Controlled switching-suitability check for already-installed HVAC circuit breakers

In cases where switching transients cause severe problems during closing operations, it is of interest to know whether controlled switching is capable of reducing transients to an acceptable level. However, the prestrike characteristic of the circuit breaker must be known, which is rarely the case for older circuit breakers. Hence, an identification method has been developed that provides assessment of the rate of decrease of dielectric strength on circuit breakers already in service. It is based on a physical prestrike model that includes the statistical scatter of the breaker characteristics. Using this model, identification of the breaker prestrike characteristic can be quickly achieved through the comparison of a set of numerically calculated prestrike patterns with the performance of a real breaker in the field. In this way, both the suitability of a circuit breaker for controlled switching and the extent of the benefit of transient reduction can be assessed with minimal effort. The applicability of the method has been successfully demonstrated on a 145 kV circuit breaker in laboratory tests.