Seismic performance evaluation of high voltage transformer bushings

The main objective of this paper is to identify the dynamic characteristics of a realistic model of a commercial transformer (230 kV) and identify the critical components that influence the dynamic response of three high voltage porcelain bushings installed on its flexible roof. For this purpose, a finite element model of the transformer is appropriately modified and enhanced. The improved model is subjected to a wide band random motion excitation and the responses at various locations are processed in the frequency domain. The dynamic response of the high voltage porcelain bushings (196/230kV) and the amplification that occurs between the base and the top of the transformer's oil tank, is assessed through detailed sensitivity analysis for a variety of potential structural modifications of the model. Each structurally modified model is investigated using a random ground motion, compatible to IEEE-693 spectrum. The accelerations are monitored at the bushings, at the corners of the cover plate and at the top of the turrets for each model and comparisons are made for the effect of each modification to be assessed. The ground motion amplifications at the cover are obtained from the spectra at the corners of the cover and at the top of the turrets. The sensitivity shows that the cover plate has the predominant influence on the response of the bushings.