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3. Electrical fundamentals

Due to armature reaction in a DC motor

  • the leading pole tips are magnetically weakened.
  • the trailing pole tips are magnetically weakened.
  • the magnetic flux is restored by moving the MNA towards the GNA.

Explanation from PART66Online

Armature reaction is the distortion of the main field by the armature's own magnetic field. In a motor the armature flux adds to the main flux at the leading pole tips and subtracts at the trailing tips, so the trailing pole tips are weakened while the leading tips are strengthened. This shifts the neutral plane against the direction of rotation.

A

Afshinarabi asked · 12 May 2026

Due to armature reaction in a DC motor ,the leading pole tips are magnetically weakened .the armature flux opposes the main field flux ate leading tip and aids it at the trailing tip :due to magnetic saturation ,the net effect is a reduction in flux at the leading tip overall demagnetization.

Community Comments (2)

S
svenj88 12 May 2026
Strictly speaking, B is correct. In a DC motor armature reaction strengthens the leading pole tip and weakens the trailing one; what you described is the generator case, where the polarity of the armature current is reversed.
A
Afshinarabi 12 May 2026
yes.you right,thanks

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