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Stray currents from overhead power lines?


Craig Thomson

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As was mentioned, the net inductance from a 3 phase supply is surely zero? But anyway, even if there is some small voltage/current induced or capacitatively coupled into the hull, surely it would be AC and as far as I’m aware ac current doesn’t create corrosion.

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12 hours ago, Loddon said:

There was an article in Wireless World many years ago about how living under power lines causes all sorts of cancers and how other countries have a 150meter exclusion zone along the line of the pylons but we don't. ;)

 

I think this may be the issue you are referring to. Photocopied and sent to many friends at the time:
ww.jpg.8f31b6bebebac0dc004008f3383e12f5.jpg

 

Download a copy here:
https://worldradiohistory.com/UK/Wireless-World/90s/Wireless-World-1990-02.pdf

 

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1 hour ago, Puffling said:

I think this may be the issue you are referring to. Photocopied and sent to many friends at the time:
ww.jpg.8f31b6bebebac0dc004008f3383e12f5.jpg

 

Download a copy here:
https://worldradiohistory.com/UK/Wireless-World/90s/Wireless-World-1990-02.pdf

 

That's the one thanks for the download will read again.

I remember the guy doing the dimmers refused to sit near them for the rest of the tour after reading that 😱

 

Edited by Loddon
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25 minutes ago, Loddon said:

That's the one thanks for the download will read again.

I remember the guy doing the dimmers refused to sit near them for the rest of the tour after reading that 😱

 

I moved my bed to site it away from a fridge sited just 2m through a partition wall in a previous dwelling. A couple of friends turned down a flat with storage heaters in the child's bedroom.
The data linking adult suicide prevalence and childhood cancers with EMF intensity is particularly troubling.

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27 minutes ago, Puffling said:

I moved my bed to site it away from a fridge sited just 2m through a partition wall in a previous dwelling. A couple of friends turned down a flat with storage heaters in the child's bedroom.
The data linking adult suicide prevalence and childhood cancers with EMF intensity is particularly troubling.

Just re read the article, even though it's 30 years old very few if any of the points raised have been addressed, they have mainly been ignored by the electricity transmission companies and UK governments.

 

I guess I have been lucky in life as being a radio amateur and working with electricity installations  all my life puts me in a very high risk group but so far I am ok😎

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2 minutes ago, Loddon said:

Just re read the article, even though it's 30 years old very few if any of the points raised have been addressed, they have mainly been ignored by the electricity transmission companies and UK governments.

 

I guess I have been lucky in life as being a radio amateur and working with electricity installations  all my life puts me in a very high risk group but so far I am ok😎

It was exactly my feeling, and while countries such as Russia and Canada have tight regulation on electromagnetic fields from power lines, the UK effectively gives housing developers a free hand.

Interesting that you have worked in the industry. I've been in electronics for a lot of my life, but I guess the biggest risk would come from what WW calls VDUs. Sitting 1m from a massive Samsung CRT for hours can't have helped my chances. Again, like you, lucky so far.

I was a G8 for a while, never did much with it, but was a regular member at my local radio club. I cringe now when I recall operators leaning over the exposed innards of 400W linear amplifiers, the glow of the valves reflected on their face as they tweaked the coil pack!

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8 hours ago, nicknorman said:

As was mentioned, the net inductance from a 3 phase supply is surely zero? But anyway, even if there is some small voltage/current induced or capacitatively coupled into the hull, surely it would be AC and as far as I’m aware ac current doesn’t create corrosion.

I can't see overhead lines rotting steel hulls either.

 

But there were some DC high voltage lines https://en.wikipedia.org/wiki/HVDC_Kingsnorth  Apparently the losses are reduced.  I think DC is back again for international connections but for other reasons.

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Thanks for all the replies so far, it's certainly an interesting topic.

 

My main point of interest though is less the effects on human health (quite probably negative, but I also hypothesised that by living inside a big metal box one might actually be quite well protected by a Faraday cage effect ..?) and moreso the electrolytic effect such a setup might have on the outside of a steel hull.

