Classifications

• • 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
  • H02K1/16—Stator cores with slots for windings
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02K—DYNAMO-ELECTRIC MACHINES
  • H02K15/00—Methods or apparatus specially adapted for manufacturing, assembling, maintaining or repairing of dynamo-electric machines
  • H02K15/02—Methods or apparatus specially adapted for manufacturing, assembling, maintaining or repairing of dynamo-electric machines of stator or rotor bodies
  • H02K15/024—Methods or apparatus specially adapted for manufacturing, assembling, maintaining or repairing of dynamo-electric machines of stator or rotor bodies with slots
  • H02K15/026—Wound cores
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02K—DYNAMO-ELECTRIC MACHINES
  • H02K2201/00—Specific aspects not provided for in the other groups of this subclass relating to the magnetic circuits
  • H02K2201/06—Magnetic cores, or permanent magnets characterised by their skew
• • 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

Definitions

• the present invention relates to a stator for a rotating electric machine in accordance with the introductory part of claim 1, a method for manufacturing a stator for a rotating electric machine in accordance with the introductory part of claim 23, as well as a rotating electric machine in accordance with claim 31.
• rotating electric machines which are relevant in the context of the present invention comprise synchronous machines, ordinary asynchronous machines, double- fed machines, applications for asynchronous converter cascades, external pole machines and synchronous flux machines,, as well as alternating current machines, which primarily are intended to be used as generators m power stations for the generation of electric power-
• synchronous machines are discussed, but it should be noted that the present invention is not limited to such machines.
• Most synchronous machines according to conventional prior art have a field winding in the rotor, where the main flux is generated by direct current, and an AC winding in the stator.
• Stator frames for large synchronous machines are often made of steel sheet with a welded construction.
• the laminated core is normally made from enamelled 0.35 or 0.5 mm electric sheet.
• the laminated core For radial ventilation and cooling, the laminated core, at least for medium-size and large machines, is divided into stacks with radial ventilation ducts. For larger machines, the sheet is punched into segments, which are attached to the stator body by means of wedges/dovetails. The laminated core is retained by pressure fingers and pressure plates. The stator winding is disposed in slots in the laminated core, which normally have a cross section in the form of a rectangle or a trapezoid.
• One major disadvantage with larger stator cores according to the prior art is the problem of manufacturing and also transporting such cores. According to convention, the complete stator core, with the frame, is manufactured n a workshop.
• the core In order to be able to transport the stator core to the site of installation, the core is then divided along axial dividing planes into as few core sections as possible, with consideration taken to the transportation facilities.
• the core sections On the site of installation, the core sections are assembled and held together and secured by means of the stator frame, which may comprise several frame sections assembled together.
• the winding may be installed on the site or partly in the work- shop.
• An alternative, especially for very large sized machines, is to perform more of the manufacturing steps of the stator core on the site of installation, including assembling the punched electric sheets of the core, assembling the core m the stator frame, but not including punching the sheets. So called turbogenerators are considerably longer in relation to the diameter than other generators.
• Rotating electric machines have, according to conventional prior art, been designed for voltages in the interval 6-30 kV, where 30 kV normally has been regarded as an upper limit. In the case of a generator, this would normally mean that a generator must be connected to the power network via a transformer, which transforms the voltage up to the level of the power network, which will be in the range of 130-400 kV.
• a transformer which transforms the voltage up to the level of the power network, which will be in the range of 130-400 kV.
• certain attempts have been made to develop especially synchronous machines, in particular generators, for higher voltages. Examples of this are described in "Electrical World", October 15, 1932, pp 524-525, the article “Water-and-Oil-cooled Turbogenerator TVM-300" in J. Elektrotechnika, No. 1, 1970, pp 6-8, and the patent publications US 4,429,244 and SU 955 369. Unfortunately, none of these have been successful and they have not resulted in any commercially available products
• insulated electric conductors with permanent insulation, similar to cables used for transmitting electric power (such as XLPE cables), as a stator winding in a rotating electric machine.
• the voltage of the machine may be increased to such levels that it may be connected directly to the power network, without any intermediate transformer.
• an insulated conductor or cable is flexible and it is of a kind which is described more in detail in WO 97/45919 and WO 97/45847. Additional descriptions of the insulated conductor or cable concerned can be found in WO 97/45918, WO 97/45930 and WO 97/45931.
• the ob ect of the present invention is to solve the above mentioned problems and to provide a stator for a rotating electric machine of the above indicated type, which stator is designed in such a way that a new and very flexible manufacturing method will be made possible.
• the object s also to provide a manufacturing method for a stator as well as a rotating electric machine including the stator.
