"Mystery Current" burns up cable splitters

[crossman]

ELA, I agree with all your points also. I may do some experimenting of my own in our lab.

Your test with the wires closely tied together, to me, is very similar to a transformer. In the xfmr, we have many turns of the primary intimately in magnetic contact with many turns of the secondary. I guess if we stretched the primary and secondary out into straight lines, still in intimate magnetic contact, the primary would still induce into the secondary, but probably at a reduced efficiency. But, your experiment was quite different from the situation at hand, as you mention.

I can't help but think that sometimes profits can be made by hype. For example, there are many many books on UFOs. These authors have made money. There are even ghost excorscists and folks that speak with the dead, and these people make money too. For me, I am going to use my logic and knowledge and experience and base my beliefs on those things. I also believe it is wise to err on the side of skepticism. In other words, don't believe everything anyone tells you.

Still, I await with an open mind, hopefully someone else will chime in with some more evidence.

 

[crossman]

And, from the article, do we even need the five foot loop of wire? Why not just walk around with a clamp-on ammeter?

 

[RayS]

looking at the study linked to by Ghostbuster in post #20 it seems that the great size of the loop was significant. Also, what effect from having 2 sets of 3 phase conductors? Are these arranged A,B,C from top to bottom on both sides? Or are they ABC CBA, which would seem to "throw" opposite poles on each side. So far, the discussion seems to be about a single AC line.

I have no answers, just more questions...

 

[crossman]

RayS, I have not ruled out the possibility that a long stretch of 230kv powerline running next to a lower voltage powerline behind the houses, with the cable tv lines run in the front of the houses, with common grounds between the systems, could experience some induced current. I could actually accept that one, with some reservations (hoping for further evidence).

But walking around with a 5 foot loop of wire and experiencing significant current flow seems to fly in the face of reason (well, in my limited reason).

 

[ItsHot]

5 foot copper loops?

5 foot copper loops?

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.

Hey Rick! How long do you think those 5 foot "copper" loops would last in your yard?

 

[crossman]

One more thing: What we have is a single winding primary with a single winding secondary. Turns ratio is one to one, meaning the voltage ratio is one to one (assuming a perfect transformer).

Consider 100 feet of transmission line of 350 kcmil wire which is inducing voltage into 100 feet of secondary wire. Resistance of 100 foot primary is .0037 ohms. Assume a load of 200 amps. Voltage on primary winding is .74 volts.

The most that could be induced in secondary is .74 volts.

Now, with the large distance between secondary and primary, it is nowhere near 100% efficient. Maybe closer to 5%. So the secondary voltage is .037 volts.

And this is assuming that none of the magnetic field of the primary wire is being cancelled by the other phase wires. If we take that into account, I would say the voltage in the secondary would be practically zero.

So I am again going on record with the opinion of bullcr@p. Perhaps those in the know can set me straight?

 

[ELA]

ELA, I agree with all your points also. I may do some experimenting of my own in our lab.

Your test with the wires closely tied together, to me, is very similar to a transformer. In the xfmr, we have many turns of the primary intimately in magnetic contact with many turns of the secondary. I guess if we stretched the primary and secondary out into straight lines, still in intimate magnetic contact, the primary would still induce into the secondary, but probably at a reduced efficiency. But, your experiment was quite different from the situation at hand, as you mention.

Still, I await with an open mind, hopefully someone else will chime in with some more evidence.

Yes I was interested in the story and do believe there were induced currents from some source causing problems. All I have been questioning is the ring test as it seemed very strange to me.

Because I am no magnetic field expert, and do not own a gauss meter, I thought to do a test to show the absolute best case. One current carrying wire tied directly to the loop perimeter for maximum coupling. What current would it take to produce 2 amps in the ring (secondary)? By experimentation I found that to be 10 amps.

Using the first calculator I posted a link to, with two wires coupling into each other you see that the magnetic field drops off very rapidly as you move the wires apart.

All this implies a very strong magnetic field would be required to induce the 2 amps into the ring from a 100- 300 ft distance. (neglecting other real world parameters of field cancelations)

All of that was just to get a feel for orders of magnitude involved in trying to get such a current induced into the ring.

