Abstract:
A prefabricated ground mat with cathodic protection adapted to protect persons from induced electrical potentials in a pipe or other electrical conductor buried below a ground-level surface, adapted to protect test stands, valve sites, metering stations, pig launchers and receivers, access portals, or other exposed, above-ground equipment which are electrically connected to the buried conductor, from such electrical potentials, and adapted to protect the buried conductor from oxidation due to the ground grid. Multiple mats may be buried between the underground conductor and the ground-level surface and electrically connected to either the underground conductor, the above-grade buried conductor, or both. The mats are made of materials such that the galvanic cell formed by the electrical union of the underground conductor with the mat cause the mat to be consumed. The present invention includes a method of protecting persons and exposed, above-grade equipment from induced electrical potentials in the buried conductor.

Description:
[0001]    This is a regular patent application based upon and claiming priority of a provisional patent application filed on Jun. 3, 2002, serial no. xxx.  
           [0002]    The present invention relates to a prefabricated ground mat made of anode material for protection of persons coming in proximity of equipment electrically connected to underground conductors in order to mitigate the effect of induced electrical potentials on the underground conductors in the vicinity of such equipment. The ground mat is also designed to protect the underground conductor from further corrosion resulting from being electrically coupled to the ground mat.  
         BACKGROUND OF THE INVENTION  
         [0003]    The mitigation of induced electrical potentials on underground pipes and other electrical conductors has been addressed by others in the past. The induced electrical potentials on these underground pipes and conductors can be caused by a myriad of sources, including electrical currents and electrical potentials caused by the transmission of power through the underground pipe itself, electrical potentials from nearby transmission cables or overhead transmission lines, radio transmission antenna or towers, and other similar sources. The electrical potentials induced on underground pipes and other underground conductors may be extremely dangerous to persons coming in close proximity to the underground conductor. A person coming within close proximity may provide an electrical path to an area of lesser electrical potential causing a discharge of the electrical potential in the buried conductor such that the person is electrocuted.  
           [0004]    Utility workers, in particular, regularly face the danger of electrocution from electrical potentials and induced alternating currents from transmission cables and induced potentials on underground conductors such as gas pipes. Most buried pipes and buried transmission cables have equipment connected to the buried conductor which is used to monitor, test, or perform maintenance and repairs to the underground conductor. For example, some underground gas pipes have metering stations throughout the length of the pipe to monitor the flow of gas. Some electrical transmission cables have metering stations to monitor oil pressure and oil temperature in the transmission cable and to detect fault conditions. These stations are typically above grade, at a ground-level surface above the buried conductor and may include access to the buried conductor or may include equipment which is connected to the buried conductor. Often times, the connections to the buried conductor are themselves conductors. For example, some underground utilities require test stands, valve sites, metering stations, pig launchers and receivers, access portals, or other exposed, above-ground equipment which are electrically connected to the underground conductor.  
           [0005]    In order to protect persons coming in proximity to or contact with the underground conductor or with any such exposed, above-ground equipment, it is necessary to mitigate the magnitude of the electrical potentials at these sites. Sometimes it is also important to mitigate these electrical potentials to avoid damage to sensitive equipment used in close proximity to an underground conductor.  
           [0006]    Prior technology to reduce electrical potentials at such access sites have included the use of grounding rods and interconnecting conductors typically custom made by workers at the desired location. This type of protective scheme led to the use of gradient control wires or conductors. Gradient control wires are set up in a matrix or array near the area needing mitigation of electric potentials. The gradient control wires act on electric potentials in the soil and earth surrounding the buried gradient control wires to bring the electric potential in the area around the wires closer to the potential of the underground conductor. This decreases the electric potential between the underground conductor and the surrounding soil near the buried wires. Hence, the voltage measured between the buried conductor and the work area are brought within acceptable, safe levels.  
