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LMRC Assistant Manager Electrical: 2020 Official Paper

Option 1 : T/3

CT 1: Network Theory 1

11608

10 Questions
10 Marks
10 Mins

Y - Δ starting:

- 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.
- 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.

Both starting current and starting torque are reduced by \(\frac{1}{3}\)