why the field winding of synchronous machine is excited by dc source

Answer Posted / siva naik

The field wdg is placed on rotor of an synchronous machine
is exicited with dc source.when the exicitation is given to
rotor of the field wdg in its current will flow. so this
current setup an flux which expernice the torque will be
setup on rotor.acc to the farady law of electro magnetic
induction. at the same time revoluoing flux will be setup
on the aramature wdg.so that the stator aramature flux of
the mmf and stationary fileld flux will not be zero.after
certain speed the magntic locking tendcy will come to
picturei.e stator and rotor poles will be magentic inter
locking so that it will rotate with synchronous speed.

If rotor field wdg is is exicited with Ac source, in wdg
alternating flux will be setup on rotor.that the stator
aramature flux of the mmf and stationary fileld flux will
zero so that the machine does not provide any output

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