Lightning and communication towers

K. R. ABHAYASINGHA

Technology has developed with an unbelievable speed during the past 2-3 decades. Most of the old electrical and electronic equipment are being replaced by the modern, efficient and remotely controlled equipment.

As I remember, in 1950s there was only one radio receiver in my village and it was powered with a large size dry battery. An aerial tied to two tall trees was there to receive the radio signals. The reception of signals was frequently disturbed during the day times and also during rain with the lightning and thunder activity.

Even though the reasons for such noises were not known by the villagers they had the practice of discontinuing the aerial-radio connection with a switch provided for the purpose.

Now we know that these disturbances in reception were caused either by the variability of signal reflection by the ionosphere which is about 60 km above sea level or by the interference of electromagnetic (EM) waves created by lightning flashes during thunderstorms.

Science has found solutions to these problems and now we can listen to any broadcasting media without many obstacles in all types of environments. In the progress of he technology, the bad effects are sometimes inevitable. But technology itself finds the solutions to the problems and goes ahead very fast.

Modern technologies

The new technologies are known to a few people while the majority has no idea about the new findings and improvements. Those who have no or a little knowledge of the modern technologies, very often make wrong statements.

They really do not like to admit their unawareness of the latest technology and in some cases they have the intention of hiding their unawareness. But the wrong statements of such personnel will lead to a number of bad results.

Most of the communication systems in Sri Lanka are not really modern or the latest and they have been imported from developed countries who have entertained the same facilities long before us.

Telecommunication technology is one of the fields that have close relations to man. Millions of Sri Lankans now use the most modern electronics in communication (mobile phones, computers, single band radio communication, walkie-talkies etc.) to enhance the efficiency of their day-to-day activities.

Satellite communication

In telecommunication between persons, the electro magnetic (EM) waves created by a caller from his phone should be received by the recipient. The old relaying technology, the usage of cables, has been already replaced by wireless communication techniques in many developed countries but poor, developing countries like Sri Lanka, who are in the transition, use both.

The latest satellite communication is pretty expensive for us since Sri Lanka does not owe even a single satellite installed in the sky and therefore we have to continue with phone-com tower-phone relaying technology for some more years to come even though it is old. Sri Lankans who travel abroad know well that some of developed countries still use such facilities as com towers.

One stage in the process of telecommunication is the installation of communication towers (com towers) for the purpose of raising the receiving and disseminating antennas to a higher level above ground to enable them to serve a large number of customers.

As it was already mentioned, this is an old technology that has been used by developed countries for a very long time even though many Sri Lankans still think that these towers are new inventions in the world and also they think that the scientists are not aware of the impacts or (bad) effects of them. (Please note that the towers may not be seen in many mega cities like Hong Kong, London, Washington and Singapore because the communication antennas can be easily mounted on or inside tall buildings in those cities. Those who are not aware of this facility may point out the absence of towers in those cities).

With the increase of installation of communication towers in the island some people have been objecting the construction of them with complains of possible enhancement of the lightning activity near the towers and of repulsions of lightning strokes to areas around the towers. Both these complaints do not have a valid scientific ground.

The effects of lightning on com towers or any kind of structure made by man have been known to scientists particularly after the time of Benjamin Franklin who disclosed many scientific facts of lightning during 1747 - 1749.

Benjamin Franklin’s findings have been the topics of many scientists in the field of lightning and the protection against lightning has been attended by the science. All tall structures or protruding objects are vulnerable to lightning. As Benjamin suggested a long time ago, they should be protected by a lightning rod which is made of a good conducting material.

Electric current

Lightning in Sri Lanka causes over 50 deaths and the damage to property is billions of rupees every year.

The electric current of a cloud to ground lightning flash is about 25,000 Amperes (25000 A or 25 kA) and the potential difference between a charged cloud and the earth is about 100 million Volts (10 8 V). Te energy of a lightning flash bringing 5 coulombs to ground is about 500 million Joules. Under certain conditions electric current of a ground lightning flash exceeds 100 KA.

During bad weather conditions with thunderstorms, lightning surges may reach a location or an object as a,

(A) Direct hit:

Travelling of a lightning flash directly from a cloud to an object.

(B) Side flash

A part of a lightning flash struck a close by tall object (like tree or tower) may spark to the conducting parts (concrete, sun shade, concrete roof top of chimney or aluminum sheet roof) of a building even without any electrical connection.

(C) Surge transfer

A part or the whole current of a lightning flash which has hit a close by telephone or power supply line or a TV antenna may travel to inside of a building via the electrical (metal) connection between the point of strike and the building.

Lightning is a natural phenomenon and stopping it is out of our control. But lightning caused hazards could be reduced with a number of precautionary measures, which are introduced in order to pass the high current surges created by a direct or indirect lightning current to the earth safely. Some of them are,

1) Install proper earth rod for the electric circuit of buildings.

A lightning flash partially conducted through a power supply circuit may be equally hazardous as a direct lightning strike. In buildings powered by the main power supply lines without the earth wire, this situation may be very serious. It is the earth rod and the earth wire which corporate in conducting the extra power surge to the earth. Therefore, the earth wire and the rod should be properly installed to make it capable to perform its job properly.

According to the standards (internationally or nationally) the resistant of the earth rod should be less than 10 ohms and the connection between the earth rod and the earth wire should be firm.

2) Use power surge diverters

Supply lines of power and communication can be installed with power diverter which is capable in directing surge currents intruding a building along supply cables as a result of a lightning flash to the ground without allowing it to travel into the interior parts of the building circuit.

