[classicsnoot]

In my limited experience [1 windmill that i am currently working on] the biggest issue we are facing is lightning strike. The windmill is located on a small island .6 miles off of the coast of Maine. the structure rises 20+ feet over the tops of the trees. The Seawind is pretty consistent so wind seemed like a good idea, but the first strike fried the innards of the turbine and compromised the lines running to the battery array [the system uses a ruggedized Ranger power management computer to charge the batteries (28 inline 1.5 amp boat batteries) from either the windmill or the diesel generator]. I know very little about all of this, but it has been left to me to get it working. The system only has to power 110v outlets [30+], a water pumping system [well pump + distro pump], and a washer and dryer. As it stands we run the Genny for ~6 hours then use the batteries for ~18 hours. The island is only inhabited for ~2 months all year, but it is still expensive and dirty. The Island is conifers rooted in primeval moss on top of pink granite. there is little to no dirt, and i have limited access to TNT and my biggest rock drill bit only goes down 2 feet, so the grounding system (which i think is where the fault in the system is) is my biggest concern. As of now, i am going to attempt to use a surface, chemical grounding system, but, again, i don't really know what i am doing so it is pin the tail on the donkey with my hands tied behind my back. If anyone has experience with windmills and/or grounding i could desperately use some advice...

[Animats]

You need a lightning protection consultant. Lightning protection is a solved problem - power lines, large communication towers, and wind farms are struck all the time, without serious problems. Doing it right can get expensive, but is quite possible.

Grounding on hard rock is tough. There are methods for measuring ground conductivity, and in a situation like that, you'll need them.

[ghshephard]

We have a lot of our equipment tested in Florida (where they have some large testing centers) for lightning tolerance. I've been told, that you don't actually verify the equipment can be safely struck by lightning - as anything that is hit by lightning, is immediately destroyed. The objective is to ensure that equipment nearby a lightning strike doesn't suffer secondary damage (possibly from a power surge in the line). We install lightning arrestors near our electronics, but anything that actually gets hit is replaced.

Airplanes though, are supposedly struck by lightning, and continue to work. I'm guessing that this has something do do with them being suspended in air, and not having a connection to ground.

[Animats]

Antenna towers get hit all the time, and the transmitters and receivers survive if installed properly. First, there's a spark gap between the antenna and ground, with big metal contacts, copper or silver, a short distance apart. That diverts most of the lightning bolt to ground. Then the feed line for the antenna has a big inductor, a coil made of heavy busbar, usually in a grounded can. This is often placed through the wall of a grounded metal equipment enclosure.

The inductance blocks a fast risetime lightning bolt, forcing the energy to the spark gap. A few hundred volts will still get through that. So following that there's a gas tube protector, which is essentially a neon tube which will ionize and short to ground. (Phone lines also have those at the central office end.) Following that is a MOV, as in a surge suppressor, to dump the remaining surge into ground. What's left after than can be tolerated by most RF electronics intended for such applications.

If this didn't work, radio wouldn't work in Florida. It's not that this stuff is expensive compared to the equipment it protects. It's that the front end stuff is big; #4 copper cables, big spark gap units, heavy ground rods, and solid metal equipment enclosures with welded seams.

Somewhere right now, a cellular tower is taking a lightning hit and restarting itself without damage.

[ghshephard]

You seem to know a lot about this, so all I can do is reiterate that when we take our electronics to florida to be tested, our QA guys make it clear that no company's electronics are designed to survive a lightning strike - including ours. (Though we are designed to resist a 22 calibre bullet). We install a lot of lightning arrestors, mandatory in Florida, São Paulo, Singapore -- and we seem to do fine in those areas (knock on wood) - but I've been told that's to prevent a nearby lightning strike from running down the antenna line into our electronics. If our RF gear (which is mounted outdoors in weather rated containers) gets hit with a direct strike - 100% guaranteed destruction.

[eigenvector]

I think you and GP are actually agreeing. The goal of a lightning protection system is to ensure that when a structure (antenna, wind turbine, transmission tower, etc.) is hit by lightning, the lightning energy is provided with a low impedance path to earth such that any sensitive equipment inside or attached to the structure is not exposed to currents and voltages beyond its design limits.

