curious loops of wire on HV transmission pylons

I was being chauffered around Illinois this weekend, and was able to get a better look at something I've seen while driving. Now, I figured out a bit more of what I was looking at.

So, on HV transmission lines, they have 3 (or 6, if it is a double feeder) phase wires, and typically 2 shield wires on top. Generally, the shield wires are grounded at each pylon. Well, I noticed that every mile or so, there is a loop of wire mounted flat to the pole. Now, while not being the driver, I was able to see that the shield wire is interrupted and the loop is in series with the shield wire. Driving along the same feeder for a while, I was also able to see that the loops always seemed to be on the same shieled wire, they did not alternate from one wire to the other.

These loops appeared to be about 2-3 feet in diameter and consist of a number of turns, with a silvery round object in the center. It was not clear at a distance, but the wires may NOT have been insulated, they appeared to be a silver color.

So, I have been wondering what these are. Are these to add inductance to the shield wires, so as to not add a shorted turn to what is, in effect, a huge air-core transformer? But, doesn't grounding the shield wire at each pylon defeat that? Or, is the resistance of the earth so much greater than the wire resistance that it doesn't matter?

Or, is this to prevent shorting out the power line data transmission signals?

Anybody know?

Thanks,

Jon

Reply to
Jon Elson
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Are you sure that the loops you see are not fiber cable?

There are often communication fibers along with the ground wires at top.

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Reply to
Tauno Voipio

This took 5 seconds to find: "It is necessary to have constantly operational monitoring systems which uses electric powered devices for transmission of electricity over high voltage transmission lines. This paper investigates a source of power to feed these ancillary service loads since the conventional power supply systems are infeasible. The voltage induced in the shield wires of an HV transmission line is tapped off, regulated and used as a power source. We use a dc-dc converter inorder to get a regulated dc output. The results obtained shows a feasible and cost effective alternative for power source."

Reply to
bloggs.fredbloggs.fred

Your google-fu is much better than mine!

Thanks, that also explains the silver boxes in the center of the coils. But, actually, why do they need the coils?

Thanks,

Jon

Reply to
Jon Elson

Sounds like it may an air-core transformer method of coupling discussed here:

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Reply to
bloggs.fredbloggs.fred

voltage on an earthed conductor is minimal. A transformer solves that & can protect from shorts to live.

NT

Reply to
tabbypurr

Several months ago I asked if something like that could be used to power logic in appliances. I guess it is feasible then.

Reply to
Tom Del Rosso

Indeed, there is a cable product that is BOTH. Not something I use, but something that I'm aware of. Those cables have to be there anyway, the right-of-way is already there, so the minor cost differential to add fibers is exactly that. Not useful or economical in my plant, but then, I don't have any HV transmission lines...

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Reply to
Ecnerwal

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