A capacitor-start single phase induction motor is switched on to supply with its capacitor replaced by an inductor of equivalent reactance value. It will

A capacitor-start single phase induction motor is switched on to supply with its capacitor replaced by an inductor of equivalent reactance value. It will

Right Answer is:

Small hp motor can start but large hp motor will not start

SOLUTION

  • If capacitor-start single phase induction motor is switched on to supply with its capacitor replaced by an inductor of equivalent reactance value then small hp motor can start but large hp motor will not start,
  • The Single-phase Induction motor is not self-starting because of phase shift between the main winding and starting winding is practically zero and the current lags the voltage.
  • To make it self-start there should be sufficient phase displacement between current and voltage.

    Capacitor Start Phase Difference

  • The start winding and run winding are already inductors, so adding inductance in series with the start winding does not produce much phase difference between the start and run windings hence the torque is not developed until there is some phase shift between these two windings.
  • The winding inductance creates a phase delay. It is only used on small motors because of its low efficiency, but it is smaller and more reliable than designs that require a start capacitor on a separate winding.

    Split phase difference
  • The capacitor is used in a single-phase Induction motor for creating a phase shift. The addition of a capacitor creates a phase shift of 90 degrees between the two windings which makes it self-starting.
  • The addition of an inductor for a high Hp motor won’t make the motor self-starting ( even if it starts it will rotate at very less speed) and inherently will lead to an increase in losses only. 
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