Minimum Arcing Interrupting Capability and Opening Velocity of Vacuum Interrupters: An Impact of Contact Diameters

Controlled switching technology operates circuit breakers at the minimum arcing time for short-circuit current interruption. Our previous study shows a relationship that the minimum arcing time of a vacuum interrupter (VI) decreases while the average opening velocity increases. However, there is no report to reveal an impact of contact diameters on this relationship. The objective of this paper is to reveal an impact of contact diameters on the relationship between the short-circuit current minimum arcing interrupting capability and opening velocities of vacuum interrupters. Three contact diameters of 65 mm, 58 mm and 50 mm were investigated in this paper. The three contacts were cup-type axial magnetic field contact. The contact material was CuCr50 (50% of Cr). Each pair of contacts was arranged in a VI. The VIs were driven by an electromagnetic repulsion mechanism whose average opening velocities can be adjusted from 2.7 to 6.0 m/s. Short-circuit current interruption tests are carried out in a synthetic circuit. The tests were carried out 4-6 times to determine a minimum arcing time under a certain average opening velocity. The short circuit interruption tests had a current of 31.5 kA (RMS) with a TRV peak of 73 kV. Experiment results show that the minimum arcing time decreased with the increasing average opening velocity and it kept a constant when the average opening velocity reached a critical value. Also, contacts with a smaller diameter could achieve a shorter minimum arcing time.