Synchronous Induction Motor
applications where high starting torque and constant speed are desired then
synchronous induction motor can be used. It has the advantages of both
synchronous motor and induction motor. The synchronous motor gives constant
speed whereas induction motors can be started against full load torque.
a normal slip ring induction motor having three phase winding on the rotor .The
motor is connected to the exciter which gives D.C. supply to the rotor through
slip rings. One phase carries full D.C. current while the other two carries
half the full D.C. current as they are connected in parallel. Due to this D.C.
excitation, permanent poles (N and S) formed on the rotor.
it is run as a slip ring induction motor with the help of starting resistances.
When the resistances are cut out the motor runs with a slip. Now the
connections are changed and the exciter is connected in series with the rotor
windings which will remain in the circuit permanently.
motor is running as induction motor initially high starting torque (up to twice
full load value) can be developed. When the D.C. excitation is provided it is
pulled into synchronism and starts running at constant speed. Thus synchronous
induction motor provides constant speed, large starting torque, low starting
current and power factor correction.