As you have stated, when you then consider the non ideal and real world magnetic coupling to this ring (field cancelations, opposite current directions, long distance from source, etc) it seems highly improbable for them to measure the currents stated.

Like you though I remain open minded - knowing I am no expert in this realm. Always trying to learn new things.

 

[crossman]

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

Hey ELA:

It just dawned on me. No, we cannot consider this as a current transformer because with a current transformer, the primary wire is running THROUGH the center of the secondary loops. This causes all the loops of the secondary to be of proper polarity to add together to make a much higher voltage.

In our case, the origin of the magnetic field is on the outside of the CT. Totally different situation.

Get a CT and go walk around some electrical panels and transformers or even power lines and see if we get any voltage produced. I am going to say NO.

 

[ELA]

Hey ELA:

It just dawned on me. No, we cannot consider this as a current transformer because with a current transformer, the primary wire is running THROUGH the center of the secondary loops.

Didn't say it was. Said "think of it like" and "with terrible coupling". This was just to demonstrate the math that followed- in theory.

 

[crossman]

I didn't mean to sound harsh. My apologies if I did.

I was just pointing out that a CT with the primary wire running through the center is hugely different than a CT with the primary running outside of the loop.

 

[winnie]

Crossman,

I like the way you are thinking, but I belive that you have made a few errors.

In post #37, you make a differentiate between flux lines 'cutting throug' conductors versus the net flux through the center of the loop. My understanding is that these two ways of looking at the issue are _equivalent_. The rate at which flux lines cut the conductors is equivalent to the rate change of net flux enclosed by the loop. So you can figure your voltage either way.

When you did your analysis of the voltage drop on the HV line versus the voltage drop in the coil, you suggested that the resistance drop in the primary limits the voltage that could be induced in the coil. This is not the case. Any current induced in the secondary would create a magnetic field which would result in a magnetic voltage drop on the primary. If the secondary were very well coupled to the primary, you would have a transformer and could induce lots of voltage in the secondary, at a cost of lots of voltage drop in the primary. You are correct in that with a 1:1 turns ratio the voltage on the primary is equal to the voltage on the secondary, but this is the magnetically induced voltage, and ignores any voltage drop.

I belive that your diagram expresses why the coupling between the transmission lines and a random five foot coupling will be very weak. There will only be a slight difference in the flux cut by one side of the coil versus the other side, which is another way of saying that the net flux flowing through the coil would be extremely small, and thus a very small voltage induced in the coil. The only reason that you get high currents in this case is that you have a low voltage applied to a dead short.

For the most part, if the transmission line is balanced, then the net current on all three conductors will be balanced, and most of the magnetic field canceled out. But there will be some net field, and for most line configurations, there will be a significant 'rotating field' component, just like in an electric motor. This rotating field could induce voltage in a coil somewhere in the vicinity. It won't be a strong field, but if you set things up properly you might get something.

I saw this in action at the Glen Canyon dam, while on a tour: power from the generators to the step up transformers was routed via conductors with perhaps 18" of separation. So you had three _large_ 'pipes' side by side carrying current from each set of generators to each set of transformers. At one point these pipes were vertical. Someone had placed an empty coffee can open side down on a spindle, between two of these pipes. The can was merrily spinning away, a very small mechanical load on a 'parasitic' induction motor.

Finally, a clamp on current sensor works with a primary that goes _through_ a magnetic core, but which is laying parallel to the secondary conductors. For some high frequency applications, two wires side by side going through the center of a ferrite bead is enough of a 1:1 transformer.

-Jon

 

[ELA]

No Problem Crossman.
I find this a difficult medium to communicate through. What you write is not always as clear to others as it seems in your head and others often interpret things differently than you might intend.

I like your use of pictures as that is very helpful (like 1000 words one might say)

I just went back and read the report again and see how they tried to compare the current induced in their test loop to the bigger loop formed by the cable wiring.
The different magnetic fields from the various power wires must have been aligned, phase shifted, etc. just right huh? :roll:

 

[electricalperson]

probably wrong about this but

http://www.dtvcity.com/access/jensen-vrd1ff.html wonder if that will help

 

[electricalperson]

i was right about being probably wrong. i read that article the OP posted. very interesting :grin:

 

[crossman]

I like the way you are thinking, but I belive that you have made a few errors.

