Lighting Protection

Lightning Protection

Why do we need LPS (Lightning Protection System)?

We have to protect buildings and structures from lightning strikes and possible fires, or from the consequences caused by load independent active lightning currents. In order to get above goal, we must use Lighting Protection system (LPS)

Damages caused by lightning

We can categories damages due to lightning,

  1. Due to Damage to a structure
  2. Due to Damage to a service (Power, water, gas, data networks)

Sources of damages

  1. Due to Lightning flash to the structure
  2. Lightning flash near the structure
  3. Due to Lightning flash to the service
  4. Lightning flash near to the service

Types of damages

  1. Injuries to living beings (due to touch and step potential)
  2. Physical harm (mechanical destruction, fire, explosion)
  3. Failure in electrical or electronic systems due to electromagnetic impulse triggered by lightning

Types of losses

  1. Due to Loss of human life
  2. Loss of essential service to the public
  3. Due to Loss of cultural heritage
  4. Economic loss (caused by damaged buildings, structures and services)

Process of Lightning Protection System

  1. It should intercept thee lightning flash
  2. Lightning current should be conducted to the earth
  3. Current should be dissipated to the earth
  4. It should create an equipotential bond to prevent hazardous potential difference between LPS, structure and internal circuits.

Qualities of Lightning Protection System

  1. It must not cause mechanical or thermal damages to the structure
  2. It must not cause sparking which may cause fire or explosions
  3. In order to minimize the risk of injuries to occupant, step and touch voltages should be limited to desired values
  4. It must limit damage to internal electrical and electronic systems
Lightning protection zones
Lightning protection zones

Lightning Protection Zone (LPZ)

LPZ0A -Direct flash, full lightning current

LPZ0B – No direct flashs, partial lightning / induced current

LPZ1 – Internal of building 

External LPS Design Considerations

An external Lightning Protection System consists of:

1. Air termination system

  • Air rods
  • Catenary (or suspended) conductors
  • Meshed conductor network

2. Down conductor system

3. Earth termination system

  • Type A arrangement
  • Type B arrangement
  • Foundation earth electrodes

Position of Air Termination System

Three main methods are recommended for decide the position of the air termination systems

  1. The rolling sphere method
  2. The protective angle method
  3. . The mesh method

Rolling Sphere Method – Lighting Protection system

In this method, it will identify the areas which need protection by considering the possibility of side strikes to the structures.

Rolling sphere method
Rolling sphere method

Striking Distance (Last Step)

It can be clearly seen that the corners are exposed to a quarter of the circular path of the sphere

  • This mean if the last step fall within this part of the circular path it will terminates on the corner of the buildings.

Corners of structures are vulnerable to lightning strikes

Rolling sphere method
Rolling sphere method

Lightning Protection Levels  

In order to define lightnings as sources of interference, lightning protection levels I to IV are defined as below

Lightning current for each LPL
Lightning current for each LPL

Max values are Design of products such as Lightning protection components

Min values: Design Lightning protection systems (e.g. radius of rolling sphere)

Maximum Values of Rolling Sphere Radius

There are different radius of the rolling spheres that correspond to the relevant Class of Lightning protection systems.

Maximum value  of rolling sphere radius corresponding to LPS Lighting Protection
Maximum value of rolling sphere radius corresponding to LPS

Protective Angle Method – Lighting Protection system

The protective angle method is mathematical simplification of the rolling sphere method and also use for verify the rolling sphere results.

Protective Angle Method Lighting Protection
Protective Angle Method

Application of Protection using Angle Method

  • Unlike the rolling sphere method, the protective angle method is not used for determine which part of a structure requires protection.
  • It use to show the effectiveness of the designed lightning protection system.

Determination of Protective Angle

Determination of protective angle Lighting Protection
Determination of protective angle

Mesh Method – Lighting Protection system

  • A “meshed” air-termination system can be used universally regardless of the height of the structure and shape of the roof.
  • This method is suitable where plain surface requires protections if the following conditions are met with requirements.
  • Air termination conductors must be positioned at roof edges, on roof overhangs and on the ridges of roofs with a pitch in excess of 1 in 10(5.70)
  • No metal installation protrudes above the air termination system due to Lightning vulnerability.

Determination of mesh size

Maximum values for mesh Lighting Protection
Maximum values for mesh

LPS Design Values

Maximum values of rolling sphere radius also mesh size and protective angle

LPS Design Values Lighting Protection
LPS Design Values

Reference

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