Suppression of Pip and Crater Formation During Interruption of Alternating Current Circuits

Abstract

The effect of adding W and Ni to Ag contacts in a slowacting switch has been evaluated. The experiments were performed in ac, 5.1 A and 12.4 A (peak), 220 V (rms) circuits. The erosion structure on the Ag contacts was a single pip and crater on each electrode. The addition of 10 percent by weight W to the Ag caused the erosion structure to change: many pip and crater structures were observed covering the contact surfaces (~60 structures after 120 000 switching operations) and the Ag-W contacts exhibited much greater arcing than the pure Ag contacts did, but the operating life nevertheless increased about 6 times. The Ag-W contacts failed by welding together. The addition of Ni (15 percent by weight) to the Ag resulted in a more uniform erosion of the contacts' surfaces and the duration of the arcing on closing and opening was very similar to that of pure Ag. After 160 000 operations very little loss of contact material was observed. These results are discussed in terms of the effect of the additives on the motion of the arc and the effects of the arc on the motion of the con- tacts.