WO1999030405A1

WO1999030405A1 - High voltage winding

Info

Publication number: WO1999030405A1
Application number: PCT/SE1998/002123
Authority: WO
Inventors: Peter Stering; Bo HERNNÄS; Åke ÖBERG; Rolf Gustafsson; Torbjörn IMRELL
Original assignee: Abb Ab; Imrell, Anne-Marie
Priority date: 1997-11-25
Filing date: 1998-11-23
Publication date: 1999-06-17
Also published as: EP1040549A1; SE510950C2; CN1279835A; CA2308594A1; SE9704337L; AU1358399A; BR9815028A; JP2001526454A; SE9704337D0

Abstract

A high voltage winding having a jointed, multi-wire, electrically insulated cable (10) being part of an electrical machine, a method of jointing said insulating conductor at manufacture, assembly or repair, and an electrical machine having such a high voltage winding. The multi-wire insulated cable comprises a core having a plurality of conductor wires (12, 23, 33, 43a, 43b, 53a, 53b, 53c, 63, 73), electrically insulated from each other, strands and a multi-layer cable insulation provided around the composite multi-wire conductor. The cable insulation comprises a first, inner semiconductive layer (14) surrounding the conductor, a layer of a solid insulation (16) provided around the inner semiconductive layer, and a second, outer semiconductive layer (18) surrounding the solid insulation. The joint connects and electrically contacts two cable cores (20, 30, 50, 60, 70). All strands in each cable core are at the joint arranged in electrical contact with each other.

Description

High Voltage Winding

TECHNICAL FIELD

The present invention relates to electrical or electromagnetical devices, comprising a high voltage winding, and adapted to be used for some electric technical purpose, electrical machines. By "electrical machines" is thus meant statical electrical machines such as transformers or reactors as well as rotating electrical machines such as synchronous machines but also double-fed machines, applications in asynchronous current rectifier cascades, outer pole machines, synchronous flow machines or alternating current machines.

In a first aspect the invention relates to a high voltage winding comprised in an electrical machine and comprising an insulated conductor. More specifically the invention according to this first aspect relates to a high voltage winding according to the preamble of claim 1. Specifically the invention relates to a high voltage winding comprising an insulated conductor, composed of a plurality of strands, which are electrically insulated from each other. For the purpose of this application "high voltage" means voltages up to the highest voltages being used for generation, transmission or distribution of electrical power.

In a second aspect the invention relates to a method in manufacture, mounting, service or other maintenance or repair work, for jointing such an insulated conductor, which is included in a high voltage winding and comprising a plurality of strands, which are electrically insulated from each other. The inventive method is fast, simple and reliable, and secures a good electrical contact between strands which are parts of the jointed conductors, and thereby a good electrical contacting in the joint.

A third aspect of the invention relates to an electrical machine comprising a high voltage winding having such a jointed, insulated conductor.

BACKGROUND OF THE INVENTION AND PRIOR ART

Although the following description mainly relates to and exemplifies both prior art and the present invention by high voltage windings being part of electrical, rotating machines, and thereby in the first place high voltage stator windings, the present invention is applicable for essentially all types of electrical machines, also comprising static machines such as transformers and reactors. In the present applica- tion the expression "high voltage winding" means a winding which in use is at a voltage level of 20 to 800 kV, preferably a voltage level over 36 kV. Transformers and reactors comprising such high voltage windings are used for exchanging electrical energy between two or more systems, for transferring or distributing electrical power, and the high voltage windings are thereby used for electromagnetic induction in ways known per se. Transformers and reactors having high voltage windings according to the present invention, are primarily intended to be used for power ratings from a few hundred kVA up to in excess of 1.000 MVA, and voltage ratings from a few kV up to the highest transmission voltages amounting to 400 to 800 kV or higher.

