US 1370731 A
Description (OCR text may contain errors)
y P. H. CHASE. l CABLE AND METHODU 0F MAKING THE SAME. APPLICATION FILED ILOV- 2, IQIGAIIENEWED AUG. 9, 1920.
I Patented Mar. 8, 1921;
@a1/@OHM nue/WISO@ 3&9 his @Hoa/mags UNITED "STATES PATENT oi-Flea4 PHILIP H. CHASE, OF CYNWYID, PENNSYLVANIA.
CABLE AND METHOD OF MAKING THE SAME.
of Cynwyd, in the county of Montgomery fand State of Pennsylvania, have invented an Improvement in Cables and Methods of Making'the Same, of which the following is a specification. n
This invention relates to electrlc; cables, and with regard to certain more specific features, to cables for high-voltage power work.
Among the objects of the invention may be noted the provision` of a simple andimproved method ofconstructing a cable to relieve or equalize the dielectric stressesv and to decrease the dielectricl losses incident to high-voltage work; the provision of a cable lso constructed as to minimize the eddy currents and other disadvantagesdue to .currents induced by the alternating currents flowing through the yconductors or due to short-circuit f currents; the provision of a cable constructed to facilitate the vconduction of heat from the interior of the cable to the exterior thereof; the provision of an efficient and durable sheath substantially continuous for the purpose of permitting material equalization or dissipation of electrostatic stresses and decrease of dielectric losses, and
likewise substantially continuous and offering a lowresistance to the passage of heat from the interior fof the cable toward the, eX-
terior thereof, but offering a material and yeffective resistance fto the flow of eddy cur'- rents and any other deleterious currents, which may be refererd to as electrodynamic currents to distinguish them from the electrostaticstresses and 'losses in the cable; and the provision of a stress7relieving`-sheath having preferably a high fusing point and ample mechanical strength to :prevent 1njury or breakage if the cable A1s bent, and
v having sufficient heat-conductivity, heatstorage capacity, and heat-radiating power to minimize the danger of fusing of the sheath during short-circuit conditions.l i
Other objects will be in part obvious and in ypart pointed out hereinafter.
The invention accordingly `comprises the. features of construction and operation, 'combinations of elements, arrangements of parfts, steps and sequence of steps which are exemplified in the structure hereinafter described and the scope of the application of ,which will ybe indicated in the following claims.
In the accompanying drawings, 1n which Specification 'of Letters Patent.
Patented Mar. 8, y1921.
' Apilication led November 2, 19"16,`Seria1 No. 129,218. Renewed August 9, 1920.' Serial No.` 402,299.
are shownY one or more of various possible embodiments of the invention,
Figure 1 is a perspective of a conducto with its layer of insulation, showing a sheath in the form of a tape being wound around said insulation.
Fig. 2 is a face view of modified forms of tape. I
Fig. 3 is a similar view of other modifications.
Fig. 4 is a view similar to Fig. 1, showing a sheath in the form of an insulating tape covered with conducting foil.
Fig. 5 is an enlarged section on the line Fig. 6 is a face view of a modified form of conducting foil on insulating tape such as used in Fig. 4.
Fig. 7 is a transverse section through a 'three-conductor cable, showing one embodiment of my invention applied thereto.
Fig. 8 is a similar sectlon through a threeconductor cable ofV the sector type.
Fig. 9 is a sectional view of a modified form of three-conductor cable.
Similar reference characters indicate similar parts throughout the several views of the drawings. Y
In considering this invention in its relation to the prior art, it may be noted; that with the increasing use of electric cables, especially cables for three-phase alternating current at high voltages and often for heavy currents, there has been an increasing appreciation of the losses-and deficiencies incident to thepassage of high-voltage alternating current through conductors in close proximity to one another, as in cables. Many attemptshave been made to classify the losses and deficiencies with a view to discovering the factors affecting them, and a number of methods and arrangements have been devised for constructing cables in such a lway, as to reduce these losses and deficiencies singly or together. The present invention provides af method and cable construction designed to minimize the several losses, coincidentally with minimum accompanying disadvantages, and for multipleconductor cables to increase the carrying capacity for a given temperature difference between the interior. and exterior thereof. As the description progresses, it will be seen. that the requirements of efficiency, low cost, mechanical strength and durability under abnormal service conditions, are adequately met in the method and apparatus of the present invention.
