EP4625445A1

EP4625445A1 - Bushing, electrical apparatus and method

Info

Publication number: EP4625445A1
Application number: EP24166812.8A
Authority: EP
Inventors: Jan Czyzewski; Robert Platek; Cenk Kurtulus; Orhan Akbas
Original assignee: Hitachi Energy Ltd
Current assignee: Hitachi Energy Ltd
Priority date: 2024-03-27
Filing date: 2024-03-27
Publication date: 2025-10-01
Also published as: WO2025201783A1

Abstract

A bushing (100) for a liquid-insulated electrical apparatus (200) is disclosed. The bushing (100) comprises
an electrical conductor (101) and an insulator body (110) through which the electrical conductor (101) extends, wherein the insulator body (110) comprises a main part (112) and an outer cover (150), the outer cover (150) covering the main part (112) at least in a middle part area (180), wherein the main part (112) and the outer cover (150) are fixed to each other, the main part is made of thermoplastic (115) and the outer cover (150) is made of elastomeric material (151) and wherein the insulator body (110) comprises a weather shed (116), the weather shed (116) being formed by a projecting part (181) of the main part (112) which is covered by the cover (150).

Description

The present disclosure relates to a bushing and a liquid insulated electrical apparatus comprising the bushing. The electrical apparatus may be a transformer or a switchgear, for example. The present disclosure further relates to a method for manufacturing a bushing, in particular a method for manufacturing the bushing described herein.
A bushing, for example, enables a conductor to pass through a wall of an electrical apparatus, providing electrical insulation between the conductor and the wall.
It is desirable to provide a bushing that provides a reliable operation. It is further desirable to provide a method for manufacturing a bushing that is reliable and cost-effective.
Embodiments of the disclosure relate to a bushing. In particular, the bushing is configured for a liquid insulated electrical apparatus. Further embodiments of the disclosure relate to a liquid insulated electrical apparatus comprising the bushing. Further embodiments of the disclosure relate to a method for manufacturing a bushing, in particular a bushing of at least one of the embodiments described herein. Every feature described with respect to the bushing, the apparatus, and the method is also disclosed herein with respect to the other ones of the bushing, the apparatus, and the method, even if the respective feature is not explicitly mentioned in the context of the specific aspect.
The bushing comprises an electrical conductor. The bushing comprises an insulator body. The electrical conductor extends through the insulator body. The insulator body comprises a main part. The main part can also be referred to as "insulator core". For example, the main part comprises a hollow cylinder shape. The conductor extends through this hollow cylinder.
The insulator body comprises an outer cover. The outer cover covers the main part at least in a middle part area. The cover covers the outward facing portions of the main part. In particular, an inner side facing the conductor is not covered by the cover. The middle part area, for example, is the area between axial end sides of the main part. Axial end sides, for example, are not covered by the cover. For example, a majority of the outward facing portion of the main part is covered by the cover, for example more than 750, more than 80%, more than 90% or more than 950 of the outer surface of the main part exposed to air and/or arranged outside the apparatus is covered by the cover. Another part of the surface of the main part which is exposed to the insulating liquid inside the apparatus is also not covered by the cover.
The outer cover is fixed to the main part. The outer cover is fixed to the main part. The outer cover adheres firmly to the main part. The outer cover covers the main part at least partly. The outer cover houses the main part at least partly. The cover can also be referred to as housing or insulator housing. In particular, the cover covers a creepage length of the bushing when installed on the electrical apparatus.
The main part is made of thermoplastic. In particular, the thermoplastic material comprises a high elastic modulus and mechanical strength, even at elevated temperatures, and is resistant to thermal degradation. It is also resistant to chemical degradation, in particular by electric insulation liquids, for example by transformer oil and natural or synthetic esters.
For example, the thermoplastic material is at least one of polyether ether ketone (PEEK), polyphenylene sulfide (PPS), polyphthalamide (PPA), polyethersulfone (PES), polyetherimide (PEI), polyamide (PA), and semi-aromatic polyamide. For example, the main part and/or the projecting ribs comprise a glass fiber reinforcement. Thus, the thermoplastic material is reinforced by the glass fiber filler. For example, the thermoplastic material is one of the listed polymeric materials filled with glass fibers. In particular, ceramic materials can be omitted. The thermoplastic material enables the avoidance of ceramics for the main part.
The outer cover is made of elastomeric material. In particular, the elastomeric material is a rubber or comprises rubber. For example, the elastomeric material is silicone rubber or comprises silicone rubber. For example, the outer cover provides a hydrophobic surface. The outer surface of the outer cover does not easily collect contamination and is efficiently cleaned by rainwater during operation or in a cleaning procedure provided when servicing the bushing.
