On seismic response of substation equipment and application of base isolation to transformers

This paper presents seismic performance of electric substation transformers, and discusses advantages and considerations in the use of base isolation as a viable hazard mitigation option. Substation transformers and bushings are the most critical elements within the power delivery system and their performances during past earthquakes in the U.S. and abroad have not been satisfactory. Finite-element analyses indicate that the interaction between these two critical elements has a significant effect on seismic vulnerability of substations. In light of dynamic characteristics of this equipment, base isolation can be very effective in mitigating this adverse interaction. Furthermore, due to high-inertia reduction, base isolation can also have beneficial effects on the long-term longevity of transformers and on foundation performance during seismic events. Larger displacement demand and uplift, however, are issues that must be considered in the application of base isolation. Through an actual case study (433.3-MVA transformer in a high-voltage substation), a simplified model of the transformer bushing will be developed and the results of fixed base case and base isolated case are compared. Moreover, design concepts will be investigated that will demonstrate larger displacement can be accommodated; and that considering transformer geometry, peak ground acceleration, amount of inertia reduction, and isolator's friction coefficient for this transformer uplift is not an issue.