• stator and the rotating electric machine should be suitable to be used for h gh voltages, by which is meant electric voltages primarily exceeding 10 kV .
• a typical work- ing range for such a machine may be 36 - 800 kV, preferably 72,5 - 800 kV.
• stator including the advantageous features as defined in claim 1.
• a corresponding method is defined in claim 23.
• the object is also achieved by means of a rotating electric machine in accordance with claim 31, comprising a stator as defined in any one of the claims regarding the stator.
• the stator of claim 1 is characterized in that said stator is built of at least two self-supporting stator elements of a substantially annular disc shape, and that the axial length of said stator elements is defined by one or more dividing planes perpendicular to the longitudinal axis of the stator.
• a stator with this design is consequently made up of a number of elements which also may be described as "slices".
• This design is particularly advantageous for turbogenerators since it offers a possibility of assembling the generator, preferably on site, of shorter elements which are much more easily transported.
• their axial length is preferably more than 0.5 m.
• An ordinary turbogenerator may for example thus be divided into between 2-15 disc elements or slices, depending on the length of the generator.
• a likely size for a disc element may be 0.5 - 4 m.
• the number of disc elements into which the stator is divided depends on where one chooses to set the limit for the length, primarily with regard to easy transportation and general handling of the elements.
• the corresponding method is characterized n axially joining together at least two self-supporting stator elements of a substantially annular disc shape, the axial length of said stator elements being defined by one or more dividing planes perpendicular to the longitudinal axis of the stator.
• the design of the stator according to present invention will also make it possible to construct much larger, longer, and heavier generators, since the transportation is much facilitated.
• to make the disc elements self- supporting is not only an advantage from a transportation point of view but is also an important feature in order to make the generator able to withstand the dynamic conditions during operation and to avoid vibrations.
• the winding is provided by means of an insulated conductor which comprises at least one current-carrying conductor, a first layer having semiconducting properties provided around said conductor, a solid insulating layer provided around said first layer, and a second layer having semiconducting properties provided around said insulating layer.
• the method defined n claim 23 includes the corresponding feature.
• the windings are preferably of a type corresponding to cables having solid, extruded insulation, of a type now used for power distribution, such as XLPE-cables or cables with EPR- msulation.
• a cable comprises an inner conductor composed of one or more strand parts, an inner semiconducting layer surrounding the conductor, a solid insulating layer surrounding this and an outer semiconducting layer surround- mg the insulating layer.
• Such cables are flexible, which is an important property in this context since the technology for the stator and method according to the invention is based primarily on winding systems in which the winding is formed from cable which is bent during assembly.
• the flexi- bility of an XLPE-cable normally corresponds to a radius of curvature of approximately 20 cm for a cable with a diameter of 30 mm, and a radius of curvature of approximately 65 cm for a cable with a diameter of 80 mm.
• the term "flexible" is used to indicate that the winding is flexible down to a radius of curvature in the order of four times the cable diameter, preferably eight to twelve times the cable diameter.
• the winding should be constructed to retain its properties even when it is bent and when it is subjected to thermal or mechanical stress during operation. It is vital that the layers retain their adhesion to each other in this context.
• the material properties of the layers are decisive here, particularly their elasticity and relative coefficients of thermal expansion.
• the insulating layer consists of cross-linked, low-density polyethylene
• the semiconducting layers consist of polyethylene with soot and metal particles mixed in.
• the insulating layer may consist, for example, of a solid thermoplastic material such as low-density polyethylene (LDPE) , high-density polyethylene (HDPE) , polypropylene (PP) , polybutylene (PB) , polymethyl pentene (“TPX”) , cross- linked materials such as cross-linked polyethylene (XLPE) , or rubber such as ethylene propylene rubber (EPR) or silicon rubber.
• LDPE low-density polyethylene
• HDPE high-density polyethylene
• PP polypropylene
• PB polybutylene
• TPX polymethyl pentene
• XLPE cross-linked polyethylene
• EPR ethylene propylene rubber
• the f ⁇ st, inner, and the second, outer, semiconducting layers may be of the same basic material but with particles of conducting material such as soot or metal powder mixed in.
• the mechanical properties of these materials, particularly their coefficients of thermal expansion, are affected relatively little by whether soot or metal powder is mixed in or not - at least in the proportions required to achieve the conductivity necessary according to the mven- tion.
• the insulating layer and the semiconducting layers thus have substantially the same coefficients of thermal expansion .
• EVA/NBR Ethylene-vmyl-acetate copolymers/nitnle rubber
• EBA ethylene-butyl-acrylate copolymers
• EBA ethylene-ethyl-acrylate copolymers
• ESA EAA
• EVA may also constitute suitable polymers for the semiconducting layers . Even when different types of material are used as base in the various layers, it is desirable for their coefficients of thermal expansion to 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 appear, or any other damage, and so that the layers are not released from each other.
