Protection of power plant transformers using digital technology

The following specific areas of transformer protection are addressed in this paper. (1) Power plant transformer protection: overexcitation and differential restraint; generator step-up unit (GSU) transformer ground fault protection; and auxiliary/start-up and industrial transformer protection; (2) Transmission substation transformer protection: overexcitation (V/Hz); protection; and sudden pressure relay (SPR) blocking. (3) Distribution substation transformer protection: underfrequency/undervoltage load shedding. (4) Distribution substation logic schemes: bus fault logic; feeder back-up logic; and two-bank substation load shedding. This paper concentrates on protective functions within digital multifunction transformer relays as well as the logic that can be applied with this technology.