Patent Grant
7311553
This application is related to U.S. patent application Ser. No. 10/988,838, concurrently filed herewith and entitled “Stepped Compression Connector,” of inventor Carl R. Tamm, the subject of which is hereby incorporated by reference.
The present invention relates to a compression connector assembly which reduces the detrimental effects of aluminum oxidation on electrical connections. The compression connector includes a bushing insert for providing an electrically clean and intimate current path from a cable to the tubular bore of a bushing insert.
A compression connector typically includes a hollow tubular section which is deformed with a special tool. The tool compresses the outer periphery of an electrical connector onto a stranded electrical conductor.
Typically, in transmission lines, stranded electrical conductors are utilized. Stranded electrical conductors have a steel core overlaid by one or more layers of conductive aluminum stranding. These cables have multiple layers of individual strands. The individual strands are laid in an opposite direction to an adjacent underlying layer, making each layer distinctive from its adjacent layer by its direction.
The advent of increasing power demands results in electrical connectors being operated at much higher current levels. Consequently, higher current levels result in much higher temperatures. The increased load on the electrical grid amplifies the current density and thermal stress of the entire system. Therefore, compression connectors, are weak links in the system, and are failing at an increasing rate.
The majority of failures occur in aluminum compression connectors and conductors. The reasons for these failures are two-fold. First, the vast majority of new connectors and conductors being installed are aluminum. Second, high integrity aluminum connections are difficult to achieve due to oxidation. Aluminum oxide is a highly effective electrical insulator, and is detrimental to the integrity of a compression connector on an aluminum conductor.
Aluminum has a very high chemical affinity with oxygen, causing aluminum oxide to form easily. By simply exposing aluminum to air, a very thin oxide film will form on the aluminum surface. As a result, oxide layers forming on both the cable and connector are a reason for concern. Conductivity of the electrical interface between the connector and the conductor is severely reduced when oxides are present.
The surfaces of the conductor stranding are continuously exposed to oxygen. Consequently, an oxide coating forms on the conductor stranding and must be penetrated during the installation process to form an electrical connection. Compression connectors only make contact with the outermost periphery of the conductor stranding and cannot physically access the inner layers. Thus, penetrating the oxide coating on the inner layers improves the integrity of the connectors.
Presently, the most effective method of cleaning the conductor is to unlay the strands of the outer layers. The inner layers are exposed and are cleaned by vigorous brushing. Consequently, the formation of tenacious, highly resistive aluminum oxide is reduced.
The problem with this cleaning method is that it is highly time consuming and very difficult to accomplish in the field. The process of unlaying the stranding of the conductor a sufficient distance from the end to allow cleaning of individual stranding is laborious and tedious. While this method is possible in a typical laboratory condition, where the conductor may remain supported and still, the method is often unsuccessful in the field. Performing the cleaning steps successfully on an aerial platform, such as a bucket truck, is highly improbable due to difficultly to dealing in handling the individual conductive strands. The strands must be held in a suitable manner to brush them with sufficient force to effectively remove the oxide layer. Therefore, this method typically is not done in the field.
In addition, difficulties arise when the strands are re-layered into their original position. Compression connectors are designed with minimal space to receive the design standard of the outer diameter of the conductor. Consequently, if the strands are not re-layered to provide the original diameter of the conductor as manufactured, the conductor cannot be inserted into the compression connector designed therefore.
Additionally, the above method does not solve the problem of the rapid formation of oxides. After the stranding is brushed and a large portion of the old oxide coating removed, new oxides form immediately on the clean surfaces exposed to oxygen. The newly formed oxides formed on the surface of the aluminum strands prevent the passage of current between the innermost strands of the conductor through each successive layer and the compression connector.
Another prior art cleaning method requires the use of an abrasive material such as a sand paper. The sand paper is wrapped about the periphery of each individual strand for abrading the oxide layer. However, the abrasive material will also wipe away the oil coating of the inhibitor designed to provide the oxygen barrier needed to prevent the re-growth of the oxide layer which the cleaner is attempting to remove.
Lastly, abrasive inhibitors are also used to enhance the electrical performance of connectors. During the compression process, a gritted inhibitor is forced hydraulically through interstitial spaces between the strands. The inhibitor abrades the oxide layer as it progresses. However, this method works well only on the outer layer. Rarely, does any significant amount of the gritted inhibitor find its way to the inner layer interstices. Thus, the current being carried by the inner layers of the conductor meets a high resistance interface. As a result, the outer layers have higher current densities and increase the temperature of the conductor, particularly at the connector interface.
While the aforementioned methods help to some degree, nonetheless a continuing recurrence of connector failures in electrical grid infrastructures necessitate improvements to enhance the integrity and longevity of the electrical connectors of the infrastructure.
