# Errors in Three-Phase Transformer Schematics

#### peajay

Joined Dec 10, 2005
67

The image:

Here I think that the connections of T1 and T2 which previously went to T3 should be connected to nothing rather than together. As the schematic is drawn, it shows the circuit with shorted T3 coils, not with open T3 coils as the text says.

I think every schematic on that page is in error, in that the bottom set of A-B-C lines is backwards, and should be C-B-A to be correct. (or the connections from the transformers should be reversed) Of course, everything I know about three phase transformers I learned from that page, so I probably shouldn't be questioning it, but at least the Y-Y and ∆-∆ connections I think should be A to A, B to B and C to C. The others I can't claim to really understand, but I would think that the A phase in the Y configuration should match with the B and C phases with the ∆ configuration, but in the images on that page it goes to A-B in one and A-C in the other. Like I said, I don't really know, but it doesn't seem right.

Anyway, I have to say this site is awesome. I was actually going to make my own electronics site once, but then I found this one and realized it was way better than what I was planning to do. I was going to make my own site because once I had some things straight in my head, I thought it'd be nice to explain them better than the books and websites I had to learn them from, but then I saw that this site explains them exactly they way I had planned to. So instead I just tell everyone to come here.

#### Dcrunkilton

Joined Jul 31, 2004
422
Originally posted by peajay@Dec 11 2005, 04:48 AM

The image:

Here I think that the connections of T1 and T2 which previously went to T3 should be connected to nothing rather than together. As the schematic is drawn, it shows the circuit with shorted T3 coils, not with open T3 coils as the text says.

I think every schematic on that page is in error, in that the bottom set of A-B-C lines is backwards, and should be C-B-A to be correct. (or the connections from the transformers should be reversed) Of course, everything I know about three phase transformers I learned from that page, so I probably shouldn't be questioning it, but at least the Y-Y and ∆-∆ connections I think should be A to A, B to B and C to C. The others I can't claim to really understand, but I would think that the A phase in the Y configuration should match with the B and C phases with the ∆ configuration, but in the images on that page it goes to A-B in one and A-C in the other. Like I said, I don't really know, but it doesn't seem right.

Anyway, I have to say this site is awesome. I was actually going to make my own electronics site once, but then I found this one and realized it was way better than what I was planning to do. I was going to make my own site because once I had some things straight in my head, I thought it'd be nice to explain them better than the books and websites I had to learn them from, but then I saw that this site explains them exactly they way I had planned to. So instead I just tell everyone to come here.
[post=12370]Quoted post[/post]​

On your first point concerning the open-delta, I think that I have been able to verify to my satisfaction that the short needs to be removed. The fact that my very old "Standard Hnadbook for Electrical Engineers" made a reference to shorting out the 3rd transformer, which does not appear in the open-delta somewhat confused the issue for me. After consulting other references, I can find no actual diagram with a short across the line, which makes no sense anyway. The delta is open in other references. Therefore, I will fix that.

The other diagrams may not actually be technically incorrect as long as no single pair of phases has been swapped which would reverse motor rotation. Two swaps would keep rotation the same. The phases shift in doing a delta-Y or Y-delta transformation. So, the output phases do not exactly correspond to the input phases. However, irregardless of technicalities, the widely accepted convention is along the lines that you suggest for the other transformer diagrams. I will be changing the wiring of those as you suggest to un-confuse this issue. This will make our diagrams look more like other references.

Dennis Crunkilton

#### Dcrunkilton

Joined Jul 31, 2004
422
Originally posted by Dcrunkilton@Dec 11 2005, 03:08 PM
On your first point concerning the open-delta, I think that I have been able to verify to my satisfaction that the short needs to be removed. The fact that my very old "Standard Hnadbook for Electrical Engineers" made a reference to shorting out the 3rd transformer, which does not appear in the open-delta somewhat confused the issue for me. After consulting other references, I can find no actual diagram with a short across the line, which makes no sense anyway. The delta is open in other references. Therefore, I will fix that.

The other diagrams may not actually be technically incorrect as long as no single pair of phases has been swapped which would reverse motor rotation. Two swaps would keep rotation the same. The phases shift in doing a delta-Y or Y-delta transformation. So, the output phases do not exactly correspond to the input phases. However, irregardless of technicalities, the widely accepted convention is along the lines that you suggest for the other transformer diagrams. I will be changing the wiring of those as you suggest to un-confuse this issue. This will make our diagrams look more like other references.