The effect of contact opening velocity and the moment of contact opening on the AC erosion of Ag/CdO contacts

This paper presents experimental results on the influence of contact opening velocity and the moment of contact opening with respect to the start of the AC current cycle on arc energy and contact erosion when breaking an AC resistive circuit. The test currents are 5.6 A, 14.7 A and 26.3 A, and the contact material is Ag/CdO (90/10). A computer controlled test system allows the control of the contact velocity profiles with constant velocities up to 0.8 m/s, and also enables the synchronization of the contact opening with a point on the AC current waveform. Contact erosion is evaluated by measuring the mass loss or gain changes of the cathode and anode. The results show that increasing the contact velocity from 0.1 m/s to 0.8 m/s leads to the increase of the arc energy. The material transfer from one electrode to another is shown to depend on the current, the polarity of the moving contact, the moment of the contact opening with respect to the start of the AC current cycle, and the opening velocity of the contacts.