US1995356A - Submarine communication conductor - Google Patents

Description

Mgrch 26, 1935. v E G 1. 95356 SUBIARINE COMMUNICATION CONDUCTOR 'Filed March 19, 1929 wvmrm M E [:00

TORWEY Patented Mar. 26, 1935 UNITED STATES OMMUNICATION vSUBMZARIINE C CONDUCTOR Victor E. Legg, East Orange, N J., assignor to Bell Telephone Laboratories,

Incorporated,

New York, N. Y., a corporation ofNew York Application March 19, 1929, Serial No. 348,175

Claims.

This invention relates to high frequency submarine cable conductors, more especially designed for transmission of telephony over relatively great distances. a

A fundamental difiiculty in long distance submarine cable telephony is the increase of effective resistance of the cable conductor (or conductors in multiple core cables) at frequencies above the range normally used for long distance submarine telegraph service andmore especially at the upper end of the telephone frequency range around- 2000 cycles per second. For carrier frequencies above 2000 cycles the difficulty is still greater.

The ordinary stranded conductor consisting of a central copper core with several fiat strands laid thereabout has a direct. current conductivity about 97% of that'of solid copper. In such a conductor or in a' solid conduction-oi #4 size (5.189 millimeters in diameter) the resistance is increased about 17.5% at 2000 cycles; This causes a large increase in the attenuation of the cable at such frequencies and is one of the limiting factors in long distance submarine cable telephone communication.

It has usually been assumed that a braided or stranded conductor composed of fine wires is not suitable for the conductor in such a cable because of its lack of compactness by virtue of which a given amount of copper has a diameter considerably increased as compared to the diameter of a solid or stranded conductor of the 'ordinary form containing the same amount of copper, which necessitates the use of an increased amount of insulation and an amount of armor material. Also the void spaces in such a conductor cause. considerable difficulty with the insulating material owing to the fact that if a cable having such void spaces were laid the outside pressure would tend to deform the structure until the void spaces were filled up.

In'this specification the term reentrant type conductor" will be used to include all conductors consisting of a number of small strands, braided, twisted or otherwise so laid together that each conductor passes at frequent and regular intervals from the interior to the surface of the conductor. A conductor in which-each strand passes regularly and uniformly from. the center to the external surface will be termed symmetrical conductor of the reentrant type.

- Experiments have indicated that above a certain frequency (depending upon the size of the conductor) the alternating current resistance loss will be less in a braided or stranded conincreased ductor than in a solid conductor of the same physical diameter. For a large conductor such as would be used in a relatively long submarine telephone cable this frequency is about 2500 to 3000 cycles per second. Consequently, a fea- 5 ture of this invention comprises the use of reentrant type braided .or' stranded conductors (sometimes known as Litzendraht for submarine carrier frequency cables.

However, also at lower frequencies there may 10 be obtained important advantages in the use of reentrant type conductors.

In accordance with another'feature of the present invention the void spaces in a conductor of the reentrant type, are reduced. Experi- '15 ments have indicated that the voids in reentrant type conductors, in which the'separate strands are enameled, may be reduced to such an extent that the conductor has a direct current conduc-. tivity equal to 90% of that of solid copper of the same physical diameter and in the .case of insulation with metallic oxides still better results may be obtained. I

In the case of an ordinary telephone or high frequency cable conductor which is not loaded, the insulation between the strands may consist of a layer or coating on the individual strands of enamel, cellulose acetate or other suitablematerial.

In the case of a loaded conductor the insulation of each strand may be of a heat resistant material. Alternatively, however, the copper employed'may be of a recently developed kind which is deoxidized and does not become reducedand embrittled in the presence of reducing agents at high temperature in which case'the'insulation need be only sufficiently heat resistant to remain an insulator and may be applied with an organic binder or other material capable of producing reducing gases. 40

A feature of the invention resides in the methods by which a reduction of the voids in a reentrant type conductor is accomplished.

Another feature of the invention relates to the manner in which the remaining void spaces are rendered innocuous and relatively unobjectionable.

When refractory insulation upon the individual strands is to be employed it may consist of oxides of copper upon the surface of the strands with or without the application of powdered' talc or alundum (A1203) or of one or a plurality of other refractory oxides or materials. The alundum may be applied in a manner already known in the publishedpatent literature by binding it with glycerol which is boiledofi, after the conductor is assembled, by a preliminary heat treatment at about 400 .to 500 C. When-deoxidized copper is employed the glycerol need not be boiled ofi. t r

A particular method of applying a metallic oxide-other than copper is toplate the strands with an adherent metal capable of being chemically reduced to an'adherent'oxide such, for example, as chromium and oxidizing the metal to produce the oxide, 'for example, in this case,

' chromium oxide.- Another method, which is preferred, is to coat the conductors with copper oxideby ordinary oxidation methods. 7

' It is also withinthe scope of the invention to.

plate highly resistive materials directly upon the strands.

Thereduction of voids in the conductor may.

be accomplished by drawing, swaging, rollingbr by a combination of these methods.

