A transistorized overvoltage relay

PERHAPS the most important single protective device in any aircraft electric system is the overvoltage relay. Overvoltage conditions cannot only cause serious damage to connected load equipment and to the power generation equipment, if not removed, but can cause the loss of the entire electric power system. Overvoltage relays are designed to have inverse time-voltage characteristics because most of the damage caused by overvoltage is because of overheating. To obtain overvoltage protection and still not get nuisance operations on normal system transients, the relay must operate very rapidly on extreme overvoltages and relatively slowly on slight overvoltages. Upon completion of the time delay the relay contacts close the trip coil of the generator control relay, thus de-energizing the faulty system.