Thus, a continuing need exists to provide improved compression connectors.
Accordingly, a primary object of the present invention is to provide a compression connector assembly and a method of securing a cable having a bushing insert for providing an electrically clean and intimate current path from all layers of conductor stranding to the tubular bore of the bushing insert and connector.
Another object of the present invention is to provide a compression connector assembly and method of securing a cable which are relatively simple to assemble, use, and replace in comparison.
A further object of the present invention is to provide a compression connector and method of securing a cable with improved performance by reducing the number of actual interfaces, thereby enhancing the integrity of the connection and providing assurance of a low resistance interface with each layer of conductor stranding.
Yet another object of the present invention is to provide a compression connector with a reduced size, the shorter compression connector assembly reducing extrusion and birdcaging of the conductor stranding.
The foregoing objects are basically attained by providing a compression connector assembly for securing a cable. The compression connector assembly includes a bushing insert and gripping sleeve. The bushing insert includes a tubular bore, an exterior surface, a conductor receiving end, and a conductor engagement end. The gripping sleeve has an inner recess and an outer surface. The gripping sleeve is adjacent to the conductor engagement end. The tubular bore and the inner recess are substantially coaxial and define a cable securing passageway.
The foregoing objects are also attained by providing a method of securing a cable having a plurality of conductive strands forming multiple layers to a full tension deadend or other compression connector. The method includes trimming the cable to expose at one underlying layer and a core layer, cleaning the underlying layer to remove any oxide coating, and placing a bushing insert over the underlying layer. The at least one underlying layer is disposed within an inner bore of the bushing insert. The core layer extends through the bushing insert and into an inner recess of a gripping sleeve. The bushing insert and gripping sleeve are then positioned within a full tension deadend. The full tension deadend is then laterally compressed for securing the cable thereto.
Other objects, advantages and salient features of the invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the invention.
Referring now to the drawings which form a part of this original disclosure:
Referring initially to
As depicted in
As best seen in
Tubular bore 20 has an axial length and cross-sectional diameter approximately equivalent to that of a corresponding layer 16 of stranding 14. Tubular bore 20 is preferably stepped. If stepped, tubular bore 20 has a first innermost diameter 44 substantially equal to the innermost aluminum layer 38c to which contact is made and a second innermost diameter 46 which is substantially equal to a second outer layer of aluminum 38b to which contact is made. Moreover, if a plurality of outer aluminum layers are necessary (e.g. 38a), additional steps will be provided.
Tubular bore 20 also includes a diameter transition portion 48. Diameter transition portion 48 forms a tapered section disposed between successive diameter steps of tubular bore 20 and tapers in a direction towards the exterior surface 22. Diameter transition portion 48 serves to guide the end of the strand layer into its respective bore.
As best seen in
According to a second embodiment of the invention, bushing insert 118 is depicted in
According to a third embodiment of the invention,
Gripping sleeve 228 has an inner recess 230 and an outer surface 232, and is positioned adjacent to conductor engagement end 226. The unitary, one-piece compression connector assembly 210 reduces the number of parts required for assembly. Consequently, manufacturing and inventory costs are reduced, while assembly is facilitated.
In
Slits 50a-c also minimize required compressive forces. The number of slits 50, 50a-c utilized will be determined by the overall diametrical size of the gripping sleeve 28. Slits 50, 50a-c may be axially, transversely, or helically positioned on the gripping sleeve 28. Although not illustrated, slits 50, 50a-c could be also be used with the unitary compression connector assembly 210 of
Bushing insert 18 is generally manufactured by one of impact extrusion, cutting, milling, or swaging of metal stock. Bushing insert 18 can be made from any conductive metal or metal alloy (e.g. copper, aluminum, nickel, etc.) Preferably, bushing insert 18 is substantially cylindrical in shape. However, bushing insert 18 may be any polygonal shape or combination of polygonal shapes.
Gripping sleeve 28 is manufactured by one of impact extrusion, cutting, milling, or swaging of metal stock. Gripping sleeve 28 can be made from any conductive metal or metal alloy (e.g. copper, aluminum, nickel, etc.), but preferably from aluminum.
Prior to use, bushing insert 18 tubular bore 20 and gripping sleeve 28 inner recess 30 should be brushed and prepared to remove oxides and inhibit their reformation. Additionally, tubular bore 20 and inner recess 30 may also be provided with any number of textures known in the art for disrupting or prohibiting oxide formation.