           [0007]    The use of a matrix of gradient control wires has been used and is known in the art. For example, U.S. Pat. No. 4,114,977 to Polidori discloses a connector for joining grounding grid wires at their nodal points of intersection. The grounding grids consist of a matrix or crossover network of conductors buried underground and connected to above ground equipment and buried grounding rods. Such grounding grids also serve to quickly dissipate fault current as well as induced currents.  
           [0008]    Another example of a custom made gradient control grid is one sold by Platt Brothers &amp; Co., Inc. This company produces a PLATTLINE zinc ribbon used to dissipate induced currents on underground pipes. The PLATTLINE zinc ribbon product may be installed in a grid-like configuration by laying out cut lengths of the ribbon in a grid pattern and then the points of intersection are either crimped together with copper rings or welded in place.  
           [0009]    However, the use of gradient control wires and grids for step voltage and touch voltage mitigation has always involved the custom installation of the wires by workers in the field. It has involved cutting conductors and custom building the matrix or array of gradient control wires at location. There is a need for a gradient control system whereby a prefabricated array or matrix can be easily installed between underground conductors and surface-level equipment to mitigate induced electrical potentials and currents. There is a need for a gradient control system that does not require the manufacture of the grid at location. There is also a need for a gradient control ground grid that provides both electric potential mitigation and cathodic protection to the underground conductor to which it is electrically connected.  
         OBJECTS OF THE INVENTION  
         [0010]    It is an object of the present invention to provide a prefabricated grounding grid with cathodic protection to protect persons from induced electrical potentials in a pipe or other electrical conductor buried below a ground-level surface through mitigation of such potentials in a volume of space near the grid.  
           [0011]    It is another object of the present invention to provide a prefabricated grounding grid with cathodic protection to protect test stands, valve sites, metering stations, pig launchers and receivers, access portals, or other exposed, above-ground equipment which are electrically connected to an underground pipe or other buried conductor from induced electrical potentials and currents.  
           [0012]    It is a further object of the present invention to provide a prefabricated grounding grid with cathodic protection which protects buried conductors from oxidation due to the ground grid.  
           [0013]    It is an object of the present invention to provide a prefabricated, substantially planar pre-formed mat having a predetermined pattern of intersecting and electrically connected anode material for burial underground between a buried conductor and equipment at a ground-level surface generally above the buried conductor.  
           [0014]    It is another object of the present invention to electrically connect a buried prefabricated grounding mat to exposed, above-ground equipment generally located over a buried conductor such that any electrical potentials emanating or originating from the buried conductor whether or not induced by other sources are mitigated in a volume of space near the mat to make areas in proximity to the mat safe for persons and sensitive equipment.  
           [0015]    It is a further object of the present invention to provide a prefabricated electrical potential mitigating mat having a pattern of intersecting and electrically connected anode material defining predetermined polygonal shapes having predetermined dimensions.  
           [0016]    It is yet another object of the present invention to provide a prefabricated electrical potential mitigating mat with cathodic protection which is coated with an aluminum alloy to slow the oxidation rate of the mat.  
           [0017]    It is another object of the present invention to provide a system to create a safe environment for persons and equipment above buried conductors such that induced electrical potentials and induced currents present on the buried conductors are mitigated by providing a plurality of interconnected prefabricated planar mats having a predetermined pattern of intersecting and electrically connected anode material adapted to be buried between the buried conductor and a ground-level surface above the buried conductor.  
           [0018]    It is a further object of the present invention to provide a method of protecting persons and exposed, above-ground equipment from induced electrical potentials in a pipe or other electrical conductor below a ground-level surface by providing at least one substantially planar, pre-formed cathodic mat having a predetermined pattern of intersecting and electrically connected anode material, burying the mat underground between the ground-level surface and the pipe or other electrical conductor, and electrically connecting the mat with the exposed, above-ground equipment.  
