How to protect against lightning damage?

[Rob Beckers]

A customer of mine recently had a lightning strike. It fried their inverter and wind charge controller. The sad part about it was that the wind generator had only been fully operational for about 2 weeks (It had actually been up there spinning without a charge controller for several months, but we had just hooked it up to the rest of the system). A postmortem seems to indicate the lightning didn't strike the tower/turbine, but somewhere nearby that caused induced voltage on the well-pump wiring, on the AC side, which in turn fried the electronics.

This event has me wondering what can be done to avoid damage from lightning. I know nothing is absolutely foolproof when it comes to lightning, what I'm looking for are 'best practices' when it comes to a wind turbine install. With tall towers there is no way to prevent lightning from striking, it's probably going to happen (again). What I want is to minimize the chance of damage. Radio towers get struck many times, without damage to equipment.

This particular install has ground rods at all 5 points of the tilt-up tower (tower and 4 guy wire points). All are bonded with a ground wire running around the 4 guy points. There's a Delta surge protector at the foot of the tower, and a Delta surge capacitor where the 3-phase wiring of the turbine goes into the charge controller. All the grounds are bonded together, including the house ground. This immediately indicates one weak point; There's no surge protection on the AC side.

One of my questions is what you think about those ubiquitous Delta surge protectors. They are used a lot in wind and solar installs. I've heard some swearing by them, others saying they're not worth the money and next to worthless (they're essentially filled with sand, that's supposed to 'conduct' at a specific voltage). If anyone has done measurements on them, such as hipot tests to see if/when they conduct, I would very much like to hear about it. Ditto if there is something different and/or better out there!

I'm sure I'm not alone in looking for better information on lightning protection. So let's hear it.

-RoB-

[Stuart Forthman]

If i understand you right all the guy wires should isolated. The fact that lighting can strick many miles away the current can and will find the path of least resistence therefore the wind genarator should be grounded. What you have done is to create a way to atract lighting.

[Ralph Day]

From all my reading and other forums as i understand it, if you get an actual strike...duck and cover. Most of the damage incurred by re systems from lightning come from the electromagnetic pulse (emp) which the wires and such pick up and send to ground so to speak. Rember the emp research regarding atmospheric nuclear weapons testing? and the results of emp on the electric grid from solar flares? Crossing fingers has worked for me so far.:D

Lots of voodoo involved as you can't actually induce a strike, nor would you want to.

ralph

[Rob Beckers]

Fact is that large communications towers get hit frequently and they will take almost every hit without any damage whatsoever. Lots of electronics in there, and yet nothing fries. In other words, it's entirely possible to install a tower such that it'll eat a lightning strike without breaking things.

As to guy wires, please make sure every one of them is grounded. It's really a very bad idea to not ground guy wires. The idea of grounding is to provide a low-resistance path for the energy to follow. Low-resistance is good, because it means the structure has to dissipate less of the energy. An ungrounded tower is going to get hit by lightning just about as often as a grounded one (maybe even more often, I'll get to that in a moment). Do you think that it makes any difference for lightning, after traveling several kilometers through well insulating air, to draw another arc of a few meters and jump from a guy wire or other part of the tower to earth? The problem with arcing is that it will do real damage, it welds, it melts metal, it produces lots of heat. Worse still, the charge that doesn't go to ground may follow the leads into the house and set it on fire by arcing.

For guyed towers the recommended grounding procedure is a ground rod at every guy point, another one at the tower itself, ground every guy wire and the tower to the ground rods, and run a bare ground wire underground from guy point to guy point (around the tower), then onward to the tower center. All those ground points need to be tied together electrically. Finally, also run a bare ground wire from the tower center grounding point, outside of the conduit so it's in the soil, to the house, and tie it in with the house-ground. An important note is that copper ground wire should never be directly connected to load-bearing galvanized structures (including guy wires). Galvanic action will strip the zinc from the galvanized steel, causing it to rust, and eventually to fail. You don't want this to happen to your guy wires. This procedure seems to be the consensus from talking to other wind installers.

