"Mystery Current" burns up cable splitters

[crossman]

I received the following link in my email, from Mike Holt:

http://www.powerlinesystems.ca/documentation/CaseStudy_Sept07_MysteryCurrent.pdf

It discusses a situation where the magnetic field of a high voltage transmission line was inducing current flow and burning up cable tv boxes at residences. I got to wondering about what is stated in the link concerning induced currents.

My question:

The strength of a magnetic field is determined only by the magnitude of current, right? It is not the voltage that causes the magnetic field?

To illustrate what I mean, let's take two situations:

#1) 100,000 volts, coil with XL = 10,000 ohms, Current = 10 amps

#2) 100 volts, coil with XL = 10 ohms, Current = 10 amps

Is the magnetic field of #1 equal to the magnetic field of #2?

 

[spsnyder]

Magnetic Flux Density, B, for an infinate wire is, B= Ф(unit vector) μIl/2pi r. So yes the magnetic field in both cases are the same.

 

[crossman]

So then, I am having trouble believing the findings in the link posted above. I just don't see that an induced voltage from an overhead transmission line could cause the relatively large current flow which burned up the cable tv splitters.

Points:

The current flow in the 230,000 volt transmission lines wouldn't have been some huge astronomical number of amps. Look at the wires themselves. They aren't that huge to be carrying thousands of amps.

The magnetic field strength decreases with the square of the distance. Wouldn't the magnetic fields of the service entrance be more of a factor than some wires way up on some transmission towers?

Since all the conductors of the transmission tower run in somewhat close proximity as compared to the distance from the houses, doesn't the magnetic field of one conductor tend to cancel the magnetic field of the other conductors?

If the transmission line conductors are acting like a "primary" of a transformer, shouldn't we only consider the length of wire which is closest to the homes? Maybe the length from one tower to the next? And the voltage drop on that specific length would actually be very very low.

Anyway, I just can't see the part of "we walked around the homes with a 5 foot diameter loop of wire and we measured over 1 amp in the wire".

I would appreciate anyone's thoughts on this. I just can't see this happening because of inductance. If inductance from the power lines can do this.... sounds like a way to really get some of that "free energy" that was being discussed in another thread.

 

[micromind]

In linework, inductance seems to be more of a function of voltage than current. I state this because in my experience, grounding an open overhead line will produce a bigger arc when it's near a high voltage (60KV or higher) line than a medium voltage one (34.5KV or lower).

I realize that a bucket truck, a hotstick, and a ground lead is not exactly a scientific study, but you learn quickly to 'slam it in' a bit faster with higher voltages.

 

[winnie]

The magnetic flux density is caused by the current flow...but it doesn't fall off as the square of the distance.

For a single long conductor, the flux density falls off as 1/distance. But of course you have more than one conductor, and (hopefully) balanced current flow on the lines. In such case, the flux density falls off in a complex fashion, slower than 1/x near the wires, faster than 1/x^2 away from the wires.

As they've drawn things, I'd guess that the multi-ground-neutral conductor on the poles is in a significant 60 Hz field, and that the cable company ground was out of it, such that there was significant flux change coupling the loop.

-Jon

 

[crossman]

Thanks for the thoughts, Winnie. Do you feel that taking a five foot diameter loop of wire and walking around the area could cause a significant current flow in the wire?

A 230KV transmission line would most certainly be way up in the air on large steel towers, right? And the houses most certainly would not have been directly under the lines in the right of way. They would have been a pretty good distance away from the power company right of way?

Do you see that a "single wire primary" (no loops to increase the field strength) at 60 Hz could induce voltage and current into a single loop secondary possibly several hundred feet apart?

Edit: I just reread your last sentence. It makes sense that it wasn't the current in the phase conductors, it was current taking a path to and through earth which would be in closer proximity to the "secondary" conductors in question.

Still, I just can't help but feel that this company is trying to drum up business by creating a scare, sort of like the global warming epidemic. Of course this is all my opinion based on ignorance.

 

[ELA]

I was interested in the test they did with the 5' diameter coil. The induced current seems sort of high for being so far from the power lines?
They also mentioned different currents were measured from front to back of the house.

Here is a link that speaks somewhat along these lines:

http://infoventures.com/emf/bener/bu-paper/bu43ni01.html

 

[RayS]

I received the following link in my email, from Mike Holt:

http://www.powerlinesystems.ca/documentation/CaseStudy_Sept07_MysteryCurrent.pdf


To illustrate what I mean, let's take two situations:

#1) 100,000 volts, coil with XL = 10,000 ohms, Current = 10 amps

#2) 100 volts, coil with XL = 10 ohms, Current = 10 amps

Is the magnetic field of #1 equal to the magnetic field of #2?

umm, if we assume the number of turns in the coil is the same. And in this example, (parallel lines overhead) I guess it is. I'd be thinking stray current in the earth, not induction. I could expect some real voltage from electrostatic, but not at any significant currents.

 

[Rampage_Rick]

I'm reading that and thinking to myself "all right! free electricity!"

Just set up a bunch of 5' copper loops in your yard... :grin:

Interesting methodology for the investigation.

We have several 115kV lines just down the street from us, with our service crossing perpendicular below it. One of the old-school phone techies was telling me about how many years he was working nearby and a metal D-ring on his ladder was jumping around throwing sparks due to the eddy current. I didn't really believe that much current could be inductively coupled.

