EP3826034A1 - Traversée électrique présentant des performances thermiques améliorées - Google Patents

Traversée électrique présentant des performances thermiques améliorées Download PDF

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Publication number
EP3826034A1
EP3826034A1 EP19210998.1A EP19210998A EP3826034A1 EP 3826034 A1 EP3826034 A1 EP 3826034A1 EP 19210998 A EP19210998 A EP 19210998A EP 3826034 A1 EP3826034 A1 EP 3826034A1
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EP
European Patent Office
Prior art keywords
conductor
central tube
emissivity
coating
electrical
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP19210998.1A
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German (de)
English (en)
Inventor
Teresa Gargano
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Hitachi Energy Ltd
Original Assignee
ABB Power Grids Switzerland AG
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Filing date
Publication date
Application filed by ABB Power Grids Switzerland AG filed Critical ABB Power Grids Switzerland AG
Priority to EP19210998.1A priority Critical patent/EP3826034A1/fr
Publication of EP3826034A1 publication Critical patent/EP3826034A1/fr
Withdrawn legal-status Critical Current

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    • 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
    • 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
    • H01B17/54—Insulators or insulating bodies characterised by their form having heating or cooling devices
    • 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
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F27/00—Details of transformers or inductances, in general
    • H01F27/02—Casings
    • H01F27/04—Leading of conductors or axles through casings, e.g. for tap-changing arrangements

