3 winding transfromer model

L

Thread Starter

Lespoils

Hi,

I am doing a plant modeling on easypower for shortcircuit calculations and i ran into problems modeling a 3-winding transformer (xfo). I work from a single line diagram (SLD). i will try to be as explicit as possible.

The problem in short is i have only two impedances on the SLD, and Easypower asks for 3. I suppose the info i have is for primary to secondary (ps) and primary to tertiary (pt)and EasyPower needs secondary to tertiary (st). maybe i'm wrong.

Here's what i have:

the xfo is Delta-Wye with a neutral resistance on both secondary and tertiary

10.0/14.94 MVA
25/13.8kV
z=8.1% @ 10MVA
Rn=100A const. 2500A, 10s

6.5/9.7 MVA
25/2.4/1.385kV
z=6.9% @ 6.5MVA
Rn= 500A, 10s

Now the problem i have is EasyPower needs this table to be filled (hope it shows ok):
R1 X1 R0 X0 MVA base
Zps
Zpt
Zst

Now im thinking Zps = 8.1% and Zpt = 6.9%. How do i get R1 X1 R0 X0 from the Z= X% and how do i get info for the Zst ?

All help welcomed,

Lespoils
 
Lespoils...

stop hitting you head against a brick wall! You said it yourself... "Maybe I'm wrong"!

It can't be done! You end up with 3 equations having 2 unknowns.

Is the 3-winding Xfmr being considered because the 2-winding solution results in Short-Circuit Duty that is too high?

I suggest you search Web for a comparable 3-Winding unit of 16.5/10.0/6.5 MVA or having ratio 1./0.6/0.4!

Regards,
Phil Corso
 
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