A 500 kV substation circuit breaker experiences an SF6 gas leakage fault during its re-energization startup process.The inspection finds that the swing arm support seat of the circuit breaker operating mechanism is broken.It detectes the failure parts of the operating mechanism by macroscopic inspection

component analysis and electron microscope scanning.The results of analysis indicate that the arm support bracket of the operating mechanism has a chemical composition segregation

and the casting process had defects.Long-term opening and closing action causes the support seat of the lever arm to crack and fail under dynamic action.During the current closing process

the arm support bracket fractures and breaks

causing the arm bearing to shift axially

which leads to the failure of the operation mechanism transmission system's self-balance.The linkage continues to move under the instruction of closing

the shearing force generated by the failure of the force balance system.Affected by this

the mechanical jamming occurres between the transmission parts

ultimately causing the impact of the trip indicator on the enclosure and the escape of SF6 gas from the gas chamber.