JPH0419678B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to electrical cable terminations and connections and methods of forming them. When terminating or splicing continuously shielded high voltage cables, remove the shield at such length from the termination or splice that electrical breakdown will not occur along the insulation surface of the shield from the exposed conductor. Removal of the shield causes a discontinuity in the electric field and as a result there is significant electrical stress at the ends of the shield. In order to reduce this stress and prevent damage to the cable insulation during use, resistors are used as described in, for example, U.S. Pat. Many methods have been proposed to provide stress control through sexual or capacitive effects. However, each of the conventional techniques has problems. For example, the method disclosed in Japanese Patent Application Laid-Open No. 49-81895 is
It uses many parts, is complex, and requires precise placement of parts relative to each other. ring 51,5
Spacers such as 3 serve to assist in accurate placement. The insulating layer 29 is formed from three elements and is molded to provide a taper.
It can only be formed by law. This molding method is expensive compared to extrusion. Electrical stress control is provided by the stress cone effect provided by the tapered insulation encapsulated by the grounded outer conductive element. Such conventional technology has the following problems. () Complex parts must be assembled together with precise placement. For the stress cone, its narrow end must be placed in the correct position at the end of the cable shield, otherwise the electrical stress will be high. Therefore,
The work requires a high level of skill. () Parts can be manufactured by sophisticated molding methods, but cannot be manufactured by cheaper extrusion methods. () One set of components cannot be used for different cable sizes and constructions, so if the cable core (i.e. conductor and dielectric and shield) has a different size or shape, another set of components may be used. , and it is necessary to prepare various sets of parts. According to the present invention, these problems of the prior art are solved. One aim of the invention is to form the connection or termination by means of a protective sleeve with a very simple construction. Accurate electrical stress control is ensured, and thus desirable electrical stress control is obtained even if the operator does not fit accurately enough. Another object of the invention is to form the connection or termination by means of a protective sleeve that can be produced by inexpensive extrusion methods. Another object of the invention is to form connections or terminations with a protective sleeve that can accommodate a wide range of cable sizes and constructions in one set of parts. Accordingly, in accordance with one aspect of the invention, there is provided a shielded connection between two electrical cables, each cable having a conductor surrounding the conductor and truncated at the end to expose the conductor. a conductive cable shield that surrounds the dielectric layer and is truncated to expose the dielectric layer;
The cables are connected within a protective sleeve that provides electrical stress control of the connection, including a tubular insulating inner layer, a tubular conductive outer layer, and a stress gray between each cable and the insulating inner layer. a stress grading layer, the stress grading layer being at least partially electrically resistive and electrically connected to and overlapping the respective cable shield; and the electrically conductive outer layer being electrically connected to and overlapping the respective cable shield. , separated from the cable shield by the insulative inner layer, the insulative inner layer overlapping each cable shield for a length at least equal to the thickness of the portion of the insulative inner layer overlapping the end of the cable shield, and the insulative inner layer overlapping the respective cable shield for a length at least equal to the thickness of the portion of the insulative inner layer overlapping the end of the cable shield; characterized in that the electrical connection between each cable shield is formed at a point on the cable shield that is spaced from the end of the cable shield by a distance at least equal to the thickness of the insulating inner layer portion that overlaps the end of the cable shield; A connection is provided. In another aspect of the invention, a method of protecting and shielding a connection between two shielded cables, each cable comprising:
A shielded electrical cable comprising a conductive wire, a conductive layer, and a conductive cable shield surrounding a dielectric layer, the method comprising: truncating the conductive cable shield to expose the dielectric layer; trimming the dielectric layer to expose the conductive wire; encapsulating the connection of the cable by a protective sleeve that is exposed and provides electrical stress control of the connection, the protective sleeve comprising an at least partially electrically resistive innermost stress grading layer, a tube-shaped an insulative inner layer and a tubular conductive outer layer, the method includes arranging the stress grading layer such that the stress grading layer overlaps the exposed conductor and extends beyond the exposed conductor and overlaps the respective cable shield; a conductive outer layer is placed in electrical contact with the stress grading layer at the overlap with the respective cable shield, and is arranged to separate the stress grading layer and the conductive outer layer in the region between the overlap and the exposed conductor. an insulative inner layer is placed over each cable shield for a length that is at least equal to the thickness of the portion of the insulative inner layer that overlaps the cable shield termination; A method is provided, characterized in that the electrical connection between is formed at a point of the cable shield remote from the end of the cable shield by a distance at least equal to the thickness of the portion of the insulating layer overlapping the end of the cable shield. In yet another aspect of the invention, the termination of a shielded electrical cable includes a conductor, a dielectric layer surrounding the conductor and truncated to expose the conductor, and a dielectric layer surrounding the dielectric layer. A shielded electrical cable comprising a conductive cable shield with the ends truncated to expose the dielectric layer, the cable being terminated within a protective sleeve to provide electrical stress control at the termination. The protective sleeve comprises a tubular insulating inner layer, a tubular electrically conductive outer layer, and a stress grading layer between the cable and the insulating inner layer, the stress grading layer being at least partially electrically resistive. electrically connected to and overlapping the cable shield, the conductive outer layer comprising:
