Overall Lightning Protection System

Introduction:

Lightning is a natural phenomenon and it cannot be avoided whereas the damages due to lightning can be reduced by providing proper lightning protection system (LPS). A Lightning Protection System consists of both the external and internal lightning protection system. An External LPS provides protection against physical damages whereas an internal LPS provides protection for electrical and electronic systems

Overall Lightning Protection System:

• An overall Lightning Protection System contains
• Properly designed Air termination system for capturing the Lightning strikes.
• Down conductor system having sufficient cross-sectional area for safely conducting the lightning impulse current from air termination system to earthing system.
• Good earthing system for dissipating the lightning energy into the ground as soon as possible without a considerable increase in Ground Potential Rise.

• Interconnecting the earthing of LA, system earthing and telecommunication system earthing below the ground level to form a single integrated earth termination system.
• Equipotential bonding of exposed water pipes, metal parts, and structures to avoid the difference in potential.
• Surge protection modules for power lines and telecommunication cables.

External Lightning Protection System:

An External Lightning Protection System will provide protection to the buildings and structures from the damages due to direct lightning strikes.

An external Lightning Protection System is intended to

     1) Safely capture the lightning flash. (Air terminal system)

     2) Conduct the lightning current safely from air terminal to the earth. (Down conductor system) 

     3) Dissipate the lightning current into the earth. (Earth termination system)

Internal Lightning Protection System:

The function of the internal LPS is to protect electrical and electronic equipment inside the structure from the lightning impulse surges by using equipotential bonding or a separation distance along with surge protection devices.

Some of the major sources of transient over-voltages are as follows

• Lightning
• Industrial and switching surges
• Electrostatic discharges (ESD)
• Nuclear electromagnetic pulses (NEMP) 

Among these, lightning is the natural source of impulse surges. The sources of damages due to lightning strikes are shown in Figure 2 and are as follows.

     1) Lightning strikes on a structure.

     2) Lightning strikes near the structure.

     3) Lightning strikes on a transmission line

     4) Lightning strikes near a transmission line.

Physical damages due to lightning strikes on the structure shall be protected by using an External Lightning Protection system whereas the electrical equipment shall be protected from lightning impulse currents by using Surge Protection Modules.

The damages of electrical and electronic equipment are either caused by the lightning strikes on the power lines or by the induction due to the impulse currents. Hence this can be classified as the indirect effects of lightning strikes. The indirect effects of lightning strikes are shown below in Figure3.

The protection against the failure of internal systems due to lightning impulse current limits.

• Surges due to lightning flashes to the structure.
• Surges due to lightning flashes nearby the structures.
• Surges transmitted by lines connected to the structure. 
• The magnetic field directly coupling with apparatus.

The system to be protected shall be located inside Lightning Protection Zone 1(LPZI) or higher. The protection measures for any LPZ shall comply with IS/IEC 62305-4.