transformer sequence impedance 1

[tonyflair]

I have 3 single phase transformers that have no physical common bond between each other except for the fact that there terminals are connected delta-wye (from a generator (delta) to the main bus (wye)). Each transformer is 250 kVA, 600V-25kV, Z%=6.02.

For simulation purposes, I want to consider the positive sequence and zero sequence impedances for the above 3 phase transformer bank.

Is the positive sequence impedance -> 0+j0.0602 (approx.)
and is the zero sequence impedance equal to the positve (since that wye side is solidly grounded) even though this 3 phase transformer is make up of 3 single phase transformers ?

Is the positive sequence equal to the zero sequence in this case ?

Thanks a lot

 

[jghrist]

The zero-sequence, as seen from the wye side, is equal to the positive sequence 6.02% in this case. The zero-sequence as seen from the delta side is infinite.
[tt]
o-----o o-+--ZZZZ----o
| 6.02%
Delta | Wye
|
o----------+----------o
[/tt]