Analysis of transformer seismic performance based on three-dimensional seismic isolation

Prior studies on power-transformer seismic safety emphasize retrofitting and horizontal isolation, yet the strong vertical motions typical of fault-rich southwestern China still endanger transformers. This work therefore proposes and validates a three-dimensional (3-D) isolation strategy for high-voltage transformer. A full-scale finite-element (FE) model reveals that steel pedestals couple with high-voltage bushings, introduce new vibration modes, and sharply amplify seismic demand. Six ground motions—far-field, pulse-type near-fault, and near-fault with large vertical components—are then applied to both the original and horizontally isolated configurations. Near-fault inputs drive valve-side bushing stresses beyond yield and trigger uplift as well as increased overturning risk, confirming the insufficiency of horizontal isolation alone. To resolve these issues, an anti-overturning 3-D bearing—combining a multiple-friction-pendulum mechanism for bidirectional horizontal flexibility with stacked disc springs for vertical compliance—is developed, tested, and accurately reproduced by an equivalent FE model. Retrofitting an 800 kV transformer with these bearings cuts horizontal and vertical responses by over 50 % for PGAs above 0.4 g, lowers bushing stresses below yield, suppresses vertical accelerations, and virtually eliminates overturning. Thus, where vertical seismic components are large, the proposed 3-D isolation bearing simultaneously curtails three-axis vibrations and enhances overall stability, offering a robust protection pathway for EHV transformers.