Star Motor Connection

Schneker · Apr 28, 2014

Hi folks,

When I connect up a motor in Star supply goes to U1 / V1 / W1 and links fitted across U2 / V2 / W2 (depending on how terminals are marked)

Out of curiosity what would happen if supply was connected to U2 / V2 / W2 and U1 / V1 / W1 were linked out?

My initial thinking is motor would run in reverse, however as assumption is the mother of al xxxxups though I'd ask.

For the record I've not seen or done this so can't specify motor type, sort start, VSD or anything. It's purely a "what if" type thing.
Its amazing how the mind can wonder when you have too much time on your hands!

Cheers in advance.

Hawk · Apr 28, 2014

http://www.electriciansforums.co.uk/commercial-industrial-electrical/10495-star-terminal-block-arrangement.html

Darkwood · Apr 28, 2014

Never really give it a thought but now you ask i would say nothing would change it will still work as before.

Dont forget its the supply phase rotation that decides the direction of the motor which hasn't changed you have only flipped the windings around.

Exchanging 2 phases is the way to normally change the direction either by inverter parameter option or physically changing them over... this changer the direction the magnetic field rotates in.

Hmmm! got me thinking now!..

Note! ... This is the case for the 3ph standard induction motor under discussion and some motors will have direction altered when windings are reversed.

Schneker · Apr 28, 2014

I know what you mean about getting you thinking, I was reading a different thread and for some reason just started thinking about this.

As I say it's of no importance at all, just more of an "If a tree falls in woods" type thing.

Cheers.

Darkwood · Apr 28, 2014

Its this kind of thinking and curiosity that will put you one step ahead of the next guy because you seek understanding instead of parrot fashion learning and when a difficult issue arises you'll be the one that is more likely to resolve it so dont eat yourself up at questioning such a thing.

GMES · Apr 28, 2014

I don't think it would make a difference i am pretty sure the star point is whatever you make it when you wind the motor, and as DW said to change phase rotation, you simply swap any 2 of the 3 phases.

silva.foxx · Apr 28, 2014

TRY IT! :reddevil:

Then let us know the outcome, please.

happysteve · Apr 28, 2014

(Trainee).

Assuming 3ph standard induction motor...

Your motor will still rotate in the same direction. The only thing that will change is the rotation phase relative to your supply. By which I mean, say you had a marker on your shaft, a high speed camera and an oscilloscope so that you could see the voltages of all three phases. With your supply going to U1, V1, W1 (U2, V2, W2 shorted out) your marker would be in a certain position (say, 2 o'clock) when L1 was at the peak voltage. With your supply going to U2, V2, W2 (U1, V1, W1 shorted) your marker would be at the opposite position (in this example, 8 o'clock) when L1 was at the peak voltage.

If your motor's shaft position depended on the absolute phase of the incoming supply, or (perhaps more likely) interacted with another motor such that the absolute phase mattered (imagine two motors whose shafts were connected by something like a chain... now try twisting one of them by [360 deg divided by the number of poles] ) then it would matter. If it's a standalone system... meh.

Similar thing if you rotate all your connections, e.g. instead of:

L1 -> U1
L2 -> V1
L3 -> W1

... you did:

L1 -> W1
L2 -> U1
L3 -> V1

... the direction would be the same, but the marker on your shaft would be 120 deg different (ahead?).

(Trainee).

Knobhead · Apr 29, 2014

40 years of playing with motors and never given it a thought. Drew it out and then something stirred in the back of my mind. I have done it when I had to change the supply cable to a motor. It was a big cable so it was easiest to swap the star point over.

Now here’s another one for you consider. What happens if the star point is swapped on a ∆Y Dyn11 transformer?