Two identical 196 kV porcelain transformer bushings were evaluated for their response to severe earthquake shaking. Tri-directional earthquake simulator testing was undertaken to investigate the dynamic response of the bushing, to provide data for correlation with the analytical studies, to qualify one of the bushings for moderate earthquake shaking (per IEEE 693), and to evaluate the response of one bushing to extreme shaking effects. For earthquake testing, the bushing was mounted at 20° to the vertical in a stiff support frame. Spectrum-compatible ground motion records derived from earthquake motions recorded during the 1978 Tabas earthquake in Iran and the 1994 Northridge earthquake in California were used for testing. One bushing passed the IEEE 693 qualification tests for moderate shaking, and the other bushing survived extreme earthquake shaking with negligible damage and passed the IEEE 693 qualification tests for earthquake shaking at the High Level. The modal properties calculated by linear dynamic analysis and experimentation correlated reasonably well. Parametric studies identified the mechanical properties of the rubber gaskets separating the porcelain units as the key factor influencing the dynamic response of a transformer bushing.
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