Double Revolving Field Theory of Single Phase Induction Motor
two magnetic fields represented by quantities OA and OB of equal
magnitude revolving in opposite directions as shown in fig:
resultant of the two fields of equal magnitude rotating in opposite directions
is alternating. Therefore an alternating current can be considered as having two
components which are of equal in magnitude and rotating in opposite directions.
above, it is clear that when a single phase alternating current is supplied to
the stator of a single phase motor, the field produced will be of alternating
in nature which can be divided into two components of equal magnitude one
revolving in clockwise and other in counter clockwise direction.
stationary squirrel cage rotor is kept in such a field equal forces in opposite
direction will act and the rotor will simply vibrate and there will be no
the rotor is given a small jerk in any direction in this condition, it will go
on revolving and will develop torque in that particular direction. It is clear
from the above that a single phase induction motor when having only one winding
is not a self-starting. To make it a self-starting anyone of the following can
(i) Split phase
Shaded pole starting.