A high voltage winding for the voltage level in question, and arranged according to known techniques in a rotating machine, such as a generator, is composed of a number of insulated, rectangular copper wires. In a stator winding these wire strands are transposed, i.e. they change place with each other and are enclosed by a common insulation whereby wires and insulation are arranged such that the bundle of conductors obtain a rectangular cross section. Rectangular copper conductors are used since this brings about smaller eddy current losses. Such generators have commonly been designed for voltages amounting to from 15 kV up to 30 kV, which normally has been regarded to be an upper limit. This has had as a consequence that the generator has been connected to the transmission network via a transformer, which has transformed the voltage up to the voltage used in the transmission network, commonly 130-400 kV. By arranging the high voltage winding so as to comprise an insulated conductor, as previously disclosed in the yet non-published international patent application PCT/SE97/00874, (said conductor below in this application being referred to as a high voltage cable), with an electrical insulation of the same type as that of the cables used for transmission of electrical power, it has been possible to increase the voltage of the machine to such levels that it has been possible to connect it directly to the power network used for the transmission, without intermediate transformer. Such a cable and its internal construction, manufacture and installation has been described in the previous, not yet published international applications PCT/SE97/00874, PCT/SE97/00877, PCT/SE97/00901, PCT/SE97/00902, PCT/SE97/00903. The cable includes a number of strands, often having a circular cross section and made of copper, alu- minium or other suitable metal or alloy, such as an alloy based on aluminium or copper. Preferably wires having a diameter below 4 mm have been used. These thin strands have been arranged to form a conductor surrounded by a first inner semi- conductive layer, an electrically insulating layer, preferably a layer comprising a cross-linked polyethylene composition and a second, outer, semiconductive layer. Thus, a high voltage cable according to the present invention does not comprise the outer protective sheath surrounding and mechanically protecting a high voltage cable for use in power distribution, against e.g. abrasion and other damage. A high voltage cable according to the present invention neither exhibits any outer insulat- ing layer on the outside of the outer, semiconductive layer. A rotating electrical machine having a high voltage winding comprising such a high voltage cable has been described in detail in the previous not yet published international patent applications. The use of such high voltage cables presupposes that the machine has been adapted to these high voltage windings, i.a. the outer semiconductive layer has been grounded in the machine, at the same time as measures have been taken, such that the resistivity of this layer has been increased considerably, considering the risk for partial discharge and the function of the outer, semiconductive layer as a ground connection, in order to reduce the heat losses otherwise occurring as a consequence of eddy currents induced in the layer. Also the winding slots in which the high voltage cable is disposed, have been modified, preferably they have been made deeper in order to make place for a thicker insulation, which has led to other constructional changes in order to prevent the occurrence of natural resonance and to provide cooling. Introduction and fixation of the high voltage cable in the slots, as well as all mechanical wear in connection with the handling of this particular high voltage cable, lacking the outer protective sheath, and the outer insulation, has also required measures to be taken. The conductor must be introduced in the recess without damaging the outer semiconductive layer, still the ground connection must be safe.

Also the strands and their connection with the inner semiconductive layer differs from common insulated high voltage cables, used for transmission of electrical power. In contrast to these transmission cables, the cable being a part of a high voltage winding is exposed to magnetic fields, inducing currents with accompanying losses. Therefore at least some of the strands in such cables are arranged to have an electrically insulating surface layer, or having an electrically insulating coating, such that all strands are electrically insulated from each other, but at the same time at least one strand in the layer in contact against the inner semiconductive layer has been arranged to be in electrical contact with the inner semiconductive layer. In this way it has been ensured that the inner semiconductive layer in operation has essentially the same potential as the strands, at the same time a uniform current distribution in the conductor has been ensured, and the eddy- current losses have been counteracted. This has preferably been achieved by using both insulated and uninsulated strands in the high voltage cable, arranged such that two uninsulated wires are not in electrical contact. The employed insulated layers should be stable during manufacture, and installation of the high voltage cable, i.e. preferably at temperatures up to 220°C. The insulating layers should also be stable during use of the electrical machine. Suitable insulations comprise insulation-lacquers such as lacquers based on formaldehyde, polyesters, polyes- terimides, polyurethanes, polyamides, polyimides, polyamidimides, thermoset plastics, extruded thermoplastics, oxides, nitrides which could be generated or coated, silicates or other ceramic compounds, preferably applied by surface coating or deposition techniques known for the deposition of thin surface layers, and generating thin layers exhibiting sufficient adhesion in combination with strength and compactness.

