Seismic Response of High Voltage Electrical Transformer–Bushing Systems

High voltage porcelain bushings mounted on transformers have shown vulnerability during past earthquakes. This is contrary to the generally good performance observed during shake table qualification testing of bushings anchored to a rigid base. The seismic vulnerability of porcelain bushings might be caused by the flexibility of transformer tanks and of bushing attachments. Current seismic qualification guidelines consider an amplification factor of 2.0 between the amplitude of the ground motion and the amplitude of the motion at the base of the bushing. This paper investigates numerically the dynamic response of porcelain bushings mounted on transformer tanks. The results of the numerical study show that large amplification occurs when the fundamental frequency of the porcelain bushing is tuned with the fundamental frequency of the transformer tank.