The elastomeric material for example is one of moldable or extrudable liquid silicone rubber, high consistency rubber, and high temperature vulcanization silicone rubber. For example, the curable elastomeric material 151 is applied in liquid form and then hardens to form the cover 150. The cover is made of silicone elastomer material resistant to degradation in outdoor environment. The elastomeric material is resistant to electric arc and to tracking and erosion and has a hydrophobic surface. The elastomeric material features the hydrophobicity recovery and hydrophobicity transfer properties, which minimizes leakage currents running along the surface of the insulator body in wet and polluted environments and reduce probability of surface discharges or electrical breakdown.
The insulator body comprises a weather shed. The weather shed is formed by a projecting part of the main part which is covered by the cover.
The weather shed increases the creepage length during operation. It also may reduce contamination of underlying parts during operation. The weather shed is made with the thermoplastic material of the main part and the elastomeric material of the cover. The cover is fixed to the main part such that firm adhesion is realized. Thus, during operation, an arc running along the interface between the cover and the main part can be avoided. The risk of a flashover making a shortcut to the long creepage length is reduced. A short and cost-efficient manufacturing process with a low material consumption can be realized. A thin wall structure of the thermoplastic material can be realized due to the material properties of the thermoplastic material. The thin wall structure of the thermoplastic material makes the time needed for heat transfer through the wall thickness short, in particular the time needed to cool down the molten thermoplastic material until it solidifies in the mold. The projecting part of the main part stabilizes the weather shed.
The weather shed is in particular not fully made out of elastomeric material but made out of the combination of thermoplastic material and elastomeric material. The shape of the weather shed is defined by the shape of the projecting part. In particular, the projecting part provides the mechanical characteristics the weather shed and the cover covers the surface of the insulator body exposed to the outdoor environment. The cover serves to provide desired properties to the surface of the weather shed exposed to an outdoor environment, for example a smooth outer surface, a resistance to tracking and erosion, a resistance to UV radiation, and/or a hydrophobic property of its surface.
The thin wall structure of the main part and the weather shed makes the creepage length large. A significant part of the creepage length runs in an area which is located below the weather shed and is therefore hardly accessible for rain or mist water, such that electrical insulation is improved.
According to an embodiment, the cover comprises a planar expansion. The cover comprises a thickness perpendicular to the planar expansion. The thickness is substantially uniform between end portions. For example, the thickness is uniform within a tolerance of 50, 25% or 300. For example, the thickness is constant and the same in most of the cover, for example in more than 750, more than 80%, more than 90% or more than 950 of the cover. In particular, a thickness of the cover transverse to an outer side of the main part is between 0.5 mm and 5 mm. At the end portions and/or in corners, the thickness may be different. For example, the cover is obliquely flanked at the end portions and/or thickened in corner portions. In particular, the cover is thick enough to cover the main part and provide the desired surface properties. In particular, the cover is not extra thick in specific places to form special elements, in particular the cover does not thicken to build a weather shed made of the elastomeric material alone.
According to an embodiment, the bushing comprises a chemical bond which fixes the cover and the main part together. The elastomer cover permanently adheres to the thermoplastic main part by the chemical bond, thus limiting possibility of water penetrating into the interface and reducing probability of electrical breakdown along the interface. The chemical bond is realized between the outer cover and the main part to connect the outer cover and the main part together. For example, the chemical bond is formed during curing of the elastomeric material during production. For example, silane-based agents that are chemically reactive both with the surface of the thermoplastic material and with the other components of the elastomeric material, in particular the silicone rubber mixture and/or other constituents of the curable elastomer composition forming the elastomeric material, in particular the curable silicone elastomer composition, are provided to establish the chemical bond. The chemical bond connects the cover and the main part together, such that the cover and the main part cannot be detached from each other without being destroyed. The chemical bond is a cohesive bond between the surfaces of the cover and the main part.
The combination of the use of the thermoplastic for the main part, the elastomeric material for the cover and the chemical bond to fix the main part and the cover to each other, for example makes the manufacturing process easier and faster. In particular, the thermoplastic has desired and preset surface properties directly after the molding process.
Self-adhesive elastomeric material in particular is suitable for low voltage usage. Faster manufacturing and low costs are realized to create a bond between the elastomeric material and the thermoplastic. For example, the bond might not be as strong as with the use of a separate primer but strong enough for the requirements and needs by a low voltage usage. In particular, the use of thermoplastic for the main part allows the use of self-adhesive elastomeric material, because these two materials bond together even without a separate primer.
