T-Model Values for Zero Sequence Network for YNyn0d1 Transformer

[dmnichol]

I'm trying to determine the zero sequence impedances for a T-model of a step down transformer so that I can perform phase to ground short circuit current calculations on the low voltage side of the transformer but i don't understand the H-L%, H-T% and L-T% format that the manufacturer supplied as shown below.

Here are the technical details on step down transformer provided by the manufacturer:
21/28/35 MVA ONAN/ONAF/ONAF
Vector group: YNyn0d1
Winding Type: Core
138 kV Grounded Wye High Side
4.16 kV Tertiary Delta
12.0 kV Grounded-Wye Low Side

Guaranteed positive sequence impedances, H-L% = 7.0
Z1 on rated MVA base, at 85°C H-T% = 10.66
and mid tap L-T% = 2.36

Guaranteed zero sequence impedances, H-L% = 6.15
Z0 on rated MVA base, at 85°C H-T% = 8.68
and mid tap L-T% = 2.53

 

[dmnichol]

Sorry the formatting didn't come out right when I submitted this. Here is what it should look like:

Guaranteed positive sequence impedances,
Z1 on rated MVA base, at 85°C
and mid tap
H-L% = 7.0
H-T% = 10.66
L-T% = 2.36

Guaranteed zero sequence impedances,
Z0 on rated MVA base, at 85°C
and mid tap
H-L% = 6.15
H-T% = 8.68
L-T% = 2.53

 

[7anoter4]

First, it is not a “T-transformer” but a “Three-windings transformer”.
The rated power of 21/28/35 MVA ONAN/ONAF/ONAF it seems to be the H-V[138 kV] rated power, only.
You have to transmit the rated power for secondary 12 kV and tertiary 4.16 kV and to say for which power level the impedances are calculated. Then, you can calculate the impedance for each one of windings.

 

[MKFPE]

Sorry for the delayed reply and I hope this is of use. I'm retired and do not look at the forum often these days.

I have uploaded an old worksheet for LibreOffice Calc, Excel, etc. I created to transform the impedances to the "T" format.

Some actual transformer data is entered from an old project, just replace with your data.

No guarantees, check the math and compare results to another calculation as a sanity check.

Note in the "T" format some impedances may be negative.

 

[7anoter4]

Sorry MKFPE it is not possible to open this excel file.