Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

utilization voltage
the voltage across the power input terminals of a piece of electrical equipment.
volts/hertz control
a method of speed control of induction machines, used below rated speed. When the volts/hertz ratio is kept constant, the current through the stator windings remains almost the same, except for very low speeds; hence, the available torque remains constant, but the speed changes due to change in frequency.
Z

See impedance
ZL
common symbol for load impedance.
ZS
common symbol for source impedance.
Z-bus
matrix which contains the impedance of each element in an electric power system.
zero-sequence reactance
the reactive component of the zero sequence impedance.
See symmetrical component
zig-zag ground
(1) a grounding arrangement which is used to supply single phase grounded circuits from an ungrounded three-phase delta connected electric power line.

(2) the winding arrangement within a grounding transformer.
zinc oxide arrester
a lightning arrester that consists of a stack of ZnO disks stacked within a vented porcelain tube. See gapless arrester.
zone of protection
the area of a power system for which a particular set of protective relays has primary protection responsibility. In typical cases, operation of any of these relays will open circuit breakers which will isolate this zone. Each major power system component (line, transformer, bus, generator) has a separate zone of protection.
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