Analysis of circuit breaker controlled switching operations - from manual to automatic

Controlled switching has been used for years to minimize switching transients in power systems. In a specific case several years ago, commissioning of a controlled switching system was initially not successful; the source of the problem was found to be in the circuit breaker (CB). However, detailed analysis proved challenging as it was difficult to distinguish whether the cause was electrical (long pre-strike) or mechanical (deviation in operating times), due to lack of mechanics related signals from the CB. This paper describes the tedious manual analysis of available data. Although not fully conclusive, recommendations for the specific installation were given and successfully implemented. Furthermore, a concept for simplifying and improving performance analysis of controlled switching operations is introduced. Key element is to include the changeover times of CB auxiliary contacts in the recordings of each operation, which is non-invasive to the CB. The information will provide a straight-forward estimate of the actual mechanical CB operating times and, in turn, (pre-)arcing times. Ideally, the point-on-wave controller itself has both interfaces for auxiliary contact signals and software features for operation assessment, thus eliminating the need for external recording equipment and manual analysis.