Answer / 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

Answer / ravikumar.g

For the alternator excitation by using the DC voltage.

For this excitation the field will genarate the residiual
maganetisim in the alternator.

When the alternator start running this excitation voltage
is induce the more voltage.

Answer / nandan bikash sarma

when we will use ac as the exitation the direction of the

magnetic field (NORTH AND SOUTH pole) will change as the

direction of the current changes This will effect the

voltage that we getting from the alternator.So we use a dc

magnetic field

Answer / sanjay kumar

the field of the alternator consists of strong
electromagnets which create a magnetic flux linkage around
it.to make this magnetic field more stronger so that this
gets locked magneticaly with revolving magnetic field thru
stator armature when ac supply is given thru stator
armature core wid ease, dc supply or dc excitation is given
to it.

Answer / sanjay kumar

the reason why ac is not given to the excitation of field
of alternator lies behind the concept of mutual
induction.if ac field'll be given again the problem starts
when field current will rise and leads to deexcite
itself.hence it will not give uniform excitation like dc
current.

Answer / lavanya

If we give ac supply nto the field pulsating flux produced

Answer / 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.

Answer / niranajn

in order to give the field excitation

Answer / somesh saran

for exciteing the alternator field

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