Temperature-Dependent Surface Charge Accumulation for Vertical and Horizontal HVDC GIL

Abstract

In this paper, the heat transfer process of DC gas-insulated transmission line (GIL) is comprehensively considered, including thermal conduction, thermal convection and thermal radiation. An electric-thermal field coupling model is established to characterize the surface charge accumulation characteristics of insulators. The temperature and insulator surface charge density distribution of a 3-D GIL model under different GIL installation ways (i.e. vertical and horizontal GIL) are obtained by finite element software. The results show that: under the identical load current, a large temperature difference (up to 5.7 °C) is shown between both surfaces of vertical GIL insulator, and the temperature on the insulator surface is distributed symmetrically along the center of the insulator. However, the temperature on both surfaces of the horizontal GIL is basically the same, but the temperature distribution varies greatly along the different radial directions of the insulator (up to 5.3 °C). By comparing the surface charge density distribution of insulators under both GIL installation ways, it is found that the surface charge density of horizontal GIL is more than 20% higher than that of vertical GIL. In addition, the volume conductivity distribution of insulator varies greatly under different GIL installation ways. The volume conductivity is positively correlated with the temperature distribution, while the normal electric field on the insulator surface is negatively correlated with volume conductivity distribution. It is hoped that this study can serve as a reference for the design and safe operation of DC GIL.