Influence of the Protective Gas Pressure on Showering in Dry Reed Contacts

We investigated the effect of a reduction of the protective gas pressure at fixed static breakdown Voltage on the appearance of showering (intermittent arcing) in dry reed contacts that break inductive circuits by using a discharge gap arid an auxiliary interruptor to simulate this condition. We found a critical pressure range, where showering, capable of causing strong erosion, is replaced by glow discharges. In the case of actually operating contacts, it was only possible to reduce showering for forty percent of the total openings by lowering the gas pressure. These results can be explained by suggesting that in the case of the discharge gap that represents a relay opening contact having large contact spacing, the showering arcs, developed from the preceding glow discharges, can be minimized by reducing the gas pressure in such a way that arc formation is inhibited. In the case of the operating contact, other mechanisms exist, such as high electrical fields and high temperature spots. These mechanisms are not affected much by reducing the gas pressure; thus showering is only partially prevented.