US2118629A

US2118629A - Electric cable

Info

Publication number: US2118629A
Application number: US58475A
Authority: US
Inventors: Richard C Waldron
Original assignee: Okonite Co
Current assignee: Okonite Co
Priority date: 1936-01-10
Filing date: 1936-01-10
Publication date: 1938-05-24
Anticipated expiration: 1955-05-24

Description

May 24, 1938. R. c. WALDRON 2,118,629

ELECTRIC CABLE I Filed Jan. 10, 1936 INVENTOR.

@lldfar' 1" e/emenf e/em e17 ATTORNEYS Patented May 24, 1938 1 PATENT OFFICE ELECTRIC CABLE Richard C. Waldron, Clifton, N. J., assignor to The Okonite Company, Passaic, N. J., a corporation of New Jersey Application January 10, 1936, Serial No. 58,475

6 Claims.

This invention is directed to an improvement in electric cables and is primarily directed to providing an electric cable construction which is particularly well adapted for vertical suspension in long lengths.

The increasing use of electric cables in long lengths for vertical suspension, as in exploration of oil wells, for example, has resulted in a demand for a conductor which will elongate and contract without breaking. The usual conductor cannot be used as stretching so elongates the copper conductor permanently that when the tension is removed and the cable contracts buckling ot the conductor results. Repetition of this action results in breaking or the conductor. This elongation cannot be overcome with the usual types of steel armor employed, inasmuch as the conductor is small and of little strength as compared with the armor, so that it must elongate and contract with the armor.

The present invention provides a construction in which the conductor will stretch and contract with the cable without deformation. My copending application Serial No. 59,204, filed January 15, 1936, discloses a construction in which stretching of the conductor is so controlled that the cable can be elongated and returned to its original length without buckling and breaking of the conductor.

In the accompanying drawing:

Fig. 1 is a part sectional view of a cable embodying my invention;

Fig. 2 is a cross section of the cable of Fig. 1;

Figs. 3 and 4 are cross-sectional views illus-. trating the relative positions of the cable conductor and core at diiierent stages of elongation of the cable;

Fig. 5 shows one strand of the unstretched cable conductor about a core of extensible substantially incompressible material;

Fig. 5A is an end view of the structure of Fig. 5;

Fig. 5B is a development of a cylinder whose diameter is the pitch diameter of the strand of Fig. 5 and whose length is the length of lay of the strand of Fig. 5;

Fig. 6 shows the core and strand of Fig. 5 with the cable in partially stretched condition;

Fig. 6A is an end view of Fig. 6;

. Fig. 6B is a development of a cylinder whose diameter is the pitch diameter of the strand of- Fig. 6 and whose length is the length of lay of the strand'of Fig. 6;

Fig. '7 shows the core and strand of Fig. 5 with the core fully stretched;

Fig. 7A is an end view of Fig. 7;

Fig. 7B is a. development of a cylinder whose diameter is the pitch diameter of the strand of Fig. 7 and whose length is the length of lay of the strand of Fig. 7;

Fig. 8 shows one type of conductor which may 5 be employed in the practice of my invention;

Fig. 9 shows another type of conductor; and Fig. 10 shows still another type;

Figs. 11 and. 12 are cross sectional views 'of modified embodiments ofmy invention, employ- 10 ing several conductors about a common center or core.

Referring to the drawing in detail, and first of all to the construction illustrated in Figs. 1 to 73 inclusive. l designates the core of my im- 15 proved cable. This core is a pliable, extensible, substantially incompressible material such as rubber, or a fibrous material such as silk or cotton threads, for example, twisted together so as to be sufliciently incompressible for my purpose 20 and yet at the same time extensible and pliable.

About this extensible, substantially incompressible core I apply the conductor 2. This conductor, in this embodiment of my invention, is composed of copper strands helically applied in parallel relation in a predetermined lay about the incompressible extensible core as will be brought out in detail hereinafter.

Directly over the conductor 2 I apply insulation 3, which may be the usual rubber or rubber compound insulation commonly employed in electric cable work.

About the insulation 3 I apply a fabric covering I which may be saturated with oil and moisture impervious material, such as Harvel, an acid condensation product made from the oil obtained from cashew nut shells.

5 designates a supporting armor consisting of stranded steel wire. These steel wires are the same as commonly employed for steel wire rope 'and may be laid up in any of the methods commonto wire rope manufacture.

