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Why Air Terminal Placement is Critical to Lightning Protection

Posted by TJ Gaines on Jun 5, 2017 8:03:00 AM

Lightning_Protection.jpgMany factors impact the effectiveness of a lightning protection system—from ground rods to conductors to air terminal placement. Above all, air terminal placement may dictate whether a lightning protection system is effective and efficient or not.

In fact, air terminal placement is now accepted as an important factor when designing and constructing an efficient lightning protection system.

Air terminal placement is essential to protecting both structures and their occupants from deadly or destructive lightning strikes. A new field-validated study of the Collection Volume Method (CVM) reveals new data-backed findings on optimal air terminal placement. 

Continue reading to learn more about CVM-based protection systems, and their proven interception efficiency level.

CVM: A Viable Alternative to Conventional Methods

The Rolling Sphere Model (RSM), the most common choice in lightning protection, is based on the Electro Geometric Model (EGM) for striking distance. The conventional RSM consists of lightning rods, exposed and placed at the highest levels of structures, and connected through downward conductors to a grounding system.

While the RSM has proven to be effective in the lightning protection field, this EGM-based model does not account for the physical basis of the upward leader inception process, or the importance of the structure height or geometry of objects on the structure.

Enter CVM-based lightning protection systems, a viable alternative to the standard models.

Based off the Eriksson’s Attractive Radius (Ra) Model, the CVM determines the ideal placement of air terminal placement. Eriksson’s Attractive Radius Model calculates the radius of protection based on lightning currents. Most importantly, the CVM takes into account a structure’s features. It evaluates the physical criteria of air breakdown, and considers the electric field intensification created by different points on a structure.

Then, it uses this information to provide the optimum lightning protection system for that specific structure. The result is the most effective air terminal placement for a selected interception efficiency level.

Field-Validated Data of the CVM

For years, the CVM was claimed to be just as effective as standard models like RSM. To prove this information, a multi-year study was created to test and validate the claims.

Thirty-three buildings with CVM-based lightning protection system were studied between 2010 and 2012. The ERICO DYNASPHERE lightning protection systems (LPS) was installed at each site, along with Lightning Event Counters (LEC). The LEC were placed around the lightning current downconductor cable to record the number of strikes to the structure’s protection system. 

The collected data confirmed that the CVM was consistent with prior claims of 84% - 99% effectiveness, based on the desired level of protection. This proves that the CVM is an effective alternative to conventional methods, and may be advantageous when:

  • Complex architecture does not allow for application of a standard installation method.
  • The architecture of a structure deems the application of a conventional lightning protection system impractical.
  • No installation method has been specified and an enhanced solution is advantageous.

With this new evidence at hand, engineers should consider the CVM when selecting the most efficient system for their next lightning protection installation.

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 Photo credit: Pixabay CC0 Public Domain

Topics: Lightning Protection