Probabilistic loss assessment of a seismic retrofit technique for medium- and high-voltage transformer bushing systems in high seismicity regions

Transformer bushing systems have exhibited vulnerability during past earthquakes. Based on past qualification tests, it was found that the seismic performance of transformer bushing systems is improved when the bushings are mounted on a rigid base, as opposed to when mounted on more flexible cover plates of transformers. The addition of flexural stiffeners on the transformer cover plates has been proven to stiffen the base of the bushings and mitigate their seismic vulnerability. In this study, the Performance-Based Earthquake Engineering framework, introduced by the Pacific Earthquake Engineering Research (PEER) center, is used to evaluate in a probabilistic sense the earthquake-induced economic losses of transformer bushing systems both for as-installed and retrofitted mounting conditions. The results are presented in the form of expected losses conditioned on seismic intensity as well as expected annual losses for locations in Southern and Northern California. The results demonstrate the ability of the retrofit approach of adding flexural stiffeners on the transformer cover plates to reduce earthquake-induced economic losses compared to the as-installed conditions/design and further enhance community recovery in the occurrence of a strong seismic event.