Seismic studies on electrical high voltage transformer - Bushing systems incorporating flexural stiffeners

Electrical high voltage bushings have exhibited vulnerability during past earthquakes. The good performance of bushings mounted on rigid base observed during shake table testing does not correlate well with their performance in the field. It is suspected that the seismic performance of high voltage bushings is improved when mounted on a rigid base as opposed to when mounted on more flexible cover plates of transformers. In this study, the seismic response of bushings was investigated numerically and experimentally for various mounting conditions. The addition of flexural stiffeners on the transformer cover plates was explored as a means to stiffen the base of the bushings and mitigate their seismic vulnerability. Linear dynamic analyses conducted on four transformer-bushing system models of various voltages, sizes and geometries showed that the simple approach of stiffening the cover plates of transformers is beneficial to the seismic response of high voltage bushings. Shake table testing was conducted on a 230kV porcelain bushing mounted on a support structure incorporating a cover plate and two stiffener configurations. Test results confirmed that stiffening the cover plates is beneficial to the seismic response of high voltage bushings.