PLC Programming

Star-Delta Starter PLC Program and Wiring - Part 3

Learn how you can run a motor with star-delta starter

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When you turn on a large electrical motor, the inrush current may damage your equipment and electrical network. As one of the prevention methods, you may choose to start the motor with star-delta starter.

In this blog post that is brought to you by RealPars, you’re going to learn how you can run a motor with star-delta starter to reduce the inrush current of the motor.

Let’s look at the schematics for the motor windings. These three upper ends are shown by U1, V1, and W1 and the other three lower ends are shown by U2, V2, and W2.

To turn the motor on, you need to connect the three-phase power to the three upper ends of U1, V1, and W1.

Now let’s see how you can connect the motor windings in star or delta connection.

For the star connection, you just need to connect the lower ends of the windings U2, V2 and W2 together. If you then connect U1 to W2, V1 to U2 and W1 to V1, the winding connection will be in delta.

When you connect the motor windings as a star, the current that the motor draws is reduced to one-third of the normal start current.

The basic concept of star-delta starter is to first run the motor in the star connection for a few seconds to reduce the start current. Then when the motor has gained sufficient speed, change the winding connections to delta.

Actually an interesting point here for the startup phase of the motor which, as I said, draws more current. If you think about this concept, this is what you can see in the other aspects of your life as well. The startup phase of anything in your life draws more energy and focus. Isn’t it interesting? There is fascinating fixed rule for starting everything in this world! What can you learn from this?!

Now that you’ve learned that by changing the winding connections you can reduce the start current of the motor, you may be wondering how you access these motor winding ends to connect power to them and also change their connection from star to delta?

There is a connection board on any three-phase electrical motor where you can access all six winding ends that we’ve explained here. In the next blog post, we’ll talk more about this connection board.