Electrical Machines
In dc machines, the field system has to be provided on stator unlike synchronous machines Where in it could be on any member, because

 it reduces field structure iron losses
 commutator action is not possible otherwise
 dc machines are comparatively low rating machines.
 it gives more uniform air-gap flux distribution

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Electrical Machines
The following statements relate to compensating winding (CW) and interpole winding (IW) of a dc machine : 1. CW neutralizes the armature reaction under a pole pitch 2. IW is connected in series with armature circuit 3. IW produces mmf in the commutating zone only 4. CWmmf is directed along the brush axis 5. Mmf produced by IW is equal to armature mmf From these, the correct statements are

 2, 3, 4
 1, 2, 3, 4 and 5
 2, 3, 4, 5
 1, 3, 4, 5

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