The net zero mass loss phenomenon on opening switching contacts with AC loading

Studies are conducted on silver metal oxide contacts on a purposed built ap paratus to investigate the extent of contact erosion under opening (break) operations, The contacts are opened between 0.1 and 0.8 ms(-1) at particula r point-on-wave, t(POW), Of the ac waveform, Current loading of up to 30 A rms, I-rms, is investigated. Contact material deposition, as well as mass l oss, is observed and is found to balance at particular current values and p oint-on-wave opening leading to a net zero mass loss on the contacts. Resul ts are presented on mass change for each contact against the two parameters of current and point-on-wave. An are duration characteristic, zeta, is plo tted against current, I-rms, which has a net zero mass loss. The characteri stic is shown to be the same for both silver tin oxide and silver cadmium o xide but is influenced by the opening velocity. The metallic and gaseous io n transfer mechanisms of the are discharge are presented as the main proces ses behind this phenomenon.