Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

alternating current (AC)
a periodic current the average value of which over a period is zero.
alternating current machine
an electromechanical system that either converts alternating current electrical power into mechanical power (AC motor), or converts mechanical power into alternating current electrical power (AC generator, or alternator). Some AC machines are designed to perform either of these functions, depending on the energy source to the dynamo.
armature current limiting
a condition wherein the stator currents are clamped at the maximum allowable limit due to excessive heating of the stator.
arrester discharge current
the current in an arrester during a surge.
bearing currents
current flow in the bearings of electrical machines, because of electromagnetic unbalance in the machine
or from using high dv inverters. The latter is able to charge up the stray capacitance present between the stator and rotor and between the rotor and shaft and thus allows motor bearing currents to flow, with resulting bearing damage.
blocked-rotor current

See locked-rotor current
branch current
the current in a branch of a circuit.
charging current
that portion of an electric power line's current which goes to charge the capacitance of the line. The charging current is not available for power transmission.
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.
current
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.
DC current constant
current with no variation over time. This can be considered in general terms as an alternating current (AC) with a frequency of variation of zero, or a zero frequency signal. For microwave systems, DC currents are provided by batteries or AC/DC converters required to "bias" transistors to a region of operation where they will either amplify, mix or frequency translate, or generate (oscillators) microwave energy.
Powered by The Filipino Engineer