Analysis of the Failure Causes in the Transmission Components of a 500kV Spring Circuit Breaker

This paper examines a severe SF6 leakage failure that occurred during the closing operation of a 500kV spring circuit breaker. Field inspection identified the failure location as the connection between the transmission main shaft and the gas chamber. Disassembly analysis revealed that the root cause was the damage to the bearing support seat inside the gas chamber, which caused the transmission main shaft to lose balance and generate eccentric force. This led to the damage of the external bearing and sealing sleeve, resulting in significant leakage. Microscopic morphology and composition analysis of the debris confirmed that the root cause was a casting defect in the bearing support seat of the transmission gas chamber, where severe alloy element segregation and numerous impurities led to structural looseness and insufficient strength. These defects made the bearing support seat unable to withstand the vibrations caused by the frequent operations of the circuit breaker, eventually leading to fracture.