Abstract: Ferroresonance overvoltage often occurs in medium voltage system of nuclear power plant, which will affect the reliability and stability of power supply system. This paper aims at the different suppression measures of ferromagnetic resonance under the 1LGA mode of variable power supply for a nuclear power plant. Starting from the excitation test of ferromagnetic resonance, through the test of secondary detuning resistance detuning effect, the test of microcomputer detuning effect, the test of PT heat capacity and the test of PT short circuit endurance. The effectiveness of ferroresonance suppression measures is verified under different conditions, such as random selection of PT combinations, combinations with the worst excitation characteristics and the largest phase difference, and combinations with the best excitation characteristics and the smallest phase difference.