Life tests on vacuum switches breaking 50 kA unidirectional current

The results of two different series of life tests carried out on vacuum switches with a self-produced axial magnetic field (in view of their use in nuclear fusion facilities) are presented. The goal was to obtain a large number (on the order of 2000) of interruptions of a unidirectional current of over 50 kA, with a recovery voltage of up to 35 kV. A first series of tests showed that the test procedure with an accelerated life test was not adequate; it was also apparent that the contact plate, designed for 50 Hz applications, had weak points when subjected to extended thermal contacts. Therefore, a new version of the switches, with modified contacts, was built. Both versions of the switches were tested with a new test procedure, and satisfactory test results were obtained.>