Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02K—DYNAMO-ELECTRIC MACHINES
  • H02K3/00—Details of windings
  • H02K3/04—Windings characterised by the conductor shape, form or construction, e.g. with bar conductors
  • H02K3/28—Layout of windings or of connections between windings
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F27/00—Details of transformers or inductances, in general
  • H01F27/28—Coils; Windings; Conductive connections
  • H01F27/288—Shielding
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02K—DYNAMO-ELECTRIC MACHINES
  • H02K1/00—Details of the magnetic circuit
  • H02K1/06—Details of the magnetic circuit characterised by the shape, form or construction
  • H02K1/12—Stationary parts of the magnetic circuit
  • H02K1/20—Stationary parts of the magnetic circuit with channels or ducts for flow of cooling medium
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02K—DYNAMO-ELECTRIC MACHINES
  • H02K3/00—Details of windings
  • H02K3/46—Fastening of windings on the stator or rotor structure
  • H02K3/48—Fastening of windings on the stator or rotor structure in slots
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02K—DYNAMO-ELECTRIC MACHINES
  • H02K2203/00—Specific aspects not provided for in the other groups of this subclass relating to the windings
  • H02K2203/15—Machines characterised by cable windings, e.g. high-voltage cables, ribbon cables
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02K—DYNAMO-ELECTRIC MACHINES
  • H02K3/00—Details of windings
  • H02K3/32—Windings characterised by the shape, form or construction of the insulation
  • H02K3/40—Windings characterised by the shape, form or construction of the insulation for high voltage, e.g. affording protection against corona discharges
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02K—DYNAMO-ELECTRIC MACHINES
  • H02K9/00—Arrangements for cooling or ventilating
  • H02K9/19—Arrangements for cooling or ventilating for machines with closed casing and closed-circuit cooling using a liquid cooling medium, e.g. oil
  • H02K9/197—Arrangements for cooling or ventilating for machines with closed casing and closed-circuit cooling using a liquid cooling medium, e.g. oil in which the rotor or stator space is fluid-tight, e.g. to provide for different cooling media for rotor and stator

