Electrical grounding apparatus and method and washer for use therewith

Abstract

An electrical grounding apparatus and method of making the same is provided comprising a plurality of electrically conductive aluminous strips arranged in a grid-like pattern having a plurality of areas of intersection. An electrically conductive washer is provided at each area of intersection and a fastener is used to hold an associated pair of strips at each area of intersection against opposed surfaces of the washer; and, the washer has a thickness which is sufficient to separate the strips and prevent crevice corrosion and has a pair of opposed surfaces with projections extending therefrom which bite into an associated conductor upon tightening the fastener to hold the washer sandwiched between the strips and thereby assure an optimum electrical connection between the associated pair of strips.

Description

BACKGROUND OF THE INVENTION

Electrical grounding apparatus or systems of the type used previously for electrical power substations by major electrical power companies generally employ copper cable arranged in a grid-like pattern having overlapped areas or areas of intersection which are heat fused together by welding, or the like. However, these previously used systems are comparatively expensive and the electric power companies have been searching for an alternate less expensive grounding apparatus which is capable of providing the required grounding protection.

Of the other known electrically conductive materials, aluminum is the most likely material which could be practically substituted for copper in this type of application. However, it has been found by extensive tests that with an alternating current density of roughly 0.5 milliamperes per square inch and above crossing the metal-electrode interface, aluminum will corrode while below this current density, there is substantially no AC corrosion of buried aluminum.

In attempting to use aluminum cable or rod, it has been found that small diameter cable does not give the required area and while the obvious answer might appear to be the use of substantially larger diameter aluminum cable such larger diameter cable would increase the cost above the cost of a system using copper. It has also been found that aluminum sheets in strip-like form are of minimum weight yet provide a comparatively large surface area which is especially desirable for a grounding system.

However, in using strips of aluminous material it was found that heat fusion of associated strips, as is generally done presently with copper cable, requires either complete welding of the overlapped strips or sealing of the unwelded overlapped portions to prevent crevice corrosion whereby it is apparent that it is necessary to fasten the overlapped strips of aluminous material in a manner which prevents crevice corrosion as well as fasten such strips so as to assure a high-strength mechanical and electrical connection therebetween.

SUMMARY

This invention provides an improved buried grounding apparatus and method of making the same which utilizes strips of an electrically conductive aluminous material arranged in a grid-like pattern having a plurality of overlapping areas or areas of intersection and such strips are uniquely fastened together at such areas of intersection so as to prevent crevice corrosion and such strips are also fastened so as to assure a high-strength mechanical and electrical connection therebetween.

Other details, uses, and advantages of this invention will be readily apparent from the exemplary embodiments thereof presented in the following specification, claims, and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings show present preferred embodiments of this invention, in which

FIG. 1 is a fragmentary plan view particularly illustrating one exemplary embodiment of a grounding apparatus and method of this invention comprised of electrically conductive aluminous strips arranged in a grid-like pattern and having a plurality of overlapped areas or areas of intersection;

FIG. 2 is an enlarged fragmentary cross-sectional view particularly illustrating a typical strip of FIG. 1 arranged in an open trench below ground level prior to burying such strip;

FIG. 3 is an enlarged fragmentary plan view of a typical area of intersection of an associated pair of electrically conductive strips comprising the grounding apparatus of FIG. 1;

FIG. 4 is an enlarged fragmentary view taken essentially on the line 4--4 of FIG. 3 and particularly illustrating a pair of electrically conductive washers of this invention and associated fasteners used to fasten an associated pair of strips at the typical area of intersection;

FIG. 5 is an enlarged top plan view of a typical washer of FIG. 4;

FIG. 6 is an enlarged fragmentary cross-sectional view showing the manner in which projections comprising opposed surfaces of the washer of FIG. 5 bite into associated electrically conductive aluminous strips comprising the grid-like pattern of FIG. 1; and

FIG. 7 is an enlarged view particularly illustrating the manner in which the electrical lead shown fastened to the grounding apparatus in FIG. 1 may be fastened utilizing similar components as used at the areas of intersection of the aluminous strips.

