US2277460A - Gas filled cable installation - Google Patents

Description

March 24, 1942. G. B. SHANKLIN GAS FILLED CABLE INSTALLATION Filed June 6, 1940 GAS FILLED Inventov: ofiv/Qq B. .Shanklin,

- Ge y is Attorney Patented Mar. 24, 1942 2,277,460 GAS FILLED CABLE INSTALLATION George B. Shanklin, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application June 6, 1940,v Serial No. 339,135

4 Claims.

The present invention relates to gas filled cables of the type in which the insulation, such as paper, on the conductors is impregnated with a compound that is retained therein by capillary action and which has little tendency to ooze from the insulation even 'under load cycles. At suitably disposed places within the cross-section of the cable-are located free feed gas conveying channels which in addition to conveying gas to the insulation also serve as conduits for receiving and conveying any compound oozing out of the paper to selected points such as the joint casings. It frequently happens that there are low spots or areas of the cable occasioned by dips therein to avoid obstructions in the path of the cable such as water, illuminating gas and other pipes, or the dips may be due to the rugged profile of the ground in which the cable is laid. Such a dip or low spot may cause compound to collect in the free feed gas channels in amount sufficient to form slugs which interfere with the free movements of the" insulating gas. To prevent the eiIects of such slugs on the free flow of gas, a small solid wall tube extending from end to end of the cable is located at some convenient place in the cross-section of each cable length and through which gas may flow from suitable tanks from end to end of a cable section it stop joints are employed to sectionalize the cable, or from end to end of the cable if stop joints are not employed.

It is important to provide means whereby access may be had to these tubes without opening or removing the joint casings or injuring them in any way. Such access is necessary for various purposes, including testing for'gas leaks in the cable enclosures, as will be described later. It is, also important to arrange the portions of the tubes entering the joint casing from connected lengths of cable in such manner that any compound within the joint casing is prevented from entering the tubes where its presence would be supplied to the tubes as well as to the free feed channels and the Joint casings.

A furtherobject of my invention is the provision of an improved method of testing the cable installation to ascertain the approximate location of a leak in the cable sheath. I

For a consideration of what I believe to be novel and my invention, attention is directed to the accompanying description and the claims appended thereto.

In the drawing, Fig. 1 is a cross-section of a gas filled cable; Fig. 2 is a longitudinal sectional view of a joint between adjacent cable lengths; and Fig. 3 illustrates a modification.

In the drawing, 5, 8 and 1 indicate conductors and 8 the paper or other porous insulation theretion. The members I2 in addition to acting as conduits or channels for gas and any compound oozing from the insulation serve as internal supports for the sheath. The ends of the channels I l terminate at the cut ends of the cable sheaths and open directly into the chambers of the joint casings as shown in Fig. 2 so that compound, if and when it accumulates, may pass into the casing chamber. This action is facilitated if one.

or both cables are downwardly inclined toward the Joint. If there are dips or low areas in a cable length between joints, the oozing compound may collect in' the channels at the dips and form cause stoppage thereof and thus defeat the pur- I pose of the tube which is'to by-pass any slug: of compound located in low areas and ensure free now of gas between widely separated points, as terminals for example.

One object of my invention is the provision of improved simplified means or arrangement of slugs.

In order to by-pass any slugs which may form in the normally free feed. channels, a solid wall tube as of copper for example is located in one of the filler spaces defining a channel. For convenience of description, the tube is located in the left hand cable length is designated as the first tube and the tube I!" located in the right hand cable is designated as the second tube. Since each tube does not entirely fill the channel, a certain amount. of gas and compound may flow alongside of the outer wall thereof. The conductors are twisted or arranged to form long pitch spirals and on that account, the channels and the members I2, and tubes I3 and I3 are similarly arranged. This means that the channels and tubes alternately appear at the top of the cable and then at the bottom.

