US3219501A

US3219501A - Manufacture of high-voltage cable

Info

Publication number: US3219501A
Application number: US205815A
Authority: US
Inventors: Victor F Volk
Original assignee: Anaconda Wire and Cable Co
Current assignee: Ericsson Inc
Priority date: 1961-05-16
Filing date: 1962-05-28
Publication date: 1965-11-23
Anticipated expiration: 1982-11-23

Description

Nov. 23, 1965 v. F. VOLK 3,219,501

MANUFACTURE OF HIGH-VOLTAGE CABLE Original Filed May 16. 1961 2 Q i F IG. I 'Q i 1 i0\ h l I4 21 I9 I6 |7 .|YgmL-2v3 24 A I3 `l l l l y u 12 Y" /f f d i Y Y g f/ y// xx 63 3 7| i 64 Eig; M I i... im gs Ei* 38 mm 52m 4n||i| 34 4| 39 49 5| 66 36 lil *j lil I!! 70 48 :EEEE-:Ei-s' g {g} A fl gg; :lil: se

54 82 83 F I G. 2

98 7 e4 88 99 97 86 a9 new 6L 1 Il Llll/l/ JI' l F l G 3 INVENTOR m VUM United States Patent i ice 3,219,501 Patented Nov. 23, 1965 3,219,501 MANUFACTURE F HGH-VOLTAGE CABLE Victor F. Volk, Hastings on Hudson, NSY., assigner, by

mesne assignments, to Anaconda Wire and Cable Company, a corporation of Delaware Original application May 16, 1961, Ser. No. 82,819, now Patent No. 3,080,446, dated Mar. 5, 1963. Divided and this application May 28, 1962, Ser. No. 205,815

2 Claims. (Cl. 15d- 53) My invention relates to pipe-type cable and particularly to the manufacture of pipe-type cable having the insu-lation thereof protected by a dielectric skid wire.

In the manufacture of high voltage cables of the type where electric conductors are wrapped with a plurality of layers of insulating material such as, for example, a plurality of paper tapes and subsequently pulled into a steel pipe which is then lled with an insulating fluid, such as hydrocarbon oil or pressurized nitrogen it is known to protect the cable cores during the pulling operation with spiral windings of bronze skid wires. These known skid wires are most conveniently formed in half-round sections with the hat side laid against the insulation and the rounded surface making low-friction contact with the inner walls of the pipe.

Cables of the type described in my application and in my application Serial Number 82,819, now U.S. Patent No. 3,080,446, of which the present application is a division are generally known as pipe-type cables and will be so styled in this application although it will be understood that my invention is not limited by the nature of the enclosure comprising the containing element of my cable. Most commonly, said containing element is an eight-inch steel pipe but it may be comprised of a nonmetallic material such as cement or plastic and may have various degrees of exibility.

The known construction of pipe-type cables having bronze skid Wires has proven to be satisfactory in almost all respects but has the one serious shortcoming that the currents induced in the skid wire may constitute a serious power loss accounting, in some instances, to as much as 2% of the power losses in the cable.

It is an object of my invention to provide a pipe-type cable wherein the skid wire is free from induced current losses.

It is another object of my invention to provide a pipetype cable in which the skid wire will remain wrapped around the insulated conductor in the event of an accidental severing of the skid wire during installation.

l have invented a high-voltage electric cable comprising a conductor, electrical insulation surrounding said conductor, and a dielectric skid wire applied spirally over the insulation. The outer surface of my skid wire is preferably in compression so that the skid wire grips the insulation and will not unwind from the insulation even if it should be broken at some point. The insulated conductor and the skid wire of my cable are surrounded by a tubular container, overall. In a preferred embodiment of my invention the skid wire is comprised of linear polyethylene and in another preferred embodiment it is comprised of nylon. My cable has an electric shield over the insulation and in a preferred embodiment a plurality of conducting means are spaced at intervals along the skid wire making electrical contact between the shield and the tubular container which in this embodiment is metallic. The conducting means will preferably extend for a complete turn of the skid wire so as to be certain to contact the container regardless of the position of rotation of the insulated conductor.

I have also invented a process for manufacturing a pipetype cable comprising the steps of insulating an electrical conductor, extruding a length of dielectric skid wire, forming the skid wire into a helix with an inside diameter not substantially larger than the diameter over the insulated conductor and wrapping the skid wire around the insulated wire while compressing the outer surface of the skid wire. Advantageously, the skid wire is annealed and cooled while in a helical form. When the skid wire is comprised of linear polyethylene, I prefer to anneal it at a temperature of 220-230" F.

A more thorough understanding of my invention will be obtained from a study of the appended drawing.

