Derive R & X of transformers from Z%? 1

[rail1996]

Is it possible to calculate the zero sequence X, positive sequence R & X if I was just given the Z% of the transformer, say 11%?
Thanks in advance.

 

[jOmega]

No.
since Z = sqr.root of x² + r²

If you also know 'x' and 'Z' you can solve for 'r' and likewise, if you know 'r' and 'Z' you can solve for 'x'.

Kind of like asking if you can determine the Current
if I tell you only the Voltage.

When there are three elements, you need to know two of them in order to find the third.

 

[jghrist]

You need to know the copper losses of the transformer to get %R = (Cu Losses in kW ÷ Rating in kVA)·100. Then %X = sqrt(%Z² - %X²).

 

[jghrist]

Correction. Then %X = sqrt(%Z² - %R²).

 

[comalcoeng]

Look up your local power transformer standard.

The Australian Standard gives a range of X/R ratios for various MVA sizes of transformers. Therefore if you don't know X and/or R you can used the X/R ratio given in your standard to solve for X (or R) in the equation above from jghrist if you are given %Z.
Should give you a reasonable approximation.

 

[comalcoeng]

I may have been a bit quick off the mark there, this is assuming you are talking about a transformer???

 

[jbartos]

Suggestion to rail1996 (Electrical) Nov 7, 2003
Is it possible to calculate the zero sequence X, positive sequence R & X if I was just given the Z% of the transformer, say 11%?
///No. The zero sequence Xo of the transformer is often obtained from the manufacturer if it is not equal to the positive sequence X1. Positive sequence R1 and X1 can be obtained from the transformer test results. The above postings do not differentiate between zero sequence reactance Xo, positive sequence reactance X1 and positive sequence resistance R1.\\