MXPA00005115A - A method of applying a tube member in a stator slot in a rotating electrical machine - Google Patents

Abstract

A method for mounting a tube member (24) in a space (23) having a shape corresponding to the shape of the tube member (24), the tube member (24) being inserted into the space (23), after which a pressure medium is heated and pressurises the tube member (24) so that this softens and expands, its outer periphery assuming the shape of the limiting areas of space (23), after which the hot pressure medium is replaced with or converted to a cold pressure medium which fills out the expanded tube member (24) and causes it to solidify and permanently assume this expanded shape, and also a rotating electric machine arranged in accordance with the method.

Description

METHOD FOR APPLYING A TUBULAR MEMBER IN A STATOR SLOT IN A ROTATING ELECTRICAL MACHINE TECHNICAL FIELD The present invention relates to rotating electrical machines such as synchronous machines. This also refers to dual feed machines, applications in asynchronous static current converters, external pole machines and synchronous flow machines, as well as AC machines designed primarily as generators in a station. of energy to generate electric power. The invention particularly relates to the stator in such machines and to a method for fixing the windings, as well as to the cooling of the stator teeth and the insulated electrical conductor constituting the winding of the stator.

BACKGROUND OF THE INVENTION Similar machines have been conventionally designed for voltages in the REF .: 120263 range of 15-30 kV, and 30 kV has normally been considered as an upper limit. This generally means that a generator must be connected to the power grid via a transformer which gradually raises the voltage to the level of the power grid, which is in the range of approximately 130-140 kV. The present invention is primarily aimed at use with high voltages. High voltages should be understood here as voltages greater than 10 kV. A typical operating range for the machine according to the invention should be voltages from 36 kV to 800 kV. The invention is secondarily intended for use in the established technical area at voltages below 36 kV. There are two different air-cooled systems for conventional cooling: the radial cooling where the air passes through the rotor through the hub and the radial channels in the rotor, and the axial cooling where the air is blown into the polar free spaces by axial fans. The stator is divided into radial air ducts created by spacers (often straight) that are welded in one place. Due to the poor thermal conductivity axially through the laminations of the stator, the air ducts must be frequently repeated. The drawback with air cooling is that the losses by ventilation are considered and that, due to the ventilation ducts, the stator becomes longer. In addition, particularly with high voltage generators with long teeth, the ventilation ducts can also weaken the structure mechanically. Liquid axial cooling, for example, cooling with water, by means of cooling tubes, for example metal, in the stator yoke has been known for some time. One drawback is that eddy currents are induced in the metal tubes if they are present in a magnetic flux that varies with time, thus leading to certain energy losses when used in an electrical machine.

OBJECTIVE OF THE INVENTION The object of the present invention is to provide a method for mounting a cooling tube in a tubular cooling channel, and also a rotating electrical machine comprising cooling tubes mounted using this method in conjunction with the direct cooling of the stator and particularly of the stator teeth in such machine. Yet another object of the invention is to eliminate the ventilation ducts, which results in shorter and stronger stators, while ensuring that the magnetic flux in the stator teeth is distributed as little as possible by said cooling. The objective is also to achieve a higher degree of efficiency. A further object of the invention is to achieve stable fixing of the cables in the stator slots by means of these cooling tubes.

BRIEF DESCRIPTION OF THE INVENTION The aforementioned objective is achieved by the method and arrangement according to the invention having the characteristics defined in the api annexed indications.

By using high voltage insulated electrical conductors with solid insulation similar to that used in cables for the transmission of electrical energy (eg XLPE cables) the machine voltage can be increased to levels such that it can be directly connected to the power grid without an intermediary transformer. The conventional transformer can thus be eliminated. The concept generally requires that the slots in which the cables are placed in the stator be deeper than with conventional technology (thicker insulation due to the higher voltage and more turns in the winding). This means that the distribution of the losses differs from that in a conventional machine which in turn involves new problems in the cooling of the stator, for example, and particularly the teeth of the stator. The insulated conductor or the high voltage cable used in the present invention is flexible and is of the type described in more detail in WO 97/45919 and WO 97/45847. The insulated conductor or cable is further described in WO 97/45918, WO 97/45930 and WO 97/45931.

