X/R ratio

[wonderchi]

Hi given,

impedance for a 12.5kV generator

z1 = 0.0016 + j0.15
z2 = 0 + j0.18
20 = 0 + 0.1

obviously there is a x/r ratio for z1, but how about z2 and zo. I am using SKM power tools to represent this generator. And it ask for x/r ratio for all impedances?

Thanks

 

[davidbeach]

Use the R component of z1 for z2 and z0. I'd actually suspect the z0 value you gave; z0 should be almost entirely R with not much X while the other two will have X dominate R as it does in your z1. Since SKM is asking for the subtransient values, you can get reasonably close if all you know is z1 by using it for z2 and the R part for z0. That does not apply for transient or steady state values, you have to know z1 for both; z2 and z0 don't change appreciably from subtransient to transient to steady state.

 

[davidbeach]

Just as an aside, isn't it redundant to refer to an x/r ratio? Isn't x/r a ratio by definition?