impedance relay
a protective relay that senses the operational impedance at a location,
i.e., the ratio of voltage to current at any given time. During fault
conditions on the protected line, the impedance relay will sense the
impedance (distance in ohms) between the location of the relay and the
fault.
Typical impedance relay characteristics are mho and reactance.
Impedance relays are widely used in sensing phase faults on transmission
lines. Ground impedance relays are available that measure the distance
to a single phase to ground fault using a modified technique.
