Inrush current arc characteristics in vacuum interrupters with axial magnetic field contact and butt-type contact

In the case of switching back-to-back capacitor banks, there will be inrush current while closing the circuits which will damage the contact surface of vacuum interrupters (VIs). The objective of this paper is to investigate the characteristics of the prestrike arc under the influence of axial magnetic field with different amplitudes of inrush current. Two groups of VIs with a rated voltage of 12kV and glass insulating shell have been tested while the metal shield in VIs has been removed. The prestrike arc is videoed by a high speed CCD. The contact travel, the voltage and current value of the prestrike arc are also measured and recorded with an oscilloscope. The experimental results may indicate the reason for the damage to contacts of VIs caused by prestrike arc. For the cup-type AMF contacts, when the inrush current is 5kA-10kA, slots on the contacts has a significant impact on the prestrike arc. It could make the electric field distribution much more nonuniform than that of the butt-type contact. When the inrush current become stronger, especially in 20kA, the axial magnetic field plays a major role. The prestrike arc is diffused for the most of time, and the contact surfaces are less damaged.