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why the excitation in synchronous machine is dc???
sanchayita
on 2011-08-17 09:30:00the rotating magnetic field is already enforced on the Stator and the rotor could now be a permanent magnet or a squirrel cage or a coil fed from an external source through a slip ring. by principle and design the slip ring option meets the requirements wherein a field of fixed orientation w.r.t the rotor but variable strength can be created mimicking a permanent magnet of variable strength.
Ajoy
on 2011-08-19 09:30:00ac supply produce time varying electric field but in the principal of sync m/c thi airgap mmf is not time varying only space varying so we use dc supply