- For having smoother output voltage from DC machines its commutation must be as ideal as possible.
- In order to have good commutation the flux density in the air gap must decrease gradually from maximum value under the center of the pole to zero on the interpolar axis.
- The flux distribution which drops abruptly from maximum to zero leads to commutation difficulties and magnetic noise.
- Thus to achieve good air gap flux distribution the pole faces are curved which improves the commutation and contributes to a smoother DC output voltage.
Why does curving the pole faces in a DC machines contributes to a smoother DC output voltage from it?