An evaluation of Ag/W and Ag/Metal Oxide arcing contact combinations for circuit breaker applications

Electrical contact manufacturers have the continuous challenge to reduce cost and improve performances with better material. Many historical practices in the selection of contacts in regard to contact erosion, welding and contact resistance have to be revisited to find updated guidelines. In this report, some contact combinations for low voltage circuit breaker applications using Ag/W as moving contact against Ag/MeO as stationary contact are evaluated on welding, endurance and contact resistance. This included metal oxides such as CdO, SnO2 and ZnO. The results are compared with the more conventional mating of Ag/W to Ag/C and Ag/WC/C which have low contact resistance but high erosion and low strength deficiencies. In these asymmetrical contact combinations, contact welding and endurance tests at 90A are compared with some composition variations. Arc erosion products and material transfer affecting changes in contact resistance are examined in composition analysis and metallography. Contact resistance vs contact force is measured to show the possible improvements to heat rise factors.