US 1780564 A
Description (OCR text may contain errors)
NGV. 4, 1930, Q OXER 1,?89554 ELECTRICAL CONDUCTOR Filed Feb. 20, 1924 :mee Ff? is ii 'd il *che dell ELECTRICAL ONID'UCTR This invention relates to electrical conductors and more particularly to conductors especially adapted for the transmission of electrical energy at extremel high voltages.
in the selection of con uctors for high tension lines various important factors must be taken into consideration, among which is the mechanical strength of the conductor, which is of primary importance in view oi' the great i@ length of span now commonly used. The climate, topography and the amount of power to be transmitted are also tobe borne in mind, and in addition, it is important to select a conductor which fulfills the several reqirements Sie and is still as economical as possible both in initial outlay and also in use. `With the voltages now frequently employed, reaching in some cases values as high as 220,000, the loss due to the corona effect is an element that must ao not be lost sight of and since tue value of such loss is a function of the voltage, frequency and superficial area of the conductor, it is desirable, all other things being equal, to use a conductor having as large a diameter as is compatible with economical tower design, etc.
Also, in the case of a large conductor, the
skin effect which causes the outer portion of the conductor to transmit more than its proportionate share of energy, makes it advanee tageous to use a conductor having a hollow or lnon-conducting core.
`Various attempts have been made to design a conductor having the desired characteristics, which have led to the production of cables having cores of various materials, such, for instance, as hemp. A hemp-cored cable, however, is unsatisfactory as the hemp rots in use and the conductor strands become disarranged. Steel-cored cable vhas also been suggested, but it is not altogether satisfactory since theweight is considerable, especially if the cable is to have a superficial area sucient to reduce corona loss. Hollow core cables have also been suggested but it is found that the unsupported hollow core is inca able of withstanding the radial stresses incifental to its use, and when the core collapses, the conductors wrapped about it are loosened and displaced.
The present invention, therefore, is directed to the provision of a conductor for use in high tension work, which has a superficial area of the desired value, and the mechanical strength required in long span lines, both for withstanding longitudinal and radial stresses, and which is further designed so that the area of the conducting metal employed is kept within economical limits. The new conductor comprises a body oi tubular shape of metal of high electrical conductivity, but of insuilicient mechanical strength to resist the collapsing and other stresses to which it would be exposed in normal use. Within this tubular shaped conducting body is a reinforcement or core which supports the body against collapse. This core, while of greater mechanical strength, is a structural shape and so constructed that its weight is not excessive. lt includes one or more members which absorb the longitudinal and radial stresses to which it is exposed in normal use, and these radial members are so constructed and arranged that they pertorm their functions satisfactorily' although they have much less weight than a solid core of the same supericial area. The core is of such size that the tubular shaped body of metal which forms the conducting path-way for the current has the desired superficial area and this tubular shaped body also has a sufficient crosssec tional area to carry the current without excessive resistance losses. The core member or members may also be used for the transmission of energy, in which event these members may be insulated from one another and from the tubular body,'and the new conductor may also be constructed with a central supporting cable insulated from the core and serving to resist longitudinal stresses. rThe new conductor, as will be apparent, represents a highly economical disposition of metal, has the large superficial area which is necessary with high voltage transmission, and its mechanical construction is suitable for present installation conditions. A
ln one form of conductor` embodying this invention, the conducting pathway for the current is of tubular form and made up of inner and outer concentric layers of metal ot high conductivity forming a hollow conducting shell. W' ith this hollow conducting shell I provide a support or reinforcement in the form of a Structural member, i. e., a member commonly referred to as a structural shape, to withstand the radial and longitudinal stresses to which the conductor maybe exposed. This member maybe of diderent types and preferably includes elements which extend radially from the axis of the conducting pathway. A
spider of structural shaped cross-section may be used extending lengthwise of the longitudinal axis and with its arms providing the necessary sup-port. This structural member may be made of the conducting metal, and `.nay be rolled to any section, but preferably has 'a multiplicity of arms radiating from a central axis7 which is the longitudinal axis oi the conductor. ln another form of reinforcement, l malte use oi" triangular or sector .'hapedA members` each formed from a dat sheet ot metal, and having one side oi ilat or arcuate form, so that a plurality of members may be assembled to form a polygonal or cir- -v cular core. With t .is form, each leg of the '.'einforcement consists of two adjacent sides of sector members and the ends of the legs are connected by a dat or arcuate side.