As pointed out at the outset of this description, the conductor 2 has little strength as compared .with the armor 5 and unless means are provided to prevent it, the conductor must elongate and contract with stretching of the cable with the. result that the conductor buckles and in a short time breaks.

I propose to overcome this defect by applying the conductor in a predetermined lay about an extensible, substantially incompressible core.

Referring now more particularly to Figs. 5 through 73, Figs. 5 and 5A show the initial position of each conductor strand;

ill)

In Fi s. 5 and 5A--initial position of each con ductor strand:

do: the diameter of the core l d: diameter of each strand of the conduc= tor 2 l w iii= pitch diameter of each strand of the con" ductor do-l-d L: length of lay of each strand of the con ductor a: length of each conductor strand for one complete turn about the core l n Figs. 6 and 6A-partially stretched conm tlon oi the strands of the conductor 4:

ds'=dia3neter of core .l under the assumed conditions ill": pitch diameter of each strand oi the conductor 2 under assumed partially stretched condition 3: percentage elongation (in decimal) for which the cable is designed -igs. 7 and 7A the conductor stretched to for which it is designed:

lianieter of core i conditions D"=pitch diameter of each strand of'the conductor 2 under the assumed conditions The conductor 2 is so designed that at the ini tial and extended positions it lies snugly on the core l, as illustrated in Figs. 5A and in. intermediate these positions the conductor is out of contact with the core, as illustrated in on. Fig. 3 illustrates an intermediate condition corresponding to Fig. 6A, and Fig. 4 a condition corre sponding to Fig. 7A.

These conditions exist only for a definite lay oi the conductor as determined by the formula under the assumed The above formula is directly concerned with cables having a rubber core, such a core being ideal in that while it is pliable and extensible it is substantially incompressible. ,As above indictated iibrous cores may be employed with good results, oiierlng sufficient support for the conductor, so far as incompressibility is concerned, and elongating and contracting sumciently without breaking.

However, metal cores eithersolid or stranded may be employed if desired for small elongations.

For small values of c the following -formula may be used:

o 'i' o In designing a cable for a given service and knowing the diameter of the conductor strands, the initial size of the core of the cable and elongation desired, the lay of the conductor strands about the core is determined by Formula (1) given above for large values of s or elongation, or Formula (2) for small values of s. Under those conditions and with the, conductor laid about the core in accordance with Formula (1) of Formula (2), initially the conductor strands are in contact with the core as shown in. Fig. 5A, for

instance, and on initial stretching of the cable the core is reduced in diameter faster than the pitch diameter of the conductor strands so that the core moves away from the conductor strands, as illustrated in Figs. 3 and 6A; while at maximum elongation for which the cable is designed which of course should not exceed themaximum elongation which the core will withstand without such as hemp for example.

Let Dx=pitch diameter c=strand l ngth which is throughout s=elongation for which cable is designed D=original pitch diamet L=lay determined from Then constant ELISG core. .30 can readily be seen that it cos, lated by the first equation is smalle culated by the second, stretchim or or distortion of the core must talre place. It is to be understood that the conduct relation as illustrated in Fig. l; or the conductor. may be in the form or a group of strands previ-.

ously twisted together as illustrated at 8a in Fig. 8; or the conductor may be in the form of tape as illustrated at 911 in Fig. 9; or a woven or braided tape as illustrated at 100 in ill.

When the conductor is in the form of a tape or braid as illustrated at 9?) and illc the thickness of the same is used in calculating the lay from Formula (1) or Formula.(2).

The above description has been made with rel.- erence t'o cables with a single insulated conductor. "Where a cable is desired composed of a plurality of insulated conductors I may employ a construction such as illustrated'in Fig. 11 wherein a pin rality oi armored cables iii are laid up about a center i i. This center may be of any of the well known types of centers used in steel wire rope, in this embodiment of my invention; each cable ill is a duplicate of the construction illustrated in Figs. 1 and 2. It is to be understood that the supporting armor wires need not necessarily be made up of strands as shown but may be solid wire.

A further modification of a multi-conduc'tor cable embodying my invention is illustrated in Fig. 12 where two cables [2 similar to the cable this embodiment of my invention the supporting armor wires it have been shown solid.

