How to predict field life using vacuum interrupters

BY FINLEY LEDBETTER, Group CBS

Utilities have widely replaced older air-magnetic and oil interrupters for circuit breakers rated at one kilovolt (kV) or higher with vacuum interrupters (VI) due to higher interrupt capability. Vacuum interrupters also last up to 10 times the expected lifetime than newer sulfur hexafluoride (SF-6) gas interrupters. Unfortunately, the downside to building a protective device with a long service life is that utility planners, technicians, and maintenance professionals believe it will last forever.

However, that misconception, plus the difficulty in field testing VIs, has placed a large portion of the U.S. industrial and utility distribution switchgear at risk of failure. Luckily, several traditional “pass/fail” testing methods and one new “predictive” field-testing method exist for verifying the isolation capability of VI-protected circuit breakers and motor controls. These three testing methods are covered in detail in this issue’s Electrical Substations Channel.