Definitions

  • Embodiments of the present disclosure generally relate to an electrical bushing having enhanced thermal performance, particularly a draw lead bushing or a removable rod bushing.
  • embodiments of the present disclosure relate to an electrical bushing having a central tube with an inner surface having a low emissivity coating.
  • embodiments of the present disclosure relate to a high-voltage transformer having at least one electrical bushing according to embodiments described herein.
  • High-voltage transformers typically include a number of electrical bushings provided therein to facilitate isolation of conductors passing through a barrier, such as a grounded transformer housing.
  • Electrical bushings for high-voltage applications include a central tube, through which a current-carrying conductor passes, leaving a gap between the outer surface of the conductor and the inner surface of the central tube.
  • the current-carrying conductor is a flexible cable, whereas in a removable rod bushing application, the current-carrying conductor is a solid rod.
  • the current-carrying conductor is made of copper.
  • a lower portion of the gap between the conductor and the central tube may be filled with oil from the transformer, while an upper portion of the gap may be filled with a gas such as air.
  • a gas such as air
  • heat transfer between the current-carrying conductor and the central tube is performed through conduction
  • heat transfer is performed through convection and radiation.
  • an insulating gas such as SF6 may be used in the transformer casing, and the entirety of the gap between the central tube and the conductor may be filled with the insulating gas where heat transfer is performed by convection and radiation.
  • the current rating of an electrical bushing is dependent on the maximum allowable temperature as prescribed by the relevant standards (for example, IEC 60137).
  • One approach for increasing the current rating of a bushing is to improve heat transfer between the conductor and the central tube by coating the conductor with a coating to increase emissivity. Paint of the conductor is common in electrical bushings to minimize the risk of discharge and enhance the dielectric performance of the bushing. Painting the conductor with a dark coating increases emissivity of the conductor, and can improve heat transfer away from the conductor by thermal radiation, improving the thermal performance of the bushing and allowing for higher currents to be conducted.
  • problems may arise when painting the conductor, as the conductor is subjected to strong electrical fields. It is critical that the coating performs at all temperatures and exhibits good adherence to the conductor to avoid discharges.
  • the current-carrying conductor is typically made of copper, which has a high emissivity
  • the central tube is typically made of aluminium, which has a comparably low emissivity. Due to the low emissivity of the aluminium central tube, heat transfer between the conductor and the central tube through radiation in the portion of the bushing filled with gas is limited. In view thereof, it is desired to overcome at least some of the problems in the prior art to further improve the thermal performance of the electrical bushing.
  • the electrical bushing 100 includes a central tube having a first emissivity, and a conductor arranged within the central tube providing a gap between the conductor and an inner surface of the central tube, wherein at least a portion of the inner surface of the central tube is provided with a coating having a second emissivity which is higher than the first emissivity.
  • a further aspect of the present disclosure further provides an electrical transformer including at least one electrical bushing 100 according to the above.
  • the embodiments described in the present disclosure allow for improved heat transfer through radiation between the current-carrying conductor and the central tube.
  • the embodiments allow for higher currents to be conducted through the bushing.
  • Fig. 1 exemplarily shows a cross-sectional view of a transformer 200 having at least one electrical bushing 100 according to an aspect of the present disclosure.
  • the transformer may be, for example, a medium-or high-voltage transformer, particularly a high-voltage transformer.
  • the term “medium-voltage” may refer to a voltage of at least 1 kV and up to 52 kV.
  • the term “high-voltage” in the context of the present disclosure may refer to a voltage of at least 52 kV.
  • the transformer 200 may include a housing 202 enclosing an internal volume 203, and at least one transformer element 201.
  • the at least one electrical bushing 100 may be mounted to housing 202 such that a conductor 102 of the at least one electrical bushing 100 may pass through housing 202.
  • the at least one electrical bushing 100 may be of the draw-lead type, wherein conductor 102 is an electrical cable.
  • the at least one electrical bushing 100 may be of the removable rod type, wherein conductor 102 is a solid rod.
  • Transformer 200 may be of the wet type, wherein internal volume 203 is filled with an insulation liquid.
  • internal volume 203 may be filled with one of the group comprising mineral-based oil, natural or synthetic ester, silicone oil, fluorocarbon-based oil, and vegetable-based oil.
  • transformer 200 may be of the dry type, wherein internal volume 203 is filled with a gas.
  • internal volume 203 may be filled with one of the group containing air, SF 6 , N 2 , C 2 H 2 F 4 and C 4 F 8 .
  • conductor 102 of the at least one electrical bushing 100 includes an upper terminal and a lower terminal, where the upper terminal is on the outside of housing 202 and the lower terminal is on the inside of housing 202.
  • Transformer 200 may further include at least one electrical interconnect 204 connecting the lower terminal of the at least one electrical bushing 100 and the at least one transformer element 201.
  • the at least one electrical interconnect 204 may include, for example, a conductive bar interconnect or a cable interconnect.
  • the electrical interconnect 204 may be solid or flexible.
  • conductor 102 of the at least one electrical bushing 100 may extend from the lower end of the at least one bushing 100 directly to the at least one transformer element 201 such that conductor 102 connects directly to the at least one transformer element 201.
  • Electrical bushing 100 includes a central tube 101 having a first emissivity and a conductor 102 arranged within the central tube 101 providing a gap G between the conductor 102 and the inner surface of the central tube 101. At least a portion of the inner surface of the central tube 102 is provided with a coating having a second emissivity which is higher than the first emissivity. By providing at least a portion of the inner surface of the central tube 101 with a coating, the emissivity of the inner surface of the central tube 101 can be increased from the emissivity of the bare central tube material so that the heat transfer by radiation between the conductor 102 and the central tube 101 is enhanced.
  • Electrical bushing 100 may further include an insulation layer 103 provided on the outer surface of central tube 101.
  • electrical bushing 100 is a graded capacitive bushing.
  • Electrical bushing 100 may be an oil-impregnated paper (OIP) bushing or a resin-impregnated paper (RIP) bushing, wherein insulation layer 103 includes a winding of oil-impregnated paper or a winding of resin-impregnated paper, respectively.
  • insulation layer 103 may further include one or more capacitive grading plates 104.
  • Electrical bushing 100 may further include an outer insulation 105, for example, a porcelain outer insulation 105 or a silicone outer insulation 105. Electrical bushing 100 may further include a head element 106, wherein the head element 106 is configured for sealing the outer end of electrical insulator 100 so that insulating liquid or insulating gas from inner volume 203 is prevented from leaking from transformer 200. Head element 106 may be further configured for locating and/or supporting conductor 102 within central tube 101. Electrical bushing 100 may further include mounting flange 107 configured for mounting electrical bushing 100 to housing 202 of transformer 200. Mounting flange 107 may further include an integrated measuring tap, for example, for measuring a temperature of insulation liquid or insulation gas inside electrical bushing 100.
  • Central tube 101 of electrical bushing 100 is typically provided as the primary structural element of electrical bushing 100.
  • the term "central tube” may refer to any tube-like element with any cross section.
  • central tube 101 comprises a tube having a constant circular cross-section.
  • central tube 101 may include a tube having a square cross-section or an oval cross-section.
  • an electrical bushing having a conductor with a square cross-section may be provided with a corresponding tube also having a square cross-section.
  • central tube 101 may include a tube having a variable cross-section with respect to its length.
  • central tube 101 may include a tube having a variable circular cross-section in the shape of a hollow, truncated cone.
  • central tube 101 may be configured to be at substantially the same electrical potential as conductor 102.