It will be seen from all of the foregoing that the present invention provides an electric cable construction in which the conductor is laid up about a substantially. incompressible, extensible core with such a lay that upon initial elongation the outside diameter of the core decreases faster than the inside diameter of the conductor helix, so that the core moves away from the conductor, while on continued elongation a point will be reached where the inside diameter of the conductor helix decreases faster than the outside diameter of the core to cause the conductor to reengage the core on maximum elongation which of course should not exceed the breaking point of the core.

To show the superiority of cables constructed in accordance with my invention over cables constructed according to prior practice, I have made a number of comparative tests using a single conductor cable. These tests in all cases essentially involved subjecting a sample of freely suspended cable to a two ton load so that the cable elongates. The tension on the cable is then relieved permitting the cable to return to its original position.

The usual type of conductor made up of nineteen strands of wire concentrically stranded broke after seventy-,eightminutes under this test. The speed of the test was approximately one cycle per minute, corresponding to elongating and contracting the cable seventy-eight times. The conductor failed due to breaking of the copper from flexing, and kinks were found approximately every six inches throughout the test length.

Another test was run employing a cable having the same total copper area as the cable first mentioned, but stranded in what is commonly known as rope stranding, that is, seven bunches 01 wire, each consisting of seven individual wires were stranded together. After thirty hours this cable failed due to kinking of the conductor, and kinks were found every four to six inches throughout the test length.

, The same test was then run on the cable of Fig. 1 of my application, employing an extensible incompressible core and a conductor of five wires stranded and applied about the core with the lay I have hereinabove described. This cable withstood a total of two'hundred and ten hours without the conductor breaking, the steel supporting wires shown at 5 in Fig. 1 breaking due to fat gue on the steel. This test shows thatmy improved cable is at least seven times as good as the old structures, and as a matter of fact at the end oi. the two hundred and ten hours the conductor showed no signs 01' kinking nor of failure.

What I claim is:-

1. An extensible electric cable comprising in combination a core of extensible, substantially incompressible material, a conductor helically applied about and in contact with said core with such a lay that initial elongation of the cable will tend to bring the core out of contact with the conductor so that maximum extension of the cable is permitted without permanent distortion of the conductor, attempted further elongation causing the conductor to re-engage the surface of said core and to become permanently distorted.

2. An electric cable comprising in combination a core of extensible, substantially incompressible material, a conductor helically applied about said core and in contact therewith, the lay of said conductor being such that upon initial elongation of the cable the outside diameter of the core will decrease faster than the inside diameter of the conductor helix, further elongation of the cable eventually causing the conductor helix to decrease in diameter faster than the outside diameter of the core finally to re-engage the core, attempted further elongation of the cable causing the conductor to become permanently distorted.

3. An extensible electric cable comprising in combination a core of extensible, substantially incompressible material, a conductor helically applied about and in contact with said core with such a lay that extension of the cable from zero extension to maximum extension .is permitted without permanent distortion of the conductor, attempted further elongation causing the conductor to engage the surface of said incompressible core and to become permanently distorted, insulation about the conductor and supporting wires about said insulation.

4. A multi-conductor electric cable comprising in combination a plurality of single conductor cables disposed about a central core, each single conductor cable comprisingsa core of extensible, substantially incompressible material and a conductor helically applied about said core and in contact therewith with such a lay that extension of the cable from zero to maximum extension is permitted without permanent distortion of the conductor, attempted further elongation of the cable causing the conductor to engage the core and to become permanently distorted, and armor supporting wire for each cable.

5. A multi-conductor cable comprising in combination a plurality of single conductor cables twisted together and each composed of a core of extensible, substantially incompressible material, a conductor helically applied about the core with such a lay that extension of the cable from zero extension to maximum extension is permitted without permanent distortion of the conductor, attempted further elongation causing the conductor to engage the surface of said incompressible core andto become permanently distorted, a plurality of similar single conductor cables laid up about said first mentioned cables, each 01 the last mentioned cables being enclosed in supporting wires.

6. An extensible electric cable comprising in combination a core ofextensible, substantially incompressible material, a conductor helically applied about and in contact with said core with such a lay that initial elongation of the cable will tend to bring the core out oi. contact with the conductor so that extension of the cable up to the breaking point of the core is permitted without permanent distortion of the conductor, attempted further elongation causing the conductor to reengage the surface of said core and to become permanently distorted.

RICHARD C. WAL'DRON.