DOL STARTER

Hello guys...
Today i will share information about D.O.L starter. which is direct on-line starter. The D.O.L starter are generally used for below 5 hp motor. some company's provide starters for 1-10 hp too.

The D.O.L starters are very basics in any industries. These starters are used to run the induction motors. Induction Motor draws more starting current during starting. to prevent such high amp and smooth starting the D.O.L are used.

D.O.L STARTER

              This is how D.O.L Starters are looks like. it may vary to manufacture to manufacture.

D.O.L Starters contains :- contactor  ,overload thermal relay, NO and NC contactor for                                                                start and  stop buttons. 

                                         (these all things you can see in  above picture)

                          This is control wiring of D.O.L Starter. as you can see in picture.

→ Generally the control wiring is on 220 V in India.(in some case the ratings are different like 110 V)

→ Procedure of  control wiring:-

(1) First the phase wire is go to the thermal overload relay NC contacts. 

(2) From the second point of NC contact the wire goes to STOP push button. (so the entire starter             current can stop by just one push button and control whole current)

(3) The second terminal of NC contact the wire goes to START push button. which is NO contact.

(4) The second terminal from NO contact the wire goes to mail contactor which is A1 in contactor. 

(5) Now we just have to put holding in our contactor so when we release start push button the                 circuit gets continuous supply. for that we have to take one wire from NC contractor's second              terminal to auxiliary contact which is NO contactor on main contractor. and the out going of              that contactor goes to A1. (without this holding step the starter runs till we press the start push            button. if we have such requirement we can do so.)

(6) Now the final wire is Neutral wire which is directly connected to A2 of main contactor.

→ Power wiring of D.O.L

    for the power wiring example...lets assume this contactor is main contactor of our D.O.L

→In the power wiring three phase power goes to this contactor. L1,L2,L3 are the incoming power lines in contactors and T1,T2,T3  are connected to thermal overload relay.

→This thermal overload relay is connected to main contactors out-going T1,T2,T3 and the out-going of this relay T1,T2,T3  is connected to motor.

→Adjust amp rating in thermal over load relay for safe point of motor. so that we can protect our motor.

→We can assemble D.O.L Starter using this parts and make our own D.O.L 

Advantages of D.O.L Starter:

1. Most Economical and Cheapest Starter
2. Simple to establish, operate and maintain
3. Simple Control Circuitry
4. Easy to understand and trouble‐shoot.
5. It provides 100% torque at the time of starting.
6. Only one set of cable is required from starter to motor.
7. Motor is connected in delta at motor terminals.

Disadvantages of D.O.L Starter:

1.  It does not reduce the starting current of the motor.
2. High Starting Current: Very High Starting Current (Typically 6 to 8 times the FLC of the motor).
3. Mechanically Harsh: Thermal Stress on the motor, thereby reducing its life.
4. Voltage Dip: There is a big voltage dip in the electrical installation because of high in-rush current affecting other customers connected to the same lines and therefore not suitable for higher size squirrel cage motors
5. High starting Torque: Unnecessary high starting torque, even when not required by the load, thereby increased mechanical stress on the mechanical systems such as rotor shaft, bearings, gearbox, coupling, chain drive, connected equipments, etc. leading to premature failure and plant downtimes.

                                                                                                                   ( ELECTRICAL ENGINEER)