Contact erosion patterns of Pd material in DC breaking arcs

Arc erosion patterns of pure Pd contacts tested with switching inductive load at 20 V, 1~4 A were determined by means of the SEM, and material transfer was measured with electronic balance. Three types of erosion patterns were observed at the different load current regions. First, the distributed craters occurred on the anode and scattered redeposited mounds surrounded by sprayed particles on the cathode when the current was less than about 2.5 A, which we called a critical transition current because it demonstrates the change of metal transfer direction. Second, if the current was larger than the critical current value, pips occurred on the anode and craters on the cathode. Third, when the current was around the critical current value, pips and craters coexisted either on the cathode or on the anode. The behaviors of electrical contact resistance and arc duration in metallic phase and gaseous phase at different load current are reported. The particle sputtering-depositing model is presented and used to explain the mechanism of material transfer process and the formation of erosion patterns. The material transfer direction is affected by an arc duration of metallic phase as well as gaseous phase. The electrical contact resistance not only depends on the surface films and surface morphology, but also is influenced by the particle sputtering