US1574076A - A cobpobation - Google Patents

Description

H. W. FISHER HIGH VOLTAGE CABLE AND METHOD OF MAINTENANCE Feb. 23 192e.

Filed Feb. 5, 1925 W/ T/VESSES Patented Feb. 23, 1926.

UNITED; STATES PATENT OFFICE.

HENRY W. FISHER, OF PERTH AMBOY, NEW JERSEY, ASSIGNOR T STANDARD 'UN- DERGROUND CABLE COMPANY, OF PITTSBURGH, PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA.

HIGH-VOLTAGE CABLE AND MIETHODy 0F MANTENANCE.

Application filed February 5, 1925. Serial No. 6,925.

To all lwhom t 'may concern:

lBe it known that I, HENRYV W. F IsHnn, residing at Perth Amboy, in the county of Middlesex and State of New Jersey, a citizen ofA the United States, haveiinvented or discovered certa-in new and usefull Improvements in High-vonage eabies and Mettons of Maintenance, of which improvements the following is a specification.

W ln Letters Patent of the United States, No. 1,418,369,`granted June 6, 1922, to Ralph W. Atkinson and myself, as joint inventors, a hollow electric cable is described, and a method of cable building, whereby the ca- ]5 pacity of a cable to carry currents of highvoltage is increased. ln Letters Patent No.

1,524,124, granted January 27, 1925, Mr.

Atkinson and I describe and claim further improvements in the structure and operationA of high-tension cables. My present invention consists in improvement upon the Structures and methods of these prior inventions.

Since in its development my present invention is most obviously applicable to the building and operation of a hollow cable, l shall describe it in such application, and in the sequel shall indicate its wider applicability.

ln the accompanying drawings Fig. lt is a view in longitudinal section, and Fig. lll

a View in transverse section, of'a cable built and adapted to be maintained in service, ac-

cording to the teaching of my present invention. Fig. lll tis a view simil-,ar to Fig.

l, illustrating the struct-ure of a joint formed in an installation, where the ends ol lengths of cable are united. Fig. lV is a\\ view, illustrating a modification of struc- A ture which may be'resorted to in the praer tice of the invention. Fig. V is a. view similar to Fig. ll and illustrating another perinissible variationin detail. The invention is applicable to' cab-le struc-tures varying widely in absolute and in relative dimenv sion-s as well; the drawings, therefore, serve primarily to show the invention in application, and are in other respects diagrammatic. In Figs. I and II, 1 indicates a group of strands of wire (ordinarily bare wire) which ein together constitute the conducting element of the cable. This group of strands is built and sustained in annular form by being laid helically upon a flexible tubular core 6, formed ordinari-ly of a helix of metal wire or ribbon, and itself pervious to the passage of fluid. Surrounding the annular group of conducting strands is the bodv .of insulation 4, and encasing all is the sheath 5, formed ordinarily of lead or of a lead alloy.

llt -is the envelop-e of insulation 4 with which my present invention has primarily to do. The envelope of insulation consists essentially of a body of pervious solid niaterial, soaked full of a material which, at least when applied, is liquid. Typically the envelope consists of wrapped-on paper tape, lilled with an` oily or resinous substance called insulating compound. For my particular work in building cables intended to carry currents of exceedingly high voltage, l use a material of great dielectric strength and fluidity, such as mineral oil. 4

The invention of the patent first mentioned above, No. 1,418,369, is practiced upon a cable in course of building, and consists, generally stated, in a particular way of lilling the envelope of paper with yinsulating compound. rlhe filling is done after the envelope of paper has been applied to the conductor, but before the cable has been sheathed in. lead, and it is done by causing the insulatingcompound to enter the envelope of paper through one surface while the air which the entering compound displaces, escapes from the opposite surface. The `invention of the second of the above mentioned patents, No. 1,524,124, is achieved while the cable continues in service, and consists in maintaining pressure upon thc fluid which fills the pervious body of insulation, to the end that air or gas present in the insulation shall be compressed, with gain' in dielectric strength, and, in case the air or gas be present in the form of bubbles within a liquid or plastic insulating compound, then the bubbles will by compression be reduced in size, and danger of leakage and breakdown will correspondingly be tained on opposite sides of the body of pervious insulation, and it may be performed upon the sheathed cable either in the shop or in the field, as may be preferred.

