Why star delta starter is preferred with induction motor?

At the time of starting an Induction motor tends to draw high-current (7 to 8 times higher than rated current ). In small motors (<5hp) it’s okay. But for larger motor the starting current may be so high that it may damage the stator coil or even the power cables.
Star-Delta starter is used to reduce the starting current . Initially the motor windings are connected in star pattern . Then after a preset time the contactors make a delta pattern and the motor runs . While connected in star pattern , voltage across the stator coils is equal to the phase voltage (line voltage /1.3 aprox) , so the value of starting current is reduced.

Star delta starter is preferred with induction motor due to following reasons:

  Starting current is reduced 3-4 times of the direct current due to which voltage drops and hence it causes less losses.

• Star delta starter circuit comes in circuit first during starting of motor, which reduces voltage 3 times, that is why current also reduces up to 3 times and hence less motor burning is caused.
• The operation of the star-delta method is simple and rugged.
• It is relatively cheap compared to other reduced voltage methods.
• Good Torque/Current Performance.
• The components require very little space.
• The most significant advantage of using Star-Delta starting is the huge reduction in the starting current of the motor, which will result in a significant cost saving on cables, transformers and switch gear. 

Star delta starter is preferred with induction motor due to following reasons: • Starting current is reduced 3-4 times of the direct current due to which voltage drops and hence it causes less losses.
• Star delta starter circuit comes in circuit first during starting of motor, which reduces voltage 3 times, that is why current also reduces up to 3 times and hence less motor burning is caused.