Seismic Protection of Electrical Transformer Bushing Systems by Stiffening Techniques

Graduate Students: Maria Koliou

Principal Investigator: Andre Filiatrault

Project Completion Date: 09-01-2010

This study investigated the seismic response of bushing structures both as installed and on fixed base as well as attempts to identify feasible approaches of stiffening the base of the transformer bushings as installed as a measure to mitigate their vulnerability under strong seismic excitation. Finite element models of four different high voltage transformers were used for performing modal and linear dynamic time history analyses in order to compare the response of the bushing structures as installed and on fixed base as well as investigate the efficiency of several retrofit techniques to ensure the bushings integrity during strong earthquake. In addition, a two stage experimental investigation, consisting of system identification testing and shake table testing, was conducted at UB’ Structural Engineering and Earthquake Simulation Laboratory (SEESL) to verify the response trends identified by the numerical studies.

Both numerical and experimental studies clearly showed that the bushing structures as installed are very vulnerable to seismic excitation as well as very flexible compared to the ones mounted on a fixed base. Moreover, these studies showed that stiffening the base of the bushings can be beneficial for their response against ground shaking. From the stiffening techniques investigated, installation of flexural stiffeners on the cover plate of the transformer tank appears to be the most efficient approach.

This project was supported by the Bonneville Power Administration (BPA).