Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

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
core loss
loss in the ferromagnetic material comprising the core of an electric machine or transformer, composed of the sum of hysteresis losses and eddy current losses. These magnetic losses are caused by time varying fluxes in a ferromagnetic structure.
Hysteresis losses are caused by friction in molecules as the dipoles in a structure change direction of alignment in response to an applied alternating voltage, while eddy current losses are resistive losses .I 2R/, due to circulating currents in the core.



See magnetic core memory
core-type transformer
a transformer in which the magnetic circuit upon which the windings are wound takes the form of a single ring. When the coils are placed on the core, they encircle the core.
See core
corona
a visible glow discharge which emanates from high-voltage conductors in regions of extremely high electric field intensity.
corona effect
flow of electrical energy from a high-voltage conductor to the surrounding ionized air. This effect only becomes significant for potentials higher than 1000 V. This effect is characterized by a faint glow, a crackling noise and conversion of atmospheric oxygen to ozone.
corona loss
the electric power lost in high voltage lines due to the radiation of energy by corona discharge.

See corona
corona resistance
capacity of a material to bear the action of the corona effect. This capacity is particularly important for polymeric materials, which have to withstand the chemical degrading effect promoted by ozone generated by the corona effect.

See corona effect
corona ring
a toroidal metal ring connected to discontinuities on high-voltage conductors to reduce local field intensity and thus discourage the formation of corona discharge.
Coulomb blockade
the situation in which a particle has insufficient thermal energy to allow the necessary energy exchange during a tunneling process. Hence, the bias supply must supply energy to the electron to account for the stored energy change in tunneling, which requires V > e/2C, where C is the capacitance (eV << kBT ).
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