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Posted By Topic: Overhead Transmission Lines

Mar 08 2019 11:03

Anyone have any options for dealing with induced voltage into structures under 220kv transmission lines. We have a property under one of the lines pretty much running parallel to the lines. Roofers want to replace a few sheets of iron but are receiving small nuisance shocks between the roof and ladder, spouting etc..
Installation wiring had been checked and voltage (30v ish) still present even with it isolated from the supply so no doubt it's from the overhead lines.

I have emailed Transpower for advice but want to know if anyone has dealt with this sort of issue before.
Obvious option is bonding the pipework, spouting, iron, but not that confident of the connection between the individual sheets of iron and don't want to get too carried away.

Any idea's, tips, advice or temp measures even?

Mar 08 2019 11:40

I heard of a farm near Tokoroa where the fence ran parallel to HV power lines and the farmer was powering an isolated shed with the induced energy. From memory he earthed one end of the fence (wire on wood posts) and used a rectifier to charge a car battery, then had 12v lighting.
But in your case the stray currents can cause metal corrosion as well as tingles.
I would use a wooden or fibreglass ladder so they are not 'completing the circuit' when they climb onto the roof, and wear gloves.
And it would be an idea to paint the GI sheets before installing (similar to mixed galv and zincalume sheets) so the overlaps do not suffer galvanic corrosion.

Mar 08 2019 11:57

Out of interest, is the dwelling immediately underneath the lines? Many countries will not allow any buildings within 500m of a 220kV line for exactly these reasons, plus there is a fair bit of peer-reviewed science that suggests depressive disorders are higher in people living under them. A very interesting subject. Also are there any signs of corrosion anywhere other than on the roof?

Mar 08 2019 12:25

Thanks for the reply's.
Yes, roof is directly under the lines. About middle of the span as well so close to it's lowest point.
Doesn't appear to be any other corrosion, although in Otara we do find the earth electrodes corrode very quickly compared to other area's we work in?
A neighbor remembers once upon a time a cable was attached to a down pipe on his property and connected to an electrode, but has since been removed many years ago. From that I suspect we are not the first to come across this issue on this property.

Mar 08 2019 12:48

There's a standard that covers dealing with similar situations for conductive pipelines; which are often run along the same 'corridor' as the HV lines.
Just can't find my copy right now.

Mar 26 2019 22:04

I had some private correspondence a few yeas back with a Canadian chap who had a property adjacent to 750KV lines. His barn had 24x7 lighting from fluorescent tubes with no wiring. He had big fat sparks from fence wires. All from capacitive coupling from the HV lines.