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

FYI:

* 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

***"Exactly"***

or;

Go = 100[PrRr+QrXr + (( (PrXr-QrRr)Â²Ã·2 ))]

***"Approximately"***

FYI:

* 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!

Scott35

_________________________

Scott " 35 " Thompson

Just Say NO To Green Eggs And Ham!