抄録
The thermal deterioration of the contacts in SF6 gas has not been generally understood. This paper describes the sulfide formation by the direct reaction of Ag and Cu to SF6 gas with moisture at a relatively low temperature, and the current carrying deterioration of contacts by such formation. The results are summarized as follows :1) the thermodynamical approach shows that Ag and Cu react to SF6 with moisture over 252°Cand 165°C, respectively, and then Ag2S and Cu2S are produced, 2)these reaction temperatures are supported by the experiments and much sulfide is produced by higher temperature and moisture and 3) the 160-280 A current carrying tests of the Ag-WC and Cu-W contacts with high contact resistance of about 1mΩ show that only the Cu-W contacts over the sulfide forming temperature were covered with a copper sulfide layer and therefore could not carry these currents after 55-130 hours. To examine the rise of contact resistance for the actual Ag-WC and Cu-W contacts by arc erosion, the switching tests of 200 A and 20, 000 operations were also carried out and the Ag-WC and Cu-W contact resistances at 0.01% occurrence probability were recognized to be 0.7 and 1.3 mΩ, respectively. Therefore it is concluded that the Ag-WC is sulfide reaction free but the Cu-W possibly produces copper sulfide under the above conditions.
