Calculation of Space Charge Density in Negative Corona Based on Finite-Element Iteration and Sound Pulse Method

Space charge distribution is a valuable indicator of ion flow field and is widely utilized to assess electromagnetic environment for transmission line. The finite-element method (FEM) is widely used to solve this problem. However, Kaptzov assumption in FEM assumes that onset voltage is unchangeable after corona occurs, which does not tally with the actual situation. This paper adopted the finite-element iteration method (FEIM), which uses empirical formula instead of assumptions to calculate the charge density. The surface field intensity is not constant in the empirical formula because the empirical formula takes the effects of space charge on surface field into consideration. So this is more consistent with actual situation. In order to verify the accuracy of the algorithm, sound pulse method is applied to measure the charge density around the conductor in the laboratory. Simulation results show that the charge density obtained in this paper agrees with the data in the experiment, which verifies the validity of the empirical formula for calculation of space charge density. Compared with a method considering Kaptzov assumption, FEIM is closer to the experiment in area around conductor line and near the ground. This indicates that empirical formula in FEIM is more effective than Kaptzov assumption in these two domains.