CONTACT EROSION PATTERNS OF PD MATERIAL IN DC BREAKING ARCS

Arc erosion patterns of pure Pd contacts tested with switching inducti ve load at 20 V, 1 approximately 4 A were determined by means of the S EM, 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 scat tered redeposited mounds surrounded by sprayed particles on the cathod e when the current was less than about 2.5 A, which we called a critic al transition current because it demonstrates the change of metal tran sfer direction. Second, if the current was larger than the critical cu rrent value, pips occurred on the anode and craters on the cathode. Th ird, 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 a nd gaseous phase at different load current are reported. The particle sputtering-depositing model is presented and used to explain the mecha nism of material transfer process and the formation of erosion pattern s. The material transfer direction is affected by an arc duration of m etallic phase as well as gaseous phase. The electrical contact resista nce not only depends on the surface films and surface morphology, but also is influenced by the particle sputtering.