Instruction for filling the Impedance tab on ETAP 12.6.0 2

[GustiGian]

I want to ask all about the instructions for filling the impedance tab for a 3-winding transformer on etap 12.6.0. I don't know much about three winding transformers and I need some help figuring out what impedance value I should use. Honestly, I am confused because based on design information about impedance is only written "17.4% base on 25 MVA 20-6.6 kV".

 

[Kiribanda]

You should get the transformer test report from the manufacturer. It should give,
1)Pos seq impedance values of PS, ST & PT
2)Zero seq impedance values of PS, ST & not given in the test data. But you may request from
the manufacturer if you want to do a somewhat accurate system study.
Otherwise use typical values from a handbook.
If the 3-wdg transformer has got a DELTA tertiary, same method to be applied.
Pl. read the help mode of ETAP user guide before everything. It explains in detail.

 

[argotier]

Is the transformer 50/25/25 MVA - 20/6.6/6.6 kV ? I mean with two LV windings, both 6.6 kV and the same power?

If this is the case, the design information only gives you:

about impedance is only written "17.4% base on 25 MVA 20-6.6 kV"

because both LV have the same impedance towards HV. It's the most likely, at least.

You only lack the LV1-LV2 impedance. Only the trx designer/manufacturer can give you this value, as it will depend on the windings design and relative placing. If you can't get the value, assume it would be greater than the HV-LV impedances (2 to 5 times) at the same power base. But this is just an educated guess.

For the zero sequence impedance, again if there is no more data available, you could estimate it if you know the vector group of the transformer.
See this other thread about it: thread238-469460

Hope it helps.

 

[GustiGian]

Thanks for your advice Sir.