Corona-generated Space Charge Effects on Electric Field Distribution for an Indoor Corona Cage and a Monopolar Test Line

The effects of corona-generated space charge on the resultant electric field near a conductor were determined both for a simulated test line and a corona cage, since both are used in predicting the corona behavior of EHV and UHV transmission lines. Programs were developed for the calculation of the potential, the electric field and the space charge distributions for a simulated test line and a corona cage. Algorithms based on the charge simulation and the finite-element methods were used to solve Poisson's equation; and the method of characteristics to solve the current continuity equation. The resultant electric field on the ground plane of the two configurations was measured with a rotating field-mill, and the results fitted well with the calculated data. It was found the electric field at the surface of the conductor increased linearly, for both experimental configurations, before the voltage reached the corona inception value; but was reduced once corona-generated space charge was produced. The space charge and density distribution in the corona cage differed greatly from that around the test line: the electric field at the surface of the conductor in the test line decreased faster with voltage than that in the corona cage, the relative difference increasing as V-app/V-on was raised. The difference reached an asymptote of about 16% when the applied voltage was about 25% above the corona inception level.