Arc restrikes yielding back-commutations in the contact gap of low voltage interrupters

Arc commutation from the arc chute back into the contact gap of a low voltage circuit-breaker caused by a high arc voltage pulse due to arc splitting was investigated in a model interrupter with the aid of a synthetic test method. In the experiment a well defined time after the arc left the contacts a high voltage ramp was applied across the contact gap. The criterion considered was the breakdown value of the voltage. Recovery time (in the range of 500 μs to 2 ms), geometry and materials of contacts (Cu, Ag/C, Ag/Ni, Ag/MeO) and walls (nongassing and gassing) were varied. Increasing recovery time increased the breakdown voltage significantly due to the decrease of the temperature in the contact area. The minimum breakdown value corresponded to the instantaneous reignition voltage. An increase of the wall distance caused an insignificant increase of the breakdown voltage due to the decrease of field distortion. Gassing wall materials caused slightly higher breakdown voltages than nongassing walls. Increasing contact gap from 2 mm to 4 mm increased the breakdown voltage. No influence was observed at lower (1.5 mm) and at higher contact gaps up to 7 mm. The influence of the contact material was generally little; Cu contacts yielded insubstantially lower breakdown voltages than the other contact materials investigated.