Online Insulation Monitoring and Fault Feeder Selection of Electric Heating Elements

Abstract

Nuclear reactor regulator electric heating elements are supplied by the neutral point ungrounded system, and the long-term high temperature and high current harsh working conditions easily lead to the supply cable insulation degradation or even ground fault. This paper solves the challenge of online insulation monitoring and wiring protection for low-voltage AC systems by signal injection. When the system is in normal operation, a low-frequency signal is injected into the neutral point in real time to monitor the system insulation resistance quantitatively and determine whether a ground fault has occurred. After a fault occurs, the magnitude of the low-frequency injection source is changed, and the magnitude characteristics of the low-frequency currents at each feeder are analyzed before and after the change in the magnitude of the injection source, and the difference is made to identify the fault line according to the magnitude of the low-frequency current change. Simulation results show that the method is more resistant to fault resistance than the traditional fault detection scheme, and can achieve a wide range and high accuracy for protection purposes.