Thanks for the complement, and there is no doubt I have been wrong before, and will be again!:grin:

In post #37, you make a differentiate between flux lines 'cutting throug' conductors versus the net flux through the center of the loop. My understanding is that these two ways of looking at the issue are _equivalent_. The rate at which flux lines cut the conductors is equivalent to the rate change of net flux enclosed by the loop. So you can figure your voltage either way.

I still think I am right on this one. Because of the geometry of the source of flux being outside of the loop, not having the source of the flux passing through the center of the loop, or not wound around a common core, the voltage produced in the top of the loop opposes the voltage in the bottom of the loop and subtracts, not adds.

See diagram: to me, the flux at the center has nothing to do with the voltage in the loop. Now, if the source of the magnetic field was inside the loop like a CT, then all the voltage is in the same direction and will add together. But in our case, each side of the loop will have voltages going from left to right(arbitrarily at a given time on the sine wave) and if we complete a loop by tieing each end together, the voltages subtract.

Diagram should say "volts" and not amps.

When you did your analysis of the voltage drop on the HV line versus the voltage drop in the coil, you suggested that the resistance drop in the primary limits the voltage that could be induced in the coil. This is not the case. Any current induced in the secondary would create a magnetic field which would result in a magnetic voltage drop on the primary. If the secondary were very well coupled to the primary, you would have a transformer and could induce lots of voltage in the secondary, at a cost of lots of voltage drop in the primary. You are correct in that with a 1:1 turns ratio the voltage on the primary is equal to the voltage on the secondary, but this is the magnetically induced voltage, and ignores any voltage drop.

I agree with you completely now that you mention that. The induction from one conductor to the other will certainly cause the impedance of the "primary" to be higher, which will cause a larger voltage drop than just the resistance of the wire. Of course, any significant voltage drop would be felt on the power lines as a drop in voltage at the load end. Now, at 200 feet between the transmission lines and the loop leaves very poor magnetic coupling indeed.

I belive that your diagram expresses why the coupling between the transmission lines and a random five foot coupling will be very weak. There will only be a slight difference in the flux cut by one side of the coil versus the other side, which is another way of saying that the net flux flowing through the coil would be extremely small, and thus a very small voltage induced in the coil.

Oops, maybe I don't understand what you mean up above in your first thought when you are talking about the flux in the center of the loop... because you obviously understand my point as expressed in the diagram. Could you further explain what you mean by flux at the center of the loop?

The only reason that you get high currents in this case is that you have a low voltage applied to a dead short.

Agreed, and is the reason I have not totally discounted the phenomenon. The resistance of a #6 copper wire is going to be very very very low and it doesn't take much voltage to push current through it. On the other hand, we have to take into account the inductance of the loop too.

for most line configurations, there will be a significant 'rotating field' component, just like in an electric motor. This rotating field could induce voltage in a coil somewhere in the vicinity. It won't be a strong field, but if you set things up properly you might get something.

Understood. But I feel the majority of that rotating field will be between the conductors, not outside them. 200 feet away would render it almost nil?

I saw this in action at the Glen Canyon dam, while on a tour: power from the generators to the step up transformers was routed via conductors with perhaps 18" of separation. So you had three _large_ 'pipes' side by side carrying current from each set of generators to each set of transformers. At one point these pipes were vertical. Someone had placed an empty coffee can open side down on a spindle, between two of these pipes. The can was merrily spinning away, a very small mechanical load on a 'parasitic' induction motor.

Very cool, and totally believable, with some reservations about the nut who placed the thing between the conductors, and even more reservations about the security of the place, which would permit someone that close to those huge conductors in the first place. And what voltage were those conductors at? I am wondering about arcs and such for the guy brave enough to stick the pot in between.

Thanks for the input! :smile: I am really interested in this subject.

 

[winnie]

On flux cutting versus flux in the center of the loop: the _total_ flux through the loop is not the issue; what is an issue is the rate change of flux through the loop. The rate change of enclosed flux is equal to the net flux that 'cuts' through the conductors per unit time.