DETAILED DESCRIPTION

Reference is now made to FIG. 1 of the drawings which illustrates a fragmentary portion of one exemplary embodiment of a ground apparatus and method of this invention which is designated generally by reference numeral 20. The apparatus 20 comprises a plurality of electrically conductive members or strips each made of an aluminous material and each designated generally by the reference numeral 21 and such strips will also be referred to, for simplicity, as aluminous strips 21. The strips 21 are arranged in a grid-like pattern defined by a plurality of spaced flat strips 21 which, if desired, may be arranged in equally spaced parallel relation intersected by another plurality of spaced flat strips 21 which may also be arranged in equally spaced parallel relation and arranged perpendicular to the first set of spaced strips 21. The strips 21 have a plurality of overlapped areas which will also be referred to as areas of intersection and each area of intersection will be designated generally by the reference numeral 22 and has unique fastening means, designated generally by the reference numeral 23, see FIG. 4, for mechanically and electrically fastening the associated pair of electrically conductive aluminous strips 21 at the area of intersection 22.

As best seen in FIG. 4, each associated pair of strips 21 at each area of intersection 22 has at least one set 24 of aligned openings therein and in this example a pair of sets of openings is provided at each area of intersection 22. Each set 24 of openings is defined by an opening 25 in the upper strip 21 and an opening also designated by the reference numeral 25 in the lower strip 21 and it will be seen that the openings 25 of each set 24 are arranged in aligned relation which in this example is illustrated as a vertically aligned relation.

A pair of electrically conductive washers 26 of this invention is provided and arranged between the associated pair of strips 21 at the associated area of intersection 22. Each washer 26 has a substantially right circular cylindrical opening 27 extending centrally therethrough, also see FIG. 5, and a pair of opposed top and bottom surfaces 30; and, the opening 27 communicates with the opposed surfaces 30. Each washer 26 is arranged between a pair of strips 21 with its opening 27 in vertically aligned relation between a set 24 of openings 25 and in this disclosure the openings 25 and 27 are substantially circular openings having roughly equal areas.

A pair of fastening devices or fasteners each designated generally by the reference numeral 32, is provided for holding the associated pair of strips 21 at each area of intersection 22 in sandwiched relation against the washers 26. Each fastener 32 of this example includes a fastening bolt 33 and fastening nut 34. The fastening bolt 33 and nut 34 are of the type manufactured by the Huck Manufacturing Company, 2,500 Bellevue Avenue, Detroit, Mich., USA, and sold under the trademark "Huckbolt."

Each bolt 33 extends through aligned openings 25 and 27 in the manner illustrated in FIG. 4 and has a head 35 adjoined by a plain substantially right circular cylindrical portion 36 adjoining the head 35 and the portion 36 has a height roughly equal to or slightly less than the overall height 37 of the strips 21 with the interposed washers 26. The bolt 33 also has a central portion provided with a plurality of axially spaced annular projections 40 thereon adjoining portion 36 and a top portion 41 which is particularly adapted to be grasped by a special tool, not shown, used to install bolt 33 and nut 34 in position.

To fasten a pair of strips together at an associated area of intersection a pair of washers 26 are installed each with its opening 27 aligned between a set 24 of openings 25. A bolt 33 is then passed through aligned openings 25 and 27 so that portion 41 extends above the top strip 21. The nut 34 is then placed around the central portion of the bolt and around its spaced annular projections 41 and the nut at this point in the installation procedure has a smooth plain cylindrical inside surface. The previously mentioned special tool is used to grasp the upper portion 41 and pull the strips 21 firmly against opposite sides of the washer 26 with such washer sandwiched therebetween. Once a predetermined tension has been exerted to clampingly engage strips 21 against opposed surfaces 30 of the washer 26 the special Huckbolt tool swages the nut 34 and permanently forms such nut against the projections 40 to define an undulating inside surface in the nut 34 having grooves 42 which receive projections 40 and projections 43 which are received within grooves 44 defined between the integral annular projections 40. The bolt 33 also has a reduced diameter portion 45 at a location above the top of the nut 34 and once a particular bolt and nut have been fixed in position the bolt is simply broken away at portion 45 by the action of the special tool.

