Quench Simulation and Detection in KSTAR PF Magnet System

Abstract

To detect quenches in the Poloidal Field (PF) magnet system is more difficult than the Toroidal Field (TF) magnet system due to excessively high inductive voltages generated by PF pulsecurrents and plasma currents. According to reference scenarios being considered so far, the maximum voltage across the PF coils is inductively generated up to about 3.5 kV during the start of plasma (SoP) stage in a very short time period. The voltage measured by compensation of the inductive voltage should be below a certain level which is called as the quench voltage threshold. However, the compensated voltage might be higher than the threshold even with the well-designed compensation schemes. Accordingly, the quench voltage threshold and the quench protection delay time should be properly determined for the quench detection not to take a false action which could cause the fast energy discharge. From the quench simulation using the calculation of hot spot temperature and the resistive voltage growth as a function of time, the proper values of the quench detection parameters of the PF magnet system were derived for the maximum hot temperature rise to be limited within 150 K.

Study on quench detection of the KSTAR CS coil with CDA+MIK compensation of inductive voltages

“…1. Geometry of the KSTAR PF magnet system, which includes CS Coils (PF1-4) and PF coils (PF5-7) [3]. …”

Performance of the Quench Detection System for the KSTAR CS Magnet System

“…1 [1], [2]. The upper and lower coils of PF1 and PF2 are electrically series-connected in the cryostat, whereas those of PF3 and PF4 are individually powered.…”

“…The upper and lower coils of PF1 and PF2 are electrically series-connected in the cryostat, whereas those of PF3 and PF4 are individually powered. The CS magnet system operates with AC currents, which generate inductive voltages across coil terminals during the operation [2]. This AC operation make it difficult for the Quench Detection System (QDS) to make a precise decision regarding a quench event because of its corresponding effects such as voltage induction, helium pressure rise, reduction or reversal of helium flow.…”