I'm still waiting to hear from an installer that's going to talk to a lightning expert. Meanwhile, I've been reading up on this a bit. There seem to be two schools of thought on the effects of grounding: One says that a well-grounded structure will remove ions from the air, making it less conducting, and therefore make it less likely for lightning to strike the structure. In effect, it makes a tall tower appear as just a little one as far as lightning is concerned. HAM radio amateurs seem to swear by this, it is popular for them to install what can best be described as an upside-down large toilet brush made from stainless steel on top of their towers. The many pointed stainless spikes are supposed to de-ionize the surrounding air (the brush is then grounded with a separate ground wire to the base of the tower). Other sources claim no benefit from grounding in lowering the chance of strikes (they still advocate proper grounding though, as this will minimize damage!).

Protecting electronics seems possible. The best documents I've found on this are from the Dehn Website. There's a basic introduction on lightning (http://www.dehn-usa.com/manager/file.asp?tableName=tblPublications&idField=publicationId&namePrefix=smImg&idValue=5) and protection, and a more in depth document (http://www.dehn-usa.com/pdf/Lightning%20Protection%20Guide%20complete.pdf). Of course, they have a vested interest in this, something to keep in mind when reading. In any event, it looks like there are devices that will short the energy from even a direct strike to ground, and by layering 'defenses' it seems possible to protect electronics from damage. It takes more than just protecting the wires coming from the wind turbine, all other entries into the house also need surge protection (grid, well-pump, phone, and possibly cable-TV/Internet). All it takes is one unprotected path. I've requested more information from Dehn, and another company that makes similar surge protectors. No idea at this time about price, if it takes thousands of dollars to protect a small wind turbine (and its inverter) it would not make a whole lot of economic sense. We'll see how it pans out.

More to follow...

-RoB-

[Stewart Corman]

started digging for new tower platform and four guy anchors
I am running the guys from an attachment plate welded to a 1" galv pipe which goes down to the "deadman" at the bottom of a 5 foot deep hole.
I figured that this will provide good grounding termination ....maybe??

Turns out that as we scraped the surface ..the soil was just dust from this lack of rain ...five feet down was no different ..never thought that the ground could get so dry, so far down ...almost thinking of leaving the top of the pipe open, so that I could pour a few gallons of water down it in future years if we see this weather situation again

Stew Corman from sunny Endicott

[Rob Beckers]

Hi Stew,

Here's an article on tower grounding (http://www.arrl.org/tis/info/pdf/0208053.pdf). This is for HAM radio purposes, but I've seen very similar descriptions for large wind turbines and commercial communications tower grounding. By the way, not mentioned in this article, the stuff that's used as ground "wire" is not the usual #4 or #6 bare copper, but 1 1/2 or 2 inch wide, #26 AWG (0.0159 inch) copper strap. If you can find it. It has much less impedance than #4 copper when it comes to lightning (because lightning is an RF phenomena, subject to skin effect where most of the energy travels at the outer few micrometers of a conductor). The larger surface area also give better conduction to ground when buried.

-RoB-

[Stewart Corman]

Rob,
thanks for the link... this is what I was looking for:

If you are constructing a new tower you can use the tower
base as a “ground rod.” Called a Ufer ground, it utilizes the
rebar that reinforces the concrete base as an excellent ground
connection. The rebar itself must be electrically interconnected
so there are no spark gaps and there must be at least 4 inches
of concrete between the rebar and the surrounding earth. If
this is done, a wire can be brought out from the rebar and attached
to the tower leg. A great big ground rod! No, you will
not blow up your concrete—the other radials with ground rods
will handle most of the strike energy. Since you must put rebar
in the concrete anyway, use it to augment your ground system.my tower, base footer, and 1" galv pipe welded together "rebar" are all connected multiple times ...the four guy anchors are similarly buried to 5 ft down and are 40 feet from the tower to spread the energy from a strike ..the only adder I can see that I didn't mention are grounding clamps on each of the guys and to the mount, at each of the anchor points.

Can't get anal about this either ..have to make some decisions on implementation that is 'reasonable".

