Fault analysis and simulation of ground-fault accident on transformer in 500 kV AC/DC grids

Abstract

An actual occurred ground-fault accident of 500 kV transformers in HVDC converter station is presented. A 2D transient electromagnetic-thermal-mechanical finite-element coupling model of 500 kV transformer is developed to analyze the transient process of failure, with consideration of the resistance-temperature relationship and plasticity displacement in the windings’ thermal and mechanical characters. To verify the proposed finite-element model, the model is calibrated by pre-fault field test of the transformer in steady state, which shows good agreement with measurement. The short-circuit current adopted in simulation is based on actual on-site measurement of the ground-fault accident. By using the proposed model, simulation results reflect the transient process and explain the post-fault inspected damage well in term of over burn regions in thermal analysis and deformation tendency in mechanical analysis when compared with field post-fault inspection photos.