Characterization of the breakdown voltage of vacuum interrupters by different procedures

This work compares two different procedures for the application of the Lightning Impulse Voltage Waveform (LIVW) with 1.2/50 ?s front/half value times: Up & Down (UD) and Always Breakdown (AwBD) to obtain the cumulative breakdown voltage distribution for Vacuum Interrupters (VIs).The voltage pulses were applied to several VIs for medium voltage applications with fixed shield and for gap lengths ranging from 4mm to 15mm. The repeatability of the results for a given procedure, as well as discrepancies, were investigated and the results compared.The AwBD procedure, where the peak voltage of each pulse is set and kept at the same arbitrary high level to collect a breakdown for each pulse, was thoroughly investigated and some experimental evidences have been discussed. This procedure is effective to collect data on many breakdowns very quickly, due to both the speed of the voltage conditioning phase and because breakdown data are collected for each pulse.