Collaborative Optimization of Conductivity and Permittivity on GIL Spacer Surface for Electric Field Regulation Under DC Superimposed Impulse Voltages

The gas-solid interface electric field distortion is an essential factor leading to surface insulation failure. This study proposes the conductivity and permittivity-graded coating layer ( epsilon -/ gamma -layer) method, aiming at regulating surface charge and electric field distribution on the gas-insulated transmission line (GIL) spacers under dc/dc superimposed impulse voltages. The iteration optimization algorithm is developed to obtain the optimal conductivity and permittivity distribution of the epsilon -/ gamma -layer. The surface charge and electric field behavior on GIL spacers with the epsilon -/ gamma -layer is investigated through the numerical simulation approach. The polarity of the accumulated surface charges reverses on both the convex and concave sides as the conductivity of the epsilon -/ gamma -layer increases under dc voltages, indicating the dominant mechanism changing from the bulk conductivity model to the surface conductivity model. The electric field distribution is also improved with the epsilon -/ gamma -layer at the optimal permittivity and conductivity distribution. Compared with the raw spacer, the maximum electric field strength with epsilon -/ gamma -layer is reduced by about 31.97% under dc, 20.56% under dc superimposed positive impulse (dc + Po.Im), 42.68% under dc superimposed negative impulse (dc + Ne.Im) on the convex surface, about 64.22% under dc, 21.37% under dc + Po.Im, and 36.46% under dc + Ne.Im on the concave surface, correspondingly. It is hoped that the results of this study could spark novel ideas for the optimal design of dc GIL spacers.