As mentioned above the high voltage cables, comprised in high voltage winding according to the present invention lack outer insulation and/or an outer protective sheath, the mechanical strain, and especially the abrasion of the outer semicon- ductive layer, must be minimised during manufacture, storage and installation. Consequently it is obvious that a long high voltage cable cannot be pulled through the slots in its entire length when installating it in a winding, such as a stator winding. The high voltage winding can comprise up to 10 km high voltage cable. Therefore the high voltage cable is subdivided in suitable pieces which thereafter are jointed. Thereby the number of joints will often be large. At the same time the strains experience will require that these joints exhibit a minimal influence on the electrical properties of the cable, whereby it must be ensured that all the strands being part of the high voltage cable are contacted. Peeling or similar mechanical methods for removing the insulation from insulated strands will thereby be to time- consuming to be economically interesting. Removal of the insulation by means of high temperature processes such as pyrolysis or burning, leaves residues that may influence both the mechanical connection and the electrical contacting. Use of chemical methods such as immersing in an etching or dissolving agent may also lead to residues of the insulation and/ or the agent used remaining on the surfaces of the strands.

THE INVENTION

An object with the present invention is to provide a high voltage winding including an easily applicable and reliable joint. The joint should be adapted to be applied with ease and reproducibly in connection with the manufacture, assembly or repair of an electrical machine, comprising such high voltage winding. This is achieved with a high voltage winding according to the preamble of claim 1 , which is characterized by the features or the characterising part of claim 1. The present invention also has as an object to provide a method for jointing an insulated conductor, in manufacture, assembly, service or other maintenance or repair work, said conductor being comprised in such a high voltage winding, and which comprises a plurality of strands which are electrically insulated from each other. This is achieved according the preamble of claim 14, which is characterized by the features of a characterising part of claim 14. In addition the present invention has as an object to provide an electrical machine comprising such a high voltage winding. Such a machine is defined in claim 26. A high voltage winding for an electrical machine comprises according to the present invention at least one jointed, multi- stranded, electrically insulated conductor, and is characterized in that the multi- stranded, insulated conductor comprises a core having a plurality of conductor wires, strands electrically insulated and a multi-layered conductor insulation which is provided around the composite, multi- stranded conductor-core, for electrical insulation of the conductor, whereby the conductor-insulation comprises an inner semiconductive layer which encloses the conductor-core, a layer of a solid insulation provided around the inner semiconductive layer, and a second, outer semiconductive layer provided on the outside of the solid insulation, all said strands being arranged in electrical with a contact with each other at the joint. Further embodiments of the aspect of the invention relating to a high voltage winding are charac- terized by the features according claims 2 to 13. Further developments relating to the inventive method are characterized by the features of claims 15 to 25.

An electrical machine having a high voltage winding, comprising a jointed, multi- stranded, electrically insulated cable, where the joint exhibits two partial conduc- tors in electrical contact and connected with each other, is in accordance with the present invention provided with a multi-wire, insulated cable. The cable comprises a conductor having a plurality of conductor wires (strands) electrically insulated from each other, strands and a multi-layered cable insulation arranged around the composite multi-wire conductor. The cable insulation comprises a first, inner semi- conductive layer enclosing the conductor, a layer of a solid insulation arranged around the inner semiconductive layer, and a second, outer semiconductive layer, enclosing the solid insulation, and wherein all strands of each cable core at the joint are arranged in electrical contact with each other. This is preferably achieved by one or both of the cable cores being arranged with a stable, electrically con- ducting connection, which is attached to the end surface of the cable core, such that the connection ties all strands comprising the cable cores together and electrically insulates the same. Alternatively this is achieved by establishing stable, electrical contact points between the strands. According to one embodiment of the invention there is provided a stable, electrically conducting connection by applying a coherent, electrically conducting binder phase layer, such as a metallic solder to the end surface of the cable core. Preferably a soft solder is used, such as a soft solder based on silver. By the coherent electri- cally conducting binder phase layer which is applied to the end surface of the cable core, it is secured that the insulated strands are in electrical contact and tied together. According to a preferred embodiment the electrically conducting binder phase layer is jointed with an electrically conducting body, attached to the end surface and to the layer, said body preferably being a part of a jointing sleeve pro- vided on a cable core.

According to an alternative embodiment the solid electrically conducting joint comprises an electrically conducting body, which is provided and attached to the end surface of the cable core by means of friction welding, said body exhibiting an es- sentially metallic bonding to all end surfaces of the strands. Preferably the electrically conducting body constitutes a part of a jointing sleeve provided on a cable core.

