Back-to-back capacitor bank switching performance of vacuum interrupters: Comparison of three contact materials

Back-to-back capacitor bank switching is a specific operation which combines an inrush current during a making process and a power frequency current interruption followed by a subsequent DC recovery voltage during a breaking process. For a vacuum interrupter (VI), the dielectric strength is mainly depends on the condition of the contact surfaces which may be damaged by a pre-arcing of the inrush currents. So the contact material and the fabrication process of the contact play an important role on back-to-back capacitor bank switching behaviors. The objective of this paper is to investigate the back-to-back capacitor bank switching performance of vacuum interrupters with three different contact materials (infiltration CuCr 50, vacuum induction melting CuCr40Te0.005 and vacuum arc melting CuCr 50). The three different contact materials are installed in nine 12kV VIs which undergo a series of back-to-back capacitor bank switching tests at an inrush current of 8 kA (peak value, frequency 3800 Hz). The experimental results show that the average value of the restrike probabilities of the VIs for each contact material are that vacuum induction melting CuCr40Te0.005 is 5.8%, infiltration CuCr 50 is 6.7% and vacuum arc melting CuCr 50 is 8.3%. For all VIs, the restrikes mainly occur between (1/4)·T and 10·T of the recovery voltage (T is a cycle of the recovery voltage that is 20 ms). Many reignitions also occur before (1/4)·T. The number of reignition follows the order of vacuum induction melting CuCr40Te0.005 (1 times) <; vacuum arc melting CuCr 50 (9 times) <; infiltration CuCr 50 (10 times).