DOL Starter
Used upto 5 HP
Does not decrease the starting current
it is cheap
It connects directly the motor with supply for starting as well as for running
Star Delta Starter
Used 5HP to 20 HP
Decrease the starting current by 1/3 times
It is costly
It connects the motor first in star at the time of starting in delta for running
Auto Transformer Starter
Used above 20 HP
Decrease the starting current as required
It is more costly
It connects the motor according to the taping taken out from the auto trasnformer