Transformer X/R Ratio

[Humble2000]

Dear Friends,

I need to specify X/R ration of a transformer and for this I am using C37.010-1979 Sec.5.4.1
However this chart does not represent the exact values of the transformer X/R as I have to guess (For example 1.5MVA XFR. whats X/R ratio)
Does anybody have an Excell spread sheets with these values ?

Thanks

 

[DanDel]

Are you talking about specifying the X/R ratio for the construction of the transformer, or for using it as a value to input for a system study?
Typically, this is a tested, or at worst, estimated value.

 

[Humble2000]

Using it for system study...
I have seen some accurate numbers like 8.32
How can somebody estimate this accurately.
Is there a formula to calculet this?

 

[DanDel]

The only way to get the actual value is from the factory test sheets from the manufacturer.

Estimates can be made, such as Table 1 in the IEEE 242 (Buff) book. For a 1.5MVA, 3-phase transformer, primary volatge up to 15kV and secondary voltage 600V or less, X/R is listed as 7.0.

 

[dpc]

If you have the transformer losses from the test reports and the impedance, the X/R ratio can be calculated. But for system study, an approximation based on typical data should be adequate for most purposes.

But just because someone uses three significant figures doesn't prove they know the answer to that accuracy.