US 1132452 A
Description (OCR text may contain errors)
c. W. DAVIS.v
MULTIPLE CONDUCTOR CABLE.
APPLICATION FILED JAN.14,1914.
1,1 32,452. Patented Mar. 16, 1915.
UNrrD sTATEs PATENT oFFIc.
CHARLES W. DAVIS, OF EDGEWORTH, PENNSYLVANIA, ASSIGNOR TO STANDARD UNDERGROUND CABLE COMPANY, F PITTSBURGH, PENNSYLVANIA', -A` CORPO- RATION oF PENNSYLVANIA.
My invention relates to the construction of multiple-conductor cables for carrying high-tension currents and its object is to increase the efficiency of cables; more specilically, by eliminating tendenciesto deterioration, to render such cables serviceable for longer time and capable of carrying higher voltage.
I shall describe my invention as applied to a three-conductor cable, but it will Abe understood that it is applicable to multipleconductor cables generally.
Three-conductor cables' are ordinarily built by surrounding the individual conductorsL (whether solid or stranded) each in its own envelop of insulation, twisting the three together into a rope with jute or like cheap filling material occupying the central triangular space and the superficial grooves formed bly and between each pair o f adjacent conductors, and inclosing the whole -rope so filled and rounded u t with what is called a belt insulation. Over the belt insu- `lation the leadV sheath or other protecting cover is applied.
The suing material referredifo (which,
ordinarily is jute) has been regarded merely as a filler, and its electric properties Ahave heretofore received no serious attention by cable engineers.
Irl f hi gh-voltage lwork, I, have discovered l the jute fillers as ordinarily employed to be themselves a source of ldeterioration and as such, by theirvery nature, restrictive. upon the wider utility of the cable; and my inven-V tion resides in the employment of materials of certain character or quality which will be effective to overcome the defect which I have discoveredv and am` now pointing out.
When the cable is-made in the`ordinary manner and high-tension alternating currents are passing in the conductors, the ma terial within the cable sheath` surrounding the individually insulatedconductors and inclosed in the belt insulation, (all of which is dielectric, and, ordinarily, jute) sub- Specicaton o Letters Patent.
jected to dielectric, stress. The intensity of vthis stress varies greatly, from the geometric center of the cable (where, theoretically, the
`-the points where each pair -of adjacent conductors 'approach one another most nearly. The nature of juteis such that, under this stress, it absorbs energy, converting the energy into heat. This effect is objectionable for two reasons: first, it is a useless waste of energy and (the-center of the cable being unventilated) the consequent rise in temperature may char thefiller, and impart heat to the insulation surrounding the individual conductors and tend'to the breaking-down ofthat insulation-for, with materials used for that purpose, the energy loss increases as the temperature rises.
I have discovered that if layers of conducting material be ,interposed between the insulation of the individual conductor and the filling material, the filling material, relieved of the stress mentioned, will cease to be subject to deteriorationand will cease to be a heat generator, and therefore will cease to be a hindrance, as it'otherwise is, to
Patented Mar. 16, 1915.
Application filed January 14, 1914. "Serial N o, 811,980.
a` Wider use of the cable. Incidentally,.it
is to be observed that such a layer of conducting material if present, Abeing a conductor of heatas well as of electricityJas is true of metals) will by its presence tendo al distribution of whateverheat may be generated locally within the insulation surrounding the individual conductors. This is a practical advantage which is brought out 1n my copending application, filed November 4, 1913, Serial No. 799,090.