According to an embodiment, the main part comprises two or more separate parts. The separate parts are stacked along a longitudinal axis of the conductor. It is also possible to provide the main part in one single piece. By providing the main part in one single piece, manufacturing and mounting of the bushing can be quick and easy. Providing the main part with two or more separate parts, for example, enables a greater freedom of design. Different functionalities can be realized in different parts of the two or more separate parts.
According to an embodiment, an upper part of the two parts is formed inclined downwards to overlap a lower part of the two parts, at least in part. For example, the weather shed is realized by the upper part. The upper part forms the weather shed which overlaps the lower part, such that the lower part is protected against rain and other contamination. The two or more separate parts of the main part are made of thermoplastic and covered with the cover made of elastomeric material. For example, all of the separate parts of the main part are made of thermoplastic and covered by the elastomeric material. For example, the main part is an injection molded body. For example, the two or more separate parts are each injection molded bodies. Injection molding realizes a simple, cost-effective and material-saving production of the main part. According to an embodiment, the projecting part of the main part is substantially covered by the cover on two opposing main sides. In particular, the projecting part comprises an upward-facing main side and an opposite downward-facing main side. Both main sides, as well as a connecting side that connects the two main sides, are covered by the cover.
According to an embodiment, the insulator body comprises an outer flange. The outer flange projects outwards from the main part for a coupling with a wall for the electrical apparatus. The outer flange is an integral part of the main part. The flange provides a mounting interface for the bushing to the electrical apparatus. For example, the bushing is fixed to the electrical apparatus at the outer flange.
According to an embodiment, the outer flange is configured to hold a gasket. This ensures that the gasket is reliably held in place during transport, installation and/or operation. The gasket reliably seals the bushing and the electrical apparatus against fluids.
According to an embodiment, a wall thickness of the main part is 10 mm or less. In particular, the wall thickness in most parts of the main part is 10 mm or less, for example 6 mm or less, transverse to the main extension of the main part which is axial in most parts and radial or inclined at the projecting part and/or the flange. A thin-walled, material-saving and quick-to-produce main part is realized.
According to an embodiment, the elastomeric material comprises a silicone rubber or consists of a silicone rubber. For example, the outer cover is made of a so-called curable liquid silicone rubber, in particular a self-adhesive silicone rubber containing chemical coupling agents able to form the chemical bond between the surface of the thermoplastic material and the cross-linked silicone rubber material. In particular, the elastomeric material is a solidified liquid silicone rubber or a self-adhesive liquid silicone rubber cured to the solid state.
In the case of self-adhesive silicone rubber, no addition primer or other auxiliary materials are necessary to form the chemical bond between the outer cover and the main bond. The chemical coupling agent is part of the elastomeric material and forms the chemical bond to the main part, in particular to the thermoplastic material of the main part. Thus, it is sufficient to apply the curable elastomeric material including the chemical coupling agent in a liquid state on the main part. The chemical bond is formed during curing of the elastomeric material to the solid state.
According to an embodiment, a primer layer is provided between the main part and the cover. The primer layer forms the chemical bond to the main part and forms a further chemical bond to the outer cover. The primer layer enables the use of an elastomeric material without a chemical coupling agent. The primer layer is applied on the surface of the main part and forms a chemical bond to the main part. The curable elastomeric material of the outer cover is applied on the primer layer and a further chemical bond between the primer layer and the outer cover is formed. Thus, the primer layer enables the fixing of the outer cover and the main part together by chemical bonds.
According to an embodiment, the liquid insulated electrical apparatus comprises the bushing according to one of the embodiments described herein or according to any combination of the described embodiments. The liquid insulated electrical apparatus comprises a wall in which the bushing is installed. The bushing enables the conductive path through the wall and provides an electrical insulation between the conductor and the wall.
The electrical apparatus may be a low voltage apparatus, a medium voltage apparatus and/or a high voltage apparatus. As an example, the electrical apparatus is a transformer or another electrical apparatus.
The electrical apparatus comprises a tank in which one or more electrical functional elements are located. For example, a winding, such as a transformer winding, may be located in the tank. The tank is filled by an insulating liquid.
According to an embodiment, the method for manufacturing a bushing comprises:

