Grounding System Fails After Lighning Strike

Is the structural steel frame properly grounded?

Ordinarily one would expect the lightning to go to ground, not jump to the generator neutral.

Have you had a network lightning specialist look at it?

The lightning surge current will always choose the lowest impedance path to ground and the most effective lightning protection systems artificially create that preferential path. However, even the most carefully designed system doesn't always work due to the unpredictable nature of lightning. Ionized air gaps, for example, can flashover and effectively become low impedance conductors; providing the voltage is sufficient to initiate and sustain the high current arc.

Thank you, is there a practical way to protect facilities...surely high value and or harzardous cannot just leave such to chance.

Yes, with a properly designed, installed and maintained lightning protection system. You cannot just get an electrician to wire metal parts to earth and throw a few surge diverters in the switchboard (lightning protection is far more complex than most people realise).

If you are the original poster, please state where the plant is (the country).

...with a properly designed, installed and maintained lightning protection system.

I'd like to hear more about that. I was once sitting at my computer, desk top, while a storm was going on outside. The pole that feeds my house was struck by lightning. The lightning traveled through my household and destroyed a satellite receiver that was plugged into the same outlet as my computer and a TV. But only the receiver was damaged, nothing else. At the far end of the house, my home theater system was destroyed, yet not the TV that was plugged into that outlet. Nothing else in the house was damaged.

In an unrelated strike, it hit the pole that fed both my house and my neighbor, he lost both a washer and dryer, a TV and a microwave oven. In that strike I lost to damage two GFI outlets. Nothing else was damaged at my house.

Who can explain that??

Is it possible that there is/was a vertical house wiring line feeding the lap top and the GFI's?

Despite all the statements that lightning follow the shortest path to ground it remains capricious and unpredictable in some circumstances. e.g. the person partially under a tree had the zipper securely and permanently welded by a strike hitting the tree. Was it the lightning or the instantaneous induced current in the short metal zipper?

The most practical way to shield critical facilities from direct and proximity lightning strokes is to effectively enclose them within a Faraday cage. It's not really a cage but rather a system created by enclosing the facility inside one or more taller structures that are effectively grounded through low footing resistance. The tall structures are generally equipped with sharp ionization points to attract lightning which is then discharged to ground. The number and height of the grounded structures depends upon the facility geometry with the intent being to ensure that the structure is within an overlapping shielding envelope to minimize the possibility of shielding failure.

One company that specializes in these kinds of systems is Lightning Eliminators & Consultants (http://lecglobal.com). You might take a look at their website to get an idea how these systems work. It's the same principle as a metal bodied automobile in a thunderstorm.

"The lightning surge current will always choose the lowest impedance path to ground and the most effective lightning protection systems artificially create that preferential path."

Don't bet the farm on it. Lightning has been known to do strange things. For example it hit a power line, followed it to a 90 deg corner and continued straight ahead to destroy a tree some distance away. Ball lightning, etc.

"due to the unpredictable nature of lightning" Like you say it is unpredictable!

Too bad you have an extended outage to cope with.

Our facility has been hit numerous times and on some cases our communication towers. We also had an employee struck while walking to his car. He was surrounded by 90 foot lighting towers and none of these were hit at that time.

Unfortunately these things occur.

And that illustrates the point. The lowest impedance path to ground may not always be obvious but you can bet the farm that in your example, at that particular time, the lowest impedance path to ground was through the air gap and the tree. It followed the power line to a 90 degree corner, presumably to a pole or tower, at which point the surge current divided. Had the pole been effectively grounded through low footing resistance, the majority of the current would have travelled to ground at that location and the travelling wave voltage would have been reflected back to the line.

Yeh right...but I'm with Stirling Sam on this!

What you say is glaringly obvious.... but is it of any practical use?

How do you measure the lowest impedance to ground at those voltages and currents? It's no good using an AVO !

Are there methods out there that can really measure that a 6" air gap is infact going to be a lower impedance path than a 1" copper strip because the air in the gap has been ionized a millisecond earlier!???

