Earth faults during RFX initial operations

RFX, the largest RFP machine, has air-core poloidal windings. A tree-shaped earthing geometry has been adopted for all the machine components, to avoid electrical loops. Nevertheless, during the first operation phase a number of accidental contacts occurred, which caused loops currents high enough to distort plasma equilibrium. These loops could be detected by means of RGM, a system designed to perform fast winding protection, but able to detect accidental earth currents as well. After careful analyses of the signals, these earth faults were always located and removed. The use of a compass resulted particularly useful in the occasion of a number of these faults, the others were detected by means of rogowski coil probes.