 

I have read about corrosion effects on pipelines in parallel with HV lines which seems to be something to do with long parallel conductors acting as a massive capacitance loop (please correct me if you have a better understanding!) and the resultant voltages leaking into the earth and corroding the pipes in the process. Is it thus probable that a similar (if much smaller) effect is acting on a boat hull earthing into the canal water? (itself also running fairly parallel to the power lines for several hundred metres)

 

If so, can anything actively be done about it? There are a dozen other boats here in a similar situation who might also like to know the answer to this ...

 

Does a galvanic isolator / isolation transformer have any effect here or is the point moot as it is independent of whether the boat is connected to shore power or not?

Edited by Craig Thomson
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1 hour ago, Tacet said:

I can't see overhead lines rotting steel hulls either.

 

But there were some DC high voltage lines https://en.wikipedia.org/wiki/HVDC_Kingsnorth  Apparently the losses are reduced.  I think DC is back again for international connections but for other reasons.

Found this article here

 

https://www.corroconsult.com/blog-news/ac-corrosion-demystified/9/3/2018

 

which details how AC currents are transformed into DC corrosion at coating defects on pipelines, via the coating defects themselves acting as diodes. The article does note that the dangers are most prescient to pipes running parallel for over 2km to HV lines and that they result in concentrated corrosion around small areas of coating defects. Whether any of this is relevant to a 40ft long boat I don't know, but it does cross my mind that having a new coat of blacking on everything except the few strips where she was resting on the slipway bearers perhaps puts these remaining unprotected areas at even greater risk of electrolytic corrosion than when the whole bottom was rust!

Edited by Craig Thomson
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17 hours ago, Ray T said:

I know it is for metal pipes but have a read of these:

 

36055659.pdf (iaea.org)

 

(1) Is living under high voltage power lines bad for our health – Emf Protection Store

 

I worked for BT in my career and in old long distance copper cables capacitance, induction and resistance was always an item needing addressing.

 

I also had to be aware of the effects of HV power lines.

 

 

I would take any information from places like "Emf protection store" with an *enormous* pinch of salt, given that their business purpose is to sell "new age eco products" to gullible people looking for something to worry about -- their website is basically full of unscientific woo-woo BS.

 

"Our mission is to provide you with a variety of shielding/protection products to ensure your favourite techno-gadgets are fun and safe to use.

By practicing EMF protection measures and using EMF protection products best-suited to your needs and lifestyle, you are refusing to feel helpless in dealing with electro-magnetic pollution and choosing instead to protect your health through prevention."

 

15 hours ago, Loddon said:

Well they would say that wouldn't they.

 

If you go and actually read the reference it does say that there *is* some weak evidence about childhood leukaemia, but also points out that this is detectable (but very small) up to 600m away -- this suggests they're not trying to cover anything up, otherwise they'd have left this out. You can also go digging elsewhere to find out more about possible causes for this, one plausible one is that it's nothing to do with EM fields directly affecting humans but might be caused by the fields from the power lines focusing cosmic rays. Of course there's no proof of this, correlation does not imply causation...

 

At the distances from power lines that we're talking about there could be significant voltage gradients especially for EHV lines (e.g. 275kV), this is why you can light up a fluorescent tube. However the impedances are very high and magnetic coupling into something like a narrowboat hull will be very weak because of spacing and the fact that the hull is a tiny fraction of a wavelength long, so any induced AC currents will be *very* small -- probably *far* smaller than those induced from mains connections to the shore which are several orders of magnitude closer and much better coupled, and also much more likely to have a local return path for any induced current.

 

So it's far more likely that any galvanically-induced corrosion/pitting is caused by local AC currents either from the boat itself or other boats nearby than overhead power lines.

 

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55 minutes ago, Craig Thomson said:

Found this article here

 

https://www.corroconsult.com/blog-news/ac-corrosion-demystified/9/3/2018

 

which details how AC currents are transformed into DC corrosion at coating defects on pipelines, via the coating defects themselves acting as diodes. The article does note that the dangers are most prescient to pipes running parallel for over 2km to HV lines and that they result in concentrated corrosion around small areas of coating defects. Whether any of this is relevant to a 40ft long boat I don't know, but it does cross my mind that having a new coat of blacking on everything except the few strips where she was resting on the slipway bearers perhaps puts these remaining unprotected areas at even greater risk of electrolytic corrosion than when the whole bottom was rust!

