Operational Experience of the 50 kA-35 kV RFX-Mod DC-Current Interruption System

This paper investigates the electrical performances of the high-dc current interruption system in use in the RFX-mod experiment. This system, called the Energy Transfer System (ETS), provides the loop voltage required for plasma breakdown utilizing the interruption of dc currents up to 50 kA, with a recovery voltage up to 35 kV. The ETS is composed of four identical units, each including Vacuum Circuit Breakers (VCBs), a transfer resistor and a counterpulse capacitor bank. The system was upgraded in 2008 to permit reliable operations up to the design target of 50 kA. A new auxiliary branch was connected in parallel to each dc-current interruption system and all the VCBs have been replaced with larger contacts surface breakers. Since this upgrade, the ETS has been working routinely and performed almost 9000 dc current interruptions, even at its nominal current without major failures. This paper, which takes advantage of the large database of ETS electrical measurements, investigates the key waveforms and parameters of VCBs (like arc U-I characteristic, close-contact resistance, recovery voltage) and correlates their variation with the faults occurrence and with the aging of the VCBs components.