single-phase induction motors require
just one power phase for its operation
they are found in domestic as well as
industrial use
main components of single-phase motors
are as follows
a rotor which is a rotating part
a stator winding which is stationary
it has got two parts one main winding
and one auxiliary winding auxiliary
winding is placed perpendicular to the
main winding
a capacitor is connected in auxiliary
winding
let's assume there is only one coil in
main and auxiliary winding to understand
it's working better
assume no current is flowing through
auxiliary winding
ac current passing through main winding
will produce a fluctuating magnetic
field
working a single phase induction motor
is simple
just put one rotor which is already
rotating inside such a magnetic field
you can note one interesting thing
the rotor will keep on rotating in the
same direction
the reason is as follows
the fluctuating field is equivalent to
sum of two oppositely rotating magnetic
fields
this concept is known as double
revolving field theory
effect of rotating magnetic field on
rotor is interesting
since magnetic field is varying
electricity is induced in rotor bars due
to electromagnetic induction
so here is a situation of current
carrying bars are immersed in magnetic
field
this will produce a force according to
lawrence law so rotor will start
rotating
but here we have got two such oppositely
rotating magnetic fields so torques
produced by them will be equal and
opposite
net effect will be zero torque on rotor
so rotor won't start it will simply buzz
but if we can somehow give this rotor an
initial rotation one torque will be
greater than other
there will be a net torque in same
direction of initial rotation
as a result the loop will keep on
rotating in the same direction
this is the way single phase induction
motors
work but one big problem remains how to
provide such an initial rotation
nikola tesla a famous yugoslav inventor
suggested one ingenious solution to this
problem
if we can cancel any of the rotating
fields we will be able to start the
motor
the auxiliary winding capacitor
arrangement is used exactly for this
purpose
auxiliary winding also produces two
oppositely revolving magnetic fields
one of them will cancel rmf of main
winding and other will get added up
resultant will be a single magnetic
field which revolves under specific
speed
such a magnetic field can give starting
torque to the rotor or the motor will
sell start
after the rotor has attained a specific
speed even if you cut the auxiliary
winding it will keep on rotating as
explained earlier
this cutting action is done through a
centrifugal switch
that's all about working of single phase
motors
thank you