Definitions

• the present invention relates to rotating electric machines such as synchronous machines, but also double- fed machines, applications in asynchronous static current converter cascades, outer pole machines and synchronous flux machines, as well as alternating current machines intended primarily as generators in a power station for generating electric power.
• the invention relates particularly to the stator of such machines and to an embodiment for cooling the stator teeth and thus indirectly also to the insulated electric conductors constituting the stator winding.
• a typical working range for a device according to the invention may be 36-800 kV.
• the voltage of the machine can be increased to such levels that it can be connected directly to the power network without an intermediate 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 regards conventional technology (thicker insulation due to higher voltage and more turns in the winding) .
• the loss distribution will therefore differ to that of a conventional machine, which in turn entails new problems with regard to cooling the stator teeth, for instance.
• the stator is then divided into radial air ducts formed by (usually straight) spacers which are welded in place. Due to the poor thermal conductivity axially through the stator laminations, the air ducts must be frequently repeated. The drawback with air cooling is that the ventilation losses are considerable and that the stator must be longer due to the ventilation ducts.
• the ventilation ducts may also result in a weak mechanical structure, especially in said high-voltage generators with long teeth.
• Water-cooled systems e.g., instead of air-cooled systems for high-voltage generators have the advantage that the radial ventilation ducts can be eliminated, resulting in shorter machines while at the same time increasing the efficiency.
• Water-cooled systems for stators in large alternating current machines are often based on hollow winding parts i.e. the electric conductors are hollow with longitudinal ducts for the coolant, in certain cases combined with cooling tubes inserted axially in the stator yoke. Constructions are known in which the stator yoke is cooled using aluminium blocks inserted at regular intervals along the axial extension of the stator. However, there is no example of direct cooling of the stator teeth with such cooling clamps since these are cooled indirectly through the water-cooling of the stator winding.
• coils for rotating generators can be manufactured with good results within a voltage range of 3 - 25 kV.
• the water- and oil-cooled synchronous machine described in J. Elektrotechnika is intended for voltages up to 20 kV.
• the article describes a new insulation system consisting of oil/paper insulation, which makes it possible to immerse the stator completely in oil. The oil can then be used as a coolant while at the same time using it as insulation.
• a dielectric oil-separating ring is provided at the internal surface of the core.
• the stator winding is made from conductors with an oval hollow shape provided with oil and paper insulation. The coil sides with their insulation are secured to the slots made with rectangular cross section by means of wedges.
• As coolant oil is used both in the hollow conductors and m holes in the stator walls.
• Such cooling systems entail a large number of connections of both oil and electricity at the end windings.
• the thick insulation also entails an increased radius of curvature of the conductors, which in turn results in an increased size of the winding overhang
• the above-mentioned US patent relates to the stator part of a synchronous machine which comprises a magnetic core of laminated sheet with trapezoidal slots for the stator winding.
• the slots are tapered since the need for insulation of the stator winding is less towards the interior of the rotor where the part of the winding which is located nearest the neutral point is disposed.
• the stator part comprises a dielectric oil-separating cylinder nearest the inner surface of the core which may increase the magnetization requirement relative to a machine without this ring.
• the stator winding is made of oil-immersed cables with the same diameter for each coil layer. The layers are separated from each other by means of spacers in the slots and secured by wedges.
• the winding comprises two so-called half-windings connected in series.
• One of the two half-windings is located, centred, inside an insulation sleeve.
• the conductors of the stator winding are cooled by surrounding oil.
• the disadvantages with such a large quantity of oil in the system are the risk of leakage and the considerable amount of cleaning work which may result from a fault condition.
• Those parts of the insulation sleeve which are located outside the slots have a cylindrical part and a conical termination reinforced with current-carrying layers, the purpose of which is to control the electric field strength in the region where the cable enters the end winding.
• the oil-cooled stator winding comprises a conventional high-voltage cable with the same dimension for all the layers.
• the cable is placed in stator slots formed as circular, radially located openings corresponding to the cross-section area of the cable and the necessary space for fixing and for coolant.
• the different radially located layers of the winding are surrounded by and fixed in insulated tubes. Insulating spacers fix the tubes in the stator slot.
• an internal dielectric ring is also needed for sealing the coolant against the internal air gap.
• the design shown has no tapering of the insulation or of the stator slots. The design exhibits a very narrow radial waist between the different stator slots, which implies a large slot leakage flux which significantly influences the magnetization requirement of the machine.
• DE 2917717 shows a cooling segment for cooling medium in an electric machine.
• the segment comprises internal cooling ducts disposed in the segment.
• US 3,447,002 shows a stator core provided with a plurality of annular grooves, in which heat conducting bodies are located, arranged tangentially one after the other in each groove with cooling tubes embedded in the cooling bodies.
• US 2,217,430 shows a dynamo electric machine with means for cooling the stator for such a machine by the circulation of water through the stator core.
• direct cooling of the teeth is a necessity and the stator winding is therefore cooled indirectly.
