Study on a Magnetic Flux Detection Coil for Detection of Normal Transitions in a Hybrid Single-phase Bi2223 Superconducting Transformer by the Active Power Method

The authors have been developing a small and light power source with a hybrid single-phase Bi2223 high temperature superconducting (HTS) transformer. The transformer consists of a primary copper coil and a secondary Bi2223 superconducting coil and can output current of 500 A. For safe operation of the transformer, it is important to detect normal transitions in the transformer and to protect it from excessive heating in the normal area. The authors have presented a protection system based on the active power method and magnetic flux detection coil. However, in the conventional method, the active power does not become zero in a superconducting state due to AC loss and therefore incorrect recognition may be caused. In this paper, the authors propose a method to reduce the loss signals by configuration and mounting position of the magnetic flux detection coil. Through experimental results for a hybrid single-phase Bi2223 superconducting transformer, the authors show that the proposed method can detect the normal transitions more accurately than the conventional one.