Investigation of the transient electrical behavior of the ITER central solenoid model coil (CSMC) during safety discharge

The electrical behavior of the ITER central solenoid model coil (CSMC) exposed to the voltage rise occurring during a safety discharge initiated by a counter acting current switch has been studied. A detailed network model has been set up to determine the transient overvoltages inside the windings of the CSMC when the coil is subjected to transient voltages. The analysis takes into account the frequency-dependent resistance of the conductor in case of high-frequency oscillations, and considers the influence of the extensive instrumentation cables of the coil. The model´s accuracy is demonstrated over a frequency range up to 30 KHz. The total inductance and capacitance of the coil model are in very good agreement with previously obtained measurements and design values. The discharge circuit has also been modeled in order to accurately simulate the discharge process. It was found that the terminal voltage generated during a safety discharge causes transient oscillations inside the windings. However, they do not cause overvoltages exceeding the maximum acceptable insulation stress. The influence of several parameters of the discharge circuit on the rise time and shape of the resulting terminal voltage was investigated. Controlling these values might be a measure to prevent excessive internal oscillations for larger coils with lower natural frequencies than the CSMC.