Methods for estimation of the vacuum status in vacuum circuit breakers

In this paper several methods are described for the estimation of the pressure inside vacuum interrupters which have been in operation for many years. 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 currents, either 10 A dc or 300 A ac. With the 10 A dc method the height of arc voltage spikes are measured and represented in a histogram. The shape of the histogram is discriminative for pressures below or above 10-2 Pa. Switching tests with currents of 200 to 400 A ac in inductive and capacitive circuits also showed different behavior for internal pressures below or above 10-1 Pa. A three phase 200 A test device with a 10 kV recovery voltage, fed from a standard 380 V supply, showed similar result

High-current interruption in vacuum circuit breakers

The aim of this project was to find a correlation between contact gap length and switching behavior of a vacuum circuit breaker. A large number of interruption experiments were executed in a vacuum chamber with butt type contacts made of Cu, CuCr 50/50 and AgWC. The currents to be interrupted varied from 2.5 to 32 kA. The rate of change of current and recovery voltage were kept at a fixed value at current zero. Many re-ignitions of the dielectric type, scattered over a wide range of re-ignition voltages, were observed and only a few of the thermal type. The total amount of energy dissipated in the vacuum chamber appears to be determinative for the type of re-ignition. On Cu severe anode spot melting was found, whereas CuCr and AgWC suffered little anode melting. The wide range of re-ignition voltage values found shows that a straight correlation with the contact gap length can not be defined. At 5 to 10 µs after current zero a `second' post arc current did appea