Mutual Line coupling in Transformer-Feeders

[mLp85]

Hi all,

I am seeking some advice on applying ground distance to transformer-feeder circuits. In this particular application, there are two separated circuits running in parallel, one of them also has an underhung circuit from another network.

I am concerned about mutual coupling during earth faults on the underhung line; however, I have not yet tried to model this scenario as I have reviewed literature that indicates a transformer-feeder arrangement will prevent circulation of the induced currents and therefore the consideration is not necessary when applying distance ground elements.

Can anyone share their views or experiences on this please?

 

[bacon4life]

What voltage level? How many miles are the circuits in parallel? For transmission lines I model mutual coupling, but I don't think it is typical to model mutual coupling for typical 15 kV distribution circuits.

 

[FacEngrPE]

Contact between lines may be a more important problem,

https://www.inmr.com/application-station-class-arresters-underbuilt-distribution-lines-3/

https://www.sciencedirect.com/science/article/abs/pii/S0378779621005526

http://psasir.upm.edu.my/id/eprint/47758/

Dominion Energy has been doing this for several years.

 

[davidbeach]

For radial lines mutual impedance can be pretty much ignored.

If the "feeders" are actually lines, and can form a loop with lines elsewhere, then mutual coupling with the underbuilt distribution feeders can do interesting things. Had a couple of interesting events several years ago where a feeder fault induced a circulating zero sequence current into the overbuilt line. That circulating current didn't bother the ground distance, but it did mess with the POTT scheme that used directional ground overcurrent for keying and reverse blocking. Changing from ORDER = QV to ORDER = Q was a sufficient fix.

But it's hard enough to have all of the line mutuals modeled, there's no practical method to model all of the mutuals between lines and underbuilt feeders.

I’ll see your silver lining and raise you two black clouds. - Protection Operations