There are other considerations as well for personnel safety, like ensuring that the ensuing ground potential rise doesn't expose someone standing near the earthing point to a shock hazard.

Going back to the original comment, lightning protection in wind turbines is more or less a solved problem. Direct hits on blades are routine and any utility-class wind turbine will be designed with an appropriate system for the area in which it is located. Now, when your turbine is on a big rock, that's a problem and you may have to blast and backfill to achieve a sufficiently low earth resistance.

[classicsnoot]

From all i have read, direct strikes on gear is a grab bag of destruction. I've read that in the Vietnam Conflict guys would get shot and the bullets would bounce off of their skin [strange effect of velocity, turbulence, and chance], so i bet there are examples of "look mom, no destruction" but i tend to side with you, at least as the guy managing this project: at no point am i going to say "cannot fail", "works everytime" or any version of the two. If you have never been to Maine, it is beautiful. If you have never built in Maine, don't get attached. The sea wind destroys everything. I kept my tools covered every day on a 42 day stint except 1, and the rust is ubiquitous. So i build to fail. The real question is, how long can i draw out the failure?

[pixl97]

Like the other poster said, lightning can be dealt with, but I'm very glad I don't have your problem. You are dealing with the worst possible combinations of landscape and expense. My honest answer is you need a specialist with the proper testing equipment measure the resistance to earth at your location. If it is very high you will likely need deep holes dug (reading about one mountain top location that needed 600' to get proper grounding, you shouldn't need anything that extreme). The combination of a chemical grounding system in a well shaft may overcome your grounding issue. But, without that proper ground any lightning protection on your tower is apt not to be the shortest path to earth and will likely fail.

http://www.copper.org/applications/electrical/pq/casestudy/m...

[stickfigure]

I'm certain there's a perfectly logical answer to this question, but I couldn't find it in 5 minutes of googling:

Why can't the ocean be used as ground?

[emiliobumachar]

Very good question. I've posted it to Stack Exchange, let's see if someone answers.

http://electronics.stackexchange.com/questions/164898/can-th...

[classicsnoot]

Judging from the (limited) SO responses, coupled with what i was told by the guy i am working for, the degradation of the cables makes the idea cost ineffective. Also, and i cannot stress this enough, in Maine you do not fluck with the Lobstermen. You don't even do anything that could be construed as tampering with their routines. Dudes are the hells angels of the small boat world. The thought of trying to explain why i look like i am cooking their profits before they can haul them up gives me the willies...

[ochoseis]

My guess is that it'd be dangerous for those who might be swimming when a storm quickly moves in.

[classicsnoot]

the water is a flat 40 F. average depth is 50' in the center. The Reach has an average flow (in/out) speed of 6 knots (underwater). The Reach moves about 1 trillion gallons of water every 6 hours between high and low (may sound hyperbolic; look up the Moosabec Reach). The tidal variation between high-to-low is ~14'. In a perfect world i would submerge a tidal generator in the deep point and power my island project AND Jonesport-Beals, but as i stated before Lobstermen do not like change, so i am pretty sure a giant underwater propeller is not on the menu... i digressed; the only swimmers are the seals, the sharks, and the daft.

[avn2109]

I too would like to know this.

[classicsnoot]

So i am going to keep a journal on this project. I must be honest that the windmill overhaul is at the top of my punt list due to the multifaceted danger [climb up, remove topper, winch down, climb down, reverse&repeat, inline battery array, wicked wind in the west] but there are a number of other cool things i am doing there: rebuilding an articulating dock, re routing the water system, planning and implementing a solar system, repairing roads, rewiring structures, and preforming black magic rituals to curse the monsters at HughesNet [jk but serious]. We are going to play around with using Pi s or Arduinos for some of the management tasks, and the Ranger Power Management system is pretty cool, if dirt simple and dangerous to mess up. All this to say, if you are interested and have any advaice for my team and i, please hit me here. I will start posting a journal and pics when we start Phase I. The island is Norton Island in Downeast/Acadia right next to Jonesport-Beals [setting for SKs The Fog]. The organization that runs the writer's residency can be found here: http://www.easternfrontier.com/ aaaand i just realized it is EFF... lol. No relation.