Idea Rajkot

A good ground is very important, maybe the most important thing, in mitigating lightning damage; the more energy you can divert to ground before it gets into the house or equipment room, the less you have to deal with through lightning and surge arrestors. More importantly, more energy diverted to ground means less can go through your electronics!

A lightning strike moves a massive amount of electrical charge around, and a single grounding point is not going to be able to cope with that flow. Even a few closely spaced ground rods are not really going to cut it; all those electrons need some space to fan out and disperse to ground. Here is what the pros do: They run a star-shaped network of flat copper strap fanning out from the tower, with ground rods spaced along (and tied into the ribbon) at twice the length of the rod. So, for 10 feet ground rods they are spaced 20 feet apart. The reason for using a copper strap is that even though lightning is in essence a direct-current event (most of the time the cloud is negative, the ground positive), there is considerable high-frequency energy involved as well and it tends to stay at the surface of a conductor (“skin effect”). Because of that, a flat copper strap of at least 1 1/2″ diameter and at least #26 AWG (0.0179″) thickness has less impedance (the resistance for high-frequency energy) than a #4/0 AWG (0.46″) round copper conductor.

The copper radials should be buried at least 8″ and preferably 18″ or more underground. A radial in wet soil will work better than the same radial in dry soil. There is also a maximum length where the radial’s impedance will prevent any additional electrical charge from traveling further down the line. Short radials do not work very well either, because of the same charge saturation problem mentioned before. A good radial is at least 50 feet, and no more than 75 feet long. If a radial comes within 4 feet of a metal object, that object should be electrically connected to the radial. More radials is certainly better, but after 4 radials one enters the domain of diminishing returns. Keep in mind that radials do not need to go in a straight line. Gradual bends around obstacles or to follow the terrain are fine.

Sharp bends add inductance, and will cause lightning to look for an easier way to get to ground. Any conductor that is going to carry lightning current should therefore have a bending radius of no less than 8″. This is not the place for neat, 90-degree angle installations. Gentle curves is what works best.

Tower-to-Ground Connections

Now that we have covered the part that goes into the ground it is time to take a closer look at the wind turbine tower itself. Here is something that is not needed: There is no point in running a grounding wire from the top of the tower to the bottom. Studies show no benefit. While steel is not as conductive as copper, there is so much of it and with such a large surface area that adding a grounding wire along the tower has no benefit. What is more, the unavoidable leaching of copper ions from a bare copper grounding wire would dissolve zinc from the galvanized tower, causing it to start rusting that much sooner.