Around the world it famous with name DOL starter or direct on line starter.This is the most common starting method available on the market and at basic stater for all motor application.The starting equipment consists of only a main contactor and thermal or electronic overload relay.The disadvantage with DOL starter is that it gives the highest possible starting current.
A normal value is between 6 to 7 times the rated motor current but values of up to 9 or 10 times the rated current exist.Besides then DOL starter draw the starting current there also exists a current peak that can rise up to 14 times the rated current since the motor is not energized from the the first moment when starting.
What is DOL starter or Direct on line starter?
The values are dependent on the design and size of the motor, but in general, a smaller motor gives higher values than a larger one.
During a direct on line start, the starting torque is also very high, and is higher than necessary for most applications.The torque is the same as the force, and an unnecessary high force gives unnecessary high stresses on couplings and the driven application.
Naturally, there are cases where this starting method works perfectly and in some cases also the only starting method that works.
For more detail,please refer the MOTOR CONTROL HANDBOOK :-