US2120889A - Stop joint for fluid filled cables - Google Patents

Description

June 14, 1938. 1 EMANUELI STOP JOINT FOR FLUID FILLED CABLES ueh Attorney Inventor: Lut@ Ea si'` b H/f/fN/H/N/H/N/...f//l Y/f d Feb. 17, 1958 presents many difficulties.

Patented June 14, 1938 UNITED STATES- aliases PATENT OFFICE Luigi Emanueli, Milan, italy assigner to Societa Italiana Pirelli, corporation of Italy Application February l'i,

1938 Serial No. 3.91,@

'l' Clanisu (Cl. MSH-268i Stop-joints are employed. in fluid filled cable systems for the purpose of subdividing the cables into sections soias to limit the hydrostatic head oi the impregnating liquid on the enclosures or sheaths of the connected cable lengths, and for the purpose of permitting the impregnatng dielectric or liquid to flow between the hollow core, oi the ca-I ble conductor and an external source of supply, such as a variable capacity reservoir 'sealed 'against the admission of air. They are also employed te segregate one section from another as regards the liquid dielectric so that in the event a lea. in one section, the liquid wili not be drained from the connected/section or sections.

On account of the fact that there is a difference of potential between the conducto and the surrounding metal parts, the probiere effectively insulating them one from the otner The greater the dit" ference of potential, the greater are the diiilculties oi' manufacture and greater care must be exercised in making an installation. Prior to my present invention, numerous installations of fluid filled cable had been made in the United States and in countries foreign thereto operating at 132,000 volts, and in Nestor all cases the cables were provided with stop-joints, for example of the type shown in my Patent 1,698,051 dated January 8, 1929 or that shown in the Eby Patent 1,819,882 dated August 18, 19'11. l

.The present invention is directed to a stop-joint for underground cable systems and is especially -designed to operate under very high voltages. Joints made in accordance with my invention are in successful operation at the present timegand, with the connected cables, are operating at the highest voltage ever used in a commercial underground cable system. As an illustration, but not as a limitation of my invention, the joint 'iilusn trated herein is designed to operate at 226,008.

volts. In order that some idea may be had of the` size of such joints as are here illustrated, it

may be stated that the joint casing is approz/:i-av

mately 101/2 feet long with an approximate siax muni diameter of 151/ inches. It is to be andere stood, however, that the dimensions given are not limitations since a change in operating voltage er a change in the insulating materials used, or both, may and in most cases would result a change of dimensions.

In such a stop-joint, a great mass of fibrous insulation is applied to the joint parts in order that they may withstand the tremendous vetta-ge to which they are subjected. The vaine of auch material as an insulating medium depends to a very great degree upon how thoroughly gas rem moved and hor,Y completely the material. is iinprega-.ated with liquid dielectric, as degosiiied oil, for example, and how completely ali voids are filled with the liquid, or both. inver directed more specifically to the Ways and ior ensuring eornpiete filing of the voids or witi n the joint and the proper insuiatioo an i iproved ne drawing which illustrates on Fig. 2 is an axial sectional view oi appro one-half ci the joint; Fig. 3 is a perspective view of a portion or one end of the joint, and Fig. i is a perspective Viewof a portion ci a beit comprising parallel tubes of insulating material.

E and 'l indicate the cables, the conductors of which are hollow and united by the two-part connectors 8 and 9 and the flexible member l0. As both halves of the joint are alike, a description. of one of them will be sufficient. The connector 8 supports the small end of'a cone-shaped insulator Il, its outer end being supported by the head l2, the latter being secured to the end meinber i3 of the joint casing. I4 indicates the factory applied insulation on the conductor and surrounding it are layers of fibrous insulation I5 arranged in step formation and all located Within ythe cone insulator.

and lulniecgtent filling by the liquid dielectric of 45 which degasii'ied oil may be taken as an example.- The casi is made halves to of as-i sembly a W the parte or the connector a u ted by the flexible member i0, the plane ci t of the casing being axial. The parte of the cas 5@ ing are soldered or otherwise secured together; Adjacent ends of the screen i@ are n'ietz'tl rings Ei? ci which one is shown. Each of these is com neet-ed to a conductor as by a lead and screw ige and hence at the same potential. 555

function of these rings is to increase the perfor'in tion tension in the regions near the two ends oi the connector which are particularly subject to electrical discharges. Each oi the rings is separately insulated before application to the joint structure and is supported internally by the enlarged end or a connector part such as ii.

