What Is The Difference Between DOL and Star-Delta Starter?

Why Use Direct On Line (DOL) and Star-Delta Starter?

DOL means the motor is connected directly to the Line (Direct On Line) using one contactor with no starting circuit to lower the high starting current. Typically the Delta part of Star-Delta.

Star-Delta uses two contactors, one to start at a lower voltage in Star and one to run at a higher voltage in Delta configuration.

For example a 400V, 3-phase power supply Star applies phase to neutral or 230V. Delta applies the full phase to phase 400V.

Since power is proportional to voltage squared the starting current is three times less with Star-Delta.

The salient difference between DOL and Star-Delta starter

D.O.L( Direct On Line )Starter

1.    It does not decrease the starting current.

2.    It is cheap.

3.    It connects directly the motor with the supply for starting as well as for running.

Star-Delta Starter

1.    It decreases the starting current to 1/3 times.

2.    It is costly.

3.    It connects the motor first in the star at the time of starting then in the delta for running.

DOL Starter Motor Wiring Diagram

DOL Starter Wiring Schematic Diagram

You may like to know:

🔻Three Phase & Single Phase Motor Starter Wiring System with Low Voltage Control.

🔻Star Delta Starter Line Diagram and Its Working Principle.

 

Significant Design Features of Star Delta Starter:

1.    Contactor usually wide voltage band which is designed for longer endurance;

2.    Relay used for reliable overload protection;

3.    Easy to install facility;

4.    All edges should be smooth and safe to use;

5.    Overall quality and performance should follow local standards.

Significant Design Features of DOL Starter:

1.    DOL Starter Contactor should be a wide voltage band;

2.    Relay for reliable overload protection;

3.    A latch on the push button should keep the stop button locked, that prevents accidental starting;

4.    Should be any hum Free;

5.    Easy & quick mounting facility;

6.    Coil should withstand wide voltage fluctuations;

7.    Earthing wire should screw up for a safety measure;

8.    Manually reset the facility after each tripping;

9.    ON/OFF indications should be visible.

Some Demerits of DOL Starter Compare to Star-Delta Starter

Sponsored:

1.    DOL starter draws very high inrush current at starting i.e. 6-8 times the rated current of the motor which restricts its use to motors upto 7.5 KW only;

2.    DOL starter will cause high Thermal Stress on motors that will reduce motor life;

3.    High Starting current will lead to dips in voltage;

4.    The unnecessary high starting torque required by the load may cause increasing mechanical stresses on the motor;

5.    DOL starter is not feasible for 10KW or above-rated motors.

DOL starter is the suitable and cheapest method to start up a motor only for more normal sizes motors, larger motors must use the star-delta starter.

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