The present invention contemplates the provision of a mechanically durable conductor so constructed and positioned within the cable as to facilitate the equalization or dissipation of stresses of an electrostatic nature, at the same time minimizing the heating and other disadvantages due to the flow of currents, for instance eddy currents, which may be said to be of an electrodynamic nature, and, particularly in the case of multiple-conductor cables, affording a path of low thermal resistance from the heated interior of the cable toward the eX- terior thereof, for the purpose of reducing the temperature within the cable for a given load, or permitting a greater load to be carried without increase of the internal temperature.
This three-fold object, of reducing electrostatic stresses and losses, electrodynamic losses, and heating, is preferably attained by winding around the insulation individual to the conductor or to each conductor, a conducting sheath offering (l) a path of low resistance to the fiow of current due to electrostatic potential differences, (2) a highresistance path or series of paths for the electrodynamic currents, such as eddy currents, and (3) a path of low thermal resistance for conducting away from the interior of the cable the heat generated therein. The sheath may extend only partly around the periphery of the conductor in certain cases, but preferably extends all around the conductor. The sheath is not intended primarily for mechanical protection, but for electrical and thermal purposes. In a threeconductor cable for three-phase alternating current, one of these sheaths is provided around the insulation` individual to each conductor, and the three sheaths are preferably in contact with a sheath external to the three conductors or with each other when the conductors are formed into a cable. Belt insulation may or may not be applied over the three conductors, before an outer sheath or covering is applied.
In order to facilitate the equalization of electrostatic stresses, the sheath is virtually electrically continuous peripherally, that is, in a plane at right angles or approximately right angles to the axis of the conductor. This equalizes the distribution of electrostatic stresses around the periphery of each conductor.
The electrodynamic losses due to eddy currents formed in the sheath by transformer action, are minimized by' laminating the sheath (that is, sectionalizing, or dividing the sheath at'short intervals of the magnitude of a fraction of a decimeter, and preferably of the magnitude of a fraction of a centimeter) in planes at right angles or at approximately right angles to the direction of the induced potential differences causing these eddy currents, and providing between the laminations either a space in the form of an open slit or corroded surfaces or varnished surfaces, or some other impediment to the flow of currents across the barrier. If for mechanical reasons, as is preferable, the laminating slits or perforations do not extend across the entire width of the conducting tape which constitutes the sheath, some eddy currents may flow around the laminations, but the paths around the laminations are so long that the resistance offered by thc paths would effectively reduce this eddy current flow to a negligible value. In any event, the sheath is broken up into disconnected or partly disconnected ele ments which still form a continuous sheath for electrostatic purposes, but which break into small elements the paths along which the eddy currents would flow so that the induced electrodynamic voltages acting in each element have to forcethe eddy currents through a comparatively long, high-resistance path or paths. As a result, there is a reduction in the magnitude of the eddy currents and in the resultant power losses and heating from these causes as well. The borders and other unbroken longitudinal portions obviously ofler a comparatively great resistance to the passage of large currents, through. the metal coverings, lengthwise of the cable.
The heating of a multiple-conductor cable is reduced because the `sheath offers a virtually t ntinuous path around the periphery of the insulated conductor; and since the sheath may be as thick as desired without involving excessive electrodynamic losses, the sheath may be made thick enough to offer a path of low thermal resistance for the rapid conduction of heat from around the insulated conductor in the central parts of the cable toward the outside sheath.
