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Electric lake? 1

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Skogsgurra

Skogsgurra

Electrical
Mar 31, 2003
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This time of the year (when calves are born with double heads and nature in general behaves in an unpredictable manner - we call it "rotmonth" because food can't take the heat and humidity very well). This time of the year, as said, we also hear new and old urban myths. One of them is the electric lake.

This happened: One guy was swimming across a little lake when he felt a tickling in his fingers. It was in a confined area and he could swim out of and into that area. He told other people about it and now it seems that most everyone can feel it - no matter where in the lake they happen to wet their feet. So, I think that most of this is due to a "me too" effect. But the first guy seems to be sure about what he felt.

There are three major pipes terminating in the lake. Two are for snow guns (not in operation during summer) and one is the outlet from a sewer station (yes, very clean). The pipes are said to be stainless steel in the ground and some plastic material in the water.

Questions:

A Anyone had this before?

B What standard measurement techniques are there?

I plan to do a "potential map" using a DMM and a surface electrode shaped as a with cylinder about 1/4 sqm external surface (an ordinary bucket - that is). I will use an iron bar that I just let drop down to the bottom and sink into the mud as a counter-electrode. I will take readings with a high-impedance DMM (it has Gohms on one range) to see if there is anything at all. After checking that, I will switch to a relevant range (all other ranges have 10 Mohms) and then take down the readings across the "offending" part of the lake. I will use a GPS to get my coordinates.

I may also bring some fishing gear.

Comments invited. Especially if you have done anything like this before.

Read all about it on Sorry only in Swedish. But there is a picture showing a couple of guys trying to "ground" the lake. ;-)

Gunnar Englund
 
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On the assumption that it is just nature that goes a bit awry at this time of year and not you Gunnar...

Standard reference electrode for soil potential measurements is a copper / copper sulphate half cell placed in contact with the earth. It's used for measuring the voltage developed by corrosion cells when ferrous pipework is buried in earth. The cathodic protection companies use dozens of them. Typically we see a few hundred mV on an unprotected pipe and a voltage more negative than -850mV for a cathodically protected pipe

Example:
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I don't suffer from insanity. I enjoy it...
 
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Thanks a lot! That's the kind of information I needed. Those electrodes are for long term supervision. I will not need to do it for more than about one hour. So I may get away with the 1/4 sqm cylinders (aka buckets). I will check for 50 Hz. And probably a little more than a few hundred millivolts. What is the impedance of the instrumentation you connect to those electrodes?

Gunnar Englund
 
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Maybe use large similar metal electrodes at each end of a piece of wood that is weighted at one end (to get the same position as a swimmer), and then measure the current (not the voltage). Check ac and dc, and don't forget to reverse the connections to double check when you find something.

Or even just hold the ends of the wires in each hand!

Happy hunting.
 
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I talked with a guy that was working with farmers mapping ground potential. He said there were potential paths from electric companies that could be found in some fields. In cow barns, ventilation fans are mounted on insulated plates so electrical and metal building grounds never connect. Cows need to drink a lot of water to produce milk. If they get a little tingle, they don't drink as much. Same goes for attaching a milking machine to that sensitive area.
 
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Sounds like fun Gunnar.

Only experience I have on that front:
I worked my way through college doing pleasure boat repair, as our town has a harbor.

One day I got a panicky call from a fresh water harbor up in the Sacramento delta a 150 miles away. Seems a guest of a a guy on a 50ft Power boat jumped off the back of the boat while it was docked. When he hit the water he was paralyzed due to an extremely strong shock. He essentially lived by virtue of his inertia carrying him to an area of lesser E-field.

Of course once I arrived and investigated it becomes apparent that they had the hot-neutral reversed and the boat's metal was live. Turns out the same problem was occurring locally in the salt water harbor. They never got shocked locally. The reason was that the human body's resistance was great enough that in the marine environment too little current was conducted to be felt. In fresh water it was a whole different story. There the human body resistance was more on par with the water and so shared more of the current.

My bet? You will find 50hz. You will also find one of those pipes are responsible. I'd throw a wired pail in the water a 100ft from the nearest pipe and then probe the pipes,(no boat needed). My guess would go with a snow machine wiring problem.

