EA001098B1 - A device in the stator of a rotating electric machine - Google Patents

Abstract

1. A device for increasing the mechanical rigidity and natural frequency of the stator in a rotating electric machine, which stator is provided with teeth (10) between the slots (8) receiving the winding, the free ends of said teeth being located in the air gap (7) between stator and rotor, characterized in that the winding comprises a high-voltage cable (1) and that a spacer (11) to increase rigidity is arranged in each space between the free ends of adjacent stator teeth (10) to tangentially fix said ends. 2. A device as claimed in claim 1 characterized in that the spacer comprises a wedge (11). 3. A device as claimed in claim 2, characterized in that the wedge surfaces converge outwardly towards the ends of the stator teeth (10) connected to each other, the wedge (11) being arranged to be subjected to a radial, outwardly directed force during assembly. 4. A device as claimed in claim 2 characterized in that the wedge surfaces diverge outwardly towards the ends of the stator teeth (10) connected to each other, an expansion means (14) being arranged between the wedge (11) and the cable (1) of the winding situated nearest to the slot (8) and secured in a seat in the slot (8). 5. A device as claimed in claim 4 characterized in that the expansion means consists of a tube (14) which is filled with a liquid compound, such as epoxy plastic, which is curable under pressure. 6. A device as claimed in any of claims 1-5, characterized by adhesive joints between the spacers (11) and stator teeth (10). 7. A device as claimed in claim 1 or claim 2 characterized in that the outer stator frame (17) is provided with a spring member (16) for tangential clamping of the outer part of the stator core (15) and to produce a tangential thrust force in the surfaces of the spacers at the free ends of the stator teeth (10). 8. A device as claimed in any of claims 1-7 characterized in that the spacers (11) which extend the entire length of the stator are designed as tie rods to pre-stress the stator core (15). 9. A device as claimed in claim 8 characterized in that a force-transmitting device (18) is arranged between the spacers (11) and the outer periphery of the stator and arranged to convert tensile stress in the spacers (11 ) to compressive stress in the stator core (15). 10. A device as claimed in claim 9 characterized in that the spacers (11) are connected together at their ends by means of transverse pieces (19) and in that the force-transmitting device consists of pressure fingers (18) extending radially on each side of the stator core (15) immediately opposite the stator teeth (10) the inner ends of said fingers protruding inside the transvers e pieces (19) and the outer ends being pressed against the core (15) by means of a clamping device (22, 23) on the stator frame (17). 11. A device as claimed in claim 9 characterized in that the ends of the spacers (11) are provided with screw threading (25) for cooperation with a nut (24) to transfer compressive force via a plate (26) to the stator teeth (10). 12. A rotating electric machine characterized by a device as claimed in any of claims 1-11 to increase the natural frequency of the stator. 13. A rotating electric machine according to claim 12 characterized in that the winding comprises at least one current-carrying conductor (2), a first layer (3) having semi-conducting properties provided around said conductor (2), a solid insulating layer (4) provided around said first layer (3), and a second layer (5) having semi-conducting properties provided around said insulating layer (4). 14. A rotating electric machine according to claim 13, characterized in that the potential of said first layer (3) is substantially equal to the potential of the conductor (2). 15. A rotating electric machine according to claim 13 or 14, characterized in that said second layer (5) is arranged to constitute substantially an equipotential surface surrounding said conductor (2). 16. A rotating electric machine according to claim 15, characterized in that said second layer (5) is connected to a predetermined potential. 17. A rotating electric machine according to claim 16, characterized in that said predetermined potential is ground potential. 18. A rotating electric machine according to any one of claims 13-17, characterized in that at least two adjacent layers have substantially equal thermal expansion coefficients. 19. A rotating electric machine according to any one of claims 13-18, characterized in that said current-carrying conductor (2) comprises a number of strands, only a minority of said strands being non-isolated from each other. 20. A rotating electric machine according to any one of claims 13-19, characterized in that each of said three layers is fixed connected to adjacent layer along substantially the whole connecting surface. 21. A rotating electric machine according to any one of claims 13-20, characterized in that said cable (1) also comprises a metal shield and a sheath.

Description

The present invention relates to a device for increasing the mechanical rigidity and natural frequency of oscillation of the stator in a rotating electric machine and to prevent destructive oscillations between the stator teeth.

Some attempts at a new approach to designing synchronous machines are described, among other things, in article \\\\\\\\\\\\\\\\\\\\\\\\\\ in the patent of the USSR No. 955369.

