Vernier reluctance motor

Reluctance motors depend for their operation on the existence of alternate zones of higher and lower permeance between stator and rotor round the periphery. In the usual form of reluctance motor this is provided by salient poles on the rotor. In the vernier form of reluctance motor it results from both stator and rotor having teeth, separated by open slots, with the number of teeth on the stator slightly different from the number on the rotor. Then there are zones where stator teeth are most nearly opposite to rotor teeth and the permeance is larger, alternating with zones where the stator teeth are opposite to rotor slots and the permeance is smaller. Such motors run `synchronously', with the rotor speed a certain fraction of the speed of the axis of the applied m.m.f. The torque obtainable depends in a rather complicated manner on the proportions of the dimensions of teeth, slots and air gap and on the waveform of m.m.f. Various relationships giving peripheral force and output are derived, and the conditions are found by which the output can be maximised. The possible output coefficient so estimated is compared with the output coefficients of various other forms of machine. It appears from this comparison that the best output coefficient possible is intermediate between the coefficients for a d.c. motor and for an induction motor. Any suggestion that the vernier construction might provide an exceptionally large output coefficient is thus disproved.