Why wont these two 20MW DY1 power transformers phase?

[imncntrl]

We have 2-20MW power transformers that we tried to phase so we could parallel.  I will call 1 of them T1 and the other MS.  T1 is a GE delta-wye (DY1) 115000-24940/14400.  MS is a WH delta-wye (DY1) multi-configuration set on 115000-24940/14400.  H1 and H3 are swapped on MS but i believe all that should do is swap my rotation.  They are both located in the same sub, fed from the same source.  The delta-wye polarity diagrams (DY1) are identical on the nameplates. Here is what the linemen read.  Remember A&C are swapped on MS and is not corrected below.
 T1-A to MS-A=28000
T1-A to MS-B=18000
T1-A to MS-C=12000
All of the other 6 combinations followed suit with the readings above.  Nothing would zero.  What is the phase shift and what are the possible reasons for this?

 

[prc]

When you swap H1 and H3,vector connection of unit MS becomes DY11. So you have to swap connections in T1 also for paralleling.

 

[imncntrl]

So I think what you are saying is that swapping H1 and H3 causes the 30 degree shift to go the opposite direction, therfore i wont have zero volts from any phase of T1 to any phase of MS?

 

[davidbeach]

Correct.

 

[DTR2011]

I am curious why you would consider swapping leads on two identical transformers.

 

[imncntrl]

prc & davidbeach Thank you very much.


Smallgreek. This stems from a reverse rotation to this sub from possibly 30 to 40 years ago. When the sub and line were rebuilt this year, they corrected the reverse rotation. This meant that when MS (the mobile sub) was brought in, they had to reverse the rotation there to match our customers. Now we are going to have to do a drop and pick to swap over to the new(er) transformer. When we do this, we will have to swap rotation on MS (just in case we have to use it again) and at the feeders going out.

 

[imncntrl]

Ok, one last question. Do the numbers above make sense at a 60 degree phase difference? When i run the numbers, i get 28000, 14400 and 14400.

 

[imncntrl]

Today was the day. H1 and H3 were swapped on MS and the two XFMR's phased. I guess the 6000 to -2000 volt difference between measured and calculated were due to loading and possibly impedance.

 

[DTR2011]

Thanks for the update and closure.