Comparison of engineering failures and seismic responses of 500 kV transformer-bushing systems in the 2022 Luding earthquake

Cemented and mechanically clamped types of end fittings (fitting-C and fitting-M) are commonly used in transformer bushings. During the Luding M s 6.8 earthquake that occurred in China on September 5, 2022, all transformer bushings with the two types of end fittings in a 500 kV substation were damaged. Post-earthquake field investigations were conducted, and the failures of the two types of bushings were compared. Two elementary simulation models of the transformer-bushing systems were developed to simulate the engineering failures, and further compute their seismic responses for comparison. The results indicate that the hitch lugs of the connection flange are structurally harmful to seismic resistance. Fitting-M can decrease the bending stiffness of the bushing due to the flexible sealing rubber gasket. Since it provides a more flexible connection that dissipates energy, the peak accelerations and relative displacements at the top of the bushing are significantly lower than those of the bushing with fitting-C. Compared with fitting-C, fitting-M transfers the high-stress areas from the connection flange to the root of the porcelain, so the latter becomes the most vulnerable component. Fitting-M increases the failure risk of the low-strength porcelain, indicating the unsuitability of applying it in high-intensity fortification regions.