Effect of insulation barrier on AC breakdown voltage of rod-plane gaps and analysis of surface residual charge property

In the limited space on the roof of the high-speed train, breakdown performance of the high voltage box can be greatly improved by introducing the insulation barrier between bus-bar and ground plane. In the paper, effect of barrier size, position and material property on ac air gaps breakdown voltage have been studied, and two typical barrier materials, polyester glass blanket (GPO-3) and epoxy resin (EP) have been compared. Further, surface potential property on the barrier after discharge has been measured by the non-contact surface potentiometer, and surface trap parameters of the two materials have been calculated. The experimental results indicate that the breakdown voltage of rod-plane gaps will be increased about 1.95 times and 1.83 times for GPO-3 and EP respectively. On the one hand, the discharge path can be lengthened by increasing the size of the barrier. On the other hand, the closer the barrier to the rod electrode, the evolution of corona region can be prevented as soon as possible before the self-holding discharge occurs. There exists obvious residual charges on the barrier surface after discharge, the initial surface potential of EP and GPO-3 after discharge are 8091 V and 3856 V respectively. Further, it has been calculated that the trap levels of the two barriers are both the deep trap, about 1.0 eV, resulting in that the residual charges remain on the barrier surface for a long time. In addition, the residual charge density of EP is more than that of GPO-3, the charge density peaks of EP are 3.33 × 10¹⁹/m³ and 2.75 × 10¹⁹/m³, which is the main reason that its breakdown voltage is lower than that of GPO-3.