Effect of Avalanche Space Charge Field on the Calculation of Corona Onset Voltage

Many researchers have suggested that the space charge field of the primary electron avalanche should not be neglected in calculating the corona onset voltage based on the streamer criterion. Some researchers consider only the space charge field of the positive ions created during the avalanche growth, while others consider only the space charge field of the electrons at the head of the avalanche. The authors suggest that both space charge fields should be considered in calculating the corona onset voltage. Computer programs are written to calculate the breakdown voltage (for uniform field: parallel-plane geometry) and corona onset voltage (for non-uniform field: point-to-plane geometry). The space charge fields of both the positive ions and the electrons are considered in the calculations. Results are obtained for air and SF6 for a wide range of geometrical parameters and gas pressures. The results indicate that the effect of space charge fields is to reduce the corona onset voltage (or breakdown voltage in uniform field geometry) by less than 5%.