Why we use Star Delta starter ?

Why do we use the Star Delta starter to drive the motor today? Will know this Star Delta Starter importance.

This question is very important, because it is asked a lot in electrical interviews. So what you have to answer inside the electrical interview, we will also know that today.

I will answer this in a practical way, so that you will understand it very easily .

Example-   Like we have a motor. Which runs through 3 face supply keys. Now I can use many ways to run this motor. Such as DOL Starter, Star Delta Starter or Soft Starter etc.

Friends, in many places we use Soft Starter instead of Star Delta Starter, but mostly we use Star Delta Starter only.

But our motor is much bigger. Which is running from HT line means running at high voltage. For that motor we use a soft starter.

Friends, now we know that on which motor we should apply Star Delta Starter, this question is also asked in the interview.

What size of motor will we use star delta starter

you just have to keep in mind that we use Star Delta Starter for 7.5 KW or larger motor. 7.5 KW means 10 HP. One thing must be kept in mind, many people say that it is necessary to install a Star Delta starter on a motor larger than 5 HP, friends this is wrong, it is not that we can run motor up to 7.5KW / 10HP on DOL starter. 

Example- Friends, if I tell you the experience of our company, then here we have also run a 30 HP motor on DOL Starter for the last 3 years. Friends, we have done this because our 30 HP motor, we do not turn that motor on and off again and again. When our motor starts once, then it keeps running without stopping for 7-8 days. So friends, we have driven this motor on the DOL Starter. If we turn this 30 HP motor off the DOL starter again and again, then our motor gets damaged. So friends, it is said that our 10 HP motor or above should be run on Star Delta Starter. So that our motor does not deteriorate and does not burn. 

But friends, now the question comes in our mind that why does our motor burn when run with DOL Starter?

Friends this is because all our motors have a current, which is less as per the load of the motor. But apart from this, there is another current inside all the motors, which we call Inrush Current .

What is a motor inrush current?

Friends, we also call the inrush current in other words as the starting current . It is quite easy to understand.

Like - we have a motor. To start this motor, it provided 3 face electrical supply. Now as soon as this motor starts, then how much current will my motor take at the time of starting it?

The starting current of this motor is always higher than the rated current of the motor. The rated current is always written on the nameplate of the motor. 

Keep this in mind - the starting current of the motor is 3 to 4 times its rated current. Three to four times means if a motor is taking 10 to 15 ampere current then friends the same motor takes 50 to 60 ampere current at the time of starting. But this motor does not take such a current, it only takes a few seconds of starting.

This motor will take more current for how many seconds of starting, it depends on the speed of motor rotor. The motor takes more current until the rotor of the motor reaches its Rated RPM after starting.

For example, if the nameplate of our motor is written at 2900 RPM. So until this motor's rotor reaches 2900 RPM, this motor will take more current.

Why does star delta starter work?

We use the Star Delta starter only to reduce this starting current. Friends, it is very important, if so much current comes out of the winding of our motor, then the winding of the motor can get burnt and the motor can get damaged. At the same time friends, we use the Star Delta starter. 

So friends, now we also understand how the current of our motor is reduced by the application of the Star Delta Starter.

Whenever you see the connection plate of the motor, you will see 6 points inside it. Now we connect it to the supply in two ways during its connection.

Star Connection 

Delta Connection

Star Connection 

When we connect the motor to the star, we shorten the three points on one side of it and add our electrical supply to the remaining three points.

Friends, in reality, the winding inside the motor is shortened to each other, and then we supply at the rest of the point, then every winding of our motor is getting 220 voltage ie single face. In this way, every single winding of the motor gets a single face in the star connection .

Delta Connection

In the delta connection of the motor, we shorten the face-to-face leaves in 6 points of our connection plate . And then we supply all the points.

Meaning that every winding of the motor is receiving 2 faces at the time of delta connection means that each winding carries 415 voltages at this time.

Why we use Star Delta starter?

If you are giving an interview in English, then you can speak this line.

Star Delta Starter is used to reduce the motor starting current (Inrush Current). Initially we connect motor winding in star but when motor RPM comes 70-80% of rated RPM we change motor connection into delta connection.

And if you are giving interviews in Hindi, then you can speak this line.

We use the Star Delta starter to reduce the starting current of the motor. While driving the motor initially, we run it in the star and when the RPM of our motor comes from 70 to 80%. Then we remove our motor from the star and add it to the delta. So that the winding of our motor is not disturbed by the starting current.