Cause analysis of the compression spring stress relaxation of circuit breaker operating mechanism in a 220 kV Substation

The energy storage compression spring of the LW35-126 circuit breaker operating mechanism has become stress-relaxed in a 220 kV substation after only one year. It was found that the height of the failed spring was 23 mm shorter than that of the new spring of this model during the first annual maintenance. In order to analyze the reason for 60Si2CrVA spring stress relaxation, the stress state of the spring service was analyzed according to the service status. By analyzing the tensile strength, composition, hardness, and microstructure of failed springs, it was found that the main cause of stress relaxation is the incorrect tempering temperature of the 60Si2CrVA spring. Excessive tempering temperature led to coarse massive ferrite and coarsened carbides, reducing the activation energy of the material’s stress process and causing premature stress relaxation failure of the spring material.