US1700476A - Submarine signaling cable - Google Patents

Description

Jan. 29,. 1929. 1,700,476

J. J. GILBERT SUBMARI NE S I GNALNG CABLE Original Filed Feb. 27, 1926 lliiis invention relates to sulnnziiiiie signeh ing.

in olii ect of the invention is to inciezise the timisinission etliciency of submarine signalcables.

i, is also ein object of the invention to i'e duce the increment of effective ieSiStnnce o'j e s. dnnnriiic signaling celole due to the presoit tei'ede tape employed to protect insnletion et the cable 'frein ravages et, teiedo is also en object oi 'the invention to pio vide nn ei'licient ifeturn path oi sigi'ieiliiip; cui'- ients of comparatively high frequencies in a eulnnei'ine cable.

eeen found that when n celile is pio y t vicedivith both teredo tape :incl continuous lending, the .leading hei/inn" the oifin of one ei inoie helical inenieeis high permeability ticncv is occasione/(tbv reason of the feet V; n coneiueieble increment in the effective the cable can' arise :troni the fes in the terede tape, theselosses tesult- "cents, which foi* convenience in y currents, flowing in the tape e of elec'tieinotive 'foi'ces set up iij/ the varying; magnetic fiul ending nieteiinl by signaling` ne flowing in the cable. in accordance this invention, this increment et effeci'esictnnce is reduced by employing; n

oi .like protective layer having high i'cf: i i `vitvl lwi, in accordance 'with tine 1nvcul'ion, this -i cicincnt of effective resistance l luv o; the tape, as for exemple, liv incfiensine` wid `i, and insulating' adjacent tui-ne of the tzije l'i'e i cncli othci. lllheie the nuling involi'ci; fiequencies Suiicientlv high to ien deiY v:tsillic return path foi the sign i :Ulviseolc, in accordance with 'the inventioA there is in vided such n' return nath comprisf helical conductors having' high conducai nv ind iizivine n` large Ditch or length of putin to* l eiv'n'iegnetizing forces, n innteiinl loss el" 'eiluced by increasing the pitch o1' length of i' .une 2, 1928.

lav. 1in accordance with the invention 'these return condnctois may lie Within the helix of the steel ninioi' 'vites for the celole, Wherelov these etnici' wines will retain the return conductors on the cable and thus enable their pitch to lie inzide greater than would ethel Wise lie pincticnlile, This long ley tenes to- Wei'd reduction et' the resistance of the return any ,given annount ot' materiel in that pn n. oiVA tends; to enable reduction in the Weight oit the material in the return path, 'for any given iesistunce of the path. n the ense of cable loaded mentioned above, this long` ley also tends te reduce loseee due to edd;Y currents in the ietuin path, these eddy currents insulting ioni electionietive forces set up in the material of the return path liv the vary ng n'iegnetic flux created in the loading; materiel ley the signaling current.

@thee objects und ndvcntnges of the in vention Will lie :apparent 'frein the following tion et' the cable o1' 1 e n dimvn to smaller l tiie cable comprises n centi-eil conn loading' Wire oitnpe i surrounding; the conductor 5, lever of nutte perchaoi like insulation preferably nvi n` Wall tliiciniess oi P oni one to seveiel millimeters ne conducto? 5 and loading infil i the inlielicei Steel urine? jute and suii'eundine y c1 ne coie li constituted luy Sulnftion El, vviief; cnil? s i3 niej; lie individunlfiv c tape 19 and 'e compound.

npose ci niotec t f educing eddy currents es es xviii lieneinted eutheifennittei,

x Thev construction and advantages-of such -a -loaded cable conductor are described in'U., S.

patents to E. Buckley 1,586,874, June 1, 192e, e. W. itimen 1,585,884, June 1, 192e,

and O. E. `Buckley 1,%8'6,863, March 18, 192i.- The teredo tape f1", for protecting the inf sulation 9 from/the attacks of the' teredov worm,`is a'he'lical wrapping surrounding a portion r,of/'the core that lies in neighborhoods Wherefthe teredo Worm is fou-nd. The length of/the core that is supplied'with'teredo tape consists of thelportion of the cable that lies in Water of a depth `less than about 10() fathoms. It is found that the teredo Worin does not ordinarily operate in depths greater than this. The teredotape is Wound on the 'core with suicient'overlap of the adjacent turns to insure against gaps in the metallic layer' l ness-aluminum) formed by the tape. For reasons explained hereinafter, this tape ispreferably of material lhaving high resistivity, 4for example, nichrome, Driver-Harris 193 alloy (nickeliron-chiomium), or Therlo (copper-manga- These alloys have resis tivity of 5 to 10 times that of brass, and also resist corrosion, so that they are suitable for Ause, in'sea-water. The teredo tape maybe of the ,order of .004 thick, and, for reasons explained hereinaftenits pitch or length of lay is preferably.,substantially as great as it can be made without undue-risk of injury to the insulating material of the core. In general the Width of the teredo tape may be three times the diameter of the core, so that for a core about 1/2 inch in diameter, the Width of l'the tape is preferably about 1-1/2 inches.

