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DIRECT ONLINE STARTER WORKING PRINCIPLE AND WIRING DIAGRAM


Scheme: DOL starter with panel
Direct on Line (DOL) Starter:
The simplest method of starting an induction motor is Direct On line(DOL) starter. The DOL starter consist of MPCB or MCCB, Contactor, over load release and fuse for protection. Thermal over load relay protect the motor from over load.  
The starter is controlled by Stop and start push buttons, an auxiliary NO contact is used for holding. Which means contactor is energized even though we release start push button. 

DOL Starter Wiring Diagram:
The control and power cable wiring shown in the diagram.

DOL starter wiring diagram

Parts of DOL Starter:

1. Contactor
2. over load release
3. NO-Normally open/start
4. NC-Normally close/stop
5. Fuse

DOL Starter Wiring:
The connection diagram of DOL starter include MCCB/MPCB, contactor, over load relay, Start push button, and stop bush button.

DOL starter wiring diagram
The 3 phase 415 volt 50Hz AC supply respectively R, Y and B are connected to contactor terminals L1, L2 and L3 via Fuse. Motor terminals U, V and W are connected to over load relay terminals. Over load Relay and contactor terminal are interconnected. 

Working Principle of DOL Starter:
When we push Start push button the contactor is closed, current flows through the contactor coil and the control circuit also. Now applying 3 phase voltage to the motor winding. The motor draw very high inrush current during starting. The motor will develop required rotor torque and begins to rotate. When the motor reaches full speed the motor current become normal. 

DOL Starter with enclouser

If we press stop push button power to the motor winding is disconnected. And supply to the motor is not available, if the motor is over loaded same operation will happen. No flow of current rotor speed come down gradually, rotor come to rest.

As the motor supply breaks, then the machine moves towards to relax. The contactor coil gets power supply even though we release start push button because it obtain supply from main contact as explained in the DOL starter wiring diagram.

Characteristics of DOL Starter:
1. Starting current is high 6 to 8 times full load current.
2. High starting torque.
3. Rotor Speed reaches within seconds.

Advantages of DOL Starter:
1. Easy to design and operate.
2. Economically cheap.
3. Provide full starting torque during starting.
4. Easy fault finding and troubleshoot.
5. Very compact easy to carry.

Disadvantages of DOL Starter:
1. For large capacity motor contactor size is big.
2. High starting current nearby 5-6 times of full load current.
3. Life of the motor will reduce.
4. DOL starters suitable only for small capacity motors.
5. Voltage dip.
6. Chance of cable melting because of high starting current.

Application of DOL Starter:

Application of DOL starter are primarily motor where high inrush current does not cause high voltage drop in the main supply.

DOL starters are used to control small capacity machines such as compressor, Pump, conveyor, blower, etc. ,

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Location: India

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