Abstract:The oil leakage remains an unobvious problem in oil-immersed transformers, which will create oil-gas interface inside transformers. The insulation strength will be greatly reduced when oil-gas interface occurs inside transformer, and it 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 a simulation model of the oil-gas interface discharge based on the finite element method has proposed, which are coupled with electrohydrodynamic model and the Poisson equation in COMSOL Multiphysics to analyze the electric field distribution and streamer development during the discharge at the oil-gas interface under DC voltage. 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.
Keywords—Oil-gas interface discharge，Insulating oil，Numerical simulation
 

Oil-gas interface discharge，Insulating oil，Numerical simulation