Discharge Path Measurement of A Vacuum Interrupter with Fixed Break after Suffering High Inrush Current

Discharge path determination of a vacuum interrupter is important for development to higher voltage levels, but no direct measurement has been carried out on a VI. The objective of this paper is to directly measure breakdown path of a VI. A VI with fixed breaks were designed and used in the experiment. The fixed break was composed a pair of fixed shields and in parallel with the movable contact gap. One of the shield was fixed to the end cover while the other one was fixed between two porcelain shell, and could be connected to the moving rod out of the VI. By measuring current of a shield and a contact separately, breakdown path could be deduced. The tested VI was firstly conditioned to a statured state with the 50% impulse breakdown voltage U 50 =221kV. Then it suffered the inrush current 30 times. Next, standard lighting impulse voltage was applied by an up-and-down method. Experimental results showed that breakdown path could be measured on both the contacts and the fixed shields, and three obvious stages could be found during lightening impulse voltage application. In stage □, breakdowns mainly occurred on the contacts as breakdown voltage raised quickly. In stage □, breakdowns occurred alternately on the contacts and the fixed shields and the breakdown voltage raised much slower. In stage □, breakdowns mainly occurred on the fixed shields and the breakdown voltage reaches the saturation region with the 50% impulse breakdown voltage U 50 =183kV.