Stable electrical contact points between the strands in the cable core has, accord- ing to one embodiment of the present invention, been established with a cable core which is inserted in a jointing sleeve, where insulated strands comprised in the cable core after or in connection with the introduction have been deformed such that by the deformation, stable electrical contact points have been established between the strands and between the outer strands and the attached jointing sleeve. Pref- erably also the attached jointing sleeve has been deformed, e.g. by clamping it around the inserted cable core. In order to ensure that stable electrical contact points have been established, in accordance with an alternative embodiment, hard and sharp electrically conducting particles have been applied to the strands at the end of the cable core or have been introduced in the insulating layer. Preferably these hard and sharp electrically conducting particles comprise an electrically conducting ceramic such as nitride, or a carbide of titanium, suitably having been applied to the insulation of the strands, dispersed in an electrically conducting contact grease. According to another alternative embodiment, at least a part of the cable core which has been inserted into the sleeve, is twisted such that by the twist- ing, the strands in the twisted part have been deformed to such a degree that the strand insulation by deformation, fully or partly, has been removed, and such that the sleeve is compressed around the twisted conductor part. Of course it is possible to combine a twisted cable core and hard, electrically conducting particles in order to establish stable electrical contact points between all strands. According to one embodiment the joint comprises a first cable core having been provided with a jointing sleeve. This jointing sleeve is provided, at the end surface of itself and of the cable core, with a pointed tip, which is run into an opposite sec- ond cable core when the joint has been established. This second cable core is thereby held together by a clamping means, such that the run in pointed tip of the jointing sleeve brings essentially all of the strands of this second cable core in electrical contact. Electrical contacting of all strands of the first cable cores against each other and against the jointing sleeve has been achieved in accordance with any of the previously described embodiments. After the jointing sleeve provided with a pointed tip has been attached and contacted, the tip of the contacted jointing sleeve has been run into the second cable core. The second cable core is clamped together with a clamping means, such that the run in tip of the jointing sleeve is electrically contacted with essentially all of the strands of the second cable core.

In order to joint a multi-wire electrically insulated cable at manufacture or repair of an electrical machine comprising a high voltage winding, by jointing and electrically contacting two cable cores of an insulating, multi-wire cable comprised in a high voltage winding according to the present invention, all conductor wires, strands, which are part of the joint, are arranged in stable electrical contact with each other, whereby it is ensured that the two cable cores are brought into electrical contact with each other. The multi-wire, insulated cable comprises a core with a plurality of from each other electrically insulated conductor wires, strands and a multi-layered cable insulation, arranged around the composite multi-wire conductor. The cable insulation comprises a first, inner, semiconductive layer enclosing the conductor, a layer of a solid insulation arranged around the inner semiconductive layer, and a second, outer semiconductive layer, enclosing the solid insulation.

According to a preferred embodiment of the inventive method an electrical conducting connection is attached against the end surface of the cable core, whereby all strands comprised in the cable core are tied together and are held in a stable electrical contact to each other. Preferably this is achieved by applying an electrically conducting binder phase, such as an electrically conducting metallic solder, onto the end surface of the multi-wire cable core. In order to lower the resistance over the joint, in certain cases an electrically conducting body is bonded with the end surface of the cable core by means of the binder phase. In order to achieve this the body is thereby attached against the end surface of the cable core, and is bonded with and brought into contact against the end surfaces of the strands, by means of the applied binder phase layer, which suitably is constituted of a soft solder, such as one based on silver. Alternatively an electrically conducting body can be friction welded against the end surface of the cable core and bonded with and brought into contact with the end surfaces of the strands. Preferably the electrically conducting body is part of a jointing sleeve of an electrically conducting material, which in this way is bonded with and brought into contact with the end surfaces of the strands.

Alternatively a cable core is inserted into a jointing sleeve, whereupon the strands are deformed such that stable electrical contact points are established between the strands and between the outer strands and the sleeve. Preferably also the sleeve is deformed, suitably by clamping it around the cable core. In order to ensure that stable electrical contact points are established also in those cases where only a limited deformation is desirable or when for some reason, such as high ductility and adhesion of the insulating layer applied to the strands, the layer does not crack or is removed, and that thus no or only insufficient contact surfaces are exposed between strands, in accordance with one embodiment of the invention, hard, electrically conducting particles are applied to the electrically insulated strands before a cable core is introduced into the sleeve. These particles will already at a limited deformation penetrate a strand insulation whereby stable, electrical contact points are established between the strands and between the outer strands and the sleeve by means of the hard particles. A preferred and very suitable way of applying the particles is to disperse the particles in an electrically conducting contact grease, whereupon the contact grease, containing the dispersed particles is applied to the strands. Of course the particles can be applied in any other suitable way, such as dry spraying of the particles or by spraying, dipping etc., dispersed in a solvent. Particles can also already when insulating the strands have been introduced into the strand insulation, provided that it had been possible to combine this with the existing requirements of electrical insulation of the strands relative to each other.