injecting thermoplastic into a first mold to form a main part of an insulator body for the bushing such that the main part comprises a projecting part,
applying an elastomeric material to at least a middle part area of an outer side of the main part, the middle part area including the projecting part, and thereby
forming a cover of the main part, which is fixed to the main part.

The projecting part of the main body is covered by the elastomeric material during production to form the weather shed out of the projecting part and the cover. Injection molding of the thermoplastic material enables a reliable, cost-effective and fast production of the main part. In particular, the thermoplastic is injected in molten state and cooled to a temperature below its melting point afterwards.
Forming the cover on the main part allows a simple and reliable realization of desired and/or preset surface properties like a smooth surface which is weather-resistant, resistant against contamination and/or hydrophobic. For example, the cover is formed using a liquid, curable elastomeric material, also referred to as elastomer composition, which is applied onto the surface of the main part and cured afterwards to form the cover.
For example, after the thermoplastic has been injected into the mold, it is cooled down below its melting temperature, which is high, typically higher than 150°C, before demolding and, according to embodiments, transferring to the second mold.
For example, the liquid silicone rubber, in order to initiate its curing, has to be heated up to an elevated temperature, typically above 100°C. When the liquid silicone rubber is injected onto that hot thermoplastic, the heat is transferred from the thermoplastic to the silicone rubber, which significantly reduces the total processing time.
For example, the thickness of the silicone rubber cover is small and uniform. This shortens the time of heat transfer to the silicone rubber needed to heat it up to the curing temperature.
Hereinafter, the bushing, the electrical apparatus and the method will be explained in more detail with reference to the drawings on the basis of exemplary embodiments. The accompanying figures are included to provide a further understanding. In the figures, elements of the same structure and/or functionality may be referred to by the same reference signs. It is to be understood that the embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale. Insofar as elements or components correspond to one another in terms of their function in different figures, the description thereof is not necessarily repeated for each of the following figures.

Figures 1 and 2 schematically show different embodiments of a bushing and an electrical apparatus, and
Figure 3 shows a flowchart of a method according to an embodiment.

