Abstract:
An active lightning protection system and method is disclosed. According to one embodiment of the invention, the active lightning protection system includes a charge sensor that senses the build-up of charge associated with an imminent lightning strike in the proximity of a structure and a charge source to supply an opposite charge into the proximity to offset the build-up, thereby reducing the possibility of a strike to the structure.

Description:
1. FIELD OF THE INVENTION  
         [0001]    The present invention relates to a system and method for detecting and actively mitigating lightning hazards.  
         2. DESCRIPTION OF THE RELATED ART  
         [0002]    Lightning strikes are one of the most common causes of service interruption within the wireless communications industry, particularly, to cellular and personal communications service (PCS) providers, and radio and TV broadcasters. Lightning occurs when there is a large build up of charged particles on the bottom side of a cloud, which in turn causes an opposite charge to build up in the ground beneath the cloud. Once the charge densities reach a certain magnitude or saturation level, the air gap between the cloud charge and the ground charge ionizes and a large current flows across the air-gap (“the lightning stroke”) usually via the tallest structure, e.g., antenna or communications tower, located on the ground. Lightning strikes to a communication structure typically cause severe damage to sensitive and expensive electrical components and more importantly, may possibly injure living organisms located in close proximity to the structure.  
           [0003]    Lightning rod protection systems provide a highly conductive path to allow the large current associated with lightning to flow from the top of a structure to the ground in order to “bleed off” the energy from the strike, i.e., the lightning&#39;s energy is kept away from sensitive equipment and living organisms. As shown in FIG. 1, a lightning rod system  100  is provided at a communications service provider structure  110  comprising a tower  112  and a building  114  housing electronic components. A lightning rod (not shown) is provided on the highest point of tower  112  and electrically coupled via cables  120  to a ring  130  inserted in the ground (grounded) at the base of tower  112 , thereby attracting and then dissipating the energy from the strike. A drawback of this type of system is that the lightning rod becomes active only after a lightning stroke occurs and does nothing to prevent lightning from occurring in the first place. Moreover, very large currents associated with intense lightning strokes may overwhelm the lightning rod system, its accessories, and perhaps also damage adjacent components and people.  
           [0004]    U.S. Pat. No. 4,679,114, which is incorporated in its entirety herein by reference, discloses a method for lightning protection through electric potential neutralization by applying a high-potential direct current (“DC”) voltage to a vertical structural post carrying on its top a member adapted to radiate an electrical field of a magnitude, polarity, and duration adjusted by a control unit in response to the condition of the atmospheric charge as sensed and relayed to the control unit by a sensor. However, a disadvantage of this method is that it requires the mounting of additional equipment on top of the structure, which can be a dangerous, expensive, and a time consuming activity. Moreover, such equipment is susceptible to damage caused by high winds and other atmospheric conditions that typically accompany lightning generating storms.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention overcomes these and other deficiencies of the related art by providing an active lightning protection system that reduces the possibility of lightning striking a structure in the first place.  
           [0006]    It is an object of the invention to protect structures, equipment, and persons working or living near those structures from lightning strikes, and to detect and actively mitigate lightning hazards.  
           [0007]    In an embodiment of the invention, an active lightning protection system and method senses a build-up of electrical charge associated with an imminent lightning strike in the ground around a structure to be protected. When the build-up exceeds a predetermined level, an opposite charge is fed into the ground around the structure or base thereof to offset the build-up and reduce the possibility of a lightning strike to the structure.  
           [0008]    An advantage of the present invention is that it decreases the possibility of lightning striking a structure. Moreover, the present invention does not require any equipment to be mounted and maintained on the upper portions of the structure protected. In addition, implementation of the present invention decreases and possibly eliminates lightning strikes to communication towers, thereby decreasing the disruption to wireless communications, and radio and television broadcast systems.  