According to one embodiment the strands and the strand insulation are deformed such that at least portions of insulation provided on a strand are removed, whereby contact surfaces occur between the strands of a cable core, by the cable core being twisted in a section at the end surface of the cable core, such that strands and strand insulation are deformed due to the twisting, whereby the strand insulation fully or partly is removed, whereupon the cable core is inserted into a sleeve. Subsequently the sleeve is compressed, and is pressing at least around the twisted section, and stable electrical contact points are established between the strands and the outer strands and the sleeve in this twisted section. Of course the cable core can be twisted in the presence of hard particles such that, as has been described above, it is ensured that sufficient and sufficiently stable electrical contact points are established.

It is also suitable to use methods offering a quick removal of at least portions of insulation present on a strand, whereby contact surfaces occur on the strand in which it bears against on other strands, and which are essentially free form residues of insulation, and any treatment medium. For example a cable core may be rapidly cooled such that the insulation becomes brittle and entirely or partly crackles, resulting in at least portions of the surfaces of the strands being exposed by flaking. This flaking can occur either in connection with the cryo treatment or in a subsequent deformation. Preferably the cryo treatment is performed by exposing the end of the cable core to a cooling air or gas stream, e.g. a stream of sub-cooled liquid such liquid nitrogen or dry ice, alternatively by the cooling effect occurring when a gas expands, the principle of Rank.

In one embodiment a first cable core is introduced and brought into contact against a jointing sleeve provided with a pointed tip. With a pointed tip is meant that the jointing sleeve comprises a protruding means of a suitable shape such that when it is run into a second cable core it provides electrical contact with all strands present in the second cable core, either directly or after this second cable core having been tightened around the run in pointed tip. Electrical contacting of all strands of the first cable core against each other and against the jointing sleeve is achieved in any of the ways previously described. After having applied and contacted the jointing sleeve provided with a pointed tip, said tip of a contacted jointing sleeve is run into a second cable core, whereby the second cable core, at the time of running in or thereafter, is clamped together with a clamping means, such that the tip of run in jointing sleeve is brought into contact with essentially all strands of the second ca- ble core.

The invention also relates to an electrical machine comprising a high voltage winding. Preferably an electrical machine comprising a high voltage winding and which is adapted for generation, transmission or distribution of electrical power such a generator, a transformer, a reactor or machine, provided in a plant for production of electrical power, a plant for transmission of electrical power or in a network for distribution of electrical power form a producer to a consumer. The invention also relates to an electrical machine such as a motor, a transformer, a reactor or any other machine located at a large consumer of electrical power, such as a larger industrial plant.

FIGURES

The invention will be explained in closer detail in the following and will be exemplified with a preferred embodiment with reference to the figures.

Figure 1 shows a cross section of a high voltage cable of the type being comprised in a high voltage winding according to the invention.

Figure 2a shows in detail a cable core, comprised in an embodiment of the invention, arranged with a layer of an electrically insulating material applied to the end surfaces of the strands, according to one embodiment of the present invention, fig- ure 2b shows an alternative embodiment with an electrically conducting body attached to and brought into contact with the end surface of the strands by means of an electrically conducting binder phase.

Figure 3 shows a cable core comprised in an embodiment of the invention where an electrically conducting body has been friction welded against the end surfaces of the strands.

Figures 4a and 4b shows in detail two strands with an intermediate insulation comprised in an embodiment of the invention. A compound comprising hard elec- trically conducting particles has been applied to insulating layer in figure 4a, and as shown in figure 4b it has penetrated the insulating layers after deformation, such that stable electrical contact points have been established between the strands.

Figures 5a, 5b, 5c and 5d illustrates an embodiment of the present invention, comprising a cable core with strands having been deformed by twisting. Stable electrical contact points have been established between the strand by the twisting.

