Spark Conditioning of Vacuum Interrupters with Very Low Breakdown Energy

Spark conditioning is an effective method to improve dielectric strength of vacuum gaps. The objective of this paper is to study the influence of breakdown energy on the conditioning effect of VIs during spark conditioning. An AC power source was adopted to provide the voltage necessary for breakdown of a commercial 40.5 kV VI sat at 1 mm gap distance. A 100 k$\Omega$ current limiting resistor was connected in series between the power source and the VI to ensure that the breakdown energy was majorly adjusted by the capacitors connected in parallel with the VI. When the parallel capacitor increased from 250 pF to 750 pF, the saturated voltage increased from 38 kV to 41 kV, and the efficiency of the conditioning was increased. Change of field emission current by a breakdown was also studied. The field emission current decreased after most breakdowns, but the change rate was different. For the cathode at breakdown, the change rate increased with increasing breakdown energy; while for the anode at breakdown, the change rate decreased with increasing breakdown energy. At last, to balance saturated voltage and conditioning efficiency, three breakdown energy control methods were proposed.