Overall Lightning Protection System

Introduction:

The main and most effective measure for protection of structures against physical damage is considered to be the lightning protection system (LPS). An External LPS provides protection against physical damage and life hazards whereas internal LPS provide protection for electrical and electronic systems. In this article, we shall explore about the overview of Internal and External lightning protection system as specified in IS/IEC 62305 standard.

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 from air termination system to earthing system.

Good earthing system for dissipating the lightning energy into ground as soon as possible without considerable increase in Ground Potential Rise.

Single integrated earthing system by interconnecting LA earthing, system earthing and telecommunication system earthing below the ground level.

Equipotential boding of exposed water pipes, metal parts and structures.

Surge protection modules for power lines and telecommunication cables.

External Lightning Protection System:

External Lightning Protection System will protect the buildings/structures from physical damages due to direct lightning strikes. An external Lightning Protection System consists of,

Air terminal system to safely capture the lightning flashes.
Down conductor system to safely conduct the lightning current to the earth.
Earth termination system to safely dissipate the lightning current into the earth.

Internal Lightning Protection System:

The function of the internal LPS is to prevent dangerous sparking within the structure using equipotential bonding or a separation distance. Internal Lightning Protection System will provide protection to the electrical and electronic equipments inside the structure from the lightning impulse surges.

The main causes of transient over voltages are,

Lightning

Industrial and switching surges

Electrostatic discharges (ESD)

Nuclear electromagnetic pulses (NEMP)

Among these, lightning is the natural source of impulse surges. IS/IEC62305 classifies the sources of damages due to lightning strikes into 4 groups and they are as follows.

Damages due to lightning strikes on a structure.
Damages due to lightning strikes near the structure.
Damages due to lightning strikes on a transmission line.
Damages due to lightning strikes near a transmission line.

Damages due to lightning strikes on the structure shall be protected by using External Lightning Protection system whereas the electrical equipments shall be protected from lightning impulse currents by using Surge Protection Modules in combination with good earthing system.

Lightning impulses are silent killer of electronic devices inside the structures. The failure of internal systems due to lightning surges are caused by,

Surges due to lightning flashes to the structure.
Surges due to lightning flashes near the structure.
Surges transmitted by the power lines connected to the structure.
Surges transmitted by the telecommunication lines connected to the structure.
Magnetic field directly coupling with the lines or apparatus.

The protection measures for any Lightning Protection Zone (LPZ) shall comply with IEC 62305-4.

Lightning Protection Zone:

Protection measures such as LPS, shielding wires, magnetic shields and SPD determine the Lightning Protection Zones (LPZ). The protection zones as specified by IS/IEC 62305 are as follows.

The different zones as specified by IS/IEC 62305 is shown below.