Inductance Compensation for the Quench Detection of the KSTAR CS Coil

Voltage-based QD is the primary way to guarantee that magnets can be protected against overheating because of its fastest response. However, central solenoid (CS) and poloidal field (PF) coils are operated in pulse currents, so resultant inductive voltages could be hundred times higher than quench detection voltage thresholds. For this reason, some inductive voltage compensation techniques have been adopted to discriminate the quench-induced resistive voltage from the voltage induced by self and mutual inductances between coils. Cowound voltage sensors and bridge circuits are used to eliminate inductive voltages, but achieving additional rejection of remaining inductive voltages is necessary. Simple comparison between bridge voltages or cowound voltages from upper and lower PF coils, which are symmetric to the equatorial plane, has been well operating for KSTAR. Another is mutual inductance compensation, where mutually induced voltages are estimated by using predefined inductances and temporal derivatives of PF coil currents and compared with measured voltages. Rogowski coils to measure the current derivatives of CS/PF coils, precompensated voltages with inductive voltages largely eliminated beforehand, and a data analysis system were prepared for the KSTAR PF 1 coil. Analysis of inductive voltage compensation was presented with the operational result in 2015 KSTAR campaign.