Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B17/00—Insulators or insulating bodies characterised by their form
  • H01B17/26—Lead-in insulators; Lead-through insulators
  • H01B17/28—Capacitor type
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B17/00—Insulators or insulating bodies characterised by their form
  • H01B17/26—Lead-in insulators; Lead-through insulators
  • H01B17/30—Sealing

Definitions

• the present invention relates to the field of high voltage power systems, and in particular to high voltage bushings used in high voltage devices forming parts of such systems.
• high voltage equipment and devices e.g. high voltage transformers, reactors, switchgear etc.
• bushings that are adapted for carrying current at high potential through a grounded barrier, e.g. a wall or an enclosure of the electric device, such as a transformer tank.
• Conventional high voltage bushings comprise an insulator made of ceramic or composite material, which is provided with sheds and which is generally hollow.
• voltage grading is performed by a condenser body or some other type of voltage grading device, through which an electrical conductor passes. The electrical conductor connects one side of the bushing, where a high voltage electric device is connected, with the other side of the bushing where another electric device is connected.
• the bushing when the first electric device is a transformer, the bushing is fitted on the transformer enclosure, such as the tank wall, and the conductor of the bushing connects the inside of the transformer with the outside, where another electric device can be connected, e.g. a bus, surge arrester or DC valve.
• the transformer enclosure such as the tank wall
• another electric device can be connected, e.g. a bus, surge arrester or DC valve.
• FIG. 1 showing a schematic cross sectional view of a bushing 1 mounted in a wall 18, such as the tank wall, in the case of a transformer.
• a high voltage conductor 10 runs through the center of a hollow bushing insulator 12 that forms a housing around the high voltage conductor.
• a condenser core 14 is provided inside the insulator housing for voltage grading of voltage stress that is built up around the high voltage conductor 10.
• a flange 16 is provided on the outside of the housing 12, by means of which the housing of the bushing is connected to ground, via the transformer tank wall 18.
• FIG. 1 is also shown how the bottom end portion of the high voltage conductor 10 forms a bottom contact 20 that is arranged to be connected to the internal components of the transformer.
• a mating internal contact 22 is provided inside the transformer.
• An upper outer terminal 24 for the conductor 10 is provided at the upper end of the bushing, opposite the bottom contact 20 end. The outer terminal 24 is electrically connected to the conductor 10 through an essentially planar interface, also forming a top cover of the bushing, in order to electrically connect the conductor and thus the transformer to an external source or device.
• a draw rod system may be used for ensuring electrical connection between the bushing and the transformer.
• This system requires a hollow conductor, with the inside of the conductor open towards the transformer oil inside the transformer. It is necessary to provide a seal inside the conductor in order for the transformer oil not to leak out to the surroundings, outside the transformer and outside the bushing.
• a traditional way of sealing off the inside of the conductor towards the outside of the transformer, for example a valve hall, is to use an expander arrangement that is assembled inside the conductor in the field, after the draw rod system is assembled.
• This expander arrangement has drawbacks in terms of the radial space it requires which entails a disadvantageous reduction in thickness of the conductor wall, and also in terms of fail-safe assembly work that is necessary at the site in the field.
• the outer terminal has to be screwed into a steel draw ring or similar located inside the conductor.
• This draw ring is in turn screwed into the conductor, thereby reducing the wall thickness of the conductor due to the necessary internal threads.
• This draw ring arrangement also requires that a sealing is provided.
• high voltage is conventionally used for voltages above approximately 50 kV.
• the upper limit in commercial high voltage devices is generally 1100 kV, but higher voltages, such as 1200 kV or even more, are envisaged in the near future.
• current levels are increasing and may be up to 4000-5000 A or even higher.
• a draw rod arrangement for a hollow conductor in a high voltage bushing comprising a draw rod attachment part and an outer terminal attachment part, wherein the draw rod attachment part and the outer terminal part are made in one piece forming a combined mounting device.
• This inventive draw rod arrangement has the advantage of combining the function of the draw ring and the draw rod mounting, whereby space is saved inside the conductor and also conductor material is saved thanks to less threads.