Copper, for instance, has over three thousand times the heat-conducting capacity of impregnated paper such as is often used in high-tension cables. Therefore the six metallic paths from the interior of a threeconductor cable to the periphery relieve the insulation over the outer part of the conductors of considerable heat-conducting duty. The temperature of the insulation next the conductors and the average temperature of all the insulation are thereby decreased, or from another point of view, the cable can be safely and economically operated at higher currents and voltages than it could without this invention. The reduction and equalization of the temperature of the insulation have a more than proportional effect on the dielectric losses, a factor of imj tend entirel portance in high-voltage cables, and also have an effect on the break-down strength of conducting tape k3 provided with diagonal laminations 4 arran ed at such an angle to the longitudinal ax1s of the tape that the laminations are approximately perpendicular to the axis of the conductor when the tape is wound helically upon the insulation 2. In order that the tape may be continuous and thus easy to wind on the insulation 2, the laminating slits referably do not exacross t e ta e but are short enough to eave at the e ges of thetape margins or borders 5. In this embodiment of the invention, the borders 5 of adjacent turns of the tape overlap and are in contact with each other, to minimize the. thermal resistance of the sheath in a direction around the periphery of the insulation and to insure continuity for electrostatic purposes. This construction, moreover, insures some extent of overlapping even when the cable is bent. The eddy currents due to potential differ# ences in a direction axially of the conductor are kept at a minimumbecause the unobstructed paths axially of the conductor` are only as long as the width of each lamination, and through this short distance the potential differences tending to set up the eddy currents will be negligible; and the eddy current paths also have long elements perpendicular to the direction of the induced potential differences, resulting in limiting theeddy currents to negligiblel values. In fact, the width of tape, width of` borders,
width of laminations, and pitch of the tape iin winding,`may be so proportioned as to keep the eddy-current losses downto an del sirable value, and this without sacri cing mechanical strength of tape or continuity of surfaces for equalizing electrostatic stresses, or low thermal resistance around the periphery of the sheath, for conducting heat to the exterior portions ofthe cable. By providing a sheath that is mechanically strong, the danger of'rupture or injury during manufacture or installation oroperation, is minimized. v
By providing such laminations at right angles to the axisof the conductor, the
sheath offers a comparatively high impediment to the passage of currents induced by short-circuit currents in the conductor.v The sheath, moreover, has large heat-dissipating' surfaces and heat-storage capacity, and thus the sheath is protected from fusing that might occur dueto the heating effect ofY The central portion 16 may bereplaced by .dling the tape during the winding operation. Margins or borders 15, similar to the borders 5 ofthe tape 3, are also provided.
laminations keyed at one or more points, as indicated at 17 such a tape combines the advantages of the tape shown in Fig. l, withv greater mechanical strength. In Fig. 3, the tape 23 is provided with marginsv or borders 25 and diagonal unbroken ortions 26, between which are the diagonaldaminations 24. The unbroken portions 26 may be replaced by laminations keyed at one 'or more points, as indicated at 27. l
In Fig 4, the insulation 32 surrounding the conductor 31, has wound helically upon it 7an insulating tape 37 to which is secured a metal tape or/foil 33 which, like the tape 3 of Fig. 1, is provided with diagonal laminations 3 4 arranged at such an angle to the longitudinal axis of the foil that the lami. nations are approximately perpendicular to the axis of the conductor when the insulating tape and the rfoil are wound helically upon the insulation 32, the margins or borders 35 being provided to add mechanical strength to the foil and t0 facilitate the handling of it during its manufacture and application to the insulating tape and to the conductor. The tape or foil may be the full width ofthe insulating tape and it may or may not be found preferable to cement or otherwise cause the foil to adhere to the in- 105 sulating tape. As shownin the enlarged section in Fig. 5 the laminations 34 are separated laterally by open slits or lperforations serving to separate the foil on either side of the slit, or the slits may be made and again closed after the adjacent surfaces have been corroded, oxidized,v or varnished, or otherwise insulated from one another to an extent sufficient vto materially decrease or prevent the passage of eddy currents betweenlaminations.4
In Fig. 6, there is illustrated a metal foil 43 carried upon an insulating tape 47, the laminations 44 and borders 45 resembling the laminations 14 and borders 15 of Fig. 2. 120
