Abstract: Abstract:Taking the unit No.1 of Sanmen Nuclear Power Company Limited as background, a test program of differential protection for generator and transformer of AP1000 unclear power unit was proposed. Considering that the current of the main transformer is limited by the load of the plant in preliminary stage, the suggested solution is to use the starting current of the mediumvoltage motor to test the correctness of the differential protection. In order to satisfy the test requirement, the current transformer in high voltage side of the house service transformer was compared with the current transformer in outlet of the generator (the generator outlet breaker is included). The rationality of the test program was verified by the calculation and comparison.

Key words: Keywords:AP1000 nuclear power unit, transformer, generator, differential protection, test, current transformer