• a further advantage is that the personnel at the mounting site does not have to be involved in assembly of mechanical parts, which leads to easier and more fail-safe assembly and cost saving.
• the draw rod attachment part of the mounting device is provided with an axial hole, through which an end of a draw rod is inserted, that in the axial prolongation of the hole there is an inner bore with a larger diameter than the hole and into which bore a threaded end of the draw rod extends, that the draw rod is mounted by means of a fastening arrangement in the inner bore.
• This fastening arrangement may comprise a washer arrangement resting against a bottom in the inner bore and a nut screwed onto the threaded end of the draw rod.
• the inner bore extends through the outer terminal attachment part.
• the outer terminal attachment part is provided with threaded holes adapted to receive screws for mounting an outer terminal contact.
• At least one sealing means arranged between the conductor and the combined mounting device.
• a sealing is used for example when there is a liquid inside an electric device onto which a bushing comprising the draw rod attachment is mounted, and it is desirable to prevent this liquid from leaking out of the electric device, via the conductor and the bushing. This is the case for a transformer filled with insulating oil, for example.
• the invention may also have the feature that it comprises an end plug for mounting over the combined mounting device, inside an open end of the conductor.
• This end plug also has a sealing function.
• the draw rod arrangement according to the invention may also comprise at least one sealing means arranged between the inner bore and a part of the end plug that extends down into the inner bore. This sealing also prevents leakage of any insulating medium that can be present inside the conductor when it is used in a bushing in a transformer.
• the outer terminal attachment part is provided with a second set of threaded holes
• the end plug is provided with corresponding holes for mounting the end plug onto the outer terminal attachment part by means of screws inserted in said holes and screwed into the second set of holes in the outer terminal attachment part.
• the end plug has also an additional set of holes adapted to receive screws for mounting an outer terminal contact.
• a high voltage bushing comprising a hollow conductor, characterized in that it comprises a draw rod arrangement according to any one of the claims related to a draw rod arrangement.
• the high voltage bushing may be characterized in that the combined mounting device is connected to the hollow conductor by being welded inside one end of the conductor of the bushing.
• the high voltage bushing may be characterized in that the combined mounting device is connected to the hollow conductor by being screwed inside one end of the conductor of the bushing. In that case there is no need for welding.
• a high voltage device comprising a bushing as defined in any one of the claims related to a bushing.
• Fig. 1 illustrates schematically, in cross section, a high voltage bushing according to prior art
• Fig. 2 illustrates schematically, in cross section, a draw rod arrangement according to the present invention.
• high voltage will be used for voltages of 50 kV and higher.
• the present upper limit for commercial high voltage is 1100 kV, but it is foreseen that the invention can be used also for higher voltages, up to 1200 kV or even more.
• the present invention will find its applicability from about 200 kV and upwards.
• FIG. 2 An embodiment of a draw rod arrangement according to the present invention is shown in Fig. 2, mounted in a conductor 38, for example in a high voltage bushing (not shown).
• the arrangement comprises a draw rod attachment part 31 , and an outer terminal attachment part 32, combined as a one piece element, in the following referred to as a combined mounting device 33.
• the draw rod attachment part 31 will in the following be referred to as the draw rod part, and the outer terminal attachment part 32 will in the following be referred to as the terminal part.
• the draw rod part 31 has a first bottom part 34 with a basic shape of a hollow cone, with the open cone bottom directed towards the inner parts of the hollow conductor 38.
• the draw rod part 31 has a second upper part 36, basically ring shaped with a central axial hole 40 through which the draw rod 42 is inserted.
• a second upper part 36 In the upper part 36, above the hole 40, there is an inner bore 44 with a diameter that is larger than the diameter of the hole 40, and this inner bore 44 extends also all the way through the terminal part 32, in prolongation of the hole 40.
• the draw rod 42 is mounted by means of a fastening arrangement, such as a washer arrangement 46 or similar resting against the bottom of the inner bore 44, and a nut 48 screwed onto the threaded top end of the draw rod.
