Simulation and analysis of charge accumulation characteristics of post insulator of transmission line for the CRAFT NNBI system

For the negative-ion based neutral beam injectors (NNBI) system, the High voltage transmission line (HVTL) is a vital link between the radio frequency ion source system and the power supply system. Under the action of DC voltage, the surface of the internal post insulator of the HVTL will accumulate lots of charge, which can easily cause the post insulator to flashover. Therefore, the study of the accumulation characteristics of the surface charge for the post insulator under DC voltage is very significative to enhance the performance of the insulation and the reliability of the operation for the DC HVTL of the NNBI system. In this paper, taking the main post insulator of the HVTL as the research object, the accumulation model of the surface charge for the solid-gas composite insulation structure is established. Through finite element analysis, the effects of the bulk and superficial conductivity on the surface tangential electric field intensity and the surface charge density under three different material models are obtained. According to the calculation results, some suggestions and strategies for restraining the accumulation of surface charge are given, which provides a theoretical basis for the selection of material properties of the solid post insulator in the HVTL of the NNBI system.