         SUMMARY OF THE INVENTION  
         [0019]    The present invention includes a prefabricated, preformed substantially planar mat made of an anode material, thus providing cathodic protection, which is used to protect persons from induced electrical potentials in a pipe or other electrical conductor buried below a ground-level surface, and which is also used to protect test stands, valve sites, metering stations, pig launchers and receivers, access portals, or other exposed, above-ground equipment which are electrically connected to the buried conductor, from such electrical potentials. There may be a plurality of such mats electrically connected together. Each pre-formed mat has a predetermined pattern of intersecting and electrically connected anode material which define voids between the anode material, such as a diamond shape or other polygonal shape. The preformed mats are buried underground between the ground-level surface and the buried conductor. The mats are electrically connected to the exposed, above-ground equipment either directly or viz-a-viz a conductor connected to the underground conductor already electrically connected to the above-ground equipment. This configuration promotes mitigation of the electrical potentials in a volume of space near the mat. The mats should be positioned below the ground-level surface such that a plane defined by the planar pre-formed mat is substantially parallel with a plane defined by the surface. The surface need not be level. The mats should not be buried more than 2 feet below the ground-level surface.  
           [0020]    The mats may be coated with an aluminum alloy material to slow the oxidation rate of the mat.  
           [0021]    The present invention includes a method of protecting persons and exposed, above-ground equipment from induced electrical potentials in the underground conductor. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    Further objects and advantages of the present invention can be found in the detailed description of the preferred embodiments when taken in conjunction with the accompanying drawings in which:  
         [0023]    [0023]FIG. 1 diagrammatically illustrates a side view of the prefabricated ground mat installed underground for protection of persons coming in proximity of equipment electrically connected to the underground pipe;  
         [0024]    [0024]FIG. 2A diagrammatically illustrates another installation configuration of the prefabricated ground mat;  
         [0025]    [0025]FIG. 2B diagrammatically illustrates a top view of the installed prefabricated ground mat from the perspective of section line A′A″ in FIG. 2A;  
         [0026]    [0026]FIG. 3 diagrammatically illustrates a planar, pre-formed zinc mat having a diamond pattern of intersecting and electrically connected anode material; and  
         [0027]    [0027]FIG. 4 diagrammatically illustrates an enlarged view of the prefabricated mat with a coating of aluminum alloy. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]    The present invention relates to a prefabricated ground mat made of anode material for protection of persons coming in proximity of equipment electrically connected to underground conductors in order to mitigate induced electrical potentials in the vicinity of such equipment. The ground mat is also designed to protect the underground conductor from further corrosion resulting from being electrically coupled to the ground mat. In addition, the electrical potential mitigating property protects equipment sensitive to induced potentials and electric currents.  
         [0029]    [0029]FIG. 1 diagrammatically illustrates the present invention. In FIG. 1, the prefabricated ground grid  10  is shown from a side view. The ground grid  10  is a substantially planar pre-formed mat having a predetermined pattern of intersecting and electrically connected anode material (described later in connection with FIGS. 2B and 4). The anode material is typically zinc but may be made of any conductive material having a more active electrochemical potential than that of the steel, cast iron and other ferrous materials to which the mat is electrically connected. Typically, underground pipes or other underground conductors are made of steel, cast iron or other ferrous metal. Because the mat  10  is electrochemically more active than the metal structures to which it is electrically connected, the galvanic cell formed by these two electrical conductors will consume the mat  10  rather than corrode the underground conductor structure. The pre-formed mat  10  in FIG. 1 is connected to mats  12 ,  14  on either side via electrical couplers  42 ,  44 . Electrical couplers  42 ,  44  may be flexible conductors such as wire, solid metal straps, braided straps, or may be rigid straps or other conductive material. The electrical couplers  42 ,  44  may be fastened or otherwise attached to the mats  10 ,  12 ,  14  by means known to those skilled in the art such as by bolt, clamp, weld, or the like. In one embodiment, the connections are made using insulated heavy gauge copper wire.  
