The picture you showed are transmission lines (as opposed to power lines, which are the ones on wooden poles that have the transformers on them used to supply houses and other buildings). Transmission lines can carry upwards of 500kV. There is a lot of complication, but even as close 20m, you're only going to experience ~30 mG (milli-Gauss) of magnetic field. The Earth's magnetic field on the surface is variable, but never goes lower than around 250 mG (all the way to 650 mG or so) and in the US a general number is 450 or so depending on how far north you live. So compared with Earth's 450 mG field, the 30 mG you get from a power line is pretty much in the "noise" of the compass measurement.
For a power line, you get up around 30mG if you are landing on top of it. I have power lines behind my house. I regularly fly within 2 or 3 meters with no problem. It might sometimes be less. Keep in mind that everyone has power lines close to you, assuming you are near any electricity. If you have buried utilities they are absolutely closer to you than overhead power lines and the earth does not stop magnetic fields. Literally anyone who takes off in a neighborhood is close to power.
Magnetic fields drop off with an inverse-square effect so if you fly very close (within 5 meters) to a transmission line, you're starting to get into more complied territory. That would actually never be something you should try.
Finley, there will always be more than one transmission line. They run parallel to the the ground. This means the magnetic field parallel to the lies is weaker than the field directly under them. You should avoid flying below them for sure. Aside from the magnetic field the EMF can interfere with your GPS reception.
TL;DR
For big transmissions lines stay as far away from them as the towers are tall. Power lines are more dangerous as obstacles than they are magnetic generators. |