Seismic qualification of transformer high voltage bushings

The paper is born as a contribution to the IEC 36A Working Group 2 "Seismic qualification of bushings" in order to evaluate the coefficients K (amplification factor between the ground and the transformer bushing flange) and R (response factor of the bushing itself) as defined in the IEC 61463. These coefficients allow the definition of the seismic severity at the flange level to be used for static calculations and vibrational tests on high voltage bushings. For the evaluation of these coefficients, both experimental on-site dynamic tests and numerical finite element analyses have been performed for a 160 MVA, 230/135 kV power transformer. The natural frequencies and the seismic response of the whole transformer (tank, oil conservator and HV bushings), subjected to different earthquakes, have been calculated. A comparison between the calculated coefficients (K and R) and those established by the IEC 61463 is illustrated.