Testing of vacuum circuit breakers: specific issues and developments

In the international IEC standards for medium and high-voltage circuit breakers no distinction in test requirements is made between circuit breakers 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 circuit breakers (VCB) 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 circuit breakers are elucidated. Because the vacuum circuit breaker has an excellent capability to interrupt current of high-frequency, the main part of this contribution focuses on the consequences for test procedures of this aspect, not encountered in SF_6- or oil breakers. In particular, the judgement of nonsustained disruptive discharges, multiple reignition and virtual current chopping in test-circuits is addressed. In addition, 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 arc interruption, and is designed to get more specific information on arc behaviour in standard high-power tests