IEC Lighning Design

[timm33333]

I need to perform lightning design based on IEC 62305. The part-2 of this standard is risk assessment which is very complicated calculations. I don’t want detailed calculations. Is there a short way to perform approximate risk assessment calculations? If I know the number of lightning flashes per year, and the dimensions and height of the structure; then can I perform some approximate quick calculations for lightning risk assessment?

 

[7anoter4]

Try NFPA 780 Annex L Lightning Risk Assesment.It seems to me as less sophisticated.

 

[timm33333]

I used NFPA-780 online software at the link:

http://www.mrlightning.com/risk.php.

It is very simple. However I was thinking that risk-assessment would give the required level and type of lightning protection system to be installed. But it looks that risk assessment only tells us whether lightning system is required or not, is it correct?

Also I changed the parameters many times in this software, but I always got the same result that lightning system is required. Even if I set the flash density as minimum, structure as non-metal & non-flammable, and building as unoccupied; still I get the same result that lightning protection should be installed. Do you have some idea under what conditions the lightning protection is “not” required?

 

[wayne440]

Do you have some idea under what conditions the lightning protection is “not” required?

Using that specific calculator, I venture a guess that there will be no situation where it will indicate that the offered product is not needed. That is similar to walking into an auto dealership and asking them if you need a car.

 

[timm33333]

Yes that makes sense. Apart from this software, what does the real risk-analysis tells us? Does it give the level and type of lightning system to be installed; or does it only tells whether lightning system is required or not?

 

[timm33333]

The reason why I asked the above question was because if the only purpose of risk-assessment is to know whether lightning-protection is required or not, then I would skip risk-assessment and directly proceed with the design of lightning-system. Because I am sure lightning-system is required in our case.

 

[ScottyUK]

The old BS 6651:1999 standard which was replaced by IEC 62305 was fairly straightforward to implement. It doesn't cover protection within structures, and the results aren't directly equivalent but if it is a rough rule-of-thumb result you're looking for it might help.

Alternatively, Furse have a time-limited trial version of their StrikeRisk software available as a free download which might be adequate for your needs.


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If we learn from our mistakes I'm getting a great education!

 

[timm33333]

Thanks, the Furse risk-assessment software is very useful. If I set the fire-risk as “low” or “ordinary”, then there are no problems because the least stringent lightning-protection (Level 4) is enough.

The problem is that some part of the plant is hazardous. So I have to set the fire-risk as “explosion”. This increases the calculated-risk dramatically and lightning-protection of level-2, level-3, and even level-4 is not enough. So I have to use the most stringent lightning-protection (which is metal-roof with natural-down-conductors.)

The fact is that only a small part of the building (about 10%) is hazardous. Do I still need to take the whole building as hazardous?

 

[IrishPower]

timm33333,

If you are reasonably certain that you need a LPS anyway, then ScottyUK’s link is probably a good place to start, as this should indicate what Lightning Protection Level you require according to IEC 62305.

As there are several different levels of lightning protection allowed for in IEC 62305, if you have a definite requirement to ensure that your installation is compliant with this standard then you will most probably end up having to carry out a risk assessment using IEC 62305 part 2 anyway. This will prove that the Lightning Protection Level you have selected is adequate - no protection, LPL IV, LPL III, LPL II or LPL I, going from the lowest to the highest level of protection. I’m not sure if there’s any simple way out of this other than to do the risk assessment as per the standard, unless other posters have spotted some loophole?

When carrying out a risk assessment using IEC 62305 part 2, you do have the option of assuming as a starting point that you have no dedicated lightning protection installed. If your risk assessment shows that the various risk levels are below the limits, then this can be used to justify that no special measures are required. However, you would need to be quite sure that you are not being over-optimistic with your input data!

If the level of risk is above the applicable limits, then you need to repeat the risk assessment using the next (higher) level of lightning protection until the residual risk is below the limits (i.e. go from no protection to LPL IV, then LPL III, etc. until you get something that works). You then move onto the second stage of the process and carry out your rolling sphere analysis to make sure that your lightning protection structures provide the necessary coverage (e.g. using a sphere radius of 60m for LPL IV, 45m for LPL III etc.).

I agree that the risk assessment methodology in the standard is fairly messy. Whether you use a risk assessment tool like the one ScottyUK linked to or whether you build an Excel spreadsheet to do this yourself, you still need decent input data for the risk assessment, or have some acceptably conservative values to use in cases where you don’t have good data… not easy!

IP

 

[timm33333]

Thanks IrishPower, it looks that I posted my last post when you were in the process of responding. So I am posting it again here:

The Furse risk-assessment software link by ScottyUK is very useful. If I set the fire-risk as “low” or “ordinary”, then there are no problems because the least stringent lightning-protection (Level 4) is enough.

The problem is that some part of the plant is hazardous. So I have to set the fire-risk as “explosion”. This increases the calculated-risk dramatically and lightning-protection of level-2, level-3, and even level-4 is not enough. So I have to use the most stringent lightning-protection (which is metal-roof with natural-down-conductors.)

Actually only a small part of the building (about 10%) is hazardous. Do I still need to take the whole building as hazardous?

 

[timm33333]

I understand that if there is metal roof, then we will not any air terminals (lightning rods). So calculations based on rolling-sphere method will not be required. Is it correct?

 

[timm33333]

I did more research and actually the whole building does not need to be classified as hazardous, the building can be broken down into zones.

The main question is the roof. Because the lightning protection level on the roof depends on the nature of the area inside the roof (hazardous or non- hazardous).

It is easy to break down the internal area into zones, but how to break down the roof into zones?

 

[cuky2000]

1)...IEC 62305....is very complicated calcs
2)...I don’t want detailed calculations.
3)... Is there a short way....?
4)...quick calc for lightning risk assessment?
5)...then I would skip risk-assessment and directly proceed with the design?
6)...The problem is that some part of the plant is hazardous
7)...So calculations based on rolling-sphere method will not be required
8)...how to break down the roof into zones?

What do you really want?

 

[timm33333]

I was not familiar with IEC-62305 when I initially started this thread. Now I have somewhat better understanding so most of my initial questions have been answered.

A small part of the building is hazardous which means that the most stringent lightning protection level (level 1) will be required for this part. The remaining part of the building is non-hazardous (which means that the least stringent lightning protection level (level 4) will be required for this part. This is easy.

The main question at this time is about roof. The lightning protection level on the roof depends on the nature of the area inside the roof (hazardous or non- hazardous). Should we have to provide the most stringent lightning protection level (level 1) for the whole roof?

 

[timm33333]

In the last post I meant to say: ""...protection level on the roof depends on the nature of the area inside the BUILDING ... ""