Low Magnetic Field Overhead Line Solutions

[FPelec]

Hello everyone, I am collecting information on low magnetic field airline solutions, specifically focusing on the various practical solutions (i.e. pylons) adopted worldwide to cope with EMF issues. In particular, I am interested in 'phase-splitting' solutions, for comparison with the solution we are beginning to install in Italy (referred to as '5-phases', see the following example).
Are you aware of anything similar? What solutions, to your knowledge, are adopted globally by utilities to reduce OHLs magnetic fields?
Thank you in advance,
fpelec

Si duri puer ingeni videtur,
preconem facias vel architectum.

 

[crshears]

So what is 5 phases and how does it work? Any good links to descriptors you'd recommend?

Also, distinct color change is visible in pic; has tower top been reconfigured from a previous design?

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[9wearSuave]

Are 2 of the phases "split" and then the 3rd phase is in the middle perhaps?

 

[FPelec]

Hello 9wearSuave, you are correct: two phases are 'split,' and the third one is in the middle.
Hi crshears, the pylon in the picture is not a refurbishment of an existing tower; the different color between the upper and the lower part should reduce the visual impact of the pylon. This solution has sometimes been applied to other 'standard' pylons in high-quality landscape areas. You can find some info in the attached paper and at page 34 of the TSO development plan:
Link
I've seen some EPRI reports on 'split phases' lines, so that I am fairly confident that split-phase solutions have been adopted elsewhere, perhaps in places with stringent limits on magnetic fields, with possibly different geometries and tower arrangement, to reduce the magnetic field or even increase SIL. Unfortunately, I didn't find any reference (and photos) to those OHLs in service.


Si duri puer ingeni videtur,
preconem facias vel architectum.

 

[cranky108]

If you want to hide the structure better, why are you using galvanized? Why not use pre-rusted, then you can add a few limbs with leaves.

 

[FPelec]

Hello, cranky108, the lattice towers in high-quality landscape areas are not galvanized but painted (the upper part in a light blue color, the lower part in green or brown). CorTen steel is a good solution, especially in mountain/wooded areas, but most people do not like "rusty" pylons as they seem "old"...

Si duri puer ingeni videtur,
preconem facias vel architectum.

 

[cranky108]

At least here, all lattice towers are old. New towers are davit arms. But out side of town we use CorTen as we are in a sort of tourist area, and everyone is concerned about looks. And in fact there a big push to underground lines.

 

[bacon4life]

There have been some experiment with 6 phase power transmission. This requires delta wye transformers to get a 30 degree phase shift, and potentially a series reactor in the normal set to equalize the impedance. The requirement for additional transformers at each end imposes an economic burden that limits this solution to only very long lines. I think there was a thread a couple years ago about it on eng-tips.

For parallel lines on a common tower, the option on the left would have better magnetic properties:
AC___AA
BB___BB
CA___CC

However, the configuration on the right is much simpler to physically route lines to tapped substation. In my region, enough of the transmission lines are asymmetrical and/or untransposed such that it causes a nearly 1% transmission voltage magnitude imbalance.