Abstract Because of its high voltage level and large capacity, the 1000kV transformer is separated into the main transformer and the regulating and compensating transformer, which is convenient for transportation. Considering the particularity of transformer structure and requirements for the polarity of differential protection, as well as the polarity change of the regulating and compensating transformer winding current transformer, caused by switching of transformer tap stalls, the relay protection of ultra high voltage (UHV) transformer is different from those with lower voltage level. This paper explains the voltage regulation mode of UHV transformer, in addition to relay protection configuration and differential protection principle of regulating and compensating transformer. And it also analyzes the current transformer polarity of relay protection device, introduces the commissioning method of regulating and compensating transformer. It may provide reference for power system construction and maintenance staff.