There is little argument that Lightning poses an enormous threat to telecommunication, radio and TV towers. These towers are constructed of steel and designed to be the highest structures in the surrounding area in order to supply communication with no interruptions. There is a higher probability of Lightning hitting the sharpest and tallest object in an area. Furthermore, lightning current reaches the ground by following the shortest and most conductive way. That is why a telecommunication tower which is a tall metal structure becomes the primary target for lightning strikes.When lightning strikes the top edge of a tower, the current flows downward to the ground and damages all electronic equipment like radomes, radios, antennas, dishes, cameras, etc… On the way to the ground, lightning current can leak and jump into nearby structures and shelters that result in permanent damage to sensitive electronic devices and equipment. Lightning arresters endeavour to attract lightning in order to divert lightning energy to earth. There are a number of different scientifically proven solutions but typically they are installed on the highest points of the structure and connected to a downconductor cable which is bonded to a grounding system and then to earth. The purpose is to attract lightning before it reaches any other object and allow the lightning current to flow down to the ground and dissipate the energy through the earth.
The system at a telecommunications facility
The system at a telecommunications facility is divided into 5 components: 1. Indoor Bonding Arrangement 2. Outdoor Grounding Layout 3. Surge Protection for Power Lines 4. Surge Protection for Telephone Lines 5. Direct Strike Lightning Protection
1. Indoor Bonding Arrangement
Correct bonding for all lightning protection system elements is essential or the system will be totally ineffective against lightning strikes. Bonding of all metallic conductors assures everything is at equal potential, so if there is a strike you are protected.
2. Outdoor Grounding Layout
Low-resistance grounding provides an efficient destination for lightning current. Some soils are composed of sand or rock , that are highly resistant and not conductive. If surrounding soils are clays or dirt with moisture present, they likely are conductive .There are local distributors that can provide the support and materials to ensure you achieve effective earthing and protection.
3. Surge Protection for Power Lines
Surge protection devices (SPDs) function either by absorbing the transient energy as heat or crowbarring the transient energy to ground (some in combination). They should be installed at main panel entries, at critical branch or secondary panels, and at plug-in outlets where low-voltage transformers convert AC power to DC current and voltage. SPDs should also be installed at signal and data line building entry points for critical electronic equipment.
4. Surge Protection for Telephone Lines
Included here are Cat. 5/6, coaxial lines, and twin lead and other copper wire circuits. Telephone punch blocks should be SPD-protected.
5. Direct Strike Lightning Protection
Lightning usually terminates on grounded objects sticking up in the air. Franklin rods, Dynaspheres and ISODC are air terminals. Benjamin Franklin designs developed in 1752, divert lightning from rods in the air via conductors to rods in the ground, protecting important assets. This part of a lightning protection system (LPS) is based upon the principles of Path of Least Impedance.
Generally, there are two main systems of lightning protection: * Isolated Systems– These are commonly specified to protect metallic assets from potential lightning hazards. Partial discharges on bare conductors may form on the cable surface during immediate voltages, which can cause thermalization or breakdown. This can potentially adversely affect sensitive tower equipment. * Non-Isolated Systems – These are mostly recommended for communication towers as they contain the lightning energy and minimise the effects and interference to sensitive equipment caused by side flash.
Isolated systems like ERICO’s (West Australian Power Protection) Isolated Downconductor(ISODC) and Dynasphere have a multi-layered insulation and semi-conductive outer sheath. An isolated down conductor system provides the same materials and cross-sectional area as other IEC standards compliant down conductor with the benefit of having highly insulated coverings.Commonly these isolated lightning protection systems are mounted on a tall support mast. An air terminal is mounted on the top of the mast, which provides required protection using the international IEC 62305 design standard.
The protection from lightning strike on radio, telecommunications and other towers sites can be protected using the right method and system.