ln the case of a spider of structural rolled shape it may be desirable, though not necessary9 to provide a. thin casing of metal of tubular form around the spider on the surface of which cable strands are laid.A Such arcasing should be of metal of high conductivity so that in this form of the conductor the tubular conducting pathway for the current is in two parts, though the inner layer may be dispensed with. When the reinforcement is formed of sector members, the arcuate portions oi these members form a substantially continuous cylindrical casing which, with the cable strands, forms a .two-part conducting layer for the current. It desired, the sector members may be placed within a sheathing of conducting metal which serves to hold the sector members in assembled relation-and, with their arcuate portions, forms a part of the tubular conducting pathway.. The cable having a core of triangular or sector-shaped members will have the desired mechanical strength for ordinary purposes but under certain conditions, as, for instance, in. unusually long spans, it may be desirable to further reinforce the core by the use of a central cable. For this pur ose the sector-shaped members are so forme that a considerable air space is formed axially of the conductor and in the space so provided there is inserted a cable which may be either of single or multi-strand construction. Preferably this cable is insulated, the insulation serving to provide a cushioning etlect in the event that unusual collapsing stress is applied to the surface of the conductor which would be sucient to cause the sectors to slide over each other and so bear against the central cable. This insulation also performs a further useful function of preventing electrolytic action in the event that the central cable is of a diderent metal from that employed in the sector members.
The details of construction and the various advantages of the new conductor may best be explained by reference to the accompanying drawings, in which Fig. 1 is a cross-sectional view of a conductor having a core formed of sector members,
Fig. 2 is a view in perspective of the conductor shown in Fig. 1, v
Fig. 3 is a view in elevation ot a slightly modified form of conductor,
Fig. l isa View in section of a conductor having a conductor -layer in the orm ot strands, and having a central cable through its core,
Fig. 5 is a sectional view of a conductor similar to that shown in Fig. l but having a different type of spider,
Fig. 6 is a view in elevation of the conductor illustrated in Fig. 4,
Fig. 7 is a view in elevation of the assembled sector members showing the axial twist which they are given, and
Fig. 8 is a fragmentary cross-sectional view of a slightly modiiied form of conductor, making use of sector members, which are insulated from each other.
Referring now to the drawings, and more particularly lligs. .l and 2, the conductor is seen to have a core consisting'of a plurality or sector-like members 8 which are of proper proportion so that when assembled they provide a circular core. lt is understood, 'of course, that instead of using sector members l may employ, with equal facility, a plurality of triangular-shaped members so that the contour of the core will be polygonal rather than circular. Each of these members may be made from a dat strip of lOG metal bent to form a pair of straight sides 9 and 10 intersectingl at an acuteangle 11 and an arcuate side 12, the edge of which as at 13, overlies the edge of the side 9. As the conductor is to be round in cross-section, the sector members lwill be properly designed so that a given number of them may Abe assembled together to provide a core such as is illust-rated in Figs. 1 and 2. Preferably these members will be finished by having the overlapping edge 18 spot-welded at spaced intervals to theedge of the side 9 and the acute angle 11 will be formed so that when -a plurality of the members is assembled to produce a circular core, there remains an air space 14 at the center. In another construction, which will later be described, this air space may be used for the housing of a reinforcing member.
With this core construction it will be seen that the arcuate portions of the several sectors may be considered to form a cylindrical conductor which is supported and strengthened against collapse by means ot a series of radial arms 15 each ot which is made up of the contacting straight sides of a pair of sector members. Should a radial stress occur at the point 16 it Will be seen that this stress acts upon an arched surface and the stress is transmitted substantially at right angles to the sides 17 and 18 of this particular sector member. These sides in turn transmit the stress to the adjacent sector members and it is absorbed throughout the structural trameivorl. Should a stress occur at the point 19 it Will be seen that the cylindrical conducting shell cannot collapse by reason of the support provided by the two arms located at this point so that regardless of Where the radial stress occurs it will be transmitted throughout the framework of the core so as to be harmless. ln the case of excessive stresses on the arched members 12, there is a possibility7 that the particular sector member involved may be forced inwardly a slight distance so as to cause a relative outward displacement of the adjacent seyctor members. rlhe provision of the air chamber 14 which extends axially of the core permits this relative movement Without resulting injury to the parts ofthe core and then when the stress is removedthe members have a tendency to return to their normal positions so that the ermanent deformation cannot occur. lt rollows then that this type ot core is perfectly adapted for resisting radial or collapsing stresses and a distribution otY the metal in it accomplishes the desired result Without the core having excessive Weight..y rllhe straight contacting sides of the several sector members may be considered to form structural members, which term l intend to refer to' members specially designed to absorb stresses and to transmit them to other members 'throughout the structure.
