Answer / md fakruddin

syn.motor isnot self starting.so we have start with some
other arrangements .one of the best ones is by damper
winding .damper winding is shorted on both side of rotor,as
by induction motor princepal motor rotate itself ,and
magnetic locking between rotor poles and stator occures and
motor runs.at no load armature current is not zero as there
are losses .and there is no relation between armature
current and load because motor hs started already .

Answer / amrita

When syn motrr is at no load, armature draws current
required for magnetisation.

As supply having some freq. so field flux continues 2
rotate at syn speed.

In syn motor speeed is constant from noload 2 full load.

Answer / phani

Due to residual magnetism some flux will be developed.

Answer / joy

Even on no load condition, the stator is connected
to 3ph ac supply. This 3ph ac supply produces a
rotating magnetic field, which links with the
rotor. Since the rotor was in a rotating condition
it continues to rotate as long as there is presence
of rotating stator flux. The rotor and stator flux
are synchronously locked with each other even on no
load condition.

Answer / kumar gaurav

IN FACT ARMTURE CURRENT FLOWS ALL THE TIME TO SET UP THE
AIR GAP FLUX "AS LEAKAGE AND MUTUAL FLUXES" WHICH ROTATES
AT SYNC. SPEED, BUT IN CASE OF LOAD REQD. MUTUAL FLUX
INCREASES AND HENCE THE CURRENT INCREASES WHILE IN CASE OF
NO LOAD 30%OF RATED CURRENT REQD. TO SET UP THE AIR GAP
FLUX.

Answer / utsav datta

After starting of the synchronous machine,armature current
is always present to set an air gap flux rotaing at
synchrous speed.

Answer / amita sharma

DUE TO RESIDUAL MAGNETISM THERE IS SOME FLUX WHICH INDUCES
EMF IN THE ROTOR AND THERE FORE THE MOTOR ROTATES.

Answer / rakesh

This is funny , how on earth could u assume that the no
load condition of a motor means open circuit condition ,
now listen the 3 phase supply given to stator produces a
rotating magnetic flux which reacts wit the initially at
rest field conductors to set up an induced emf lagging the
flux by 90* , but the field mmf set up leads the stator mmf
and rotates in the same direction as the rotating field (
note that i m already considering that the motor has
starting mechanism i.e. damper winding and later on dc
excitation ) thus the two rotating mmfs are stationary wrt
to each other but rotating at synchronous speed wrt
stator , since the rotor mmf i.e field mmf has the tendency
to follow the resultant air gap mmf so electromagnetic
torque acts that sets the rotor rotating . it must be noted
that the field mmf is proportional to field current while
the armature mmf is prprtnl to armtr crrnt , hence at no
load the armature mmf is maxm, because the arm current is
maxm, while with increase in load the current decreases and
hence the arm mmf , however the reasultant air gap mmf
always remain constant till voltage supply and the
frequemncy are maintained constant, it is only that the
field mmfs and the armature mmfs change in orientation and
magnitude.

Answer / sprabhu

Even No Load is connected the induced emf drives the
armature current as the coils are short circuited at the
ends, which makes the machine to rotate

a 3 phase slip ring induction motor is wound for 4 poles on stator and 6 poles on rotor; when 3 phase balanced voltage source at 50 hz is applied to motor it will run at a)1500rpm b)1000rpm c)750 rpm d)zero rpm

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