electrically connected to and overlapping the cable shield and separated from the cable shield by the insulative inner layer, the insulative inner layer overlapping the cable shield for a length at least equal to the thickness of the insulative inner layer overlapping the end of the cable shield; that the electrical connection between the conductive outer layer and the cable shield is made at a point on the cable shield that is at least equal to the thickness of the portion of the insulating inner layer that overlaps the end of the cable shield; A featured termination is provided. Additionally, the termination of the present invention is a method of protecting and shielding a termination of a shielded cable, the cable comprising a conductor, a dielectric layer, and a conductive cable shield surrounding the dielectric layer. A shielded electrical cable, the method is to truncate the conductive cable shield to expose the dielectric layer,
truncating the dielectric layer to expose the conductors and encapsulating the termination of the cable with a protective sleeve that provides electrical stress control at the termination, the protective sleeve being at least partially electrically resistive. an innermost stress grading layer, a tubular insulative inner layer, and a tubular conductive outer layer, the method comprising: a stress grading layer overlapping the exposed conductor, extending beyond the exposed conductor and overlapping the cable shield; disposing a stress grading layer, disposing a conductive outer layer in electrical contact with the stress grading layer at the overlap with the cable shield, and disposing a conductive outer layer in electrical contact with the stress grading layer in an area between the overlap and the exposed conductor. an insulating inner layer is arranged to separate the outer layer; the insulating layer is arranged to overlap the cable shield for a length at least equal to the thickness of the portion of the insulating layer that overlaps the cable shield end;
characterized in that the electrical connection between the conductive outer layer and the cable shield is formed at a point on the cable shield remote from the end of the cable shield at a distance at least equal to the thickness of the portion of the insulating inner layer overlapping the end of the cable shield. It is formed by the method of In this method, it is preferred that the layers of the sleeve are heat recoverable and that they are placed around the cable termination by applying heat. Preferably, the stress grading layer is itself tubular in form. The degree of overlap between the insulative inner layer and the cable shield is at least equal to the thickness of the insulative inner layer portion that overlaps the cable shield end. The electrical connection between the conductive outer layer and the cable shield is made at a point on the cable shield at a distance from the cable shield termination that is at least equal to the thickness of the insulating inner layer overlapping the cable shield termination. . It will be appreciated that overlapping layers does not necessarily mean that the layers are in contact. The insulating inner layer is preferably formed from a material with suitable electrical properties, including discharge resistance, dielectric constant and high breakdown strength, for example with fillers dispersed therein which provide excellent electrical properties, if necessary. It consists of a polymer matrix. Polymeric materials suitable for use as the polymer matrix are, for example, copolymers of polyolefins and olefins, such as polyethylene, polypropylene, ethylene/propylene copolymers and polybutylene; substituted polyolefins, especially halogen-substituted polyolefins, such as polyvinyl chloride, polyvinylidene chloride, polyfluorinated Vinylidene, Teflon 100 (polytetrafluoroethylene, manufactured by DuPont), Teflon FEP (copolymer of tetrafluoroethylene and hexafluoropropylene, manufactured by DuPont), Teflon PFA (copolymer of tetrafluoroethylene and perfluoroalkoxy residues,
Polyesters, especially segments and polyurethane. Other polymeric materials suitable for use as polymer matrices include elastomers, such as copolymers of dienes and olefinically unsaturated monomers, such as ethylene/propylene/nonconjugated diene terpolymers, styrene/butadiene polymers, butyl rubber, and diene copolymers. copolymers of with unsaturated polar monomers such as acrylonitrile, methyl methacrylate, ethyl acrylate, vinyl pyridine and methyl vinyl ketone;
Halogen-containing elastomers, such as chloroprene polymers and copolymers, such as neoprene, chloroprene, chlorinated polyethylene, chlorosulfonated polyethylene and Viton (copolymer of vinylidene fluoride and hexafluoropropylene, manufactured by DuPont); olefinic unsaturation of olefins Copolymers with esters, such as ethylene/vinyl acetate elastomer polymers, ethylene/acrylic ester copolymers, such as ethylene/ethyl acrylate and methacrylate copolymers, and especially ethylene/acrylic rubbers, such as Vamac (of ethylene, methyl acrylate and cure site monomers). terpolymer,
DuPont); acrylic rubbers such as polyethyl acrylate, polybutyl acrylate, butyl acrylate/ethyl acrylate copolymers and butyl acrylate/glycidyl methacrylate copolymers, silicone elastomers such as polydiorganosiloxane, dimethylsiloxane, methylvinylsiloxane and methylphenylsiloxane , fluorosilicone, e.g. 3,
elastomeric polyurethanes; and polyethers, such as epichlorohydrin rubber. Blends of the above elastomers and resins can also be used. Particularly good results have been obtained using polyolefins, olefin copolymers and blends of olefin polymers. The insulating inner layer is desirably, but not necessarily, made of a substantially tracking resistant, preferably non-tracking material. "Non-tracking" means a material that does not form dendrite-like carbon-based conductive deposits on its surface under the influence of high voltages. Suitable anti-discharge and anti-tracking materials comprising anti-tracking fillers are disclosed in British Patent Nos. 1041503, 1240403, incorporated herein by reference.
