Investigation of a 750 kV Reactor Fault Mechanism Caused by Internal Discharge

As one of the backbone grids of China’s northwest power grid, 750 kV lines are characterized by long transmission distances, high line power and high voltage levels. To avoid the line capacitance effects and to achieve reactive power compensation, high-voltage reactors are an indispensable component of 750 kV transmission and substation projects. However, due to the changing operating environment and product quality defects, some 750 kV reactors have caught fire and caused line tripping failures in recent years. In this paper, a typical 750 kV reactor fault is disassembled in detail and the mechanism of the fault is analyzed with on-site fault records. The main cause of the failure is the breakdown of the capacitor core at the end of the oil side of the reactor high voltage bushing. The development of this type of discharge is mainly divided into three stages: partial discharge due to material cracks caused by vibration in operation, long-term partial discharge resulting in internal gas, and breakdown of the gas-liquid mixed gap. Finally, this paper proposes engineering measures that can be taken to avoid such failures.