Answer / phani

if ac supply is given as excitation supply the poles are
changed for every half cycle .d.c suuply gives the consant
pole

Answer / aero.diwa

ACCORDING TO FARADAYS LAWS, ONLY ONE ROTATING PART(FIELD OR
CONDUCTOR)AND OTHER SHOULD BE STATIONARY.
IF IT IS NOT DONE THE FARADAYS LAWS CANT BE APPLIED.IF WE
GIVEN A.C SUPPLY TO THE ROTOR OF THE ALTERNATOR(AC SUPPLY
HAVING HAVE BOTH +VE & -VE CYCLES)& ALSO THE ROTOR IS
ROTATING PART.IN THIS THE AC SUPPLY AND ROTATING ARMATURE
BOTH ARE IN MOTION,THATS WHY THERE IS NO INDUCED EMF IN THE
STATOR(B'COZ THERE IS NO CHANGE IN FLUX i.e E=d(PHI)/dt.)

Answer / adarsh

it is not possible to use AC supply for excitation because
for the excitation need stable magnetic field which is not
possible to got in AC, AC polarity is changed in every half
cycle, so it must be need DC for excitation.

Answer / ashutosh

yes i am agree with you PHANI

Answer / rk

by appling ac there will be no relative elect field motion
between field and armture which will prevent generation of
emf.

Answer / vikas

If we give ac supply the function of the motar remains same
but the thing is that as ac voltage depends on frequency
eddy current losses increases.This can be eliminated by
laminating.

Answer / chandrashekar

we will be using coils with no of turns in place of
permanent magnet. when there is a electric power supply by
these coils we can it as excitation

Answer / don

THERE WILL BE NO DEFINITE POLES IN ROTOR,ALSO THE EDDY
CURRENT LOSSE WILL BE MORE IF AC IS GIVEN AS EXCITATION.

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