  • central tube 101 may be electrically attached to conductor 102 so as to be at substantially the same electrical potential as conductor 102, but without carrying electrical current.
  • central tube 101 may include a non-magnetic material.
  • central tube 101 may include an electrically conductive material.
  • central tube 101 may include one of the group consisting of an aluminium alloy, a nickel alloy and a copper alloy.
  • central tube 101 is manufactured from aluminium alloy so as to provide sufficient strength while minimizing the weight of electrical bushing 100.
  • Conductor 102 is provided to carry electrical current from inside transformer 200 to outside, or vice versa.
  • conductor 102 is an electrical cable, particularly a flexible electrical cable.
  • conductor 102 is a solid rod.
  • the passage of high levels of electrical current though conductor 102 generates heat, which is transferred from conductor 102 to other components of electrical bushing 100 via central tube 101.
  • the maximum operating temperature of electrical bushing 100 particularly the temperature of conductor 102, is limited. For example, according to the temperature rise test in international standard IEC 60137, the maximum operating temperatures for a resin-impregnated paper (RIP) bushing may be limited to 140 °C conductor temperature and 120 °C condenser body temperature.
  • conductor 102 includes a material which has low electrical resistance so that heat generated is minimized.
  • conductor 102 may include copper or a copper alloy for high voltage applications, or an aluminium alloy for medium voltage applications.
  • heat transfer from conductor 102 to other components of electrical bushing 100 via central tube 100 allows for heat generated to be dissipated.
  • Gap G provided between central tube 101 and conductor 102 allows for heat to be transferred from conductor 102 to central tube 101 by either thermal convection or thermal radiation.
  • at least a portion of the gap G between the conductor 102 and the inner surface of central tube 101 is filled with a gas.
  • the insulation liquid may, for example, fill 1/3 of the height of gap G, with the remaining 2/3 of the height of gap G being filled with air.
  • heat is transferred from conductor 101 to central tube 102 primarily by thermal convection in the portion of gap G filled with insulation liquid, and primarily by thermal radiation in the portion of gap G filled with air.
  • gap G provided between central tube 101 and conductor 102 is filled with insulation gas. In this case, heat is transferred from conductor 101 to central tube 102 primarily by thermal radiation.
  • the gap G between the conductor 102 and the inner surface of central tube 101 is at least 1 mm.
  • gap G may be in the range of at least 5 mm and up to 8 mm.
  • Increasing the gap G allows for a larger volume of insulating liquid and/or insulating gas to be provided between conductor 102 and central tube 101, thereby enhancing the insulation properties of the bushing, thus gap G is preferably at least 1 mm, more preferably at least 5 mm.
  • increasing the gap G increases the overall size and cost of electrical bushing 100, thus gap G is preferably at most 10 mm, more preferably at most 8 mm.
  • the inner surface of central tube 101 is provided with a coating, wherein the coating has an emissivity which is higher than the emissivity of the inner surface of central tube 101.
  • the preferred embodiment of the present disclosure includes a central tube 101 manufactured from an aluminium alloy. However, the emissivity of aluminium alloy is low, reducing the rate of heat transfer between conductor 102 and central tube 101. Increasing the emissivity of the inner surface of central tube 101 by providing a high-emissivity coating thereon allows for increased heat transfer by radiation.
  • the heat transfer by radiation can be significantly improved by increasing the emissivity ⁇ 2 of the inner surface of the central tube.
  • the inner surface of central tube 101 having a first emissivity is provided with a coating having a second emissivity, which is higher than the first emissivity.
  • the second emissivity is at least 0.3 at 120 °C.
  • the second emissivity is at least 0.5 at 120 °C, more particularly the second emissivity is at least 0.9 at 120 °C.
  • the coating applied to the inner surface of central tube 101 may include any suitable coating which has a higher emissivity than that of central tube 101, while also being able to withstand operating temperatures inside electrical bushing 100.
  • the coating may be a high temperature coating capable of withstanding an operating temperature of at least 80 °C, preferably at least 100 °C, more preferably at least 120 °C.
  • the coating may include a polymeric material.
  • the coating may include an epoxy coating, an enamel coating or a silicone coating.
  • emissivity values for a lacquer or varnish coating may be in the range of 0.8 to 0.95.
  • the coating may include an oxide coating.
  • the coating may include an anodized coating or a natural oxide layer.
  • an aluminium oxide layer may have an emissivity of at least 0.4, while an anodized aluminium coating may have an emissivity of at least 0.5.
  • the color and/or finish of the coating may be selected to further increase emissivity of the inner surface of central tube 101.
  • a black lacquer may have an emissivity of at least 0.8, while a white lacquer may have an emissivity of at least 0.95.
  • a shiny black lacquer may have an emissivity of at least 0.8, while a flat black lacquer may have an emissivity of at least 0.95.
  • the coating may have a thickness of at least 35 ⁇ m.
  • the coating may have a thickness of at least 70 ⁇ m, more particularly at least 100 ⁇ m. Since the main function of the coating is to increase emissivity, the coating can be a low thickness coating. However, if additional properties are desired such as improved corrosion resistance, then a thicker coating may be applied. It is preferable that the coating thickness is at least 35 ⁇ m so as to provide a sufficiently resilient coating which does not flake or degrade during operation of electrical bushing 100.
  • conductor 102 has a third emissivity, and at least a portion of the conductor is provided with a second coating having a fourth emissivity which is higher than the third emissivity.
  • conductor 102 may include a copper alloy, which may have a third emissivity of 0.15 for a copper alloy having a dull surface, up to 0.6 for a heavily oxidized copper alloy.
  • a black lacquer having an emissivity of at least 0.8 or a white lacquer having an emissivity of 0.95 may be applied to the conductor to enhance the heat transfer by radiation between conductor 102 and central tube 101.
  • conductor 102 due to conductor 102 extending out from the upper and lower ends of electrical bushing 100, for example for attachment to electrical interconnects, conductor 102 is subjected to significantly higher electric field gradients than central tube 101. Thus, if a coating which is applied to conductor 102 is not adequately adhered to conductor 102, the high electric field gradient may cause the coating to degrade or flake. As such, in the present disclosure, the preferred embodiment includes a coating on the inner surface of central tube 101 instead of conductor 102. However, the present disclosure is not limited thereto, and conductor 102 may also be provided with an emissivity-enhancing coating, for example, in reduced voltage applications.
  • a thermal model of an electrical bushing according to the present disclosure was constructed, the electrical bushing model including a 36 mm diameter solid rod conductor, a central tube having an internal diameter of 40 mm and a wall thickness of 4 mm, and a resin-impregnated insulation layer provided to a diameter of 110 mm.
  • a silicone insulation was modelled having dielectric shed features typical of a high-voltage bushing.
  • the total conductor length was modelled at approximately 2100 mm long, of which 1000 mm of the conductor length is in contact with air. Emissivity of the conductor was maintained at 0.6, while the emissivity of the central tube was varied.
  • the gap between the conductor and the central tube was modelled to be filled with mineral oil up to the 500 mm Z-axis level, such that the portion of the gap in the range of -450 mm to 500 mm in the Z axis is filled with mineral oil, and the portion of the gap in the range of 500 mm to 1300 mm is filled with air. Nominal operating conditions of 123 kV and 1700 A flowing through the conductor were applied.
  • the plot shown in Fig. 4 shows the temperature of the conductor on the Y axis along the length of the conductor on the X axis.
  • Two models were considered, a first model in which the central tube is not provided with a coating and has an emissivity of 0.2, and a second model in which the central tube is provided with a coating and has an emissivity of 0.95.
  • the temperature of the conductor in the model having a coated central tube is significantly lower.
  • the temperature difference between the electrical bushing having a coated central tube and the electrical bushing having a non-coated central tube can be over 8 °C. With such a temperature difference, the electrical bushing having a coated central tube can be rated at a higher operating current as compared to the electrical bushing having a non-coated central tube.

