Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

equivalent resistance
the resistance of the windings of an electromagnetic machine reflected to one side (component) of the machine.
See equivalent impedance
equivalent source
fictitious source used in the equivalence theorem.
equivalent sphere illumination (ESI)
the level of sphere illumination that would produce task visibility equivalent to that produced by a specific lighting environment.
equivalent system dynamics
a dynamical system model resulting from substituting the equivalent control into the plant's modeling equation. The equivalent system's trajectory is confined to a surface that is parallel to the sliding surface if the system's initial condition is off the sliding surface. If the initial condition is on the sliding surface, then the equivalent system's trajectory will stay on the sliding surface.
(1) manifestation of a fault at logical level. For example, a physical short or break may result in logical error of stuck-at-0 or stuck-at-1 state of some signal in the considered circuit.

(2) a discrepancy between a computed, observed, or measured value or condition and the true, specified, or theoretically correct value or condition.
See bug

See electrostatic discharge

See enhanced small disk interface

See equivalent sphere illumination
acronym for estimation of signal parameters via rotational invariance techniques. A subspace-based estimation technique based on two identical, displaced sensor arrays.
a reactive process where material is removed from a semiconductor device or printed circuit board. Usually a photosensitive material is exposed through a photomask, and either a wet chemical process or a dry plasma process is used to selectively remove material to leave a particular pattern behind after the etch process is completed.
eutectic alloy
composition with minimum melting temperature at the intersection of twosolubility curves.
eutectic alloy overload device
an overload device that employs a melting alloy as the actuating element. See also overload heater, overload relay.
(1) an unusual condition arising during program execution that causes the processor to signal an exception. This signal activates a special exception handler that is designed to handle only this special condition. Division by zero is one exception condition. Some vendors use the term "trap" to denote the same thing.

(2) an event that causes suspension of normal program execution. Types include addressing exception, data exception, operation exception, overflow exception, protection exception, underflow exception. exception handler a special block of system software code that reacts when a specific type of exception occurs. If the exception is for an error that the program can recover from, the program can recover from the error and resume executing after the exception handler has executed. If the programmer does not provide a handler for a given exception, a built-in system exception handler will
usually be called, which will result in terminating the process that caused the exception. Finally, the reaction to exception can be halting of the system. As an example, a bus error handler is the system software responsible for
handling bus error exceptions.
excess delay
the arrival times of a component of the impulse response of a wideband communication channel relative to the first arriving component. Hence the total excess delay, the difference in arrival time between the first and last significant components.
excitation system
the DC voltage source and its accompanying control and protection systems connected to the synchronous generator rotor.
a DC source that supplies the field current to produce a magnetic flux in an electric machine. Often it may be a small DC generator, placed on the same shaft of the electrical machine.
exciting current
the current drawn by a transformer primary with its secondary open circuited. It is the vector sum of the core loss current Ic and the magnetizing branch current Im . The exciting current Ie is also the current measured in the open circuit test on a transformer. The exciting current is calculated as the ratio of the primary induced EMF and the impedance of the tank circuit. On load, it is equal to the difference between the primary and reflected secondary currents of the transformer.
explosion-proof machine
National Electrical Manufacturers Association (NEMA) classification describing an electrical machine that is totally enclosed and whose enclosure is designed to withstand an internal explosion of a specified gas or vapor that may accumulate within the enclosure. The specification also requires that the design prevent ignition of the specified gas or vapor surrounding the enclosure due to sparks, flashes, or explosions of the specified gas within the enclosure.
express feeder
a feeder to which laterals are connected only at some distance from the substation. These thus traverse areas fed by other feeders and are used to supply concentrated loads or new subdivisions. See feeder, lateral.
expulsion fuse
a fuse used on primary distribution lines which extinguishes the arc that results when it blows by explosively ejecting the fuse wire from its enclosure.