Star-Delta Starter PLC Program and Wiring - Part 4

As you know, there is some sort of copper windings in every electrical motor. When you connect electricity to them, the motor turns on and starts rotating.

To make things more simple and clear, we represent all of these motor windings with three simple symbols. The upper ends are shown as U1, V1 and W1 and the lower ends are shown as U2, V2, and W2. What you’re going to learn in part 4 of Star-Delta Starter PLC Program and Wiring, is that how to reach these winding ends on electrical motors in real world.

The arrangement for the terminals is the same as I’ve previously explained for the motor windings with a small difference. For example, the motor shown in the image below has three terminals that have incoming power connected to them and are shown as U1, V1 and W1.

But the lower terminals here have a small difference compared to the previously discussed winding schematics.

In the winding schematics, the lower ends were named U2, V2 and W2.

but, on the terminal box of the motor, the first terminal is W2, the second is U2 and the third is V2.

This can be the schematic for the terminal box of a three-phase motor. With these winding ends, if you want to start the motor in star connection, you can connect these three terminals together like before.

Now if you want to start the motor in delta connection, just like what you’ve learned before, you can connect U1 to W2, V1 to U2 and W1 to V2.

To limit the current that the motor draws in the start-up phase, you need to start the motor in star connection first. When the motor gains sufficient speed, the connection should change to delta. But to do this, obviously you can’t wire the terminals in star connection and then change the connection to delta while the motor is energized and running. You need a way to be able to change the connections automatically.

For that purpose, you can simply use a contactor. In the next blog post, you’ll learn how to change the connection of the motor windings automatically using contactors.

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Star-Delta Starter PLC Program and Wiring - Part 3

‍Star-Delta Starter PLC Program and Wiring - Part 5