Figure 6 shows in a longitudinal section through a jointed high voltage cable ac- cording to one embodiment of the invention, where a first cable core comprises a jointing sleeve having a pointed tip, run into a second cable core. DESCRIPTION OF THE FIGURES

The high voltage cable 10 shown in figure 1 comprises an electrical conductor which exhibits a plurality of conductor wires, strands 12. The strands 12 preferably exhibits a circular cross section, a diameter less than 4 mm and comprises an electrically conducting metal such as copper or aluminium, or an alloy based on such an electrically conducting metal. These strands 12 are arranged in the centre of the high voltage cable 10, surrounded by an insulating system which from the centre and outwards comprises a first inner semiconductive layer 14, a tubular insulating body 16 and a second, outer semiconductive layer 18.

In the embodiment shown in figure 1 the tubular insulating body 16 comprises an extruded and cross-linked polymer composition, such as a cross-linked polyethylene composition. Also the two semiconductive layers are comprised of polymer lay- ers which have been co-extruded with the insulation, but which comprise a filler in the form of electrically conducting particles or an electrically conducting polymer, that is a polymer with intrinsic electrical conductivity. Preferably a particular filler is used, such as particles of soot, graphite or other electrically conducting modifications of carbon, metals such as silver, copper, aluminium, nickel or an alloy comprising any of these or combinations of those, an electrically conducting ceramic such as a carbide or nitride. Furthermore some of the strands 12 are arranged with a thin insulating layer 11 , whereby all strands will be electrically insulated from each other by an electrical insulation, why at least one strand 1 la is in electrical contact with the inner semiconductive layer 14. This is achieved with a high voltage cable 10 according to figure 1, which comprises both insulated an uninsulated strands arranged such that two uninsulated strands are not in electrical contact. The used insulating layers 11 are stable during manufacture, and installation of the high voltage cable 10, that is preferably at temperatures up to 220°C. Suitable insulations comprise insulation lacquers, such as lacquers based on formaldehydes, polyesters, polyesterimides, polyurethanes, polyamides, poly- imides, polyamidimides, thermoset plastics, extruded thermoplastics, oxides, nitrides which can be generated or applied, silicates or other ceramic compounds, preferably applied by known surface coating or deposition techniques for the deposition of thin surface layers, which generate thin layers exhibiting sufficient adhe- sion in combination with strength and compactness.

In figure 2a there is shown a cable core adapted to be part of a joint of a jointed high voltage winding according to one embodiment of present invention. The cable core 20 is comprised of a high voltage cable of the type shown in figure 1. On the end surface 21 of the cable core 20 has been applied a coherent electrically conducting binder phase layer 25, such as a metallic solder. A soft solder, such as a soft solder based on silver, has preferably been used. The coherent electrically conducting binder phase layer 25 applied to the end surface 21 of the cable core, ties together an electrically contacts all the strands 23 comprised in the cable core. According to the embodiment shown in figure 2b the electrically conducting binder phase layer 25 has been jointed with an electrically conducting body 26 attached to the end surface 21 and the layer 25, the body preferably being a portion of a jointing sleeve attached to the cable core 20. According to the alternative embodiment of a cable core 30 according to the invention shown in figure 3, an electrically conducting body 35 has been connected to and electrically contacted with the end surface 31 of the cable core by means of friction welding. The resulting connection exhibits an essentially metallic bonding to all the end surfaces of the strands 33, and constitutes a stable electrical contacting of all strands. The embodiment shown in figure 3, comprises also a cylindrical holder 38 for holding together the strands 33. Preferably the electrically conducting body 35 is part of a jointing sleeve attached to the cable core 30.

Stable electrical contact points between the strands of the cable core has been es- tablished according to particular embodiments of the present invention, in a cable core which is introduced in a jointing sleeve, in that the insulated strands comprised in the cable core after or in connection with introduction into the jointing sleeve have been deformed such that stable electrical contact points have been established between the strands and between the outer strands and the applied jointing sleeve by the deformation. Often also the applied jointing sleeve has been deformed, such as by clamping around the inserted cable core.

Figures 4a and 4b show in detail two strands 43a, 43b with intermediate insulation 44a, 44b comprised in one embodiment of the invention. A compound 47 compris- ing hard electrically conducting particles 48 has been applied to the insulating layer of figure 4a, and as shown in figure 4b they have penetrated the insulating layers 44a, 44b after deformation such that stable electrical contact points have been established between the strands 43a, 43b. Preferably these hard and sharp electrical conducting particles 48 comprise an electrically conducting ceramic such as a nitride or a carbide of titanium, which suitably have been applied to the insulation of the strands dispersed in an electrically conducting contact grease 47.

