MAINTENANCE of VACUUM CIRCUIT BREAKERS

- Vacuum circuit breakers maintenance should be based on the manufacturer’s instruction , generally at least once a year or every 2,000 operations, whichever occurs first
- Breakers should be inspected every time after a severe fault interruption
- Remove breaker from its enclosure

- Use a clean, dry cloth to remove all dirt and moisture from the surface of vacuum interrupters and all insulating parts
- Check the contact erosion by measuring the spring plate over-travel
- Modern vacuum interrupter has an indicator or marking to show that the level that the interrupter need to be replaced

- Check the condition of vacuum by performing an A.C. high-potential test at 70% of final factory test value for 1 minute. If the test fails, replace a new vacuum interrupter
- If no factory test value, use the formula :
70% x (2 x rated voltage + 1 Kv) a.c. at power frequency ; or
(2 x rated voltage + 1Kv) d.c. if no a.c. test set is available

- Check other operating mechanism similary as with ACBs mentioned earlier
- Operate the breaker manually and electrically several times to make sure the breaker is operating properly