• the material in the layers is elastic, and the adhesion between the layers is at least of the same magni- tude as in the weakest of the materials.
• the conductivity of the two semiconducting layers is sufficient to substantially equalize the potential along each layer.
• the conductivity of the outer semiconducting layer is sufficiently high to enclose the electrical field within the cable, but sufficiently low not to give rise to significant losses due to currents induced in the longitudinal direction of the layer.
• each of the two semiconducting layers essentially constitutes one equipotential surface, and these layers will substantially enclose the electrical field between them.
• each stator element includes a self-supporting stator core element.
• each stator element further includes a self-supporting stator frame element. It should be noted that it is not required that the stator frame consti- tutes a part of the self-supporting stator elements of the main claim, since the stator elements may very well comprise only stator core elements and the stator frame may be installed later, on the site of operation.
• the stator core elements may be made in a conven- tional manner by means of an optional number of layers of electric sheet, preferably glued together, or they may be made of a compacted metallic powder, a composite material including a magnetic powder or any other suitable material.
• the stator is advantageously provided with assem- bling means for assembling the self-supporting stator elements.
• these assembling means may include bolts arranged to be applied in corresponding axial holes in the stator core elements.
• these bolts are provided with some pretensioning means in order to firmly secure the stator elements together.
• Said bolts may be combined bolts and cooling ducts.
• Said bolts may also be combined bolts and slot key elements.
• said assembling means may comprise welding the stator elements together, or comprise an adhe- sive.
• the assembling means may comprise a flange joint applied externally on the stator frame, which in such a case also would be divided into frame parts.
• more than one flange joint is nor- mally required, the number depending on the length of the stator and the number of stator elements.
• the stator is provided with first guiding means for guiding the stator slots of one stator core element to fit the stator slots of an adjacent stator core element.
• the stator core elements are provided with holes for cooling ducts and the stator is provided with second guiding means for guiding the cooling duct holes of one stator core element to fit the cooling duct holes of an adjacent stator core element.
• guiding means are very advantageous when the stator is m a turbogenerator, since a turbogenerator may have rather long stator elements.
• Long stator elements entail high demands on tolerances for the winding slots and holes for cooling ducts in order to avoid damages to the winding and the cooling ducts when they are inserted into the slots/holes, and the provided guiding means will ensure a good correspondence between the slots/holes in two adjacent stator core elements.
• An example of a guiding element for the cooling ducts would be a short sleeve partly inserted into one stator core, said sleeve functioning as a guiding means when the adjacent stator core is installed.
• the guiding means may well be of a type which is retracted when the assembling is completed or they may be of a kind which may remain in the core after completed assembly.
• the cooling ducts may comprise premstalled, substan- tially axial, cooling ducts m the stator core.
• sealing members such as "O-rings" may be provided in the surfaces along the dividing planes.
• the cooling ducts as well as the winding slots may be skewed in shape or a straight axial shape. Concerning the insulated conductor in the winding, this may be provided with a number of advantageous features.
• the insulated conductor or cable is flexible. This feature is important in order to be able to use the cable as a winding.
• the first semiconducting layer is substantially at the same potential as the current-carrying conductor.
• the second semiconducting layer is preferably arranged to constitute a substantially equipotential surface surrounding said conductor and insulation layer. It is also connected to a predetermined potential, preferably ground potential.
• at least two adjacent layers have substan- tially equal thermal expansion coefficients; the current- carrying conductor may comprise a number of strands of which only a few are uninsulated from each other.
• each of said three layers i.e. the two semiconducting layers and the insulation layer, may be solidly connected to the adjacent layer along substan ⁇ tially the whole connecting surface.
• said layers are arranged to adhere to one another even when the insulated conductor or cable is subjected to bending.
• the cable by preference has a diameter in the interval 20-250 mm and a conducting area in the interval of 80-3000 mm 2 .
• cables with a circular cross section are used. They have the advantage of bending more easily as well as displaying better electric properties. However, in order to obtain, among other things, better packing density, cables with a different cross section may be used.
• the method according to the present invention advantageously further includes the step of axially assembling the stator elements by means of bolts being inserted into corresponding holes provided in the stator elements, which preferably are stator core elements.
• the stator elements are axially assembled by means of at least one axial flange joint being applied externally on the stator frame.
• Further steps includes inserting cooling ducts in corresponding holes provided in the stator and inserting the winding into the winding slots of the stator teeth.
• the winding is inserted axially into the winding slots. This is a simplified method of inserting the winding which is made possible by the type of flexible cable that is used.