• the terminal part 32 of the draw rod arrangement is essentially ring shaped with an inner bore 44 as described above.
• threaded holes 50 In the upper end of the terminal part, there are arranged threaded holes 50, adapted to cooperate with screws for mounting an outer terminal contact (not shown).
• the draw rod arrangement comprises an end plug 52, inserted in the open end of the conductor 38, and covering the mounting device 33.
• the end plug is mounted to the upper end of the terminal part 32 by means of screws 54 inserted in wholes 56 in the end plug and screwed into corresponding threaded holes 58 arranged in the upper part of the terminal part 32.
• One function of the end plug is to seal off the inside of the conductor with the draw rod arrangement from the outside.
• the draw rod arrangement also comprises at least one sealing 60 between the end plug 52 and the inside of the bore 44.
• This sealing ensures that the inside of the conductor is sealed off from the outside of the conductor.
• the conductor is generally open to the cooling medium inside the transformer, normally oil, and it is very important that oil cannot leak out through the end of the conductor, to the outside.
• the seal can be provided by means of an annular sealing, such as an O-ring, mounted in a groove provided in a part of the end plug 52 that extends down into the inner bore 44 of the terminal part 32, or alternatively the groove can be provided in the wall of the bore.
• an annular sealing such as an O-ring
• the end plug In order for an outer terminal contact to be mounted at the end of the conductor, and screwed into the mounting holes 50 of the terminal part 32, as described above, the end plug must also have corresponding holes 51 for the screws to pass through. It may also be mentioned that, instead of fastening an outer terminal contact in the terminal part 32, an intermediate part may be arranged externally of the end plug and the outer terminal may be attached to this part.
• the mounting device can either be screwed into the end of the conductor or welded. In the case of screwing, the mounting device is provided with external threads 59 for cooperation with corresponding internal threads in the wall of the end of the conductor. An additional sealing must then be provided between the inside of the conductor and the draw rod arrangement. An example of this is illustrated in Fig.
• sealing 62 is shown.
• This sealing is located in a groove provided between the end plug 52 and the terminal part 32.
• the sealing has an annular shape, e.g. an O-ring, and is compressed so that it fills the groove all the way out to the conductor wall.
• an annular shape e.g. an O-ring
• the described draw rod arrangement may be used in a bushing both for DC and AC applications.
• a transformer may be a high voltage device in which the inventive draw rod arrangement and high voltage bushing are used.
• inventive draw rod arrangement and high voltage bushing may also be used with other types of high voltage devices, such as reactors, breakers, generators, switchgear or any other suitable device finding an application in high voltage systems.
• electric device and high voltage device should also be interpreted as including cables, buses, surge arrestors, DC valves etc., within the context of the present invention.
• the inventive draw rod arrangement and bushing When the inventive draw rod arrangement and bushing is used in a transformer, oil is used as insulating medium inside the transformer and on the other side of the bushing the medium is air, for example in a HVDC valve hall.
• This type of bushing is generally referred to as an air-oil or air-liquid bushing.
• the draw rod arrangement and bushing according to the invention is suitable for use in many electric devices, irrespective of the media on the respective sides of the bushing, such as air-air (wall bushing), air-gas (gas switchgear), etc.
• the present invention bears no restriction as to the choice of insulation medium inside the bushing. It may for example be gas, oil, gel, or combinations thereof.
• the present invention is not limited to the described embodiment, given as example only, but may be varied and modified in many ways within the scope of the appended claims, as will be realized by a person skilled in the art.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Insulators (AREA)
• Housings And Mounting Of Transformers (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

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Country Status (4)

Cited By (1)

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Citations (2)

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• 2008
  • 2008-05-06 EP EP08155702A patent/EP2117016A1/en not_active Withdrawn
  • 2008-06-05 CN CN2008101112371A patent/CN101577155B/zh active Active
• 2009
  • 2009-04-07 BR BRPI0912208A patent/BRPI0912208A2/pt not_active IP Right Cessation
  • 2009-04-07 WO PCT/EP2009/054129 patent/WO2009135741A1/en active Application Filing

Patent Citations (2)

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