tyipcal X/R ratio for an autotransformer 1

[mvsubstation]

finding typical X/R ratios for standard transformers is pretty easy to find, however, I cannot find any information on a typical autotransformer X/R ratio. Only data I can find is from a Siemens PSSE model report on a project with an autotransformer that claims the impedance (per unit) is 0 + j0.092). Does this data make sense? (no resistance, only reactance, and thus X/R is N/A?)

 

[HamburgerHelper]

In my models, I am seeing a range of 58 to 85 for the X/R on autotransformers. That is high enough that the small amount of resistance the transformer has will play no role in short circuit or power flow calculations. Its impedance is almost entirely reactive.

 

[mvsubstation]

Thanks!! I looked everywhere for this info; Star for your help!!

 

[davidbeach]

The transformer test report provides enough information to calculate both the R and the X.

 

[dpc]

If you know the transformer losses, you can calculate the resistance, since any real power losses will appear as a resistive circuit element. Knowing the %Z and the R, you can calculate the X/R.

 

[prc]

What is the rating ( % impedance, voltage and MVA ) of the auto-transformer that you are modelling ?