Radial flux high temperature superconductor motor using bulk trapped field magnets

This team has designed, built, and successfully run a radial flux high temperature superconductor (HTS) trapped field magnet (TFM) motor. The motor was run in a zero field cooled mode. This paper conveys several lessons learned about the use of TFMs in motor and generator applications. The state of the art of bulk TFM material is reviewed. Attention is given to the difficulties of activating TFMs in a practical machine design. The difficulties are based upon (i) the cooling time needed to field-cool the TFMs; (ii) the maximum field which can be produced at the rotor using only MMF on the stator; and (iii) the maximum time for which the stator current can be high without sustaining insulation damage. This is followed by a prediction of improvements that can be expected using two significant departures from a conventional three-phase permanent magnet design. Both departures involve the addition of MMF on the rotor using a hybrid wound rotor design. Finally attention is given to predicting performance when no special activation is employed.