The embodiment of Figure 1 in particular is applicable for low voltage bushings 100. The embodiment of Figure 2 in particular is applicable for medium voltage bushings 100. Ratings may cover AC or DC voltages. For example, a range from 0.1kV to 72.5kV, in particular from 1kV to 3.6kV, is referred to as low voltage. For example, a range from 3kV to 72.5kV is referred to as medium voltage (MV), in particular lager than 3.6 kV. For example, current rating is from 100 A to 10000 A.
Figures 1 and 2 each schematically show a vertical section of the bushing 100 according to different embodiments. In particular, the bushing 100 comprises a rotationally symmetrical and/or mirror-symmetrical shape.
The bushing 100 is shown installed in a wall 201 of an electrical apparatus 200. The electrical apparatus 200 for example is a liquid insulated electrical apparatus like a transformer or a reactor. An insulating liquid 103 is arranged in a tank which is bonded by a wall 201. The liquid 103 for example is a transformer oil or a natural or a synthetic ester.
The bushing 100 provides an electrical connection of the electrical apparatus 200 through the wall 201 from an outside to an inside. The wall 201 may be on earth potential or at least on an electrical potential that is potentially different from the potential of a conductor 101 of the bushing 100. An insulator body 110 of the bushing 100 provides an electrical insulation between the wall 201 and the electrical conductor 101.
The insulator body 110 surrounds the electrical conductor 101. The electrical conductor 101 extends elongated through the insulator body 110 along a longitudinal axis 102. A part of the insulator body 110 is exposed to the air environment, typically outdoor environment, and another part of the insulator body 110 is immersed in the insulating liquid 103 of the apparatus 200.
The insulator body 110 comprises a main part 112. The main part 112 comprises a hollow cylinder shape 113, at least in a part. The main part 112 is coaxially arranged with the electrical conductor 101. For example, a center of the hollow cylinder shape 113 is the longitudinal axis 102.
The insulator body 110 comprises an inner side 114 which faces the electrical conductor 101. The inner side 114 extends along the longitudinal axis 102.
The insulator body 110 comprises an outer side 129. The outer side 129 is arranged radially opposite the inner side 114. For example, the inner side 114 is in contact with the liquid 103 and the outer side 129 is not in contact with the liquid 103.
The main part 112 is made of a thermoplastic material 115. The main part 112 with the hollow cylinder shape 113 is, for example, manufactured by an injection molding process.
The insulator body 110 comprises an outer cover 150. The outer cover 150 comprises an elastomeric material 151 or consists of the elastomeric material 151. For example, the elastomeric material 151 is silicone rubber which provides a hydrophobic surface for the insulator body 110.
The elastomeric material 151 is chemically bonded to the thermoplastic material 115 of the main part 112. The chemical bond provides a cohesive connection between the elastomeric material 151 of the cover 150 and the thermoplastic material 115 of the main part 112. In particular, the connection cannot be detached non-destructively.
The elastomeric material 151 and the outer cover 150 provides a hydrophobicity recovery and hydrophobicity transfer properties, which make the hydrophobic nature of its surface persist during most of the time of operation of the bushing, also in polluted environments, thus minimizing leakage currents running along the surface of the main part 112 in wet conditions. Thus, the probability of a surface discharge and/or electrical breakdown is reduced by the cover 150. The process of hydrophobicity recovery, after an event rendering the silicone rubber surface less hydrophobic or even hydrophilic, such as activity of plasma generated by neighboring electric arc or an extreme rainfall of long duration, is described, for example, in D. Bodas and C. Khan-Malek, Sens. Actuators B: Chem. vol. 123, p. 368 (2007). The process of hydrophobicity transfer, i.e., transferring the hydrophobic properties of the silicone rubber onto the pollution layers accumulating on its surface during service of the insulator, is described, for example, in A. Hergert, et al., IEEE Trans. Dielectr. Electr. Insul., vol. 24, no. 2, p. 1057 (2017).
The elastomeric material 151 for example is one of moldable or extrudable liquid silicone rubber, high consistency rubber, and high temperature vulcanization silicone rubber. For example, the curable elastomeric material 151 is applied in liquid form and then hardens to form the cover 150.
Self-adhesive silicone rubber can be used to produce the outer cover 150. Without being bound to it, examples for self-adhesive silicone rubber are described in EP 0 497 349 , US 4,742,103 , EP 0 493 791 A1 , EP 0 497 349 B1 , US 5,595,826 , EP 0 875 536 B1 , US 6,743,515 B1 , US 2003/0236380 A1 , and US 2005/0089696A1 , the contents of which are hereby incorporated by reference. Other examples include SILASTIC^™ SA 9940 compositions from Dow Chemical Company, Silopren^™ LSR 2740 from Momentive Performance Materials Inc., or ELASTOSIL^® LR 3070 grades from Wacker Chemie AG. The self-adhesive silicone rubber contains chemical coupling agents to form the chemical bond between the outer side 129 of the thermoplastic material 115 of the main part 112 and the solidified silicone rubber. In particular, silane-based agents chemically reactive both with the surface of the thermoplastic material 115 and with the other components of the elastomeric material 151, in particular the silicone rubber mixture and/or other constituents of the curable elastomer composition forming the elastomeric material, in particular the curable silicone elastomer composition, are provided to establish the chemical bond.
