Discharge Simulation of Typical Air Gap Considering Dynamic Boundary and Charge Accumulation

The simulation of typical air-gap discharge process is of great significance to the long air-gap discharge mechanism and UHV transmission project design. A positive fractal dynamic streamer discharge model of a rod-plane air gap was established. On the basis of the original fractal streamer model, this new model proposed an electric field calculation method based on a dynamic boundary condition, as well as a new calculation method of the time parameters based on the charge accumulation process. In the model, the electric field and the development time of the discharge step were obtained by solving the electric field distribution and charge accumulation equations. The processes of streamer starting, streamer development, charge accumulation, and discharge extinguishing were all contained in the model. Discharge process of various voltage amplitudes (235 and 595 kV), the waves of which were lighting impulses (2/50 mu s), was simulated by this model in the 1-m rod-plane air gap. As shown in the results, for a gap under 235 kV, the length of the streamer is 200 mm, the streamer development time is 5.02 mu s, the velocity is 3.98 x 10(4) m/s, and the total charge accumulation in the streamer channel is 23.2 mu C, while for a gap under 595 kV, the gap is broken down, and the streamer development time is 9.92 mu s, its velocity is 1.01 x 10(4) m/s, increasing to 1.60x10(5) m/s before discharge, and the total charge accumulation is 258.3 mu C. The model matched the test results well in the dynamic processes of the length of discharge channels, the electric field waveform, and charge accumulation. This model is meaningful to research into long air-gap streamer discharge mechanisms and leader discharge processes.