Study on size reduction of 72.5kV vacuum interrupters used in metal enclosures

We have developed a 72.5kV prototype Vacuum Interrupter (VI) several years ago. VIs for metal enclosures tend to be bigger than those for insulator enclosures due to electrical stress. In order to secure its competitiveness against gas circuit breakers, it is necessary to reduce the size and cost of VIs. To reduce the size of 72.5kV VI, we analyzed its electric field distribution inside a metal tank and adopted multi-shield structure alternatively while the previous one has single-shield structure. As a result, two types of VIs have been designed: one is a single-shield type and the other is a multi-shield type which is smaller than the single-shield one even though electric field strength of both is similar. Their insulation and breaking capabilities have been verified through some tests and compared in metal and insulator enclosure. Two prototypes of 72.5kV VI developed in this study are much smaller than the previous one. The size of single-shield type VI is over 60% smaller than the previous one and the multi-shield type VI is about 25% smaller than the single-shield.