Overhear Conductor

[Humble2000]

I had asked t local utility provide me with SC MV so I can design the substation ground grid. They have given me the Sc for the TS, instead on customer location. The conductor is 565KCMIL at 44KV AL.
I never heard of this type of conductor. I also know that the distance and the way conductors are placed makes a difference in impedance values. I really appreciate if I can get any feedback on this issue.

Thanks

 

[rcw retired EE]

You will need to design for the ground (earth) current they give you, even if it is at their station and not your location. If you can find out the length and parameters of the circuit (conductor mounting height, spacing, size GMR, circuit configuration) you would be able to determine the actual fault current at your stations with this line. However, future line changes or additions may increase the fault level. That is why using the utility data would be best, IMHO.

 

[Humble2000]

They L-G Amp is 17000Amp at the station! imagine the size of the grid you need.
I only have the size,length and type of conductor (AL)
conductor mounting height, spacing, size GMR, circuit configuration are probably the same fo all 44KV circuits( I can find that)
Size GMR?

What refernce I can use to calculate the impedance with this information?Whats the formula?
Thank you

 

[davidbeach]

Any decent power analysis text should have a description of line constants calculations. Check faq238-1287 for a number of good references.

 

[Marmite]

The protection relay application guide published by Areva has a chapter on calculating the equivalent circuits of plant and equipment including O/H lines and cables. The section on O/H lines from page 62 onwards goes through the mathematics of calculating the equivalent impedances.
See ftp://ftp.areva-td.com/NPAG/Chap5-46-77.pdf

or

http://www.areva-td.com/servlet/Con...48589697&lid=en&tab=Chapters&id=1056536208254

for the whole manual which is a handy reference.
Regards
Marmite

 

[apowerengr]

Is it possible your 565 is really 556AL? As for their short circuit values you need to perform a line fault analysis to determine the line fault point which results in the greatest portion of their available fault current returning via your ground grid - that's what provides the greatest GPR values which you need to design to.

 

[Humble2000]

conductor is called Dahila 556AL.
I have 150mm spacing between 44KV vertical configuration system.
I can not find X,R which I need to calculate Z1 and Z0.
I have heard that there is a manual from" Aluminum conductor association???" which has all the info, but I don have it.

 

[jghrist]

http://www.cable.alcan.com/NR/rdonlyres/4CA1939C-FC9C-4A9C-947E-2864F17BD247/0/AACweb.pdf

has resistance and reactance for Dahlia 556.5 kcmil AAC.

 

[davidbeach]

Between the NPAG reference from Marmite and the parameters from jghrist you have it all.

 

[Humble2000]

Thank you very much. This forum is great!!