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There are two basic lightning protection methods; lightning arresting and lightning dissipating systems. Lightning arresters attract lightning on themselves where lightning dissipators protect the site by making it invisible to lightning.
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Since 1700's, lightning protection has been taken as attracting lightning and transmitting current to ground “safely”. Products such as Lightning Rods (also known as Franklin Rods), Faraday Cages, Early Streamer Emitters all operate with the same principle. However, for the last 30 years, studies on “blocking” or “preventing” lightning resulted with many alternative systems working with this principle.
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| Hazardous Effects of Attracting Lightning: |
Attracting million volts of electrical energy to any system is a serious risk taken unnecessarily for lightning protection. Lightning arresting systems are installed directly on the structure to be protected and they try to attract lightning strike on themselves to lead the current to the ground. For the lightning to occur, one of the positive upward streamers has to meet one of the negative stepped leaders at 150 meters height above the ground. Lightning arresting systems make the risk of getting hit higher by showing themselves a target to the strike.
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When lightning is arrested, following can happen;
1.
Lightning current can find a more conductive path during its flow to the ground and step inside the building.
2.
If there is a difference in resistance between the grounding systems of the building and lightning protection
__system, lightning current can move inside the building through the grounding system after it is transferred
__under the ground.
3.
Electromagnetic field of the current travels along the down conductor and it harmfully effects the sensitive
__electronic equipment inside the building.
4.
Any failures during installation of lightning protection system and/or any corrotive occurance after the
__installation can create a non-conductive path to the current and the current can find a better way inside and
__step into the building. This can be harmful to the electronics but more importantly can be deadly for people
__living or working in the building. |
Telecommunication and Radio-TV Towers and Lightning:
There are a lot of electronic devices on a telecommunication or radio-tv tower. These towers are open to lightning strikes since that they are completely made of conductive metal body parts like galvanized steel. When lightning strike hits a tower like this, if there is no primary lightning protection on the tower, lightning current flows through the body of the tower to the legs and exits to the ground. During this flow, lightning current damages the electronics on the path it follows and most devices get permanently out of service. More importantly, the shelter by the tower contains sensitive electronic devices with worth of over 200.000 Euros and these devices can be affected either directly by the current itself or by the electromagnetic field of the current. Lightning current can also travel under the ground after it flows down and can enter the shelter from shelter's grounding system if there is no equipotential situation.
Primary lightning protection systems must be applied to these towers to avoid these damages. In many countries these types of towers are protected by lightning arresters with down conductors attached to them. Lightning arresters (mostly the
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typical Franklin Rods) attract lightning on themselves and transfer the current to the conductor. However, since the conductor is directly attached to the tower body, current finds the tower surface a better path to the ground and flows on the tower to the ground, damaging everything on its path including radoms, antennas, dishes, etc.. It is also a risk for the shelter and all electronics inside as well.
Basicly, there is absolutely no difference between protecting a tower with a lightning arrester and leaving the tower unprotected. Lightning will hit the tower top in both situations, current will flow through tower body and tower legs and the damage on the tower and in the shelter nearby is exactly the same. So, “protecting” the tower with a lightning arrester is actually an unnecessary risk.
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Lightning protection by arresting lightning strikes is an unnecessary risk, however this method has been used for many years because no other reliable method has been known in many countries. Lightning dissipation devices have protected thousands of facilities for over 30 years all around the world and real protection against lightning strikes especially on towers can be accomplished only by preventing them. This method has been open to discussions in scientific world for years and finally five years ago, scientific communities started working on an international standard for lightning dissipation systems as well.
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How Does System Work?
One of the two main fundamentals of physics states that all objects emit charges through the process of ionization and sharp objects do this faster comparing to flat planes what states the second one. This also explains why lightning mostly hits corners and sharp points instead of flat sides of a building. When the positive charges are collected at that point, with a level of concantration they are emitted faster than any other surface around which attracts lightning strike right at this point (Figure A).
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Figure A: Positive charges are collected at the top of the lightning rod and when reaching a level of concentration positive streamer is emitted. |
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Figure B: Thousands of tiny sharp points emit the positive charges before they reach to a concantration level and form a positive streamer. |
On the other hand, having thousands of sharper and smaller points creates more and faster ionization. Instead of having positive charges concentrated on the top of a single point and letting them form a streamer, emitting the same amount of charge not from a single point but through thousands of smaller points creates the dissipation process. Dissipation process mostly stops or in some cases at least delays the formation of streamers and minimizes the risk of lightning occurance at the point to be protected (Figure B).
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It is obvious that protecting the metal structures like telecommunication towers with lightning arresters or leaving them unprotected have basicly the same result; both collect the positive charges on the tower top, emit them in the form of positive streamers and one of these streamers meets with one of negative stepped leaders from the cloud and lightning hits the tower top (Figure C). If the same tower is protected by a lightning dissipator system application (Figure D), formation of positive streamers gets blocked and lightning does not hit the tower. This gives all electronic devices on the tower and in the shelter a lightning-free environment and site operates properly with no damages or failures.
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Figure C: Positive charges are collected on the tower top and form a positive upward streamer directed to the cloud. |
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Figure D: Lightning dissipators emit the positive charges so fast that this avoids the formation of streamers to reach to negative stepped leaders. |
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