chapter  18
Power Transformer Protection
Pages 28

Three characteristics generally provide means for detecting transformer internal faults [1]. These

characteristics include an increase in phase currents, an increase in the differential current, and gas

formation caused by the fault arc [2,3]. When transformer internal faults occur, immediate disconnec-

tion of the faulted transformer is necessary to avoid extensive damage and=or preserve power system

stability and power quality. Three types of protection are normally used to detect these faults: over-

current protection for phase currents, differential protection for differential currents, and gas accumu-

lator or rate-of-pressure-rise protection for arcing faults.