Suitable results may be obtained by drawing the conductonthrough a series-of devices each consisting of grooved opposing .wheels free to ro= tate, each successive device having a space between the rollers smaller tha the preceding and that of the final being equal othe diameter to which the conductor is to be reduced.

An unloaded conductor for carrier current cables maybe e'm'ployed without the application.

of mechanical force to reduce the diameter. In such case, the conductor is impregnated with a liquid 4 bituminous material, Chattertons' com pound or melted rubber, to fill up the void spaces.

This may be accomplished by running the iconductor through a vacuum and thence directly into an extruding machine containing such filling material under pressure.

If the conductor is to be it will ordinarily be reduced in diameter-by mechanical force suitably applied and then the magnetic material will be applied. After this the loadedlcdnductor will be heat treated in one of the several manners well known in the art.. In such a case, of course, only a conductor having heat resistant insulation material on the strands may. be employed.- In the case-of a loaded conductor the impregnating material is applied in such a manner as to function also as a pressure equalizing substance for the magnetic material and a'suitable thin layer a few thousandthsof an inch thick isleft upon the outer surface of the magnetic material for this purpose.

Gutta percha or similar insulating material is applied in the usualmanner to form a core which may be used in a single conductor cable or in a twin or other multiple conductor cable.-

In a particular case enameled deoxidized #16 -(B 8; S gauge) copper conductors were doubled,

twisted, redoubledand retwisted until a conductor of 16 strands was formed; This-conductor was run through a swaging machine. The copper content, as indicated by the direct current resistance was about 90% that of solid copper as compared to about 97% in the case of a stranded The increased conductor of the ordinary type. resistance, however, is more than counterbalanced. at a relatively low' frequency. another case 27- strands of #16 enameled wire were braided. This conductor was drawn througha die which reduced it to a cross-section of 300-mils and a length swaged to 239 mils formeasurements. As compared with solid copper this conductor had 87% copper content. Alternating current resistance measurementsindicated that the inefficiency due to the increased direct current magnetically loaded,.

resistance would be counteracted above a relatively low frequency.

Another way of preparing a symmetrical conductor of the reentrant type? is to twist together three small wires and. then twist together three strands of the resultant wires and continue twist-- ing three by three until a 2'7- or Sil -strand conductor is formed. In such a conductor each strand occupies thesame relatively distant position measured from the central conductor as ,any other strand.

The invention is not limited in application to telephony or high carrier frequencies but may be employed for telegraph cables operating on frequencies in the voice range or higher. The unloaded reentrant type conductor may be'employed in a coil loaded cable.'.

including a ing the various .parts'cut away for inspection of I the next innerportion.

None of the figures are intendedto be drawn to show relative dimensions. V In Fig. 1 the core comprises a conductor having strands 1 with an enamel coating 4a. each pas'singfrom the central to the external portion of the conductor, a bituminous filler 2,-between the strands and a layer 3 of insulation.

Fig.2 is an attempt to-show the irregular crosssectional shapes taken ata' particular point by the strands 1 under the influence of a'swaging process. The layer of oxide 4 appears disproportionately thick. -Draft ing technique" doesnot make it feasible to show in the various figures the semi-liquid fillerbetween the strands or the spaces it occupies, except around. the exterior of the strands at 2. Insulation 3 is of known type such as guttapercha.

In Figs. 3 'and'4, in addition to the strands l of the swaged co'nductonfiller 2, coating 4 and insulation 3, the loading tape 5 is' shown surrounded by an excess portion 6 of-filler material functioning as a pressure equalizing substance.

What is claimed is:

1. The method of manufacturing amany stranded conductor of the reentrant type which comprises applying. a metallic oxide to the strands, laying the strands together by a braiding or twisting operation which causes each strand to be reentrant and reducing the void spaces by i the application of mechanical force of the type including rolling, swaging and, drawing.

laying a plurality of said strands together to form composite strands, and spirally laying a plurality of said'composite strands togethergand thereafter reducing-the void spaces. in the, resulting structure by the application of mechanical force of the type including rolling, swaging anddrawing.

3. A deep having a-principal conductor which is a-many stranded conductor of the reentrant type having its voidspaces' filled with impregnating material in which the reentrant type? conductor is sea high frequency signali cable 2. The method of manufacturing a conductor h for a deep sea. signalingfcable which comprises lightly insulating a plurality of strands, spirally of reduced diameter as by swaging and is composed of insulated strands, the whole being impregnated with material .01 the class including Chattertons compound, bitumen and melted rubber to completely fill the residual voids and insulated with thermoplastic material.

4. A deep sea signaling cable having a principal conductor which is a many stranded'eonductor of thereentrant type forcib1y compressed and having its void spaces filled with impregnating material having between the strands an insulating material which is'heat-resistant and a magnetic pose of increasing the inductance thereof.

5. A deep sea signaling cable having a principal conductor which is a many stranded conductor of the reentrant type having its'void spaces filled with impregnating material in which the individual strands forming the conductor lie compactly together and have generally polygonal cross-sections whereby the void spaces are reduced to a minimum.

VICTOR E. LEGG.

material applied about the conductor for the pur-

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