Stew Corman from sunny endicott

[Rob Beckers]

Stew, an Ufer ground works so well in large part because of the presence of concrete: Its salts make the earth more conductive and it presents a very large surface area. Not sure from what you write if you were planning on concrete, but just sticking steel into the ground isn't the same. Of course, lots of burried metal will form a nice ground, it's just not an Ufer ground.

-RoB-

P.S. Good protection of electronics seems possible, though not cheap. I'm starting to get pricing in for surge arrestors and surge protectors. Some of those are intended to take a direct lightning hit and survive.

[Stewart Corman]

Thanks for your amplification Rob.
The steel piping is welded together and is currently imbedded in 1/3 yard of concrete at the bottom of the pit.

I have changed the design as of today after consulting with a buddy, and the four corner pipes will be imbedded in concrete like a sono tube cylinder from the bottom slab up to the surface.
Center void area will simply be filled with the excavated hard pan to the surface.
I may even have some concrete welded wire boxwork to imbed within each cylinder.
It was decide that a "platform" at the surface really offered no structural benefit however could allow freezing under it to heave it in the middle

Yes , the guy pipe anchors will also have a gob of cement thrown down at the bottom where a steel car brake rotor acts as the "dead man"

IMHO ..I am not getting any younger!
those 94# bags of Porland was a bit much to handle and lifting a 5 gal bucket of #2 gravel up to the mixer isn't "light" any more !!

BTW:
An important note is that copper ground wire should never be directly connected to load-bearing galvanized structures (including guy wires). Galvanic action will strip the zinc from the galvanized steel, causing it to rust, and eventually to fail. You don't want this to happen to your guy wires. This procedure seems to be the consensus from talking to other wind installers.

I had thought that when we visited Ralph, that a ground wire was attached to each of the four guy wires at each anchor?? This was a factory kit ..can you and/or Ralph Please comment on specifics

Stew

[Rob Beckers]

The proper procedure for grounding guy wires is to run the excess of the top guy wire down to the other guys, attach them using wire clips, and finally to a ground wire. Unless you use something special that connection to the copper wire will still corrode, but it won't do any structural damage. If you really want to I suppose it's possible to find something that is made to connect dissimilar metals without causing galvanic corrosion. That'd be an optional detail though.

Below is a picture from the ARE tower manual that helps illustrate what I'm trying to say.

-RoB-

[Ralph Day]

Hi Stew

I had the tower/turbine down and installed the new SWWP blades last weekend. Less noise and am looking forward to less "blade tip flutter" aka 'farts of the gods".

Where the copper ground wire had to be removed from the guys for lowering the tower (only on one set of guys) i noticed no corrosion, pitting, or anything untoward. I do spray these areas with Fluid Film every year to preclude problems removing wire clips, so maybe that has something to do with it. Fluid Film creeps everywhere once it's applied.

Having trouble getting customer support from SWWP. ther's a rumble still when the turbine transitions power states but the thrust bearing had no play, only the pivot bushing. this may end up being a self repair job...have the local fixit whiz make me a bushing and replace the bearing and it at the same time. Fun, fun, fun.

ralph

[Stewart Corman]

Thanks to Rob and Ralph for the clarifications.
I knew I was looking at something, but the specifics weren't clear at the time.

I can see now the benefit of using the galv guy wire tail to electrically connect all the guys at an anchor station, then the copper ground wire is not attached to anything mechanical and is easily serviced.

Ralph, I will presume the "Fluid film" is like WD-40 ?

Stew

[Rob Beckers]

Stew, WD-40 is not a lubricant or anti-corrosion agent. It's does very poorly at that (despite what it says on the can), it's a penetrant oil, for loosening stuff. It doesn't lubricate, doesn't last any amount of time, and I've been told it's too acidic for use on metals (unless you like corrosion). For covering things to prevent corrosion I use an oil that's normally sprayed on car's underbody to protect from the salt in winter (it's probably a Canadian-only thing, called Crown T40). While I lived in the states I used LPS no. 3 for this purpose (I'm sure there are many brands making similar stuff). I just wanted to say that in general it's a good idea to stay away from WD-40, other than to clean off metal, or loosen nuts.

