US2176749A - Joint for gas-filled cables - Google Patents

Description

Oct. 17, 1939 I SHANKUN 2,176,749

"JOINT FOR GAS-FILLED CABLES Filed Dec. 30, 1938 Fig.5

6A8 FEED CHANNEL COMPOUND 6A5 FILLED Inverwtor: George B. Shanklin,

by 3 His Attorheg.

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Patented Oct. 17, 1939 UNITED STATES JOINT FOB. GAS- FILLED CABLES George B. Shanklin, Schenectady, N. Y., assignor to General Electric Company, a corporation or New York Application December 30, 1938, Serial No. 248,491

Claims.

In my application for Letters Patent, Serial No. 224,170, filed August 10, 1938, there is described and claimed a new type of cable which briefly stated comprises a number of conductors, each 5 insulated by a body of paper in the form of tapes which are applied thereto layer by layer. The conductors are spirally assembled to form a cable and are enclosed in a sheath made of lead or equivalent metal. The paper is impregnated by 13 an insulating material or compound which has little tendency to flow and is retained in the paper by capillary attraction. At some stage in the manufacture and while suitably heated, the cable is permitted to drain so that excess compound is removed from the paper and other parts as fully as possible. This may be done before or after the sheath is applied. The so-called filler spaces between the insulated conductors when cabled are, in connection with the sheath, utilized as free channels for a neutral insulating gas, such as nitrogen, for example, which is continuously maintained under a positive pressure of the order of 15 to 20 pounds per square inch. Although all reasonable efforts are made to remove such surplus compound as is not retained in the paper by capillary action before the cable is installed -for use, experience has demonstrated that after the cable is put into operation and subjected to heating and cooling cycles due to load changes,

39 it may happen that such cycles cause an additional amount of the compound to be released from the paper insulation and enter the channels. As the channels should be kept as free of compound as possible so as not to restrict the flow 5 of gas from end to end of the cable or selected parts thereof, such as a length between stopjoints, it becomes important to provide means for collecting the excess compound in such a manner and at such a place or places as not to interfere with the freedom of movement of the gas.

The object of myinvention is the provision of improved means, suitably located along the length of the cable, whereby excess compound released from the insulations on the conducting parts 45 while the cable is in service may effectively be removed without exposing the contents within the sheath to the injurious effects of atmospheric air and moisture and prevent injury to the cable in? cident to the undue restrictions of the gas feed 50 channels. 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. I

55 In the drawing which is illustrative of my invention, Fig. 1 is a view partly in elevation and" partly in section of a joint for a three phase gasfilled cable; Fig. 2 is a cross-section taken through the center of the joint; Fig. 3 is a cross-section through a cable; Fig. 4 shows a reinforcement for the joint casing, and Fig. 5 illustrates an auxiliary sump.

Each cable comprises three conductors 3, l and 5, each insulated with a suitable number of layers of a good grade of cable paper, the paper 10 being applied in the form of tapes of suitable and rather narrow width. The paper is impregnated with a compound which has little tendency to flow even when heated and is retained in the paper by capillary attraction. Around each insulated conductor is a snugly appliedwrapping of thin metal 6 which acts as an electrostatic shield. These shields contact with each other and with the inner wall of the impermeable lead sheath I. Between the conductors are so-called filler spaces on 8 of substantially triangular form. These spaces are utilized as gas feed channels extending lengthwise of the conductors and are filled with a neutral insulating gas, such as nitrogen for example, under positive pressure. Due to load 25 changes and consequent heat cycles, if any of the impregnating compoundescapes from the paper, it enters the filler spaces or gas feed channels and is temporarily retained therein. The ends of the cable sheaths and feed channels are open so that the compound will gradually flow or issue therefrom into the joint casing 9.

