Types of Primary Lightning Protection Systems

History of Primary Lightning Protection

The simplest type of lightning rod was designed and built in 1753 by Benjamin Franklin. This lightning rod, named after this great scientist as the "Franklin rod," is used in Faraday cage type lightning protectors with the same kind of lightning rods.

 

Types of Primary Lightning Protection Systems

Primary lightning protection systems have two main types:

  1. Passive Primary Protection System
    The passive primary protection system includes components that do not have an active power source and perform the primary lightning protection function based on design conditions. The Franklin lightning rod is the simplest and most basic lightning rod, consisting of a single pointed rod. The cone angle from its tip is exactly 45 degrees, but in practical calculations, this angle is considered to be 35 degrees to increase reliability.

Active Primary Protection System
The active primary protection system refers to lightning rods that, by using energy received from an external source or generated autonomously, ionize the surrounding air and provide greater safety.

Active lightning rods, in terms of their energy requirements, are divided into two groups:

  • Dependent lightning rods, which require an external power source such as a battery or mains electricity to operate.
  • Autonomous lightning rods, which obtain energy through an internal mechanism from the surrounding environment to activate. These include...

The lightning rods include:

  1. Atomic
  2. Wind or piezoelectric
  3. Solar
  4. Electronic-capacitive

Among the four types of active lightning rods mentioned above, electronic-capacitive lightning rods are the most widely used in buildings.

Passive Primary Lightning Protection System
These lightning rods are divided into three main categories:

  • Simple lightning rod
  • Air wire system
  • Mesh system

Methods to Prevent Direct Lightning Strikes

 Methods for Designing Lightning Protection Systems

To determine the installation location of lightning rod terminals, the following three methods exist:

  • Protective angle method
  • Mesh method
  • Rolling sphere method
  • Protective Angle Method
    This method is applicable for sloped surfaces. On these surfaces, lightning rods are installed vertically relative to the horizon so that the desired protective angle range is achieved. This method is usually used to complement the mesh method in buildings that have protrusions on flat surfaces. It is the simplest method for locating lightning rods and is used for Franklin lightning rods; however, it is not as effective and reliable as the rolling sphere method. Additionally, this method is not suitable for buildings taller than 20 meters.

Angular Method

Coverage Angle Based on the Height of the Lightning Rod Tip Above the Protected Surface and Protection Classes I to IV

Mesh Method
In this method, copper strips are installed in a crossed pattern on the external surface of the building so that the distance between these strips... Copper, corresponding to the numbers related to the protection class. For buildings taller than 60 meters, this method is also applied to 20% of the walls in the upper section of the building.


Mesh Method

Rolling Sphere Method:
In this method, a hypothetical sphere is rolled over the structure, and the parts of the structure that come into contact with the sphere are considered susceptible to lightning strikes and need protection. Lightning rod terminals must be installed in these areas. This is the most comprehensive yet simple method for determining the locations of lightning rod terminals.

Rolling Sphere Method

After reviewing the design methods of primary lightning protection systems, here we provide more explanation about the types of passive primary lightning protection systems.

Simple Lightning Rod or Franklin Lightning Rod
This lightning rod was first invented and built by Benjamin Franklin, which is why it is known as the Franklin rod. Below, you can see an example of the coverage radius of a simple lightning rod based on the NFC 17-100 standard.

Simple Lightning Rod and Determining Coverage Radius Based on the Protective Angle Method

Among the advantages of this type of lightning rod are its ease of installation and cost-effectiveness. However, it has a limited coverage radius. Due to its simple installation, this lightning rod is recommended for radio stations, satellite dish antenna sites, and buildings with small protected areas.

Air Wire Terminal System
This type of protection involves using one or more overhead air wires above the area to be protected. These wires are supported by towers on two sides of the protected area and are grounded through the same towers.

Required components:

  • One or more overhead conducting wires
  • Two towers to support the wires
  • Separate grounding system for each down conductor
  • Equipotential bonding of grounding systems

Designing the air wire system requires additional mechanical studies, including the mechanical strength of the towers, ground resistance to support the towers, foundation calculations, and the towers' resistance against wind and weather conditions.

Advantages of the Air Wire System:

  • Reduction of electromagnetic radiation effects in addition to lightning protection
  • Distribution of lightning current among multiple down conductors
  • Protection of open areas

Disadvantages of the Air Wire System:

  • Complexity and high cost of implementation
  • Often impractical due to the complexity of building designs
  • Cannot be installed in accessible areas, such as near elevator equipment

Overhead Wire Protection System

Faraday Cage or Mesh System
This system includes several air terminals (Franklin lightning rods) installed on elevated surfaces or the highest parts of towers and similar structures. These terminals are connected to each other by a network of copper strips and linked from one or multiple points using copper strips or bare copper wires to the corresponding grounding network.

Mesh System or Faraday Cage

The number of air terminals required to protect buildings using the Faraday cage protection system depends on the roof area of the building, the height, and the spacing of the terminals, which varies according to different applicable standards. The standards for these lightning rods include: IEC 62305, BS 6651, NFPA 780, and NFC 17-100.

Table for Selecting Mesh Dimensions and Number of Down Conductors Based on Protection Levels I to IV

Advantages of the Mesh System:

  • Reduction of electromagnetic radiation effects in addition to lightning protection
  • Distribution of lightning current among multiple down conductors

Disadvantages of the Mesh System:

  • Complexity and high cost of implementation
  • Often impractical due to the complexity of building designs in most cases
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