-RoB-

[Ralph Day]

I'll agree with Rob here. WD-40 stands for water displacement 1940. Originally a water displacement product developed for the US military...wd40 is its' original milspec disignation (or so i've been told). People in the know only use it as a penetrant, it leaves wax behind too, not good for firearms actions.

Fluid Film is a product name and it's Lanolin based, not petroleum based. it will weep out of car body panels for years if applied as i do...heavily. It comes in a spray can which is great for running out to the nuts and bolts on the tower. whenever it's down i hit the coupling bolts with it as well. There might be something like it at a NAPA or Carquest type store in the US (aftermarket car parts).

ralph

[Rob Beckers]

The last few months I've been studying up on lightning, grounding, and lightning protection. I've written a summary for my business site (http://www.solacity.com/Lightning.htm), the information could be interesting for anyone that has a wind turbine (or other structure) that is exposed to lightning. In essence it describes what lightning is and how it behaves, what the best practices are to mitigate damage, and how that can possibly be translated into a practical solution for the small-scale turbines we are generally talking about here. Your comments are welcome!

Currently I am investigating serious lightning and surge arrestors. They are not cheap! But for a $50K wind turbine install in an exposed location it may make sense. The plan is to eventually offer this as an optional package for wind turbines.

-RoB-

[Laurie Forbes]

For covering things to prevent corrosion I use an oil that's normally sprayed on car's underbody to protect from the salt in winter (it's probably a Canadian-only thing, called Crown T40). While I lived in the states I used LPS no. 3 for this purpose (I'm sure there are many brands making similar stuff).-RoB-

Rob, I've Googled Crown T40 and came up with a bunch of unrelated stuff (it's surprising how many products etc are named "T40"). Anyhow, do you have a source for it and any comments on how it would compare to Fluid Film for protecting weather exposed steel that cannot be painted (I am specifically referring to the blade shafts and bearings on my turbine head).

[Rob Beckers]

The lack of Google results would be because I misspelled the name (are you seeing a pattern yet? ;) ). It's actually Krown, and the web site is www.krown.com. There's a place in Calgary that's listed as a dealer, they should sell T40:

Airways Brake & Muffler
1936-30th Ave. N. E.
Calgary
AB
T2E 7B2
(403) 291-1951

Not sure what Fluid Film is or how it behaves, so no comment on that.

-RoB-

[Ralph Day]

Fluid film is a rust preventative/treatment product. It's available in spray cans and bulk. If you try to spray the bulk, it's the consistency of cow snot...thick and heavy.

It will fizz if put on rust, some type of chemical reaction to neutralize the rust process i think. IT does creep, a long way. If sprayed on something rotating,, it will likely work it's way out quite a ways. I used it on the inside of my turbine tower and spray it on the ubolts securing everything anytime it is let down. No rust on any of the zinc plated fastners after 3+ years.

Before using FF to rustproof some cars i tested finishing nails coated and not coated, in a variety of solutions...water and salty water. The coated nails did not rust, even after the salty solutions completly evaporated away. I like the stuff, but it does have an odour. I am not allowed to spray cars with it anymore (significant other is sensitive to perfumes/solvents/odours of many kinds). I just buy the 5 gallon pail of Carquest snot instead.

Ralp;h

[Laurie Forbes]

I wonder how applicable these agents are for spraying on bearings (one would not want it to solidify or get v viscous).

My problem is protecting the blade shafts (which cannot be painted as they won't slide through the bearing if so) and especially the bearings themselves from the weather (the whole shebang could be enclosed but, if so, the blade shafts would have to be sealed somehow w/o introduction of much friction). Maybe the typical spring loaded shaft seals would work and friction would not be a problem if kept lubricated (?). Come to think of it, that just might work as there should be enough vibration/jiggling of the flyweights to overcome any reasonable degree of seal starting friction.

An enclosure would also serve to prevent ice buildup on the mechanism. It would be bulky though (to accomodate motion of the flyweights). An effective spray would be a lot easier and may be workable even if the bearings have to be replaced eventually. OTOH, an enclosure would also serve to trap moisture if any happened to leak in.

I wonder how corrosion resistance common ball bearings (pillowblocks in this case) are? I suppose one could use stainless but they are pretty pricey.