Over the cone insulator is applied bands of ilbrous insulating material 2li, either in the form of layers or laminations of tape or sheet material, a small amount of fibrous tape being first applied over the portion of the cone insulator adjacent the ring i3 to enlarge the diameter and make the outer surface more nearly cylindrical. An additional wrapping or band of iibrous insulating material 2l is applied over the screen iii and over a part of the insulator ill). Another reinforcing insulation, indicated at 2t, is applied over` the insulation 2t. Surrounding the insu.- lation 2li on the cone are belts 23 and 24, each comprising small tubes 25 made of insulating material, all strung together or held in place to form an annulus by cords 2t which pass completely through them. By passing the cords through the tubes and permitting the tubes to make contact along their sides, the necessity of individually anchoring each tube is avoided. After the belt is applied, the ends oi the cord or other fastening means are tied or otherwise united. It is desirable to use two such cords located near the ends of the tubes to prevent relative displacement thereof. By making the tubes relatively small in diameter andso numerous that they contact with each other along their peripheral surfaces in axial planes, they form an annulus which presents relatively smooth internal and external surfaces and because of that fact, they snugly t the supporting surface and also form or define an outer surface over which relatively thin insulation may smoothly and evenly be wound or applied in layers to form a cylinder as contrasted to an irregular surface composed of high and low spots as would be the case if the tubes were widely spaced. it is advantageous tol slightly bevel the internal ends of the tubes so as to ensure smooth surfaces and free passage ci the liquid therethrough. The right hand belt 23 serves as a support for one end of the overlying cylindrical body of brous insulation 2 and also as a means to permit the passage of liquid dielectric axially therethrough. The left hand belt 24 supports the right hand end of a tubular body of insulation 28, the opposite end of which is supported by the rigid cone insulator. It will be observed that there are liquid containing spaces or chambers such as 29, 30 and 3i. If it were not for the belts of tubes, they would be wholly or largely shut off from the liquid dielectric within the joint casing and as a result the effective insulation would be greatly decreased.

32 indicates a relatively long cylinder of insulating material which is supported ln concentric relation with the axis of the joint by spaced belts 33 and 34, each comprising parallel tubes of insulating material as best shown in Fig. i and previously described. The tubes of belt 33 serve to convey liquid dielectric between the space or chamber 35 and space or chamber 3U. The tubes of the right hand belt 34 serve 'to convey liquid dielectric between the annular space or chamber 3D and the outermost annular space or chamber 3b. From Fig. 3, it will be seen that the belts 24 and 33 are located in the same plane with the cylindrical body of insulation 28 beatadas@ tween them. rihe tubes of the inner belt 24 are desirably slightly smaller in diameter than those of the outer belt and fewer in number because the diameter of the joint in this plane is less. The belts by reason of their construction are exible so that they may easily be wrapped around the parts o the joint and because the tubes are united by flexible means such as cords, it becomes a simple matter to secure them in place. Liquid dielectric is supplied to and received from the outer chamber 36 oi the joint casing by the iitting 3l carried by the outer main casing 38 of the joint. Liquid dielectric is admitted to and received from the hollow core cable by the iitting i6 mounted on the end cap of the joint casing. rlhis fitting when the cable is in service is connected to a variable capacity reservoir to compensate for variations in volume of the liquid in the core of the conductor. The liquid dielectric flows into and out of the hollow conductor 39 through the connector and through the space between the insulation on the conductor and the cone into the end chamber 40 of the joint casing. The joint casing is also provided with a tting di whereby the lling and draining thereof is facilitated.

As previously indicated, the belts act as supports for masses of insulation and also serve as channels to convey liquid dielectric from one more or less isolated space or chamber' to another or others and in so doing prevent the formation of dry spaces which otherwise would be only imperfectly filled with liquid.

it is a characteristic feature of my improved construction that the solid or mass insulation outside of the cone insulators is arranged in the form of tubular elements and that between certain of the elements are arranged flexible belts which serve the double purpose of supporting the outer or surrounding elements and affording dennite passages for the liquid. The belts form a unit assembly and being iiexible conform to the shape of the body encircled thereby and are easily secured in place. Due to the numerous tubes of which each belt is composed, there is no danger 'of a stoppage of the free circulation of the liquid dielectric. The tubes being assembled and united to each other as they are, there is no danger of a workman making an error in the application of the belts.

