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

Are commutation from the are chute back into the contact gap of a low volta ge circuit-breaker caused by a high are voltage pulse due to are splitting was investigated in a model interrupter with the aid of a synthetic test me thod. In the experiment a well defined time after the are left the contacts a high voltage ramp was applied across the contact gap. The criterion cons idered was the breakdown value of the voltage. Recovery time (in the range of 500 mu s 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 breakdo wn value corresponded to the instantaneous reignition voltage. An increase of the wall distance caused an insignificant increase of the br eakdown voltage due to the decrease of field distortion, Gassing wall mater ials caused slightly higher breakdown voltages than nongassing walls. Increasing contact gap from 2 mm to 4 mm increased the breakdown voltage. N o 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 conta cts yielded insubstantially lower breakdown voltages than the other contact materials investigated.