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Friday, August 19, 2022

Induction Motor Starter ? || DOL (direct on line) starter

Here we are going to discuss about Induction Motor Starter ? || DOL (direct on line) starter. In an industry, there are a lot of induction motor used for their specific work. For induction motor, it need to give supply from source so that rotating magnetic flux will created and it will helps to rotate the rotor certain lag by synchronous speed. Before buying or placing an induction motor, we need to know about its rated voltage, operating frequency, rated current, rated power and so on.

What is induction Motor Starter ?

Induction motor starter means how the connection will be done to the motor from supply for motor operation. It means how can we connect supply to the motor so motor will run after supply power. Also, starter include on/off or start/stop of the motor as requirement. There are different types of method for induction motor to start. Mostly, a simple connection is done which is known as DOL ( direct on line) starter because this is very easy and cheap method for induction motor starter.

DOL (direct on line) starter

In this type starter, the induction motor is directly connected to the supply line. It can be star connection or delta depending on requirement or desire. In star connection, phase voltage will be root 3 ( √3 ) times less that the line voltage but its phase current and line current will be same. That mean, on same line voltage, the star connection provide less power as compared to delta connection. But in delta connection, it draw more current so it produce more heat and losses also winding insulation/coating maybe worn out. 

Simple connection of DOL

This is the simple connection to the motor (maybe star or delta).
Induction Motor Starter

In general, star connection is done in the industry for its easy connection and less heat. For control, we need to put NO switch and NC switch. NO switch means "normally open" switch and NC switch means "normally closed" switch i.e. NO switch is in open condition before and after operation ( It will be closed only when we operate/push the switch after and before that it will be in open condition) and NC switch is in closed condition before and after the operation ( It will be open only when we operate/push the switch after and before that it will be in closed condition). Also for control mechanism, it required contactor, we also already discuss about it earlier. This is a simple connection diagram for DOL starter. Here NO switch will help to start the motor by energizing the contactor after pushing the NO switch and the motor will run until NO switch is push continuously. After push off, it will go to its normal stage (open condition) i.e. motor will stop. If we push the NC switch, it will stop the motor while motor is running.


DOL starter on Induction Motor

The above diagram is a simple DOL starter which is normally not use because one need to push the NO switch all motor running time which is tedious job for any people especially, if motor need to run for long time. For that problem, we have a solution by connecting the NO switch of contactor. NO switch will hold the position on contactor that maybe closed or open.
Note :- For holding purpose, We always use NO switch of contactor. 

Real field/practical DOL starter

Practical DOL starter on Induction Motor

This is a practical DOL starter which is generally used in our system or in an industry. Here NO on contactor will hold the circuit so that after one time pushing the NO switch, it will hold the circuit and operate it until NC switch is not pushing.

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