Per Impedance Data, Resistances and Reactances of Transformers tend to follow normal patterns according to the ratings.
The Graphs I have seen for %R and %X, are determined by measurement of load loss on Z test.
This would relate to the entire Transformer - including the Core, not just a single winding.
(I mention the Core for its losses and etc.).
Quantities expressed in Per-Unit or % are the same regardless of whether they are are referred to the Primary side or the Secondary side.
Per the second question, Per-Unit quantities are one thing - as listed above, but the Transformer's Regulation will result in situations where if the load current and Secondary voltage are at rated values, the Primary voltage must exceed rated value.
This is found by using this Equation:
Ep = Es+Is(Rs+jX)+IpRp
* Ep = RMS volts at primary terminal (phasor);
* Es = RMS volts at secondary terminal (phasor);
* Ip = RMS amperes in primary (phasor);
* Is = RMS amperes in secondary (phasor);
* Rp = Ohms resistance of primary winding;
* Rs = Ohms resistance of secondary winding;
* X = Ohms reactance of Transformer.
The excess is the Regulation.
Regulation for Lagging Power Factor is:
Gr = [(Rr+Pr)Â²+(Xr+Qr)Â²]Â¹/Â² -1
Go = 100[PrRr+QrXr + (( (PrXr-QrRr)Â²Ã·2 ))]
* Go = regulation, in percent;
* Gr = regulation, in per-unit;
* Pr = Load Power Factor in per-unit;
* Qr = (1-PrÂ²)Â¹/Â²;
* Rr = resistance of transformer in per-unit;
* Xr = reactance of transformer in per-unit.
Then there's Efficiency ratings!
Hope the information from Wocolt and myself are sufficient.
If you need additional data, feel free to post away!
Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!