How is the EM field that surrounds high voltage power converted to produce a current through a wire? How much electricity can be produced without coming in contact with the wire?

Could the EM field be used for a guide to travel along by sensing the field strength? Could a drone battery stay in float mode while traveling along a power line?

The drones would act essentially like a transformer loop connected to the transmission line (which can also be seen as a transformer loop) through electromagnetic induction.

Florescent lights powered by EM field. enter image description here

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    \$\begingroup\$ fyi: Our EE.SE chat is a better venue for a question like this. \$\endgroup\$ Jan 16, 2017 at 3:39
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    \$\begingroup\$ not a chance ... \$\endgroup\$ Jan 16, 2017 at 3:51
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    \$\begingroup\$ You probably could harvest enough energy to power an extremely efficient aircraft (think a large R/C sailplane), the engineering challenge will be avoiding contact with the wires in the case of wind gusts (even allowing for an on-board rechargeable battery for peak needs). Figuring out the optimum aircraft size and distance would be interesting - it's tempting to guess a wingspan between .5 and 1.5 of the distance between phases. Don't forget flight attitude in the presence of crosswinds. \$\endgroup\$ Jan 16, 2017 at 4:22
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    \$\begingroup\$ I totally agree with @Chris. I think it would be difficult to harvest enough energy for a vertical lift drone, but it might be reasonable to get enough energy for a powered sailplane at a safe distance. \$\endgroup\$ Jan 16, 2017 at 4:45
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    \$\begingroup\$ what a fun idea \$\endgroup\$
    – Neil_UK
    Jan 16, 2017 at 6:51

2 Answers 2


This is definitely a fun one, because the closer you get to the power lines the more power you can extract. It's not dangerous to touch the lines at one point while away from the ground, so the best solution may be to have a quadcopter-like craft with a clamp-on current transformer "claw" extending from it. The current generated could be considerable. Random example transformer. That one generates a current that's about 1% of that in the primary - but in this case the primary could be >1000A! Easily enough to fast-charge a small or medium sized drone.

Fly for a bit, then cling to the wire like a bird to recharge.

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    \$\begingroup\$ A bird might be difficult, what about a bat? \$\endgroup\$ Jan 16, 2017 at 18:33

Hmm. Perhaps use a long ferroelectric rod, held crosswise. It's a capacitive ballast in series, working a bit like a metal antenna, except it's insulating. So, no explody flaming events if it should touch across the 300KV line.

Too bad that it's all based on 60Hz. Weight of copper/iron coupling components goes inverse to frequency. A 100KHz power system gives enormous coupling for the same weight of components, when compared to 60Hz. (It's almost like they were designing it to make power-theft difficult!)

Also, note that the EM field of a big 3-phase line is mostly concentrated between the lines, and out to about one line-spacing around all three. In other words, the three lines act somewhat like coax or twisted-pair, each partially shielding the others, with the fields dropping rapidly to zero at a distance. Must needs fly really close.

A conductive plasma connection would work better. With x-ray lasers "burning a path," you could tap tens of kilowatts and run quite large motors as well as the lasers. So, a propellor-lifted flying saucer with built-in death-rays. Idea: pulse your x-ray lasers at 15KHz to provide high frequency switching supply, for low-weight supply electronics, and AM car radios go crazy from the supply harmonics, plus the 'plasma tweeter' ultrasonic output makes dogs howl whenever it's nearby.