1303432 and 1337951. The insulating inner layer has a dielectric constant of 2 to 6 and at least
It preferably has a volume resistivity of 10 ¹⁰ Ω·cm, preferably at least 10 ¹² Ω·cm. The electrically conductive outer layer may consist of a woven or twisted metal braid, but is preferably a layer of a polymeric matrix with electrically conductive fillers dispersed therein, in which case the sleeve further comprises an electrically conductive material. It may have a woven or twisted metal braid located around the outer layer. The polymer matrix may be comprised of any of the above polymeric materials or a mixture of these materials, and the conductive filler may be comprised of metal particles or conductive carbon black. Suitable carbon blacks are currently commercially available, such as HAF,
You can choose from SPF, EPC, FEF and ECF types. Particularly good results have been obtained with the conductive polymer composition described in GB 1294665, incorporated herein by reference. The electrically conductive outer layer preferably has a polarity of 10 to 70, preferably 10 to 20, e.g.
Contains 17 parts by weight of conductive filler. The electrically conductive outer layer preferably has a volume resistivity of less than 5×10 ⁴ Ω·cm, most preferably less than 100 Ω·cm. The cable connections and terminations of the invention are formed by precisely engaging the protective sleeve with the cable to be protected. Proper engagement refers to material properties that closely match the contours of the underlying substrate. Such precise engagement is achieved by using a sleeve made of elastomeric material or heat recoverable material or both. In order to avoid the possibility of undesired voids forming between the sleeve and the termination or connection surface, that surface and/or the inner surface of the tube may be coated with suitable void fillers, such as grease or heat-activated adhesives, sealants, etc. Or it may be covered with mastic. If desired, the sleeve can be formed in situ by sequentially engaging successive tubular layers with successive cable terminations or connections. A laminate of tubular layers can also be used, and in one preferred embodiment the sleeve consists of a single tubular article having an insulating inner layer and a conductive outer layer.
The term "tubular layer" refers to a layer preformed as a hollow tube that can be slid over a cable or as a sheet that can be placed around a cable to effectively form a tube in a single wrap. means layer. Furthermore, for the avoidance of doubt, references herein to "tubular layers" do not include structures formed in situ by repeatedly spirally wrapping tape around a cable. If the tube-like article is elastic, it can be brought into precise engagement with the electrical cable fitting by simply pushing it onto the electrical cable, and its elasticity allows it to conform closely to its contour. In other embodiments, the resilient tubular article can be held in a stretched state by internal or external retaining members that can be removed or moved to relieve the elastic stress and properly engage the tubular article with the appliance. to recover. In yet another embodiment, the tubular article is bonded to the retaining member and the bond is weakened and restored, such as by solvent treatment or mechanical treatment. Preferably, however, the sleeve comprises a heat-recoverable tubular article. Although these articles typically return to their original shape before being deformed when heated, the term "thermally recoverable" as used herein refers to articles that, when heated, adopt a new shape even if they have not been previously deformed. Also included. In their most common form, such articles are disclosed, for example, in U.S. Pat.
3957372, which exhibits elastic or plastic memory properties. In other articles, elastic materials are used as secondary
The elastic member is maintained in a stretched state by the first member, and the second member is weakened by heating to restore the elastic member. The disclosures of these patent specifications are incorporated herein by reference. The insulating inner layer and the conductive outer layer may each be independently thermally recoverable, or if the sleeve is thermally recoverable as a whole, one or both layers may be elastic. In contrast to tubular articles that have hitherto been proposed for the protection of cable terminations and connections, the sleeves used in the present invention can, if desired, be resilient, at least in a stable state. or can be formed to have a substantially uniform cross-section along its entire length in the free recovery state;
Therefore, the sleeve can be made by a relatively inexpensive extrusion method. This is a significant advantage over prior art structures that often require sophisticated molding techniques. Although less desirable, the sleeves used in the present invention can of course be made by other methods, such as molding or casting, as appropriate. However, the preferred manufacturing method is multi-layer extrusion, with subsequent treatment if necessary to render the extruded product resilient. This treatment includes crosslinking, for example with ionizing radiation or chemical crosslinking agents, followed by expansion using, for example, a pressure differential or a mandrel. Ground continuity is provided across the cable termination or connection by connecting the conductive outer layer of the sleeve to the shield. To connect the conductive outer layer to the shield, the ends of the sleeve may be shaped such that the conductive outer layer is in direct physical and electrical contact with the shield. Alternatively, indirect electrical contact can be provided by a conductive member fitted to the end of the sleeve. Such a member may be, for example, a metal string or a molded part made from a conductive polymeric material that is heat recoverable if desired. Alternatively, electrical contact can be provided by spirally wrapping a metal braid around the conductive outer layer and connecting the ends to the shield, for example by soldering. The molded part may for example be an annular member with a grooved surface adapted to fit over the end of the sleeve and may have an inner coating of a sealant, such as mastic or hotmelt adhesive, and It is advantageous to protect the material from the environment.