At least a middle part area 180 of the outer side 129 of the main part 112 is covered by the cover 150. The middle part area 180 in particular comprises the outer side 129 between a vertical upward end at a holder 126 and the wall 201. Parts of the outer side 129 which could come in contact with the environment without the cover 150 are covered by the cover 150. In particular, the cover 150 is arranged at the outer side 129 in areas, where a creepage length 187 extends between the holder 126 and the wall 201. For example, the inner side 114 of the main part 112 which is in contact with the liquid 103 is not covered by the cover 150.
The holder 126 of the upper part 121 serves as a compression means for the conductor seal 140, while the external part of the upper part 121 serves as the weather shed 116 of the insulator body 110.
The main part 112 comprises a projecting part 181 or a plurality of projecting parts 181. The projecting parts 181 of the main part 112 are covered by the cover 150.
The projecting part 181 with the cover 150 thereon form a weather shed 116. The weather shed elongates the creepage length 187 and protects other parts of the insulator body 110 against contamination.
The cover 150 comprises a thickness 182 perpendicular to the outer side 129. The cover 150 covers the main part 112 in a planar manner and the thickness 182 is perpendicular to the planar extension of the cover 150. The cover 150 comprises in most parts the same thickness 182 within normal tolerances of for example 50 or less. For example, the thickness 182 is constant and the same in most of the cover 150. For example, the thickness 182 of the cover 150 transverse to the outer side 129 is between 0.5 mm and 5 mm. The thickness may be different in the corners, for example as connection 119 where an outer flange 118 is connected or at end portions 183, 184 of the cover 150. For example, the end portion 183 is the vertical end adjacent to the holder 126 and the second end portion 184 is the end adjacent to the wall 201.
To form the weather shed 116, the projecting part 181 is covered by the cover 150 on a first main side 185 which is facing away from the wall 201. The projecting part 181 is also covered by the cover 150 on a second main side 186 which is facing the wall 201.
The design and material of the insulator body 110 with the main part 112 allows a thin wall structure of the main part with a reduced wall thickness 124. For example, the wall thickness 124 comprises a value of 10 mm or less, for example 6 mm or less.
The insulator body 110 comprises the flange 118 which radially projects outwards from the outer side 129 of the main part 112. The flange 118 is configured to provide a mounting of the bushing 100 to the wall 201. A gasket 160 is arranged between the flange 118 and the wall 201 to provide a fluid-tight connection.
As shown in Figure 1, the main part 112 is provided by an upper part 121 and a separate lower part 122 according to embodiments. The lower part 122 comprises the hollow cylinder shape 113 and the flange 118. The upper part 121 is arranged on an end of the lower part 122 facing away from the wall 201 along the longitudinal axis 102.
The upper part 121 is inclined with respect to the longitudinal axis 102 and overlaps the lower part 122 in part. The upper part 121 forms the weather shed 116. The cover 150 covers the first main side 185 which faces away from the conductor 101 as well as the second main side 186 which faces the conductor 101. For example, areas of the upper part 121 directly adjacent to the lower part 122 or to a conductor seal 140 are not covered by the cover 150. In particular, those parts of the upper part 121 where the creepage length 187 extends are covered by the cover 150.
The outer side 129 facing away from the conductor 101 of the lower part 122 is covered by the cover 150. In addition, the flange 118, in particular on those parts facing away from the wall 201 and facing away from the conductor 101, is covered by the cover 150. Thus, the whole extension of the creepage length 187 between the holder 126 and the wall 201 is covered by the cover 150, except possibly a narrow gap 109 between the upper part 121 and the lower part 122. The gap 109 is small enough such that the creepage length 187 does not extend through the gap 109.
The upper part 121 is fixed to the conductor 101 by the holder 126. During manufacturing, the lower part 122 is arranged on the wall 201 such that the flange 118 is supported on the wall 201. Inside the tank, the conductor 101 is supported via an insulating support 107 at the wall 201. The conductor seal 140 is arranged on the conductor 101 and pressed vertically along the longitudinal axis 102 against a seal seat 125 of the lower part 122 by the upper part 121. This compression force is maintained by fixing the upper part 121 with the holder 126 at the conductor 101.
The transition between the upper part 121 and the lower part 122 at the gap 109 is sealed via the conductor seal 140.
Figure 2 schematically shows an embodiment with the main part 112 formed of one single piece. The main part 112 comprises two projecting parts 181 covered with the cover 150 to form two weather sheds 116. According to further embodiments, more than two weather sheds 216 or just one single weather shed 116 are provided.
A hood 128 is provided to press the conductor seal 140 against the seal seat 125 of the main part 112 and against the conductor 101. The hood 128 is fixed to the conductor 101. For example, the hood 128 comprises an electrically conductive material like a metal. Thus, the creepage length 187 extends between the hood 128 and the wall 201 or, as shown in Figure 2, a flange clamp 111 which is electrically conductive.