Thus, in the device according to the invention the windings are preferably of a type corresponding to the cables having extruded, solid insulation, such as those currently used for energy distribution, such as XLPE cables or cables with EPR insulation. Such a cable comprises an internal conduit composed of one or more parts in strands, an inner semiconducting layer surrounding the conductor, a solid insulating layer surrounding it and an outer semiconductive layer, which surrounds the insulating layer. Such cables are flexible, which is an important property in this context, since the technology for the device according to the invention is based mainly on the winding systems, in which the winding is formed from conductors that are flexed during assembly. The flexibility of an XLPE cable normally corresponds to a radius of curvature of approximately 20 cm for a cable of 30 mm in diameter, and a radius of curvature of approximately 65 cm for a cable of 80 mm in diameter. In the present application, the term "flexible" is used to indicate that the winding is flexible up to a radius of curvature of the order of four times the diameter of the cable, preferably eight to twelve times the diameter of the cable. The winding must be constructed to retain its properties even when it is flexed, and when subjected to thermal or mechanical stress during operation. It is vital that the layers retain their adhesion to one another in this context. The material properties of the layers are decisive here, particularly their elasticity and the relative coefficients of thermal expansion. In an XLPE cable, for example, the insulating cable consists of low density polyethylene, crosslinked, and the semiconductor layers consist of polyethylene with particles of carbon black and metal mixed together. Changes in volume as a result of temperature fluctuations are completely absorbed as the changes in the radius in the cable and, thanks to the comparatively slight difference between the coefficients of thermal expansion in the layers in relation to the elasticity of these materials, the Radial expansion can take place without adhesion between the layers that are lost. The material combinations established above should be considered as examples only. Other combinations that meet the specified conditions and also the conditions of being semiconductive, for example having a resistivity within the range of 10-i - 10 ° ohm-cm, for example, 1-500 ohm-cm, or 10-200 Ohm-cm, they fall naturally within the scope of the invention. The internal and external semiconductor layers may be of the same basic material, but with conductive material particles such as carbon black or metal powder mixed together. The mechanical properties of other materials, particularly, their coefficients of thermal expansion, are affected relatively little either because if the carbon black or metal powder is mixed together or not - at least in the proportions required to achieve the necessary conductivity according to the invention. The insulating layer and the semiconductor layers in this way have substantially the same coefficients of thermal expansion. The copolymer of ethylene-vinyl acetate / nitrile rubber, butylimp-polyethylene, ethylene-acrylate copolymers and ethylene-ethyl-acrylate copolymers can also be suitable polymers for semiconductor layers.

