Cable Data & x/r ratio

[whycliffrussell]

Cable Data:

Can someone tell me where to get 'reputable' copper cable impedance data. I know that cable impedance depends on many factors (spacing, insulation, shielding,configuration, construction). Is there a way that the above paramaters can be incorporated into a formula to figure out the cable impedance?

X/R Ratio:

Is there a standard procedure for what to do when you when you've been given the short circuit current at a stack, and a load on the end of a downstream cable, but no X/R ratio for the available short circuit upstream.

I've heard that you can use the X/R ratio of the transformer...but unfortuantely I have no even been given that data. All I konw is that the stack has a given SC current and that it feeds three other downstream stacks which are a combined load of 333 kVA?

Any suggestions at all on this one?

 

[dpc]

My suggestion is to get a good reference book on calculation of short circuit currents. The IEEE Red Book is a good starting point. Textbooks by Stevenson and Paul Anderson are a good resource.

If you're dealing with industrial systems, I'd recommend "A Practical Guide to Short Circuit Currents" by Conrad St. Pierre.

The cable impedance calculations can be somewhat complicated if you're looking for a high degree of precision. The resistance is also temperature dependent, so any perceived accuracy in your reactance data must be tempered with the fact that you almost never know the actual conductor in the conductor and it is generally not uniform.

Transformer X/R ratio can be calculated if you know the %Z and the losses. Or you can use approximate value from Red Book for similar size units.

 

[cuky2000]

To estimate the X/R ratio of a transformer, see the enclose link

http://cuky2000.250free.com/XFMR_XoverR.jpg

 

[dpc]

Correction - should have said "you almost never know the actual conductor **temperature** in the conductor....

Glad it's Friday....