A Relay for Ungrounded Shunt Reactors

A relay having high sensitivity and rapid speed of operation for detecting the neutral overvoltage associated with internal faults in ungrounded shunt reactors is described. Design features and development of the relay, and results from tests conducted at a typical reactor installation are presented. The relay demonstrated successful detection of simulated layer-to-layer reactor faults in about one cycle and sufficient immunity to false operation during the test series to be left in service for further evaluation. A comparison between the conventional reactor protection and that afforded by the new relay is illustrated.