Even when used in different types of material as a base in the various layers, it is desirable that their coefficients of thermal expansion be substantially the same. This is the case with the combination of the materials listed above. The materials listed above have relatively good elasticity, with an E modulus of E < 500 MPa, preferably < 200 MPa. The elasticity is sufficient for any minor differences between the coefficients of thermal expansion for the materials in the layers to be absorbed in the radial direction of the elasticity so that no cracks or other damage appear, and so that the layers are not released one from the other. The material in the layers is elastic, and the adhesion between the layers is at least of the same magnitude as in the weakest of the materials. The conductivity of the two semiconductor layers is sufficient to substantially equalize the potential along each layer. The conductivity of the outer semiconducting layer is sufficiently large to contain the electric field in the cable, but at the same time sufficiently small to not cause significant losses due to the currents induced in the longitudinal direction of the layer. In this way, each of the semiconductor layers essentially constitutes an equipotential surface, and the winding composed of these layers will substantially enclose the electric field therein. Of course, there is nothing that prevents one or more additional semiconductor layers from being accommodated in the insulating layer. The invention relates to a method for fixing the cable in a high voltage generator by means of a preformed triangular tube of XLPE, which during the operation is also used for the cooling of the windings and the tooth section of the stator core. At the time of assembly, the preformed tube is inserted into the triangular space between the cables and the tooth. The shape of the tube should provide enough free space to allow easy insertion of the tube. When the tube is in place, it is heated to a temperature of 125-130 ° C at which it can be formed. In addition, an overpressure is applied to the inner side of the tube in order to press or press the tube against the wires and the wall of the groove. The heating and pressurization of the tube are achieved by heating and pressurizing a pressure medium, causing the tube to soften and expand, whereby its outer periphery assumes a shape that fits against the cables and the wall of the tube. slot. While retaining the overpressure, the tube is then cooled by the exchange of the hot pressure medium against a cold pressure medium, for example, cold water, which fills the expanded tube and causes it to solidify and permanently assume this form expanded. The tube will now act as an elastic element absorbing the thermal expansion of the cables during the operation. The tube is also used as a cooling tube during operation, the overpressure of the cooling medium provides a resting pressure on the cables. This pressure against the cables and the wall of the groove, also provides heat transfer. The tubes are placed against one of the walls of the slot in each or in all the spaces between the cables. The invention also relates to a rotary or rotary electric machine provided with cooling tubes / fixing means mounted by this method. The machine comprises the cooling tubes that run axially, made of a dielectric material, for example a polymer, and drawn through the interspaces of the triangular cables on the teeth of the stator. The tubes are expanded in the interspaces so that good heat transfer occurs when the refrigerant is circulated in the tubes. The tubes run in the stator yoke and in the stator teeth along the entire axial length of the stator and, if necessary, these can be spliced into the stator teeth. The polymeric cooling tubes are non-conductive, and therefore the risk of short-circuiting is eliminated, nor can swirl currents occur in them. The polymeric cooling tubes can also be cold flexed and extended through several channels of non-spliced cooling tubes, which is a great advantage. The polymeric cooling tubes can be produced from many materials, such as polyethylene, polypropene, polybutene, polyvinylidene fluoride, polytetrafluoroethylene, as well as filled and reinforced elastomers. Of these materials, high density polyethylene, HDPE, is preferred since its thermal conductivity increases as the density increases. If the polyethylene is crosslinked, which can be achieved by breaking or dividing a peroxide, cross-linking with silane or pattern formation by radiation, its ability to withstand pressure at increased temperature is improved, at the same time it disappears the risk of voltage corrosion. The cross-linked polyethylene pipe, for example, of XLPE from Wirsbo bruks AB, is used, for example, for water pipes. In a method and a device according to the invention, the windings are preferably of a type corresponding to the cables having solid, extruded insulation, such as those currently used for energy distribution, such as XLPE cables or cables with EPR insulation . Such a cable comprises an internal conductor composed of one or more parts in strands, an inner semiconductor layer surrounding the conductor, a solid insulating layer surrounding it, and an outer semiconductor layer surrounding the insulating layer.

Such cables are flexible, which is an important property in this context, since the technology for the device according to the invention is based mainly on the winding systems in which the winding is extended back and forth in a plurality of turns, for example without being spliced at the ends of the coil as required when the winding in the core consists of rigid conductors. The flexibility of an XLPE cable normally corresponds to a radius of curvature of approximately 20 cm for a cable of 30 mm in diameter, and to a radius of curvature of approximately 65 cm for a cable of 80 mm in diameter. In the present application, the term "flexible" is used to indicate that the winding is flexible up to a radius of curvature of the order of eight to twenty-five times the diameter of the cable.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail with reference to the designations in the accompanying drawings.

Figure 1 schematically shows a perspective view of a section diagonally through the stator of a rotary electric machine; Figure 2 shows a cross section through a high voltage cable according to the present invention; Figure 3 schematically shows a sector of a rotary electric machine; Figure 4 shows a cross section through part of the sector shown in Figure 3, where the cross section is marked by a rectangle.