My invention, therefore, primarily consists in applying to the faces of the individually insulated conductors bodies of con' ductingmaterial. In applying this body of conducting material, I am careful to provide that it. shall not completely envelop the individual. separately insulated conductor, and it shall not extend circumferentially around it to an unnecessary extent, and this for the following reasons: y
First, if the individuallyl insulated conductor be wholly surrounded in metal foil vor in a layer of conducting material of some other character, the belt' insulation ordinarily applied around the twisted and filled rope, becomes valueless as insulation, and,
therefore, ther presence o'f theV conducting` layer would, if it extended all the way around, necessitate the increasing of the thickness of the insulation of the individual conductors and the economy of the belt insulation would be lost. N
A second reason against a conducting layer wholly surrounding each individually insulated conductor is this: Insulation, however carefully made and however carefully applied, cannot be produced with absolute uniformity: there are necessarily and unavoidably points in any insulating envelop which are weaker than other points. In the making of multiple-conductor cables, the components are laid side by side, and, it will be understood, there is some danger that in the assembling, two such weak points in the insulation of two conductors may be brought opposite one another. In such case, a breakdown of insulation iS a present danger and such Aa condition is a flaw in cable-making. But, since considerable flaws in insulation are few and far between, the danger noted is remote, and easily guarded against by the cable-maker i testing his product before putting it on tlhe market. But, if the cornponents of the cable are enveloped before being bunched, each in a skin of conducting material,- and then placed skin to skin, the .effect is to bring all 'weak points of the insulation of two adjacent ycables opposite one another, and so insulation otherwise entirely adequate becomes quite inadequate if envel-l oped in foil. I therefore apply theV metal foil or other conducting layers only to so much of .the surfaces of the separately insulated conductors as hold between them filling material subjected to the great and destructive strains already defined.
Referring to the accompanying drawings, which form part of this specification, Figures 1 to 5 show, each of them, in cross seci tion, a three-conductor cable embodying my invention, the specific details being various, thus indicating that my invention in its broader aspect is not limited to details of construction. Fig. 6 is a view in perspective of a central filler constructed according to my invention in one of its alternate forms; and Fig. 7 shows in end elevation another form of my central filler.
Fig. 1 shows the three conductorsl, each covered with its own insulation 2, bunched to form a cable. The inner surfaces of the bunched insulated conductor are faced with conducting material. This facing material is indicated at a-b, -d, e-f. As has been said it may be metal foil; it may be wirenetting; it may be paper rendered conductive by a coating of metal; or it may be any other conducting material of proper shape for the intended use. The strains against which provision is intended are at a maximum near the point of nearest approach of adjacent cables; accordingly, the metal facing will preferably extend, as shown in Fig. l, from the center of the cable outward beyond such points of closest approach. The individual insulated conductors, when they are bunched, are given a slight twist, to form a. rope; accordingly, the metal facing, if applied to the individual conductors before `bunching, will be laid around the individual conductors in a long spiral, so that when the ca-ble is completed they will occupy their intended positions. If the insulation upon the individual conductors be of wrapped-on paper, as is ordinarily the case, the strip of conducting material may be laid on and retained beneath the outermost turns of the wrapping. The central filler inclosed between the metallized surfaces of the bunched insulated conductors may be of whatever character 'preferred-it may be jute, for, as has been explained, the presence of the metallized surfaces prevents the objectionable results otherwise attendant upon the use of jute.
As shown in Fig. 2, the layer of metal, instead of being applied to the surfaces of the insulated conductors, may be applied' to the surface of the filler. And, for reasons already given, the body of the central filler will in this case preferably be extended between each pair of adjacent conductors beyond the points of nearest approach. Thisr central bqdy, covered with a layer of conducting material may be formed of jute and the conducting layer may be a flexible sleeve, so that the whole may be shaped as the cable is assembled; or the entral body may be formed of a material hich can be molded or pressed to permanent shape. In Fig. 3 such" a material is illustrated. The filler is formed of rolled paper, impregnated with -an insulating compound which is fluid when hot, and is pressed to shape in a die and allowed to cool and harden. The dielectric properties of such a filler are far superior to those of jute; and, as I have explained in a co-pending application, filed on even date herewith, Serial No. 811,979, a filler so made constitutes another and distinct invention of mine.4 But, for the purposes of this case, it is suiicient to describe a filler made of material which may be'shaped, for with such material my invention is more readi tised.
