How to Select Lightning Dissipation Systems for Towers and Antennas Hear No RF Evil - See No RF Evil |  |
| How to Select Lightning Dissipation Systems for Towers and Antennas Posted: 25 Jul 2012 09:17 AM PDT LBA Static Dissipation Systems are designed to prevent lightning strikes to your tower and antennas. These systems have been around for many years in a number of forms, with a proven track record. Keeping in mind that there are no guarantees with any lightning protection system, there are some guidelines to be considered when selecting the appropriate system for maximum protection of your structures. These systems have a bit of an identity crisis, having been called static dissipators, static dissipation arrays, streamer-delaying air terminals, lightning dissipaters, static charge dissipation arrays, spot dissipaters, linear array dissipaters, streamer emission delay terminals, and more! All these names refer to devices using point discharge phenomena to retard and reduce the potential of lightning strokes to their protected devices.  Towers and antennas are prime lightning targets! Choosing the appropriate dissipater for a specific application requires a number of performance issues be considered such as: radius of dissipater electrode cross section, construction material of the dissipater, number and density of electrodes and the configuration of the dissipater on the structure it is designed to protect. Different forms of devices are used to protect tower or mast tops, and the attached items like antennas, meteorological instruments, lighting devices, sailboat rigging, and a host of other things. The radius of the dissipater electrode cross-section is important. The laws of physics indicate that a sphere one centimeter in radius has a maximum charge breakdown of about 30,000 volts, depending on air pressure, temperature and humidity. At this point discharge into the atmosphere occurs. As the radius is reduced the amount of charge potential also reduces preventing the buildup of ground charge, thus preventing a strike.  Sailboat mast and light protected by a dissipater air terminal The number and density of dissipater electrodes or ionization brushes also plays a vital part in choosing the dissipater array. Dissipater needs are determined by the structure to be protected and rate the dissipation should occur to prevent a strike. The density is important as they must not be too close to one another causing inter-point interference. LBA dissipaters have been optimized for these characteristics. Conductivity and durability are vital qualities in the materials used in static dissipation arrays. Obviously the system must have a long life and give good service. Ionization brushes are typically made of stainless steel. A good conductor must provide maximum discharge of current during operation. A properly constructed dissipater, such as those from LBA, is constructed to absorb a lighting strike, in the rare case that occurs. The best dissipaters conform to UL and NFPA codes for air terminals. Often, UL-listed dissipater air terminals replace conventional "lightning rods" in code-compliant building and structure protection systems. LBA dissipater air terminals are UL-listed and are used in this manner. The natural dissipater points inherent in all objects are a place to start in configuring dissipation on a structure. The natural dissipation points typically occur at the top and corners of the structure or antenna. Enhancing these natural points on the structure is the most effective way to support the charge dissipation function. As a practical matter, the array configuration should be tailored to the structure and not the other way around.  Tower sideflash dissipater assembly There has been controversy about whether or not static dissipater systems work. The discussion ranges from yes they definitely do to no they definitely do not work. There are no guarantees of perfect performance. Often, poor performance has been tied back to improper design and application. Where there is consensus it is on the fact that static dissipation does no harm, but there is a wide body of empirical evidence that well designed systems provide cost effective protection of structures from the damage caused by lightning strikes. In the final analysis, the buyer's objective is finding a cost effective technology to reduce the threat of lightning strikes to his critical infrastructure. In choosing the appropriate system, the buyer should assess the availability of technical assistance for the technology selected, the installation cost, the quality and ease of installation and the manufacturer's service after installation. Here is how a GPS community base station used static dissapaters available from LBA for lightning protection, as described by Utah County, Utah staff:  Utah County Communications uses antenna dissipation systems "A concern in the installation of the system was the antenna’s vulnerability to lightning strikes since the area in which the Security Center is located boasts one of the highest lightning strike counts in the valley. The grounding and lightning arrestor system in place on the telecommunications tower provides a high degree of protection. However, in addition to this system, we decided to install a static dissipator system and an antenna cable surge suppressor". LBA can assist you in protecting against lightning We offer a range of qualified and code-compliant static dissipation systems at http://www.lbagroup.com/international/tower-lightning-protection.php#tower. Our applications are backed up by a professional engineering staff.    |
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