Operational and Performance Overview of the 50 kA–35 kV RFX-Mod DC-Current Interruption System

Abstract

This article investigates the electrical performances of the high direct current (dc) interruption system in use in the reverse field experiment (RFX)-mod experiment. This system, called the energy transfer system (ETS), provides the loop voltage required for plasma breakdown inside the toroidal vacuum vessel, utilizing the interruption of dc currents up to 50 kA, with a recovery voltage of up to 35 kV. The ETS is composed of four identical units, each including the vacuum circuit breaker (VCB, each composed of two Vacuum Interrupters (VIs), in series), a transfer resistor, and an artificial zero current network. The system was designed in the 1980s and upgraded in 2008 to permit reliable operations at the full current of 50 kA. A new auxiliary branch was connected in parallel to each dc-current interruption system and all the VIs have been replaced with units with a larger contact surface. Since this upgrade, the ETS has been working routinely, and so far has performed almost 9000 current interruptions. By taking advantage of the large database of ETS electrical measurements, this article investigates the key waveforms and parameters of each VI (arc U-I characteristic, close-contact resistance, and recovery voltage) and correlates their variation with the fault occurrence and with the aging of the VCB components.