One of the most important aspects of designing a lightning protection system is to check that the entire installation is effectively protected. To do this, it is necessary to determine the protection zone provided by the lightning conductor and ensure that all parts of the structure are within that zone.
PROTECTION BEGINS AT THE DESIGN STAGE
Before selecting an air terminal or defining its location, it is essential to answer a fundamental question: does the installation require a lightning protection system?
In Spain, this assessment is carried out in accordance with the Technical Building Code (CTE), and more specifically according to Basic Document DB SUA 8, which establishes a risk analysis procedure to determine in which cases a structure must be protected and what level of protection must be applied. However, the CTE does not specify how to design the system or how to calculate the protection zone. Once the need to protect the structure has been established, reference must be made to the specific standards governing the design of these systems.
WHICH STANDARD DEFINES THE PROTECTION ZONE?
The calculation method depends on the protection system chosen. For conventional systems, the design is carried out in accordance with the IEC 62305-3 series, which provides methods such as the rolling sphere, the protection angle or the mesh method.
In the case of Early Streamer Emission air terminals (ESE), the reference standard in Spain is the UNE 21186 standard, based on NF C 17-102. It defines the method for determining the protection zone as a function of the height of the air terminal, the protection level and the initiation advance time of the air terminal (ΔT).
Each technology has its own design method, but they all pursue the same objective: ensuring that the structure is protected against direct lightning strikes.
| Standard | What does it define? |
|---|---|
| CTE DB SUA 8 | It determines in which cases a structure requires lightning protection by means of a risk assessment. |
| IEC 62305 | It establishes the design criteria for conventional lightning protection systems. |
| UNE 21186 | It defines the design method and the calculation of the protection zone for ESE air terminals. |
what is the protection zone?
The protection zone is the volume within which a structure is protected against direct lightning strikes, in accordance with the criteria defined by the regulations. In the case of Early Streamer Emission air terminals (ESE), the UNE 21186 standard establishes the method for determining this protection zone from different project parameters.
The main factors taken into account in the calculation are the following:
- The height of the air terminal with respect to the reference plane.
- The protection level required for the installation (I, II, III or IV).
- The initiation advance time (ΔT) of the ESE air terminal.
- The geometry of the structure to be protected.
From these parameters, it is possible to determine the corresponding protection radius and to verify that all exposed elements lie within the protected zone. Although this method is based on mathematical formulas defined by the standard, its purpose is to ensure that the designed system provides sufficient coverage to protect the entire installation.
TWO WAYS OF REPRESENTING THE SAME PROTECTION ZONE
One of the most frequent questions among designers and installers concerns the fact that the regulations allow the protected zone to be represented in two different ways. In the case of Early Streamer Emission air terminals (ESE), this calculation can be carried out using two methods provided for in the current standards.
- Formula method (UNE 21186):
The protection radius of an ESE air terminal depends on its height (h) with respect to the surface to be protected, its initiation advance time (ΔT) and the chosen protection level (r). For 2 ≤ h ≤ 5:
for h ≥ 5 :
- Graphical method (CTE DB-SUA-8):
When an Early Streamer Emission air terminal (ESE) is used, the protection volume of each tip is defined as follows:
Below the horizontal plane located 5 metres below the tip, the protected volume corresponds to that of a sphere whose centre is located on the vertical of the tip, at a distance (D), and whose radius is: R = D + ΔL
Where:
- R: the radius (in m) defining the protected zone.
- D: the distance (in m) indicated in table B.4 depending on the protection level.
- ΔL: the distance (in m), depending on the initiation advance time Δt of the air terminal, expressed in μs.
ΔL = Δt shall be adopted for values of Δt less than or equal to 60 μs, and ΔL = 60 m for values of Δt greater than 60 μs. Both methods lead to the same result when applied correctly.
FROM CALCULATION TO THE PROTECTION SOLUTION
That is why it is increasingly common to use tools that make it possible to model the installation and visually verify the coverage of the system before its implementation.
At INGESCO, we have developed CALCULUS, a free software tool designed to facilitate the calculation and design of lightning protection systems in accordance with the standards in force. With CALCULUS, it is possible to automatically calculate the protection zone of an Early Streamer Emission air terminal (ESE), graphically visualise the protected volume, compare different design solutions, optimise the location of the air terminals and generate the technical reports for the project. In this way, the calculation is no longer merely a manual operation, but becomes a genuine design support tool within the framework of a global engineering project. At INGESCO, we approach every project with an integrated vision. Before selecting an air termination system, we analyse the characteristics of the installation, its environment and the applicable regulations in order to define the most suitable solution for each situation.
Do you need to calculate the protection zone for your project? You can do it easily with CALCULUS or contact our technical team if you would like support in defining the most suitable solution for your installation.