Referring to Fig. 2, I4 indicates the joints between the ends of adjacent conductors. In accordance with the usual practice, each comprises a metal connector for, each pair of conductor ends and an applied wrapping of suitable insulation. The joints are enclosed in a chambered casing I5 which i wipe soldered at IE to the sheaths of the cables. The sheaths are broken away to show the ends of the spiral members I2 and the channels. Because the solid wall tubes I3 and Ill are co-extensive in length with the cable lengths, and because it is desirable to cut back as little as possible of the cable ends, each tube is provided with a short length of tubing forming an extension thereof so that the total required length may be obtained and also to provide the necessary flexibility to permit training of the tubes to their proper respective positions. To the first gas tube I3 is connected a short length of flexible tubing H, such as copper, by means of a coupling I8. The outer end of the tubing terminates with an open end just under the upper wall of the casing I5. The end should be well above the level of any compound collecting in the chamber of the casing as well as above the channels in the cable. indicates a normal level of compound, and it will be noted that the ends of the coiled channel members l2 are well above the level shown. In service, the compound level may be above or below that shown.

To the right hand or second gas tube I3 is connected by a coupling 20, a piece of tubing 2| made of copper which is longer than the tubing I1 because it is terminated outside of the joint casing. To carry out this feature, a small opening is made in the wall of the casing and covering it is a chambered fitting 22 that is soldered or otherwise secured to the casing. The fitting has a central opening or chamber of a diameter substantially greater than that of the tube. tube 2i is bent upwardly and passes through the opening after which it is secured in. place by a soldered joint 23. Fig. 2 shows the end of tube 2| soldered in place at 23, a described. It is understood, however, that the invention is not limited to this particular method of sealing the tube end in place. Any effective method will. do. For example, a gas tight compressed assembly can be used instead. The chamber oi? the fitting is closed by a screw th and located between the metal p9. a gasket for ensuring a gas tight joint or seal. In. sembling the joint the tube N is pulled into the fitting by any suitable means.

It will be noted that the tubing iii forming an extension of the second tube I passes thro an the upper wall of the casing as distinguis ed from passing through an end oi? the casing the wiped soldered joint. This is important for several reasons. It is very difficult to a tube through a wiped joint and have it fluid tight; also it is more difiicult to wipe a joint where a tube projects through and hence is in the way of the wiping operation; also such pipes would have to be substantially longer. By the arrangement shown, the thin wall and rather delicate tube 2! is fully protected from injury due to external causes.

It is important to arrange the solid wall tubes I3 and I3 in series as regards the flow of gas, also The dotted line IS The -aded cap 2M :1

to fill the chamber of the casing with gas under pressure, also to provide means whereby one of the tubes I3, for example the right hand or second tube, may be. directly supplied with gas under pressure independently of the other or left hand tube. This has the advantage that the tube I 3 may be blown out by higher pressure without ailecting tube I3. Tube I3 may be blown out through gas admitted under suitable pressure from a joint casing at the left without afiecting tube I3. These features are important to the user of the cable in caseof trouble or in testing. To accomplish this a screw threaded elbow 25 is mounted in the cap 24 of the fitting and to this is connected by suitable compression type fittings 26, a short length of pipe 21. The pipe enters a T 28 which has a pipe 29 secured therein by a compression type fitting 3D. The other end of the pipe is suitably connected to the cap SI of fitting 32 which is generally similar to the fitting 22 except that no tube enters it. The portion of the casing under the second fitting 32 is provided with a port or opening 34 through which gas may enter or be discharged from the joint casing. The T 28, when desired, may have .a pipe 33 entering it for supplying the solid wall tubes I3 and I3 with gas under pressure. In the case of the second tube I 3, the filling is direct, and in the case of the first tube I3 the filling takes place through the joint casing. If this additional feature of supplying gas is not necessary or desired, the T may be omitted and a length of pipe connecting both of the fittings substituted. The parts above described which are external to: the joint casing are and can readily be made heavier than the tubes and are therefore much betteradapted to withstand possible injury. Because of the small cross-sectional area of the filler spaces between conductors, the tubes are necessarily small. Only one joint casing is shown but it is to be understood that each joint casing between lengths of cable aresimilarly constructed and arranged.

