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COMPARISON OF A SQUIRREL-CAGE AND A SLIP RING (OR PHASE WOUND) INDUCTION MOTORS

26. COMPARISON OF A SQUIRREL-CAGE AND A SLIP RING (OR PHASE WOUND)
INDUCTION MOTORS.

Property Squirrel cage induction motor Phase wound induction motor
Starting The motor can be started with a star-delta starter and it eliminates the hazards of slip rings, brush gear etc. The motor requires slip rings, brush gear, short-circuiting device and starting resistance etc.
Overhang Less Large
Space factor in slots Better Poor
Cooling The losses can be dissipated much efficiently since the end rings are bars and there is more space for providing an efficient fan. Most of the space, is taken up by the overhang and less space is left for the provision of a good cooling fan; thus the cooling is not quite efficient.
Efficiency High efficiency only for machines, which are not redesigned for high starting Low efficiency.
Starting torque For plain squirrel cage motor starting torque is poor which cannot be increased in an ordinary way. Starting torque can be increased by the insertion of external resistance in each phase of the rotor
Copper losses Since overhang is less and space factor is better the copper losses are small. Due to large overhang and poor space factor, the copper losses are more.
Maintenance Less More
Cost Cheaper (since there are less components and less labour required for winding). Costlier