Multi-coupled commutation analysis in EAST poloidal field quench protection circuits based on fuse model

Abstract

Abstract The poloidal field (PF) power supply (PS) system provides megawatt controllable energy to 14 PF coils in Experiment Advanced Superconducting Tokamak (EAST). The quench protection (QP) circuit in PF power supply system is designed to implement the superconducting coil protection in case of quench. A fuse employed in QP circuit plays an important role in diverting the coil current into the discharge resistor. However, the fuses in 12 QP circuits may turn off at different time due to different self-inductance of coils and initial current. Moreover, the PF circuits are quite complex due to the mutual coupling among the superconducting coils. This means that in fuse melting time the current variation in one of the coupled circuits may produce undesired current rising on the other PF circuits. This phenomenon has been found in experiment with the shot number 82,248. To analyze the multi-coupled commutation in QP circuit, a detail fuse model is necessary. This paper presented a detail fuse model at first. The fuse model consists of a two-dimensional pre-arc model considered the cooling effect of sand and a zero-dimensional arc model. Then the fuse model is integrated with the commutation circuit equations and the mutual coupling coils model. All described models are coded in a parallel computing program. Finally, the proposed integrated model is validated by comparing to an engineering test experiment data without plasma on EAST. The computed value is close to the experiment data, and the current rising phenomenon found in experiment is explained by the combined affection of time lag of fuses turn-off time and mutual coupling. The presented model is utilized to analyze the quench protection circuit response in a large variety of different conditions to ensure the safety of coils in quench scenarios. Furthermore, it might be applied in fuse design