Abstract:
The goal of the thesis is to develop a novel technique to ~nhance the starting torque
and starting performance of a three phase squirrel cage induction motor by changing
the material composition of the end connections of the rotor. Magnetic materials
show significant skin effect properties at power frequency. This property has been
exploited in this research work to change the resistance of the end connections of the
rotor to enhance the starting perfonnanee of the squirrel cage induction motor.
Commercially available iron strips having relative pem1eability of the order of 5000-
6000 have been introduced in the rotor end connections for the purpose. At start, the
rotor induced current has a frequency of 50 Hz which shows skin effect large enough
to increase the rotor resistance. As the starting torque of the motor is a function of
rotor resistance, the starting torque increases appreciably together with the decrease
in the starting current. As the motor acquires its rated speed, the frequency of the
rotor current decreases, diminishing the skin effect and thereby reducing overall
resistance of the rotor. Thus the overall performance of the motor remains virtually
unaffected.
At first, experimentally determined motor parameters were used in MATLAB and
the performance of the motor was evaluated to ascertain the impact of skin effect on
the modified rotor end connections. The simulation results show appreciable
enhancement in the starting perfom1ance of the motor. Using the simulation
software, the optimum size of the magnetic materials placed at the end connections
has been determined to achieve high starting torque without affecting the overall
running performance of the motor. The dimension thus obtained is used to modify
the end connection of the rotor for experimental verification of the simulated results.
The experimental results are in good agreement with the simulated ones. It is worth
mentioning that, the starting current is also reduced significantly, as expected.
For further validation of the experimental results analytical study has also been
carried out with the help of software package SLIM.
