Lightning Strikes

[daleh007]

Since you potentially have an object higher than anything nearby how do you deal with the possibility of lightning striking your wind gen. or tower?

Daleh

[jacquesm]

wear your rabbits foot

ground your tower with a grounding rod of its own at the base of the structure

keep your rectifiers at the base of the tower or in your battery vault so you can exchange them if lightning does hit your stuff without pulling everything down (or hits near your stuff, rectifiers are semiconductors and don't need a whole lot to kill them)

bury your cable

put a DC surge arrestor with proper ground before your windpower disconnect

make sure your whole installation has a proper ground (10 ft rod, measure the ground resistance to make sure it really works)

put an AC surge arrestor in the outgoing line of your inverter on the cable to your service panel

If you see a thunderstorm approaching it is good practice to shut down your windmill using a short circuit switch at the base of the tower and to disconnect it from the wiring running to the inverter.

If a thunderstorm is IN PROGRESS, or really nearby for gods sake stay away from the tower and the wiring, and do not attempt to shut it down, unless you think your life needs a bit more sizzle. (see the rabbits foot above).




All of this is NO guarantee, lightning strikes where it feels like and when it feels like, and any amount of precautions can be overcome by a particulary vicious storm.

no rabbits (or other small furry animals) have been harmed in the creation of this posting

[jacquesm]

sorry, forgot one:

bury your wire as deep as you can in open terrain. 3 ft is a minimum ! more is better.

This may need a bit of explaining. Wherever lightning strikes it creates an expanding current surge from the point of impact. This can create substantial voltages across wiring, unless these voltages get shorted out by the surroundings of the wiring. Deeper ground is usually wetter, and most of the effect happens at or near the surface. Burying deep also reduces the chance of lightning 'finding' your cable.

[daleh007]

Thanks for your comments. I guess I'll have to do some thinking about this one. The problem will be getting anything 10ft into the ground as there is little surface soil, maybe a couple of feet, and signs and septic systems are usually blasted to get through the rock.

[jacquesm]

rocky ground eh ? That makes it a LOT harder to get a proper ground. Ask a local electrician what kind of tricks they use. There are machines that vibrate a groundrod in (if it's loose rock, if it's bedrock it's even harder). A possible way would be to situate your mill near a well head and find a ground on that (rebar).

I got lucky here, I have my tower (no windmill yet, but working hard on one) on a hill which is literally full of rocks, and on the first try my groundrod sank in all the way.

Wellheads are usually on lower ground though, and you want your windmill as high as you can get.

One way to look at it is that you gain almost as much as you lose, your ground is going to be hard to make, but putting up the tower & guys is a breeze, you can simply anchor in bedrock.

[JW]

 007,

This may prove interesting. There was a good discussion here about this.

 do search for "lightning strikes again" or,

 http://www.fieldlines.com/story/2003/9/19/82225/2621

-JW

[Nando]

Dale:

A metallic pipe must be installed higher that the tip of the mill blade, I usually install them about 3 meters higher than the blade tip.

Good electric bonding to the tower and a good pair of ground rods with less than 0.1 ohm between them.

There are other requirements to include in the protection scheme, like voltage limiters.

Regards

Nando