Answer / sindhejs

Since the suplly is of 3 phase sinusoidal in nature, flux
produced due to htis in the stator is of alternating in
nature.This flux is cut by the stationary conductor on the
rotor, thus eddy currents are induced in the rotor circuit
by Lenz's law.To overcome force produced by these currents
and induced flux the rotor starts rotating in the direction
of flux.

Answer / surya

in indction motor, motor windings alos plays a very
important role. these are also placed 120 degree apart. so
when you apply 3 phase supply, it forms a magnetic pole in
the stator. as the 3 phase supply is sinusoidal, the formed
magnetic pole starts rotation in one direction,that is the
synchronous speed of motor. as per farday's law of
electromagnetic induction, when a conductior cuts the
changing magnetic field and it's circuit is closed, an emf
is induced in it. so an emf causes curent to flow which
experiences force on conductor. rotor starts rotating.
for better understanding make a diagram of 3 phase
windings 120 degree physically apart. r-y-b and simulate
the 3 ph supply. hope this is informative.

Answer / manav

The three phase windings of stator of a 3-ph ind. motor are
placed 120 deg space displaced.
Also the supply given to these is a 3-ph supply with time
lag of 120 deg b/w each phase.
thus, the expressions for mmf of each phase at any instant
at an angular position $ in air gap is given by:

Fr=Fm*cos(wt)*cos($)
Fy=Fm*cos(wt-120)*cos($-120)
Fb=Fm*cos(wt+120)*cos($+120)

adding all these three gives the resultant:

F=Fr+Fy+Fb= (3/2)*Fm*cos($-wt)

This is like a travelling wave [F=Fm*cos(kx-wt)] that
rotates with speed w.

Answer / govind

in ac motor is only stator & rotor, then how magnetic field
is rotate around the armeture

Answer / dinesh verma

in indction motor, motor windings also plays a very
important role. these are also placed 120 degree apart. so
when you apply 3 phase supply, it forms a magnetic pole in
the stator. as the 3 phase supply is sinusoidal, the formed
magnetic pole starts rotation in one direction.

what is meant by phase transformation ratio in induction motors?

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