In this example, a special bolt 33 and nut 34 have been used to provide the required fastening action in association with each washer 26; however, it will be appreciated that commercially available standard threaded nuts and threaded bolts may be used in lieu of the nuts 34 and bolts 33.

Each electrically conductive washer 26 has a thickness indicated at 46, see FIG. 6, which is sufficient to provide spacing between a pair of associated strips 21 and thereby prevent crevice corrosion which could occur if the strips were comparatively close to or against each other. Further, the washer 26 has projections in the form of roughly V-shaped projections 50 extending from each of its opposed surfaces 30 and the projections 50 are particularly adapted to bite into an associated strip 21 and define a trough or freshly formed indentation 51 free of an oxide coating which assures optimum electrical contact between the washer 26 and the strip 21 and hence an optimum electrical connection between the overlapped strips 21 at each area of intersection 22.

The V-shaped projections 50 extending from each surface 30 are arranged to assure at least one unobstructed flow path from the center portion of the washer 26, such as, from the opening 27 toward the outer periphery of the washer 26. In this example, the washer 26 is in the form of a disc-like washer having a right circular cylindrical outside surface 52 interconnecting the peripheral edges of the opposed outside surfaces 30 and the projections 50 extending from each surface 30 are arranged in a continuous spiral pattern as indicated at 53 to thereby assure that any flowable substance between a strip 21 and the associated surface 30 of the washer 26 when subjected to being clamped therebetween is free to flow outwardly toward the surface 52. In the normal use of each washer 26, a joining compound 54, shown by dots in FIG. 6, is employed to lower the electrical resistance and make the joint comparatively air and moisture tight. The compound 54 serves to fill any voids in the joint and prevents water from entering and forming a corrosion product which would tend to increase the electrical resistance of each connection at each area of intersection. The spiral arrangement of the projections 50 assures that excess joint compound will move in the spiral pattern from the center of the washer 26 outwardly through the continuous spiral channel 55 defined by the V-shaped projections 50 whereby the joint compound 54 can not be trapped as would be the case if the projections 50 were to be concentric projections.

The projections 50 are preferably V-shaped each having a sharp apex 56; however, it will be appreciated that such projections may have other configurations provided that such other configurations provide a biting action into an associated strip and for similar reasons as outlined above for the projections 50.

In this disclosure of the invention, the grounding apparatus 20 is shown as being defined by a plurality of strips 21 made of an aluminous material arranged in a substantially rectangular grid-like pattern defined by a plurality of parallel strips 21 arranged in one direction and a plurality of parallel strips 21 arranged in a direction perpendicular thereto. However, it will be appreciated that the grid-like pattern of the strips 21 may be any geometric pattern with the strips 21 being provided with areas of intersection wherein such strips are uniquely fastened as described above.

The grounding apparatus is particularly adapted for use at an electrical power substation and for such use the distance between parallel strips 21 would be approximately 8 to 35 feet. To bury the apparatus 20 a plurality of intersecting trenches, one of which is shown in FIG. 2 and designated by the reference numeral 60, are dug in a pattern corresponding to the pattern of the apparatus. Each trench is dug so that its associated strip 21 is buried a suitable depth 61 below ground level and for a typical substation such depth would be about 18 inches. After placing the strips 21 in their trenches such trenches would be filled with earth or similar material, to completely bury the apparatus 20.

It will be appreciated that at least one electrical conductor 63 is connected to the grounding apparatus, as shown at 64 in FIGS. 1 and 7, and such conductor has a flattened terminal end portion 65 provided with openings 67 therein and portion 65 may be fastened to a strip 21 at an area of intersection which is designated generally by the reference numeral 66. The area of intersection 66 is substantially identical to the area of intersection 22 and employs a pair of washers 26 and with each washer 26 utilizing a bolt 33 and nut 34 which are fastened in position as described previously. Each bolt 33 at the area of intersection 66 is inserted through associated openings 25, 27, and 67 of strip 21, washer 26, and conductor 63 respectively.

The strips 21 are preferably flat aluminous strips of rectangular cross section and a typical strip for an electrical substation has a width of 41/4 inches, a thickness of 0.070 inch, and may be as long as 100 feet or more.