Attached to the end head i2 is an end bell 42 which flares outwardly to the wall of the casing 38 and is secured thereto. The purpose ci this bell is to provide voltage gradients both radial and lateral which are within the safe working Values of the several insulating materials employed. The end bell is provided with a number of grooves or notches 43 which establish connection between the chamber supplied by the fitting 3l? and the central part of the joint casing.

The center of the joint is provided with a thick covering of fibrous insulation 44 over which is applied a relatively thin tubular body of insulation 45, the latter being separated from the metallic casing of the joint by an annular space to which the liquid has free access.

IThe use of iexible belts has been described in connection with stop-joints as they have great utility in connection therewith but they may also be used with advantage in other types of joints where it is important to keep the solid insulation fully exposed to the action of the liquid dielectric.

The wrappings of fibrous insulating tape and sheets are referred to herein as solid insulation to distinguish them from the liquid dielectric. In

some instances, the sheets or tapes arewound in layers directly on some interior part and are immovable when once applied, While in other instances, as the cylinder 28, for example, the cylinders are wound and then slipped endwise into place in the end bells 42. It will be apparent that flexible belts of the character described are not limited in their use to cable joints since they may be'used wherever desirable in electrical apparatus as a means for insulating one conductor means from another and where it is important to maintain complete lling and circulation of liquid dielectric. It will also be apparent that while the greater part of the liquid dielectric will flow back and forth through the tubes as it expands and contracts, a certain amount will ow through the small spaces dened by the periph-- eral surfaces of the tubes and the solid insulation upon which the belt is supported or between said surfaces and the wrapped-on insulation covering and supported by the tubes.

The belts are so constructed as to have sufriciently good dielectric strength in a radial direction, that is toward the joint casing, having at the same time passages or channels for the liquid which greatly facilitate the impregnation of the internal parts of the joint casing.

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

1. An electrical conductor means, a metallic enclosure therefor, a lling of liquid dielectric for the enclosure, and a exlble belt comprising insulating tubes arranged side by side and surrounding the conductor means and located between it and the enclosure and through which the dielectric is free to ow.

2. An electrical conductor means, a metallic enclosure therefor, a lling of liquid dielectric for the enclosure, insulating tubes surrounding the conductor means and located between it and the enclosure and through which the liquid dielectric is free to ow, and exible means located near the ends of the tubes for holding them in side by side relationship to form a flexible belt and for securing the belt around the conductor means.

3. A cable joint comprising electrically connected conductors, bodies of liquid impregnated insulation of cylindrical form enclosing the conductors, the ends of certain of the lbodies being in spaced relation, a flexible belt arranged between one of the bodies and that immediately thereunder to support the former, the belt comprising a relatively large number of small diameter tubes arranged in close side by side axial arrangement and united to prevent relative displacement, a sealed casing enclosing the parts of the joint, and a filling of liquid dielectric for the casing which permeates the bodies and flows freely through the tubes as the liquid expands and contracts with temperature changes.

4. A cable joint comprising electrically connected conductors, a body of insulation surrounding one of the conductors, a exible belt surrounding and supported by the body, the belt comprising a relatively large number of small insulating tubes arranged side by side and extending parallel to the axis of the conductor, a cylindrical body of solid insulation, one end of which is supported by the belt, a second belt of similar construction concentric with the first and supported by the cylindrical body, a second cylindrical body of solid insulation surrounding the second belt and supported thereby, the bodies being in radially spaced relation with liquid containing chambers between, a sealed casing for the joint parts, and a nlling of liquid dielectric for the casing which flows into and from the chambers through the tubes as the liquid expands and contracts due to temperature changes.

5. A cable joint comprising electrical conductors arranged end to end, a connector for uniting them electrically, a body of solid insulation surrounding one of the conductors, a flexible bel*u comprising a plurality of insulating tubes arranged side by side, means for flexibly uniting the tubes and securing them over the body of solid insulation, a body of solid insulation surrounding the belt and supported thereby, a casing for the joint, and a lling of liquid dielectric for the casing which circulates through the tubes and prevents the formation of voids.

6. A belt for the purposes described comprising a plurality of relatively small tubes of insulating material having perforations near their ends, and means for uniting the tubes to form an annulus comprising cords of insulating material which extend through the perfor-ations, the ends of the cords being united to secure the belt in place.

7. A cable joint comprising conductor means, a metallic enclosure therefor, a filling of liquid dielectric for the enclosure, and a flexible belt comprising insulating elements disposed side by side in axial relation and surrounding the conductor and exible insulating means for securing the belt as a unit assembly in position around the conductor.

LUIGI EMANUELI.

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