Classifications

• • 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
  • 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
  • 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
  • H02K15/00—Methods or apparatus specially adapted for manufacturing, assembling, maintaining or repairing of dynamo-electric machines
• • 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 in a first aspect to a rotating electric machine of the type described in the preamble to claim 1, e.g. synchronous machines, but also double-fed machines, applications in asynchronous static current converter cascades, outer pole machines and synchronous flow machines.
• a second aspect of the invention relates to a method of the type described in the preamble to claim 15.
• the machine is intended primarily as generator in a power station for generating electric power.
• the machine is intended for use with high voltages.
• High voltages in this respect are electric voltages in excess of 10 kV.
• a typical operating range for the machine according to the invention may be 36 to 800 kV.
• Similar machines have conventionally been designed for voltages in the range 6-30 kV and 30 kV has normally been considered to be an upper limit. This generally means that a generator must be connected to the power network via a transformer which steps up the voltage to the level of the power network, i.e. in the range of approximately 100-400 kV.
• XLPE crosslinked polyethylene
• coils for rotating generators can be manufactured with good results within a voltage range of 3 - 25kV.
• 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 con ⁇ ductors 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.
• coolant oil is used both in the hollow conductors and in holes in the stator walls.
• Such cooling systems how ⁇ ever, entail a large number of connections of both oil and electricity at the coil ends.
• 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 lami ⁇ nated 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 that part of the winding which is located nearest the neutral point is located.
• 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 clean ⁇ ing 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 dimensions for all the layers.
• the cable is placed in stator slots formed as circular, radially disposed 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 here 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 means a large slot leakage flux which significantly influences the magnetization requirement of the machine.
• the present invention is related to the above-mentioned problems associated with avoiding damage to the exterior of the cable during insertion into the stator slots and avoiding wear against the surface caused by vibration during operation.
• the object of the present invention is to provide a machine in which this problem is solved.
• This object is achieved according to the invention in that a machine of the type described in the preamble to claim 1 is given the special features defined m the characterizing part of the claim and in that a method of the type described in claim 17 comprises the special measures defined in the characterizing part of this claim.
• a lining in the slot By thus arranging a lining in the slot, contact is eliminated between the outer layer of the cable and the parts of the stator core forming the walls of the slots.
• the material in the lining must be thermoformable so that it can be given a complicated configuration corresponding to that of the slot walls and substantially retain its shape after moulding. A lining can thus be obtained which is m contact with the slot walls, even if their profile is unusual, and without other aids such as glue or the like to hold the lining in place.
• the slots of a rotating electric machine are provided with some kind of lining, e.g. through US-3 943 392, US-3 130 335, and US-1 974 408.
• These linings are not for high voltage machines, and are used in machines with another type of insulation system to that required in a machine according to the present invention.
• this type of lining cannot be used to solve the problem of protecting the uncovered outer layer of such an insulation system.
• US-2 749 456 reveals the arrangement of a lining in the stator slots of an electric motor to be known per se.
• the machine here is not one for high voltage.
• the motor is designed in such a way that it is able to operate immersed in water and the lining is arranged to insulate the cable windings from the water.
• the problems encountered with the high-voltage levels are not relevant and the aim is not to provide any mechanical protection.
• the material in the lining is extruded polyvinyl chloride, which limits the freedom to produce a lining with properties enabling its use for a machine according to the present invention due, for instance, to formability, profile and thickness.
• a machine according to the invention with slots having varying width in radial direction, with alternating narrower and wider parts.