In the drawing:

F-IG. l is a lengthwise cut-away View of a cable made in accordance with my invention.

FIG. 2 is a schematic plan view of a process for forming the skid wire of my invention.

FIG. 3 is a schematic elevation of a process for applying the skid wire of my invention.

Referring now to FIG. 1:

A pipe-type cable designated generally at 10 has a conductor 11 wrapped with strand shielding 12 of semiconducting carbon black paper and insulated with a heavy wall 13 built up of a plurality of layers of insulating paper. The wall of insulation 13 is covered with a conducting shield 14 of copper tapes. The shield 14 is shown applied directly over the insulation 13 but there may be intermediate layers of carbon black tape or of impervious tapes applied for the purpose of preventing moisture from entering the insulation 13 during the processes of storing, shipping, and installing the cable. The conductor 11, strand shielding 12, insulation 13, shield 14, and any intermediate layers between the insulation 1-3 andthe .shield 14 constitute .a unit 16 that I shall hereinafter call an 4insulated conductor. Over the insu-lated conductor 16 I have applied two

skid wires

17, 18, 180 apart. Although I have chosen to apply two skid wires my invention is not restricted to this number. For example a single skid wire might be :applied at 1/2 the pitch that I have chosen for my two wires or a larger number such as three or four might be applied having a longer pitch.

The

skid wires

17, 18 have each a substantially flat surface 19 facing the insulated conductor 16 and a rounded outer surface 21. A steel pipe 22 constitutes a tubular container for the insulated conductor 16 covered by

skid wires

17, 18. Although for the sake of simplicity I have shown only one insulated conductor 16 in the pipe 22, three such insulated conductors are generally inclosed in the pipe, each of the conductors being identical to the insulated conductor 16 yand having skid wires applied identically to the

skid wires

17, 18. The pipe 22 is filled with an insulating iluid such as an insulating oil which can penetrate the insulation 13 or a gas such as nitrogen maintained under super-atmospheric pressure.

It is a feature of my invention that the

skid wires

17, 18 are comprised of a dielectric, or insulating material of which linear polyethylene is a preferred example. The purpose of the

skid wires

17, 18 is to protect the shield 14 .and the insulation 13 from the effects .of abrasion against the pipe 22 during installation. The method of installation -requires that the insulated conductor 16 lbe unwound from reels and dragged into the pipe 22 by means of a cable fastened to the conductor 11. Commonly three insulated conductors such as 'the one designated 16 .are pulled into the pipe 22 simultaneously from three diierent reels.

Prior to my invention bronze armor wires similar to my skid wires 17, 1S were wrapped around the core 16 to protect the insulated conductor during installation. These known armor wires had the disadvantages that they readily picked up induced electric currents from the conductor 11, that they added considerably to the weight of the insulated conductor 16, and that they had a relatively high coefficient of friction against the walls of the pipe 22 compared to the

skid wires

17, 18 of my invention. My skid

wires

17, 18 are formed of a tough, resinous material which will not transmit electric current, has high resistance to abrasion, and has a very low coefficient of friction. Polyethylene may be used for my

skid wires

17, 18 or the vinyl resin known as rigid polyvinyl chloride. However, I prefer to form my skid wires from linear polyethylene or from nylon. By linear polyethylene I refer to polyethylene resin with a pressure of about 0.941 or higher. This polyethylene is made by a low density process such as the Ziegler process and is extremely tough and abrasion resistant.

Nylon is a generic term for a family of polyamide resins characterized by high tensile strength, tou-ghness and abrasion resistance and by a low coefficient of friction. Both the linear polyethylene and nylon which I prefer for the .skid wires of my invention are well known materials of commerce for which I make no claims of invention as such.

Where the pipe 22 is a metallic pipe and it is considered desirable to ground the shield 14 periodically along the length of the cable, one or both of the

skid wires

17, 18 are wrapped at spaced intervals with

metal bands

23, 24. The bands 23, 2.4 are conveniently applied to the skid

wires

17, 18 at spaced intervals prior to Ithe application of the skid wires to the insulated conductor 16. Although I prefer to use

bands

23, 24 made fro-m bronze or stainless steel it will be understood that helical windings of metal wire may be substituted for the bands or the surface of the skid wire may be coated with conducting paint. One of the principal advantages of my invention resides in the high electrical resistance of the

dielectric skid wires

17, 18 as compared with the bronze arrnor wires known to prior ar-t. This high electrical resistance prevents induced electrical currents in the skid wires. It is important, therefore, that the conducting