a tape or Wire of magnetic material Wound helically on the conductor as described above, the lines of magnetic induction produced by current in the conductor tend to follow the helical path afforded bythe tape or wire, this tendency being' greater the higher the permeability of the loading material. 'lhat is, the lines of magnetic induction are not single loops around the conductor, but have the forni of a helix which takes a large number of turns around the conductor in one turn of the loadingtape before crossing an air gap to an adjacent turn ofthe loading tape, the pitch of the helix of the lines of induction being slightly less than the pitch of the tape, so that a line of induction follows the tape for, say, twenty turns around the conductor,

.then reaches thev rear edge of the tape and jumps backward across the small air ,gap to the adjacent turn and continues folowing the tape in the original direction and 7o sense for another twenty turns, then again of the cableto the other and if the cable carried a Steady, direct current and Awere not subject to theeffect ofthe eaitths iield, the nlines of induction lWould-be continuous from one .end of the cable tothe other.) There exists, therefore, in the -loading'material a component of the magnetic induction parallel to the axis of the conductor, which may be termed the longitudinalor axial component /of the induction, this component `being approximately proportional vto the permeability and to thev thickness of the loading material. It is also dependent upon .the angle of lay of the loading tape or-Wire.. All other conditions being the saine, the component of magnetic induction parallel to the axis of the conductor Will be greater theV greater the Width conductor, which is proportional tol the time rate ofchange of the axial or longitudiv nal component of magnetic induction. This electromotive force causes a current to flow in the tape, and the energylosses resulting from this current ductor. In other Words, the losses in the .teredo tape give rise to an increment in the effective resistance of the cable conductor.

" This resistance increment can bel shown to iiovv arel taken vfrom the energy of the signaling current in the conv los be proportional to the square of the frequency of the sinusoidal current, and to vary inversely With the thickness and resistivity of the teredo'itape, and to fall ofiI rapidly as the pitch or lay of the teredo tape is increased,

provided that .its adjacent turns are insulated.v

It has been found from measurements of actual Wire and tape loaded conductors for submarine cables that at a frequency 0f 60 cycles per second, the increase ineffective resistance due to ordinary brassteredo tape may amount to .1 ohm per mile. In the case ofa fairly heavy telegraph cable, the effect of this resistance incren'ient is to increase the attenuation .constantofl the taped sections by as unich as 3%. For cables of lighter weight than this, the effect 0n the attenua* tion constant will be less, since the resistance of the central conductor is higher. The effect is not very serious in the case of a long telegraph cable, since the frequency of signal-l ing is low and ordinarily the taped portion of the cable is comparatively only a small LAL fraction of the total cable length. For a telea large fraction of its length, theeffect is more serious. -In either case'the magnitude of the resistance increment due to the electromotive-forces induced in the teredo tape, can be reduced by using in place of the customary brass tape, as described above.`suit able materiall such as nichrome, Driver-Harris 193 alloy, or Therlo. As noted above, these alloys have resistivity of 5 to 10 times that of brass, and the currents dueto the electromotive forces set up in the teredo tape are proportionately less, as are also the` corresponding values of resistance ,increment in the cable conductor.

It is also of advantageto increase the lay of the teredo tape, by increasing its width to, for instance, a value of the order of three times the diameter of thecore, and to insulate adjacent turns of the tape, especially where they overlap. This insulation` she vn at 12, Fig. 3, may be effected by providingl the teredo tape with an insulating cover of oxide, for example, or by applying,T to it an insulating compound at the time it is being served on the core. In thisway the resistance aiforded by the tape to the inducing'electromotive force is increased, since the current is caused to flow in the direction of the tape rather than in the shorter direction in a plane at right angles to the central conductor, which is the direction of the inducing electromotive force. Even where brass tape is used, this is of advantage,