lli/lith the type of core just described and made up by assembling together a plurality ot sector members ot proper cross-sectional contour is unnecessary to provide a special layer or" conducting material since the arcuate sides 12 ot the several sector members, combine to provide a cylindrical conductor which may be given a cross-sectional area sui'licient to carry currents ordinarily transmitted on high tension lines. When the sectors themselves are to provide the conducting metal, it is desirable that they should be made oif a material of high conductivity, as, for instance, copper. However, when no separate conducting sheath is employed7 it will be necessary to provide retaining members for the sectors 'to hold them in their proper relative positions and for this purpose there may he employed straps or clamps 20, which may be spaced along the conductor at the requisite .tance to prevent displacement ot the sector members under Working conditions. @rdinarily, these straps or clamps may be spaced a foot or so apart.
Under certain conditions it may be desirable to provide a core of greater mechanical strength than would be secured by using the core alone With the straps. ln this case the conductor may have the form illustrated in Fig. 2, in which the core is made up as betere, oit a plurality of sector members providing the desired cylindrical structure on the outside of which there is placed a conducting sheath 21. This may take the form o a strip of metal rolled to encase the core and then having its tree edges held together by a "folded or crimped seam such as is illustrated at 22. rllhe conductor having the core structure Jformed of sectors and encased in a conducting sheath is illustrated in cross-section in Fig. 1. lith this type of conductor7 the sheath provides the current path and also retains the core members in proper relative position. 'llhe sheath thus gives added strength and it the members should be displaced by unusual radial stresses, the sheath would assist in restoring the core to circular form, a result which would occur upon the application of a longitudinal force to the cable.
ln Fig. 4 there is 'illustrated in cross-section a somewhat modiiied form of conductor construction in which the core is reinforced by the use of a central cable. rllso in this form of conductor the conducting sheath includes the arcuate portions ot the sector members and an outer tubular layer consisting ot a plurality of separate strands Which are Wrapped around the outer surface or the core. ln this type ot conductor there are used a plurality of the sector members 8 but the angle 23 betvveen the tivo sides whichy lie radially is so formed that there is provided an axial air space 14; which is ot greater proportions than that illustrated in Fig. 1. laying within this air space is a cable 2l., encased a sheath ot insulation 25. 'l`hi cable and its insulation are ot sich torni a substantially to lill the provided and the. cable gives increased s 'engrth and stiftness to the conductor7 anc, at the saine time, the insulation serves as a cushioning layer so that should unusual collapsing` stresses be applied to the surface or" the conductor the sector members will bear against the surtacc ot the insulation and., althouga permitted to slide over each other a. sligl t distance, are prevented from being injured and also iin'juring the cable. The insulation may serve a further purpose since it the 'cen al cable is to be made of a. uitlerent metal 'from that used in the sectors, the insulation protccts this metal so that detrimental electrolitic effects are avoided. fn this type of conductor 'the conducting layer includes the arcuate portions or" the sector 'members and instance, as the straps illustrated, in Fig. 3,l
may be employed.
In Fig. there is shown a somewhat modified conductor construct-ion in which the metal supporting spider is given across-sectional form of a cross 27 although other shapes may be employed. This s ider or supporting member may be rolled rom any desired metal having the necessary strengthbut is preferably made of the conducting material itself which will ordinarily have the necessary strength for this structural purpose. The structural member or reinforce* ment which is axially twisted is encased in a layer 28 of metal of high conductivity and l -the conducting pathway for the current includes this layer and the outer enveloping layer 26 made of strands spiralled about the inner layer in the usualmanner.
It is to be understood that the core formed in accordance with any ofthe methods above described is preferably given an axial twist in the formation of the conductor. This is illustrated in connection with the core formed of sector members in Fig. 7, where it will be seen that the member 29 Iwhen viewed from the right hand end of the core has a twist in the clockwise direction. This is true vof course of the members of other types forming this core and the pitch when so formed will depend on the shape employed, the purpose being to provide a support-for the tubular shaped conducting shell at points closely enough spaced to prevent the collapse of the shell. This twisting of the sector members vassists in holding them together and further strengthens the core since the position of the supporting arms will vary at different points along its length and the point of junction of each, arm with the shell lengthwise of the conductor, will take diiferent points along `a circular path, and thus serve to take up and distribute radial stresses more effectively. The axial twisting just described is also used in connection with the spider core shown in Fig. 5. This axial twisting may be readily applied to the core during the construct-ion of the conductor.
