Current-interruption testing of vacuum switching devices

In the international IEC standards for medium and HV switching devices no distinction in test requirements is made between switching devices with different arc-quenching media, like SF6, oil and vacuum. This had led to the situation that due to the different technology of arc interruption applied, various aspects of the prescribed test-procedures have a different weight in terms of severity for various types of breakers. Additional test-requirements and interpretations that are specific to vacuum switching devices have been formulated commonly by the joint major test laboratories. In this contribution, the background and practical application of several procedures, now generally adopted by certifying test-laboratories, regarding the peculiarities of vacuum switching devices are elucidated. Because the vacuum switching device has an excellent capability to interrupt current of high frequency, the main part of this contribution will be related to the consequences for test procedures of this aspect that is not encountered in SF6 or oil breakers. In particular, the judgment of non-sustained disruptive discharges, multiple re-ignition and virtual current chopping in test-circuits is addressed. Results of a new high-resolution high-frequency current-zero measuring system are presented. This system is able to give insight into the high-frequency arc phenomena in the immediate vicinity of are interruption, and is designed to get more specific information on arc behavior during standard high-power test