Isn't it all based on experience and 'best practice' ?

It's good to see your front right paw is active this morning.

Yeah, the impulse strength difference between a 6" air gap (90 kV critical at standard temperature and pressure) and the voltage drop over a 1" copper strip due to its inductance (Ldi/dt) can be measured. However, you are correct, it does ultimately come down to experience, best practice and knowledge.

Unfortunately, there is no system that can guarantee 100% effective lightning protection. In an earlier post I mentioned protection with a Faraday cage in this particular case but that only guarantees protection of the facility from direct and proximity strokes to some high confidence level. Lightning (or switching surge)travelling waves might still enter the facility through external lines and cables so they would also have to be protected with suitable overvoltage protective devices.

"How do you measure the lowest impedance to ground at those voltages and currents? It's no good using an AVO !"

There is a test that can measure your entire grounding system and make sure your grounding system has low impedance (I believe it can measure higher impedance at higher, near lightning frequencies too, it measures at a variety of frequencies). It is called Smart Ground and provides you with a detailed report that you can take actions on. Ironically, Lightning Eliminators & Consultants (mentioned above) also provides this service. I believe that a few other companies also provide this service, including the creators of the system, some professors in Mississippi?)

The lightning surge current will always choose the lowest impedance path to ground

I can't say I've ever seen proof of that. Many people say that electrical current follows the path of least resistance. I've never seen proof of that either. In fact, I've seen loads of proof to the contrary. For example, if I put two resistors in parallel in a circuit, I have found that invariably, the current flows through both in inverse proportion to their resistances. It's almost as if the electrons have never been told that they have to take the single path of least resistance.

A guy named Georg Ohm did some early work with these relationships. I think of some of the stuff he said as darn near law.

OMG! I agree with Blink!

Perhaps it is best to say that MOST of the current will USUALLY follow the lowest impedance path to ground. When you watch lightning in the sky as it ionizes the atmosphere and lights up its path(s), don't you usually see many forks? Is not that the very epitome of our visualization of what lightning looks like? It has divided AND conquered!

With that much electrical energy coming to ground in so little time it is a wonder that most of it usually follows a single path, at least that we think we see. Anecdotal evidence says lightning did this, then it did that, then, totally inexplicably it jumped way off there and did that...as if it all happened in series. Why couldn't there be multiple paths in parallel AND series, with varying impedances and varying currents? And what happens when one path leads to a high impedance (capacitance) that quickly breaks down and discharges out the other side? In the mean time, some of this extreme EMF has forked and bridged to another path.

In reality the whole thing is just one big, unpredictable, complex, dynamic and fast-changing electrical circuit, where Ohm's Law surely applies just as it does in any other electrical circuit. We can only hope, with a little luck and a great deal of experience, to help nudge most of the destructive power onto a path that leads quickly to ground without allowing any stops or other jumping off points along the way.

Robert Burns, the renowned Scottish poet, said it the best in his Scots-English dialect:

But Mousie, thou art no thy lane,
In proving foresight may be vain:
The best laid schemes o' mice an' men
Gang aft agley,
An' lea'e us nought but grief an' pain,
For promis'd joy!

(From "To a Mouse" )

We can only hope, with a little luck and a great deal of experience, to help nudge most of the destructive power onto a path that leads quickly to ground without allowing any stops or other jumping off points along the way.

Or maybe catch it and store it???

Lets........NOT go down this road again. The power in a lightning strike is very small (very small duration high power pulse, still = very small amount of power). Besides the cost of the equipment to store the pulses and the safety issues will always blow this type of idea out of the water, where it will sink into an watery grave at the bottom of the ocean and sit there rusting away.

Intersting use of the term very small...

Ive read the thread about harvesting lightning..

I was disappointed by the blanket 'can't be done' attitude.

The point is NOT to harvest lightning as such...but to harvest the charge before it discharges as lightning.