Water-cooled and oil-cooled synchronous machine, described in the journal ί. Е1ек1то1есЬи1ка, designed for voltages up to 20 kV. The article describes a new insulation system consisting of oil-paper insulation, which allows you to immerse the stator completely in oil. At the same time oil can be used as coolant and at the same time as isolation. To prevent oil from leaking from the stator to the rotor, there is a dielectric oil holding ring on the inner surface of the core. The stator winding is made of hollow oval-shaped conductors with oil and paper insulation. The side parts of the coil with insulation are fixed in grooves of rectangular section by means of wedges. Both in hollow conductors and in holes in the stator walls, oil is used to cool them. However, such cooling systems require a large number of both electrical and hydraulic connections at the ends of the coils. In addition, thick insulation leads to an increase in the radius of curvature of the conductors, which, in turn, causes an increase in the departure of the winding.

The aforementioned U.S. patent relates to a part of a stator in a synchronous machine, which contains a sheet magnetic core with trapezoidal grooves for the stator winding. The grooves narrow as the need for isolation of the stator winding decreases towards the inside of the rotor, where the part of the winding nearest to the neutral point is located. In addition, part of the stator contains a dielectric oil-holding cylinder located near the inner surface of the core. This part may increase the requirements for the magnetic part of the device compared to a machine without this ring. The stator winding is made of oil-filled cables of the same diameter for each layer of the winding. The layers are separated from each other by spacers installed in the slots, and secured with wedges. A feature of the winding is that it contains two so-called semi-windings connected in series. One of the two semi-windings is located centrally inside the tubular insulation. The stator conductors are cooled by the surrounding oil. The disadvantages of a system with such a large amount of oil are the risk of leakage and a lot of cleaning work in the event of an accident. Those parts of the tubular insulation that are located outside the grooves have a cylindrical part and a conical end, reinforced by current-carrying layers, the purpose of which is to control the electric field in the area where the cable enters the end of the winding.

It is clear from USSR patent No. 955369 that another attempt to increase the nominal voltage of a synchronous machine is that the oil-cooled stator winding contains a known high-voltage cable of the same size for all layers. The cable is placed in the grooves of the stator, made in the form of circular radially arranged holes, the dimensions of which correspond to the cross-sectional area of the cable and the necessary place for their installation and for the refrigerant. Various radially arranged layers of the winding are surrounded by tubular insulation and fixed in it. In the groove of the stator tube is fixed insulating struts. Due to the oil cooling in the internal air gap, it is necessary to install an internal dielectric ring to create a seal to prevent leakage of the oil coolant. There is no narrowing of the insulation or stator slots in this design. In this design there are very narrow radial constrictions between the various stator slots, which implies a large leakage flow in the groove and significantly affects the magnetization requirements of the machine.

The problem to which the invention is devoted is related to an AC high-voltage electric machine, primarily intended for operation as a generator at a power plant for the production of electricity. Such machines have traditionally been designed to work at voltages in the range of 15-30 kV, and 30 kV were considered as the upper limit. This, in general, means that the generator must be connected to the power supply network through a transformer, which amplifies the voltage to the level of the power supply network, that is, to 130-400 kV.

When using high-voltage insulated electrical conductors in the stator winding, hereinafter referred to as cables, with permanent insulation, similar to those used in electric power transmission cables (for example, cables with PE insulation with intermolecular bonds (ХЬРЕ)), the voltage in the machine can be increased to such a level that this machine can be connected directly to the power supply network without an intermediate transformer. Therefore, a step-up transformer is not required.

In general, this concept implies that the grooves in the stator in which cables are placed are deeper than usually required (thicker insulation due to higher voltage and more turns in the winding). This creates new problems associated with the natural frequencies of mechanical vibrations in the region of the teeth between the stator slots. In a deep slotted stator, destructive oscillations can occur in the air gap region due to resonance with a disturbing force, usually electromagnetic forces with a frequency of 100 Hz for a machine with a nominal output frequency of 50 Hz.

The aim of the present invention is to solve this problem and, thus, prevent oscillations between the stator teeth. This goal is achieved using the device described in the claims.

Below the invention will be described in more detail in connection with the accompanying drawings, where in FIG. 1 shows a cross section of an insulated electrical conductor that is used according to the invention and in this description is called a cable;

in fig. 2 shows a view of the sector of the stator core in the axial direction;

in fig. 3 and 4 show an axial view of the end of a groove located in an air gap in the stator core according to two embodiments of the invention;

in fig. 5 shows an axial view of a sector of a stator core according to a third embodiment of the invention;

in fig. 6 shows an axial view of a sector of the stator core according to another embodiment of the device according to the invention;

in fig. 7 shows a section in the axial direction through the part of the stator corresponding to that shown in FIG. 6 and in FIG. 8 and 9 show the end part of the stator core near the air gap in the radial and axial direction, respectively, with a partial section.