I like your plan, sink a bucket out form the "detected anomaly" area and then work a grid pattern. You should be able to draw a perfect map with the voltage increasing directly towards one of those pipes.

Be careful as you would be subject to much more of a shock with a remotely positioned ground reference than a swimmer who is only looking at a 6-7foot 'step' potential.

Do keep us posted!!

Keith Cress
Flamin Systems, Inc.-
 
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That's a lot of "down to the earth" advice. Thanks Keith.

Yes. I will keep you informed - if I survive.

Search the local papers if you don't hear from me any more. The headlines will be something like this: "Galen ingenjör dödad av elektricitet i insjö" (Mad Engineer eletrocuted in lake).

Gunnar Englund
 
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Suggest you make sure both your electrodes are made of the same thing - wouldn't like to see you fooled by using a plain iron electrode on one end of your DMM, and a galvanized bucket on the other.

A.
 
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Cannot avoid that, for practical reasons. But I am looking for AC and I will put a high-grade capacitor in series with the DMM. I think that 10 nF and 10 Mohm will be OK. The resulting attenuation will be less than 0.1 percent. A lot less, actually.

But surely. That is one of the problems I wanted to have a view on.

My main question remains: Anyone knows about standarad procedures in cases like this? Are there any?

Gunnar Englund
 
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skogsgurra

Very interesting post. I especially love the photo of the guys "grounding" the lake.

I believe you will find some very interesting things happening in that lake. You do not mention the depth of the lake and the proximity, if known, between the pipes that terminate in the lake. Maybe some correlation. Is there anyway to check the potential difference between the pipes directly?

It may also be interesting to measure the potential difference across the surface of the lake between 2 boats 50' to 100' apart.

In the US, Mike Holt has done considerable research on stray voltage sources and even attempted to coin a new name for them.

Please keep us posted as to what you discover. And save a few fish for me!

Bigbillnky,C.E.F.....(Chief Electrical Flunky)
 
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I vote for the pipes too. Somewhere there is a VFD, or some electrical equipment.
Or could there be some farmer or cottage owner with a pump drawing water for his garden or swimming pool.
Then again is the lake deep enough to be a secret UFO base?
 
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Is this where the big black thing rises, dripping, from the water, and starts ray-gunning everything?

Gunnar I can't find anything on mapping electrical potentials in a lake. I think you're on your own..

One further comment would be; I bet a metal boat completely screws up any measurements taken from it.

Keith Cress
Flamin Systems, Inc.-
 
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Yes. That is more or less granted. But there are little plastic things that can carry my 2+ stones.

Did a preliminary test with electrodes. I got around twenty ohms resistance between two buckets at 1 inch distance in water. That indicates less than ten ohms probe resistance. So I know that probing can be done easily and I do not have to think about circuit loading.

I will, as I said, use an iron bar that I drop to the bottom. I will attach "ailerons" to it so it drops vertically and sinks into the mud (no rocks on the bottom of these lakes). I will use the iron bar as a reference and attach an isolated cable (100 metres) to it so I can plot AC voltage level in an area being circa 200 metres in diameter.

I figure that the iron bar will have a much lower resistance to mud than the cable will have to the water. I have measured about 12 kohms (AC 20 V/1.7 mA) between a 100 m cable that was soaked in water for an hour. Resistance remained stable for the last 50 minutes. Even the worst ground rod in moist dirt will give me less than 50 ohms. So I think that I will get 10 - 20 ohms between iron bar and mud/bottom.

I estimate that I will have less than five percent error due to resistance in "ground connection", leakage between cable and water and resistance between probe (bucket) and water. That also includes instrument errors. So the outcome will be valid in that respect.

Gunnar Englund
 
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Methinks Gunnar is in need of a "quest" to explain to his wife why he is spending so much time on a boat in the lake.

"This is important RESEARCH, woman! The chores will have to wait!"
 
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You could taste the acidity in the water, I'd have thought, long before it'd start to irritate you. eg lemon.

Gunnar, you'll need to calibrate against a non-tingling lake as well. Sounds like a nice career in summertime, boat, volt meter, GPS, a few beers.... like fishing but without the tedium.


Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
 
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