• the teeth are also exceptionally long in comparison with conventional generators and this also necessitates direct cooling of the teeth.
• the object of the present invention is to provide an arrangement of the type described in the introduction which will permit direct cooling of the stator teeth while cooling the cables constituting the stator winding indirectly.
• the present invention relates to an arrangement for cooling the stator teeth, and indirectly the stator winding, in a high-voltage electric machine such as a high-voltage alternating current generator.
• the arrangement comprises radially-running tubes, electrically insulated, and placed in loops through the stator teeth at a certain axial distance from adjacent loops.
• the arrangement also comprises radially extending cooling clamps containing cooling tubes in which coolant circulates.
• the cooling clamps are inserted in the stator at approximately the same axial distance as conventional air-ventilation ducts.
• the tubes run along the entire radial length of the stator teeth.
• At least one of the semiconducting layers preferably both, have the same coefficient of thermal expansion as the solid insulation.
• Figure 1 shows schematically a perspective view of a section taken diametrically through the stator of a rotating electrical machine.
• Figure 2 shows a cross sectional view of a high-voltage cable according to the present invention
• Figure 3 shows schematically a sector of a rotating electric machine
• Figure 4 shows a first embodiment according to the present invention
• Figure 5 shows schematically a second embodiment according to the present invention
• Figure 6a-6d show sections through one of each of four embodiments of cooling-tube teeth according to the invention
• Figure 7 shows a cooling circuit according to the present invention.
• FIG 1 shows part of an electric machine in which the rotor has been removed to show more clearly the arrangement of a stator 1.
• the main parts of the stator 1 constitute a stator frame 2, a stator core 3 comprising stator teeth 4 and an outer yoke portion 5 defining a stator yoke.
• the stator also comprises a stator winding 6 composed of high-voltage cable situated in a space 7 shaped like a bicycle chain, see Figure 3, formed between each individual stator tooth 4.
• the stator winding 6 is only indicated by its electric conductors.
• the stator winding 6 forms a end-winding package 8 on both sides of the stator 1.
• the insulation of the high-voltage cables has several dimensions, arranged in groups depending on the radial position of the cables in the stator 1.
• stator frame 2 In larger conventional machines the stator frame 2 often consists of a welded sheet steel construction.
• stator core 3 In large machines the stator core 3, is generally formed of 0.35 mm sheet of electrical steel divided into stacks with an axial length of approximately 50 mm, separated from each other by 5 mm ventilation ducts forming partitions. In a machine according to the present invention, however, the ventilation ducts are eliminated.
• each stack of laminations is formed by fitting punched segments 9 of suitable size together to form a first layer, after which each subsequent layer is placed at right angles to produce a complete plate-shaped part of a stator core 3. The parts and the partitions are held together by pressure legs 10 pressing against pressure rings, fingers or segments, not shown. Only two pressure legs are shown in Figure 1.
• FIG. 2 shows a cross-sectional view of a high-voltage cable 11 according to the invention.
• the high-voltage cable 11 comprises a number of strands 12 of copper (Cu) , for instance, having circular cross section. These strands 12 are arranged in the middle of the high-voltage cable 11.
• Around the strands 12 is a first semiconducting layer 13, and around the first semiconducting layer 13 is an insulating layer 14, e.g. crosslinked polyethylene (XLPE) insulation.
• XLPE crosslinked polyethylene
• FIG 3 shows schematically a radial sector of a machine with a segment 9 of the stator 1 and with a rotor pole 16 on the rotor 17 of the machine.
• the stator winding 6 is arranged in the space 7 in the shape of a bicycle chain, formed between each stator tooth 4.
• Each stator tooth 4 extends radially inwards from the outer yoke portion 5.
• FIG 4 shows a simplified view of a first embodiment of the invention with a cooling tube 18 forming a cooling tube loop in a cooling clamp 19 having substantially the same shape as the segment 9, with tooth parts 20 between which the characteristic slot resembling a bicycle chain is formed.
• Figures 4 and 5 have been simplified to rectangular shape in order to simply illustrate the principles of the embodiments.
• a cooling tube loop 21 is formed by one end of the cooling tube 18 being connected to an inlet loop 22 and its other end being connected to an outlet loop 23.
• a coolant thus flows in the cooling tube 18 from the inlet loop 22 at the outer side 24 of the cooling clamp, into the cooling clamp 19, and into a cooling clamp stamp 25 towards its tip, whence the cooling tube 18 passes from tooth to tooth in a space 26 formed between the air gap and an uppermost high-voltage cable 27.
• This space is taken up by a slot wedge, not shown, which can be visualized cut at the transition of the tube, allowing passage for said tube.
• This slot wedge can also be divided into about thirty small wedges to allow place for the tube bends.
• An advantageous embodiment of a cooling clamp in the present invention may be a tube cross section formed by bending the tube to a rectangular shape which is then formed into loops, the cooling tube loops being permanently cast in aluminium on a lid.
• FIG. 5 shows a simplified view of a second embodiment of the invention with a cooling tube 18 forming a cooling tube loop in a cooling clamp 19 of substantially the same design as the segment 9 with tooth parts 20 between which the characteristic slot resembling a bicycle chain is formed.
• a cooling tube loop 21 is formed in this embodiment by one end of the cooling tube 18 being connected to an inlet loop 22 and its other end being connected to an outlet loop 23.
• a coolant thus flows in the cooling tube 18 from the inlet loop 22 at the outer side 24 of the cooling clamp, into the cooling clamp 19, and into a cooling clamp stand 25 towards its tip, whence the cooling tube turns at the tip, see the arrow, and extends back outwardly in the same cooling clamp stand to once again form a similar tooth loop in the next tooth.
