US 3579863 A
Description (OCR text may contain errors)
United States Patent  Inventor Martin H. McGrath 200 E. 15th St., New York, N.Y. 10003  Appl. No. 834,795  Filed June 19, 1969  Patented May 25, 1971 [5 4] VIP JACKET UNDER SKID WIRE OF PAPER POWER CABLES 7 Claims, 4 Drawing Figs.
 US. Cl 174/10, 174/25, 174/105  ..H02g 15/20  174/10, 102, 23-26, 120
 References Cited UNITED STATES PATENTS 2,222,932 11/1940 Bennett 174/10 2,597,222 5/1952 Bennett Primary ExaminerLewis I-I. Myers Assistant Examiner-A. T. Grimley Attorney-Sandoe, Hopgood & Calimafde ABSTRACT: Oil-impregnated paper cables are kept dry during storage, shipment and installation by covering the cable, under the skid wire, with a sheath comprising a laminated tape of aluminum coated with plastic on both sides. The plastic seals the seam of the sheath, and as the cable is pulled into a pipe the sheath is ruptured or torn in a haphazard manner by use of pliers, about once for each turn of the reel, to create breaks in the sheath which permit rapid and thorough evacuation of the completed system and also permit normal interchange of the pipe filling oil on load cycle changes.
PATENTED mzslen 3579.863
CABLE MAKING & OIL IMPREGNATION I I2 smo WIRE f APPLICATION APPLICATION SHIPPING V FIBROUS PAPER 7 32 METALIZE -l 34 33 PLASTIC TAPE 4 (s5: Fig.3)
ALUMINUM FOIL 40 POLYETHYLENE-42 F IG. 4.
INVENTOR W \ANMQA M W 3 Mu.
SKID WIRE OF PAPER POWER VIP JACKET UNDER CABLES Oil-impregnated paper power cables, particularly of the LII type which is pulled into steel pipes and-kept under oil or gas pressure, must be kept absolutely dry duringstorage or shipment, and it is desirable to prevent the picking up of moisture by the cable during the time that it is being installed. During installation, the first part of the cable exposed to the, atmosphere only a short time may not pick up any moisture, but since pulling a long-length cable into a pipe may take hours, the last part of the cable may have a greater moisture content than the first part, particularly under conditions of high relative humidity.
This invention can be used for paper-insulated cables and also for cables insulated with fibrous plastic such as the paper" tapes made of webs of randomly arranged, highly dispersed, continuous filament fibers of polymeric material bonded primarily at filament crossovers. This material, made by duPont, is sold under the name Spunbond.
This invention provides a laminatedmoisture-impervious sheath which is wrapped around the cable before there has been any significant drainage of oil from the cable structure. The sheath is applied, somewhat loosely, by folding a tape longitudinally around the cable progressively as the cable advances with continuous motion. The sheath is preferably a laminate made of aluminum foil coated with polyethylene and it is similar to the inner sheath disclosed in .lachimowicz US. Pat. No. 3,206,541 of Sept. 14, 1965.
Although the sheath of this invention is intended to protect the cable from moisture prior to the pulling of the cable into a pipe, the sheath is placed under the skid wire of the cable so that the sheath need not be removed as the cable is pulled into the pipe; but during installation of the cable it is necessary to perforate the sheath at spaced locations along'its length so that the perforations permit normal interchange of the pipe filling oil on load cycle changes.
Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.
BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION OF PREFERRED EMBODIMENT FIG. 1 is a diagrammatic showing of the method by which the cable of this invention is made. The cable is manufactured in cable-making apparatus which makes the cable in a conventional way and the cable is impregnated with oil or with dry nitrogen or other fluid for protecting the insulation from moisture. Cable 12 comes from the cable-making apparatus 10 and a sheath 34 is applied over the insulated cable at a sheath-applying station 14. An atmosphere of dry gas such as nitrogen is used to replace the air layer around the cable before and during the application of the sheath. This is done as soon as practical afier impregnation of the cable, and in any event before there has been any significant drainage of oil from the cable structure.
From the sheath-applying station 14, the cable 12 passes through a skid wire-applying station 16 which is preferably part of the same apparatus as applies the sheath and the finished cable 12] passes from the skid wire-applying station 16 to a reel 18 onwhich the cable is wound preparatory to shipping. The ends of the cable wrapped on the reel are capped to prevent loss of the impregnating fluid, this step being carried out in the conventional manner. When the reel 18 is shipped to the place of installation, the cable 12f is unreeled and fed into a pipe 20. As the cable unwinds, the outer sheath, under the skid wire, is perforated. This is-most conveniently done by gripping the sheath with a pair of pliers and tearing the sheath at spaced locations along its length. Such a perforation can be madefor every revolution of the reel as'it unwinds, or perforations can be made closer together, if desired. The purpose of the perforations is to permit normal interchange of pipe-filling oil on load cycle changes when the cable is in use. 1
ln actual practice, the jacket or sheath 34 is applied around the cable and sealed in the manner described in" US. Pat. 3,206,541 while in an atmosphere of drynitrogen.
