Power Transformer %Z Measurement

[BigJake]

Anyone have a site that describes how a Transformer's Percent Impedance is measured either at the factory or in a lab?

I recall that it is done by short-circuiting the high voltage side and then increasing the low voltage side voltage until full rated current is reached in the high voltage side. (Full rated current will not have been reached on the low voltage side.) The ratio of the voltages HV to LV is called the voltage impedance drop?

Please help clarify this for me and put me onto some good sites if you have them.

No audio transformers or theoretical calculations, please!

Thanks!

 

[DanDel]

I believe that what you state is correct, but what I thought was that the test involved shorting the LV side and applying voltage to the HV side until FLA flows in the LV winding.
It would result in the same value if you energized from the HV side or the LV side, and the percentage of voltage used compared to nominal(on the energized side) is the percent impedance.
As an example, a transformer rated at 5%Z, if energized with 5% of the rated voltage on the primary side, will cause full rated amperage in a shorted secondary.
I believe this is the standard 'Short Circuit Test' for transformers.

 

[BigJake]

I understood that Full load amps in the shorted low voltage side would be very high compared to that in the shorted high voltage side and is avoided if possible.

Thanks for your reply!

 

[busbar]

Depending on what “theoretical” means, in ANSI regions this type of test is formally detailed {with diagrams} in IEEE C57.12.90-1993 §9. The standard comments that the tests can be done by energizing either side of the transformer, so I guess it mainly depends on the local convenience of test voltage and source-voltampere capacity. [I didn't see any integral calculus in my old copy.]