Page 738 - Basic Electrical Engineering

Figure 9.5 Split-phase single-phase induction motor: (a) single-phase induction motor with main
winding and starting winding; (b) connection diagram; (c) phasor diagram showing splitting of two
currents, I and I ; (d) split phasing with a capacitor in the starting winding circuit to increase the
m
a
angle of phase splitting

When a poly-phase supply is given to a poly-phase winding, a rotating
magnetic field is produced. This we have seen in the case of three-phase

induction motors. For a two-phase motor also, a rotating magnetic field will
be produced. A single-phase induction motor with an auxiliary winding is
similar to a two-phase motor. The current flowing through the windings will

have a phase difference of 90° or somewhat less than 90°.
Creating a phase split in the currents flowing through the two windings

will help produce a rotating magnetic field effect on the rotor. The rotor will
develop a starting torque and start rotating. The direction of rotation will

depend on the way the connections of windings are made across the supply.