NUMERICAL EVALUATION FOR EROSION OF ELECTRICAL CONTACTS MOUNTED ON CONTROL RELAYS.

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The sample contact was made from silver oxidation cadmium (Ag/CdO), silver oxidation tin (Ag/SnO2), which had been spotlighted as a material without cadmium, silver tin (Ag/Sn), silver (Ag), and palladium (Pd). These contacts were mounted on the test relays, which had the contact force 0.45N and opening force 0.15N.By repeating the make-only-operation and break-only-operation in the resistance circuit of direct current 30v-10A, the shape change of pip on the contact surfaces and sticking occurrence condition were examined.On the Ag/CdO12wt% contacts, the break-only-contacts had no large pip ; the make-only contacts had a large pip on the negative electrode. Between the height H and the root diameter Dr of a pip, and the initial contact gap G, it was discovered that the contact sticking rose, when it reaches the relationship between "H/G>0.5 and H/Dr>0.5". These numerical values are useful for the judgment for the replacement of the relay, when the electric system equipment is checked.Though the Ag/SnO_212wt% contacts had a comparatively large pip on the negative electrode, the contact sticking did not arise because a large pip suddenly collapsed. The Ag/Sn9.5% contacts had the welding in the contact period carrying current. The Ag contacts showed that the root diameter of pip was thick, and the height was low. The Pd contacts showed that the large pip appeared on the anode, and suddenly collapsed.By measuring the intensity of spectral components from switching arc, which induced the transferred pip, temperature and atomic density in the arc column were measured, and the contact erosion was examined.