• the stator may be assembled on the site of installation of the rotating electric machine. 11
• the present invention has the advantage that t provides a stator core that is both simple with regard to the manufacturing method and easy to transport and install on the final site of operation. This is particularly advantageous for use in turbogenerators, but it is naturally not limited to such generators.
• FIG. 1 shows a partial schematic view in perspective of a stator according to the present invention
• FIG. 2 shows a schematic view of a stator with a first embodiment of assembling means
• FIG. 3 shows a schematic view of a stator with a second embodiment of assembling means
• Fig. 4 shows a cross section of an insulated electric conductor.
• FIG 1 a stator 1 according to the present invention, with a portion cut away for clarity reasons.
• This stator includes a stator core 2 and a stator frame 6.
• the stator core is built of stator teeth 3 and is provided with a schematically illustrated winding 4.
• the stator is divided, along a number of dividing planes (of which only three are 8, 9, 10 are represented in figure 1), perpendicular to the longitudinal axis 11 of the stator, into a number of self- supporting stator elements, of which only three stator elements 12, 13, 14 are shown entirely.
• the number of dividing planes and the number of stator elements may be any number deemed suitable according to the preferences. of the manufacturer, the user, etc. It is believed that most frequently it will be transportation limitations that are decisive when determining the number of elements, based on the maximum axial length £ of each element that may be transported.
• Each of these stator elements 12, 13, 14 comprises a stator core element and a stator frame element.
• the dividing planes are in the illustrated embodiment dividing the stator into stator elements of equal size, i.e. equal axial length £ ⁇ .
• a division into elements of different axial lengths is naturally also conceivable.
• stator may be described as if it was sliced into three slices, where each slice, i.e. stator element, is of a substantially d sc shape.
• end elements are, in the represented embodiment which includes the frame, provided with protruding frame elements but this does not adversely affect the general impression of a disc shape.
• FIG 2 is illustrated a first embodiment of assembling means for the stator core 15, in the form of bolts 16 inserted into holes arranged in the core. These bolts are preferably provided with some sort of pretensionmg means.
• the stator core is divided into two stator core elements 18, 19 by means of the dividing plane 20. In this case, the core elements are illustrated with an equal axial length £ 3 . It should be noted that in this schematic illustration the core is represented as being much shorter, in comparison with its diameter, than what would normally be the case.
• the core also includes a cooling duct 17.
• the stator 25 illustrated in figure 3 is divided into three stator elements 27, 28, 29 along two dividing planes 30, 31.
• the stator elements are of different axial lengths, the two end elements being of a longer axial length 5 than the centre element, which has the axial length £ .
• the stator frame is correspondingly divided into three supporting frame parts 35, 36, 37, for support against part of the external peripheral surface of the stator core, as well as part of the axial ends of the core.
• the elements are assembled axially by means of two flange joint devices 33, 34 provided on the supporting frame parts 35, 36, 37. Accordingly, the frame parts are provided with flanges at their respective adjoining ends, which are connected by means of screws or bolts .
• the flanges may be welded to the frame parts or fastened in any other suitable way.
• the cable 40 includes at least one current-carrying conductor 41 surrounded by a first semiconducting layer 42. Outside said first layer is provided a layer of solid insulation 43. Surrounding the insulation layer is then provided a second semiconducting layer 44.
• the current-carrying conductor may include a number of strands -, 46, of which at least some are insulated from each other.
• the three layers of the cable are arranged to adhere to each other even when the cable is bent.
• the cable is consequently flexible and this property is maintained during the entire life of the cable.
• the illustrated cable also differs from conventional high voltage cables in that it does not have to include any outer layer for mechanic protection of the cable, nor does it have to include any metal shield which normally is provided on such a cable.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Iron Core Of Rotating Electric Machines (AREA)
• Manufacture Of Motors, Generators (AREA)
• Insulation, Fastening Of Motor, Generator Windings (AREA)
• Windings For Motors And Generators (AREA)

Applications Claiming Priority (3)

Publications (1)

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Family Applications (1)

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• 1997
  • 1997-10-13 SE SE9703719A patent/SE512717C2/sv not_active IP Right Cessation
• 1998
  • 1998-10-12 PL PL98339770A patent/PL339770A1/xx unknown
  • 1998-10-12 WO PCT/SE1998/001833 patent/WO1999019969A1/en not_active Application Discontinuation
  • 1998-10-12 BR BR9813030-7A patent/BR9813030A/pt not_active IP Right Cessation
  • 1998-10-12 AU AU96568/98A patent/AU9656898A/en not_active Abandoned
  • 1998-10-12 CA CA002306929A patent/CA2306929A1/en not_active Abandoned
  • 1998-10-12 CN CN98809665A patent/CN1272245A/zh active Pending
  • 1998-10-12 EP EP98950560A patent/EP1023760A1/en not_active Withdrawn
  • 1998-10-13 ZA ZA989333A patent/ZA989333B/xx unknown
• 2000
  • 2000-04-07 NO NO20001827A patent/NO20001827D0/no not_active Application Discontinuation

Non-Patent Citations (1)

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