         [0030]    In FIG. 1, the pre-formed mat  10  is buried underground between the ground-level surface  30  and the underground conductor  20 . The underground conductor  20  in FIG. 1 is shown as a pipe. As discussed above in the background of the invention, the underground conductor  20  may be a power transmission cable, a gas or oil pipe, or any other conductive utility pipe. The surface  30  in FIG. 1 is illustrated substantially level. However, the ground-level surface need not be level. It may be curved or graded, depending upon the topography of the location. The ground-level surface refers to the surface of the ground at a level where persons may be in contact or in close proximity to equipment used to access, monitor, repair or otherwise work near underground conductors. Accordingly, a ground-level surface may be a right-of-way ditch where utilities may be found, for example, on the side of a road.  
         [0031]    The earth  32  below the ground-level surface  30  may be the naturally occurring mixture of soil and rocks, or may have been replaced with rocks or soil having a predetermined conductivity and/or drainage capability.  
         [0032]    In FIG. 1, mat  10  is electrically connected to underground pipe  20  via electrical conductor  60 . Electrical conductor  60  may also be a flexible conductor such as a wire, solid metal strap, braided strap, or may be a rigid strap or other conductive material. The connection between electrical conductor  60  and mat  10  and pipe  20  may be made through any means known to those skilled in the art such as by bolt, clamp, weld, or the like. Although only one conductor  60  is shown, more than one conductor may be used. For example, each of mats  10 ,  12 , and  14  may include a separate conductor electrically connecting the respective mat to the buried pipe  20 .  
         [0033]    Underground pipe  20  in FIG. 1 is electrically connected to a flush-mounted or surface mounted test station  50  via another electrical conductor  62 . Electrical conductor  62  is similar to and may be connected in the same manner as described above in connection with electrical conductor  60 . Test station  50  provides personnel  70  above the underground conductor  20  with access to test ports which provide information regarding the state of the underground conductor. For example, access port  52  may be a valve port connected to pipe  20  via line  64  giving access to the gas or liquid in the pipe. Access port  52  may be a monitoring port to which sophisticated monitoring equipment may be connected which utilizes information sent via cable  64 . In yet another example, line  64  may be a thermocouple test wire which a person  70  may use to gather information regarding the condition of pipe  20  and the contents of the pipe.  
         [0034]    Test stand  50  may also be connected to a sacrificial anode  80  to provide the test stand and other electrically attached equipment with cathodic protection. For example, in FIG. 1, test stand  50  is connected to a magnesium anode  80  via electrical conductor  66 .  
         [0035]    In FIG. 1, flush-mounted test stand  50  is shown connected to table  54  via grounding cable  68 . Table  54  is shown with monitoring equipment  56  above. This depiction is merely exemplary, as there are many configurations which may occur, depending upon the environment, the type of underground conductor  20 , the reason for the station, and the proximity to the underground conductor or pipe. There may be a control house  90  above the location, or the pipe may have an access pipe  22  rising from the main conduit as shown in FIG. 2A. Similar features and components have been given the same reference numerals throughout the drawings.  
         [0036]    In FIG. 2A, underground pipe  20  has a pipe riser  22  giving access at the ground-level surface  30 . Riser  22  may be a pig launcher or similar access port for a pipeline.  
         [0037]    Preformed mats  10 ,  12 ,  14  are shown buried underground at a depth d. Depth d is typically 18 to 24 inches. Preferably, the preformed mats are buried 18 to 24 inches deep, that is, the mats are not buried deeper than, substantially 24 inches. In FIGS. 2A and 2B, Mats  10  and  12  are overlapping and attached via electrical couplers  48 . Electrical couplers  46 ,  48  may be a bolt, rivet, weld or other system to connect mat  10  to mats  12  and  14 . In FIG. 2A, mat  10  is electrically connected to the riser  20  via conductor  60 .  