In accordance with a further alternative embodiment, illustrated with figures 5a, 5b, 5c and 5d at least section 59 of the cable core 50 inserted into a sleeve 55 is twisted, such that by the twisting, the strands 53, 53a, 53b, 53c in the twisted part 59 have been deformed to such a degree that the strand insulation 54, 54a, 54b, 54c by the deformation, entirely or partly has been removed, and such that the sleeve is compressed around the twisted conductor part, see the detail shown in figure 5d.

According to the embodiment of the present invention shown in figure 6 the joint which is part of the high voltage winding comprises a first cable core 60 which has been provided with a jointing sleeve 65. The jointing sleeve 65 is in its own end surface and the end surface 61 of the cable core provided with a pointed tip 650, which is run into an opposite second cable core 70 when the joint has been established. This second cable core 70 is held together by a clamp 75 such that the run in pointed tip 650 of the jointing sleeve electrically contacts essentially all strands 73 of this second cable core. Electrical contacting of all strands 63 of the first cable core 60 against each other and against the jointing sleeve has been achieved by means of any of the previously described embodiments. After the jointing sleeve 65 having a pointed tip is applied to the first cable core 60 and brought in contact against the strands 63 comprised in this cable core 60, the contacted pointed tip 650 of the jointing sleeve has been run into the second cable core 70. The other cable core 70 is tied together with a clamping means 75, such that the run in pointed tip 650 of the jointing sleeve is electrically contacted with essentially all strands 73 of the second cable core.

Claims

1. A high voltage winding for an electrical machine, comprising a jointed, multi-wire electrically insulated cable (10), comprising a joint exhibiting two cable cores (20, 30, 50, 60, 70) connected to each other and electrically contacted, characterized in that the multi-wire insulated cable comprises a core with a plurality of conductor wires (12, 23, 33, 43a, 43b, 53, 53a, 53b, 53c, 63, 73), which are electrically insulated from each other, strands and a multi-layered cable insulation provided around the composite multi-wire conductor, whereby the cable insulation comprises a first, inner, semiconductive layer (14), enclosing the conductor, a layer of a solid insulation (16) provided around the inner semiconductive layer, and a second, outer semiconductive layer (18) enclosing the solid insulation, whereby all strands in both cable cores at the joint are arranged in electrical contact with each other.

2. A high voltage winding according to claim 1, characterized in that at least one cable core (20, 30, 40, 60) comprises an electrically conducting connection (25, 26, 35, 65) provided against the end surface (21, 31) of the cable core, whereby the connection ties together and electrically contacts all strands (23, 33, 65) comprised in the cable core.

3. A high voltage winding according to claim 2, characterized in that the insulated strands (23) are electrically contacted and bonded together by means of a coherent, electrically conducting binder phase layer (25) applied to end surface of the cable core.

4. A high voltage winding according to claim 3, characterized in that the applied electrically conducting binder phase layer (25) comprises a metallic solder.

5. A high voltage winding according to claims 2 or 3, characterized in that the electrically conducting binder phase layer (25) is provided against and jointed with an electrically conducting body (26).

6. A high voltage winding according to claim 2, characterized in that the solid, electrically conducting compound comprises an electrically conducting body (35), provided at the end surface (31) of the cable core by means of friction welding, said body exhibiting an essentially metallic bonding to end surfaces of all strands (33).

7. A high voltage winding according to claims 5 or 6, characterized in that the electrically conducting body (26, 35) constitutes a part of a jointing sleeve (55, 65).

8. A high voltage winding according to claim 1, characterized in that one cable core is inserted in jointing sleeve (59, 60), insulated strands (53, 53a, 53b, 53c, 63) comprised in the cable core, are deformed and at stable electrical contact points have been established between the strands and between the outer strands and the applied jointing sleeve (55, 65) by the deformation.

9. A high voltage winding according to claim 8, characterized in that the stable electrical contact points comprises hard and sharp electrically conducting particles (48).

10. A high voltage winding according to claim 8, characterized in that the hard and sharp electrically conducting particles (48) comprises an electrically conducting ceramic, such as a nitride or a carbide of titanium.

11. A high voltage winding according to claims 9 or 10, characterized in that the hard and sharp electrically conducting particles (48) are applied to the strand insulation, dispersed in an electrically conducting contact grease (47).

