Study of shield potential to understand the arcing behaviour of vacuum interrupters during short-circuit current interruption

The vacuum interrupter is extensively employed in the medium voltage switchgear for the interruption of the short-circuit current. During the interruption process an arc is formed between the opening pair of the contacts. A metal shield is used to protect the ceramic from the metal vapours depositing on it during arcing. A voltage gets induced in the shield during the arcing process. The magnitude of this voltage could be an indication of the arc mode and arc motion, which would in turn give indications of the performance of the contacts of vacuum interrupter. This paper investigates the relationship of the shield potential with the arc voltage, arc current, travel of the moving contact, type of contact and the vacuum interrupter geometry. Through this study the paper would explore the utilization of shield potential as a diagnostic parameter during short-circuit evaluation of the vacuum interrupter.