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EP19210998.1A 2019-11-22 2019-11-22 Traversée électrique présentant des performances thermiques améliorées Withdrawn EP3826034A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP19210998.1A EP3826034A1 (fr) 2019-11-22 2019-11-22 Traversée électrique présentant des performances thermiques améliorées

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP19210998.1A EP3826034A1 (fr) 2019-11-22 2019-11-22 Traversée électrique présentant des performances thermiques améliorées

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EP3826034A1 true EP3826034A1 (fr) 2021-05-26

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3564108A (en) * 1969-08-14 1971-02-16 Rca Corp Coaxial transmission line
GB1530929A (en) * 1976-02-07 1978-11-01 Felten & Guilleaume Carlswerk Transformer bushings
US4358631A (en) * 1980-09-10 1982-11-09 Mitsubishi Denki Kabushiki Kaisha Heat dissipating electrical bushing
US20100051306A1 (en) * 2006-10-31 2010-03-04 Abb Research Ltd High voltage bushing

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3564108A (en) * 1969-08-14 1971-02-16 Rca Corp Coaxial transmission line
GB1530929A (en) * 1976-02-07 1978-11-01 Felten & Guilleaume Carlswerk Transformer bushings
US4358631A (en) * 1980-09-10 1982-11-09 Mitsubishi Denki Kabushiki Kaisha Heat dissipating electrical bushing
US20100051306A1 (en) * 2006-10-31 2010-03-04 Abb Research Ltd High voltage bushing

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