Paralleling of Dyn11 transfromer with Dz0 Transformer 2

[sramesh]

Good day to you

LV switch board with 2 incomers + Buscoupler(with sync facility) is currently fed by one 2.5 MVA 6.6kV/415V, Dyn11 transformer and Proposed to add one more transformer from second source of 11kV. Engineering Contractor proposes a Transformer of 2.5MVA 11kV/415V Dzn0 vector connection. Request your opinion on what will be phase angle in the secondary side of both Transformer and will it be possible to parralel both transformers?

your valuable inputis appreciated

Ramesh

 

[jghrist]

Not without an interposing transformer or phase-shifter. See faq238-1090

 

[waross]

I hope that there is a misunderstanding here. Possibly in the information given to the contractor.
Is there a phase difference between the 11kV system and the 6.6 kV system that you haven't told us about?
Is one of these systems fed from an islanded generator?
Parallel operation as it pertains to vector groups assumes that both the primaries and secondaries are connected in parallel.
You are connecting systems in parallel, not the same as transformers in parallel.
There may be a vector shift between the systems due to multiple transformation steps on the way to 11kV and 6.6kV respectively.
The contractor may know something that we don't, do some more checking. You do want an answer before you proceed with this installation. It may be OK or you may need a different transformer.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[dpc]

Not possible to say without additional information on the 6.9 kV and 11 kV systems, as Bill indicates.

As jghrist says, there will be definitely be a phase shift between those two transformers, but this could be compensating for existing phase difference between the two primary sources.

 

[sramesh]

Thanks Bill and DPC,

Both the sources are from the same national 132kV Grid, I will check the upstream transformer schemes of 6.6 and 11kV sources.

Thanks again for the quick responses

Regards
Ramesh

 

[jghrist]

I didn't catch that the two primaries are from different systems. The Dzn connection might be to allow for different primary system phasing. As noted by others, there is no way to know without knowing the phase relationship between the 6.6 kV and 11 kV systems.

 

[dpc]

If possible, I recommend checking the transformer nameplates yourself and making careful note of the phasor relationships. Or have someone take photos of the nameplates and send them to you. This is not something to delegate or to trust a system one-line on.





David Castor

http://www.cvoes.com

 

[nawao]

In the 2.5MVA 11kV/415V Dzn0 transformer, the LV phasor is in phase with the HV phasor while in the 2.5 MVA 6.6kV/415V, Dyn11 transformer the LV phasor leads by 30 degrees the HV phasor, so you cannot parallel both transformers.

 

[dpc]

nawao,

If you assume the 11 kV and 6.6 kV sources are in phase, you are correct. But we do not yet know that.

David Castor

http://www.cvoes.com

 

[pwrtran]

And the phase rotation either A-B-C or A-C-B for each source.

 

[sramesh]

Thanks to all for the inputs,It is clear after site verification, The incoming scheme of both the lines are different and the new transformer is proposed Dzn0 will compensate the phase angle differnece.


Thanks again

Regards
Ramesh

 

[dpc]

All's well that ends well. Thanks for the feedback.

David Castor

http://www.cvoes.com