Capacitive current switching duties of high-voltage circuit breakers: background and practice of new IEC requirements

Capacitive current is switched in power networks in a number of situations, such as the charging current of overhead lines, cables, GIS installations of the load currents of capacitor- and filter banks. In each of these situations, the current to be interrupted is small or very small. Nevertheless this interruption duty has to be considered with the utmost care. Above all, this is due to the inherent risk of re-establishment of arcing ('restrike') because of severe voltage stress after interruption. Restrike may cause high over voltages depending on the network topology and can lead to damage to circuit components. This concern is reflected in a major revision of the relevant IEC standard (IEC60056) that is presently under consideration. In the revised edition, the concept of a 'restrike-free' circuit breaker is abandoned and the regime of testing is sharpened.