Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

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.
conductance
(1) the reciprocal of resistance.
(2) a characteristic that describes the availability and the mobility of conduction electrons within a material. The values range from zero for a perfect insulator to infinity for a perfect conductor. The units are siemens.
(3) the ability of a substance to carry a thermodynamic flow, such as current, heat, energy, etc. conducted emission an RF current propagated through an electrical conductor.
conducted noise
unwanted electrical signals that can be generated by power electronic switching circuits. Conducted noise can travel through the circuit cables as common-mode or differential mode currents and can interfere with control circuits or other electronic equipment.
conductivity
(1) the reciprocal of resistivity.
(2) a measure of a material's ability to conduct electrical current. Conductivity . is the ratio of the conduction current to the electric field in Ohm's Law: Jc = σE
conduit
a pipe through which an electrical cables are laid.

cone of protection
a method used to determine the extent of protection to surrounding structures afforded by a tall, grounded structure like a steel tower. Proposed prior to the "rolling ball" model, this method suggests that any structure which can fit within a right circular cone whose vertex is at the top of the tower will be protected from lightning strikes by that tower. The angle of the cone's vertex is a matter of some controversy.

See rolling ball
constant-current transformer
two-coil transformer with a moveable secondary coil used to provide constant output current to
a variable load. Constant current is maintained by mounting both the primary and secondary coils on the center element of a shell-type core and allowing the secondary coil to move up and down with changes in demand for load current. Increasing current demand due to a reduction in load impedance causes the secondary coil to move away from the primary coil. Increasing the coil separation increases flux leakage and reduces the secondary output voltage. The reduced output
voltage counteracts the demand for more current. Increases in load impedance reverse the process. Movement of the secondary coil is controlled automatically by attaching the secondary coil to a counterweight and pulley assembly and orienting the coil windings such that their flux directions oppose. Increases in secondary current increase the magnetic repulsion between the coils, which, aided by the counterweight, moves the secondary coil away from the primary. Reductions in secondary current produce the opposite effect.
constant-horse power drive
a variable speed drive that is operating in a speed region where it is capable of delivering rated power. For DC machines, this region is above base speed and is achieved by field weakening. For AC induction motors, this region is above rated speed and is achieved by increasing the frequency of the applied voltage.
constant-torque drive
a variable-speed drive that is operating in a speed region where it is capable of maintaining rated torque. For DC machines, this region is below base speed and is achieved by reducing the applied armature voltage. For AC induction motors, this region is below rated speed and is achieved by reducing the frequency of the applied voltage.
continuous duty
National Electrical Manufacturers Association (NEMA) classification describing an application in which a machine operates for long periods of time at relatively constant loads.
continuous rating
term often used to refer to the manufacturer's nameplate ratings for an electrical machine, which are the rated operating conditions guaranteed by the manufacturer for continuous-duty operation.
See continuous duty
controller
(1) the entity that enforces the desired behavior as specified by the control objectives of the controlled process by adjusting the manipulated inputs. The values of these inputs are either predetermined or decided upon (computed) using on-line, i.e., real time, decision mechanism of the controller based on the currently available information. See also controlled variable.
(2) a device that generates the input to the plant or process. The role of the controller is to force the controlled variable of the plant or process to behave in a desired manner.
(3) a unit that directs the operation of a subsystem within a computer. For instance, a disk controller interprets data access commands from host computer (via a bus), and sends read/write, track seeking, and other control signals to the drive. During this time, the computer can perform other tasks, until the controller signals DATA READY for transfer via the CPU bus.
convective heat transfer
the process by which a moving fluid transfers heat to or from a wetted surface.
converter
a generic term used in the area of power electronics to describe a rectifier, inverter, or other power electronic device that transforms electrical power from one frequency and voltage to another.
copper loss
electric loss due to the resistance in conductors, windings, brush contacts or joints, in electric machinery or circuits. Also referred to as I2R, the losses are manifested as heat.
core
(1) the operating image of a process (sometimes used to refer to the part residing in physical memory), often written to disk if the program crashes (dumping core). Since magnetized ferrite rings (cores) were once used in main memory to store a single bit each. The name remained and now core memory means the same as main memory,
although currently, main memory is chip-based. See also magnetic core memory.
(2) the ferromagnetic portion of a transformer or electric machine on which the coils are mounted. Typically made of laminated magnetic material, encircled by the windings, that provides a low reluctance path for magnetic flux.
(3) the central region of an optical fiber. The refractive index of the core must be higher than that of the cladding so that the optical power is guided through the fiber by total internal reflection at the core-cladding boundary. The core refractive index may be constant or may decrease with distance from the axis to the cladding. See also graded index and step index optical fiber.
(4) the section of a nuclear reactor in which the chain reaction is contained, comprising fuel rods, control rods, moderator, and coolant.


See core lamination
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