Further Results on the Assessment of Performance of Seismically Isolated Electrical Transformers

Keywords: Earthquake engineering, seismic isolation, power transformers, risk assessment, probabilistic analysis, ground motion intensity measures, spectral shape, near-field motions

Abstract: This report presents results on the probability of failure in a lifetime of 50 years of non‐isolated and seismically isolated transformers at ten locations in the Western US. This study considers: (a) scaling the ground motions for use in the incremental dynamic analysis by adjusting the spectral acceleration at the fundamental period (or effective period for isolated transformers) instead of the peak ground acceleration (PGA) in the earlier studies, (b) correcting for the spectral shape effects, which were ignored in the earlier studies, and (c) accounting for uncertainties, which were neglected in earlier studies. Moreover, the report presents sample results for near‐field motions, which do not differ much from the results obtained for far‐field motions. The results of this report, documented in numerous tables, may be used to decide on the benefits offered by a seismic isolation system depending on the location of the transformer and the form and properties of the seismic isolation system. The benefit is assessed on the basis of the probability of failure in a lifetime of 50 years. The information may also be used to assess the seismic performance of electric transmission networks under scenarios of component failures.