Answer Posted / sunil guru

DOL-- As its meaning suggests "DIRECT ON LINE" the motors are provided the direct supply without any changes & this starters are only used for protection purpose (not for soft starting of the motor)and are preffered only upto 10 Hp motors in industries....

STAR DELTA--- are preffered beyond DOL range
first reduced voltage(1/3 of supply V) is given to the motor & as it reaches 70-80% of its rated speed full V is given. (it is the function of changing 4m star to delta)is done to reduce the starting current and to protect the motor.......

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