Analysis and Monitoring of the Fuse Conditions in Nuclear Power Multiphase Brushless Excitation System

In multiphase brushless excitation systems of nuclear power plants, each phase of the rotating rectifier is equipped with two parallel fuses to protect the rotating diode from overcurrent. However, a monitoring scheme to assess the fuse conditions is currently lacking. Given that the fuse disconnection can result in a one-phase open circuit in the rectifier, it is imperative to introduce a fuse monitoring system. First, considering the impact on the system, the abnormal fuse conditions can be equivalent to an increase in resistance. Then, the frequency-domain characteristics of the exciter's stator field currents are derived under various fuse conditions. Subsequently, simulations and prototype experiments are conducted to validate the theoretical analysis: when fuse resistance increases, the field current exhibits even-order harmonics; as the fuse resistance grows, the ratio of the second and fourth harmonics in the field current gradually diminishes. Finally, a monitoring scheme, which is validated through real exciter experiments, is proposed to monitor the fuse conditions and diagnose the one-phase open-circuit fault. The early warning of abnormal fuse conditions can help to take measures to avoid the occurrence of severe phase-open circuit faults.