Contact behavior and gas phenomena in a vacuum switch

摘要

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.ududInitially a conditioned vacuum switch opens a circuit with a small, momentary arc. This arcing releases gas from the electrodes so that with continued operation a definite rise in gas pressure within the switch was observed. The rate at which gas is evolved was seen to depend both on the value of the interrupted current and on the circuit voltage, increasing either for increasing current or for increasing voltage. Further, definite evidence of getter-action or electrical clean-up of gas in the switch was obtained. Thus the resulting gas pressure was found to be due to that part of the evolved gas not removed by getter-action; and a limiting equilibrium case was found in which the gas evolution and getter-action balance each other to give a constant operating pressure for indefinitely continued switch operation. Moreover, the pressure range throughout which satisfactory operation in possible was determined to be from that of the best obtainable vacuum to one of the order of [...] mm. In addition, the tests included rupture of currents that gave excessively high current densities, and demonstrated that current break is possible even with severe heating of the contacts. Similarly, a limiting value of current density of the order of 10,000 amperes per square inch appeared to be permissible without effecting serious damage to the contacts. And, in general, copper, the metal most desirable from a commercial standpoint, was found to give better operating results than either of the other two metals investigated.