This article conducts in-depth experimental and mechanistic analysis research on the fault problem of multi column parallel overvoltage protection devices in ultra-high and extra high voltage series compensation devices. This type of device has a lower voltage and much lower leakage current than conventional arresters under normal operating conditions, making traditional monitoring methods ineffective. Therefore, once the resistor in a parallel unit deteriorates or malfunctions, it may cause widespread arc flashover, leading to the breakdown of the entire column resistor. This article uses various types of “fault resistor’’ as fault simulation samples, by conducting impulse current tests, the waveform characteristics of current and voltage under different fault states were explored, and the impact of “fault resistor’’ faults on the entire proportional unit was verified. The experimental results show that the presence of “fault resistor’’ significantly reduces the energy tolerance of the device, and the fault develops rapidly, with significant fluctuations in the current waveform. By using polytetrafluoroethylene material to isolate the arc, the arc was successfully prevented from spreading from a single resistor to the entire column, thus avoiding a complete set of faults. The research results of this article provide important theoretical basis and experimental verification for fault warning and design improvement of multi column parallel overvoltage protection devices, and have significant engineering application value.