 

[LarryFine]

Anybody considered the possibility of earth gradients, leakage current, real voltage on the cable, bad neutral somewhere, etc?

 

[steve66]

My question:

The strength of a magnetic field is determined only by the magnitude of current, right? It is not the voltage that causes the magnetic field?

Maybe, but I'm not quite yet convinced that's true. There is also a electric field between the wires that changes at 60 hz. I don't think I've had to think about the difference between electric and magnetic fields since school. But I seem to remember something about every electric field creates a magnetic field, or at least every AC electric field creates a magnetic field. So is it possible that the E field could induce a current in another conductor? And maybe that current could be larger than one induced by a B field with a lower voltage source?

Not that I'm not skeptical about the entire story. The writer gave absolutely no proof that the transmission line generated the currents.

Steve

 

[crossman]

I just find it hard to believe that a 5 foot diameter, single loop of wire would have 1 to 2 amps flowing in it. This would mean that any completed metal paths in the vicinity would have current in them. Car bodies, aluminum doors, sheet metal patio roofs, garbage cans...

 

[ELA]

Could you oversimplistically think of the 5' wire coil test as a shorted current transformer with terrible magnetic coupling?

Such that: 15 ft of # 4 wire (~.004 ohms)
with 1-2 amps of current flowing in it = .004 watt secondary?

Seems like this test could be a little dangerous if the loop were not shorted? Like opening the scondary of a current transformer when current is flowing in the primary?

.004 volts / 1 ua = 4000 volts?

or did I take too many short cuts? :roll:

 

[nakulak]

Anybody considered the possibility of earth gradients, leakage current, real voltage on the cable, bad neutral somewhere, etc?

yeah, I'd agree with that (as some one else mentioned - stray currents). Its easy to jump the gun and assume its induction from the high voltage lines. Of course, that doesn't rule out that there might be stray current from the overhead lines either. It is especially likely in the summer time when the lines sag.

 

[winnie]

Anybody considered the possibility of earth gradients, leakage current, real voltage on the cable, bad neutral somewhere, etc?

I don't know if the professionals involved considered these sources of current, but the solution that they proposed would tend to fix the problem.

They put the CATV shield ground in closer proximity to the POCO neutral, on the same poles and presumably sharing the same grounding electrodes. At the same time that they reduced the loop area for near field magnetic pickup, they also reduced the electrode spacing for earth gradient pickup. And probably remade all of the connections on the CATV components.

If the source were a bad neutral, then I'd hope that it was caught earlier on...but moving the cabling as described would tend to mask the problem.

Given the tales of farmers stealing electricity with induction coils under high voltage lines, I wonder if these consultants pull out their loop of wire whenever they need a placebo to get the POCO to move on their desired fix

-Jon

 

[winnie]

I don't think I've had to think about the difference between electric and magnetic fields since school. But I seem to remember something about every electric field creates a magnetic field, or at least every AC electric field creates a magnetic field.

Yup, a changing electric field will produce a magnetic field, and a changing magnetic field will produce an electric field, thus electromagnetic waves and all that fun stuff.

One would have to go through all of the math, but I'm pretty sure that the 'near field' magnetic effects would dominate here.

-Jon

 

[TxT]

What's the link to the "free electricity"....i have got tot read about that.

 

[ELA]

No Free Power for me today!

No Free Power for me today!

It was bothering me so I built a test loop like theirs -but I cheated and made it 4 ft in diameter and only used #8 wire. Less unwieldy.

To test the loop I ran 10 amps through a single conductor taped to the circumference of the test loop. With 10 maps primary I got 2 amps in the test loop.

I moved the primary 1 foot away from the test loop keeping 10 amps primary and repeated. Secondary went down to 0.4 amps.

The coupling reduced to 20% due to a 1 foot separation.

I then went exploring with my magic ring.
Unfortunately I could not detect any free power in either my front or my back yard

I even tried sitting under some 138KV distribution lines with my new free power sucker but alas no free power for me!

 

[dbuckley]

... but alas no free power for me!

If you want free power then start driving earth rods and capitalise on all that stray current floating around

 

[ghostbuster]

It was bothering me so I built a test loop like theirs -but I cheated and made it 4 ft in diameter and only used #8 wire. Less unwieldy.

To test the loop I ran 10 amps through a single conductor taped to the circumference of the test loop. With 10 maps primary I got 2 amps in the test loop.

I moved the primary 1 foot away from the test loop keeping 10 amps primary and repeated. Secondary went down to 0.4 amps.

The coupling reduced to 20% due to a 1 foot separation.

I then went exploring with my magic ring.
Unfortunately I could not detect any free power in either my front or my back yard

I even tried sitting under some 138KV distribution lines with my new free power sucker but alas no free power for me!

Try reading the comments posted on the newsletter page.

The magnetic field measured and witnessed by the utilities and the electrical inspection dept. was between 100-150 milligauss.What was the field under your 138 kv. line??

All other field measurements were also witnessed at site.All house power (150 houses)and cable systems were 100% isolated in this entire area.All neutrals were not carrying any current because the power was turned off in this entire area.

http://mikeholt.com/newsletters.php?action=display&letterID=507