Low-Resistance of zero-point Extinction Circuit Breakers
In this method, the arc is interrupted at a current zero instance. At that instance, the air between the separating contacts is unionized by introducing fresh air, SF6 gas, or oil between the contacts. Naturally, this method is used for an AC arc interruption.
By using a combination of shunt and series coils, the circuit breaker can be made to trip when the energy reverses. Circuit breakers may trip, when a local breaker or fuse immediately clears the difficulty.
To ensure that the service is uninterrupted, automatic re-closing schemes are often used for circuit breakers feeing to overhead lines where self clearing faults (e.g. a bird fault) can occur. After tripping, an automatic scheme operates to re-close the breaker with a short delay giving an opportunity for the fault to clear. If a short-circuit still exists, the breaker trips once again. The breaker attempts to re-close two to three times and if the short-circuit persists it remains permanently locked out.