Operational Characteristics of HTS Coils With Flux Diverters in Semipersistent Mode Under Alternating Magnetic Field

This paper deals with the effect of magnetic flux diverters on the current decay behaviors of high-temperature superconducting (HTS) coils which operate in semipersistent current mode (PCM) under alternating magnetic field. In superconducting synchronous machines, the HTS field coil can be designed to operate in PCM to obtain a steady magnetic field during operation. Due to the alternating magnetic field from the armature winding, the HTS field winding experiences an external magnetic field. As a result, the additional magnetization ac loss in the field coil would be induced, and it affects the current decay characteristics. In order to improve the current decay behavior of the HTS field coil, the use of flux diverter made of magnetic material can be considered. In this paper, we experimentally investigated the current decay characteristics of HTS field coils with magnetic flux diverters under alternating magnetic field. The measurement setup, which is composed of HTS field coil and armature coil, was fabricated. The measurement test of the current decay on the HTS field coil in PCM operation was carried out as functions of the amplitude and frequency of the armature coil.