Electrical Engineers and Master Electricians (EEAME) Portal

Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

the beneficial effect provided by an overcurrent device when it acts to interrupt short-circuit current.

a transformer test conducted by placing a few percent of rated voltage on the voltage side while the low voltage winding is shorted. By measuring the voltage, current, and input power, it is possible to calculate the equivalent winding impedance for the transformer equivalent circuit.

subtransient current

the fault current that flows during the subtransient period when the generator and motor apparent impedances are their respective subtransient impedances.

subtransient open-circuit time constant

See quadrature-axis transient open-circuit time constant and direct-axis subtransient open-circuit time constant.

swing curve

a sinusoidal variation of a parameter, such as the critical dimension or the dose-to-clear, as a function of resist thickness caused by thin film interference effects.

symmetrical fault current

the total current flowing to a fault less the DC offset current. In many cases, fault current calculations are expressed in terms of symmetrical amps.

tap changing under load (TCUL)

a type of transformer in which the output voltage can be adjusted while the load is connected to the transformer. The voltage is adjusted by changing the turns ratio of the primary and secondary coils. That, in turn, is accomplished by bringing out connections (taps) at several points on the coil. Changing from one tap to another either adds or subtracts turns from the coil and raises or lowers the voltage, respectively.

time overcurrent (TOC) relay

an over-current relay that has intentional, selectable, time delay. The time delay is chosen so that the relay will operate more slowly than downstream relays or fuses, and more quickly than upstream relays or transformer fuses. Relay and fuse curves are generally displayed on time-current curves.

time-current characteristic curve

(1) a relay time-current curve is a curve showing the time versus current characteristic of a time overcurrent (TOC) relay.

(2) a fuse time-current curve shows the melting and clearing times of a given fuse or family of fuses.

(3) a coordination time-current curve shows the relationship of the operating and clearing characteristics of coordinating devices (TOC relays and fuses) on a power system.

time-current curve

See time-current characteristic curve

transformed circuit

an original circuit with the currents, voltages, sources, and passive elements replaced by transformed equivalents.

transient current

the fault current that flows during the transient period when the machine apparent impedance is the transient impedance.

transient open-circuit time constant

See quadrature-axis transient open-circuit time constant and direct-axis transient open-circuit time constant.

transient short-circuit

time constant pass and stop bands are critical. A longer filter length generally implies that the filter can have a steeper transition band to a similarly shaped shorter length filter.

vacuum capacitor

a capacitor with a vacuum between its plates.

vacuum circuit breaker

a power circuit breaker where a vacuum chamber is used as an insulating and arc clearing medium.

vacuum insulation

any insulation scheme which depends upon the dielectric capabilities of a high vacuum.

Flexible Alternating Current Transmission System

A static equipment used for the AC transmission of electrical energy. It is meant to enhance controllability and increase power transfer capability. It is generally a power electronics based device.

See FACTS