Analysis and recommendations on a 500kV dead-tank circuit breaker bushing explosion accident

This paper studies a bushing explosion accident in a 500kV substation dead-tank circuit breaker. Through protection operation sequence inversion, disassembly trace analysis, and assembly process verification, it reveals the chain fault mechanism caused by incorrect bushing bolt assembly. The main cause of the accident was the use of hex socket bolts for the bushing grounding shield, which did not comply with the design standard. This induced long-term mechanical stress, leading to radial cracks originating from 12 bolt holes at the lower end of the bushing. During the initial fault, the bushing exploded, causing the conductive rod to pull upward and triggering a "triple discharge path" involving the conductive rod–inner shield–outer shield. After SF6 gas leakage, insulation degradation caused a secondary ground discharge. This case provides new insights for the prevention and control of hidden structural defects in dead-tank circuit breakers.