding span equals the span between adjacent magnetic poles. Windings with span less than the distance between adjacent magnetic poles are called short-pitch, fractional-pitch, or chorded windings.

See coil pitch
color preference index (CPI)
measure appraising a light source for appreciative viewing of colored objects or for promoting an optimistic viewpoint by flattery.
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
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
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.
compensating winding
a winding found in DC machines that is placed in the faces of the main field poles, and connected in series with the armature winding, to produce an mmf equal and opposite to the mmf of the armature, thereby reducing the effect of armature reaction.
(1) operations employed in a control scheme to counteract dynamic lags or to modify the transformation between measured variables and controller output to produce prompt stable response.
(2) the alteration of the dynamic behavior of a process by the addition of system blocks. These are usually connected in cascade with the original process on either its input or its output variables, or both. See also compensator, pre-compensator and post-compensator.
a system block added to an existing system (or process) to produce a combined transfer function that improves its performance when connected in a closed loop configuration. See also compensation, pre-compensator and post-compensator.
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).
compound-rectifier exciter
a source of field current of a synchronous machine derived from the phase voltages and currents of the machine. The phase voltages and currents of the machine are fed through transformers, then rectified in order to provide DC quantities to the field winding. The components of the exciter are the transformers (voltage and current), rectifiers (including possible gate-circuitry), and power reactors; exclusive of all input control elements.
computer relay
a protective relay that digitizes the current and/or voltage signals and uses a microprocessor to condition the digitized signal and implement the operating logic.
See digital relay
computer-aided design (CAD)
field of electrical engineering concerned with producing new algorithms/programs which aid the designer in the complex tasks associated with designing and building an integrated circuit. There are many subfields of electrical CAD: simulation, synthesis, physical design, testing, packaging, and semiconductor process support.