Referring again to Figs. I-III of the drawings7 the hollow cable adapted to my present invention is formed with a space left vacant between the envelope 4 of pervious solid insulating material,in this case wrapped-on paper-and the lead sheath 5. This space is continuous longitudinally of the cable, throughout intervals suflicient at least for the practical enjoyment of the invention. The cable body is in this particular case shown to be wrapped under its sheath with a helix 7 of suitable materizl and a -material of thickness suliicient to afford spaces of substantial depth between the turns of the helix and beneath the subsequently applied lead sheath. This helical wrapping may conveniently be a wrapping of wire or of metal ribbon. It will be perceived that in the finished cable this wire or ribbon serves as a spacer, holding the cable body central within the sleeve whose inner diameter exceeds the diameter of the cable body. The space between insulating envelope and lead sheath may be about three sixteenths of an inch deep. The operation of the lead press used in forming the sheath about the cable body is highly developed, and expedients by which to produce the linished cable with the desired space between the turns of the spacer and beneath the sheath are within the knowledge of the art. Thus in the finished cable I have 'a body of permeable insulation, enveloping the conductor and accessible over both its inner and its outer surface.

The pervious body of insulation 4,-ordinarily, wrapped-on paper-may or may not at thebuilding of the cable be filled within- Sulating compound. But whether the paper envelope has been filled or not, .when the cable is installed connections aremade by which one of the opposite surfaces of the body of insulation may be submerged in a iiow under elevated pressure of insulating -1 compound, while from the opposite surface of the body of insulationthere is escape for fluid underrela-tively low pressure. erably the procedure is this: Insulating f compound, such for example as mineral o'il,

. is forced under pressure from a point preferably mid-way in the length of a cable under treatment, first through the spiral space s which surrounds the core beneath Prefflow in that direction may -be checked. This may conveniently be accomplished by closing the breathing holes in junction boxes and terminal boxes through which the disl placed air has up to that time been escaping. The pressure upon the body of oil within the helical space surrounding the cable body is now effective to cause the oil to flow centrally through the envelope 4 of pervious material, and as it flows to displace the air or other gas present in the envelope and to cause it to pass into the central hollow within the cable, and to escape thence at the cable ends. Eventually, as this condition continues, oil will fill the hollow Within the cable, and continued How willltend to carry from the envelope 4 of permeable material all traces of air or other gas entangled within it in the form of bubbles. And of course the pressure is effective to reduce the size of any bubbles which by chance might remain.

I'have said that the pervious body 4wh/ich constitutes the cable insulation may or may not be filled with mineral oil or its equivalent, before the application of the lead sheath. And I pause here to consider the matter in certain practical aspects. It is possible, practically, to apply the lead sheath to the dry cable, and thento proceed with the practice of my invention. To do this a large tank must be provided, within `which, by heating and the exhaustin of air,

Abeen effected, impregnation-with mineral oil orits equivalent may be effected, after the Imanner already described.

'sheath 5. As 'the wave of oil advances, it l By -way of alternative the body of porous l insulation 4 may preliminarily be filled with mineral oil or its equivalent. In'such ca'se the cable Willbe carried Vimmediately from the tank within which filling is effected, to f the lead press. The ditliculty presents itself of maintaining the structure unimpaired, and specifically of preventing ,the oil from draining away, or ofsupplying more as the oil inevitably drains away, in testing,- shipping, and installing. It is quite possible to establish suitable connections, and to maintain a supply of oil under pressure, to supply any oil which may under the circumstances suggested, be lost to the structure. Of course it is possible in such case to introduce the fresh supply of oil centrally, and

to provide a suitably packed orifice of escape, and to collect again so much of the oil v as shoul escape through that oriiice.

