Analysis of the Failure of a Vacuum Circuit Breaker Applied on a Consumer - Utility Interface

In recent years the optimization of energy usage in large industrial facilities has led to the installation of electrical-generation units. If the capacity of these units is adequate, all or part of the plant electrical-distribution system may be operated unsynchronized with the electric utility. It is essential that the devices used in the plant-utility intertie be reliable, and yet these devices may be exposed to voltage stresses higher than at any other point in the plant electrical-distribution system. The effects of a loss of vacuum in one phase of a 15-kV-class circuit breaker applied between two potentially out-of-phase electrical systems is described. The effects of the electrical transients that resulted are chronicled. In addition, the effects of out-of-phase switching tests performed on the failed breaker and an undamaged identical breaker are discussed; and a description of an air circuit-breaker failure under similar circumstances is presented, along with a theoretical analysis of the overvoltages that were observed during the tests.