I still don't claim it's practical, or sensible...but I was surprised at the paucity of ideas.

PS. I'm willing to be shot down here...isn't the term lightning conductor a misnomer? Isn't the point of it to allow localised discharge to avoid a strike rather than 'attracting' a strike?

Perhaps I should re-phrase. The amount of energy you can extract and store using current technologies is very small due to the large, short-duration voltages and currents available. Currents for example can easily exceed 40kA and voltages are enormous.

If someone knows of a safe way to average out the lightning strike energy or store the charge buildup to make energy storage more viable (and at least a bit safer) I would be very interested (most of my experience is in the field of power generation and transmission, with lightning protection after the fact).

These sort of ideas generally are not, and have never been, viable, but sometimes that is only because someone hasn't come up with a unique way to solve or bypass the problems inherently associated with it. However since this is not regarding free energy generation using magnets I am happy.

Any good links out there regarding current developments in lightning or charge storage (that are not out and out scams or backyard tinkers with dodgy test results)And no, I will not accept the "take a big field of capacitors and connect a TV aerial up to it" thinking.

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Sometimes saying it cannot be done pushes people to go out there and accomplish it to prove you wrong. Hooray for human nature.

And no, I will not accept the "take a big field of capacitors and connect a TV aerial up to it" thinking.

Sometimes "thinking outside the box" just means getting a much bigger box!

I agree, this is a bad idea, and dangerous, especially for any person or small organization to attempt this on their own. Perhaps some researchers may work out a way to make this practical, but at the moment it does not appear to be so.

However, please do not state that the power in a lightning strike is very small. If it was there could not be so much destruction. Voltage alone, although extreme, cannot do anything without Current, and Power is Voltage multiplied by Current. Rather it is the available energy (Power multiplied by time) that is very small. Power is instantaneously extremely high, but short-lived, so the energy that might be captured would be very small.

Power and energy. Incorrect usage of terms previously. Apologies. Stand by while I insert more Tea and try and wake up this morning. (well it sort of looks like a yawn).

Engineers with who I have talked say this should not have happened.

You can't tell lightning what it 'should' do!.

The daft thing was leaving an unused antenna in position!

Easy to be wise after the event...

Lightening has done its work.The Engineers did not perform their duty .So the damage. No one can do any thing about the loss but can learn a lesson to avoid such happenings in future. The LP ( lightening Protection) system is a very important part of electrical systems. IEEE 80 chapter 9 gives clear idea as to how to construct a LP system and how to maintain it.Normally all Electricity Companies and Electrical Agencies and Electrical Departments give clear Instructions for their Engineers and mandatory instructions for their organisations. All practicing engineers have to maintain it meticulously to avoid such damages due to Lightening .For Ammunition and Explosive Factories if LP system is not maintained it can cause extensive damage ,loss of life due to explosion due to lightening . These organisations maintain a perfect record of LP earthing readings taken at particular intervals and if any defect noticed corrective maintenance work will be carried out and recorded. Pre monsoon tests are always taken to ensure proper functioning of LP system. The Lightening Arrestors of Generating Stations and Substations needs regular preventive maintenance. If these precautions are taken and LP system is well maintained there is no fear of lightening striking these units.

I find it very odd that the strike "re-entered" from the building ground. I think it would be far more likely that either there was a second point of entry for a strike on the neutral that passed through the generator on it's way to ground, or there was a flashover from the structure to the neutral.

Lightening is the same as any electrical current. It takes the path of least resistance from an area of high potential to an area of low potential. There has to be a complete circuit! Ground to cloud strikes are not going to take the path indicated in the question. The analysis is suspect. If the strike goes up the generator neutral, it then has to come out of the generator somewhere and make its way to the communication antenna.

It would make sense if the structural steel is NOT grounded. Then there is a legitimate path from the generator casing to the structural steel through some connection and then to the antenna.

Take some measurements. Is there a good ground from the structural steel to the station grounding system? If not, this will not be the last time that you have trouble.

