Quench Detection System for the KSTAR Superconducting Toroidal Field Coil

Abstract
A high reliability of the quench detection system is required for protection of the superconducting coil. The primary system is the quench voltage detection (QVD), which uses resistive voltages, while the secondary system uses hydraulic parameters, such as the temperature, pressure and mass flow. To set up the criteria of QVD for the Korea superconducting tokamak advanced research (KSTAR) toroidal field (TF) coils, we studied the quench behaviors of a TF coil, where quench was initiated after a transient disturbance had been applied to the initial heated zone, which was located near the highest B-field region in the winding pack. Hot-spot temperatures and quench voltages were analyzed after quench initiation. The threshold voltage and the maximum tolerable delay time for QVD were determined so that hot-spot temperatures were kept within an allowable temperature range. The simulation indicates that the threshold voltage is 100 $imes$ 150 mV and that the delay time is approximately 1s. Based upon this analysis, the TF QVD was fabricated and tested in the experiment on the KSTAR central solenoid model coil (CSMC). Additionally, the self and the mutual inductive voltages measured at the QDV should be compensated for below the threshold voltage. For this reason, a simple compensation method was proposed and was proven to decrease the inductive voltages by less than 50 \%.
Keywords: KSTAR, QVD, Hot-spot temperature, Quench

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