Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

disturbance
a sudden change or a sequence of changes in the components or the formation of a power system. Also called fault.
diversity combining
a communication technique that combines the signals received through different, possibly independent channels. The most common methods of combining are maximum-ratio combining, equal gain combining, selection combining, and switched combining.
diversity frequency
a method for increasing the reliability of digital communications in which multiple copies of the signal, or other types of redundant information, are transmitted. Frequency diversity implies that the received signal occupies a much wider bandwidth than the minimum bandwidth needed to carry the information.
diversity path
a form of diversity in which multiple copies of the signal are created via different paths from the transmitter to receiver.
diversity selection
a form of diversity reception in which the receiver selects the strongest signal among the copies received. The weaker signals are simply ignored.
dropout
equipment misoperation due to an interruption, noise, or sag.
dropout current
the current at which a magnetically-operated device will revert to its de-energized position.
dropout voltage
the voltage level where proper equipment operation is hindered.
dual-cage rotor
a three-phase induction motor rotor with two separate squirrel cage windings, that give the effect of varying rotor resistance. The outer cage has high resistance to obtain high starting torque, while the inner cage has low resistance to reduce losses at full load.
dual-element fuse
a fuse constructed with two different types of fusible elements in series. One element is designed to melt very quickly in the presence of fault current. The other is designed to melt after a time delay when exposed to overload conditions. The fusible elements are somewhat similar in operation to the thermal and magnetic elements of an inverse-time circuit breaker. Dual-element and time-delay are often used interchangeably.
fault detection
based on circuit duplication and comparison. One module is designed using positive logic and the other module uses negative logic. This assures detecting common mode faults.
dust cover
a cover to protect the terminals of a pad-mount transformer.
dust-ignition-proof machine
a machine designed with a casing or specialized enclosure to safely contain any internal ignition or flammable substances or components, and prevent them from igniting external flammables such as explosive gases, vapors, and dust particles.
duty cycle
(1) the ratio of the turn-on time of a semiconductor switch to the sum of the turn-on and turn-off times;

Turn-on / (Turn-on + Turn-off)

(2) the mode of operation that an electric machine is classified, in consideration of thermal limits, e.g., continuous operation, intermittent operation.



See duty ratio
duty ratio

See duty cycle
dynamometer
a rotating device used to measure the steady-state torque and power output of rotating machines. Dynamometers
generally provide precise control of the load torque applied to a test machine, and power output is determined through precise speed measurements.
earth electrode system
a network of electrically interconnected rods, plates, mats, or grids installed for the purpose of establishing a low-resistance contact with earth. The design objective for resistance to earth of this subsystem should not exceed 10 Ω.
earth wire
an overhead wire which is maintained at ground potential for purposes of lightning shielding and system grounding.
earthing

See grounding
economic dispatch
a generation scheme in which units are utilized such that the greatest profit is generated for the utility.
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