Development and Experimental Evaluation of a Prototype of the TF Secondary Quench Detection System for KSTAR Device

A prototype of the toroidal field (TF) secondary quench detection (SQD) system was developed and implemented with the Korea Superconducting Tokamak Advanced Research (KSTAR) device to carry out the design verification of the SQD. The SQD can detect a quench based on the change of absolute pressures (APs) and mass flow rates of helium in the cooling lines of the TF coils. If the primary quench detection system of the TF coils cannot detect a quench or the fast discharge of the TF coils cannot be carried out as planned, SQD should work to prevent the TF coils and the peripheral structures from severe damages. In addition, SQD should operate in the reliable and stable condition against the disturbances caused by the poloidal field coil discharge, plasma perturbation, and any faults of subsystems of the KSTAR device. The 2-out-of-3 (2oo3) voting configuration was applied to the SQD to enhance the reliability and stability of quench detection. The prototype SQD consists of AP and differential pressure transducers, signal interfaces, logic solvers, and interlock systems. All the transducers were selected from metallic types with no electronic circuit in order to reduce the failure rates caused by strong electromagnetic field and radiation around the tokamak. The transducers were installed in the manifolds of the helium inlet lines of the KSTAR TF coils. Their signals were amplified and compared with the reference voltage for quench decision in the signal interface unit. The quench signal generated by the signal interface unit was transmitted to the 2oo3 voting modules of the logic solvers. The design requirements of SQD were verified through testing the prototype SQD in the 2014 KSTAR campaign.