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
  • 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
  • H01F27/30—Fastening or clamping coils, windings, or parts thereof together; Fastening or mounting coils or windings on core, casing, or other support
• • 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
  • H01F27/30—Fastening or clamping coils, windings, or parts thereof together; Fastening or mounting coils or windings on core, casing, or other support
  • H01F27/306—Fastening or mounting coils or windings on core, casing or other support

Definitions

• the present invention relates to a winding of an air cooled conductor wound power transformer or a winding of a reactor the winding of which being provided with spacers between the conductor windings to enable air cooling and earthing in a winding structure held mechanically together.
• Today's power transformers are normally oil cooled.
• the transformers are provided with a core consisting of a number of core legs connected by yokes and windings constituting coils (primary, secondary, regulated) which are immersed in a sealed tank filled with oil.
• the heat, generated in the coils and core is removed by oil circulating internally through the coil and core and released in to the surrounding air via the walls of the vessel .
• Oil circulation may either be forced by pumping the oil around or it may be natural due to temperature differences in the oil .
• the circulating oil is cooled externally through air- or water cooling devices. External air cooling of oil may be forced and/or effected through natural convection.
• the oil has an insulating function besides its role as conveyer of heat in oil cooled transformers for high voltage.
• Dry transformers are normally air cooled. They are normally cooled by natural convection as today's dry transformers are used at low power loading.
• the present technology related to axial cooling ducts, produced by means of a corrugated winding, is disclosed in GB 1.147.049, axial ducts for cooling of windings embedded in cast resin is disclosed in EP 83107410.9 or the use of cross flow fans at peak load is disclosed in SE 7303919-0.
• conventional power transformers are provided with special rings so that the stability of the windings is ensured against short circuit forces.
• the windings are mounted as a unit on the core. A series of plates is thereafter mounted in series which is tightened against a barrier cylinder. The whole installation is mounted in line on a lower spacer ring.
• a compression ring which prestresses the windings is located between the yoke of the core and the windings.
• the short circuit forces must consequently be absorbed by the yoke of the iron core by means of its clamps which keep the lamination in place.
• windings there is no iron core in the event of windings being used to compensate for reactive power in a reactor.
• the windings in this case are formed solely of a coil.
• a conductor is known through US 5 036 165, in which the insulation is provided with an inner and an outer layer of semiconducting pyrolized glassfiber. It is also known to provide conductors in a dynamo-electric machine with such an insulation, as described in US 5 066 881 for instance, where a semiconducting pyrolized glassfiber layer is in contact with the two parallel rods forming the conductor, and the insulation in the stator slots is surrounded by an outer layer of semiconducting pyrolized glassfiber.
• the pyrolized glassfiber material is described as suitable since it retains its resistivity even after the impregnation treatment.
• the object of the invention is to produce a new type of winding in a power transformer or a reactor comprising a high voltage cable having an outer semiconducting layer.
• the winding is provided with spacers, which are arranged to produce cooling ducts between concentric winding turns, as well as constituting means for axially prestressing the winding.
• the problem of short circuit forces in the winding is hereby solved so that the clamps, previously absorbing forces in for example transformers, may be produced lighter and smaller in size. This results in reduced eddy currents in the clamps hereby reducing the total eddy current losses.
• the windings are hereby in the form of a mechanically compact and integral winding unit which may absorb stresses, such as short circuit forces, without transmitting the forces to the iron core in a transformer.
• a further object of the invention is to provide axial cylindrically formed ducts between each winding turn in the windings wherein the cooling agent is correctly distributed in order to meet the cooling requirements of the windings.
• the cylindrical ducts are created by spacers which are inserted during winding of the coil.
• the cooling flow is produced by fans and the spacers are dimensioned such to produce the flow in the ducts which meets the individual cooling requirements of the windings.
• Another advantage of the present transformer design is that the windings are mounted on cable drums in the cable factory, prior to being installed around the iron core on site which is a great improvement in the production technique of these types of transformers .
• the present invention relates to a winding of a power transformer or a reactor.
• the winding comprises a high voltage cable which is wound around a transformer core of the transformer design.
• the winding is provided with a plurality of spacers extending axially along the length of the winding, separating each cable turn of the winding radially in order to create among other things axial cylindrical cooling ducts.
• the winding is thus arranged with axial cylindrical cooling ducts between each winding turn, arranged on the outside, which ducts are created by spacers during winding of the core.
• the spacers are also arranged to axially clamp the winding together to form an integral winding unit which among other things may absorb mechanical short circuit forces .
• spacer is arranged with an elastic layer in order to absorb vibrations which may arise in the winding.
• the windings are composed of cables having solid, extruded insulation, of a type now used for power distribution, such as XLPE-cables or cables with EPR-insulation .
• 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 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 primarily on winding systems in which the winding is formed from cable which is bent during assembly.
• the flexibility of a XLPE-cable normally corresponds to a radius of curvature of approximately 20 cm for a cable 30 mm in diameter, and a radius of curvature of approximately 65 cm for a cable 80 mm in diameter.
• 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.
• Windings in the present invention are constructed to retain their properties even when they are bent and when they are subjected to thermal 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 lay 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 (PMP), 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
• PMP polymethyl pentene
• XLPE cross-linked polyethylene
• EPR ethylene propylene rubber
• the inner and 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 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 invention.
• the insulating layer and the semiconducting layers thus have substantially the same coefficients of thermal expansion.
• Ethylene-vmyl-acetate copolymers/nitrile rubber, butyl graft polyethylene, ethylene-butyl-acrylate-copolymers and ethylene-ethyl-acrylate copolymers may also constitute suitable polymers for the semiconducting layers . Even when different types of material are used as base m the various layers, it is desirable for their coefficients of thermal expansion to be substantially the same. This is the case with 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 m the radial direction of the elasticity so that no cracks or other damage appear 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 magnitude as 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 large to contain the electrical field m the cable, but sufficiently small 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. There is, of course, nothing to prevent one or more additional semiconducting layers being arranged in the insulating layer.
• Figure 1 shows schematically an axial view of the centre of the winding according to the present invention
• Figure 2 shows a view A-A according to Figure 1 of a winding coil provided with spacers according to the invention
• Figure 3a shows a partial view through an upper end plate according to the present invention
• Figure 3b shows a partial view through a lower end plate according to the present invention
• Figure 4 shows a view through a high voltage cable according to the present invention.
• Figure 1 shows a cross-section through a power transformer 1 provided with a winding coil 2 with windings 3 arranged in spiral form beginning with a lower end plate 4 and wound upwards .
• the windings may but need not be connected to each other.
• Different windings with different cable diameters are part of the embodiment shown in the Figure .
• each winding is provided with axial spacers a, b, c to fit into the axial position of each winding of the coil.
• a plurality of spacers 8, 9 is inserted between each winding turn 5, 6, 7.
• a first spacer 8 is hereby inserted between a first winding turn 5 and a second winding turn 6 arranged concentrically .
• a second spacer 9 is inserted between the second winding turn 6 and a third likewise concentric winding turn 7, and so forth.
• Each spacer 8, 9 of the winding coil 2 is clamped to the lower endplate 4 and tightened by clamping means 10 against an upper end plate 11.
• the first spacer 8 is thicker than for example the second producing a broader duct between the winding turns.
• the winding coil constitutes a self containing part, independent of the iron core, which does not need to be supported against the iron core in order to compensate for all of the occurring short circuit forces .
• the winding structure may but need not be in contact with the iron core at the so called window.
• the winding coil 2 surrounds a leg 12 of the iron core which leg, at its lower and upper end, is connected to a yoke 13 so as to be in contact with another leg (not shown) .
• Spacers 8, 9 are either cylindrical or rectangular in cross-section and are provided at least at the one end with a clamping means in the form of a nut with a screw or wedge arrangement . As shown in Figure 2 the spacers 8 , 9 are placed radially outwards from the leg 12 of the iron core with the end plates 4, 11 in a "spoke" formation.
• Spacers 8, 9 Five spacers are placed radially through each "spoke" of a winding coil of the present type. Spacers 8, 9 produce additionally axial cylindrical cooling ducts 13, 14 between each radially positioned winding 5, 6, 7. The winding turns are air cooled in that air is pressed through the ducts by fans (not shown) . Spacers 8, 9 are placed throughout the winding coil 2, and are axially longitudinal. The spacers are inserted between the winding turns during winding of the coil.
• each winding coil is surrounded by a cooling duct wherein cool air is arranged to flow. Cooling requirements differ between windings which implies that there are different cooling flows in the concentric ducts. In order to achieve the correct cooling of the ducts, as indicated above, the latter are arranged in radial direction according to their different dimensions.
• the first spacer 8 is of metal or reinforced plastic, coated with a rubber layer 16, which functions as a > to C o T o o tr
• FIG 4 shows a view through a high voltage cable 111 to be used in a winding according to the present invention.
• the high voltage cable 11 comprises a number of strands 112 with circular cross-section of for example copper (Cu) . These strands 112 are arranged in the centre of the high voltage cable 111.
• a first semiconducting layer 113 Around the strands 112 there is arranged a first semiconducting layer 113.
• an insulating layer 114 of for example XLPE-insulation.
• the concept of a high voltage cable in the present application does not comprise thus the outer shielding screen that normally surrounds such a cable for power distribution.
• the high voltage cable has a diameter in the interval of 20 - 250 mm and a conductor area in the interval of 40 - 3000 mm 2 .
• the invention is applicable to both a power transformer and a reactor.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Coils Of Transformers For General Uses (AREA)

