Insulation of Current Leads for Superconducting PF-3 Coils of SST-1

Abstract

Conventional copper current leads (CLs) for superconducting magnets of SST-1 are fabricated to operate in dc condition for Toroidal field coils and fast current ramp up to 10 kA for Poloidal field (PF) coils at low temperature under vacuum. Two pairs of CLs are required to be installed with PF-3 coil terminals in current feeder system chamber (CFSC) for shaped plasma operation in SST-1.The PF coils of SST-1 are subjected to the induced voltages of around 1 kV due to Ohmic coil discharge. In past few campaigns, high induced voltages on PF coils due to Ohmic coil discharge have caused arcing inside the CFSC between high potential PF CLs and grounded thermal shield. This arcing resulted in severe damage to the PF current leads and helium hydraulic lines. We report the development and implementation of Paschen leak tight electrical insulation for cylindrical CLs with variations in diameter and geometry along its length. The developmental procedures include the sample preparations and optimization of insulation processes. The scales down version of CLs samples were prepared after the investigation of curing kinetics of insulation resin at 140 °C and 110 °C. The high voltage testing of these insulation samples was carried out up to 28 kV at room temperature (RT) before and after multiple thermal shocks. These insulation samples were also tested up to 5 kV dc and 80 K temperature in Paschen test setup. The insulation resistance and breakdown voltage of these samples found to be more than 100 GΩ and 28 kV, respectively at RT.