Lightning - Earthing ?

Hi

I thought id ask here as id guess someone has already had or seen this problem ( not that its a problem until you get a strike!)

I have a small project where i will be controlling a lot of 24vdc solenoid operated divertor vales each with pnp sensors, lots of level probes and some 3 phase 400V ac rotary valves.

These are all situated outside on some 100 Tonne Sylos some 40 ft from ground level and about 100 ft high ( I have not measured this ).

Now the controls are no problem at all, the sylos are erected on a large steel girder structure, the sylos are all on weigh cells also.

Had a thought the other night about "What if" in bad weather the sylos get hit by lightning ?

Yeah............... Sad isnt it, a few glasses of red, relaxed at home and im still pondering on the next project!!!

Well anyways all of my stuff is normally inside machinery so this is a little different. The customer has little knowledge ( clueless )!

Now i can advise on this and they will probably follow it through.....

What sort of "EARTHING" for a lighting strike should i suggest ?

Is this project in Europe or North America?..I only ask becouse the codes can be different..The last project i worked on that required grounding for Lightning (It was a large anttena on a roof) required specific cables and connectors..(Can you spell BIG Bucks!!!) The grounding inside the building was funky to..I can remember what went on for that part..but the roof was a nightmare...

If you are in N.America i would get an engineer involved..That way when (Not IF) These silos are struck by lightning the equiptment wont be your problem if it fries...

The old CYA...

D

If the silo is metal, ground it. If not, ground anything that is, ladder, conduit,etc.

If possble, put a ground rod on it. And lightning rod, too!

No sharp bens or 90* angles in the ground wires.

Lightning likes a smooth flow to the ground.

However, a good kink, or wrapping the wires around a broomstick handle acts like a choke (coil), a blocks most (READ not all) lightning and damage.

But MOV's between the wires, and from each wire to ground.

There are types of lightning

1. Cloud-to-cloud( not very common )
2. Cloud-to-air ( Not very common )
3. Intra cloud( Flashes are redistributing the charge within the
cloud )
4. Cloud-to-ground ( these flashes are very common and are able to
cause severe damage )
5. Groud-to-cloud ( These rare flashes originate from the ground
particularly from tall buildings.


I think that your project is in Number 5

There are international standard IEC 1312-1 defines a zone model to protect equipment against severe lightning damages

As you have said the frame of the building is bonded together with the ground that`s good!

I suggest that you use the star point earth connection- Galvanic couplings can be suppresed by connecting the electrical equipment to the system earth using one cable path for eachtrical circuit

I visit some plant they use surge arrester with is installed in the roof-top of there plant for protection of lightning,that connect to the plant grounding system.


Another option is the use of SPB ( Surge Protection Barriers )
This is to protect the equipment in your plant,One brand that I
use in our plant is Pepperl+Fuchs

As for our system power I used MCG surge protection to eliminate
loss of damage equipment due to power surge cause by lightning,The brand is sentinel.

Hope this help!

4. Cloud-to-ground ( these flashes are very common and are able to
cause severe damage )
5. Groud-to-cloud ( These rare flashes originate from the ground
particularly from tall buildings.

Click to expand...

All lightning that reaches the earth is from ground to cloud. My final paper was about lightning because i'm always in awe during a thunderstorm. I found the followning at space.com because i'm too lazy to write it myself...

Thunderstorms are caused by rapidly rising and falling currents of air. The friction from this moving air creates electrical charges within a cloud. Water droplets and ice pellets fall, carrying charged electrons to the lower portion of the cloud, where a negative charge builds. A positive charge builds up near the top of a cloud.
[font=Arial, Helvetica, sans-serif]How lightning strikes[/font]

Another thing to consider is the combustibility of whatever the silos hold. If it's some sort of powdered or ground product (wheat, coal etc) then a spark could literally blow your silo up. You can buy lighting rods for buldings that consist of thick copper wire on top of the highest point well and truly grounded at the bottom of the building.

Dave,

I have done considerable work in the desgin of lightning protection systems, mainly for ammunition storage magazines and explosive materiel manfacturing buildings. You can't mess about with those, when it comes to lightning protection.

If your silos have 1/4" thick steel metal walls, then they qualify as "self-protected" against lightning strikes, or another way to think of it is that the metal of the structure itself is thick enough, tall enough, and conductive enough to perform the same task that specific rods or pole masts would. The thing you must make sure of for a self-protected system is to have the metal structure well-connected to earth itself. The most efficient way to to that is to use a Ufer Grounding System to connect your silo support columns to the concrete foundations. You can do the traditional method also and run a ring of large bare copper cable around the base, buried about 2 to 3 feet deep, and thermal-welded (best) or bolted (okay) to the silo supports.

If your silo tanks are mounted on load cells, that prsents a slight problem, in that the load cells insulate the main silo body from Earth. You have to install jump-around cables from the silo to the structure, to shunt the lightning currents around the load cells. The shunts need to run generally vertically, with no more than 45-degree bends.

Some people make a big deal about which way the currents flow, up or down. It doesn't really matter, the results are the same. If a charge builds up so that it can jump up to a mile from cloud to ground (or ground to cloud), then you are looking at about a million volts, and there is not much way to stop it. You can only hope to divert it slightly.

Best Regards,
Lancie

P.S. I get a kick out of hearing people talk about lightning and how to be safe from it (you can't). Here are some of my favorites:

"There's lightning! Let's go indoors where we will be safe!"

(Where you are protected by all of maybe 0.125"-thick roof shingles, a 0.75"-thick plywood board, and 0.50" of gypsum wallboard, from 300,000 Amps that has jumped through thin air for thousands of feet?)

"Don't open an umbrella when it is lightning". (Or, if on the golf course, don't hold a metal club when it is lightning.) It will attract the strike. (Yeah, Right. you really think it will make any difference? Open up those umbrellas. At least you will be dry toast!)

"When you are in an open field during lightning, drop to the ground and roll into a ball. It won't hit you then". (All this will do is get your clothes covered in mud. I have never seen anyone actually do this, so I guess most people are willing to take a chance?)

"Lightning never strikes twice in the same place." (I should be safe then, since a large ball struck my living room floor and rolled around in it for several seconds. It scared the cat silly.)