Seismic Protection of Electrical Transformer-Bushing Systems Incorporating Flexural Stiffeners
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abstract
High voltage bushing structures are one of the most critical as well as most vulnerable components of electrical substations during strong seismic excitation. Rehabilitation of existing bushing structures and proper design of new ones could significantly reduce potential earthquake-induced damages to electrical utilities. Several experimental and numerical studies conducted to investigate the seismic performance of transformer bushings have indicated that improved seismic performance may be achieved for transformer bushings mounted on rigid surface compared to those mounted on actual, more flexible, transformer tanks. In this project, the seismic response of transformer-bushing systems both "as installed" and mounted on rigid base was investigated. The efficiency of adding flexural stiffeners on the top plates of transformer tanks as a measure to stiffen the bushings' base in order to mitigate their seismic vulnerability was also investigated. This study was divided into two parts. The first part consisted of a series of numerical finite element analyses for different bushing configurations ("as installed", mounted on a fixed base and stiffened with flexural stiffeners on the top plate of the transformer tank) of a 230kV (high voltage) bushing structure. The second part focused on shake table tests of a typical porcelain 230kV bushing mounted on a surface incorporating stiffeners. Both the numerical and the experimental investigations clearly showed that the bushing "as installed" is very flexible compared to the one mounted on a rigid base, and, thus, more vulnerable to seismic excitation. The results of both the numerical and the experimental studies show that the incorporation of flexural stiffeners on the top plate of the transformer tank is beneficial to the seismic performance of high voltage bushing structures.