Of course, if molded parts are used to make electrical contact, the inner coating sealant will be electrically conductive. In some cases, the spaces adjacent to the exposed conductive material, such as the area around the crimped center conductor of the cable connection and/or as previously described, may be
Alternatively, it has been found advantageous to use a void-filling material in the space close to the shield end to minimize the possibility of destruction due to ionization of the air in the void. Such materials may be greases such as silicone greases, mastic or hot melt adhesives. Empty = Filling material is electrically insulating,
It may be conductive or semi-conductive; if semi-conductive it is generally used in localized areas and does not exhibit significant stress grading effects. A particularly suitable void-filling material is described and claimed in German Patent Publication No. 27 48 371. This West German Patent Publication is hereby incorporated by reference. The invention finds application in the terminations and connections of high voltage cables operating at voltages up to 15 kV and above, and especially even higher, for example up to 40 kV or in some cases 72 kV. For example, at high operating voltages, e.g. up to 40kV or up to 72kV, the layer of stress grading material in the sleeve overlapping the cable shield may be completely resistive or a combination of resistive and capacitive electrical It may have impedance characteristics. The stress grading layer is at least partially resistive and extends from the exposed conductor to the cable shield. The innermost stress grading layer is preferably semi-conductive and comprises a polymer matrix having a conductive filler, particularly carbon black, dispersed therein. Suitable polymeric materials and carbon blacks for use in the polymer matrix include those described above. The amount of carbon black in the stress grading material depends in part on the type of carbon black and polymer matrix used, but preferably the material comprises 5 to 150 parts by weight of carbon black per 100 parts by weight of resin. Or, for example, British Patent No. 1470501,
Compositions having non-linear electrical resistance properties as described in US Pat. The disclosures of the above patents are hereby incorporated by reference. Instead of the polymeric material described above, the innermost stress grading layer may also comprise a fluid coating, such as the mastic described in GB 1,526,397. The innermost stress grading layer is in the range of 10 ⁷ to 10 ¹⁰ Ω·cm, e.g. 10 ⁹ Ω·cm, measured at a frequency of 50 Hz.
Preferably, it has an intrinsic impedance close to cm. Advantageously, the stress grading layer used in the sleeve has a direct current resistivity in the range from 10 ¹⁰ to 10 ¹¹ Ω·cm. The innermost stress grading layer extends along the shield from the exposed conductor when the protective sleeve is installed so that (although not required) the stress grading layer extends along substantially the entire length of the sleeve. You may. It has also been found that this allows the entire sleeve to be formed by relatively inexpensive extrusion techniques without the use of other forms of stress grading, such as stress grading cones. The thickness ratio of the insulating inner layer to the conductive outer layer is dictated to some extent by the required electrical properties of the sleeve, but generally the insulating inner layer has a thickness of 2 to 15 mm, preferably 3 to 10 mm. and the conductive outer layer is 0.5
It has a thickness of ~5 mm, preferably 1-3 mm. 4
It has been found that additional electrical stress control is required for electrical cables carrying voltages for which an insulating inner layer thickness of up to mm is no longer sufficient. Therefore, an innermost stress grading layer is usually required for cables carrying voltages of 15 kV and above. For cables carrying 35kV or more, it may also be necessary to slope the insulating inner layer at a point adjacent to the shield termination, as described below. However, it is preferred that the insulating inner layer has a substantially uniform cross-section over at least 60%, and most preferably 75% of its length in the central portion. For cables carrying voltages lower than 35 kV, it is most preferred that the insulating inner layer has a substantially uniform cross-section over its entire length, at least in the stable or free recovery state. However, the present invention also includes providing a taper in the insulative inner layer to create a stress cone adjacent the cable shield end. However, preferably such a gradient does not extend beyond the cable shield, but merely provides a "step" in the insulative inner layer from a larger cross section to a smaller cross section. For cables up to 15kV, the insulating inner layer is
It overlaps the cable shield by a length that is at least equal to the thickness of the portion of the insulating inner layer that overlaps the cable shield termination. The reason why the length of the overlap is limited in this way is as follows. Since the cable shield is held at ground potential and the cable conductors are at high voltage, areas of high electrical stress occur when the cable shield and dielectric layer are truncated for connection or termination. That is, when considering the potential gradient along the dielectric layer, the potential gradient changes rapidly at the end of the shield. Therefore, when forming connections (or terminations), it is necessary to minimize this electrical stress, at least to the extent that no electrical discharge occurs. Electrical stresses can cause electrical breakdowns, and therefore an area that must be particularly protected is the end of the cable shield. Protection of the cable shield terminations can be achieved by replacing the air adjacent to the cable dielectric layer with an insulating inner layer having a higher dielectric strength (i.e., overlaying the dielectric layer with an insulating inner layer); The inner layer must extend beyond (ie, overlap) the end of the cable shield. However, if the overlap length is short, the electrical stress at the end of the cable shield can be very high, especially if the insulating inner layer does not overlap the cable shield, creating a gap between the insulating inner layer and the cable shield. becomes larger and an electrical discharge occurs there. Therefore, in order to prevent discharge, it is preferable