PROTECTION AGAINST DANGEROUS LIGHTNING STRIKES AND THEIR SECONDARY EFFECTS
Abstract:
Traditional methods of lightning protection may actually increase the likelihood of lightning-related damage. The answer to proper lightning protection lies not in channeling lightning, but in preventing the charge from accumulating in the first place. This article describes a system designed to lower the voltage differential between the ground and the charged cloud to below the lightning potential.
Lightning: those dramatic bursts of white-hot voltage from the heavens that can instantly incinerate trees, ignite fires and knock out power and communications lines. Each year, lightning causes massive damage to business facilities across America. The destructive power of lightning is so great that even structures equipped with traditional lightning rods can suffer extensive damage.
Strikes on petroleum industry facilities demonstrate the tremendous destructive power of lightning activity and its after effects. Millions of dollars worth of petrochemical products and facilities are destroyed worldwide each year by lightning and related phenomenon, and lives are often lost as a result of individuals being in close proximity when these facilities ignite or explode. For example, in the Nigerian fire of 1990, a 670,000-barrel tank of light crude was set on fire by lightning, destroying the tank and its contents.
Even if the facility is not directly struck by lightning, secondary effects such as bound charge and electromagnetic pulses can fry sensitive circuitry in the vicinity. Failures may be catastrophic or a momentary or long-term lockup, requiring replacement, repair, reprogramming or rebooting.
The danger of a lightning strike is exacerbated by so-called "prevention" devices such as lightning rods and early streamer emitters, which are designed to collect and channel the force of a strike to ground. This 200-year-old technology was never intended for protection of modern high-tech automated facilities, but rather barns and other wood structures of that era. These devices actually bring millions of volts and thousands of amps into close proximity to sensitive electronics systems and flammable products. Companies promoting such devices choose to ignore the underlying problems or the physics involved in protecting contemporary systems. No matter what claims are made about such devices, using them only increases the risk of lightning-related damage.
What exactly causes the terrifying yet fascinating phenomenon of lightning? More importantly, what can be done to prevent it from damaging your business and data? Let's start with the source. An electrical storm contains clouds called thunderheads - electrically charged bodies suspended in the atmosphere. The air serves as an insulator, separating the electrical charge of the cloud from the ground or other clouds. These charges continue to build during the storm, inducing a similar charge of opposite polarity onto the earth. The earth charge is concentrated at the surface just under the cloud and is roughly the same size and shape as the cloud, establishing a strong electrical field between the cloud and ground. As a storm intensifies, charge separation continues within the cloud until the air between the cloud and earth can no longer act as an insulator and a strike occurs. Charge neutralization (the strike) is caused by the flow of electrons from the cloud to the earth such that there is no charge difference between the two bodies. The process is similar to shorting out the terminals of a battery. When structures sit between the earth and the clouds, they are likewise charged. Since they short out a portion of the separating air space, they can trigger a strike.
Fig. 1 How the dissipation array system works.
Fig. 2 A DAS mounted to a tower at a process industry.
The lightning strike hazard for a given facility depends on a number of factors, including the facility's location, size and shape. The characteristics of a structure - its height, shape, size and orientation - influence the hazard. Taller structures tend to collect strikes from storm clouds in adjacent areas and trigger additional strikes as well. In mountainous areas, even lower structures will trigger lightning. The larger the structure size, the greater the hazard of lightning exposure. For example, longer power transmission lines attract more strikes. A 50-mile stretch of transmission line in central Florida could expect as many as 1500 strikes per year.
Given the random and destructive nature of lightning strikes, how can businesses protect their valuable facilities and electronic equipment - and the lives of their employees? The answer lies not in channeling lightning, but in preventing the charge from accumulating in the first place.
One technology, the dissipation array system (DAS), is being touted as the ultimate solution for lightning protection. DAS is based on a natural phenomenon known to scientists for centuries as the point discharge principle or charge transfer. A sharp point in a strong electrostatic field will leak off electrons by ionizing the adjacent air molecules, provided the point's potential is raised 10,000 V above that of its surroundings. This principle is demonstrated by what scientists call natural dissipation. The ionization produced by trees, grass, towers, fences and other structures can naturally dissipate up to 90 percent of the total energy generated by a storm, thereby preventing the formation of lightning.
The DAS employs the point discharge principle by providing thousands of points with specific point separation, which simultaneously produce ions over a large area. This ionization process prevents the formation of a streamer, which is the precursor of a lightning strike, and creates a flow of current from the point(s) into the surrounding air, as shown in Figure 1. Under storm conditions, this ionization current increases exponentially with the storm's electrostatic field, which can reach levels as high as 30,000 V per meter of elevation above earth during a mature storm. The charge induced on the site by the storm is removed from the protected area and transferred to the air molecules. These charged molecules then move away from the site. Thus, DAS prevents strikes by continually lowering the voltage differential between the ground and the charged cloud to well below the lightning potential, even in the midst of a worse-case storm. This differential has been measured at up to 6000 percent.
Because it prevents rather than redirects lightning, DAS is possibly the best long-term solution to lightning strike problems. One company, Lightning Eliminators and Consultants Inc. (LEC), based in Boulder, CO, has long been at the forefront of DAS development. In the three decades since LEC introduced DAS to the US marketplace, it has been the only lightning protection system proven to prevent lightning strikes to any protected facility. The system has accumulated more than 20,000 system-years of history with a 99.7 percent reliability.
To date, thousands of DASs have been installed worldwide in applications ranging from communications towers to tank farms and electrical power lines to public buildings. DAS has been used to protect facilities as large as three square kilometers and structures as high as 1700 feet. Figure 2 shows a DAS installation on a process industry tower and a DAS mounted on a communications tower is shown in Figure 3. Figure 4 shows a technician installing a DAS.
Fig. 3 A DAS mounted to a communication tower.
Fig. 4 Technician installing a DAS.
Summarizing its benefits, DAS is simple (the design is straightforward, reliable and effective), passive (it consumes no power; it is activated by the energy of the storm itself) and universal (DAS can be used to protect any kind of building, tower, power line or large complex plant). Basic system concepts are custom engineered for each individual facility and specially designed to account for size, height, area storm patterns and altitude. The DAS is preventative (it completely eliminates lightning strikes and all related secondary effects from the protected area and avoids problems inherent in lightning rod systems, which attract energy and attempt to conduct it to ground) and guaranteed effective (if a strike does penetrate the DAS-protected area, LEC will upgrade the system capability at no additional cost to the user for one year from the date of installation and/or recertification).
DAS is currently providing complete lightning protection to an extensive list of customers and facility types, including many Fortune 500 firms such as Federal Express, PPG Chemical, Union Camp, Exxon, Mobil Oil and Texaco. The National Fire Protection Association, 780 committee is examining DAS technology to determine how it can be incorporated into its fire protection standards because current lightning rod standards were recently shown to have no basis in physics.
LEC specializes in designing, manufacturing and installing integrated, engineered systems to prevent and eliminate all lightning-related problems. For more information on how the dissipation array system can protect a facility, contact LEC Inc. at 6687 Arapahoe Road, Boulder, CO 80303, (303) 447-2828; fax (303) 447-8122 or e-mail: marketng@lightningeliminators.com. The company's Web site is located at www.lightningeliminators.com.