To obtain the best drainage effects by the feed channels, it is desirable to have the cables slope slightly toward the joint containing casing. The relation of the conductors one to the other inside of the metal sheath is shown in Fig. 3. Before the ends of the cable lengths are connected-the joint casing is slipped endwise over one of the cable lengths. I .30

The corresponding ends of each pair of conductors are united by a connector It made in the form of a metal sleeve with a slot or opening II- to receive solder. The particular connector means for uniting conductor ends is not material to my invention since other and well-known means may be employed. After the connectors are applied, they are covered with a wrapping of treated fabric or other suitable insulating tape it to the required thickness and shape. .The so amount of such tape will depend upon the voltage to which the conductors are subjected. Since the cable largely depends for its successful operation on having the gas feed channels in the cable well drained of excess compound or impregnant, it is desirable'to supportthe joints in a region above the bottom of the casing and out of the compound that would otherwise clog the ends of the feed channels leading into the joint casing. This is done by providing a block ot-wood or other suitable insulating material IS, the ends oi. which are beveled and rest on the inner wall of the casing, as best shown in Fig. 2. The three conductors and the block are then bound together by the binding band II which may be made of several turns of cord or other insulatingmaterial. Over the tape on each connector is a wrapping of thin metal l5 forming electrostatic shields. The

shields are in contact with each other and are desirably grounded either to the joint casing or to the cable sheaths.

The casing 9 may be made of lead and initially isor may be in the form of a tube 01 substantially uniform diameter. Since the casing in addition to enclosing the joints also acts as a sump to receive any excess compound oozing out of the paper insulation, it can be eccentrically mounted with respect to the axis of the connected cables. In other words, the center line of the casing can be below that of the sheathed cables, thereby increasing the sump capacity in those cases where this is desirable. In effect, the casing has two chambers I6 and H of suitable cubical capacities, the former containing only the joint and gas under positive pressure and the latter more or less of the surplus insulating compound and a body of gas above it.

After the joints are made, the casing is moved axially to the position shown in Fig. 1, after which the ends thereof are beaten or hammered down so as to make a reasonably good fit over the.

sheaths of the two cables. unite the casing ends with the sheaths by wipe soldered plumbing wipes i8. Desirably these wipes are relatively large and massive so as to form adequate supports for and reinforce the casing ends, and also to ensure the joints against leakage.

Because the casing is considerably larger in diameter than the cable sheaths and because it is subjected at all times to the pressure of the gas which, as previously stated, may be or the order of 15 to 20 pounds per square inch, it is desirable to reinforce it so as to adequately resist the efiects of the internal gas pressure. For this purpose the casing is wrapped externally with a relatively narrow metal tape IQ of which galvanized steel is an example. In practice the turns of the tape are desirably separated by a relatively narrow space, as one-fourth of an inch for example. To prevent corrosion of the tape and possible electrolysis between the tape. and easing a good coating of durable waterproof paint is applied to the casing and tape. The first end of the tape may be soldered to the casing, as indicated at 20, and then wrapped with a large number 01' turns, the final end also being soldered The next step is to to the casing. Because oi. the possibility of a turn rupturing and releasing the others at some subsequent'time due to conditions induced by the surrounding atmosphere in the manhole or from any other cause,'it is desirable to spot solder most or all 01' the turnsto the casing at one or more points, as indicated at 2|.

The casing has fittings 22 and 23 through which gas under pressure may be introduced into it, suitable sealing plugs or caps 24 being providedto seal the openings therein. A drain plug 25 is also provided on the under side of the casing by which the compound in chamber l1 indicated for example by the dotted line 26, may be drained from time to time.

As above indicated, any surplus compound escaping from the insulation on the conductors enters the channels and flows therefrom through the open ends of the sheaths where it accumulates in the sump or lower chamber part H, the level of any compound being below the insulated conductors and the insulation on the connectors so that excess compound when heated may drain therefrom. Either or both of the fittings on the upper side of the casing may be utilized to supply gas to the casing chamber l1, and since the cable sheaths. open into the casing, gas is free to flow from the chamber into the channels of the cables or from the cables into the chamber. The arrangement of the fittings and drainage plug is such that air and moisture are prevented from entering the casing and cables, it being noted that the gas is under positive pressure.

The tubular casing 9 is shown as being eccentrically mounted with respect to the axes of the cables since such an arrangement permits of a relatively large chamber or space for compound with a casing of minimum diameter. However,

-where a reduction in the diameter of the casing is not important, the casing and cables may be concentrically arranged.

structurally, the casing itself resembles those employed for so-called normal joints for oilfilled and solid type cable but its purpose and mode of operation are different. In an oil-filled cable, the casing has only to deal with one material, namely, oil, which completely fills the casing, whereas in the present instance, the casing has to deal with two, namely, the surplus impregnating compound escaping from the feed channels of the connected cables and the insulating gas under appreciable positive pressure. In so id type cable, there is no such thing as,drain ing the conductor insulation of compound, in fact such operation would defeat the very purpose thereof. .The joint casings of such cables are filled with a single heavy compound. 7

In those cases where the joint casing alone does not supply suilicient sump capacity, for surplus compound drainage, an auxiliary rigid metal container 21 of any desired capacity can be mounted below and connected to the bottom of the casing 9. This auxiliary sump into which compound flows by gravity has a drainage fitting 28 in its bottom similar to fitting 25, for periodic removal oi surplus compound without admitting foreign matter to the cables.