You drew flux cutting a pair of parallel conductors that are quite close relative to the distance from the power lines. At any moment in time, the flux cutting one conductor will be very similar to the flux cutting the other conductor, and so the voltage induced in each conductor will be similar. That is what you drew, and what I understand. Because similar voltage is induced in each conductor, if you tied them together at one end and measured the voltage at the other end, you would get a very small voltage.

Whatever voltage that you did measure would be caused by the _difference_ in flux cutting the two conductors. This very small difference is the rate change in the net flux enclosed by the loop. Not the total enclosed flux, but the rate change of the enclosed flux. These are two different ways of looking at exactly the same thing. You are looking at the lines of flux that go past the conductor; but once they go past the conductor they are now inside the loop, or flux that starts inside the loop ends up on the outside. But the rate change of enclosed flux is exactly equal to the net rate of flux cutting past the conductors.

Absolutely the bulk of the rotating field will be nearer (and between) the conductors. Whatever was being measured was the net changing flux that managed to make it out of the near field.

Hmm. LarryFine asked about Earth currents. We are assuming that the net current on the line is balanced, but there might very well be parallel paths or current paths through multiply grounded neutrals. If the there were _net_ current on this set of lines, then there might be considerable flux extending quite a distance.

When I was at the Glen Canyon dam, the conductors were appropriately insulated. I think that they used bus bars in oil in pipes; the outside of the pipes was about as dangerous as the outside of a conduit. The can was sitting between the insulated pipes.

Here is another fun one: on a very large scale, the solar wind can push the ionosphere around, changing the shape of the Earth's magnetic field. Have a large enough loop of wire (say the Quebec grid, or a pipeline), and this can induce a signficant voltage, enough to cause damage or trip protective devices. (As I recall, a couple of volts was induced in the Quebec grid, but at _very_ low frequencies. This was enough to drive transformers into saturation, which increased the 60Hz magnetizing current flow, which then caused breakers to trip.) Look up 'Geomagnetically Induced Currents' for a side trip.

-Jon

 

[iaov]

I think they covered this topic on Myth Busters. They put some coils of wire directly under a 230 kv line and you couldn't run a 4-20 ma instument loop with the induced voltage much less burn anything up.:smile:

 

[crossman]

You are looking at the lines of flux that go past the conductor; but once they go past the conductor they are now inside the loop, or flux that starts inside the loop ends up on the outside. But the rate change of enclosed flux is exactly equal to the net rate of flux cutting past the conductors.

I think I see your point now. Thank you for the further explanation. So what we are comparing is the flux entering the loop versus the flux which is leaving the loop, and the difference is the flux that can cause a net voltage on the loop.

When I was at the Glen Canyon dam, the conductors were appropriately insulated. I think that they used bus bars in oil in pipes; the outside of the pipes was about as dangerous as the outside of a conduit. The can was sitting between the insulated pipes.

Gotcha. When I read what you said, I visualized non-insulated pipe-type busbar conductors.

Here is another fun one: on a very large scale, the solar wind can push the ionosphere around, changing the shape of the Earth's magnetic field. Have a large enough loop of wire (say the Quebec grid, or a pipeline), and this can induce a signficant voltage, Look up 'Geomagnetically Induced Currents' for a side trip.

While doing some internet research on induced currents, I saw several that concerned geomagnetics. I'll have to check that out.

I've got another point to make about the original situation, but I need to post a diagram. I'll do that tomorow from a faster internet connection.

 

[jghrist]

On flux cutting versus flux in the center of the loop: the _total_ flux through the loop is not the issue; what is an issue is the rate change of flux through the loop. The rate change of enclosed flux is equal to the net flux that 'cuts' through the conductors per unit time.

The flux we are dealing with is caused by a sinusoidal current, so it is a constantly changing sinusoidal flux.

 

[crossman]

The flux we are dealing with is caused by a sinusoidal current, so it is a constantly changing sinusoidal flux.

Exactly. If it was a stationary, non-moving field, it would not induce any voltage in a stationary conductor.