3) Installing lightning conductor (or lightning rod).

Direct his of a lightning flash to a building is the most fatal event when the lightning hazards are concerned. Lonely and tall buildings are the most vulnerable to lightning. The lightning rod (or lightning conductor) which was first introduced by Franklin is the widely used device for protection of buildings even these days.

Continuous research in this field has been useful to apply modifications to the lightning rod to make it efficient in conducting lightning currents to the ground protecting the building and the property inside.

Protection

A lightning conductor develops an area of protection, around the base, which is a circular area with radius equal to the vertical height of the air terminal of the conductor. A good lightning conductor attracts all lightning flashes that could be otherwise attracted by the objects in the area of protection. Therefore, a good lightning conductor will protect all the objects in the protection-area from direct lighting.

A com-tower or a building of the same height with a lightning conductor installed according to the standard will have same characteristic of protection. No tower is capable of throwing lightning strokes away to the areas around it.

Damages

The tremendous numbers of towers that already exist in the island are good examples. In most of the cities, the communication towers are installed not only on the ground but also as roof top towers. Since they are provided with a standard lightning conductor, the building below the tower or the people around the tower are not affected.

If there is any truth in the complaint of the throwing of lightning by communication towers, there should be a significant rising trend of damages by lighting in locations near such towers.

But no such increasing, trend has been reported. But according to the lighting incidents in Sri Lanka, the lightning-hazards to building which have not been protected with Lightning Protection Systems are on the increase and the event does not depend on the existence of towers in the vicinity.

Lightning is a production of a special type of clouds, which is technically named as Cumulonimbus that develops between about 500 meters and about 12 kilo meters, Lightning flashes are originated as a joint electrostatic process of two charge centres, negative and positive, at altitudes 5 and 10 kilometers respectively.

Any man-made object on the ground, including the tallest towers in the world are comparatively minute objects and they are not capable of increasing or neutralising the electrostatic charges in a cumulonimbus cloud and hence no tower can change the lightning activity in and around its location.

Best example from Sri Lanka itself is, even the 160 meter high tower in Jaffna is not capable of enhancing the lightning activity in Jaffna.

Lightning rods

As a lightning rod protects an area from direct lightning a tower with a lightning rod can provide protection. Towers with standard lightning rods or Lightning Protection Systems (LPS) have been installed to protect houses and buildings in a number of villages in Sri Lanka.

For example, houses in four villages, Deraniyagala, Huldummulla, Mattamagoda (Ruwanwella) and Mitipola (Sabaragamuwa) have been protected with specially made towers.

The com towers are protected against all types of lightning hazards mainly because some damage to the body of the tower or the electronic equipment used in the base room will end up in a significant economical loss.

Service providers are very serious about this. With the installation of the LPS, the structure within the safe area are automatically protected against direct lightning. We should realise that any LPS has a limited protection area and it cannot save areas beyond that. In thunder storms, the structures in regions outside of the safe area may be vulnerable and this situations will arise with or without a tower.

LPS are installed in houses, buildings, towers etc. by a number of institutes to provide protection against lightning. But the international standards should be followed by all the technical people who perform the installation.

One of the important requirement is that the grounding resistance of the LPS should be below 10 Ohms. It is the responsible of the experts in the field to choose and recommend the perfect characteristics of the material and surge diverters for the LPS.

Environment lovers

Non technical views on com towers also are pointed out frequently. There is one group of Sri Lankans, the environment lovers, who declare their objections to erection of com towers because, they points out, the com towers spoil the beauty of the environment.

This is a valid argument but it is too late for one to be armed with such arguments because man has been spoiling the environment since he began to change the natural living practices.

Natural man never harmed the environment for his living. But cultured man has already done significant harm to the environment. Raping the environment has accelerated with the invention of technology in a number of branches like transport, construction, power generation, food production and agriculture in recent past.

Man has extended his area of activity to all sorts of topography including mountains, jungles poles an deserts. Buildings and other structure have come up even on top of hills, Millions of high tension transmission lines run over all parts of the island.

Millions of high tension transmission towers have been erected over the island spoiling the beautiful environment.

Huge hotels, factories, buildings have already covered many hilltops which were one time green caps. Among the so many millions of structures which have raped the environment the harm done by a few hundreds of com towers do not seem to be significant.

Pollute environment

Com towers are really serving the whole nation through relaying our important messages. What is the awareness of the environmentalist or environment-lovers about the huge hotels, factories, housing schemes etc. built on top of hills and other environments that would be otherwise very beautiful?

Once a tower is built, it affects the visual beauty of the environment a little but with the time it will become a part of the environment. But hotels and factories are not only harmful to the visual beauty of the location but also they pollute the environment significantly.

The concept of the depletion of the environmental beauty by towers has no firm base. Any structure including houses built on the ground spoil the natural beauty of the location.

Communication towers are usually made of metal and lightning conductors should be properly installed on all such towers for the purpose of protecting the very valuable electrical and electronic instruments associated with the communication.

A tower with a lightning conductor will provide protection from direct lightning not only to the instruments but also to any object within the area of protection of the tower. A tower does not reflect or repulse lightning flashes.

A com tower can never influence the development of Cumulonimbus clouds that produce lightning neither influence any increase or decrease of electrostatic charges inside a thundercloud whose charge centers are more than 5 kilo meters above the ground level.

However all of us have the right to inquire of the standard of any man-made structure around us. We should not concentrate our interest only at the communication towers.

(The writer is former Director of Meteorology)