Transmission Line Impedance 1

[lsuengineer]

I am in the process of trying to calculated a transmission line impedance for the purpose of distance protection. I do not have any software to model the line and was wondering if there was a more straight forward(real world) method of calculating the impedance without having to use the complicated mathmatics used in college. The transmission line is 69kv, 8 miles long, 795mcm acsr.

 

[Skogsgurra]

You are sure you understand the difference between "impedance of a HV transmission line" and "the impedance of a transmission line"? The latter one is where you may run into "complicated math" the one you need is the former one. There are text-books on it.

Gunnar Englund

http://www.gke.org

 

[cuky2000]

Here is an approximation-simplified approach to obtain resistance and inductive reactance of a transmission line:

R= Value from table (see link below)
X= 0.0754.Ln(GMD/GMR) Ohm/km to neutral @ 60 Hz

GMD= (Dab.Dac.Dbc)^1/3
GMR from ACSR cable table (see link below)

http://www.cable.alcan.com/NR/rdonlyres/BC388B10-A9C3-45B6-AA90-F5A9BA9D203D/0/ACSRweb.pdf

[sub] PS: For zero sequence and accurate values, probably you need to go for approach that is more complex and provide additional data.[/sub]

 

[SMB1]

If you could measure the line, it would be better. otherwise, get the detailed tower and line information and then used line impedance program.

 

[cflatters]

For the transmission line type type and length you mention, the 'nominal pi' method should provide a suitably simplified and valid model to calculate line conditions once you have calculate the transmission line parameters.

Take a look at the Areva website, the PRAG handbook can now be downloaded free gratis

 

[powerjunx]

lsuengineer,

"..The transmission line is 69kv, 8 miles long, 795mcm acsr."

As cuky2000 pointed out, you can also find this standard values of ohm/ft, etc thru conductor tables (usually named after the family birds) like; Power System by Stevenson in the appendices, G.E Handbook, etc.

To ease computations' hassles, you must be able to familiarize the terminology relating to transmission line, GMR, GMD, cable type, and other parameters then used computer software simulation.