• a cooling clamp may be produced with rectangular cross section of the tube by bending.
• the tube is then formed into loops, the cooling tube loops being permanently cast in aluminium on a lid or attached to an intermediate steel beam with casting compound.
• XLPE-tubes with intermediate steel beams can also be embedded and formed suitably as cooling clamps consisting of stator profiles separated by steel spaces, partially filled with filler compound, e.g. cured plastic .
• the advantage of the embodiment according to Figure 4 is that the tube acquires a larger bending radius than if it was to return to the same tooth as in Figure 5.
• FIGS. 6a-6d illustrate different embodiments according to Figures 4-5, in sections through the cooling clamp stands.
• Figure 6a shows a section through a cooling clamp stand according to Figure 4 showing an advantageous embodiment in which the cooling tube 18 of steel has been bent to substantially rectangular cross section, and the cooling tube has subsequently been embedded in an aluminium block 28 provided with a cover plate 29.
• the aluminium block may also be manufactured in two halves which are fitted together around the cooling tube.
• FIG 6b shows a section through a cooling clamp stand according to Figure 4 the cooling tube 18 of the tooth running between two beams 30, preferably of steel, acting as spacing and reinforcing beams during assembly of the cooling tube.
• FIG. 6c shows a section through a cooling clamp stand according to Figure 5.
• the cooling clamp has been produced by a flexible hollow spacer around a beam 30, preferably of steel, being placed in a loop and the intermediate space filled with a casting compound 31, after which the hollow spacer is removed thus forming a tubular duct 32.
• Figure 6d also shows a section through a cooling clamp tooth according to Figure 5 in which a flexible cooling tube 33 of XLPE-tube type, is placed in a cooling tube loop around a beam 30, preferably of steel .
• cooling media ducts in a cooling clamp stand shown here can be varied in many ways within the scope of the appended claims.
• a cast aluminium block for instance, can be made in two pieces with ducts for insertion of cooling tubes of steel or of XLPE-tube type.
• the cross-section of the cooling tube may vary from circular to oval or be substantially rectangular.
• An outer cooling circuit is arranged, see Figure 7, in which all cooling tubes 18 are connected to a closed cooling circuit 34, which in the embodiment shown comprises a tank 35 containing the coolant 36 which may be water, hydrogen gas or other coolant for the circuit.
• the tank 35 is provided with a level indicator for control and monitoring of the coolant level .
• the tank 35 is also connected to two distribution circuits consisting of an inlet loop 37 and an outlet loop 38.
• cooling clamps 19 are arranged, each comprising at least one cooling tube loop 21. All cooling clamps 19 are connected in parallel between the inlet loop 37 and the outlet loop 38.
• the coolant 36 is thus arranged to circulate from the inlet loop 37 simultaneously through every cooling tube loop 21 connected in parallel to the outlet loop 38 and on to a circulation pump 39 and a circulation filter 40 through a heat exchanger 41, e.g. a plate heat exchanger, and then back to the inlet loop 37.
• Water with a temperature of approximately 15°C is supplied from a water reservoir via the exchanger filter, not shown, of an exchanger pump 42. The water is pumped through the exchanger and back to the water reservoir.
• a water cooling system according to the present invention may consist, e.g., of cooling clamps provided with tubes inserted approximately every 5 cm along the entire stator. If the stator segments are glued the spacing between cooling clamps can be greater than 5 cm.
• the cooling clamp Since the cooling clamp must be able to support the full weight of the stator if mounted vertically, plus the pressure from any pressure rings (a total pressure in the region of 0.5 MPa), a mechanically supporting structure is incorporated in the cooling clamp as shown in Figures 6a-d.
• the cooling tubes may be of stainless steel or they may be polymer as mentioned earlier, e.g. XLPE-tubes, Wirsbo-inPEX ® , which have been hot-bent directly on the cooling plate with steel spacers as bending template.
• the steel spacers are welded in the same way as for conventionally air-cooled stators and also take up axial forces in the same way.
• XLPE-tubes may also be flattened in a furnace at a temperature of approximately 130°C and are then correctly positioned as the cover plates are pressed down on them. The plates are then welded or glued. It is important that the cooling tubes are "flat" and relatively large in order to provide a sufficient cooling surface. Steel tubes can be made smaller than XLPE-tubes.
• the casting compound can be made sufficiently heat conducting by means of, e.g., quartz-filled epoxy. The air pockets can be filled with casting compound afterwards, as shown earlier.
• cooling tubes may be of metal or polymer.
• the cooling plates may also be cast aluminium blocks.
• An interesting possibility is also to use the stator laminations as supporting structure and casting compound in the remaining spaces.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Motor Or Generator Cooling System (AREA)
• Iron Core Of Rotating Electric Machines (AREA)
• Insulation, Fastening Of Motor, Generator Windings (AREA)

Applications Claiming Priority (5)

Publications (1)

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ID=26662643

Family Applications (1)

Country Status (9)

Families Citing this family (19)

Family Cites Families (5)

• 1997
  • 1997-05-27 EP EP97925370A patent/EP0910886A1/en not_active Withdrawn
  • 1997-05-27 PL PL97330197A patent/PL330197A1/xx unknown
  • 1997-05-27 CN CN97195051.2A patent/CN1220037A/zh active Pending
  • 1997-05-27 CA CA002261638A patent/CA2261638A1/en not_active Abandoned
  • 1997-05-27 BR BR9709366-1A patent/BR9709366A/pt not_active Application Discontinuation
  • 1997-05-27 WO PCT/SE1997/000894 patent/WO1997045915A1/en not_active Application Discontinuation
  • 1997-05-27 AU AU30527/97A patent/AU3052797A/en not_active Abandoned
  • 1997-05-27 JP JP09542209A patent/JP2000511394A/ja active Pending
  • 1997-05-27 EA EA199801056A patent/EA001129B1/ru not_active IP Right Cessation

Non-Patent Citations (1)

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