The Impact of Inrush Current on Field Emission Current of Vacuum Interrupters during Capacitive Current Switching

According to the relevant IEC standards, the back-to-back capacitor banks switching tests need to withstand an inrush current of 20 kA (peak) with 4250 Hz frequency. For vacuum interrupters (VIs), the contact surfaces may be seriously damaged by the high inrush current. The objective of this paper is to investigate how the inrush current influences the field emission current of VIs under power-frequency voltage. The amplitudes of the inrush current were set as 10 and 20 kA. The samples VIs suffered the inrush current of different amplitudes twice consecutively. Then, the field emission current of VIs was measured by applying a power frequency voltage upon the contact gap of 1 mm. The experimental results show that the field emission current is unsymmetrical in contrast with the power frequency voltage's polarity. There is a critical voltage value that the applied voltage exceeds it can make the field emission current increase significantly. Besides, the more times of imposing inrush current on the contacts and higher inrush current will lead to a higher field emission current.