As best seen in FIGS. 1 and 8-10, compression connector assembly 10 is utilized for securing cable 12 from a transmission tower 62 to a full tension deadend 56. The method first requires trimming cable 12 to expose steel core 36 and at least one aluminum layer 38. Exposed steel core layer 36 and outer aluminum layer 38 are then cleaned to remove any oxide coating. Bushing insert 18 is then placed over each layer 36, 38 so that the steel core layer 36 extends through bushing insert 18 and inner aluminum layer 38 is positioned within tubular bore 20. Steel core layer 36 is then inserted into inner recess 30. Gripping sleeve 28 is positioned adjacent conductor engagement end 26 prior to insertion within full tension deadend 56. After positioning compression connector assembly 10 within full tension deadend 56, a hydraulic press 58 (
The first step of trimming cable 12 is necessary in order to expose steel core layer 36 by paring back stranding 14. More specifically, outer aluminum layers 38a-c are pared back to expose steel core layer 36 using conventional tools. The tools operate in the same fashion as a pipe or tube cutter. The tools have a specially designed bushing guide that fastens to the conductor, serving to maintain the positional alignment of a rotary cutting wheel that circumscribes the conductor as it is rotated about its periphery and is pressed deeper with successive rotations. After the tool cuts through first outer aluminum layer 38c, it and progresses deeper through successive layers until all of outer aluminum layers 38a-b are severed, exposing the steel core layer 36. The bushing guide is then repositioned to a predetermined distance dependant on the type of construction of the conductor, and a second trim cut is made, but this time only cutting deep enough to expose the innermost layer of conductive stranding which overlays the steel core. If the conductor is of the larger sizes consisting of three layers of conductive stranding, a third trimming operation is made, again at a predetermined distance, removing only the outer layer of stranding and exposing the intermediate layer.
The next step is to clean outer aluminum layers 38a-c, and bushing insert 18 with an oxide inhibitor. The exposed aluminum layers 38a-c should be brushed prior to installation of bushing insert 18. Brushing serves to remove visible dirt and grime, while removing a heavy portion of the oxide layer. A liberal amount of inhibitor is then be applied to exposed aluminum layers 38a-c. The grease compound serves to protect the immediate surface and inhibit oxygen from contacting it, thereby inhibiting the oxide layer growth.
The inhibitor contains grit, serving as an abrasive agent. As the grit bearing inhibitor is forced through layers 16 of conductor strands 14 under hydraulic pressure created during compression, it abrades the surface of strands 14 and tubular bore 20 cleaning out the oxide layer as it moves. The grit bearing inhibitor also serves to protect and aluminum surfaces 38a-c from oxygen so the oxide does not reform. Thus, clean metal to metal contact is made between tubular bore 20 and cable 12.
Once cable 12 is properly trimmed, cleaned, and coated with the appropriate inhibitor, bushing insert 18 is inserted over the exposed outer aluminum layers 38b-c, occupying the space previously occupied by the now trimmed layers of stranding 14. Bushing insert 18 serves to provide an interface between tubular bore 20 and cleaned exposed inner aluminum layer 38c.
Gripping sleeve 28 is placed over exposed steel core layer 36 of the cable 12. Compression connector assembly 10 is inserted into a body portion 60 of full tension deadend 56. Body portion 60 is then crimped onto the gripping unit with a hydraulic press 58 (e.g. circular die press, uni-grip single die compression, or conventional two-die compression assemblies) resulting in an elliptical shaped crimp section. The crimping is continued to the end body portion 60, completing the method for securing cable 12 with compression connector assembly 10.
While various embodiments have been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims.
| Number | Name | Date | Kind |
|---|---|---|---|
| 2158892 | Becker et al. | May 1939 | A |
| 2279508 | Bergan | Apr 1942 | A |
| 2533343 | Bac | Dec 1950 | A |
| 3125630 | Wahl | Mar 1964 | A |
| 3184535 | Worthington | May 1965 | A |
| 3688245 | Lockshaw | Aug 1972 | A |
| 3855568 | Cochrane | Dec 1974 | A |
| 3955044 | Hoffman et al. | May 1976 | A |
| 4252992 | Cherry et al. | Feb 1981 | A |
| 4362352 | Hawkins et al. | Dec 1982 | A |
| 4508409 | Cherry et al. | Apr 1985 | A |
| 4813893 | Sindlinger | Mar 1989 | A |
| 5002503 | Campbell et al. | Mar 1991 | A |
| 5007861 | Stirling | Apr 1991 | A |
| 5408743 | Tournier et al. | Apr 1995 | A |
| 6241553 | Hsia | Jun 2001 | B1 |
| 6905365 | Liu | Jun 2005 | B1 |
| 7192308 | Rodrigues et al. | Mar 2007 | B2 |
| Number | Date | Country | |
|---|---|---|---|
| 20060105639 A1 | May 2006 | US |
