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(-1) to 10(-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(-1) to 10(5) Pa. Current chopping of de arcs between 5 and 30 A during opening operation may be another option for determination of the pressure range by measuring the lifetime of the are, but the resolution in the vacuum range < 10(-1) Pa is too poor.