Although it has already been found of advantage, so far as transmission of high frevquencies through a submarine cable is concerned, to furnish the cable with a return conductor consisting of a copper sheath made of tape wound helically around the core, nevertheless, asvpointed out in my copending application, Serial No. 680,170, filed December 1:2, 1923, entitled Submarine cables, it is found that this method is not practical for low' frequencies, for instance, frequencies of a range from zero to 100 cycles per second. For, unless the resistance of the sheath alone is comparable in magnitude with the sca-water resistance without thecopper sheath the return resistance wiltbe increased by the addition of the copper sheatli/i'lhis is because the screening action of the sheath is such as to confine to the sheath the greater part of the return current. 'ln the range of frequencies from zero to 100 cycles per second with cables such as are now in use for transoceanic operation,

this condition would-require such a large amount of copper in the sheath that the cost and weight of the cable would be increased beyond practical limits. therefore proposes to decrease the sea-return resistance for the signaling frequency range just mentioned and, in some instances, much That applicationhigher frequencies,- by employing, in place of the usualsteel armor wires for the cable, varmor wires of high resistivity material, for example, nickel steel, chromium steel, or Krupp steel.

lVhere the cable of Fig. 1 is to be employed for signaling frequencies of the range just mentioned, its ,armor wires may, accordingly,

vbe of such high resistivity material. 7Where the cable is loaded as in the case of the cable of Fig. 1, the high resistivity of the armor wires has the additional advantage of reducing eddy current losses produced in the armor wiresby the lux in the loading materiaLin the same manner in which that flux produces eddy current losses in the teredo tape.

Fig. 2 shows a cable similar to that of Fig. l butha'vino` a metallic return path for signalingr currents, the return path comjirising maferial. of high electrical conductivity compared to that of steel. Identical elements 1n the two figures are indicated by the same re'lerence characters. The metallirI return path' is constituted by a layer of helical copper wires 31 or strips embedded in the jute 15 and lyingV between the steel armor wires 13 and the teredo tape 11 and surrounding the core 1T and tape 11. This return path is especially useful where the cable is to be employed for transmitting' fairly high frequencies, for instance, frequencies of the voice range or somewhat higher. The-wire conductors 81 may be individually wrapped with tape 19 as in the case of the armor wires 13. rlhe eddy current losses produced in the return conductors 31 by the flux in the loading` material in the manner in which such losses are produced in the tcredo tape b v that flux, 'will not be unduly large because the conductors 31 are insulated from each other and are given a long lay, for example, a pitch of the order of three feet, so thatthe currents produced in these conductors by the axial component of the magnetic flux in the loading material are forced to traverse a long path'. The length of this path is also due partly to the fact that the conductors 31 are spaced a considerable distance from the 1 teredo tape'll, thus making the diameter of the helix of wires 31 large, and also increasing the maximum permissible length of lay of the wires 31. As shown in Fig. 3, the pitch of the conductors 3l is ,greater than that of the steel armor wires 13. lt is possible to give the conductors 31 this greater pitch even where the pitch of the armor wires 13 is substantially the maximum value permissible, since the wires 81 are prevented from fallingr ott the cable by the wires 13. The long pitch of conductors 3l also has the advantage that it increases the eihciency of the copper return path as a'longitudinal conductor. On this account the conductors 3l may contain approximately 20% less copper than would be necessary'` for a given resistance of return conductor, if the return conductor were in the form of a. helical tapelaid onthe core.` With such a tape it is necessary touse a--comparatively short lay in order to avoid injury to the insulating material of the core. l i

Where desired, for instance. Where the cable 1 is to transmit frequenciesso high that loading is impracticable or inadvisable, the loading material may be omitted from the cable of Fig. 2,.the spacing ofthe return conductors from the central conductor being made suficient tov give the cable the desiied inductance'. .i It is pointed out in my copending applicati'on, Serial No. 585,619,A filed September v1, 1922, entitled Submarine signalingcables, l5' i that-an' unloaded cable with a. concentric return conductor of high 'conductivity so spaced from the central conductor can have comparatively high 'efliciency for frequencies at which loading would be inadvisable on-account of the large eddy current losses which would occur in the loading material.A

Similarly, ir desired, the loading 'material may be omitted from the cable of Fig. l,

Yvvheretlni frequencies to be transmitted by the cable are high, and some or all of the armor with copper to serve as a return cir-cuit for the cable can Well serve to transmit high freloading tape small, since, as noted above, they qiiencies. By making the pitch of the armor Wires as great as is practicable, the efficiency 35 ofthe copper` pathas a longitudinal return conductor may be made large.

In another aspect the present invention..

covers the use of a teredo layer having high permeability, as Well as'- one or more of the characteristics described above as desirable for teredor protection. In such cases the layer \vill be constituted of'material being suiicieiitly permeable to act as additional inductive loading Which becomes-more effective as its spacing from the high conductivity metallic return is decreased.

Although it is lof advantage from the point of vie-iv of eddy jcurrent losses to have the width and the pitch of the teredo tape large, it is 'of advantage' from the same point ofd view to have the Width and Vthepitch'oIfIthe component of magneticinduction parallelto theaxis of the central conductor will be greater the greater the Width' and the pitch'.

of the loading tape or wire, if other condi- .tions remain unchanged. The pitch of the teredo tape is preferably considerably greater than that of the loading tape or Wire.

