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BHEL Engineer Trainee Electrical 2019 Paper

Option 3 : \(\frac{1}{{\sqrt 3 }}\) of normal voltage

ST 1: General Knowledge

5609

20 Questions
20 Marks
20 Mins

- 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.**