'In applying the tape or foil to the insulated conductor of the several modifications herein disclosed, the foil may be wound on at the same time as the insulating tape, or the two maybe wo-und separately, and in the latter case, the insulating tape may be laid with any desired pitch compared to the pitch of .the foil, or may even be applied with the longitudinal axis of the tape parallel to the axis of the conductor; and the foil may likewise be applied with its longitudinal axis parallel to the axis of the conductor, or may surround all or part of the periphery of the insulated conductor. And there may be provided a protecting tape applied outside the foil to protect the foil from mechanical abrasion; this protecting tape, however, for multiple-conductor cables, should preferably not cover the entire surface of the foil, and should be thin enough to permit contact between the tapes or foils applied to each of the conductors and between each foil and the external sheath. lVhen the foil is laid on after the insulating tape has been applied to the conductor, the foil strip is preferably wound with a pitch less than its width, so that adjacent edges over- I lap in the manner indicated in Fig. 1, to
insure overlapping when the cable is bent, and for the equalization of electrostatic stresses. This construction, moreover, provides a low-resistance peripheral path for the conduction of heat. Or a foil may be applied with spaces between adjacent turns, and these spaces covered by a second foil. Or the foil may be wound in two or more layers, but in such an embodiment of the invention, the layers are preferably insulated from one another to an extent sufficient to prevent eddy currents from flowing from one layer to another.
In Fig. 7, there is shown in transverse section a three-conductor cable with the usual central and lateral filling bodies 55, and with the present invention applied to the cable. The conductors 51 are each provided with insulation 52 around which is laid the conducting sheath 53, which may take any one of the forms above described. The three sheaths 53, it will be noted, are at substantially the same electrical potential because they may be in contact with one another or with the belt-sheath 56, which may be provided if desired, and may or may not be laminated. The belt insulation is indicated at 54. The belt-sheath assists in the Idistribution of heat around the periphery of the cable and thus increases the conduction of heat to the external sheath. The eddy currents due to the varying or rotating magnetic field caused by the currents in the conductors, are broken up or minimized by laminations similar to those illustrated in Figs. 1 to 6. The heat generated in the interior of the cable, due to IZB losses in the conductors, to losses in the insulation, and to losses in the paths taken by the eddy currents, isreadily conducted toward the external sheath 58 of the cable by means of these sheaths 53, so that the cable can be operated at a lower internal temperature for the same current or at a higherl current for the same internal temperature.
In Fig. 8, there is illustrated a three-conductor cable of the so-called sector type, in
which the conductors 61, instead of being round, are in the form of approximately K120--degree sectors, and each insulated conductor is surrounded with a sheath, the whole being covered by an overall sheath without belt insulation. The central and lateral filling bodies are indicated by the reference numeral 65. In such a cable, the radiation of heat becomes a more important factor, and it will be noted that by applying the present invention to a cable of this type, the problem of heat conduction can readily be simplified by making the sheaths 63 heavy enough to afford a path of sufficiently low thermal resistance for the conduction of heat to the exterior of the cable. It is evident from the foregoing description, that the sheaths 63 may be omitted from most, if not all, of that part of the periphery of the individual conductors which is in contact with the external sheath 68, without sacrifice of the benefits of this invention. The other losses incident t0 the employment of sector cables are likewise reduced by the application of the present invention thereto, since the conducting paths of the several sheaths G3 and from one sheath to another in a (lirection at right angles to the axis of the cable, facilitate the equalization of electrostatic stresses, while the laminations in the sheaths prevent the formation of troublesome eddy currents.
In Fig. 9 is illustrated a further means of assisting the conduction of heat from the central portions of the cable to the external 1.
sheath 78. This means comprises heat-conducting sheets 79 around part of the periphery of the external sheath and provided with vanes 80 extending from the external sheath radially inward between the conductors 71 toward the central portions of the cable. These vanes are preferably laminated, as indicated in Fig. 9, to minimize eddy-current losses. A laminated sheath 73 individual to each conductor may be provided, as in the preceding embodiments of this invention. The customary central and lateral filling bodies are provided, as indicated at 7 5.