DESCRIPTION OF THE INVENTION Figure 1 shows part of an electrical machine in which the rotor has been removed to reveal more clearly how a stator 1 is accommodated. The main parts of the stator 1 consist of a stator frame 2, a stator core 3 comprising the stator teeth 4 and a stator yoke 5. The stator also comprises a stator winding 6 in the form of a high voltage cable, placed in a space 7 formed as a bicycle chain, see Figure 3, formed between each individual stator tooth 4. In Figure 3, winding 6 of the stator is only indicated by its electrical conductors. As shown in Figure 1, the winding 6 of the stator forms a coil-end cluster 8 on each side of the stator 1. Figure 3 also reveals that the insulation of the high-voltage cable is staggered in several dimensions depending on its location radial in the stator 1. For simplicity purposes only one cluster or coil end group is shown in Figure 1, at each end of the stator. In conventional large machines, the structure or frame 2 of the stator often consists of a welded steel plate construction. In large machines, the core 3 of the stator, also known as the laminated core, is normally made of 0.35 mm core sheet, divided into stacks having an axial length of about 50 mm and separated from one another by divisions forming ventilation ducts 5 mm wide. However, in the machine described, the ventilation ducts have been eliminated. In large machines, each stack or laminated stack is formed by placing the sheet metal segments 9, punched to a suitable size, together to form a first layer, each subsequent layer being placed transversely to form a complete laminated part. of a stator core 3. The parts and the divisions are held together by pressure clamps 10, which are pressed against the rings, fingers or pressure segments, not shown. Only two pressure clamps are shown in Figure 1. Figure 2 illustrates a cross section through a high voltage cable 11 according to the invention. The high voltage cable 11 comprises a number of parts 12 in processed copper (Cu) strands, for example, and having a circular cross section. These strand portions 12 are accommodated in the intermediate part of the high voltage cable 11. Around the strand portions 12 is a first semiconductive layer 13. Around the first semiconductive layer 13 is an insulating layer 14., for example, XLPE insulation. Around the insulating layer 14 is a second semiconductor layer 15. The concept "high voltage cable" in the present application does not thereby comprise the shell or external protective covering that normally surrounds a cable for power distribution. The high voltage cable has a diameter in the range of 20-250 mm and a conductive area in the range of 80-3000 mm2. In the figure that shows the component that forms the insulated conductor or cable, the three layers are such that they adhere to each other even when the cable is flexed. The cable shown is flexible and this property is observed throughout the service life of the cable. Figure 3 schematically shows a radial sector of a machine with a sheet metal segment 9 of the stator 1 and a pole 16 of the rotor on the rotor 17 of the machine. It is also clear that the high voltage cable 11 is accommodated in the space 7 similar to a bicycle chain, formed between each tooth 4 of the stator. Space 7 is shown in the Figure, in the form of a bicycle chain, although as shown in Figure 4, according to one embodiment of the present invention, one side of the slot is comple flat. Figure 4 shows four cable parts 18 of the high voltage cable 11, the parts of which are fitted within the slot 20 of the stator tooth, asymmetric, having a corrugated side 21 in order to fit against the parts of the cable and the cable. flat side 22. This shape of the stator tooth slot 20 results in triangular spaces 23 of each cable portion 18. In each and in some of these spaces 23, tubular members 24 are placed which have been preformed to correspond to the shape of the space 23, although of a smaller dimension in order to allow easy insertion into the space 23. The term " "tubular member" designates in the subsequent the function of the member as "cooling tube" and as a "fixing means". The tubular member 24 is inserted into the space 23 and a pressure medium is heated by pressurizing the tubular member 24 which will soften and expand, with its outer periphery assuming the shape of the restriction area of the space 23, bounded by the second semiconductor layer 15 of the cable parts and the flat side 22 of the stator tooth slot 20, after which a constant pressure is maintained, the hot pressure medium is replaced by a cold pressure medium filling the expanded tubular member 24 and causes it to solidify and permanently assume this expanded form. It is possible to use the same pressure medium, although at different temperatures. In this case, the temperature of the hot pressure medium will be higher than the softening temperature of the tubular member, while the temperature of the cold pressure medium will remain below the softening temperature of the tubular member. In order to prevent expansion of the free portions of the tubular member, for example, the parts located outside the stator, these parts are provided with expansion protection before the cooling tube pressurization is initiated. Each tubular member 24 is made of a dielectric material, for example, a polymer, preferably XLPE, in order to prevent electrical contact with the tooth plate 4 of the stator or with the second semiconductor layer 15 of the cable parts 18. During expansion, the thickness of the wall of the tubular member 24 is reduced. The tubular member 24 is allowed to expand until 50% of its original wall thickness remains G. The wall thickness and other properties of the tubular member are chosen in order to ensure that, after being expanded, the remaining wall thickness. be sufficient to fill -comple the space between the outer periphery of the tubular member and the second semiconductor layer 15 of the cable parts and the flat side 22 of the stator tooth slot, respectively. The material of the tubular member is determined with respect to factors such as the thermal conductivity coefficient, the coefficient of linear expansion as well as the hot forming property. Although the described embodiment refers to a triangular cable interspace, other forms of interspaces are possible, for example, the cables can be accommodated at a larger radial distance, whereby an interspace in the form of an hourglass is formed in the which a preformed cooling tube / means of fixing the hourglass shape can be accommodated according to the present invention. It is also possible that the tubular means before being expanded has a different cross-section than the space itself, for example an elliptical cross-section, but that the tubular member has a wall thickness which allows sufficient expansion.It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (19)

