So as to achieve sparkles commutation, brushes are always placed on

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Electrical Engineering XYZ MCQ

So as to achieve sparkles commutation, brushes are always placed on:

  1. MNA
  2. GNA
  3. Either of above
  4. None of above

Correct answer: 1. MNA

Explanation: In case of DC machine, to achieve sparkless commutation, brushes are placed on the MNA (Main Neutral Axis). The MNA is the axis along which there is no induced emf when the coil is rotated in the magnetic field, and it is where the direction of current changes or where the production of zero electromotive force (e.m.f.) occurs.

Under no-load conditions, the MNA coincides with the GNA (Geometric Neutral Axis). However, under loaded conditions, the armature reaction causes a distortion in the main magnetic field, leading to a shift in the neutral zone. To ensure sparkless commutation under both loaded and unloaded conditions, brushes are positioned on the MNA.

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