Instead of having the conducting sheath laid on the outside of the insulation individual to a conductor, the sheath may be embedded in the insulation surrounding the conductor. for such purposesv as grading of the insulation. Many if not all of the advantages incident to the use of this invention in a sheath outside the insulation may be attained by applying the invention to such an intermediate sheath. Furthermore, it may be advisable to have the intermediate sheath continuous for the whole length of the cable in order to maintain the sheath at a predetermined potential, and it will be noted that an intermediate sheath constructed according to the present invention may i3' readily be made electrically continuous throughout the length of the cable for this purpose, without sacrifice of the advantages incident to its use.
From the above, it will be seen that the several objects of the invention are realized, and other advantageous results attained.
As various possible embodiments might be made of the above invention and as various changes might be made in the embodiments above set forth, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.
Having thus revealed my invention, I claim and desire to secure by Letters Patent of the United States:
1. An electric cable combining a conductor, insulation around said conductor, and,
a conducting sheath surrounding the conductor to facilitate the dissipation of electrostatic stresses, said sheath being slitted across part of its Width to reduce currents therein.
2. An electric cable combining a conductor, insulation around said conductor, and
a conducting sheath surrounding the con ductor to facilitate the equalization of electrostatic stresses' and the-conduction of heat around the periphery of the insulation, said sheath being perforated across part of its Width to decrease losses due to currents therein. y,
3. An-electric cable combining a conductprginsulation surrounding the conductor, and conducting material surrounding the insulation and affording a Ypath or paths aroundthe insulation to equalize the electrostatic stresses, said material being perforated across part of its Width in a direction to break up currents therein.
4. An article of the class described, combining a conductor, insulation surrounding said conductor, a protecting covering outside the insulation, and conducting'material in the insulation and surrounding said conductor, said material affording a substantially continuous peripheral path for the relief of electrostatic stresses andhaving a series of short relatively insulated paths axially of the conductor to offer a comparatively high impediment to the passage .of eddy currents.
5. In a multiple-conductor cable, in combination, a body of conducting material'covering the individual insulated conductorl and extending around such individual conductor to reduce electrostatic stresses and perforated across part of its Width in planes substantially at right angles to the axis of the conductor, the material surrounding one conductor being in electrical contact with the material surrounding an adjacent con ductor.
ving divided intoaxially short and relatively 6. In a high-tension cable including three or more separately insulated conductors', a substantially. complete integument of conducting material covering the opposing faces of each of the assembled insulated conductors and extending substantially around said conductors to form an'A electrostatic shield, said material bein slitted across part of its Width and offering a comparatively loW-resis'tance path to the passage therethrough of heat energy, but offering a comparatively high impediment to the passage therethrough of eddy currents.
7. In a high-tension cable including three or more separately insulated cnductors, a substantially complete integument vof conducting material covering the opposing faces of each of the assembled insulated conductors, and extending substantially around said conductors and acting asA an electrostatic shield, said material offering a comparatively low-resistance path to the passage therethrough of heat energy in Ia substantially peripheral direction but beinsulated sections in order to offer a comparatively high resistance to the passage of 'eddy currents therethrough.
8. In a high-tension cable including three v or more separately insulated conductors, a substantially complete integument of conducting material covering the opposing faces of each of the assembled insulated conductors andextending substantially around said conductors, said material acting as an 'electrostatic shield and offering a comparatively 10W-resistance path to the passage therethrough of heat energy in a substantially peripheral direction but offering a compar'atively'high resistance to the passage 105 of eddy currents therethrough; '9. As an article of manufacture, a conducting Web for electric conductors, said web being provided With laminationspso disposedj as to be 'substantially circumferential 110 of the 'conductor when the, web is applied thereto, the laminations extending only part Way across the Width of theWeb to provide unbroken borders or margins at either side of the web` to facilitate handling of said web.
