why dc supply is given to the field of alternator

Answer Posted / ashis

DC supply is given to field of alternator in order to provide more excitation to it,so that it will magnetically luck with the rotating armature flux.if ac supply is given then-
-direction of magnetic field will change continously,which will effect in output voltage.
-uniform excitation cannot be made due to +ve,and -ve haif cycle of ac.
-it may happen rotor will not rotate at all

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