Electricity: conductors and insulators – Lightning protection – Rods
Reexamination Certificate
1999-09-10
2001-10-23
Han, Jessica (Department: 2838)
Electricity: conductors and insulators
Lightning protection
Rods
C174S00400R, C361S221000
Reexamination Certificate
active
06307149
ABSTRACT:
The invention described herein was made by employees of the United States Government and may be manufactured and used by and for the Government for governmental purposes without payment of any royalties thereon or therefor.
1. Field of Invention
This invention relates to the prevention of lightning strikes by draining ambient static charge from the atmosphere through a static charge dissipation system while suppressing shifted radio waves due to the electromagnetic interaction of the lightning protection system and any incoming radio waves.
2. Background of the Invention
Lightning is the result from the electrical interaction between the clouds and between the clouds and the earth ground. This electrical interaction results from the friction caused by the air currents within the clouds. As the charged cloud passes through the atmosphere, there is a corresponding footprint of oppositely charged particles following the cloud on the earth ground. When the resulting electric potential exceeds the electrical breakdown potential, a lightning strike occurs.
Traditionally, there have been two types of lightning protection systems that attempt to control the effects of a lightning strike. First was developed the traditional lightning rod system that consisted of straight metal rods attached to the highest point of a structure. The rod was then connected to a large wiring system that directed the lightning strike to the earth ground. The second major system to be developed was the static dissipation system which consists of a series of fine wires which drain the ambient static charge from the atmosphere to prevent the occurrence of a lightning strike.
The first lighting protection system was the traditional lightning rod, which is a straight metal rod that is mounted on the tallest point of a structure. Multiple rods are placed on the structure and then electrically connected to the earth ground by large copper cabling. This cabling is on the order of a #0 wire to a ½″ copper bus line. This cabling is requires a large amount of copper which is quite expensive and difficult to acquire.
Unfortunately, traditional lightning rod systems have only one point of dissipation per rod. Each rod then directs all of the lightning discharge through the copper cabling to the earth ground. This produces extremely high currents over a short time periods and requires extremely low electrical impedance of the rods and the cabling, the electrical connections between the rods and cabling, and between the system and the earth ground. The large cabling and the low electrical impedance dissipate the very high amplitude currents that the system is exposed to during the lightning strike which can easily destroy the system if not be adequately discharged into the earth ground.
This lightning rod system also does not prevent the lightning strike but directs the strike to a more desirable location (i.e. earth ground). It conducts the electrons from the lightning bolt itself via a sharp point on the end of the rod; however, the point quickly dulls due to corrosion, which decreases its effectiveness.
In addition, lightning rod systems cannot prevent radio frequency fields from emanating from the rods or the cabling. It has been shown that a lightning strike actually consists of a series of discharges that produce rapidly expanding and contracting electromagnetic fields. These fields induce electrical currents in nearby wires and electrical equipment. While vacuum tube equipment was relatively unaffected by such induced currents, solid state electronic devices can be easily damaged even when not in use or connected to a power source.
The second traditional system is a static dissipation system. Such systems use many small metallic points connected to a central point to create a passively ionized field to continually discharge the ambient static electric field. Each of the metallic points discharges a small amount of potential difference between the cloud and the earth ground creating a continuous low level current flow. This constant drainage prevents the ambient static charge around the static dissipater from reaching the electrical breakdown potential that could result in a lightning strike.
One such example is set forth in U.S. Pat. No. 4,605,814, entitled “Lightning Deterrent” issued to Gillem on Aug. 12, 1986, which discloses a cable having a multiplicity of fine conductive wires captured within the strands of a cable, emanating therefrom in a brush-like manner. In use, the cable is formed to mimic the outside shape of the structure to be protected to dissipate the ambient static charge to minimize the possibility of a lightning strike.
Unfortunately, it may not be practical to surround the outside shape of a larger structure with a single cable of this nature. In addition, there are no provisions made to prevent electromagnetic interference damaging nearby electronic devices.
Another example of a static dissipation system is U.S. Pat. No. 4,910,636, “Static Electricity Dissipater”, to Sadler et al, issued Mar. 20, 1990, which sets forth a static dissipation system in which a series of fine wires emanate from a conductive center rod into a mushroom-like form. The conductive wires emanating from the conductive base dissipates the ambient static charge. With proper installation, this minimizes the electric potential differential between a protected structure and the atmosphere and therefore reduces the likelihood of a lightning strike to the structure.
Unfortunately, this system requires the fine wires to be extensively heat treated and wound such that the wires are unconditionally straight for optimal performance. Further, this system commonly replaces the lighting rod of a traditional lightning protection system and requires a very low contact resistance. This limits the choice of what materials can be use to construct the system. The combined system also requires very large cabling connecting it to earth ground and low contact resistance between interconnecting parts and between the cabling and the earth ground.
Another example of a static dissipation system is set forth in U.S. Pat. No. 5,073,678, entitled “Spline Ball Terminal (SBT)”, issued to Sadler et al on Dec. 17, 1991. This patent sets forth a spline ball terminal dissipation array that requires a specific number of elements, having a specific length and a specific orientation to each other. This system also is attached to a traditional lightning protection system with large cabling and low impedance requirements.
In addition to reducing the complexity of the grounding system required for the operation of the lightning protection system, there is also a need for lightning protection systems which does not contaminate the surrounding radio frequency fields.
One such system that needs lightning protection as well as non-contaminated radio frequency fields is the land based radio frequency automatic direction finding system (ADF) as set forth in Commonly Assigned U.S. Pat. No. 5,898,402, entitled “A Wide Aperture Radio Frequency Data Acquisition System” issued to Kilpatrick on Apr. 27, 1999, hereby incorporated in its entirety by reference. The ADF system uses a number of antennas laid out in a specific pattern on a moderately level earth ground surface. To determine the angle of arrival of a particular signal, the system depends upon the precise measurement of the instantaneous amplitude and phase of the incoming radio wave (IRW) at a minimum of three of the receiving antennas in the ADF antenna array. The measurements are then correlated to determine the angle of arrival of the IRW.
If the incoming IRW is contaminated by any additional IRW, then it may be impossible to determine the angle of arrival of the incoming IRW. Additional IRW can be generated by the interaction between the incoming IRW and other metallic structures such as the cabling and dissipation structures such as lightning rods or static dissipaters of prior art system as set forth above. The metallic portions will transmit an additional IRW with a random phase and possib
Bentley, Jr. William Ferrel
Houston William Carles
Zini Richard Ralph
Bentley, Jr. W. Ferrel
FCC/Enforcement Bureau
Han Jessica
LandOfFree
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