that the length of the overlap is long. However, it is economically advantageous to keep the insulating inner layer as short as possible, and since it is necessary to make an electrical connection between the cable shield and the conductive outer layer that extends beyond the connection for ground continuity. Preferably, the length of overlap between the insulating inner layer and the cable shield is as short as possible. Therefore, with regard to the length of the insulating inner layer, contradictory practical issues arise: the shorter the length is, the better from an economical point of view, while the longer it is safer from the point of view of electric discharge. It was discovered that in order to practically meet both of these requirements and to minimize electrical stress, it was necessary to make the length of the overlap at least equal to the thickness of the insulating inner layer. . By overlapping the insulating inner layer and the cable shield according to the invention,
It is also advantageous to prevent electrical discharges that the point where the conductive outer layer is connected to the cable shield is sufficiently spaced from the end of the cable shield. Furthermore, since higher operating voltages naturally use thicker insulating inner layers, making the overlap length at least equal to the thickness of the insulating inner layer automatically increases the overlap length and reduces the overlap. It is also advantageous in that it can be held securely. Preferably, the insulative inner layer has a substantially uniform cross-section, and the substantially uniform cross-section of the insulative inner layer includes the cross section of the portion that overlaps the cable shield termination, such that the length of the overlap of the insulative inner layer is At least equal to the thickness of the insulating inner layer at that point. More preferably, the overlap length is 2.5 to 6 times the thickness of the insulating inner layer. However, in the majority of cases, a substantially uniform cross-sectional thickness of 3
No further significant electrical improvement is obtained using overlap lengths greater than a factor of 6, especially 6 times. For cables higher than 15 kV, an innermost stress grading layer is preferably provided, in which case both the innermost stress grading layer and the insulating inner layer preferably overlap the shield termination by the required amount. For cables over 35kV,
At least the insulating inner layer, preferably both the insulating inner layer and the stress grading layer, overlap the shield termination by the required amount, and the insulating inner layer preferably slopes toward the cable shield termination at its end, as described above. The central portion has a substantially uniform cross section. As explained earlier, the innermost stress grading layer has a resistance intermediate between the insulating inner layer and the conductive outer layer, so even if the innermost stress grading layer extends from the conductor connection to the cable shield, A small amount of current, called "leakage current," flows along the stress grading layer from the cable conductor toward the cable shield without excessive conduction forming. This ensures that at the connection, the potential gradient along the cable dielectric layer from the cable shield to the conductor is not as large in any part, thus controlling the stress and reducing the possibility of discharge. It is thought that it will become. Preferably, the innermost stress grading layer is present for a length of at least 60% of the length of the sleeve, most preferably at least 75% of its length.
In some embodiments, the stress grading layer is present along the entire length of the sleeve. Desirably, at least that portion of the sleeve in which the stress grading layer is present has a substantially uniform cross-section in the steady state or free recovery state. That is, it is desirable that the layer thickness ratio be constant over the length of the stress grading layer so that its general cross-sectional shape does not vary substantially. Often the stress grading layer is centrally located along the length of the sleeve. The thickness of the innermost stress grading layer will be determined to a certain extent by the required electrical properties of the sleeve, but typically the innermost stress grading layer will have a thickness of 0.5 to 4.0 mm. It is necessary to make electrical contact between the resistive innermost stress grading layer and the electrically conductive outer layer at least after the sleeve has been properly engaged with the electrical cable termination or connection, which occurs at the end of the sleeve. This can be done by suitable shapes or by providing means for making electrical contact between both layers. Electrical contact between the innermost stress grading layer and the electrically conductive outer layer may be direct or indirect. In its simplest form, for example, the sleeve end is shaped such that during engagement both the conductive outer layer and the stress grading layer contact the cable shield, thereby making an indirect electrical contact through the shield. . Alternatively, the end of the sleeve can be formed such that the insulating inner layer terminates just before the innermost stress grading layer and the conductive outer layer to provide direct electrical contact between the two layers. . Another possibility is to make an indirect electrical contact by a conductive member fitted to the end of the sleeve. Such a member may be, for example, a metal string or a molded part formed from a conductive polymeric material which may be heat recoverable if desired. The invention is applicable to the protection of terminations and connections of single-phase and three-phase electrical cable shields. If three-phase cables are used, each conductor should be provided with a protective sleeve consisting of a conductive outer layer, an insulating inner layer and a stress graded innermost layer, or alternatively each conductor should be provided with an insulating inner layer and a stress graded innermost layer. The sleeve may be completed by one conductive outer layer that provides the innermost layer of insulation and surrounds the three insulated conductors. The present invention will be explained by way of examples and with reference to the accompanying drawings. Referring to the accompanying drawings, FIGS.