• the wider parts preferably have a circular cross section to allow passage of the cable, and are connected by waisted parts constituting narrower parts.
• the slots thus acquire a profile similar to that of a bicycle chain.
• the advantages of the lining according to the invention are particularly noticeable with such an embodiment where it has a corresponding profile.
• the lining material is suitably fibre-reinforced, preferably with aramid fibres, so that it will withstand mechanical damage. Since it is thermoformable, the lining can be made relatively thin, approximately 0.1 - 1.0 mm, preferably 0.2 - 0.5 mm, which means that it takes up little useful room.
• the lining includes spring means. This is achieved in an advantageous manner by manufacturing the lining in two layers with spring elements between the layers.
• a resilient lining offers the additional advantage that the cables can be positioned so that the vibrations are absorbed.
• the method according to the invention defined in claim 15 describes how the lining can be manufactured and applied in the slots in a simple and expedient manner. Moulding the lining in the manner described enables a thin lining with complicated profile to be produced which can easily be inserted into the slot.
• the method enables the lining to be inserted axially into the slot, thus simplifying assembly.
• a slot with "bicycle-chain profile” the sheet which is to form the lining is shaped by a roll having alternating raised and indented parts.
• the lining is suitably manufactured from a sheet material comprising aramid fibres, which has a thickness of approximately 0.2 - 0.5 mm.
• Figure 1 shows schematically an axial end view of a sector of the stator in a machine according to the invention
• Figure 2 is a partial enlargement of a detail from Figure 1 showing part of a slot
• Figure 3 shows an alternative embodiment of the slot profile m a view corresponding to Figure 2
• Figure 4 shows an alternative embodiment of the lining according to the invention
• Figure 5 illustrates a step in the manufacture of a lining according to the invention
• Figure 6 illustrates the profile of a lining according to the invention in axial section
• Figure 7 is a section along the line VII-VII in Figure 6, and
• FIG 8 is a cross section through a conductor used in the machine according to the invention.
• the stator is composed in conventional manner of a laminated core of sheet steel divided into sector-shaped sections, one of which is shown in the figure. From a yoke portion 3 of the core situated radially outermost, a number of teeth 4 extend radially in towards the rotor 2 and are separated by slots 5 in which the stator winding is arranged. In this machine intended for high voltage the slots 5 have considerably greater depth than what is usual.
• the cables 6 in the windings are high-voltage cables which may be of substantially the same type as high-voltage cables used for power distribution, so- called crosslmked polyethylene (XLPE) cables.
• XLPE crosslmked polyethylene
• One difference is that the outer mechanically protective sheath that normally surrounds such a cable has been eliminated.
• the cable thus comprises only the conductor, an inner semiconductor layer, an insulating layer and an outer semiconducting layer. The semiconductor layer, sensitive to mechanical damage, is thus exposed on the surface of the cable.
• each slot 4 has varying cross section with alternating wide parts 7 and narrow parts 8.
• the wide parts 7 are substantially circular and surround cable parts, and the waist parts between these form narrow parts 8.
• the waist parts serve to radially position each cable part.
• the cross section of the slot as a whole also becomes slightly narrower in radial direction inwards. This is because the voltage m the cable parts is lower the closer they are situated to the radially inner part of the stator. Slimmer cable parts can therefore be used here, whereas increasingly coarser cable parts are required further out.
• cables of three different dimensions are used, arranged in three correspondingly dimensioned sections 9, 10, 11 of the slots 5.
• Figure 2 shows how a lining 12 according to the invention is arranged abutting the walls of the slot 5.
• the lining is made of profile-rolled, hard-calendered aramid fibre, e.g. of the type known under the trade name NomexTM, but may alternatively be made of glassfibre, reinforced epoxy, thermoset plastic or the like.
• NomexTM is available in a standard thickness of 0.17 mm and a suitable thickness for the lining lies in the interval 0.1 - 1.0 mm.
• the lining material should have good thermal conducting properties and may either be electrically insulating or manufactured with a certain resistivity to earthing inside the slot.
• the lining 12 has a profile corresponding to the profile of the slot walls with their alternating narrower parts 8 and wider parts 7.
• the figure illustrates how the cable is composed of a conductor 6a in the core, preferably formed of twisted copper strands, surrounded by a semiconductor layer 6b, an insulating layer 6c and an outer semiconductor layer 6d.