' In eit er case, after installation the flow of oil through lthe body of insulation 4 should be continued, until no sign remains of air still carried out with the emerging oil. The jointing 03E-such a cable as this is an important matter, and requires particular attention. lf a paper-wrapped joint be Imade, care should be exercised to have the Wrapped-on insulation within the joint of equal penetrability, as nearly as may be, with Athe insulating body 4 upon the cable proper. For, if there were great disparity here,feither too much oil or too little oil might penetrate'the joint insulation. lndeed this joint insulation might, in a given case, never become thoroughly saturated.

lBy wa` of alternative, a joint structure may be built of tubes of great. dielectric strength, and oil being introduced through the hollow within the cable, and low-presv ure conditions being established externally of the tube but within the joint casing, oil may be caused to ow through the seams, where the tubes of, the joint insulation meet the cable insulation proper, and thus all the space within the joint casing may be filled with oil. Preferably theJ joint installation will consists of a number of thin tubes formed of bakelite or equivalent material, held apart by fins of high puncture material and equally spaced.

After an installation has otherwise been completed, flow of oil will be maintained until` assurance is had, that the entire cable is thoroughly lilled with oil.

My invention involves the maintenance of the cable installation during service under such conditions of pressure inequality as l`- have described. l may or may not maintain a constant and appreciableow of oil .through the paper, butv l do in any case maintain pressure conditions such as to cause flow in case of leakage at any point, and

such as to cause migration as the body of( oil expands and contracts locally under varying conditions of temperature. Thus ingress of air and moisture is guarded against under the ordinary conditions and accidents of service.

lt is very diiicult to make a cable which may not have at some point an imperfection. The manufacturer can never guard perfectly against carelessness in manufacture, and it is practically inevitable that in a given length of cable there shall be points of weak. ness, where under high voltage there is danger of break-down. By resorting to my invention, which in its essential features l now have described, small irregularities here and there in the structure of the envelope of paper insulation, such as are practically inev1table, cease to be'points of weakness. The

ysleeve 8 the conductors l themselves may be united by soldering. Thus the interior holf low is made to extend continuously, throughout the length of the installation,.-or throughout so much of the length as is convenient. Within the casing 9 which in its generalefeatures is such a casing as is usual in making joints, the conductor-ends andthe connecting sleeve may be wrapped in paper filled' with mineral oil, or enclosed in an equivalent insulating envelope. The joint casino' 9 may be provided at the top with a illlng hole l0 and with a screw-cap l1 applicable thereto, so-that when oil under pressure is introduced into the cable structure, in the manner already described, the air initially present in the spiral spaces surrounding the core and beneath the sheath will escape to the joint, and as oil continues to flow the casing 9 will be lilled with oil, immersing the insulated union of the cable ends. When the casing 9 is so filled with the flowing mineral oil the screw cap ll may be applied, and, the path of flow of oil through the joint casing being closed, the oil under pressure will now penetrate the envelope 4 of paper insulation whichasurrounds the conductor l. This penetration will occur throughout all the length of the cable. rlhe oil so penetrating the envelope 4 of paper will enter and till the hollow space within the cable.

At the ends of the cable there may be escape for oilthrough U-shaped lengths of pipe to tanks arranged to receive the overflow. And at the point of escape the fiow may be cut off at proper time, or so regulated that the desired condition of pressure may throughout the extent of the cable be maintained upon the mineral oil within the in- .s sulating envelope. y

Pressure may be exerted upon the oil on the outer side of the insulating envelope in any suitable way, as by a pump, or by means of an elevated tank. aiording suh'icient hydrostatic head. And pressure regulating means of any preferred sort may be provided at the ingress of oil to the cable.

lf the length of cable be great, connections may be made and the mineral oil be introduced within -the cable sheath at a plurality of properly spaced points.

lily invention has been developed in designing a cable to carry voltage of magni- -of oil may or may not continue.

tude hitherto unknown for underground work132,00 0 volts, for eXample. And by adopting the invention the danger to the insulation of great voltage stress is so far reduced a's to be practically eliminated.- The expense of maintenance will be found to be relatively a small matter, comparedv with the gain of having a cable strong to endure such very high voltage as that indicated.

When once installation has been made and the cable has been filled with oil, flow A slow migration atleast of the oil while the cable is in service iscertainly permissible, and the security incident to movement of the oil is manifest. My invention still, however, will be. practiced, though there be no actual progress of the oil, but only such ebb and How as may be incident to heat variations. In case a leak should open in the cable sheath there will ofcourse be iow, and the pressure conditions are constantly maintained, so thatin the event of such an accident flow under pressure will begin and continue. Ingress of moisture is thus guarded against, the integrity of the insulation is maintained at full dielectric strength, and at the same time the escape of oil may be a tell-tale, by which to detect the accident which has occurred to the sheath.