CLAIMS Having described the invention as above, the content of the following claims is claimed as property:

1. A method for mounting tubular members in a space having a shape corresponding to the shape of the tubular means, characterized in that the tubular or tube means is inserted inside the space located in a tooth slot of a stator, of a rotary electric machine that has high voltage cable windings, after which, a pressure medium is heated and pressurizes the tube means, so that it softens and expands, assuming its outer periphery the shape of the space restriction area, then whereupon the hot pressure medium is replaced with or converted to a cold pressure medium that fills the expanded tube means, and causes it to solidify and permanently assume this expanded form, after which the tubular means is used as a cooling tube.

2. A method according to claim 1, characterized in that the tube means acts as a cooling tube on the one hand, and as a fixing means for the high voltage cable, on the other hand.

3. A method according to any of claims 1-2, characterized in that the tube means is allowed to expand until 50% of its original wall thickness remains.

4. A rotary electric machine with at least one tube means mounted according to the method according to any of claims 2-3, characterized in that the stator is provided with stator teeth extending in an inward direction from a stator yoke, whose teeth one between the other form the stator tooth grooves, in which the stator windings are provided, and because the grooves are provided with at least one half pipe made of dielectric material, each inserted into a space that it extends substantially axially through the stator and formed before the cable portions and a uniform side provided in the stator tooth groove.

5. A machine according to claim 4, characterized in that the tube means is made of polymeric material.

6. A machine according to claim 4, characterized in that the tube means is made of high density polyeene (HDPE).

7. A machine according to claim 4, characterized in that the tube means is made of cross-linked polyeene (XLPE).

8. A machine according to any of claims 4-7, characterized in that the space is triangular and also that the tube means is triangular.

9. A machine according to claim 8, characterized in that the tube means are accommodated in all spaces in a stator tooth groove.

10. A machine according to any of claims 8-9, characterized in that the high voltage cable is of a type comprising a conductor having a plurality of strand parts, an inner semiconductor layer enclosing the conductor, an insulating layer which it encloses the inner semiconductor layer, and an outer semiconducting layer that encloses the insulating layer.

11. A machine according to claim 10, characterized in that the high voltage cable has a diameter in the range of 20-250 mm and a conduction area in the range of 80-3000 mpr.

12. A machine according to any of claims 4-11, characterized in that the insulated conductor or high voltage cable is flexible.

13. A machine according to claim 12, characterized in that the layers are arranged to adhere to each other even when the insulated conductor or the high-voltage cable is flexed.

14. A machine according to any of claims 4-13, characterized in that at least two adjacent layers of the winding of the machine have substantially the same coefficients of thermal expansion.

15. A machine according to any of claims 4-14, characterized in that the winding is flexible and comprises a current conducting core surrounded by an internal semiconductor layer surrounding the core, an insulating layer of solid material enclosing the inner semiconductor layer, and an outer semiconductive layer enclosing the insulating layer, the layers adhere to each other.

16. A machine according to any of claims 4-15, characterized in that the layers are made of materials having an elasticity and a relationship between their coefficients of thermal expansion such as changes in the volume of the layers, caused by variations in temperature during the operation, they can be absorbed by the elasticity of the material, so that the layers maintain their contact with each other to the temperature variations that occur during the operation.

17. A machine according to any of claims 4-16, characterized in that the materials used in said layers are of high elasticity.

18. A machine according to any of claims 4-17, characterized in that the coefficients of thermal expansion for the materials in the layers are substantially the same.

19. A machine according to any of claims 4-18, characterized in that each of the semiconductor layers is arranged to constitute a substantially equipotential surface. . METHOD FOR APPLYING A TUBULAR MEMBER IN A STATOR SLOT IN A ROTATING ELECTRICAL MACHINE SUMMARY OF THE INVENTION A method is described for mounting a tubular member (24) in a space (23) having a shape corresponding to the shape of the tubular member (24), the tubular member (24) being inserted into the space (23), after which means of pressure is heated and pressurizes the tubular member (24), so that it softens and expands, assuming its outer periphery the shape of the space limiting areas (23), after which the medium Hot pressure is replaced with or converted to a cold pressure medium which fills the expanded tubular member (24) and causes it to solidify and permanently assume this expanded form, and also a rotating electrical machine accommodated according to the method.