Switching performance of two 24 kV vacuum interrupters in series

The breaking capability of two vacuum interrupters in series and their behaviour with added grading capacitors has already been reported in preliminary publications. In the first part of this paper the dependence of breaking capability of the series arrangement on arcing time, recovery voltage and test current is compared with the performance of a single tube. Within these investigations the influence of the test current on the breaking capability of the double arrangement is shown. The second part of the work deals with the performance of the series arrangement during the re-ignition of one of the tubes. Tests with simultaneous openings of the contacts are presented which demonstrate that even one of the two tubes is able to withstand the total transient recovery voltage (TRV) in case of re-ignition of the other tube. Immediately after arc-extinguishing the previous re-ignited tube is able to recover and to take its part of the total TRV again. As a result the double arrangement is able to interrupt the test current.