Experimental analysis of ion parameters during the forced vacuum arc interruption

The paper presents experimental measuring results of the ion decay time during the post-arc phase after a forced interruption of diffuse vacuum arc. Arc current of amplitudes 400 A and 600 A was switched-off using counter-pulse current with falling rates from 2 A/μs u to 67 A/μs in a laboratory test circuit. The used voltage, current and contact parameters were representative for a low-voltage vacuum switch. The decay process of ion current was observed, using a retarding field analyser. First, a series of introductory measurements concerning probe calibration were performed. The decay times of ions were measured as function of the falling rate of the counter-current, and mean values from about 60 μs at arc current falling rate 2 A/μs up to 35 μs at arc current falling rate 67 A/μs were measured. Only a small dependence of the decay time from the arc current value (400 A or 600 A) was observed. The decay time decreases significantly with increasing of the counter-current failing rate. The results are proposed as a parameter in the modelling of post-arc phenomena of low voltage vacuum switches.