Shunt reactor (herein after referred to reactor) is the key equipment for reactive power compensation in uktra high voltage (UHV) and long-distance transmission projects. Reactor fault poses a threat to safe and stable operation of power grid. In this paper the reactor fault phenomenon of a 1 000 kV transmission line at a UHV substation in Zhejiang Province is studied. It is found through the oil dissolved gas analysis that the reactor has suffered from arc discharge fault. Then

the fault is confirmed again through online partial discharge test and ultrasonic discharge detection and the discharge position is located at column A and column X of the reactor. The fault is finally confirmed through inspection after disassembly that discharge has occurred at the grund shield on the surface of the reactor core column. In order to trace the cause of insulation breakdown further

the correlation analysis among sudden change of dissolved gas in oil

maximum discharge of partial discharge and power grid events is carried out. It is found that the sudden increase of acetylene in reactor has obvious correlation with the occurrence time of partial discharge

with a delay of about 2-3 days. This time delay reflects the diffusion process of acetylene in oil. The sudden increase of acetylene in the shunt reactor oil exhibits a time sequence correlation with the line switching operation and voltage transients. The line switching and voltage transients lead to the insulation breakdown of reactor

thereby triggering discharge

which is the fundamental reason for the abnormal growth of acetylene. This paper can provide a reference for fault tracebility of reactor at other high-voltage substations.