Air gap flux density in DC machine

[swayam007]

Why is it that the air gap flux density is flat topped at no load. What happens to it's shape when machine is loaded?

 

[jim hardy]

Is flux = mmf/reluctance? Is air gap constant under pole piece?


Have you looked up "Armature Reaction" ?

Unloaded, the only MMF is that from the field current. When armature current begins to flow, armature mmf changes shape flux .

Surely your textbook shows diagrams...