Two dimensional modelling of streamer inception and propagation in transformer oil

The characteristics of the initiation and the propagation of streamer in the transformer oil are investigated through a two-dimensional axially symmetric needle-to-plane electrode model. The simulation model is based on the approximation of hydrodynamic drift-diffusion, in which transformer oil is treated as a kind of dense fluid and the fluid physical processes of the streamer are dominated via three drift-diffusion equations regarding to positive ions, negative ions and electrons coupled with Poisson equation. In numerical calculations, the finite element method based on advanced computing software is used in solving the model. Through the simulation, the distribution of electric potential, space charge density, electric field and particles of electrons, positive ions and negative ions can be obtained. By means of the above parameters, the streamer current, streamer propagation speed, and the threshold of inception voltage can be calculated. The streamers under different of applied voltage amplitude, polarity, and the shape of electrode are modeled and discussed. The amplitude influences the speed of the streamer, and the shape of electrode has a comprehensive impact. Also, the difference between positive and negative streamer is presented.