An example of a relatively recent innovation in protection concept introduced to the IEC standard IEC 62305. Is the Isolated LPS (Lightning Protection System). The Isolated LPS can be described as protection measures (e.g. lightning conductors) that achieve sufficient 'separation' distance, electrically and/or physically, between that which is conducting the Lightning Current; and that which is to be protected from the effects of the lightning current. This separation distance is what gives this methodology its label i.e. 'Isolated' design. It does NOT mean the system is electrically isolated from earth (a common misconception). It just refers to the physical distance achieved between the lightning current and the item being protected.
What's the difference?
In simple terms, the conventional 'non-isolated' Faraday Cage type of protection system (LPS) is typically happy to attach conductor arrangements directly to the structure or asset being protected with little or no separation. Whereas, the isolated design pro-actively goes out of its way to maintain geometric and/or electrical separation. This can be achieved with free-standing masts (or poles) which stand someway off the item being covered. Or, in some cases, it is possible to achieve a meta-separation by using proprietary non-sparking conductors.
For most cases, the conventional non-isolated direct fixing method can work adequately as a minimum. But what if the asset you want to protect from the lightning attachment is explosive or flammable? Is it a good idea to have anywhere up to 200 kA of lightning current flowing next to something that could level an entire site if the unthinkable happens because of a poor or damaged joint in the system? Or maybe an uncontrolled event (lightning) enters a haz-zone, just at the wrong time?
Let's take a look in slow motion at what a typical 100 kA lightning current can do by induced coupling to a panel or similar. Bear in mind, this is an induced (secondary) effect and not even the full directly connected lightning current itself.
Why Isolated LPS?
So, knowing the Isolated LPS provides a physical distance between the point of lightning attachment and the contents (or structure) being protected; gives a much higher level of protection when compared to conventional designs for ATEX / hazardous zoned areas. The downside can be an extra input needed on the civils side to install the foundations, especially on the taller masts. However, this can pale into insignificance when considering the consequences of a flash at the wrong time.
Watch the 'isolated' protection concept applied to a typical bio-digester type plant below:
Notice how the haz-zoning (shown in yellow) is accounted for so that the lightning stroke cannot penetrate these areas. And the lightning is effectively kept out of the LPZ0B zone (shown in red).
An often unintended positive consequence of applying the Isolated LPS. Is the surge protection measures within the LPZ0b area are significantly reduced.
Assuming the Isolated design is sufficiently and appropriately designed, only partial lightning current is seen within the LPZ0B protected area. Therefore, with appropriate bonding, in most cases, the SPD can be very light or even omitted (with care and input from a fully qualified specialist).
Getting the right advice
Designing Lightning Protection for critical assets that have an ATEX component is, without a doubt, the domain of the specialist consultant. And yes, I would say that wouldn't I? ... But it's true!
We've been fortunate enough to have seen countless designs from very competent well-known building services consultancies, lightning protection installation contractors, and electrical engineers. But when it comes to ATEX areas. Having an independent specialist consultant with no vested interest to guide you through the minefield that is high-risk LPS design is a must if you are serious about de-risking.
If you're in any doubt - just drop us a line (obligation-free).
This post is written by Ian Griffiths, Principal Engineer at GreyMatters, an Earthing & Lightning Consultant of 27 years, one of the top 1% accredited CDEGS consultants and professional advisor to international utility companies, data-centre and infrastructure developers.