bands

23, 24 should be applied only at spaced intervals `on the

skid wires

17, 18 and not from a continuous conducting path along the cable. By spacing my conducting means 23, 24 I effectively prevent any appreciable power losses from induced currents. The pipe-type cable constitutes relatively expensive engineering installation requiring considerable advance Aplanning and preparation for a Successful installation. If, in the course of pulling the insulated conductor 16 into the pipe 22, any accident were to befall the conductor 16 requiring the withdrawal of the conductor from the pipe and its return to the factory the financial losses would be great. Such an accident would be the severing of one or both of the

skid wires

17, 18 due to cutting edges on the inside of the pipe 22 or to foreign objects in the pipe. If the

skid wires

17, 18 were merely wrapped around the insulated conductor 16 the outside surface 21 of the

skid wires

17, 18 would be under tension and the inside surface 19 would be under compression in accordance with well known bending formulas and the

skid wires

17, 18 would spring away from the insulated conductor 16 at any point where a break should occur and would, indeed, become loose for the full length of the cable. It would be impossible to make repairs in the field where the

skid wires

17, 18 had become loosened over any long length of the cable. It should be further noted that the -

skid wires

17, 18 protect the cable not only during the process of pulling the insulated conductor 16 into the pipe 22 but also after the pipe has been lled with insulating iiuid and the cable energized the

skid wires

17, 18 are relied upon to protect the shield 14 and insulation 13 during the writhings that take place because of expansion in the conductor 11 caused by current loading. If the

skid wires

17, 18 were applied so as to produce tension in the outside surface 21 not only would the skid wires tend to spring open if they were broken but any sm-all cuts or abrasions of the surface would become focal points for tearing under the inliuence of the tension or stretch in the surface and such tearing might eventually extend through the entire thickness of the skid wire and result in a break. I have overcome the above mentioned obstacles by so applying the

skid wires

17, 18 that the outer surfaces are in compression rather than tension. This has the twofold advantage of making the skid wires more resistant to abrasive a-ction and of guaranteeing that they will remain snugly 4bound to the insulated conductor 16 even though a break may occur at some point. If a break should occur in a skid wire in the field it is a relatively simple matter to repair it so long as the skid wire does not spring open and the delay and expense of returning -the cable to the factory is avoided.

In order to produce compression rather than tension in the outer surface of my skid wires 17, 18 I first form them into a helix and anneal them in this form. This can best be understood by reference to FIG. 2. In FIG. 2 the skid wire 17 that has preferably been formed by extrusion into a half-round or similar section is paid from a reel 31 through vertical guide rolls 32 onto a polished mandrel 33. The mandrel 33 is mounted in a bearing 34 and driven through the shaft 36 by

spur gears

37, 38. The shaft 36 is, in turn, driven by a motor, not shown. As the polished mandrel 33 rotates, turns 39 of the skid wire 17 form around the mandrel and are urged to the right by the wedging action of block 41. As the turns 39 slide down the mandrel 33 they pass through an oven 42 which heats them to a temperature sutiicient to anneal the skid wire 17 but not sufiicient to cause distortion or to cause the turns 39 to adhere to each other or to the mandrel 33. In the case of linear polyethylene the length and temperature of the oven 42 are sufficient to raise the linear polyethylene skid wire to a temperature of 220-230" F. As the turns 39 of the skid wire 17 leave the oven 42 they pass under a cooling spray 43 of water from a spray head 44 fed by a water pipe 46 to a source of cooling water not shown. The cooling spray 43 is caught in a trough 47 drained by a pipe 48. In order to prevent the cooling water from cooling the mandrel 33 in the oven 42 an insert 49 of material having a low heat conductivity divides the mandrel 33 from a polished extension 51 which supports the turns 39 while they are in the cooling spray. The insert 49 has the same diameter as the

mandrels

33 and 51 and is preferably made of Teflon which is a good heat insulator, 4and also has a low coefficient of friction to permit sliding of the turns 39. As the turns 39 slide from the cool end of the mandrel 51 they are guided by a chute 52 through a traverse 53 tonto a reel 54. The reel 54 is driven by means of the

sprockets

56, 57 and chain 58 by the motor 59 powered through the slip rings 61, 62. The reel 54 is housed in a frame 63 driven through a sprocket 64, chain 66, sprocket 67, shaft 68, sprocket 6g, chain 76, and sprocket 71 to rotate at the same speed as the

mandrels

33, 51. The

mandrel

33, 49, 51 has a diameter less than the diameter of the insulated conductor 16 and is so chosen that when the

skid wires

17, 18 are wrapped around the insulated conductor 16 the outer surface 21 of the skid wires will be in compression and the tension on the inner surface 19 of the

skid wires

17, 18 will not be so great as to cause tearing at this surface. With a half-round skid wire 17 of 1/4 inch diameter, I prefer to use a mandrel diameter about of the insulated conductor diameter but I do not wish to be limited to this ratio since the optimum dimensions will be inuenced by the particular material of the skid wire, by its cross-sectional dimensions, and by the pitch at which the skid wire is applied to the insulated conductor.