I Vhave described the flow of liquid insulation under pressure after installation has been made. Manifestly, this flow of liquid insulation may be practiced in the shop upon the still unlaid lengths of cable, and after such performance the ends of the lengths of cable may be sealed and so maintained in condition for installation.

I have described the invention as achieved in causing the oil under pressure to penetrate the envelope of insulation in a direction from circumference to center of the essentially cylindrical structure. Manifestly the connections, may be reversed and the flow established from the hollow within th cable outward. f

. I have described the invention in application specifically to a hollow cable. Manifestly it is applic-able Wherever a body of insulation enveloping a conductor is accessible over its opposite surfaces. In Fig. IV, for example, I Show a cable in which a conductor l, which may be understood to be a compact body of strands, is contained within an envelope 4a of wrapped-on paper; and the so enveloped conductor is enclosed within a sheath 5a. Between conductor 1a 'and envelope 4 and again between envelope 4a and sheath 5 are spacing bodies, conveniently in the form of open helices 7a and 54', affording on vopposite surfaces of the body of insulation 4 access, for the practice of the invention in the manner described.

The inner face of the sheath may be formed with projections, and so spaces may beafforded to achieve Athe ends indicated. In such case, as the electrical engineer will perceive, it will be desirable to Wrap the cable body beneath the sheath with a closeiitting wrap of wire gauze or its equivalent. This is illustrated in Fig. V, vwhere the body of insulation 4 is shown to be provided with a pervious, metallized surface l2, and the lead sheath 5 is shown to be formed internally with outstanding bands or welts 13,

which welts immediately engage the metalli'zed surface l2 of the body 4.

I claim as my invention:

l. In a cable structure the combination of a conductor, an envelope of permeable insulation surrounding the conductor, an impermeable sheath surrounding the Whole, the opposite surfaces of the envelope of insulation being accessible to a stream of liquid insulating material, a conduit for liquid leading to the envelope of insulation over one of the opposite surfaces thereof, and a body of liquid insulating material under pressure filling the said envelope of permeable insulation and the approach thereto through said conduit.

2. In a cable structure the combination of a hollow conductor penetrable by a stream of liquid, an envelope of permeable insulation surrounding said conductor, an impermeable sheath surrounding said envelopeof insulation with a space interval between, a liquid conduit opening through the sheath to the space interval between sheath and insulating envelope, and a body of liquid insulating material under pressure filling all the structure.

3. The method herein described of build ing a cable which consists in enclosing a conductor within an envelope of'permeable insulation and the so-enveloped conductor within an impermeable sheath, the said envelope of insulation being exposed over its opposite surfaces-to the flow of a. stream of liquid, and then causing a stream of liquid insulating materialiunder `pressure to ll and sweep through the said insulating envelope. y

4. The method herein described of building a cable which consists in enclosing a hollow stranded conductor within an envelope "of permeable insulation and then enclosing with an interval between, the so-enveloped conductor within an impenetrable sheath, the said sheath having an opening through it for the passage of a stream of fluid, and then causing a stream of liquid insulating material under pressure entering the cable structure to filland sweep through said enf velope of insulation.

5.. In a cable installation a cable struct-ure in which a conductor is enveloped in a body of perineable insulating -material exposed over opposite surfaces to the flow of a stream of liquid, and a body of liquid insulating material under pressure filling the said envelope of ,insulation and the approaches thereto.. l

6. The method herein described of `maintaining the dielectric strength of cable insulation under the vicissitudes of'practical ,operation which consists in providing an insulating envelope of permeable material lilled and immersed in a stream of liquid insulation and, maintaining pressure upon such stream of liquid insulation.

7. In a'cable installationa conductor arranged inan electrical circuit, a sheath surrounding and separated at an interval from said conductor, and a stream of insulating fluid flowing through the v'space at which conductor and sheath stand apart.

8. In a cable structure the combination of a conductor, an envelope of permeable insulation surrounding the conductor and acces- `my hand.

.HENRY W. FISHER.

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