The starter which can be used to reduce the voltage during starting of an induction motor is:

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ALP CBT 2 Electrician Previous Paper: Held on 22 Jan 2019 Shift 2

Answer 1

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.
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.
The starting torque will 1/3 times that it will 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.