From what has been said, it will be seen that each solid wall tube has one of its ends secured to and supported by a chambered fitting and that its other and open end terminates in another joint casing remote from the first and above the level of any compound contained therein and requires no fitting. Such an arrangement not only avoids passing each solid wall tube through a wiped soldered joint but it rigidly supports one end of the tube and permits of the use of relatively heavy external fittings and pipe connections which are not easily damaged. In making a wipe soldered joint between the casing and sheath ends, hot solder is first poured over the parts to be united to heat them,'then solder at a lower temperature while iii a semi-plastic state is by suitable pads wiped by a circular movement aro nd the parts. Whereas it been proposed to or. d the solid wall gas tubes through the wipadiiliculty is encountered in the wiping operation by reason of the presence of the tube. In particular, difllculty is experienced in getting the solder to completely fill the small space on the underside of the tube adjacent the sheath. Stated another way, the projecting tube forms a bump which interferes with the smooth application of the solder entirely around the tube and the joint between the casing and sheath. Even the smallest leak around the tube will cause a loss of gas from the installation. Because the tubes of necessity have thin walls there is also danger of pinching the tube or even breaking it in the region of the solder when the tubes outside of the casing are trained to their proper positions or during the various jointing operations. It is also to be borne in mind that all of the work of jointing has to be carried out in manholes where space is at a premium and where conditions are generallyunfavorable to fine work.

The arrangement has the advantage that access may always be had to the second tube from the outside of the casing by merely removing the cap on the fitting, or it may be done by opening one of the compression fittings. Since only one tube need be accessible from the outside of the casing, the structure -as a whole is thereby simplified. It also has the advantage that external control of the gas conditions is obtained by simple and. reliable means and this with a minimum danger of gas leaks. Leakage of gas from the interior of the cable installation is prevented due prin-. cipally to the fact that the soldered joint '23 in the fitting 22 is small and hence easily made gas tight and to the use of the well packed caps on the fittings. Also, the surfaces of the two fittings which engage and are supported by the casing are small and for that reason may easily be made tight by soldering.

Because the ends of the conductors occupy angular positions determined by the lay of the conductors and are relatively stiff and for that reason cannot readily be moved angularly from their respective positions, because in many instances the joints and their wrapping very largely fill the joint casing leaving little room for the gastubes and because it is important to have the tube fitting located at the top of the joint casing where it is readily accessible, the arrangement shown in Fig. 3 may be employed. In this figure, the end of the solid wall tube I! is terminated close to the inner wall of the casing as before, the tube being long enough so that it can be bent around one or more of the joint coverings if necessary. The other tube 2i is longer and instead of terminating directly in a fitting, as in -ing into the casing. Desirably the tube 21, particularly the portion located outside of the joint casing, is made sufiiciently strong to minimize injury due to external causes. The portion or tube located outside the casing may be regarded as a conduit connecting the tube with the chamber of the fitting. As stated above, the conduit may be stronger than the tube within the casing. The cap 39 of the fitting may be united with the extended end of the tube 2| in my suitable gas tight manner, as by soldering. When it is desired to make the connection between parts readily removable, a compression type fitting 40 may be employed. For convenience of illustration, the tube opening 35 and the fitting 31 are shown as located in the same axial plane but this may or may not be the case in an actual cable installation. The tube 35 may be located wherever it is the most convenient having due regard to the respective positions of the cable ends. The opening will commonly be made by the splicer when aswhether or not compound slugs, such as previ-- ously described, exist at low points or dips in the cable run. If such slugs exist, .gas fiow past theseexist at low points or dips in the cable run, the

Fig. 2, passes through an opening 35 in the casing sembling the joint. The lengths of solid wall tube in the cable, with access to the tube ends as described, furnish a convenient means of locating accidental gas leakage along the cable line. The test locating method used depends upon points in the regular. free feed'channels I2 is stopped, but the compound free tube for example [3 readily by-passes these slugs and gas how towards the point of leakage continues only in the tube lengths and the joint casings connecting the tube ends. sary to shut off the tube lengths from the joint casings and temporarily stop the flow of. gas through the tubes. This can be conveniently done by disconnecting anyone of the external fittings, such as 26 or 40, and temporarily plugging the disconnected ends. The slugs on each side of the point of leakage then limit the gas supplied to the leak to a relatively short section of the cable line and the gas pressure in this isolated section falls below that in the rest of the line. The leaky section can be readily located by pressure readings at-each joint along the line until the low pressure point is reached.