The insulator body 110 is fixed to the wall 201 by the flange clamp 111. The flange clamp is a separate part which is fixed to the wall 201, for example by a screw connection with the mounting element 123, and exerts a force on the flange 118. The flange 118 is fixed between the flange clamp 111 and the wall 201. The mounting element 123, for example is a threaded stud welded to the wall of the electrical apparatus and extending through the opening and a nut threaded on the stud holds the flange in place.
In the embodiment shown in Figure 2, the electrical conductor 101 extends only partly along the main part 112. An electrically conductive conductor extension 108 is electrically and mechanically connected with the conductor 101 and extends further longitudinally across the wall 201. For example, the conductor 108 is made from an electrically conductive metal. It is possible that a longer electrical conductor 101 which extends further across the wall 201 is provided and that the conductor extension 108 is omitted.
Figure 3 shows a flowchart of a method for manufacturing the bushing 100 according to an embodiment. In a first step 301, the molten thermoplastic material 115 is injected into a first mold to form the main part 112. In particular, the mold is designed such that the projecting part 181 is formed at the main part 112. It is also possible that the main part is formed by the injection molding process without the projecting part 181.
To form the bushing according to the embodiment of Figure 1, the step 301 comprises a plurality of first molds to form the upper part 121 and the lower part 122 of the main part 112 separately.
In a step 302, the curable elastomeric material 151 is applied to the outer side 129 of the main part 112, in particular to at least the middle part area 180 of the outer side 129. The curable elastomeric material is applied to the projecting part 181. In other words, a curable elastomer composition is applied, which, after curing to the solid state, forms the elastomeric material 151.
In particular, the main part is cooled below a given temperature value before step 302.
In a step 303, the cover 150 is formed by the elastomeric material 151 applied in step 302, for example by curing the elastomeric material to the solid state. For example, the cover 150 is fixed to the main part 112 by a chemical bond which is formed during step 303.
According to embodiments, step 302 comprises placing the main part 112 into a second mold and injecting the curable elastomeric material 151 into the second mold such that the curable elastomeric material 151 covers the outer side 129 at least in part. Thus, the cover 150 is made by an injection molding process. The insulator body 110 is manufactured with a two-component injection molding process.
Alternatively, step 302 comprises an extrusion of the curable elastomeric material 151 on the outer side 129 such that the curable elastomeric material 151 covers the outer side 129 at least in part.
For example, the step 302 comprises an application of the curable elastomeric material 151 which comprises a chemical coupling agent. The chemical coupling agent is provided to form the chemical bond during step 303 between the thermoplastic 115 and the elastomeric material 151.
For example, a so-called self-adhesive silicone rubber is applied during the step 302. The curable elastomeric material 151 applied during step 302, for example, is a so-called liquid silicone rubber containing the chemical coupling agent able to form the chemical bond between the surface of the thermoplastic material 115 and the cross-linked silicone rubber material of the elastomeric material 151. In this case, no additional primer is necessary. As part of the elastomeric material 151, the chemical coupling agent forms the chemical bond to the main part. Thus, it is sufficient to apply the elastomeric material including the chemical coupling agent in a liquid state on the main part 112. The chemical bond is formed during curing of the elastomeric material 151, in particular during curing of the curable elastomer composition to the solid state.
Alternatively, a primer is applied onto the outer side 129 during step 302 before applying the uncured elastomeric material 151. The elastomeric material 151 is applied onto the primer. The primer establishes the permanent chemical bonding between the thermoplastic material 115 and the elastomeric material 151. For example, the primer comprises constituents able to chemically react with the outer surface 129 of the thermoplastic material 115 and with the constituents of the reactive liquid silicone rubber mixture forming the cover 150.
The different features of the different embodiments according to Figures 1 to 3 can be combined with each other in any combination. The bushing 100 according to the different embodiments and the method for manufacturing the bushing 100 each provide a bushing 100 which is easy to manufacture, cost-effective and provides a reliable insulation. A short manufacturing process time and low material consumption is possible. The elastomeric material 151, in particular the cured self-adhesive silicone rubber, provides a desired smooth surface. A long creepage length 187 is realized by the weather shed 116 with a thermoplastic core formed by the projecting part 181 and the silicone housing formed by the cover 150. The self-adhesive liquid silicone rubber material provides a permanent chemical bond between the main part 112 and the cover 150. Thus, a reliable bushing 100 is provided.

