The European development of a full scale switching unit for the ITER switching and discharging networks

The European Fusion Programme included since the mid-1990s, the development of a full scale, full rating current commutating unit (CCU) to be used as a centre-piece of the ITER magnet protective circuits. The CCU is mainly composed of a by-pass switch (BPS) in parallel to a vacuum circuit breaker (VCB). Both full scale switches were subjected to extensive testing in conditions simulating the actual ITER operation. The operation in absence of the saturable reactor series connected in the ITER reference design was successfully assessed. Interruption tests at low current and full counter-pulse capacitor voltage, were also satisfactorily performed. The tests included an extensive and novel characterisation of the interrupting capability of the vacuum circuit breaker in the presence of an external magnetic field as in the actual location of installation in ITER.