Underground cable installation crossing existing underground cable

[Laly]

Hello everyone, I'm currently working on a project where the new underground cable route will be crossing an existing undergound cable route at various locations. The existing and new underground cable systems are both 34.5 kV. The idea is that the new cables need to be sized and spaced accordingly such that they don't cause any derating in the existing cables due to heating effects. I'm taking a look at the Neher-McGrath method but it seems to deal more with derating of cables based on one system. Anyone has any information/references I can look at on derating of cables based on systems that cross or are in near proximity of each other? Not having much luck with search online.

Thank you

 

[dpc]

If they are crossing at right angles, you don't have to worry much about derating.

The Neher McGrath is applicable - heat is heat. It doesn't matter what the source of the power is.



David Castor

http://www.cvoes.com

 

[Marmite]

There was a paper by Dorison at JICABLE in 2003

http://www.see.asso.fr/jicable/2003/pdf/A94.pdf

which was developed into IEC 60287-3-3.
There are rating tools such as Cyme and Crater which utilise the IEC method.
The calculations for crossing cables are very complicated. To get a conservative result assume that the cables are side by side, or better still increase the separation until they are thermally independent. That will also have the added benefit of improved security of supply.
Regards
Marmite

 

[desrod]

The guys at Cyme can run the case for you. Its cheaper than buying the toll/software and learning how to use it!

Desrod

 

[mrcheese]

Ignoring the heat from any crossing is a mistake. Heat and EMF are not the same and cannot be treated the same way. Good information here

http://www.neher-mcgrath.com.

The crossing calculation is even more complex than the normal neher-mcgrath calculation but there are several software packages that can handle it.

Ohm's it not just a good idea, Its the law.