Although the high resistivity metallic layei for affording protection against the teredo has beenspecifically shown and described as ay helical tape, it should beunderstood .that such disclosure is notintended as precluding a broader view of the invention.

lVhat is claimed is: 'l

1. A lcontinuously loaded submarine `sig naling cable core comprising an electrical conductor having loadingmaterial applied thereto, the loading material being surrounded by insulation, a helical metallic tape on said core, said tape having its adjacent turns overlapping, and insulation betiveen the over-- lapping portions.

2. The combination vvith a continuously loaded submarine signaling cable core comi prising-an electrical conductor surroundedv by helical loading. aid .by a layerof insulation having a Wall thickness of at least a millimeter,` of a 'helical metallic tape. on said core, saidtape having a thickness ofthe order of severalv thousandths of an finch. and `having resistivity at least twice that of brass. n

.f 3. A continuously loaded submarine signaling cable core, and a helical metallic tape thereon having a. pitch substantially. greater than twice the diameter of vsaid core and having its adjacent-turns overlapping and insulated fiom each other. 1

4. A continuously loaded submarine cable c ore comprising an electrical -conductor surrounded by insulation and a helicalinetallic tape on said core, said tapefhaving'resistivity.

at least several times that` of brass, and having its adjacent turns overlapping and insulated from each other.

' 5, A continuously loaded submarine cable comprising a conductor,loading material, in-

sulation around said conductor and loading material, a metallic layer outside said insula` tionA serving as protection'against the teredo,

said' loading material .being so associated with said conductor that a component of iiux is set up through the coil formed bysaid metallic layer in the direction bf the length ofthe cable bythe signaling currents in said conductor, the resistivity of said `protective material being high compared with that of iron.

6. A continuously Iload-ed subn'iarinesignaling cable Jcore comprising an electrical conductor surrounded by a layer of loadingmaterial, a layer of insulation around tsaid loading material and a strip of metal of. high resistivity compared with brass around said Ainsulation ivithncoi'itiguous edges' thereof oveilappingand insulated from each other.

7. A submarine signaling cable, comprisinga central conductor continuously loaded with a helicall loading,nienibeifhaving high 'permeability at low inagnetizing forces, a substantiallyconcentric.return conductor for said central conductoi,\an d electrical insulallO tion between said conductorsrsaid return coiiduct-or having high' electrical YVconductivity compared to that of steel, and said return conj ductor comprising helical elements having a pitch of the orderof at least a foot.

`8. 'A submarine signaling cable comprising a central conductor continuously` loaded with a helical loading member havinghighpermeabillty at loW magnetizing forces, a substantially concentric returnl conductor torl at least one foot.l

9. A submarine cable comprising a central conductor, electrical insulation surrounding said central conductor, a layer of helical Wires surrounding said insulation, said Wires having conductivity high inv comparison to that of steel, and helical metallic armor members surrounding said helix of Wires, said ffarmor members.

Wires having a pitch greater thanthat of said 1.0. A continuously loaded cable comprising a central conductor, a helical element of high permeability and high resistivity forining a layer thereabout, insulation surrounding said layer, and a layer ofy helically laid ytape outside said insulation having high resistivity compared With brass and having a greater pitch than said rst mentioned helical element. 1

l1. A submarine signaling cable comprising a loaded conductor, insulation thereabout, i

teredo tape external to the insulation, a return path externalto the teredo-tape, said path comprising a plurality of Wires of metal highly conductive as compared to iron, separated from each other and from the teredo tape by material of Conducting properties very poor as compared to iron.

12. A submarine signaling cable comprising a continuously loaded central conductor, insulation surrounding said conductor, teredo tape external to said insulation, a return path external to said teredo tape, said path comprising a plurality of Wires of metal highly conductive as compared to iron, separated from each other and from the teredo tape by material of conducting properties very poor as compared to iron, armor Wires surrounding said return path and poor conducting material, the Wires of said return path having a pitch greater than that of said armor Wires.

13. A signaling cable comprising a signaling conductor, a return circuit path spaced from said signaling conductor comprising armor Wires and a separate layer of Wires terial of considerably greater conductivity than the armor Wires, said separate layer of Wires being spaced from each other and from the armor Wires by material having insulating properties similar to jute.

14. A cable in accordance with claim 13 in which the conductor isV providedwith plastic insulation and the armor Wires are spaced from the plastic insulation by material having insulating properties similar to jute.4

In Witness whereof, I hereunto subscribe my name this 26th day of February, A. D. 1926.

JOHN J. GILBERT.

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