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 (
$\varepsilon $
-/
$\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
$\varepsilon $
-/
$\gamma $
-layer. The surface charge and electric field behavior on GIL spacers with the
$\varepsilon $
-/
$\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
$\varepsilon $
-/
$\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
$\varepsilon $
-/
$\gamma $
-layer at the optimal permittivity and conductivity distribution. Compared with the raw spacer, the maximum electric field strength with
$\varepsilon $
-/
$\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.