12. A high voltage winding according to claim 8, characterized in that the cable core (50) which is inserted into the sleeve at least partly (59) is twisted, and in that the strands (53, 53a, 53b, 53c) in the twisted part are deformed and that the strand insulation (54a, 54b, 54c) entirely or partly have been removed by the deformation and that the sleeve is compressed around the twisted conductor part.

13. A high voltage winding according to any of the preceding claims, characterized in that a first cable core (60) comprises a jointing sleeve (65), which in its own end surface and in the end surface of the cable core is provided with a pointed tip (650) which is run into an opposite second cable core (70), and in that the second cable core is held together by a clamping means (75) such that the pointed tip of the run in jointed sleeve is brought into contact with essentially all strands (73) of the second cable core.

14. A method of jointing a multi-wire, electrically insulated cable (10) in manufacture, assembly or repair of an electrical machine comprising a high voltage winding, whereby two cable cores (20, 30, 50, 60, 70) in the jointing operation are connected and brought in electrical contact, characterized in that the multi-wire, insulated cable comprising a core having a plurality of from each other electrically insulated conductor wires (12, 23, 33, 43a, 43b, 53, 53a, 53b, 53c, 63, 73), strands and a multi-layered cable insulation provided around the composite multi-wire conductor, and the cable insulation comprises a first, inner semiconductive layer (14) enclosing the conductor, layer of solid insulation (16) arranged around the inner semiconductive layer, and a second, outer semiconductive layer (18) enclosing the solid insulation, whereby all strands in those cable cores at the joint are brought into electrical contact with each other.

15. A method according to claim 14, characterized in that an electrically conducting compound (25, 26, 35, 65) is attached to the end surface (21, 31) of the cable core whereby all strands (23, 33, 63) comprised in the cable core are tied together and electrically contacted.

16. A method according to claim 15, characterized in that an electrically conducting binder phase (25) is applied to end surface (21) of the multi-wire cable core.

17. A method according to claim 16, characterized in that an electrically con- ducting metallic solder (25) is applied to end surface (21) of the multi-wire cable core.

18. A method according to claim 14, 15, 16 or 17, characterized in that an electrically conducting body is tied (26) together with the end surface of the cable core by means of the binder phase (25), whereby the body is provided against the end surface (21) of the cable core and is tied together with and brought into contact against the end surfaces of the strands (23).

19. A method according to claim 14, characterized in that an electrically con- ducting body (35) is friction welded against the end surface (31) of the cable core whereby the body is provided against the end surface of a cable core and tied together with and brought into contact against the end surfaces of the strands (33).

20. A method according to claim 18 or 19, characterized in that a jointing sleeve of an electrically conducting material (55, 65) is tied together with the end surface of the cable core, whereby the sleeve is provided against the end surface of the cable core and is tied together with and brought into contact against the end surfaces of the strands (53, 63).

21. A method according to claim 14, characterized in that the strands (53, 53a, 53b, 53c, 63) are deformed such that stable electrical contact points are established between the strands.

22. A method according to claim 21 , characterized in that hard, electrically conducting particles (48) are applied to the electrically insulated strands(43a, 43b), the cable core is inserted into a sleeve and the strand insulation (44a, 44b) is penetrated by the hard particles when sleeve and strands are deformed, whereby stable electrical contact points are established between strands and between the outer strands and the sleeve by the hard particles.

23. A method according to claim 22, characterized in that the hard electrically conducting particles (48) are dispersed in an electrically conducting contact grease (47) and in that the contact grease comprising the dispersed particles is applied to the strands.

24. A method according to claim 21, characterized in that a cable core (50), is twisted in a section (59) at the end surface of the cable core, in that strands (53a, 53b, 53c) and strand insulation (54a, 54b, 54c) are deformed by the twisting, whereby the strand insulation entirely or partly is removed whereupon the cable core is inserted into a sleeve (55), and in that the sleeve is compressed around the twisted section, whereby stable electrical contact points are established between the strands and between the outer strands and the sleeve.

25. A method according to claim 21 , characterized in that a first cable core (60) is inserted into and brought into contact against a jointing sleeve (65) provided with a pointed tip (650), in that the pointed tip of the jointing sleeve is run into a second cable core (70), whereby the second cable core is held together by a clamping means (75) such that the pointed tip of the run in jointing sleeve is brought into contact with essentially all of strands (73) of the second cable core.

26. An electrical machine comprising a high voltage winding according any of claims 1 to 13.