Overhead Earth Wires

[ElectralJohn]

Is there a formula which calculates the relative proportions of earth fault return current through:
1) an overhead earth wire strung on the same poles as the faulted line; and
2) the body of the earth.
I have seen results for item 1) which include one component of earth fault current in the earth wire flowing back towards the substation and a smaller component flowing outwards away from the substation.

 

[jghrist]

See IEEE Std 80-2000 Section 15.9. There several methods presented, none of which use a simple formula. Also, commercial grounding programs such as WinIGS and SES CDEGS use more complicated approaches.

Some of the current will also return in earth wires not on the same poles as the faulted line, such as outgoing distribution feeders.