Transformer Tap Change and Short Circuit Impedance

Some number crunching is needed...I have the feeling that your numbers presented are mismatched/contradicted, causing some confusion as to what it is you are actually after - for me anyway.

Are you presenting a hypothetical question with a hypothetical transformer (winding) ratio of 6.93:0.44 from a real world transformer with a ratio of 6.6/0.44?

Have a look at LINK (some cool reading) & LINK

This is a real transformer.

6.93 is refering HT winding 6.6kV x1.05 (tapping of +5% on the primary winding where this transformer is having tapping of -5%, -2.5%, 0%. +2.5% and +5%).

Transformer input is 6.6kV.

Basically, for the above transfomer, customer's single line (existing plant) shows that transformer is having different impedance of 6.25%, 6.14% and 6.04% at different substation due to considering of voltage drop. From a guess, I would say that :

Z=6.25% is at 0% primary voltage tapping

Z=6.14% is at +2.5% primary voltage tapping

Z=6.04% is at +5% primary voltage tapping

However, I would like to know how to derive %Z at a given % tapping.

Eugene

Eugene,

Did you figure this out?

~Hubbard