There may be some truths in this post. I know of boats that have not been blacked or had anode for the last 25 years and have not suffered massive corrosion probably because the whole area of the hull is exposed.

Yet boats with anodes all over and blacked every 2 years have suffered deep pitting corrosion around areas where the blacking has been scraped off.

 

The abandoned rusty all over mud hoppers don't seem to rust either and some have been in the water since the beginning of time it seems.

Edited by Tracy D'arth
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52 minutes ago, Craig Thomson said:

Found this article here

 

https://www.corroconsult.com/blog-news/ac-corrosion-demystified/9/3/2018

 

which details how AC currents are transformed into DC corrosion at coating defects on pipelines, via the coating defects themselves acting as diodes. The article does note that the dangers are most prescient to pipes running parallel for over 2km to HV lines and that they result in concentrated corrosion around small areas of coating defects. Whether any of this is relevant to a 40ft long boat I don't know, but it does cross my mind that having a new coat of blacking on everything except the few strips where she was resting on the slipway bearers perhaps puts these remaining unprotected areas at even greater risk of electrolytic corrosion than when the whole bottom was rust!

Not sure about the provenance of an non-peer-reviewed paper that says, "In simple terms the voltage is the power that drives the current through the resistance." (my emphasis)

 

eg see https://www.bbc.co.uk/bitesize/guides/zsgtw6f/revision/1

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2 hours ago, Mike Todd said:

Not sure about the provenance of an non-peer-reviewed paper that says, "In simple terms the voltage is the power that drives the current through the resistance." (my emphasis)

 

eg see https://www.bbc.co.uk/bitesize/guides/zsgtw6f/revision/1

And to repeat the point again, induced voltage (and therefore current to drive any galvanic corrosion) for AC coupling is proportional to the parallel length of the conductors, and a 2km pipeline is 100x longer than a 20m narrowboat, so the (non-reviewed) paper doesn't prove anything for boats. It's like saying that because hitting somebody over the head with a sledgehammer is definitely dangerous, so is hitting them with a feather... 😉

 

Yes I work with analysing electromagnetic coupling on a daily basis, even though the frequencies in my case are a billion times higher and the dimensions a billion times smaller the effects are very much the same...

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On 12/07/2021 at 16:39, Tracy D'arth said:

I don't think it has ever been proven but there must be a possibility of current as I know of one guy in a bungalow who had managed to get his fluorescent tube lights to strike up because he was under a 400kV line. He never turned them off!  He was eventually prosecuted by the power company for the theft of electricity. 

 

Fluorescent tubes strike at a very low current - you can get one to strike off 12v at less than an amp for a 12 inch tube if you push the frequency up.

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16 minutes ago, StephenA said:

 

Fluorescent tubes strike at a very low current - you can get one to strike off 12v at less than an amp for a 12 inch tube if you push the frequency up.

What really strikes up fluorescent tubes is lots of volts at low current -- 1000V or more for a long tube if there are no heaters/starters connected -- so the voltage field (several kV/m) from an overhead EHV line (e.g. 400kV) will do this just fine if you hold one vertically. But once they've struck as the current goes up the voltage drops (negative resistance), so if they're excited by stray fields like this you can't get much power into them (current is small) so they won't go very bright.

Edited by IanD
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I thought corrosion from stray currents only occurred with direct currents, as one end of the boat acts as an anode and the other a cathode. Hence cathodic protection on some bridges, which passes a current into the steel reinforcement of the bridge to reverse the effect. Overhead lines are AC, so every 50th of a second the current would reverse,  reversing the effect?

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20 hours ago, Jonkx said:

I thought corrosion from stray currents only occurred with direct currents, as one end of the boat acts as an anode and the other a cathode. Hence cathodic protection on some bridges, which passes a current into the steel reinforcement of the bridge to reverse the effect. Overhead lines are AC, so every 50th of a second the current would reverse,  reversing the effect?

The problem is that interfaces between different materials (e.g. metals and corrosion) can form diodes -- not very good ones, but still enough to mean the resistance to current flow in the two directions is different, which converts some of the AC current to DC.

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