Contact resistance characteristics of Ag material in breaking low-load DC arcs

Contact resistance of Ag contacts was determined from nonload to 4 A under switching inductive load conditions. The tested results show that three characteristic contact resistance variations corresponding to three types of contact morphologies exist, and there are a critical transition load current and a critical transition operation cycle. When the load current is less than 0.2 A, which is called critical transition current, the contact resistance at the beginning of the operation, which is less than critical transition operation cycle, is like that in nonload condition, i.e., low and stable. If the load current is larger than this critical value, the contact resistance is, however, high and unstable during the whole test process. It is demonstrated that this phenomenon is attributable to arc occurrence probability and arc duration. Both mechanical factors (wear and mechanochemical reaction) and electrical factors (arc erosion and heat corrosion) are considered to be dominant in different load currents and different operation periods