To accomplish the above, it is obviously necessary to shut off only one end of each tube length. That. explains why tube end I! is not also brought outside the joint casing, and the necessary control fittings thereby simplified at reduced cost.

Where no complete compound slug stoppages by-pass tube I3 still furnished a useful purpose in locating leaks. A gas flow meter can temporarily be inserted at a convenient external fitting, such as 26 and 40, and the direction of gas flow, the amount of gas fiow, and the pressure drop read. The point of leakage can be readily traced down in this way. Large leaks can be more quickly located by merely reading the gas flow and pressure drop at two or three selected joints along the line and calculating flow resistance as a function of cable length. The tube l3, being of uniform bore and entirely free of compound furnishes a uniform flow resistance for this purpose, not offered by the channels II, which usually have non-uniform and uncertain flow resistance because of the heavy compound clinging at random to the channel walls.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A gas filled cable installation comprising lengths of insulated conductors, joint means for uniting them, compound impregnating the installation which is liquid at cable operating temperatures, impervious sheaths for the conductors, a chambered casing for each joint means forming a sump and providedwith openings'located in its wall between the ends thereof, the ends of thethereof and conveying it to the sump, first and second solid wall gas conveying tubes, one in each cable length, for by-passing slugs of compound contained in the channels thereof, the first tube having an open end terminating in the casing above the level of the channels, a first chambered fitting covering one of the openings in the casing wall, a second chambered fitting also mounted on the casing and covering another of its openings To locate the leak, it is first neces lengths of insulated conductors, Joint means for uniting them, compound impregnating the insulation which is liquid at operating temperatures of the cable, impervious sheaths for the conductors, a chambered casing for the joint sealed at its ends to the sheaths and provided with an opening located between its ends, free i'eed channels within the sheaths opening into the casing chamber for feeding gas under positive pressure to the insulation and receiving liquid oozing from the insulation and conveying it to the casing chamber, a chambered fitting closing the opening in the casing with its chamber in communication with the opening, and first and second solid wall gas conveying tubes located within the sheath for by-passing slugs of liquid contained in the channels, the first tube having an open end terminating within the casing chamber above the level of the channels, the second tube conveying gas to and terminating in the chamber of the fitting so that gas may flow between the tubes through the intermediary of the casing chamber.

3. A gas filled cable installation comprising jointed lengths of insulated conductors, compound impregnating the insulation which is liquid under operating temperatures or the cable, impervious sheaths for the conductors, chambered casings for the joints, each secured to and connecting adjacent sheath ends and having an opening in its wall in spaced relation to the ends thereof, a chambered fitting secured to the wall of each cas ing for closing the opening therein, a free ieed channel within each the sheaths for supplying gas under pressure to the conductor insulation and receiving compound oozing from the surlface thereof, the channels opening at one end into a Joint casing, a solid wall gas conveying tube located within each of the cable lengths for bypassing slugs of compound contained in the feed channel thereoi', one end oi. each tube extending outside the casing and being provided with conduit means connecting it to a fitting, the other end opening into the casing of another Joint at a point above the level of any compound contained therein, said conduit means being located outside of each casing and conveying gas between the end of the tube extending outside the casing and the open end of another tube located in the same casing through the intermediary o! the casing chamber.

4. A gas filled cable installation comprising lengths of insulated conductors, Joint means for uniting them, compound impregnating the insulation which is liquid at operating temperatures of the cable, impervious sheaths for theconductors, a chambered casing for the joint sealed at its ends to the sheath and provided with an opening located between its ends, free feed channels;

within the sheaths opening into the casing chamber for feeding gas of positive pressure to the insulation and receiving liquid oozing from the insulation and conveying it to the casing chamber, a chambered fitting closing the opening in the casing with its chamber in communication with the opening, first and second solid wall gas conveying tubes located within the sheaths of the respective conductors for by-passing slugs of liquid contained in the channels, the first tube having an open end terminating within the casing chamber above the level of the channels and the second tube terminating outside the casing, and conduit means connecting the end of the second tube terminating outside the casing with the chamber of the fitting and conveying gas so that the gas may flow between the tubes through the intermediary of the casing chamber.

GEORGE B. SHANKLIN.

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