Reference Signs

100 bushing
101 electrical conductor
102 longitudinal axis
103 liquid
107 support
108 conductor extension
109 gap
110 insulator body
111 flange clamp
112 main part
113 hollow cylinder shape
114 inner side
115 thermoplastic material
116 weather shed
118 outer flange
119 connection
121 upper part
122 lower part
123 mounting element
124 wall thickness
125 seal seat
126 holder
128 hood
129 outer side
140 conductor seal
150 outer cover
151 elastomeric material
160 gasket
180 middle part area
181 projecting part
182 thickness
183 first end portion
184 second end portion
185 first main side
186 second main side
187 creepage length
200 electrical apparatus
201 wall
301-303 method steps

Claims

A bushing (100) for a liquid-insulated electrical apparatus (200), the bushing (100) comprising an electrical conductor (101) and an insulator body (110) through which the electrical conductor (101) extends, wherein the insulator body (110) comprises a main part (112) and an outer cover (150), the outer cover (150) covering the main part (112) at least in a middle part area (180), wherein the main part (112) and the outer cover (150) are fixed to each other, the main part is made of thermoplastic (115) and the outer cover (150) is made of elastomeric material (151) and wherein the insulator body (110) comprises a weather shed (116), the weather shed (116) being formed by a projecting part (181) of the main part (112) which is covered by the cover (150).
The bushing of claim 1, wherein the cover (150) comprises a planar expansion and a thickness (182) perpendicular to the planar expansion, the thickness (182) being substantially uniform between end portions (183, 184).
The bushing of claim 2, wherein the thickness (182) of the cover (150) is between 0.5 mm and 5 mm.
The bushing of any of the preceding claims, comprising a chemical bond which fixes the cover (150) and the main part (112) together.
The bushing of any of the preceding claims, wherein the main part (112) comprises two or more separate parts (121, 122) stacked along a longitudinal axis (102) of the conductor (101) .
The bushing of claim 5, wherein an upper part (121) of the two parts (121, 122) is formed inclined downwards to overlap a lower part (122) of the two parts (121, 122) at least in part.
The bushing of any of the preceding claims, wherein the projecting part (181) of the main part (112) is substantially covered by the cover (150) on two opposing main sides (185, 186) .
The bushing of any of the preceding claims, the insulator body (110) comprises an outer flange (118) that projects radially outwards from the main part (112) for a coupling with a wall (210) of the electrical apparatus (200).
The bushing of claim 8, wherein the outer flange (118) is configured to hold a gasket (160).
The bushing of any of the preceding claims, wherein a wall thickness (124) of the main part (112) is 10 mm or less.
The bushing of any of the preceding claims, wherein the elastomeric material (151) comprises a silicone rubber.
The bushing of any of the preceding claims, wherein the cover (150) comprises a chemical coupling agent in the elastomeric material to form a chemical bond with the main part.
The bushing of any one of claims 1 to 11, comprising a primer layer between the main part (112) and the cover (150), wherein the primer layer forms a chemical bond to the main part (112) and a chemical bond to the cover (150).
A liquid-insulated electrical apparatus (200) comprising the bushing (100) according to any one of the preceding claims and a wall (201) in which the bushing (100) is installed.
A method for manufacturing a bushing (100), comprising:
- injecting thermoplastic (115) into a first mold to form a main part (112) of an insulator body (110) for the bushing (100), such that the main part (112) comprises a projecting part (181),

- applying an elastomeric material (151) to at least a middle part area (180) of an outer side (129) of the main part (112), the middle part area (180) including the projecting part (181), and thereby

- forming a cover (150) of the main part (112), which is fixed to the main part (112).