Applications Claiming Priority (5)

Publications (1)

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Family Applications (1)

Country Status (11)

Families Citing this family (7)

Family Cites Families (2)

• 1997
  • 1997-11-28 SE SE9704419A patent/SE9704419D0/xx unknown
• 1998
  • 1998-02-02 WO PCT/SE1998/000160 patent/WO1998034243A1/en not_active Application Discontinuation
  • 1998-02-02 JP JP53280298A patent/JP2001509964A/ja active Pending
  • 1998-02-02 AU AU58911/98A patent/AU5891198A/en not_active Abandoned
  • 1998-02-02 CN CN98801962A patent/CN1244286A/zh active Pending
  • 1998-02-02 BR BR9807137-8A patent/BR9807137A/pt not_active IP Right Cessation
  • 1998-02-02 KR KR1019997006997A patent/KR20010049163A/ko not_active Application Discontinuation
  • 1998-02-02 EA EA199900706A patent/EA001636B1/ru not_active IP Right Cessation
  • 1998-02-02 EP EP98902357A patent/EP0956568A1/en not_active Withdrawn
  • 1998-02-02 CA CA002276441A patent/CA2276441A1/en not_active Abandoned
  • 1998-02-02 UA UA99074420A patent/UA54486C2/uk unknown

Non-Patent Citations (1)

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