In this lesson you’re going to learn how to change the winding connections of a three
phase motor from star to delta and vice versa using contactors.
To run a 3 phase motor under normal circumstances, you connect the three phase power to the incoming
terminals of the motor in the terminal box. But to better control the motors run request,
you can add a contactor here in the way of incoming power. I’ll call this the main
contactor. If you want the motor winding connections
to be in star, you can add a contactor here and then connect the power contacts of the
contactor to the W2, U2 and V2. If you short circuit the other ends of the
contactor’s contacts like this, when these contacts are closed these three motor terminals
will be connected and the motor winding connection will be in star. So I’ll call this the Star
contactor. With this wiring, when both the main and star
contactors are energized at the same time, you can say that the motor has started in
star connection. In this situation the main contactor works to flow the power to the motor
and the star contactor connects the right side motor terminals together and sets the
connection in star. Simple, right? Now let’s see how you can connect the motor
windings in delta. To do this you need to add another contactor.
I’ll call this the delta contactor. To connect the motor windings in delta, just as you did
for the star connection, you should first wire the three main contacts of the contactor
to the right side motor terminals. You then need to wire the other ends of the contactors
contacts to L1, L2 and L3 respectively. Now what happens in this situation? When both
the main and the delta contactors are energized and the contacts are closed, U1 will be connected
to W2, V1 will be connected to U2 and W1 will be connected to V2 and this is what you need
to have the motor winding connections in delta. So when the main and star contactors are energized
at the same time the connection will be in star and when the main and delta contactors
are energized the connection will be in delta. There is no buttons on these contactors where
you can demand the contactors contacts to be closed or opened. So to energize the contactors,
you have to connect them to an industrial controller like a PLC. In the next lesson,
you’re going to learn how you can control these contactors using a PLC.
That’s it for today’s video lesson.
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