           [0009]    The foregoing, and other features and advantages of the invention, will be apparent from the following, more particular description of the preferred embodiments of the invention, the accompanying drawings, and the claims.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    For a more complete understanding of the present invention, the objects and advantages thereof, reference is now made to the following descriptions taken in connection with the accompanying drawings in which:  
         [0011]    [0011]FIG. 1 depicts a typical conventional lightning rod system; and  
         [0012]    [0012]FIG. 2 is an active lightning protection system according to an embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0013]    Preferred embodiments of the present invention and their advantages are discussed in the context of preventing lightning from striking communication towers. Nevertheless, the inventive concept is designed to prevent a lightning strike to any type of structure, such as, but not limited to residential and commercial buildings, industrial plants, and other tall structures.  
         [0014]    Referring to FIG. 2, an active lightning protection system  200  is illustrated according to an embodiment of the invention. Particularly, active lightning protection system  200  comprises a charge sensor  210  and a charge source  220 . Charge sensor  210  is coupled via electrical cables  212  to one or more active sensing elements (not shown) in proximity to the tower  112 . For example, sensing elements can be disposed in the soil at or near the base of the tower  112  and/or on the legs of the tower  112 . These sensing elements may surround all or a portion of tower  112 . The sensing elements are in contact with the ground to measure the polarity and/or magnitude of charge within the soil to determine if a charge build-up is occurring. If a charge build-up occurs and exceeds a predetermined level, e.g., the level designating a high probability of a lightning strike occurring, sensor  210  signals charge source  220  via a communications link  216  to actively supply a DC current with the proper polarity and magnitude to dissipate the charge build-up in the ground. For example, charge source  220  supplies charge through electrical conductors  222  to inputs  224 . Charge source  220  can be any type of source configured to supply DC charge, e.g., a DC current source, one or more large storage capacitors, an alternating current (“AC”) source coupled to an AC-DC converter, and the like. Inputs  224  are disposed in proximity to the tower  112 . For example, inputs  224  can be in the ground, on the legs of the tower  112 , or in atmosphere near the tower  112 . Preferably, if the sensors are placed on the tower legs, then the inputs  224  are placed solely in the nearby ground and not on tower legs. Similarly, if the sensors are placed in the nearby ground, then the inputs  224  placed on the tower legs and not in the ground near the sensors. In a preferred embodiment, conductors  222  and ground inputs  224  are disposed underneath the ground surface or electrically insulated in order to prevent charge discharge to surface objects.  
         [0015]    In operation, the build-up of excess charge in the ground beneath and around the protected structure generally precedes a lightning strike. When an opposite charge is actively injected into the surrounding ground area or tower base during this build-up, the potential difference between the ground structure and the charged cloud is decreased, if not entirely neutralized. This results in the protected structure becoming electrically neutral or effectively invisible to lightning. Accordingly, the possibility of a lightning strike occurring to the structure is greatly diminished.  
         [0016]    In an another embodiment of the invention, a processor is coupled to sensor  210  and charge source  220 . The processor polls each sensing element in real time or at a necessary time interval to detect ground charge build-up. Control logic within the processor activates and controls charge source  220  once the predetermined charge or field strength level is exceeded.  
         [0017]    In another embodiment of the invention, lightning protection system  200  can further comprise a display device, communications electronics, warning indicator, a programmable interface, memory, a printer, or a combination thereof. A display device displays information relating to the operation of the system, such as, but not limited to, charge polarity and charge magnitude measured by the sensing device. Such information can also be communicated to a remote location via a communication device, the identification and implementation of which is apparent to one of ordinary skill in the art. The communication device can also be adapted for receiving signals. For example, lightning protection system  200  can be in a stand-by or an off-state, and only becomes activated when a remote signal, such as a storm warning, is received. Moreover, operational logs may be printed out or stored via a respective printer and storage memory. A warning indicator, such as a siren or other type of signal can be useful to warn people in the vicinity of the structure of the high possibility of a lightning strike and/or the activation of the lightning protection system. A programmable interface can enable a programmer to program the processor, e.g., set or change the predetermined level that activates charge source  220 .  
         [0018]    In an alternative embodiment, sensor  210  can measure charge build-up at other locations, such as, the atmosphere around tower  112  or on the tower itself.  
         [0019]    Although the invention has been particularly shown and described with reference to several preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined in the appended claims.