Improvement of Flux Deflection With Light-Weight Magnetic Material

Intensified magnetic flux generated by high-temperature superconducting (HTS) field-pole magnet has been studied for the key to improve the machine efficiency of industrial application. An increase of the critical current density allows a further improvement of the operating current in HTS ship propulsion motors. In our previous work, an effect of flux deflection to the critical current of HTS magnet was evaluated. Magnetic flux deflection is a technique to control perpendicular flux to the a-b plane of the HTS tape by magnetic material. Thanks to the magnetic properties of the material, heat loss reduction was confirmed. In this paper, the outcome of the verification experiment with a lightweight magnetic material FINEMET adopted as magnetic flux deflector will be described. In response to the results which increase of the total weight of HTS winding by mounting a magnetic material, weight reduction of the magnetic flux deflector is necessary for practical employment. Compared with the carbon steel, FINEMET has higher saturation magnetic flux density and higher permeability. I-V curve was measured while a pair of the magnetic flux deflectors were installed on the prototype HTS coil connected to the DC current source. In the case of adopting light-weight magnetic material, the reduction of heat generation was confirmed to be 27% which is equivalent to the previous material. At the same time, a weight reduction of 73% was achieved. Results show that FINEMET is effective to improve flux deflection. It is one of feasible material which can be adapted to the field-pole magnet of practical HTS propulsion motor.