As shown in Fig. 7, the layer of conducting material, instead of being applied to and sustained by an underlying body, may be made heavy enough to sustain its proper shape, and the body within may be dispensed with, the filler then becoming merely a properly shaped tube-ordinarily of metal. And it will be understood, without specific illustration, that the filler may be a solid body of retal or other conducting material.
Referring to Fig. 3, it will be seen that` the metal layer may be applied to the surfaces of the individually insulated cony pracductors, not only toward the center of the group, but also beyond the points where each pair of adjacent conductors approach one another most nearly. Here layers (of metal foil or other conducting material) c-Z, 'rn-n, o-p, cover` the opposing but divergent surfaces of the conductors; and they by their presence relieve the lateral lilling material of those prejudicial strains already mentioned, and they also serve to assist in dissipating whatever heat may be generated within the insulation of the individual conductors. Theextent of the metal layer around the individual insulated conductors will depend on conditions of intended service. In no ease will the layer extend all the way around, for,.over the outermost portion of the surface, its presence is disadvantageous. Its value is greatest in the vicinity of the center, and beyond the points where the individual conductors approach one another most nearly, its value decreases; andthe limiting consideration is this, that, the greater its circumferential extent, the more objectionable is the presence of the layer, for reasonsv already explained.
Fig. 4 illustrates a pref which the central filleriscovered with a conducting integument while the laterals are formed according to and possess the advantages of my invention of the application last referred'to above, Serial No. 811,979. The laterals here are preferably molded or pressed, being formed of coiled paper saturated withan insulating compound of high specific inductive capacity; and the whole capable of enduring dielectric strains equally in all directions.
Fig. 5 shows both central and lateral fillers covered with conducting integuments.
It will be understood from what has gone before, and without' further illustration, that, just as the central filler may be made solid or tubular, and wholly of conducting material, so these lateral fillers also may be made whollv of conducting material and may either be tubular or solid.
It remains only to remark that the conducting bodies whatever their circumferential extent around the individually insulated conductors, and however they may be introduced, need not be continuous throughout the length of the cable, but, for example, may be applied in bands T around a previously shaped filler, with intervals between adjacent bands. This is illustrated in Fig. 6.
I claim as my invention:
1. In a multiple conductor high -tension cable, a body of conducting material covering the inner face of. the individual insulated conductor and extending part way around such individual conductor.
erred form, in`
2. In a high-tension cable including three or more separately insulated conductors, an incomplete integument of conducting material covering the opposing faces of each of the assembled insulated conductors and extending outwardly beyond the point where each pair of adjacent conductors approach one another most closely.
3. In a multiple-conductor hightension cable, the combination of a plurality of individually insulated conductors symmetrically assembled around a central filling body, said central filling body being covered with an integument of conducting material, such integument incompletely surrounding said individually insulated conductors. v
4. In a multipleconductor high tension cable, a central body filling the space formed by and between the assembled insulated conductors, said filling body being covered with an integument of conducting material, and a facing of conducting material incompletely surrounding each insulated conductor and applied to the opposing surfaces of each pair of adjacent msulated conductors beyond the point of their closest approach, one to the other.
5. In a multiple conductor high tension cable, a central body filling the space formed by and between the assembled insulated conductors, said iilling body being covered with an inte umentof conducting material, and lateral' lling bodies formed of material caable of enduring electrical stress equally in allvdiiections. l
6. In a multiple conductor high tension cable, lateral filling bodies filling the spaces formed by and between the assembled insulated conductors and the sheath and covered with integuments of conducting material.
7. In a multiple conductor high -tension cable, a central body filling the space formed by and between the assembled insulated conductors, sai filling body being `covered with an integument of conducting material and strips of conducting material incompletely surrounding each insulated conductor and covering the opposed faces of each pair of adjacent insulated conductors, outside the points of closest approach.
8. In a multiple conductor high tension cable, a facing of conducting material upon the inner face 4of the individual insulated conductor, such facing being noncontinuous longitudinally of the cable.
In testimony whereof I have hereunto set my hand.
. CHARLES W. DAVIS. Witnesses:
E. S. SIMKENs, FRANCIS J. ToMAss'oN.