Transformer Polarity

[habmann]

OK guys, I'm trying to put a subtractive polarity transformer into a substation that previously had an additive transformer. The new and old transformers were both delta-wye grounded.

Does any one have a link to information on how I will have to change the phases coming into and out of the station to allow this new transformer to phase in properly with the existing system.

Thanks

 

[dpc]

Just go by the transformer nameplate. Additive versus subtractive polarity is a transformer construction/winding issue and should not be an application concern.

You DO need to verify that the phase shifts are the same if this is a delta-wye transformer. This should be indicated on the nameplate.

 

[jghrist]

I don't think I've seen additive and subtractive polarity applied to three-phase transformers. ANSI standard for all three phase delta-wye or wye-delta transformers is for X1 to lag H1 by 30° with H1-H2-H3 phase rotation. I'm not sure what vector group a subtractive polarity delta-wye transformer would be. If these are banks of single-phase transformers, then they can be connected to have the same secondary phase relationship. You would just have to exchange X1 and X2.

It would help if you could link to a photos of the nameplates or winding diagrams.

 

[stevenal]

Jghrist,

I disagree. Subtractive versus additive tells you where the bushings are physically located. X1 marks the polarity end of the winding wherever it happens to exit the can.

Nameplates are not always correct. Always take voltage readings prior to closing the switch.

 

[jghrist]

Stevenal,

For single-phase ANSI standard distribution transformers, The X1 bushing coincides with with the H1 bushing on positive polarity transformers, but with the H2 bushing on negative polarity transformers. See p. 15.14 of

http://www.mhprofessional.com/downloads/products/0071467890/0071467890_ch15.pdf

 

[habmann]

Thanks for the quick reply guys.

When we put the new subtractive transformer in where there was once an additive transformer, there was a 30 degree phase shift between the phases on the secondary of the transformer and the rest of the system. Obviously this is an for our customer as they want the ability to parallel stations.

Basically as best i can tell, by changing from additive to subtractive there is a 180 degree phase shift in the secondary vector diagram. I'm looking for information on what phases i could switch to correct the 30 degree difference.

 

[stevenal]

Jghrist,

I stand by my statement. The difference in the two in your link is the physical location of the X1 and X2 bushings. In both cases Vx1x3 is in phase with Vh1h2. In order to parallel these two transformers, connect H1 to H1, H2 to H2, X1 to X1, X2 to X2 (if used), and X3 to X3.

 

[stevenal]

habman,

A 30 degree shift means one of your delta wye transformers is not. It is either wye wye or auto. There is no way to fix this by swapping phases.

 

[NAZ55]

This is the best link I found regarding typical transformer polarities

http://www.kilowattclassroom.com/Archive/TransfPol.pdf

 

[pwrengrds]

A lot of this discussion depends on if you will be paralleling the transformer or not. If you are paralleling the 30 degree phase shift is going to be a problem. If not then just worry about the differential 87T relay and phase rotation.