Electrical Question

A mu-metal shield.

Contrary to the rumor you heard, these do not work very well, regardless of the metal used. The key is to direct the magnetic field around the region to be shielded not just between source and sensitive device.

A car.

The further you drive away from the transmission line, the smaller the magnetic field you'll detect from it.

How would that affect the magnetic field?

There would be no magnetic field.

Superconductors use a concentric cable with all three phases placed in a circular fashion like copper tubing of different diameters separated by a dielectric. Due to the arrangement of all three conductors in one cable the magnetic flux of one phase will cancel out the effect of the other phase.

And then you have the Meissner effect that expels all magnetic flux when the superconductor reaches operation temperature. Like the age old question "What would happen if you would drop a magnet down a superconducting tube?" It would free fall when it enters the tube.

You are describing standard magnetic field canceling that comes from twisted cabling. It has nothing to do with superconductivity. Room temperature copper wires twisted together will not generate a magnetic field. Now the logistics of superconducting cables makes gathering them close to each other almost mandatory but this produces many complications from just the simple mechanics of the forces these magnetic fields and cryogenic fluids produce and preventing the magnetic fields from quenching the superconductor.

Besides the OP asked how to reduce the magnetic field from an [existing] transmission line, not how to design a better transmission line.

Oh. I thought you were being serious for a minute. My mistake.

"which type of instrument is used to reduce the magnetic field of a High voltage transmission line?"

a wire with a grounded shield?

a faraday cage?

a magnetic field reduction device (MFRD)?

A simple Faraday cage will do nothing to stop or divert static or slow (60 Hz) magnetic fields. A Faraday cage stops electrostatic fields.

Yes, but a complex one will stop both. After all, one of the most common uses of a Faraday Cage is the prevention of propagation and reception of RF energy, which is clearly electromagnetic.

You reckon a Faraday cage would have much effect on a magnetic field at 50 or 60Hz?

John,

As long as it is constructed from the right materials, basically layers of mu metal and soft iron mesh/sheets. From the Wikipedia article that you referenced above:

"...mu-metal shields are often made of several enclosures one inside the other, each of which successively reduces the field inside it. Because mu-metal saturates at such low fields, sometimes the outer layer in such multilayer shields is made of ordinary steel..."

There was also a discussion in this thread.

... but it (what you're describing) is not necessarily a Faraday cage, which could (depending on the frequencies it's designed to shield against) be made of chicken wire.

It does meet one of the definitions though:

"...A Faraday cage or Faraday shield is an enclosure formed by conducting material or by a mesh of such material..."

Form follows function. Yes I know, Faraday originally intended it for electrostatic shielding, time has extended its usage.

No, you are changing the definition of a Faraday shield to suit your opinion. A Faraday shield fabricated from material with a relative magnetic permeability sufficiently greater than unity will also shield magnetic fields inside the shield. There is no specification on the magnetic permeability of Faraday shield material, just that it is conductive.

A brain that can perform a cursory internet search.

At the risk of bursting bubbles and expelling the Meissner effect, there is no instrument, "used to reduce the magnetic field of a High voltage transmission line".

Period: End of story! That's it. Finished.

See ya later, boys.

Wrong! An OFF switch to stop the flow of current will work.

That, sir, is NOT an instrument.

They did not say a measuring instrument. All tools can be called an instrument.

You are hallucinating. Better get a better hat!

"which type of instrument is used to reduce the magnetic field of a High voltage transmission line?"

OOPS, maybe I'm hallucinating.

I need to lay off the tequila and coffee.

Still if a switch is an instrument, what is a boa constrictor?

A stage prop for an exotic dancer.

Scottsdale AZ, circa1979. Her name escapses me but she danced with a Boa.

Those were the days. Young, single, good job........................................

build a house of soft iron walls with windows having iron bars as well. Best design could be like Alcatraz cell holes.

shyam said:

"build a house of soft iron walls with windows having iron bars as well. Best design could be like Alcatraz cell holes."

this will work, as long as the roof and floors are also iron or bars. no hole can be greater than 1/4 wavelength (λ/4) in any dimension because RF propagates through holes larger than that.

If we assume (it really wasn't stated) that the question had to do with AC power transmission lines, then the unadjusted wavelength at 60 Hz (which is not RF) is 1,694,000 ft, a quarter of that (776 +/- miles) is still a mighty big hole!!!

The magnetic field is generated by the current. A transformer raising the voltage will reduce the current for the same amount of power and reduce the magnetic field. That is not really an instrument, but I doubt if you can find an instrument that will reduce a magnetic field and of course the voltage has to be AC.

A former associate of mine (a PhD chemist) once told me, and I quote, "opinions are like a$$holes. Everybody has one, and most of them stink"!

Credit to, Marshall G_ _ _ _ _.

We constantly prove that here, all of us it seems, do it.

I'm sticking to mine, instruments do not affect magnetic fields.

You are all wrong anyway (except the statement about opinions). Read the OP again, paying attention to the semantics...

"which type of instrument is used to reduce the magnetic field of a High voltage transmission line?"

The poster did not ask how to reduce the effects of the magnetic field, he wants to alter Oerstead's Law. The only thing that will do that is to reduce the current flow, so the "instrument", if one accepts the concept of aparatus as instruments, would be some sort of high voltage Variac.

I further reject the "switch as instrument" concept because if switched completely off, the high voltage line is no longer transmitting, thereby voiding the semantical premise. By the same token, said Variac would need to limit the reduction only to the lowest point of still being considered high voltage.

All that said, I do enjoy the amount of pointless banter we are allowed to engage in here, often at the expense of one-shot-wonder posts.

JR, You're right, plenty of guess work, especially when it seems clear that the poster put his language through a translator to make the post.

I suspect the OP lives near a power line and was wondering how to "protect" his family in which case we should have told him not to worry. If he's an engineer then the answer is to properly transpose the lines. Even worse, another assumption could be that these are in the air when in fact they could be underground cables, in which case the answer is lay them in trefoil instead of flat, put them in the same conduit, or use a multicore shielded cable.

GIGO still rules until posters are forthright with the conditions surrounding their questions.

I think you're right, I was just having some fun with semantics.

I live directly adjacent to 230kV power lines. No cancer, no issues, other than the fact that my Wife is bat s--t crazy. But then again, she was that way before we moved here. I was kind of hoping the EM fields would somehow straighten her up, but alas, the effects of these things are seriously over blown...