1 is a cross-sectional view of various forms of sleeves or splice covers used in the present invention placed on a cable; FIG. Example 1 The jacket 8 and shield 9 of a cable 7 insulated with 20 kV cross-linked polyethylene were cut down to expose the graphite-impregnated cloth layer 10, the graphite layer 11, and the dielectrics 12 and 13, as shown in FIG. , simulating a 24kV straight connection. A portion of the dielectric 13 is removed to expose the conductor 14, and the dielectric regions 15 on both sides of the conductor are coated with conductive paint to a length 10 to simulate a welded joint.
I created an area of cm. Painted area 15
The length of the dielectric material exposed on both sides of the exposed conductive wire between the graphite layer 11 and the graphite layer 11 was 12 cm. A Raychem SCTM stress grading tube with a resistivity of 10 ¹¹ Ω·cm was placed over the connection and recovered to form a stress grading layer 16 in contact with the shield 9 that conformed to the contour of the connection. A Raychem BBIT insulating tube 17 with a wall thickness of 4 mm at the time of recovery (i.e. 4 mm wall thickness when fully recovered) is recovered over the stress grading layer 16 and a thin layer of silicone grease is applied to the first A second BBIT tube 18 of the same wall thickness was applied to the surface of the recovered insulating inner layer 17 and then recovered on top of the first tube. 2 BBIT tubes 1
The lengths 7 and 18 were such that after recovery, about 1 cm of the first insulating inner layer and about 1 cm of the innermost stress grading layer were exposed at both ends of the connection. Finally, a layer of graphite was sprinkled on the outer surface of the second insulating inner layer to restore the Raychem CNTM conductive tube 19 over the connection. The length and recovered diameter of the conductive tube were chosen such that upon recovery the conductive tube makes electrical contact with the stress grading layer 16 and exposed portions of the cable shield 9 at both ends of the connection. Five such connections were made and they had a discharge extinction voltage (DEV) of at least 17kV (0.5pC
(measured according to IEEE43-1975 at a discharge amount of) and 50kV
was found to have a discharge of no greater than 60 pC at . That is, a book having an innermost stress grading layer overlapping the conductor and cable shield, an electrically conductive outer layer in electrical contact with the stress grading layer, and an insulating inner layer between the stress grading layer and the electrically conductive outer layer. It can be seen that according to the sleeve of the example, electrical stress is reduced, so that a connection portion in which discharge is less likely to occur can be obtained. Example 2 Epihalohydrin stress grading substance 2 as described in UK Patent Application No. 45036/76
50 square millimeters of copper conductor 20, polyethylene dielectric 21 by the method described in Example 1, except that 50 was applied to the crimped and exposed conductor 20, and the insulating part was formed together with the conductive part by coextrusion. The 15 kV connection shown in FIG. 2 was formed between two 15 kV polyethylene cables consisting of a graphite layer 22, a graphite impregnated cloth layer 23, a metal shield 24, and an outer jacket (not shown). Reference number 26 indicates a heat-shrinked stress grading tube extending the entire length beyond the connection. The connections are insulated by a heat-shrinked layer or tube 27 and enclosed within a heat-shrinked conductive layer 27A. The layer of insulating material 27 is co-extruded with the outer conductive layer 27.
It is formed integrally with A. Four connections are made by varying the distance between the center of the connection and the shield 24 between 12 cm and 18 cm, with an AC breakdown value of at least 105 kV and an AC breakdown value of at least 200 kV.
positive wave DC impulse
impulse) limit and less than 0.5pC at 30kV
It was found that it has DEV. That is, a book having an innermost stress grading layer overlapping the conductor and cable shield, an electrically conductive outer layer in electrical contact with the stress grading layer, and an insulating inner layer between the stress grading layer and the electrically conductive outer layer. It can be seen that according to the sleeve of the example, electrical stress is reduced, so that a connection portion in which dielectric breakdown and discharge are less likely to occur can be obtained. Example 3 As shown in Figure 3, the 11kV straight connection section is
10kV cross-linked polyethylene insulated cable and copper conductor wire 2
9. It was formed between a 11 kV paper insulated cable consisting of a paper insulating layer 30, an aluminum foil 31, a lead sheath 32, and a cross tape. The connection part is a stress grading layer 35, a BBIT insulation layer 36, and a double extrusion layer 37.
and metal braid 39, each element having the characteristics used in Example 2. Apply 45kV to these five connections for 1 minute, +
10 impulses at 140 kV, followed by 10 impulses at −140 kV, 25 cm underwater, 200 kV (AC) applied, 70°C
It was subjected to a continuous test consisting of 125 load cycles.
