The Impact of High Voltage Power Transformer Base Design on Bushing Seismic Amplification

ABSTRACT High voltage power transformer bushings (230 kV and above) are a known seismic vulnerability, often failing during significant earthquakes and causing potential disruption to the power supply. This occurs most commonly when the dynamic resonance between the transformer tank and the mounted bushing causes excessive amplification of the seismic demands to the bushing, leading to failure. This study evaluates multiple existing transformer designs that include stiffness discontinuities near the foundation, and the impact on the system dynamic response that results from mitigating these discontinuities with simple and potentially retrofittable blocking below the tank corners. The results of the study show that modifying the transformer bases to have an increased stiffness between the foundation and transformer tank causes a reduction in seismic high voltage bushing stress—with an average reduction of 37%.