Cageless induction machine

A novel type of a.c. machine is described which has an asynchronous mode of operation but which does not rely on induced currents or losses in the rotor. It has a polyphase stator winding and a laminated rotor with `directional¿ magnetic properties, and thus closely resembles a reluctance motor. In contrast to the reluctance motor, however, two rotating main fields are produced, and the machine is self starting (without a cage winding) and runs up to a speed which is inversely proportional to the sum of the two pole numbers. It may also be run synchronously by doubly feeding the stator winding with alternating and direct current. The machine is basically a low-speed device. On theoretical grounds, it was expected to have an asynchronous performance comparable with that of a conventional squirrel-cage induction motor, but this has not been borne out in practice. It is shown, however, that there is scope for further development by making use of an axially laminated form of rotor construction.