why dc supply is given to the field of alternator

Answer Posted / anthony

To begin with if ac is given then the problem would be
that the field flux linking with the armature , i.e.imagine
the arm. cond. looking into the field flux , as the field
flux passes the arm. conductor (field = consider ac
excitn.) the arm would see two zeros, one being the natural
zero of ac excitation and the other being the zero produced
due to the field's continous forward motion . Hence the
nett emf produced would however reach one zero in halfcycle
but would have intermediate sags in its waveform (imagine
this concept from the view of the arm . cond.). This is the
reason why the arm. is not given ac excitn.

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