Impact of inrush current on field emission current and voltage distribution in series vacuum gaps

Although vacuum technology is commonly used in power systems, challenges still remain for vacuum circuit breakers (VCBs) to cope with the requirements of capacitor bank switching duties as the insulation performance can deteriorate by inrush current. In order to reduce the restrike probability, vacuum interrupters (VIs) in series are recommended. The objective of this paper is to investigate the field emission current I e characteristics and voltage distribution in series vacuum gaps after making inrush current. The results show that I e of the VI pre-stressed by inrush current is much higher than that of the new one and I e has a conditioning effect. It is found that the insulation performance of two pre-stressed VIs in series is not significantly improved compared to a single VI. But the insulation performance of a new VI and a pre-stressed VI in series is significantly improved. Moreover, the voltage distribution of two VIs in series can be estimated by I e . It is found that each VI only withstands about 50% of the applied voltage when two pre-stressed VIs are in series. However, the new VI can withstand >70% of the applied voltage when a new and a pre-stressed VI are in series.