In Fig. 8 there is illustrated a conductor of modified form in which there is used a plurality of sector members 30, each of which is insulated from the others and `also from the outer layer of strands of metal bf high conductivity. Each of the sector members, therefore, may be used as a separate conductor'. The sides of these sector members which lie radially are separated by insulating layers 31, and a reinforcing member 32 which may take the form of a stranded cable, is placed at the axis of the conductor. The insulation encloses this reinforcing member, as illustrated. The insulation' also extends over the outer faces of the sector members which together make 'a substantially cylin` drical shell, and in rthe forni illustrated a layer of strands 34 of high conducting material is wrapped around the core so formed. This type of conductor provides a plurality of insulated paths for the currents, since the sector members are of metal and may conduct current and the outer strands are also conducting. These strands form a layer of high conductivity around the central core but this layer may be replaced by the encasing sheath.. If desired, this type of conductor can be used without the encasing layer, in which event the clamps 20 vwould be employed. I
In the production of these conductors substantially the same method is used Athroughut with such incidental changes as may be necessary by reason of differences in the core construction. In the formation of the conductor illustrated'in Fig. l, for instance, there will be provided a plurality of strips of metal, in this case five, since there are five sector members. These strips will be continuously drawn from the supplies'and will pass to bending machines which will bend them to sector form and may, if desired, spot weld the overlapping edges at spaced intervals. The sector members so formed are next led to a point where they take their proper relative positions to form a circular core and are then passed through a machine which continuously 'applies the sheath 21, folding and crimping the edges of the sheath as the conductor is formed.
'The finished conductor is then led to a reel 'duce theL desired spiral conformation in the In the formation of the sector members. conductor illustrated in Fig. 3, the steps in the production are similar to those previously described except that 'the sheath is no longer applied but instead spaced straps are crimped in place around the Asector member at theadesired intervals. The construction illustrated in Fig. 4 is similarlyproduced but the sector members are'given a slightly modified form so as to provide a greater central space and as these members are assembled the insulated cable 24 is placed along their axis. This core then has wound upon it a plurality of strands which are drawn from separate supplies and wound about the surface of the core with a spiral configuration, according to-wellknown methods. In the production of the conductor shown in Fig. 5 having the spider core encased within-layers of metal of high conductivity and forming a conducting pathway for the current,-the core is rolled to appropriate form by rolling machines and, as it passes therefrom, is twisted axially and then 4encased in the conducting layer 28. Thereafter the layer 26, which, with the layer Q8, provides a conducting pathway, is wrapped about the core in the usual manner. Thereafter, the wires 26 which provide the conductors are wrapped about the core in the usual way.
ln the vconstruction illustrated in Fig. 8, the sector members are separated by layers of insulation, either as they are assembled, or else the sector members are lirst covered with insulation and then these insulated sector members assembled to form the core. ln the assembly of the sector members, they are laid about a central cable 32, which is insulated from the sector members as illustrated. Thefcore may be held in assembled relation by means of straps or clamps, or else by the use of a sheathing, such as 21.
As was previously pointed out, conductors for the transmission of alternating current at extremely high voltages should have a considerable superficial area because of corona loss and since the skin effect tends to cause a concentration of the current in the outer shell of the conductor, it is preferable that the conductor should either be hollow or else have a non-conducting core. ln the conductor here illustrated it will be seen that the #desired superiicial area is readily obtained without increasing the weight of the conductor since the thickness of the structural members will be designed to meet the stresses which the conductor may receive in use and by the proper design andarrangement of these members, the required strength may be obtained without using excessive weights of metal. The conducting shell which may either consist of the arcuate portions of the several sector members or else a separate shell may be applied over the surface of the core. This shell will be of any desired cross-sectional area and its size will, of course, depend on the currents which are to be transmitted.' By con-l structing the conductor with the central reinforcing members illustrated vin lFig. 4, a considerably greater degree of mechanical strength is obtained and the cable is given further stiffness and resistance to collapsing stresses. The conductor illustrated in Fig. 8 affords a further' desirable feature in that a plurality of currents may be simultaneously transmitted and this type of conductor is useful not only in high tension transmission, but also in transmission of voltages of less than the extreme value.
It will be seen that I have provided a conductor which meets the several requirements of high tension electrical conductors and which may be given great strength to resist both longitudinal and radial stresses.
