If normal supply voltage is applied to the stationary motor then a very large initial current is taken by the stator for short while. This will lead to excess copper losses in the winding which will overheat the motor. This will produce line voltage drop, that in turn, will affect the operation of other electrical equipments connected to the same line and heavy starting current may damage the motor winding. In order to avoid these problem, a starter is used to start the induction motor safely.
The motor is designed to operate as delta connected motor under normal conditions. The motor starts as a star connected motor and the voltage per phase is VL/√3. The starting torque is reduced as it is directly proportional to square of stator voltage and there is jerk while switching from star to delta.
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| Star-Delta Starter |
Start Mode
The 3 pole 6 way switch is kept in start mode. This will connect terminal R', Y' B' of stator winding to each other. This act as star point. The supply is connected to R,Y,B terminal of the stator winding. Thus in start mode the stator winding is connected to form the star.
Run Mode
The 3 pole 6 way switch is thrown in run position once the motor accelerate. This will connect the terminals in following manner:
R→B', Y→R', B→Y'
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