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

1. In combination, a pair of cables arranged end to end, each having conductor means, insulation thereon containing an impregnating compound from' which the excess is drained before the cables are put into use, open ended impervious sheaths for the conductors, open ended feed channels between the insulations and the sheaths, insulated connectors for uniting the conductor means, a chambered casing for the connectors into which the open ends of the sheaths and channels extend, the chamber being of suiiicient cubical capacity toreceive gas and also form a sump for whatever compound may be discharged from the cables due to heat cycles by the feed channelsand to retain the compound below the level of the insulated connectors, and a filling of insulating gas under positive pressure for the cable channels and the casing,

2. In combination, a pair of cables arranged end to end, each having conductor means. insulation thereon containing an impregnating compound from which the surplus is drained before the cables are put into use, open ended impernectors and a second portion as a sump to receive excess compound issuing from the channels and sheaths, the sump being located below the connectors, a fitting mountedon the casing through which gas may be admitted thereto, a second fitting mounted on the under side of the casing for draining compound from the sump, and a filling i of insulating gas under positive pressure for the portion of the casing above thelevel' of compound contained in the sump and also the channels.

3. In combination, a pair of cables arranged end to end, each comprising insulated conductors with open ended feed channels in the spaces between them, impregnating material retained in the insulation by capillary attraction, the surplus material being initially drained from the insula-v tion and the channels, an impervious metallic sheath having an open end permitting excess impregnating material to drain therefrom and from the feed channels should occasion arise due to heat cycles when the cable is in operation, insulated connectors uniting corresponding conductors, a chambered metal casing wipe soldered at its ends to the sheaths and receiving compound therefrom, the casing having sufficient cubical capacity to form a sump for receiving excess impregnating material from the feed channels of the connected cables and also an enclosure for the connectors located above the level of material in the sump, fittings for admitting gas to the chambered casing and for draining excess impregnating material therefrom, and a filling of neutral gas under positive pressure the chamber of the casing located above the level of any impregnating material therein and the channels of the cables.- t

4. In combination, a pair of cables arranged for that portion of end to end, each comprising insulated conductors with open feed channels in the spaces between them, impregnating material sulation by capillary attraction, the excess material being initially drained from the insulation and the channels, and an impervious metallic sheath having an open end permitting excess impregnating material to drain therefrom should occasion arise due to heat cycles when the cable is in operation, insulated connectors uniting corresponding conductors, a chambered metal casing secured at its ends to the sheaths and receiving compound therefrom and the channels, the casing having sufficient cubical capacity to form a sump for receiving excess impregnating material from the channels of the connected cables and retained in the inalso form an enclosure for the connectors located above the level of material in the sump, fittings for admitting gas to the chambered casing andfor draining excess impregnating material therefrom, a filling of neutral gas under positive pressure for that portion of the chamber of the casinglocated above the level of any impregnating material therein and the channels of the cables, and a tape wrapping for the exterior wall of the casing to prevent it from disrupting due to the internal pressure caused by the gas.

5. In combination, a pair of cables arranged end to end, each comprising an insulated conductor, an open ended feed channel extending longitudinally of the conductor, impregnating material retained in the insulation of the conductor by capillary attraction, the excess. material not so retained being initially drained from the insulation and feed channel, an impervious sheath having an open end permitting excess impregnating material, due to heat cycles, to drain therefrom and from the feed channel, an insulated connector uniting the conductors, a chambered casing sealed to the sheaths of thecables and enclosing the connector and forming a sump located below tlt: level of the feed channel for receiving the excess impregnating material draining from the cables, an auxiliary container connected to the casing and into which impregnating material therefrom is free to flow by gravity, and a filling of neutral gas under positive pressure for the feed channel and the chamber of the casing.

GEORGE B. SHANKLTN.

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