All connections passed. That is, it can be seen that according to the sleeve of this example having the innermost stress grading layer, the conductive outer layer, and the insulating inner layer, a connection part that is less likely to cause electrical breakdown even when used underwater can be obtained. Example 4 As shown in FIG.
It was formed between two 10 kV cables consisting of a semiconductor layer 42, a metal shield 43 and a jacket 44. Connections were made as described in Example 3, with the addition of applying a band 42a of conductive paint to the edge of each semiconductor layer. Four similar connections were tested and at least
Has a discharge extinction voltage of 18kV, 30kV in 25cm water,
It was found to pass 336 load cycles at 95°C. That is, according to the sleeve of the present example, which has the innermost stress grading layer, the conductive outer layer, and the insulating inner layer, it is possible to obtain a connection part that is less likely to cause electrical discharge and less likely to cause electrical breakdown even when used underwater. Recognize. Example 5 As shown in Figure 5, a heat-recoverable co-extruded tubular 5-8 kV connection sleeve was constructed with a 1 mm (unexpanded) outermost resistivity of 1000 Ωcm made of conductive high carbon-doped polyethylene. a layer 51 of 5 mm (non-expandable) made of insulating modified polyethylene, an intermediate layer 52 of volume resistivity of 5×10 ¹³ Ω·cm, and an innermost layer 52 of 1 mm (non-expanded) consisting of a stress grading layer. It was made from layer 53. This tube is made heat-shrinkable by cross-linking with electron beam irradiation.
It was expanded under heat with an expansion ratio of 3.5:1. Sleeve 2.5 cm onto each cable shield 55
Restored on top of the crimp connection so that it only overlaps. The outermost layer 51 was grounded to each shield 55 by a wire 56. It has been found that the sleeve of this example, which has the innermost stress grading layer, the conductive outer layer, and the insulating inner layer, provides a connection portion with good electrical properties. Example 6 The procedure of Example 5 was repeated using a coextruded tube with the innermost layer of hot melt adhesive providing an insulating inner layer, a conductive outer layer, and a stress grading layer. Five connections were made with the following dimensions.

[Table] The following tests were conducted on these connections according to IEEE-48-1975. Test DEV 7.5kV (<0.3pC discharge) 35kV AC at 60Hz for 1 minute
25kV AC at 60Hz for 6 hours without destruction or flashover
Impulse voltage 95kV test without destruction or flashover (4) 15 minutes DC 65kV negative polarity
No breakdown or flashover These results indicate that the sleeve of this example, in which the length of overlap of the insulating inner layer with the cable shield is at least equal to the thickness of the insulating inner layer overlapping the end of the cable shield, has no dielectric breakdown or flashover. It can be seen that a connection portion having good electrical properties such as less occurrence of discharge can be obtained. Thus, the overlap with the cable shield by the insulating layer is important. The stress grading layer further reduces electrical stress in the area of the cable connection or termination. By reducing the voltage gradient (V/m), the likelihood of electrical discharge occurring is reduced. A conductive outer layer extends as an outer component over the connection or termination, electrically interconnecting the shields of the integrated cables and providing grounding from one cable to another in the connection area. Maintain continuity. The conductive outer layer serves to prevent electromagnetic radiation from the cable from escaping into the cable air and causing radio interference.

[Brief explanation of drawings]

1 to 5 are cross-sectional views showing sleeves of various shapes according to the present invention described in each embodiment. 14, 20, 29, 40... conductor, 1, 16,
26, 35, 46, 53... Stress grading layer, 6, 17, 18, 52... Insulating inner layer,
5, 19, 51... Conductive outer layer, 3, 4, 9, 2
4,43,55...Cable shield.

Claims (1)

[Scope of Claims] 1. A shielded connection between two electrical cables, each cable comprising a conductor, a dielectric layer surrounding the conductor and truncated to expose the conductor, and a dielectric layer that surrounds the conductor and is truncated to expose the conductor. A shielded electrical cable comprising a conductive cable shield surrounding the layers and truncated to expose the dielectric layer;
The cables are connected within a protective sleeve that provides electrical stress control of the connection, including a tubular insulating inner layer, a tubular conductive outer layer, and a stress gray between each cable and the insulating inner layer. a stress grading layer, the stress grading layer being at least partially electrically resistive and electrically connected to and overlapping the respective cable shield; and the electrically conductive outer layer being electrically connected to and overlapping the respective cable shield. , separated from the cable shield by the insulative inner layer, the insulative inner layer overlapping each cable shield for a length at least equal to the thickness of the portion of the insulative inner layer overlapping the end of the cable shield, and the insulative inner layer overlapping the respective cable shield for a length at least equal to the thickness of the portion of the insulative inner layer overlapping the end of the cable shield; characterized in that the electrical connection between each cable shield is formed at a point on the cable shield that is spaced from the end of the cable shield by a distance at least equal to the thickness of the insulating inner layer portion that overlaps the end of the cable shield; connection. 2. Each insulating inner layer and/or stress grading layer overlaps the respective cable shield by a length equal to at least 2.5 times the thickness of the portion of the insulating inner layer overlapping the cable shield end. connection part. 3. The connection portion according to claim 1 or 2, wherein the length of the overlap is not more than 6 times the thickness of the insulating inner layer portion that overlaps the end of the cable shield. 4. A connection according to any one of claims 1 to 3, wherein the insulating inner layer has a substantially uniform wall thickness over its entire length. 5. The insulating inner layer of the protective sleeve has a first layer of minimum thickness that overlaps each cable shield by a length at least equal to the substantially uniform minimum thickness.
