Simulation and Analysis of Transformer Oil Interface Discharge under DC Voltage

The oil leakage remains an unobvious problem in oil-immersed transformers, which will create an oil-gas interface inside transformers. The insulation strength will be greatly reduced when the oil-gas interface occurs inside a transformer, which will be much easier to cause discharge and major accidents which threatens the stable operation of state grid. However, there is a lack of research on the discharge characteristics of the oil-gas interface caused by oil leakage or gas accumulation inside the transformers, and the discharge mechanism is not clear yet. So in this paper, the spherical electrode model based on CIGRE method II was selected to carry out the discharge test, and the discharge development process was photographed by ICCD. And the electric field distribution and streamer development in the discharge at the oil-gas interface under DC voltage were analyzed by coupling the electrohydrodynamic model and Poisson equation in COMSOL Multiphysics. The simulation results show that the discharge channel is formed above the interface, and then develops toward the interface until the discharge ends, which is basically consistent with the experimental shooting results. This paper reveals the discharge characteristics of the oil-gas interface of the transformer through simulation and experiments, which maintains practical significance for analyzing and diagnosing the nature of discharge faults inside the transformers.