AC MACHINES-1 (66761) Theory
14. Realize the principle of starting of a 3-phase induction motor.
Starting of an Induction Motor
A three phase Induction Motor is Self Starting. When the supply is connected to the stator of a three-phase induction motor, a rotating magnetic field is produced, and the rotor starts rotating and the induction motor starts. At the time of starting, the motor slip is unity, and the starting current is very large.
The purpose of a starter is not to just start the motor, but it performs the two main functions. They are as follows.
- To reduce the heavy starting current
- To provide overload and under voltage protection.
The three phase induction motor may be started by connecting the motor directly to the full voltage of the supply. The motor can also be started by applying a reduced voltage to the motor when the motor is started.
The torque of the induction motor is proportional to the square of the applied voltage.Thus, a greater torque is exerted by a motor when it is started on full voltage than when it is started on the reduced voltage.
There are three main methods of Starting of Cage Induction Motor. They are as follows.