Methods for estimation of the vacuum status in vacuum circuit breakers

In this paper several methods are described for the estimation of the press ure inside vacuum interrupters which have been in operation during many yea rs. The methods are applicable without demounting the interrupters and use only electrical measuring techniques. According to these methods the vacuum circuit breakers are subjected to synthetic circuits, switch off limited c urrents, either 10 A de or 300 A ac. With the 10 A de method the height of are voltage spikes are measured and represented in a histogram. The shape o f the histogram is discriminative for pressures below or above 10(-2) Pa. S witching tests with currents of 200 to 400 A ac in inductive and capacitive circuits also showed different behavior for internal pressures below or ab ove 10(-1) Pa. A three phase 200 A test device with a 10 kV recovery voltag e, fed from a standard 380 V supply, showed similar results.