The

skid wires

17, 18 are applied to the insulated conductor 16 by means of a planetary cabler 81 (FIG. 3) with the reel 54 mounted in a cradle 82 which remains horizontal or rotates slowly 4as desired, because of the planetary gear 83 rotated through the idler 84 against a xed gear 86 by the mounting plate 87. The size of the fixed gear 86 can be varied in relation to the planetary gear 83 to compensate in known manner for the difference between the diameter of the insulated conductor 16 and the coil 17. The skid Wire 18 is shown similarly mounted on the cabler 81. A rotating die 88 is driven through the sprocket 89, chain 91, sprocket 92, shaft 93, sprocket 94, chain 96 and sprocket 97 (which is itself driven by a chain and motor not shown) at the same speed as the mounting plate 87` The die 88 has helical grooves 98, 99 which guide the

skid wires

17, 18 in helical form around the insulated conductor 16. Because of the grooves 98, 99 in the die 8S the skid wires 17, 1S are fir ly gripped during the wrapping operation and the necessary force is easily applied to increase the diameter of the helix and put the outer surface of the skid wires in compression.

Iclaim:

1. In the process of manufacturing a pipe-type cable comprising an insulated conductor having a predetermined diameter, the steps of:

(A) extruding a length of dielectric skid wire,

(B) continuously wrapping said skid wire around a mandrel to form a helix having a diameter smaller than the diameter of said conductor,

(C) continuously Sliding said helix from said mandrel,

(D) while on said mandrel continuously annealing and, while on said mandrel, subsequently cooling said helix,

(E) and then immediately continuously taking up a length of the helixed wire on a reel, said length being great compared to the length of said mandrel, and

(F) wrapping said skid wire around the insulated con- `ductor while compressing the outer surface of said skid wire.

2. In the process of manufacturing a pipe-type cable comprising an insulated conductor having a predetermined diameter, the steps of:

(A) extruding a length of linear polyethylene skid w1re,

(C) continuously sliding said helix from said mandrel,

(D) While on said mandrel, continuously annealing said helix at a temperature of 220-230 F. and, While on said mandrel, subsequently cooling said helix,

(P) wrapping said skid wire around the insulated conductor While compressing the outer Surface of said skid wire.

References Cited by the Examiner UNITED STATES PATENTS 8/ 1947 Roberts 156-144 XR 8/1947 Morgan.

2,628,214 2/1953 Pinkney etal.

3,091,261 5/1963 Waddell 156-143 XR EARL M. BERGERT, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,219,501 November 23, 1965 Victor P. Volk It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

In the heading to the drawing, line 3, and in the heading to the printed specification, line 6, for "May 16, 1961",

each occurrence, read Jan. 16, 1961 column 3, line 10, for "pressure" read density line 11, for "density" read pressure line 39, for "from" read form Signed and sealed this 2nd day of August 1966 (SEAL) Attest:

ERNEST W. SW'IDER EDWARD I. BRENNER Attesting Officer Y Commissioner of Patents

Claims

1. IN THE PROCESS OF MANUFACTURING A PIP-TYPE CABLE COMPRISING AN INSULATED CONDUCTOR HAVING A PREDETERMINED DIAMETER, THE STEPS OF: (A) EXTRUDING A LENGTH OF DIELECTRIC SKID WIRE, (B) CONTINUOUSLY WRAPPING SAID SKID WIRE AROUND A MANDREL TO FORM A HELIX HAVING A DIAMETER SMALLER THAN THE DIAMETER OF SAID CONDUCTOR, (C) CONTINUOUSLY SLIDING SAID HELIX FROM SAID MANDREL, (D) WHILE ON SAID MANDREL CONTINUOUSLY ANNEALING AND, WHILE ON SAID MANDREL, SUBSEQUENTLY COOLING SAID HELIX, (E) AND THEN IMMEDIATELY CONTINUOUSLY TAKING UP A LENGTH OF THE HELIXED WIRE ON A REEL, SAID LENGTH BEING GREAT COMPARED TO THE LENGTH OF SAID MANDREL, AND (F) WRAPPING SAID SKID WIRE AROUND THE INSULATED CONDUCTOR WHILE COMPRESSING THE OUTER SURFACE OF SAID SKID WIRE.