Residual Mechanical Stress Detection of Epoxy Based Bushing in C-GIS

The epoxy resin casted bushing plays a key role as a current-carrying, insulation and support in cabinet-type gas-insulated switchgear (C-GIS), but the superposition of internal residual stresses and complex mechanical loads induce frequent crack, breakdown or even disintegration of the bushing under operating conditions, which seriously threatens the safe and stable operation of substation and distribution systems. In this paper, the effect of ultrasonic method and drilling method on the detection of residual stresses in 35kV C-GIS bushings is studied, and the effect of residual stresses on the operational reliability of the bushign is verified by using partial discharge and bending tests. The main conclusions are as follows: the residual stress detection method based on the acoustoelastic effect found that the residual stress distribution in the epoxy bushing was -50~20 MPa. The detection results of the drilling method showed that the residual stress distribution in the bushing subsurface was -7.5~7.6 MPa, which was consistent with the position of residual stress detected by the ultrasonic longitudinal wave method, but the method has some limitations due to the depth of drilling. The existence of residual stresses increases the partial discharge of epoxy bushing after mechanical load operation, which also causes a significant decrease in their mechanical strength. Therefore, it is necessary to strictly control the casting process of epoxy resin insulators and develop residual stress detection methods.