an adjacent second portion of progressively increasing thickness to provide electrical stress control; and an adjacent third portion of substantially uniform maximum thickness extending into the area of the exposed conductor. The connection portion according to any one of items 1 to 4. 6. The connecting portion according to any one of claims 1 to 4, wherein the insulating inner layer, the conductive outer layer, and the stress grading layer are integrally formed by coextrusion. 7. Connection according to any one of claims 1 to 6, in which an empty filler is located between the cable and the sleeve in the region of the cable shield end. 8. Connection according to any of claims 1 to 7, wherein the protective sleeve is applied by recovery, preferably thermal recovery. 9 A method of protecting and shielding a connection between two shielded cables, each cable comprising a conductor, a dielectric layer, and a conductive cable shield surrounding the dielectric layer. an electrical cable, the method comprising: truncating the conductive cable shield to expose the dielectric layer; truncating the dielectric layer to expose the conductor; and enclosing the cable connection by a protective sleeve that provides electrical stress control at the connection. the protective sleeve comprises an at least partially electrically resistive innermost stress grading layer, a tubular insulative inner layer and a tubular electrically conductive outer layer, the method comprising: a stress grading layer overlapping the exposed conductor and extending beyond the exposed conductor and overlapping the respective cable shield, such that the conductive outer layer is in electrical contact with the stress grading layer at the overlap with the respective cable shield; and an insulating inner layer is arranged to separate the stress grading layer and the conductive outer layer in the region between the overlap and the exposed conductor, and the thickness of the insulating inner layer that overlaps the cable shield termination is at least Place the insulating inner layer overlapping each cable shield by an equal length, and make the electrical connection between the conductive outer layer and each cable shield at least as thick as the portion of the insulating inner layer that overlaps the end of the cable shield. A method characterized in that it is formed at points on the cable shield that are spaced apart from the ends of the cable shield by equal distances. 10. The method of claim 9, wherein the layers of the sleeve are heat recoverable and are placed around the cable connection by applying heat. 11 Termination of a shielded electrical cable, the cable comprising: a conductor, a dielectric layer surrounding the conductor and having the ends truncated to expose the conductor, and a dielectric layer surrounding the dielectric layer and having the ends truncated to expose the dielectric layer. A shielded electrical cable comprising a conductive cable shield that
The terminations are terminated in a protective sleeve that provides electrical stress control for the termination, which includes a tubular insulative inner layer, a tubular conductive outer layer, and a stress grading layer between the cable and the insulative inner layer. the stress grading layer is at least partially electrically resistive and electrically connected to and overlapping the cable shield, the electrically conductive outer layer is electrically connected to and overlapping the cable shield, and the insulating inner layer spaced apart from the shield, the insulative inner layer overlaps the cable shield for a length at least equal to the thickness of the portion of the insulative inner layer that overlaps the distal end of the cable shield, and the electrical connection between the conductive outer layer and the cable shield is formed. , formed at a point on the cable shield at a distance from the end of the cable shield at a distance at least equal to the thickness of the portion of the insulating inner layer overlapping the end of the cable shield. 12 Each insulating inner layer and/or stress grading layer shall be at least 2.5 times thicker than the portion of the insulating inner layer overlapping the cable shield termination.
12. A termination according to claim 11, which overlaps the cable shield by a length equal to twice. 13. The termination section according to claim 11 or 12, wherein the length of the overlap is not more than 6 times the thickness of the insulating inner layer portion that overlaps the cable shield end. 14. Claims 11-13 wherein the insulating inner layer has a substantially uniform wall thickness over its entire length
Termination part described in any of paragraphs. 15. The insulative inner layer of the protective sleeve has a first portion of minimum thickness that overlaps the cable shield by a length at least equal to the substantially uniform minimum thickness;
Claims 11-12 having an adjacent second portion of progressively increasing thickness to provide electrical stress control and an adjacent third portion of substantially uniform maximum thickness extending into the area of the exposed conductor. Termination part according to any one of Item 14. 16. The termination section according to any one of claims 11 to 14, wherein the insulating inner layer, the conductive outer layer, and the stress grading layer are integrally formed by coextrusion. 17. Termination according to any of claims 11 to 16, in which a hollow filler is located between the cable and the sleeve in the region of the cable shield termination. 18 The protective sleeve is applied by recovery, preferably thermal recovery.
Termination part according to any one of Item 7.