- A single-phase repulsion-induction motor combines the constant-speed characteristics of the single-phase induction motor with the good starting characteristics of the repulsion motor.
- The stator of this machine has a simple single-phase winding like that of single-phase induction motor. The rotor, however, is built up of laminations, each of which has two concentric sets of slots. These slots contain two distinct windings; in the outer slots is wound a commutator winding similar to that of a D.C. armature, while in the inner slots is a cast aluminium squirrel-cage winding which clamps the laminations.
Fig. 17 (a) illustrates an armature for a repulsion induction motor complete with a squirrel-cage winding.
Fig. 17. (a) Repulsion induction motor.
At starting and during the acceleration period, the magnetic flux produced by the stator embraces only the commutator winding in the outer slots owing to the high reactance of the squirrel-cage. The motor starts up virtually’ as a repulsion motor and develops a high starting torque: As the motor speeds up the reactance of the squirrel-cage decreases. so that this winding assists the commutator winding to supply the running torque.
Fig. 17 (b) shows the speed-torque characteristic of repulsion-induction motor.
Merits. The repulsion-induction motor has the following merits:
(i) High starting torque.
(ii) Fairly good speed regulation.
(iii) Major virtue is the ability to continue to develop torque under sudden, heavy applied loads without breaking down.
Uses. Such motors are suitable for all single-phase power applications which require a high starting torque and constant speed when running; they also operate at a very high power factor. They are particularly well adapted to drive machine tools, lifts, hoists, mixing machines, centrifugal pumps, fans and blowers.