Seismic Analysis of a 500-kV Power Transformer of the Type Damaged in the 2008 Wenchuan Earthquake

Abstract

As indispensable electric power equipment in substations, high-voltage power transformers have experienced severe damage in past earthquakes. This paper illustrates an earthquake-damaged 5-kV power transformer: all three 55-kV bushings fractured, oil conservator supports were sheared off, and leaked transformer oil caused a fire. A detailed finite-element model of the power transformer was developed. The modal and response-history analyses using the finite-element model were conducted to investigate possible reasons for the power transformer earthquake damage. The results indicated that the local modes of the transformer components, such as bushings and turrets, and the oil conservator dominate the power transformer vibration. Spectral accelerations at the top flange plates of the turrets on the transformer tank were significantly amplified for the transformer bushings. Peak resultant bending moments at the bottoms of the air-side insulators of the 55-kV bushings subjected to the Wenchuan earthquake motions exceeded their bending capacities. Accelerations for the oil conservator were also greatly amplified, thus the oil conservator supports suffered large translational and torsional deformations to the earthquake motions. It is concluded from the earthquake damage and seismic analyses that this type of power transformer is vulnerable to strong earthquakes because the earthquake effect is not adequately considered in the power transformer structural design.