Electrons move from ground to cloud. The electron flow path may have been from ground through the generator neutral and then jumping to the communication tower from the machine.

Generator neutrals typically are grounded through a small resistance to limit fault currents, which also makes it tough for a strike to take this path because the structural steel is definitely a lower resistance path if it is connected to the plant grounding system.

It is not clear if the antenna was installed on the same structure of the generator house. Assuming it is , the question arises about the grounding of antenna structure and lightning protection of the building.

If the building structure is not earthed so as to form a least resistance path to ground, lightning current will find the path by itself and this can very well be involving the neutral ground .Other than jumping current from antenna wires, it will most likely be the structure which has passed the lightning current.

A closer examination of the structure and joints will lead to some clue.

To express our view more details of the plants are necessary. For example:

1: Location of the number 1 Generator in the plant.

2: Location of the Earthing system of the building.

3: Location of the earthing system from the Generatore.

4: Location of the commonucation antena from the Generatore Earthing system.

5: Connection of the earthing system of the Generatore with plant earthing system.

6: Howmaney earthing points are there in the building.

7: This is an old building. What is the condition of the existing earthing system. Is it not rusted and destroyed?

8: What are the electrical specifications of the earth there.

9: What are the composition of the earth of the site.

10: The condition of the existing underground water level in the area.

11: the height of the commonucation system with respect to the earthing rods of the plant.

12: distance between the earthing rods of the building.

13: General view of the building showing the existing earthing rods and their distances from one another on the building, the location of the communication antena in the building and the location of the generator 1 in the building.

What reasoning you have expressed shows that you have tried to say that current from the earth comes to the generator is not possible. So it means that there are some other reasons for that to be found for the safety of the plant in the future.

<Engineers with who I have talked say this should not have happened. We will appreciate any counsel and direction on resolving this issue>

Life must go on -and safer, surer---with better application of accumulated Science and technology!

Can't leave it to Fate.

Firstly- see what is happening in the field of Nanotech-Elmag Shielding:

<This one from Virginia State Univ-USA

Sensitive electronic devices like cell phones and computers require shielding from electromagnetic interference (EMI). Such shielding - which must be electrically conductive - has traditionally been made of metal, which poses a weight problem in the push to miniaturize and lighten electronics. In response, Gupta led a team that has developed an ultra-lightweight nanocomposite that outperforms conventional shielding.

This new nanocomposite material is a mixture of plastic, carbon nanotubes and a foaming agent, making it extremely lightweight, corrosion-proof and cheaper to produce than metal. The carbon nanotubes play a key role in creating these unique properties, explained Gupta. Most notably, experiments revealed that only 1 percent to 2 percent of the material's composition needed to be comprised of nanotubes to increase the electrical conductivity by 10 orders of magnitude. The addition of carbon nanotubes also increased the material's thermal conductivity, improving its capacity to dissipate heat.

Now to Counsel and Direction:

Lightning is not mystery- plain 200 year old well-documented Electrostatics:

So what went wrong?

• Somebody failed to guide the Antenna-tower-top charge with a sure low-resistance conductor to 15m below ground level-into ground water stratum.
• Somebody failed to ground the Generator winding Neutral to 15m below ground level -into ground water stratum.
• Somebody failed to ground the Boiler/generator- Building Rebars by welded extensions to low resistance nodes and then connect theses nodes via well-maintained Earth conductors to 15m below ground level -into ground water stratum.
• If 15m does not get fairly conductive ground water ,go deeper till you get one-no shortcuts!!
• I hope IEEE rewrites their norms as bluntly as I have written above. You cannot be over-cautious.

Coming to this one above- about foamed shielding plastic/Nanotube Composites- just buy big sheets and wrap the Gensets and Ground these sheets to the same grounwater Stratum.

Question: Are you interested to have a quotation for a Caterpillar 1500kW Diesel Generator.....500 hours on the V12 virually New, fully contaned in a steel container. Can send Photos.........

Peter