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Armature Reaction in DC Motor

Definition of Armature reaction-Interaction between main field flux (which is generated by the stator on supplying the external current) and the induced field flux ( which is generated in the armature of the machine) is called armature reaction.Due to the armature reaction the strength of the main field flux become slightly weak

Armature Reaction in Motor

armature reaction in dc motor


When external current is fed to the stator of the DC motor then a magnetic flux is setup in the stator of the motor.When this induced magnetic flux is cut by the conductors of the armature then according to lenz's law an emf is induced in the armature conductors,due this induced emf a current start to flow in the armature conductor.Due to this armature current a magnetic flux is setup in the armature.This induced magnetic flux interact with the main field flux and the resultant flux is strengthened at the leading pole and weakened at the trailing pole

Due to armature reaction sparking occurs at the brushes due to the delay in commutation.To minimize the effect of armature reaction interpoles are placed in the main field pole.Interpoles generates the required voltage to neutralize the emf of self induction in the armature.Motor poles have a polarity opposite to that of the following main pole in the direction of rotation of armature.Since the interpoles are connected in series with the armature, the change in the direction of the armature current,changes the polarity of the interpole.  

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