FIG; 2 shows the construction of the preferred embodiment of the electrical cable of this invention. Referring to both FIGS. 2 and 4, the cable includes a conductor 24 which is here which maybe made of paper or a fibrous plastief'paper of polyethylene and containing no cellulose.
The tape 30 can be made of a material manufactured bydu- Pont and sold under the name Spunbond." Such a'tape is made of randomly arranged, highly dispersed, continuous-filament fibers of polymeric material bonded primarily at filament crossovers. It has a very low moisture content and does not hold moisture. It is sufficiently porous to permit the easy circulation of oil or other impregnating fluid through the insulating layer of the cable. The tape 30 is wound in successive layers with helical convolutions which preferably overlap adjacent convolutions.
The insulation 28 is covered by an insulation shielding layer 32. This shielding layer 32 is preferably a helically wound layer of tape or tapes. A primary shielding and moistureproof seal assembly 33 is applied after impregnation. This may be a metallized plastic tape in accordance with conventional practice.
The outer sheath 34 is applied over the shielding layer assembly 33 and is applied loosely enough so as to permit some longitudinal circulation of liquid or gas along the cable inside of the sheath 34. A skid wire 36 is applied over the sheath 34, the skid wire being applied in a conventional manner.
The sheath 34 is of a laminate construction, as best shown in FIGS. 3 and 4. It consists of a thin layer of metal foil 40, preferably aluminum, though copper and other metals can be used. The metal foil 40 is protected againstcorrosion on both sides. On its inner side it has a coating 42 of polyolefin, and preferably polyethylene containing reactive carboxyl groups which cause the polyethylene to chemically bond to the metal foil 40. On the other side'of the foil 40, the metal is protected by a coating 44 which has an inner portion 46 of the same polyethylene copolymer as is used for the coating 42; but an outer portion 48 of the coating 44 is preferably polyethylene homopolymer fused to the polyethylene portion 46 so as to form a homogenous coating with reactive groups limited to the part of the coating adjacent to the foil 40.
The sheath 34 is made from a tape having a width somewhat greater than the circumference of the shielding 32 (FIG. 2) and this sheath is applied longitudinally to the cable and folded around the cable with a longitudinally extending seam 50. The seam 50 is formed by first tuming" up the edges of the seam, then fusing the confronting faces of the turned-up edges together and subsequently folding the edges over, as shown in FIG. 4.
In the manufacture of cable with the sheath of this invenwhich'the coating is fonned, but'the reactive groups may extend somewhat less than half the distance from the foil 40 to the outside of the coating 44.
The thickness of the foil and the thickness of the coating can be varied; but it is important to have the sheath 34 made of material which can be torn easily for convenient perforation when inserting the cable into a pipe. The range of thickness of the foil should be between 0.5 and 1.5 mils. The range of thickness of the coatings 42 and should be between 3 and 7 mils.
in addition to the feature of providing for flow of oil or gas longitudinally between the cable and the inside of the sheath 34, the use of a-shea'th which is loose on the cable has the further advantage that it can be more easily gripped and torn by pliers when inserting the cable into the pipe. Such perforations are illustratedin FIG. 1 and designated by the reference character 57.
The preferred embodiment of the invention has been illustrated and described, and the invention is defined in the appended claims.
lclaimz- 1. An electrical cable assembly comprising a conductor surrounded by its completed application of insulation and comprising a power cable for use in a pipe under oil or gas pressure, a sheath for protecting the cable from moisture during "storage, shipping and installation, said sheath comprising a groups varies'in radial extent depending-upon the way in I being sealed by a bonding of the polyolefin on both sides of the seam. v
3. The electrical cable assembly described in claim 1 characterized by the sheath being a laminated tape of metal 'foil coated on both sides with polyethylene and wrapped longitudinally around the cable with a longitudinal scam, the opposite longitudinal edges of the tape forming tabs that have their inside faces confronting one another and bonded together over areas of said faces to seal the sheath, and the tabs lying generally along the circumferential extent of the insulation to maintain a substantially circular cross section of the cable assembly.
4; The electrical cable assembly described in claim 3 characterized by the metal of the foil being aluminum and the polyethylene being a copolymer of polyethylene with reactive carboxyl groups for tenacious adherence of the polyethylene to the aluminum.
5. The electrical cable assembly described in claim 1 characterized by the sheath being made of metal foil coated on both sides with adhesive polyethylene and with the adhesive polyethylene that is on the outside of the sheath coated with a polyethylene homopolymer.
6. The electrical cable assembly described in claim 5 characterized by the metal being aluminum and the adhesive polyethylene being a copolymer of polyethylene with reactive carboxyl groups.
7. The electrical cable assembly described in claim 6 characterized by the aluminum foil having a thickness of about 0.7 mils, the copolymer on the inside of the sheath having a thickness of about 5 mils, the copolymer on the outside of the sheath having a thickness of about 2 mils, and a layer of polyethylene homopolymer of about 3 mils thickness bonded to the copolymer on the outside of the sheath.