As explained above, the strips 21 are preferably made of an aluminous material and the washers 26 are also preferably made of an aluminous material together with the bolts 33 and nuts 34. Further, these aluminous components are preferably made so that the alternating current density at any location on the apparatus 20, including all areas of intersection, is less than 0.5 milliampere per square inch.

However, it is to be understood that the concept of this invention may be employed to define a grounding apparatus which has strips arranged in a grid-like pattern, washers similar to washers 26, and bolts similar to bolts 33, and nuts similar to nuts 34 which may be made of other electrically conductive materials which are compatible with each other when buried and capable of providing grounding protection.

The washer 26 of this invention may be of any suitable size and configuration and in one application of this invention such washer was made of 6061-T6 aluminum alloy with a 1 inch outside diameter, a 13/32 inch diameter opening 27 therethrough, a thickness of 1/4 inch, a typical overall height of roughly 0.015 inch for projections 50, and a typical radial spacing from apex 51 to adjacent apex 51 of 0.025 inch.

In the above description, mention was made that an aluminum joining compound 53 is provided between each surface 30 and an associated strop. Although any suitable compound may be used for this purpose, compounds which have been used successfully include a compound sold under the trade name of "No-Oxide-E" by the Dearborn Chemical Co., Merchandise Mart, Chicago, Illinois; and "T and B Joint Compound" sold by Thomas & Betts Company, 2,838 Butler St., Elizabeth, New Jersey.

In this disclosure of the invention, the grounding system is shown utilizing a washer of the character described above and associated components for the purpose of interconnecting strips or components which extend transverse each other in an intersecting manner; however, it will be appreciated that the concept disclosed herein is fully applicable in a similar manner as described above for splicing strips of a grounding system for the purpose of increasing the length of a particular strip, for example.

While present exemplary embodiments of this invention, and methods of practicing the same, have been illustrated and described, it will be recognized that this invention may be otherwise variously embodied and practiced within the scope of the following claims.

Claims

What is claimed is:

1. An electrical grounding system adapted to be buried underground and comprising, a plurality of electrically conductive strips arranged in a grid-like pattern and having a plurality of areas of intersection and wherein immediately adjacent pairs of strips at each area of intersection are arranged transverse each other, a set of aligned openings in an associated pair of said strips at each of said areas of intersection, a plurality of electrically conductive washers corresponding in number to said plurality of areas of intersection with each washer being arranged between the associated pair of strips at its area of intersection and each washer having an opening therethrough which is aligned with an associated set of aligned openings and having an outside surface, a plurality of fasteners corresponding in number to said plurality of areas of intersection with each fastener extending through the associated set of openings and the opening in its associated washer, each of said fasteners holding the associated strips at its area of intersection in sandwiched relation against its associated washer, each washer having a thickness which is sufficient to separate said strips and minimize crevice corrosion and having a pair of opposed surfaces, each of said opposed surfaces having projections extending therefrom which bite into an associated strip upon tightening the associated fastener to hold the washer sandwiched between its strips at the associated area of intersection to thereby assure a substantially resistance free electrical connection between said strips at each area of intersection, said projections extending from each surface of each washer being arranged in a continuous spiral pattern from each washer opening to its outside surface with said projections defining an unobstructed spiral channel from the center portion of the washer to the outside thereof, each spiral projection having a substantially V-shaped configuration including a sharp apex enabling easy biting thereof into an associated strip, said biting providing an indentation and freshly exposed metal free of an oxide coating, and each V-shaped spiral projection having a vertical height which is roughly one-half the radial distance between the apexes of immediately adjacent projections, said vertical height assuring forming of said indentation as well as assuring said unobstructed spiral channel.

2. A system as set forth in claim 1 and further comprising an electrically conductive joining compound between each of said opposed surfaces and its associated strip, said compound helping to make the joint air and moisture tight while preventing corrosion between adjacent surfaces, and said spiral channel assuring that excess compound flows outwardly from the center of an associated washer at an associated area of intersection to assure said biting.

3. A system as set forth in claim 1 in which each of said strips, washers, and fasteners is made of aluminous material.

4. A system as set forth in claim 3 in which each of said strips has a rectangular cross-sectional configuration.