FIG. 1 illustrates a cross section of an insulated electrical conductor or cable 1 used in accordance with the present invention. Cable 1 includes a conductor 2 with a circular cross section consisting of a plurality of strands made, for example, of copper. This conductor 2 is located in the middle of cable 1. Around the conductor 2 there is a first semiconducting layer 3. Around the first semiconducting layer 3 there is an insulating layer 4, for example of polyethylene with intermolecular bonds. Around the insulating layer 4 there is a second semiconducting layer 5. Therefore, in this case, the cable does not contain an external protective sheath, which usually surrounds the cable for power distribution.

FIG. 2 shows a portion of a stator plate 6 intended for a new high voltage alternator. These plates of the stator 6 are stacked on top of each other, forming the stator core. It is annular and surrounds a rotor (not shown) with an air gap 7. The grooves 8 for laying the cable go through the stator axially and are deeper than in conventional machines. This causes the aforementioned disadvantages of the stator, which has low natural frequencies, and these oscillations easily arise in the teeth of the stator 10.

According to FIG. 3, to solve this problem, it was proposed to insert a spacer or a slot wedge 11 into the space of the groove 8. The wedge is made of non-conducting material that is non-magnetic, tough and durable, for example, fiberglass-reinforced plastic (epoxy plastic), and stretched to the full stator length axial direction. This wedge is inserted through a force applied in the radial direction, as indicated by the arrow 1 2, during the assembly process, thus providing tangentially tight connections between the stator teeth in the air gap around the entire stator. This rigid connection increases the natural frequency of oscillation and provides a significant increase in the rigidity of each individual tooth and even an increase in the bending rigidity of the entire stator core. Another important advantage is that the tangential electromagnetic forces in the air gap, created by the rotor poles, are distributed more evenly between the teeth.

As can be seen in FIG. 3, the wedge 11 does not touch the cable 1 and does not act on it with a force directed radially - the closest cable is shown in the drawing. As is clear from FIG. 2, unlike conventional generators, the grooves 8 are made in the form of a bicycle chain with recesses for each cable 1, which is thus fixed in the radial direction. In known generators, the cable grooves had a constant width, and the cables were compressed by a radial force due to a slot wedge that did not give any tangential load. Thus, the known slot wedges perform an entirely different function compared with slot wedge 11, made according to the present invention, the only function of which is to create Ρ _ΤΑΝ tangential prestress, which ensures a sufficiently rigid and strong connection between the free ends of the stator teeth.

FIG. 4 shows another embodiment of the device according to the invention. Here, wedge 11 has the opposite shape, as well as wedge-shaped surfaces interacting with it on stator teeth 10. Under pressure, the wedge in this case is squeezed out towards the air gap, and cable 1 is fixed in the radial direction in the innermost area of its socket . Thus, a known tube can be used, which expands, being pumped, between cable 1 and wedge 11. Fill tube 14, for example, with a liquid epoxy compound, which solidifies under pressure. Such a tube was previously used in conventional generators to clamp the conductors forming the winding in the groove in the direction outward to the base of the groove, that is, for a function that is absolutely not needed in the present case.

A third embodiment of the invention is shown in FIG. 5. Here tangential compression between the stator teeth is achieved by means of wedges 11 due to the tension force P applied to the stator core 1 5 by means of external structures in the form of ties, cords 16 or the outer stator body 17. A stator consisting of segments is joined together in the final assembly so that when the tension force acts on the external structure, an opposing compressive force arises in the stator teeth and wedges in the air gap.

As described above, in FIG. 3 and 4 spacers 11 are wedge-shaped. However, they may also have parallel faces if a tangential rigid connection is achieved in accordance with FIG.

five.

Glue joints can be made between the struts 11 and the teeth 10 of the stator, either as the only locking means or before fixing by tangential compression.

FIG. 6-9 illustrates how slot wedges made according to the invention can also be used to achieve a compressive prestress in the stator core 15. The pressure pins 18 are mounted on each side of the core 15, directly opposite the teeth of the stator 10, acting as a force transmitting device for converting the tension force in the wedges 11 into a uniformly distributed compressive force in the stator core 15. To achieve this, the ends of the wedges are connected together by means of crossbars 19, which interact with the pressure fingers 18. In the shown embodiment, crossmembers 1 9 are connected to the wedges 11 by means of pins 20 capable of sliding in crossbars 19, which are loaded from outside by compression spring 21. One end of the pressure pins 18 is captured below the cross member 19, allowing it to carry out the load of the cross member and thus the wedges in the outward direction from the lamellar core 15. The other end of the pressure pins 1 8 is clamped between two devices 22 and 23 connected to the stator housing 17.

