Calculation of Transient Voltages of ITER Poloidal Field Coils

The ITER magnet electrical insulations have to withstand transient voltages, which occur at normal operation, during the fast discharge and if a ground fault appears. Fast transient voltage excitations can lead to voltage oscillations and non-linear voltage distribution within the superconducting coils of ITER because of their large dimensions and large number of turns. The calculated voltages on different kinds of insulations will yield data for test voltages and waveforms required for insulation co-ordination of the coils. The calculations were made exemplary for poloidal field (PF) coils PF 3 and PF 6. The values of the frequency dependent self and mutual inductances of the turns were calculated with detailed Finite Element Method (FEM) models of the coils and implemented as lumped elements in the detailed network models. The values of the capacitances between the turns were calculated analytically. The voltage excitations on the coil terminals of the PF 3 and PF 6 coils were calculated with simplified models of PF coils, central solenoid (CS) coils, their power supplies and their electrical circuits. The calculated voltages on the coil terminals were used as voltage excitations to calculate in detail the voltage distribution within the PF 3 and PF 6 coils. The voltages on ground, layer, and conductor insulation were calculated with detailed network models of these coils. The calculated maximum voltage on ground insulation during the fast discharge of the PF 3 and PF 6 coils are within the specified design voltages. The voltages on turn insulation are higher than the specified design voltages.