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AIM:-
To study the construction, working principle and performance characteristics of Synchronous Induction Motor.
APPARATUS REQUIRED:-
3 Phase Synchronous Induction Motor with loading arrangement
Auto Induction Starter panel – 1
TPDT knife switch - 1
Tachometer - 1
THEORY:-
In the 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.
Consider a normal slip ring induction motor having three phase winding on the rotor as shown in the figure.
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.
Initially 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.
As the 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.
PRECAUTIONS:
1. The motor should be started without load.
2. The rotor resistance starter should be kept in the maximum resistance position while starting.
3. The field potential divider should be kept in the maximum resistance position.
PROCEDURE:
1. Note down the name plate details of the motor.
2. Connections are given as per the circuit diagram.
3. Close the TPST switch in order to supply the rated voltage to the motor.
4. Start the motor by closing the TPDT switch (position 123) with the rotor resistance starter in maximum resistance position to run the motor at rated speed.
5. Change the position of TPDT switch (position 1’2’3’) in order to excite the rotor by DC source where the excitation should be given gradually through the potential divider to maintain the synchronous speed.
6. The resistance if the stator can be measured using Dc supply with voltmeter and ammeter or directly using a multimeter.
RESULT:
The working principle and performance characteristics of the synchronous induction motor have been studied.