Abstract: As the main operating mechanism of high voltage level, the hydraulic spring operating mechanism is prone to frequent pressure and other failures, and in severe cases, it can cause the circuit breaker to lock, thereby expanding the range of faults. Through the analysis of a 500 kV GIS circuit breaker frequent pressure problem, the on-site inspection of the energy storage control loop is not abnormal, after disassembly,it is found that there are cracks in the inner wall of the working cylinder, resulting in the high pressure area and the low pressure area are connected, and the pressure is frequent. Through macroscopic inspection, metallographic detection, energy spectrum analysis, material review,mechanical performance testing and other methods, the crack causes were deeply studied. Combined with the operation principle of the hydraulic mechanism and the comparison of the working cylinder materials, it was finally determined that the reason for the frequent pressure of the mechanism was the poor processing quality of the working cylinder, and the finished material had relatively many microscopic defects,resulting in axial stress concentration and cracks in the working cylinder. Based on this, the treatment scheme of the same type circuit breaker is given to avoid equipment outage caused by the same problem and ensure the safe operation of the power system.

    Key words: circuit breaker; working cylinder; frequent pressure; stress concentration