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Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

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.
D'Arsenval meter
a permanent-magnet moving-coil instrument with a horseshoe form magnet. It measures direct current only.
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.
field reversing
a method of achieving a reversal of rotation of a DC motor by reserving the field flux.
fractional horsepower
National Electrical Manufacturers Association (NEMA) classification describing any "motor built in a frame smaller than that having a continuous rating of 1 horsepower, open type, at 1700 to 1800 rpm."
horsepower-rated switch
a manually operated switching device designed for motor circuit applications. It is designed to interrupt the rated overload current at rated voltage of a motor with a horsepower rating that is less than or equal to the horsepower rating of the switch.
Institute of Electrical and Electronics Engineers (IEEE)
a professional organization of electrical engineers and computer scientists. The world's largest professional organization.
integral horsepower motor
a motor built in a frame as large as or larger than that of a motor of open construction having a continuous rating of one horsepower at 1700-1800 rpm.
inverse-time circuit breaker
a circuit breaker in which the allowed current and time are inversely proportional. It contains a thermal element and a magnetic element in series. The thermal element is designed to trip as a result of heating over time in response to overload currents, while the magnetic element is designed to trip magnetically, with no intentional time delay, in response to short-circuit currents. Also called a thermal-magnetic circuit breaker.
manually-controlled shunt capacitors
a bank of shunt capacitors that are controlled via SCADA signals from an operating center as opposed to local automatic control by voltage sensing.
National Electrical Manufacturers Association (NEMA)
an electrical trade association that establishes standards for electrical equipment. In the case of electric motors, NEMA establishes standard frame sizes, starting torque, starting current, and other quantities for a given horsepower machine.
Oersted
Oersted, Hans Christian (1777-1851) Born: Rudkobing, Langeland, Denmark

is best known as the discoverer of electromagnetism. Oersted was a strong teacher and did much to bring Danish science up to world-class standards. Oersted predicted the magnetic effect of electric current in 1813, but was unable to prove it until 1820. The publication of his results spurred the work of Faraday and Ampere. Oerstad went on to make other contributions in other sciences. He did not, however, return to his study of electricity.
persistent current
a current circulating in a closed structure without applied potential. Examples are the supercurrent in a superconducting magnet and the current in a closed mesoscopic ring in a magnetic field.
reverse breakdown
the diode operating region in which significant current flows from cathode to anode, due to an applied voltage exceeding the breakdown voltage.
reverse engineering
the reverse analysis of an old application to conform to a new methodology.
reversing motor starter
a motor controller capable of accelerating a motor from rest to normal speed in either direction of rotation. Some reversing motor starters can go directly from forward to reverse (or vice versa), while others must be stopped before a reversal of direction can take place. Both electromechanical and electronic reversing starters are available.
submersible transformer
a transformer, used in underground distribution work, which is capable of operation while submerged in water.