Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

the flow of charge, measured in amperes (1 ampere = 1 coulomb/s).
current density vector field
the field (commonly denoted J ) that is related to the electric field intensity vector field by the conductivity of the medium that the fields are located in. One of the quantities found on the right side of Ampere's Law. The units are (amperes/square meter).
current distribution factor
in economic dispatch studies, the proportion of a power line's total current which is contributed by a particular generating plant.
current limiting
the output current is limited to a preset level even under a shorted output condition. This can be accomplished by reducing the output voltage to prevent the current limit from being exceeded.
current limiting fuse
a fuse that limits the level of fault current from that which is available. It operates by developing a substantial voltage across the fuse following the melting of the fuse element.
current regulator
a device used to control the magnitude and phase of the current in DC, AC or other electrical variable speed drives. May use different control strategies like hysteresis current control or ramp comparison current control.
current transducer
a device used to measure current in a variety of applications including variable speed drives. May give out a current proportional to the measured current or a voltage proportional to the measured current. Electrical isolation may be obtained by using a current transformer (cannot be used at DC) or a hall effect transducer that can be used down to DC.
current transformer (CT)
(1) a transformer that is employed to provide a secondary current proportional to primary current flowing. The primary "winding" is often created by passing the system conductor or bus bar through an opening in the device
and the secondary is typically rated at a standard value to match common meters and display units. Current transformers are used in current measurement, protective relays, and power metering applications. The load (meter) on a CT should never be removed without first shorting the secondary of the CT, otherwise dangerous voltage levels may result when the load is removed.
(2) a device which measures the instantaneous current through a conductor of an electric power line and transmits a signal proportional to this current to the power system's instrumentation. current unit a protective relay that monitors the magnitude of a power transmission line's current flow.
current withstand rating
the current withstand rating of a device is the maximum short term current that can flow in the device without causing damage.
See ampacity
current-limiting device
when operating within its current-limiting range, a current-limiting device is open in 0.25 cycle or less and limits the maximum short-circuit current to a magnitude substantially less than the short-circuit current available at the fault point.
cylndrical-rotor machine
a synchronous machine with a cylindrical rotor containing a distributed field winding and an essentially uniform air-gap. This design is limited to two and four pole machines (3600 and 1800 rpm at 60 Hz) and is usually used in large generators.
See salient-pole rotor machine