01 January 2005
Lightning strikes: Protection concepts
By Peter A. Carpenter
The risks from lightning are real, and traditional lightning protection devices do not adequately cover all risks. Over the last 30 years, significant technology improvements have given us a proactive approach in lightning protection, including the integration of charge transfer technology, strategic surge protection, and a unified grounding system. When eliminating the strike to the protected zone and the associated structure, you can reduce or eliminate the secondary effects of lightning.
If a lightning strike could put a facility out of business, or even out of action for a few hours, consider whether the cost of preventing all future lightning risks would not easily offset the cost of installing a charge transfer system (CTS) lightning elimination system. It is inexpensive insurance.
A large thunderstorm can produce over 100 lightning flashes a minute, and even a modest storm cloud can generate the energy of a small nuclear power plant (a few hundred megawatts). A drilling rig can shut down for hours or days due to equipment damage, or a chemical plant can potentially catch fire due to lightning.
None of the traditional systems are 100% effective. New technologies have demonstrated it is possible to eliminate the strike altogether. The CTS has proven its effectiveness as a system to prevent lightning from striking the protected area-such as chemical plants, nuclear power plants, oil and petroleum facilities, and off-shore drilling rigs.
The direct effects of a lightning strike are physical destruction and subsequent fires. When a direct strike hits a facility that contains flammable materials, the flammables can be vulnerable to the bolt, the stroke channel, or the heating effect of the strike. The petroleum industry's history provides ample evidence of the destructive nature of lightning. Lightning-related phenomena destroy millions of dollars of petrochemical products and lives in many parts of the world.
The secondary effects of a direct or nearby strike include the bound charge, electromagnetic pulse, electrostatic pulse, and earth currents. The bound charge (and subsequent secondary arc) is the most common. Statistics indicate the secondary effects cause most of the petroleum-related fires. These fires often self-extinguish after the free or isolated vapors burn.
The electrostatic and electromagnetic pulses induce high-voltage transients onto any conductors within their sphere of influence. These transients will cause arcing between wires, pipes, and earth. The cause or mechanism of secondary effects are not always easy to identify. Conventional protection will not influence any of these secondary effects other than to increase the risk of an event. Air terminals collect strikes and encourage a stroke termination close to flammable materials. The trend toward micro-miniaturization in electronic systems development brings an increasing sensitivity to transient phenomena.
Prevention system options
In most cases, you can adapt one or more products to solve any lightning protection problem. Lightning is the process of neutralizing the potential between the cloud base and earth. Any strike prevention system must facilitate this process slowly and continuously. The dissipation array system is one of the most common configurations of a CTS and can prevent a strike to the protected area and the array itself.
To prevent a lightning strike to a given area, a system must be able to reduce the potential between the site and the storm cloud cell, so the potential is not high enough for a stroke to terminate within the area. That is, the protective system must release the charge induced in the area of concern to a level where a strike is impractical. (Charge induction comes about because of the strong electric field created by the storm and the insulating quality of the intervening air space.)
Atmospheric scientists have found that much of the storm's energy dissipates through what is called natural dissipation, which is ionization produced by trees, grass, fences, and other similar natural or man-made pointed objects that are earthbound and exposed to the electrostatic field a storm cell creates. A storm cell over the ocean will produce more lightning than the same cell over land because the natural dissipation of the land will reduce the storm's energy. Consequently, a multipoint ionizer is simply a more effective dissipation device, duplicating nature more efficiently.
Behind the Byline
Peter A. Carpenter is with Lightning Eliminators & Consultants, Inc. in Boulder, Colo.
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