As shown in the right parts of FIG. 8 and 9, the tension force in the wedge 11 can be transformed into a compressive force in the stator core 1 5 not by means of crossbars 19, but by means of nuts 24 interacting with a screw thread 25 at the ends of the wedges 11. The compressive force from the nuts 24 is transmitted to the core 1 5 the stator through the plate 26, for example, of laminated fiberglass.

As shown in FIG. 6-9, the slot wedges used to install the stator teeth in the tangential direction are also used as screeds to achieve the required compressive force in the stator core.

The invention is also applicable to other electric machines, for example, double excitation machines, devices for use in cascades of an asynchronous static current converter, machines with an external pole and machines with synchronous flow, in particular, if their windings are made of insulated electrical conductor described above and operating preferably in the voltage range of 36,800 kV.

Claims (21)

CLAIM 1. A device for increasing the mechanical stiffness and natural frequency of oscillations of the stator in a rotating electric machine, in the stator of which there are teeth (10) between the grooves (8) where the winding is placed, and the free ends of these teeth are located in the air gap (7) between the stator and the rotor, while the winding includes a high-voltage cable (1), and in each gap between the free ends of adjacent teeth (10) of the stator is installed increasing the stiffness of the spacer (11) for fixing these ends in the tangential direction. 2. The device according to claim 1, characterized in that the spacer contains a wedge (11). 3. The device according to claim 2, characterized in that the surfaces of the wedge converge outwardly to the ends of the stator teeth (10) connected to each other, the wedge (11) being installed so that it is exposed to a radial outward force during assembly. 4. The device according to claim 2, characterized in that the wedge surfaces diverge outward to the ends of the stator teeth (10) connected to each other, and between the wedge (11) and the winding cable (1) closest to the groove (8) and fixed in the slot in the groove (8), expansion means (1 4) are installed. 5. The device according to claim 4, characterized in that the expansion means comprise a tube (14) that is filled with a liquid compound, for example, epoxy plastic, which hardens under pressure. 6. The device according to one of claims 1 to 5, characterized in that between the spacers (11) and the teeth (10) of the stator there are adhesive joints. 7. The device according to claim 1 or 2, characterized in that in the outer case (17) of the stator there is a spring part (16) for tangential compression of the outer part of the core (15) of the stator and create a tangential opposing force in the surfaces of the spacers at the free ends of the teeth ( 10) the stator. 8. The device according to one of claims 1 to 7, characterized in that the spacers (11) are elongated along the entire length of the stator and are made in the form of couplers that create prestress in the stator core (1 5). 9. The device according to claim 8, characterized in that between the spacers (11) and the outer circumference of the stator, a force transmitting device (18) is installed, which converts the tensile forces in the spacers (11) into the compressive force in the stator core (1 5). I 0. The device according to claim 9, characterized in that the ends of the spacers (11) are connected by means of crossbars (19), and the transmitting force of the device contains push fingers (18) extending radially from each side of the stator core (15) directly opposite the teeth ( 10) the stator, the inner ends of these fingers passing inside the cross-members (19), and the outer ends press on the core (1 5) by means of a clamping device (22, 23) on the housing (1 7) of the stator. II. The device according to claim 9, characterized in that at the ends of the struts ( 11) there is a screw thread (25) for connection with a nut (24) for transmitting compressive force through the plate (26) to the teeth (1 0) of the stator. 12. A rotating electric machine having a device according to one of claims 1 to 11 for increasing the natural frequency of the stator. 1 3. A rotating electric machine according to claim 12, characterized in that the winding includes at least one current-carrying conductor (2), around said conductor (2) there is a first layer (3) with semiconducting properties, around said first layer ( 3) there is a solid insulating layer (4), and around the specified insulating layer (4) there is a second layer (5) with semiconducting properties. 1 4. A rotating electric machine according to claim 13, characterized in that the potential of said first layer (3) is substantially equal to the potential of a conductor (2). 1 5. A rotating electric machine according to claim 13 or 14, characterized in that said second layer (5) is configured to form a substantially equipotential surface surrounding said conductor (2). 1 6. A rotating electric machine according to claim 15, characterized in that a predetermined potential is applied to said second layer (5). 1 7. The rotating electric machine according to clause 16, characterized in that the specified predetermined potential is the potential of the earth. 1 8. A rotating electric machine according to one of paragraphs. 13-17, characterized in that at least two adjacent layers have essentially equal coefficients of thermal expansion. 1 9. A rotating electric machine according to one of claims 13-18, characterized in that the current-carrying conductor (2) includes a plurality of cores, only a small part of which are not isolated from each other. 20. A rotating electric machine according to one of paragraphs. 13-19, characterized in that each of these three layers is fixedly connected to the adjacent layer essentially over the entire surface of the connection. 21. A rotating electric machine according to one of claims 13-20, characterized in that the cable (1) also contains a metal screen and a sheath.