Short Circuit impedance of an ABB Three winding transformer 2

[Eelctrical]

Hi, can you help me to read the data of the short circuit impedance of an ABB Three winding transformer. I have to put the values in to a equivelant Circuit (75MVA, 110/11kV).

Thank you

 

[argotier]

Hi Eelctrical, what i can get from the data you posted is that you have a 75/37.5/37.5 MVA - 110/11/11 kV three winding transformer.
The rated impedance at full power (75 MVA) with both LV windings working (37.5+37.5) is 14.5% (@75 MVA).
With only one LV winding at its full capacity (37.5 MVA) you get an impedance of 13.7%(@37.5MVA).
Lastly you have an impedance of 27%(@37.5 MVA) between both LV windings.
It seems there is also a 90kV for the HV winding that changes all the impedances.
Do you have more info? The nameplate would be useful.
Hope this helps.

 

[Eelctrical]

Hi argotier, thank you so much for Your reply. The way you read it also makes sense. But it seems still difficult to convert into a equivelent Circuit With Three windings. I have understood it in this way: Take the 15%-14.5%-14% as already calculated value Zp Zs1 Zs2 seperately, and derived the equivelant Circuit. However, the Note 1, that disabeys with my assumption.

I have tried to find more information as well, but unluckily no more, there was no nameplate provided.

 

[argotier]

It should be stated more clearly in the datasheet, frankly.
For the equivalent circuit perhaps this helps (from IEC 60076-8):

You already have the Zab,Zbc,Zca (or Z1-2,Z2-3,Z1-3 in this case) impedances and you can get the Za,Zb,Zc to make the circuit. Be sure to reference all the impedances to the same power.

 

[prc]

I believe Note 3 values are the measured values at max, rated and min taps. HV seems to have dual ratings by connecting winding parts in series and parallel to get 110 & 90 kV. Za, Zb and Zc can be calculated as per formula in IEC. You will find that Za value will be almost zero. Design is done like this so that any loading on one LV will not affect the voltage on the other LV winding terminal.

 

[Eelctrical]

@argotier @prc, thank you for Your kindly reply. Yes, I have checked With ABB, prc is right, they are measured at the max, rated and min taps.

According to za=0 (ideally), then Zb can be derived from 13.7% between windings 1-2 37.5MVA 110V/11kV and the same as Zc. 14.5% (1-2&3), 75MVA, 110/11kV gives the paralleled Zb//Zc when both LV windings are Powered. What do you think?

https://www.eng-tips.com/viewthread.cfm?qid=464578

 

[Eelctrical]

@PRC, I am very amazed by Your post and answers. That is the reason I join in this forum actually. How I can ask questions to you directly? Please let me know.

Thank you.

 

[prc]

Electrical, there is nothing great in my answer. I am doing similar work for many years...that is all. In this forum we do not share any mail id. If you have any query on transformers(not the ones that you can get from google or text books) you can raise as a separate question and we shall try to answer.