Most of the hi tension transmission wires I see around Thailand are like those back home, they are in threes. However, a while back I saw a grouping of 4 wires- 4 each side of the tower. Can anyone explain that set up for me please?

Thanks.

If you seen something like this ...

Photo Credit

Or this ... http://s3.freefoto.com/images/13/60/13_60_91_web.jpg (photo too big for the post)

The '4th' wire is the top one and it's for Lightning protection. The wires are grounded at intervals and basically function as continuous lightning rods, attracting lightning bolts and conveying them around the current-carrying wires to the earth.

I think the Yanks call them "static lines".

If they are connected in the "delta" configuration, only three wires are required, no ground.

If they are connected in the "WYE" configuration, there are four wires, a ground is one of them.

The high tension wires on the towers near me are connected in the "WYE" configuration, 4 wires, but the three phase on the electric poles on the street are connected in the "delta" configuration, only 3 wires.

If you want a better explanation just google "wye connected electrical systems".

If you seen something like this ...

Photo Credit

Or this ... http://s3.freefoto.com/images/13/60/13_60_91_web.jpg (photo too big for the post)

The '4th' wire is the top one and it's for Lightning protection. The wires are grounded at intervals and basically function as continuous lightning rods, attracting lightning bolts and conveying them around the current-carrying wires to the earth.

I think the Yanks call them "static lines".

No, that wasn't it, and I do know the difference between the wires with the big insulators and the ones without.

The towers I saw had four wires with the big insulators and two of the ones without. So, like your picture, but with another set under the 6 hi tension wires.

Wish I'd taken a photo, but didn't.

Anyway, thanks for replying.

Like these?

Sadly, I have no idea why 4 wires

Thank you Crossy, for that picture.

I spent ages looking at pictures of hi tension line towers on the internet trying to find one like that, without success, and it's amazing how many different tower versions there are.

I know what I saw, but I was doubting that I'd ever be able to prove it.

Like these?

7--1773916-high%20voltage%20power%20pylons_1.jpg

Sadly, I have no idea why 4 wires

HVDC? Not likely I agree.

Like these?

7--1773916-high%20voltage%20power%20pylons_1.jpg

Sadly, I have no idea why 4 wires

What!

Crossy stumped on an electrical question

The OP should get a prize

Not wanting to leave this hanging I asked on the IET forum (using the photo I posted earlier).

It could indeed be HV DC, there's an amazing amount around the world including a link between Thailand and Malaysia http://www.energy.siemens.com/br/pool/br/transmissao-de-energia/transformadores/hvdc-high-voltage-direct-current.pdf (page 23, but no photos of the towers in that document).

More here http://en.wikipedia.org/wiki/High-voltage_direct_current