Pressure estimation in vacuum circuit breakers

The pressure of vacuum switching elements after production is checked normally by Penning or magnetron methods (combined electrical and magnetic field). Vacuum in the range of 10/sup -1/ to 10/sup -4/ Pa can be measured in this way. After assembly into circuit breakers however, these methods are not applicable. HF interruption performance during the make operation was proposed earlier as a possible alternative. Further investigations show that differences in the number of HF prestrike current loops can be found in the pressure range of 10/sup -1/ to 10/sup 5/ Pa. Current chopping of dc arcs between 5 and 30 A during the opening operation may be another option for determination of the pressure range by measuring the lifetime of the arc, but the resolution in the vacuum range <10/sup -1/ Pa is too poor.<
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