Transient Electrical Voltages Within ITER Poloidal Field Coils

Abstract

High-voltage insulation co-ordination of the coil system is essential for reliable operation of ITER. Transient electrical excitations occur on the terminals of superconducting coils, for example in case of a fast discharge of the coils and if a failure occurs within the components of the electrical circuit. Transient voltage on the coil terminals may lead to non-linear voltage distribution and oscillations within large superconducting coils because of their large dimensions and high number of turns. Thus, the internal voltages may even be higher than the voltages on the coil terminals. This effect depends on the rise time of the excitations and was measured within the ITER Toroidal Field Model Coil which is about three times smaller than the ITER toroidal field (TF) coil. The calculations of the transient electrical behavior of the coils provide a basis for high-voltage insulation co-ordination and definition of test voltages and waveforms. The high voltage tests during the manufacturing process will control the quality of the electrical insulation and ensure reliable operation of the coils. The transient electrical behavior of ITER poloidal field (PF) coils was calculated using the PF 3 and PF 6 coils as examples. Maximum voltages for ground, layer and turn insulation were calculated for four scenarios. Results of these calculations are presented in detail in this paper.