Andrew S. Whittaker, Gregory L. Fenves, and Amir S. J. Gilani
Earthquake Spectra 20, 205 (2004)
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The earthquake performance of 196-kV, 230-kV, and 550-kV porcelain transformer bushings was studied by earthquake-simulator experimentation and analysis. The fundamental frequencies of the 196-kV, 230-kV, and 550-kV bushings were identified to be approximately 15 Hz, 18 Hz, and 8 Hz, respectively, using resonance-search testing on the simulator. The corresponding damping ratios were between 2 and 4 percent of critical. The 196-kV and 230-kV bushings survived severe earthquake shaking and were qualified to the High Level per the IEEE 693-1997 standard. The discrepancy between excellent behavior in the laboratory and poor behavior in the field of these types of bushings calls into question the procedures used for qualification of substation equipment. The 550-kV bushing survived shaking at the moderate performance level with limited damage and minor oil leakage. Current procedures for fragility testing of transformer bushings were evaluated and found to be neither appropriate nor conservative.