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A 3-phase squirrel cage induction motor is started with Star-Delta starter. What is the starting current of the motor?
1. 3-times the current with DOL
2. 1/3 times the current with DOL
3. 1/6 times the current with DOL
4. None of these above

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Correct Answer - Option 2 : 1/3 times the current with DOL

Star-Delta Starter:

In the star-delta starting method of induction motor, a two-way switch is used to connect the stator winding in star while starting and in delta while running at normal speed.

Star-Delta starter in a three-phase induction motor is used mainly to reduce the starting current.

In the star-delta starting method of induction motor, the starting current is reduced approximately by 1/3 times as compared to the original.

The starting torque will 1/3 times that it will be for delta-connected winding.

During starting the stator winding is star connected, so that voltage over each phase in the motor will be reduced by a factor of 1/√3 of that would be for delta connected winding.

Hence a star-delta starter is equivalent to an auto-transformer of ratio 1/√3 or 57.73 % reduced voltage.

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