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When a DC series motor runs on no load:

When a DC series motor runs on no load: Correct Answer the speed of motor is very high

A DC series motor should always be started with load because at no load it will rotate with dangerously high speed

Important:

  • When the motor is connected across the supply mains without load, it draws small current from the supply mains
  • This current will flow through the series field and armature, the speed tends to increase so that back emf may approach the applied voltage in magnitude
  • The increase in back emf weakens the armature current and hence the field current
  • This cause again increases the speed so the back emf
  • Thus, the field continues to weaken and speed continues to increase until the armature produced such centrifugal force that it is coming out from its shaft and gets damaged

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