US 3502791 A
Description (OCR text may contain errors)
- March 24, 1970 W.G.DIAHLSTROM V 3,502,191
POWER CABLE Filed Dec. 12, 1968 4 r l y y CONDUCTOR V5 N TOR rm 6. OAHLSTROM' I Attorney United States Patent Office 3,502,791 POWER CABLE Walter G. Dahlstrom, Worcester, Mass., assignor to United States Steel Corporation, a corporation of Delaware Filed Dec. 12, 1968, Ser. No. 783,265 Int. Cl. H01b 7/04, 9/00 US. Cl. 174115 9 Claims ABSTRACT OF THE DISCLOSURE This invention relates to electrical power cable and, more particularly, to improvements in mine trailing cable used to provide power to shuttle cars in mines. Such cables are attached at one end to a source of power in the mine and at the other end to a reel on the shuttle car. As the car moves in the mine, the cable is either paid out or taken up depending upon the direction of travel of the shuttle car. These cables usually have at least two parallel rubber insulated conductors surrounded by an integral rubber jacket. The conductors are separated from one another by the jacket or by such devices as a fabric strip. The cable may include grounding wire. The cable must be flexible and be able to withstand much mechanical abuse. Movement of the insulated conductors within the jacket is restricted such as by a cement bonding the insulated conductor to the jacket. This restricts the movement of one insulated conductor with respect to the other so that one insulated conductor cannot elongate relative to the other, which may result in buckling of the jacket and actual penetration through the jacket.
These cables are usually fabricated by extruding insulation material, for example about .0625 inch thick for a size 4 A.W.G., 600 volt rated cable, over the conductors individually and then extruding the jacket over the insulated conductor and grounding wires.
Insulating properties and mechanical strength of the cable have been improved by substituting a thin polyolefin insulation for the relatively thick rubber insulation. This permits increasing the jacket thickness while retaining the same external dimensions, thus providing more mechanical protection to the insulated conductors. However, since attempts to bond the insulated conductors to the jacket have been unsuccessful, these polyolefin insulated cables have a shorter life than if they were bonded because movement of the insulated conductors has buckled and ruptured the jacket. Even if a bond between the insulated conductors and the jacket could be developed,
it would still be necessary to control the bond to facilitate terminating and splicing the cable.
According to my invention, the conductors are insulated and joined by a connecting web of insulating material in a single extrusion. The web is then perforated. The jacket material penetrates the perforations and mechanically locks the separate conductors and jacket in fixed position with respect to each other.
It is, therefore, an object of my invention to provide a multiple conductor cable in which the conductors and jacket are mechanically locked from movement with respect to one another.
Another object is to provide such a cable in which the conductors resist buckling and do not penetrate the jacket.
A further object is to provide such a cable wherein the conductors do not move with respect to each other.
3,502,791 Patented Mar. 24, 1970 A still further object is to provide such a cable in which the insulation is not bonded to the jacket.
These and other objects will be more apparent after referring to the following specification and attached drawing in which:
FIGURE 1 is a cross-sectional view of the improved cable of my invention; and
FIGURE 2 is a plan view of a fragment of an insulated conductor and web assembly of my invention before the application of the protective jacket and ground wires.
Referring now to the drawing, reference numeral 2 indicates two spaced apart generally parallel stranded conductors surrounded by insulation 4. Conductors 2 may be copper, aluminum, or other suitable conducting material in any suitable form such as the seven-wire strand shown. Insulation 4 is preferably an insulating compound containing polymers of a polyolefin with a suitable wall thickness for the voltage rating and size of the cable, for example about 0.020 inch for a 600 volt size 4 A.W.G. cable. However, polymers of polyvinyl chloride, chlorosulfonated polyethylene, polyisoprene, butadiene-styrene, ethylene-propylene, or polychloroprene are also satisfactory. The insulated conductors 2 are connected by a web 6 of the insulating material integral with the insulation 4. Web 6 has perforations 8 throughout the length of the cable. A protective jacket 10, preferably a compound containing polymers of polychloroprene, surrounds the insulated conductors 2 and the web 6 filling the perforations 8, thus locking the jacket to the insulation-web structure. Jacket 10 may also be other jacketing materials commonly used for electrical cables, such as compounds containing polymers of polyvinyl chloride, chlorosulfonated polyethylene, polyurethane or butadiene acrylonitrile-polyvinyl chloride. A pair of grounding wires 12 of suitable capacity and material are embedded in jacket 10 one on each side of web 6.
Web 6 should be thin enough to maintain the desired flexibility of the cable while being thick enough to keep conductors 2 separated. Web 6 may be as thin as 5 mils. Perforations 8 are preferably round or elliptical. The surface areas of the perforations 8 with respect to the surface area of the web 6 should be no more than nor less than 10%.
Web 6 is shown as being located generally in the plane passing through the axes of the conductors. While such a location is preferred, other configurations would also be satisfactory, such as a web in a plane parallel to the plane passing through the center line of the conductors but tangent to the outer circumferences of the insulation.
Ground wires 12 may be omitted or replaced by a single ground wire or by more than two ground wires depending on the current-carrying capacity required and geometry of the cable.
While the cable is shown with two conductors, other combinations such as a flat cable with three parallel conductors and two connecting webs would have the same desirable characteristics.
In making the cable, a single extrusion is required for the insulation and web. The perforations may be made in a conventional manner as the conductor assembly leaves the extrusion die. The jacket is then extruded over the conductor assembly and ground wire.
The jacket rubber penetrates the perforations and thus locks the jacket to the conductor assembly. This results in a cable insulation that has a tendency to resist twisting and to lie flat, and facilitates the separation of the jacket and the insulation for splicing and terminal connections. The preferred construction of the cable is with the insulating material and web as an integral assembly, but the flexibility and spacing control could also be effective with the web and insulation of different materials bonded or cemented to each other.
While several embodiments of my invention have been. shown and described, it will be apparent that other adaptations and modifications may be made.
1. A multiple conductor power cable comprising two generally parallel spaced apart electrical conductors, a layer of electrical insulating material surrounding each conductor, a perforated web joining the layers of electrical insulating material along longitudinal edges of the web, and a jacket of protective material surrounding said web and the insulated conductors, said protective material penetrating the perforations to mechanically lock the conductors and jacket in fixed positions with respect to each other.
2. A cable according to claim 1 in which said jacket material is a compound containing at least one polymer of the group consisting of polychloroprene, polyvinyl chloride, chlorosulfonated polyethylene, polyurethane, and butadiene acrylonitrile-polyvinyl-chloride.
3. A cable according to claim 1 in which the area of the web perforations is between approximately 10% and 90% of the web area.
4. A cable according to claim 1 in which the said web is in substantially the same plane as the axes of said conductors and is integral with said layers of insulating material.
5. A cable according to claim 4 in which said insulating material is a compound containing at least one polymer of the group consisting of polyolefin, polychloroprene, polyvinyl chloride, chlorosulfonated polyethylene, polyisoprene, butadiene-styrene, and ethylene-propylene.
6. A cable according to claim 5 in which said jacket material is a compound containing at least one polymer of the group consisting of polychloroprene, polyvinyl chloride, chlorosulfonated polyethylene, polyurethane, and butadiene-acrylonitrile-polyvinyl-chloride.
7. A cable according to claim 6 including a pair of grounding conductors within the jacket, tone on each side of said web generally parallel to said two conductors.
8. A cable according to claim 7 in which the area of the web perforations is between approximately 10% and E. A. GOLDBERG, Primary Examiner US. Cl. X.R. 174-113,