10. As an article of manufacture. a conducting web for electric conductors, said I web comprising ian insulating tape and a n metal foil secured thereto, the `lfoil being provided with laminations so disposed as to /be substantially circumferential of the con- I ductor when the .foil is applied thereto, the laminations extending only part way across the width of the foil to provide unbroken 125 borders or margins at either side of the foil.
11. As an article of manufacture, a metal foil for cables, said foil having laminations so disposed as tobe substantially circumferential of the cable conductor when the foil is applied thereto, the laminations extending only part way across the width of the foil to provide unbroken strips at either side of the foil.
12. As an article of manufacture, a metal -foil for cables, said foil having laminations so disposed as to be substantially circumferential of the cable conductor when the :toil is applied thereto, the laminations extending only part way across the width of the foil to provide unbroken strips at the lateral edges of the foil and longitudinally of the foil between .said lateral edges.
13. As an article of manufacture, a metal foil for cables, said foil having laminations so disposed as to be substantially circumferential of the insulated cable conductor when the vfoil is applied thereto, the edges of the foil at the laminations being provided with insulating material to offer substantial resistance to the passage of current across said laminations.
14. The method of makingr a cable, which comprises insulating a conductor and winding around the insulation a conducting tape provided with laminations disposed at such an angle that said laminations are at substantially right angles to the directions of the potentials causing the flow of eddy currents after the tape is applied, the edges of the tape overlapping to afford a continuous electrostatic shield for the conductor.
15. The method of making a cable, which comprises insulating a conductor and winding helically around the insulation a conducting tape provided with laminations extending substantially across said tape and disposed at such an angle that said laminations are at substantially right angles to the conductor after the tape is applied, the edges of the tape overlapping to afford a continuous conducting path circumferentially ot' the conductor, the laminations minimizing the formation of eddy currents in the sheath.
16. The method of making a cable, which comprises applying an insulating tape to an insulated conductor, winding helically upon said tape a laminated conducting web of metal foil oifering a low-thermal-resistance path circumferentially of the conductor and a high-electrical-resistance path axially of the conductor; and covering said web With a second-insulating tape.
17. VThe method of making a cable, which comprises .winding helically upon an insulated conductor'an insulating tape with a laminated conducting web of metal foil se-' cured thereto, and offering a low-resistance path circumferentially of the conductor and 60 a high-resistance path axially of the conductor; and covering said web with a second insulating tape.
18. The method of making a multipleconductor cable which com rises applying an insulated tape to each ot a plurality of insulated conductors, winding helically upon each of said tapes a laminated conducting web of metal foil offering a low-resistance path to heat and -a high-resistance path to eddy currents, assembling the conductors so that the several webs contact with one another, and inclosing the assembled conductors in a protecting sheath.
19. The method of making a multiple-conductor cable which comprises applying an insulated tape to each of a plurality of insulated conductors, winding helically upon each of saidtapes a laminated conducting web of metal foil offering a low-resistance path to heat and a high-resistance path to eddy currents, partially covering each of said webs with a second insulating tape to protect the webs, assembling the conductors so that the several webs contact with one another, and inclosing the assembled conductors in a protecting sheath.
20. In a multiple-conductor cable, in combination, a conductor, insulation therefor, and a body of conducting material covering said insulation and extending around said conductor, and comprising interlocking laminations arranged in planes crosswise of the direction of the induced voltage.
21. In a. multiple-conductor cable, in combination, a body of conducting material covering the individual insulated conductors and extending around said individual conductors and laminated in planes crosswise of the direction of the induced voltages, and a body of conducting material surrounding the conductors thus covered and serving to distributerthe heat around the periphery of the cable.
22. In a multiple-conductor cable, in combination, a body of conducting material covering the individual insulated conductors and extending around said individual conductors and laminated in planes crosswise of the direction of the induced voltages, and a belt-sheath surrounding the conductors thus covered and serving to distribute the heat around the periphery of the cable and thereby increase the conduction of heat to theA external sheath, said belt-sheath being likewise laminated.
' In testimony whereof I have signed my name to this specification this 2nd day of November, 1916.
PHILIP H. CHASE.