         [0038]    [0038]FIG. 2B diagrammatically illustrates a top view of the installed prefabricated ground mat  10  from the perspective of section line A′A″. In FIG. 2B, preformed mat  10  is overlapping preformed mats  12  and  14 . The typical overlap is approximately 3 to 4 inches. Electrical couplers  46 ,  48  are shown as bolts with washers. In FIG. 2B, another mat  16  is present on the other side of the pipe riser  22 . The preformed mats  10 ,  12 ,  14 , and  16  have a diamond pattern, i.e., the pattern of intersecting and electrically connected anode material of the mat define diamond shaped holes. The pattern of the anode mats may be designed for different applications. For example, some soils are more conductive than others requiring less surface area on the pre-formed mat  10 . It may also be desirable to have less surface area to inhibit the rate of consumption of the mat.  
         [0039]    [0039]FIG. 3 diagrammatically illustrates another embodiment of the mat  10  having a mesh-like pattern. Mat  10  has a width w and a length l. The dimensions of the mats vary, but are typically 4½ feet wide by 9 feet in length. Mat  10  in FIG. 3 has insulated electrical couplers  70 ,  72  on either end of the mat. These couplers are used to join a plurality of mats laid side by side.  
         [0040]    [0040]FIG. 4 diagrammatically illustrates an enlarged view of the pre-formed mat  10  defining hexagonal-shaped holes. The holes can vary in size, but have a typical dimension D of ½ inch. Other mat designs defining multi-sided or polygonal shaped holes may also be implemented. The mats  10  may be manufactured by stamping holes into large planar sheets of the zinc material. The mats may be treated with chemicals or coated with special paints to inhibit the rate of consumption of the mat. For example, in FIG. 4, zinc mat  10  has been coated with an aluminum alloy paint mixture  92  which inhibits the consumption rate of the underlying zinc material. This protective coating is especially useful in applications where the soil exhibits high conductivity properties.  
         [0041]    The preformed grounding mat  10  is easy to install, cost-effective, and provides a safe zone of mitigated induced electrical potentials. For a typical site, an area approximately 10 feet by 10 feet is excavated around the above-grade structure to a depth of 1 to 1½ feet. Two 4½×9 feet sections of mat  10  are laid out on either side of the above-grade structure to be grounded. For example, in FIGS. 2A and 2B, mats  10  and  16  are laid out on either side of pipe riser  22 . The areas of the mats  10  immediately surrounding the above-grade structure are removed by either snipping or melting away. When fitting the mats around the above-grade structure, enough material of the mat  10  should be removed such that the mats overlap by approximately 3 inches. Spacing between the above-grade structure and the surrounding mats should be approximately 1 to 2 inches. For the mats  10  having diamond-shaped voids, the mats  10  should overlap such that the diamond-shaped voids align. Using stainless steel bolts, washers and nuts, the overlapping mats should be fastened together by passing the bolt through the diamond-shaped void in the overlapping areas. The bolts should not be over-tightened. In the preferred embodiment the bolts should be placed at approximately 1 foot intervals along the overlap. After tightening the bolts, an insulating patch is placed above and below each of the nut and bolt fastener so that an area around each bolt is protected from the surrounding soil.  
         [0042]    Once the mats are secured together, the mats are electrically connected to the above-grade structure. In FIG. 2A, the mat  10  is electrically connected to pipe riser  22 . However, the mat  10  may be connected to the test station  50  in FIG. 1. Alternatively, the mat  10  is electrically connected to the underground conductor  20  (as shown in FIG. 1), or may be connected to both the above-grade structure  22  or  50  and the buried conductor  20 . Again, these connections may be through a heavy gauge wire or the like. In the preferred embodiment, the connection points are covered with an insulative material so as to protect the mat  10  in the areas immediately around the connection from being consumed first.  
         [0043]    The above-described method of installing the preformed mats  10  is exemplary. There are numerous means to connect the mats together, including that shown in FIG. 1 where the mats  10 ,  12  and  14  do not overlap, and instead are connected together via electrical connectors  42 ,  44 . Similarly, the electrical connectors between the mat or plurality of mats may also be embodied in numerous conductors, as described earlier.  
         [0044]    The claims appended hereto are meant to cover modifications and changes within the scope and spirit of the present invention.