Abstract: The rotating asynchronous machine (RAM) system in the power stations of China General Nuclear Power Group (CGN) includes three types of generators —i.e., Shangdian generator, Zhongchuan generator and Remeng generator. The Shangdian generator is under self-shunt excitation, and the other two types are under phase compound excitation. When setting the overcurrent protection of RAM generators with different excitation modes, the power stations don’t consider the influence of excitation difference on value setting and delay time setting of overcurrent protection, and there may be dangers of overcurrent protection refusal and protection mismatch with other abnormal condition protections (malfunction). In this paper, the PSACD models of RAM generators with different excitation modes are established. The influence of excitation difference on the short circuit current decay process of RAM generator is illustrated by theoretical analysis and simulation, and the correctness of simulation analysis is verified by prototype experiment. Based on the theoretical analysis and simulation results, the setting value and delay time of RAM generator overcurrent protection under different excitation modes are set reasonably, which has been applied in the power stations of CGN.