Segmented-rotor disc motor

The steady-state synchronous behaviour of a large-airgap, single-sided segmented-rotor disc machine is investigated theoretically and experimentally. Two methods of calculating normal forces using Maxwell's stresses are described. Their predictions are compared with measured results. A two-axis model is shown to give acceptable results for large-airgap machines but the use of the harmonic airgap flux density is preferred for small airgaps. Equivalence is drawn between Maxwell stress and energy methods in an Appendix. Prediction of the synchronous performance of a prototype motor by existing methods of analysis is shown to be possible provided that an airgap fringe factor is included in calculation of the direct and quadrature axis reactances. Experimental and theoretical results for torque, current, power factor and efficiency are presented and compared. The pull-in capability of a reluctance motor was found to deteriorate when operated with a large airgap, and ways of overcoming this problem are suggested.