• the purpose of the lining is to eliminate the risk of damage to the outer semiconductor layer 6d. Such damage may occur during winding of the cable when the cable is inserted through the slot with the risk of being scratched against the edges of the steel sheets and also due to wear caused by vibration and thermal movement of the cable.
• FIG 3 shows an alternative embodiment of the slot profile where alternate waist parts 8 are in the form of a "half" waist since one wall of the slot runs in a tangential plane 13 to two adjacent circular parts.
• the lining 12 has a corresponding shape.
• Figure 4 shows an alternative embodiment in a section corresponding to that shown in Figure 2, but constituting an enlarged detail section of only one slot wall.
• the lining 12 has two layers 12a, 12b of aramid fibre. Between these a rubber layer 14 is arranged.
• the purpose of the rubber layer is to yieldingly position the cable, thus absorbing vibrations therein.
• the rubber layer need not be coherent but may be replaced with a number of separate rubber elements between the aramid layers.
• the rubber layer or rubber elements adhere to the aramid layer by means of a glue which releases at approximately 60°C. Some other material with equivalent elastic properties may naturally be used instead of rubber.
• the aramid fibre layer itself may be made with equivalent elasticity.
• Figure 5 illustrates a step in the manufacture of a lining intended for use in the slots of a machine according to certain embodiments of the present invention.
• a sheet of aramid fibre e.g. NomexTM with a thickness of approximately 0.5 mm, cut to suitable dimensions, is hot- moulded between a rotating cylinder 21 and a moulding tool 22.
• the figure illustrates moulding a lining covering the entire inner surface of the slot, i.e. both its wall surfaces.
• the middle 27 of the cylinder will thus represent the part of the lining which will lie at the bottom of the slot.
• the lining is folded or bent around the mid-line of the rolled sheet and the fold is given a radius of curvature corresponding to that in the bottom of the slot.
• the sheet may possibly be thinner at its mid-point during the rolling, or it may be provided in some other way with markings to facilitate folding.
• the cylinder consists of a number of rollers 23 having concave cylindrical profile 25 which are joined together, and the moulding tool 22 has a shape conforming with the ball-shaped counter-supports 24 for the cylindrical parts of the lining and cylindrical pins 26 between them for the waist parts of the lining.
• the rollers 23 of the cylinder 21 have different profile radii, the rollers situated nearest the mid-point 27 having the largest radius, those situated furthest out having the smallest radius and those situated between having a radius between the other radii. This is in order to produce a profile in the lining which corresponds to the various cable dimensions used in the slot, as described in connection with Figure 1.
• the aramid-fibre sheet When the aramid-fibre sheet has been given its profile in the hot-moulding process and then folded at about its mid-line, it will have the shape illustrated in Figure 6, folded at the lower end (bottom of the slot) and open at the top (slot opening) . Shaped thus, the lining can easily be compressed and inserted axially into the slot, where it will snap out to fit against the slot walls.
• the lining is suitably given an axial extension greater than the axial length of the slot so that a short portion 30, 31 protrudes outside the slot at one or both ends. This can then be folded out as shown in 30 to ensure that the lining is not displaced in axial direction.
• Figure 8 shows a cross-sectional view of a high-voltage cable 6 according to the present invention.
• the high-voltage cable comprises a number of strands 31 of copper (Cu) , for instance, having circular cross section. These strands 31 are arranged in the middle of the high-voltage cable 6.
• a first semiconducting layer 32 Around the strands 31 is a first semiconducting layer 32, and around the first semiconducting layer 32 is an insulating layer 33, e.g. XLPE insulation.
• a second semiconducting layer 34 Around the insulating layer 33 is a second semiconducting layer 34.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Insulation, Fastening Of Motor, Generator Windings (AREA)

Applications Claiming Priority (5)

Publications (1)

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Country Status (4)

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• 1997
  • 1997-05-27 EP EP97924474A patent/EP1016190A1/de not_active Withdrawn
  • 1997-05-27 CN CN97195038.5A patent/CN1220048A/zh active Pending
  • 1997-05-27 AU AU29887/97A patent/AU2988797A/en not_active Abandoned
  • 1997-05-27 WO PCT/SE1997/000896 patent/WO1997045934A1/en not_active Application Discontinuation

Non-Patent Citations (1)

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