Generator-transformer unit for the safe operation of the power system to normal work and the quality of electric energy plays a decisive role. Meanwhile generator transformer itself is very expensive electrical equipments, it should focus on the various faults and normal operations, the installation of improved performance of relay devices. For the installation of generators differential protection、 transverse differential protection for generator turn-to-turn faults、 stator single phase earth fault protection、negative current protection; For transformer installed gas protection、differential protection、impedance protection; For generator-transformer unit established the total differential protection.