Enhancement of External Insulation Performance for Vacuum Interrupters by External Shields

Abstract

A vacuum interrupter’s (VI) external and internal-vacuum insulation performance are equally important. To enhance the external-insulation performance of high-voltage and/or compact VIs, many materials with high-insulation properties have been used as external-dielectric protection. However, these materials are expensive and may cause environmental problems. This paper proposes external shields to enhance the VIs’ external-insulation performance. Four dimension parameters of an external shield, i.e., distance between the external shield and ceramic envelope L, height that the external shield covers by the ceramic envelope L, and the external shield’s radii R1 and R2, were investigated to determine the appropriate external shield to significantly improve the VIs’ external insulation. Results of electric-field simulation of a 40.5 kV VI revealed that the four dimensions of the external shield were L = 2 mm, H = 4 mm, R1 = 3 mm, R2 = 3 mm. Moreover, the external insulation performance of the 40.5 kV VI was evaluated by a power-frequency-voltage withstanding experiment, which revealed an average external-flashover voltage of 76.7 kV for three VIs without the external shield. The average external-flashover voltage for three VIs with external shields on the end surfaces of the ceramic envelope was 96.1 kV. Further, the average external-flashover voltage increased by 25.4% with the external shields, indicating that the external shields are effective for enhancing the external-insulation performance of VIs. Moreover, the external shields are suitable for high-voltage and/or compact VIs.