US2938943A - Electrical cable for heavy currents - Google Patents

Description

May 31, 1960 H. HORN ELECTRICAL CABLE FOR HEAVY CURRENTS Filed Nov. 26, 1954 GLASS RIBBON ELECTRIC CONDUCTOR METALLIC SHEATH METAL THREADS HEAT-SENSITIVE INSULATION INSULATING COMPOUND POROUS IMPREGNATED ELEC'I'RICALLY CONDUCTIVE LAYER INVENTOR. H EI N Z HO I? N %-m Nut 41,

QT'TORNEYS heat-protection,

United m Patent 1 1 .Germany,' a corporation of Germany Fi'led No'v. '26, 1954, seam. 471,443

4 Claims. (Cl. 174--102) This invention relates to electrical cable of the type having an impregnated paper or other heat-sensitive insulation surrounding the conductor and which, in turn, is surrounded "by a protective aluminum sheath. The invention has particular reference to an improved cable of this character provided with a heat protecting layer between the aluminum sheath and the heat-sensitive insulation to protect the latter from high temperatures occurring during application of the sheath to the cable.

In the manufacturev of electrical cable having an aluminum sheath, the usual practice is to extrude or press the aluminum around the cable core comprising the conductor and insulation. Due to the high temperatures encountered in thus applying the aluminum, some provision must be made to protect the underlying core from damage by the heat, particularly at those regions of the cable length where the sheath press or extruder is stopped to introduce a new charge of aluminum into the container, that is, at the regions of the so-called stops. Heretofore, various expedients have been used to provide this one of which is a simple heat protection layer of heat-resisting material, such as asbestos, fine glass, or the like. To increase the heat protection, however, it has also been proposed to provide a double heatprotective layer arranged on the cable insulation in the regions of the stops, this layer consisting of a wrapping of metal ribbon or metallized paper ribbon arranged directly around the cable core, and a wrapping of glass ribbon surrounding the first ribbon. In order to relieve electrically the protecting layer of glass ribbon, which is not impregnated with the oil or other impregnator of the cable insulation, the underlying metallic wrapping may be electrically connected at intervals with the metal sheath of the cable. As an alternative, it has also been proposed to wrap the cable core with a metallized paper ribbon folded at the edge to form a heat-insulating air space between the cable sheath and the cable core, the metallized part of the ribbon lying on the outside so that it is in electrical contact with the metal sheath of the cable, whereby the heat insulating space is kept free from electrical charge. Both of these arrangements have the disadvantage that one of the heat-protecting layers is always filled at least partly with air, which allows migration of the oil or other impregnator from the insulation into the heat-protection layer. This migration may in time cause a depletion of the impregnator in the insulation, or it may cause a deterioration of the impregnator due to chemical reaction between the impregnator and the oxygen in the heat-protective layer.

The present invention has for its principal object the provision of an improved cable of the character described having a heat-protecting arrangement which avoids the above-noted disadvantages.

A cable made according to the invention comprises a porous, electrically conductive layer, which is preferably of carbon black paper, arranged directly around the cable core, and a layer of glass ribbon arrangedaround the free of electrical charge; and

2,938,943 Patented May 31, 1960 ICC layer of carbon black paper or the like, and located underneath'the aluminum sheath of the cable, the glass ribbon layer being interlaced with copper or other metal threads to insurean electrical connection with the porous conductive layer. With this construction, the heat protecting layer consisting essentially of fine glass is kept the electrically conductive layer sealing the cable core, due to its porosity, is permeable to the impregnator of the cable insulation and, therefore, may be impregnated simultaneously with the cable core. Thus, deterioration of -the impregnator through contact with air in the finished sheath cable is avoided. At the same time, the heatprotective layer filled with impregnator may serve as a reservoir for the impregnator during temperature changes of the cable.

For a better understanding of the invention, reference may be had to the accompanying drawing in which the single illustration is a cross-sectional view of a preferred form of the new heavy-current cable.

Referring to the drawing, the cable as there shown comprises a plurality of conductors 1, each of which is surrounded by insulation 2. The insulation 2 may be of any suitable material, but is preferably paper wrapped around the conductor and impregnated with oil. The wedge-shaped spaces between the insulated conductors are filled with a suitable insulating compound 3, such as any of the compounds conventionally used for this purpose. The cable core thus formed by the parts 1, 2 and 3 is wrapped with carbon black paper forming a porous electrically-conductive layer 4. A layer of glass ribbon 5 is wrapped around the layer of carbon black paper 4, and the glass ribbon layer 5 is interlaced with copper threads 6. These copper threads are embedded in'the glass ribbon layer 5 and are exposed at the opposite faces of this layer. The glass ribbon making up the layer 5 may be of the conventional fiber-glass type, except for the addition of the copper threads 6 with which the glass fibers are interlaced or interwoven.

The protective aluminum sheath 7 is pressed or extruded around the glass ribbon layer 5.

It will be apparent that the carbon black paper 4 forms a non-metallic porous layer which is electrically conductive and is wrapped directly on the cable core. Because of the porosity of the layer 4, the cable core may be impregnated with the oil or other impregnator after the layer 4 has been applied, so that the cable core and the conductive sealing layer 4 are impregnated simultaneously. Thereafter, the glass ribbon layer 5 may be wrapped around the layer 4, followed by pressing or extruding of the aluminum sheath 7 over the glass ribbon layer. The copper threads 6 which interlace the glass ribbon layer 5 serve to form an electrical connection between the aluminum sheath 7 and the layer 4 of carbon black paper.

In the preferred construction, along the entire length of the cable between the underlying core and the overlying aluminum sheath. However, in some cases it may sutfice to arrange these layers 4-5 only in the regions of the stops of the aluminum sheath, where there is the greatest need for heat-protection of the underlying cable core. Accordingly, the appended claims are not to be construed as limiting the invention to an arrangement in which the heat-protecting layer extends over the whole length of the cable.

I claim:

1. In a heavy-current electrical cable having a cable core including a conductor and a heat-sensitive insulation surrounding the conductor, and a protective metallic sheath surrounding the cable core, the improvement which comprises a porous, impregnated electrically-conductive layer interposed between the cable core and the the layers 4 and 5 extend sheath, a layer of glass ribbon wrapped around said porous conductive layer between said last layer and the sheath, and metallic threads interlacing the glass ribbon layer and providing an electrical connection between said impregnated porous conductive layer and the sheath.

2. The improvement according to claim 1, in which said porous conductive layer is carbon black paper.

3. The improvement according to claim 1, in which said threads are copper threads embedded in the glass ribbon layer.

4. The improvement according to claim 1, in which said heat-sensitive insulation is impregnated paper, said porous layer being impregnated with the impregnator of said insulation.

References Cited in the file of this patent UNITED STATES PATENTS Aime Nov. 1, 1938 Jacob Aug. 7, 1945 Rasero Dec. 23, 1947 Beaver Oct. 24, 1950 Holmes July 15, 1952 FOREIGN PATENTS Great Britain Mar. 30, 1936 Great Britain Feb. 10, 1943 Germany July 8, 1949

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