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I was conducting some robotics tests on a old wind turbine today, and noticed strong magnetic fields around the steel tower. This magnetic field does not exist on other modern wind turbines at the same site. I am completely baffled by this, so I’m hoping I can find some answers here.

These turbines are located in San Gorgonio Path near Palm Springs, CA. They are Nordtank 65 wind turbines, decommissioned about a decade ago. The towers are steel, bare, without paint. Overall they have very little rust as the climate is very dry and hot. The turbines still contain their generators, which contain magnets. But I don’t think these magnets are very strong.

Using a decent mechanical compass, I can clearly see about 40 degrees of deflection as I walk towards the base of the tower from about 10 feet away. I tried this on all 6 decommissioned Nordtanks, all of them exhibited the same behavior. I tried on modern 0.5 MW turbines nearby while they are generating, but the max compass deflection I got was about 5 degrees at a distance about 5 inches away from the tower itself.

When I first observed the magnetic field, my theory was that the turbine tower was still heating up from the morning sun. Due to Seebeck effect, there could be current flowing in the material as the base is cooled by the foundation buried into the ground. However the deflection on the compass did not stop even though the temperature stabilized.

What could have caused this? I would love to find out!

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    $\begingroup$ What type of steel tower ? Monopod tube ? Four tubular legs or angle with structurals ? The mills and fab shops do some handling with electro- magnets. For oil/gas, pipe are usually inspected for flaws with electro-mag techniques. They should be demagnetized afterwards but I have heard of many weld problems because the pipe is still magnetic. And the current from field welding can magnetize the structure. So it could have been magnetic originally. And in service, what about the cables bringing the power down, they have some magnetic fields, $\endgroup$
    – blacksmith37
    Commented Jul 11, 2019 at 23:53
  • $\begingroup$ @blacksmith37, it's a monopod tube, about 20 meters tall. THat's a good point on in the inspection technique. I'm going to try and find some info on whoever made these towers...hopefully they are still in business. As of the cable, they produce AC... will they still have an effect? $\endgroup$
    – Anshuo Liu
    Commented Jul 12, 2019 at 18:42

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It is a well established fact that ferrous metals become magnetised over time due to the earth's magnetism. The towers have been aligned with the field of torque sufficiently long enough to absorb electromagnetic energy that polarised the structures. This can be removed by exerting a substantial shock to the entire structure or heating it up beyond 768°C to realign the ionic crystalline bonds.

The cyclic heating and cooling process over decades has caused intensive stresses at molecular level that induce electronic field polarity exhibited by electromagnetism too. Rub 2 pieces of mild steel together long enough and they become magnetic. Try it with a couple dining knives. This is essentially what has been happening to the metal crystals all this time: friction.

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