Analysis of Charging Strategy for a Large Conduction-Cooled HTS Magnet under AC Conditions

A large-bore conduction-cooled high-temperature superconducting (HTS) magnet has been designed and fabricated at Institute of Electrical Engineering, Chinese Academy of Sciences (IEE, CAS). The magnet consists of ninety REBCO double-pancake (DP) coils with an inner diameter exceeding 450 mm, which is operated with alternating current (AC) to generate an ultra-low frequency alternating magnetic field. When the HTS magnet is charged up/down, it will be exposed to an alternating magnetic field and suffer large losses, which has a negative effect on the thermal stability of the magnet. In addition, the amplitude of the alternating magnetic field generated by the magnet is affected by the radial shunt of the turn-to-turn resistance. In this paper, the effects of charging speed and current amplitude on the losses and magnetic field of the HTS magnet under AC operating conditions were investigated. Firstly, an analytical model of the magnet was developed based on the equivalent circuit model and the finite element method. Subsequently, an optimized charging strategy was proposed to improve the alternating magnetic field to satisfy the application requirements better while ensuring the thermal stability of the magnet. Finally, the effectiveness of the strategy was verified by conduction-cooled experiments. The proposed charging strategy can effectively improve the alternating magnetic field while reducing the losses of the magnet. It provides guidance for the charging process of conduction-cooled HTS magnets under AC conditions in the future.