Multi-layer power cable with metal sheath free to move relative to adjacent layers

Abstract

An electrical power cable with a stranded conductor, a semi-conductive stress control layer around the conductor, a layer of insulation around the stress control layer, a semi-conductive insulation shield laser around the layer of insulation, an imperforate metal strip with overlapping edge portions around the shield layer and a polymeric jacket around the metal strip. The strip is free to move with respect to the jacket and the shield layer with expansion and contraction of the cable elements with temperature changes, and the overlapping edge portions of the strip are bonded together by an adhesive which permits the edge portions to move relative to each other with such temperature changes without creating fluid passageways between the edge portions. A cushioning layer can be between the shield layer and the strip and preferably, the cable is water sealed.

What we claim is: 
     
       1. In an electrical power cable operable throughout a predetermined temperature range and comprsing a stranded conductor formed by a plurality of wires stranded together and in conductive contact with adjacent wires, a semi-conductive stress control layer around said conductor, a layer of insulation around said stress control layer, a semi-conductive insulation shield layer around said layer of insulation, an imperforate metal shield around said shield layer, said metal shield to being formed by a metal strip with overlapping edge portions, and a jacket of polymeric material around said metal shield, wherein the improvement comprises a metal shield which is free to move with respect to said insulation shield layer and said jacket with expansion and contraction of said metal shield, said semi-conductive stress control layer, said insulation, said insulation shield layer and said jacket when said cable is subjected to temperature changes in said predetermined range and an adhesive bonding said overlapping edge portions together, said adhesive permitting said edge portions to move relative to each other without causing a fluid passageway between said edge portions when said cable is subjected to temprature changes in said predetermined range whereby fluid is prevented from passing between said overlapping edge portions and buckling and fractures of said metal shield is prevented even though said cable is subjected to repeated temperature changes within said range. 
     
     
       2. An electrical power cable as set forth in claim 1 wherein said metal shield is free of a bond with said jacket, whereby said jacket may be readily stripped from around said metal shield. and is free of a bond with said insulation shield layer. 
     
     
       3. An electical power cable as set forth in claim 2 wherein said adhesive is a hot melt adhesive which has a predetermined softening temperature and an application temperature higher than said predetermined softening temperature and higher than the highest temperature in said predetermined range. 
     
     
       4. An electrical power cable as set forth in claim 1 wherein said metal strip is bare and is selected from the group of metals consisting of copper, aluminum and steel. 
     
     
       5. An electrical power cable as set forth in claim 4 wherein said adhesive is a hot tneli adhesive which has a predetermined softening temperature and an application temperature higher than said predetermined softening temperature and higher than the highest temperature in said predetermined range. 
     
     
       6. An electrical power cable as set forth in claim 1 wherein said adhesive has the following properties: Viscosity: Min. 2000 mPas @ 175° C.   Ultimate tensile strength: Min. 300 psi @ 25° C.   Elongation: Min. 250% @ 25° C.   Softening point without melting: .Iadd.Min. .Iaddend.80° C.   Application temperature: at least 130° C.   
     
     
       7. An electrical power cable as set forth in claim 1 wherein said adhesive has the following properties: Viscosity: 2000-7000 mPas in the range 175°-180° C.   Ultimate tensile strength: 300-1100 psi @ 25° C.   Elongation: 250-780% @ 25° C.   Softening point without melting: 80°-205° C.   Application temperature: 130°-265° C.   
     
     
       8. An electrical power cable as set forth in claim 1 wherein said adhesive has a softening temperature in said predetermined temperature range and a melting temperature and an application temperature above said predetermined temperature range. 
     
     
       9. An electrical pwoer cable as set forth in claim 1 wherein any otherwise empty spaces within said jacket are filled with water sealing material. 
     
     
       10. An electrical power cable as set forth in claim 1 further comprising a cushioning layer around said insulation shield layer and intermediate said insulation shield layer and said metal shield. 
     
     
       11. An electrical power cable as set forth in claim 10 wherein said cushioning layer is a layer of tape containing a water swellable material. 
     
     
       12. An electrical power cable as set forth in claim 1 further comprising water swellable particles intermediate said insulation shield layer and said metal shield.