.cause disarrangementand loosening of the conductor strands laid upon it. By including in the core a plurality of radial structural members, the collapse of the tubular body of metal which serves asl a conducting path is prevented. The sector members or structural shaped spider represent a convenient method of providing these radial members and the sector members are particularly useful because, in the event that excessive stresses are placed upon them, they have a tendency to move across each other in such a way as to accommodate the cable to the lconditions to which it is exposed. This type of core is also particularly useful in that the arched members which extend between the ends of the radial members together provide a substantially tubular body of metal which can be used as a conducting path, so that a core made of these sector members need not be encased in a :further sheath of conducting material, so that with this typel of conductor the core and the tubular conducting body are produced by the. same elements. `With the structural shaped one-piece core used in Fig. 5, a sheath of conducting material is desirable.
The new conductor may be handled and supported in place according to the methods now-in use and it affords the further advantage that by changes in the size and shape of the parts of which it is composed, it may be designed to meet the requirements of varying surface conditions and in each form the metal of which it is composed hascthe most economical distribution. T have found, for eXampl'e',-"that the metal of which the conductor is'composed is most economically used when the cross-sectional area of the metal is less than approximately (1% of the total cross-sectional area. The value will depend,
ot course. on the total cross-sectional area, but when the cross-sectional area of the metal employed does not exceed the value above referred to the greatest economy appears to be obtained. However, local conditions may require that this value should exceed 61% but under anv circumstances the conductor made in accordance with the principles of this invention will be seen to have much greater resistance to longitudinal and radial stresses than the hollow conductors ordinarily emploved and it will have a superficial area which prevents excess corona losses, while the cross-sectional area of the current path is sutlicient to permit the 'low of current without undesirable resistance losses.
It is to be understood that in all the con- 'ductors produced in accordance with this invention, and as illustrated in the drawings,
radial stresses and consisting of a plurality.
of radially disposed metal structural members extending throughout the length of the shell, said core having' spaces extending lon gitudinally through it and dened by said -members..
3.- An electrical conductor which comprises a substantially cylindrical shell of conducting material. supported to withstand collapsing stresses by means of a plurality of internal metallic structural members radially' disposed, said members deiining longitudinal spaces extending from one end of the shell to the other, and a reinforcing member disposed along the axis of the shell to support the structural members.
4. An electrical conductor which comprises a plurality oi hollow sector members of conducting material assembled to iorm a substantially cylindrical core, the adjacent walls of each pair of sector members forming a radial supporting arm. and vthe curved walls of the sector members forming a shell for conducting the current.
5.13m electrical conductor which comprises a plurality of sector members, assembled to form a substantially cylindrical core, and a sheath of a metalbf high con ductivity encasing the core.
6. An electrical conductor which comprises a plurality of sector members, assembled to vform-a substantially cylindrical core, and a plurality oi strands of metal ol high conductivity wrapped about the core and iorming a substantially cylindrical shell for carrying the current.
7. An electrical. conductor which comprises a plurality ci hollow sector members ot' metal, having; an axial spiral conformation. and assembled to form a substantially cylindrical core, and means enclosing the core to hold its elements together,
8. An electrical conductor which comprises a plurality of hollow sector members of conducting material assembled to torin a substantially cylindrical core, and. a reim forcing member extending along the axis of this core 9. n electrical conductor which comprises :Weasel avplurality ci2 hollow sector members of corr du'cting'rn material assembled to form a substantially cylindrical core, and a reinforcing member extending axially of this core and insulated from the sector members. l
10..An electrical conductor which comprises a plurality of sector members assembled to form a substantially cylindrical core, a reinforcing member extending axially of this core, and a sheath of metal oi high conductivity encasing the core.
ll. An electrical conductor which comprises a plurality of hollow sector members of conducting material assembled to form a substantially cylindrical core` a central rein- "forcing member lying in the axis oi this core, and means for maintaining these sector members in assembled relation.
l2. An electrical conductor which comprises a plurality oia insulated hollow sector members oi conducting material assembled to form a substantially cylindrical core with the adjacent sides of each pair oi sector members Jforming radial arms, and means for maintaining* these sector members in assembled relation.
'13. en electrical conductor which com` prises a plurality of hollow sector members l5. ln electrical conductor, the combination oi a. p'urality ci members extending through the'lengg'th-.oi the conductor and arranged radially within the conductor, these members' together forming a reinforcing structure, and arched members of metal connectingg the ends of the radial members and together forming a substantially tubular me tallic; shellsupported by the radial members against collapse i6. In an electrical conductor, the combination ci a plurality ot hollow metallic members of sector shape. these iembers being so formed as to have relatively great mechanical strength and being assefnfnlefA to form a substantially cylindrical conducting member, and means enten-ding around. the assembled sector` members for retaining them in their assembled relation.