The Relationship between Exchange of Applied Voltage Polarity and Growth of Transferred Pip on Ag/CdO Make-only Contacts in a DC 42V-10A Circuit

摘要

Some Ag/CdO12wt% contacts mounted on electromagnetic relay are operated as make-only contacts in a DC42V-10A resistive circuit that exchange the voltage polarity of applied voltage to these contacts every tens of thousands of operations. In this experiment, we took photographs of transferred pip from bi-direction and measured arc duration, number of bounces and contact resistance. The following results were obtained by this experiment. On make-only contacts, the pip was formed on cathode surfaces with the material transfer from anode to cathode. While the first and second polarity exchange, pip was formed to the other side contact when the height of pip was lowers. However, polarity exchange was repeated many times, it became easy for the collapse of pip. And disorder of material transfer that the height of pip was hardly changed and anode side pip was grown up occurred after the collapse of pip. At this time, the total arc duration was less than 150μs.