Economy motivated increase of DC time constants in power systems and consequences for fault current interruption

Partly due to economic considerations, dc time constants of short circuit currents have increased in recent years. This has consequences for circuit breakers, that should interrupt these currents. As a result, the asymmetrical peak value and the arcing time are increased. An analysis is given of arcing time and arcing energy as a function of circuit- and circuit breaker parameters, and the impact on testing. Another factor that can increase the asymmetrical peak factor drastically is the scatter that the three poles (either naturally, either deliberately) have in their instant of closing. It is demonstrated that switchgear, intended for synchronized (´soft´) switching of ungrounded capacitor banks can produce unexpectcdly large asymmetrical current when closing into a short circuit. Finally, the use of local (co-)generation may cause extended periods in which no natural current zero occurs. In this respect (among others) circuit breakers have to meet special requirements, that usually go beyond standard circuit breaker requirements.