Answer / k.prakashchandra

You can not have fixed north and south poles in the field
with AC

Answer / raja

When ac supply is provided, the poles will alternate between north and south pole for each half cycle of supply. so there wont be any magnetic interlocking with stator to run at synchronous speed as the polarity changes at the rate of supply frequency. hence for magnetic locking DC supply is used for excitation

Answer / sunit saini

the working principle of syn/mac. is mag. locking which is
not possible in ac

Answer / lokesh

We need a statoinary magnetic flux in synchronous machine,
this flux will be cut by the rotor.

Answer / anil

Yes we can have a ac in rotor.But then we will not call it as a rotor.It will be stationary but this rotor has to be connected to a 3phase supply .Then it will produce a rotating magnetic field which will interact with the stator and create emf.

Answer / ert

BT SUBMIITIN

Answer / shailesh_358

DC excitation provides high starting current required for
excitation

Answer / madhu

to make sym machine self starting

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