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Repulsion-start Induction Motor

  • As its name implies the repulsion-start induction motor starts as a repulsion
    motor with its brushes set to the maximum torque position. When the load has been accelerated to about 75 per cent of synchronous speed, a built in centrifugal device places a shorting ring in contact with the com mutating bars, converting the armature to squirrel-cage rotor. The motor then runs as induction motor on its induction characteristic (Fig. 16).
  • Although at one time this type of motor was used almost exclusively where high starting torque was required, it has been replaced in nearly all cases by the capacitor motors because of the following reasons:

(i)                           Requires more maintenance.

(ii)                        More expensive.

(iii)                      Makes quite a bit of noise on starting.

(iv)                      Causes radio interference when starting.

(v)                         Cannot be reversed easily.

Repulsion-start motors, despite these disadvantages, are still used in integral-horsepower sizes because of the following reasons:

(i)            High starting torque.

(ii)            Low starting current.

(iii)            Ability to accelerate a heavy load more rapidly than high-capacitance dual capacitor motors.