Bushing, electrical apparatus and method

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 part, the main part (122) is made of thermoplastic (115) and the external cover (150) is made of elastomeric material (151), wherein the elastomeric material (1 51) comprises a self-adhesive silicone rubber or consists of a self-adhesive silicone rubber, and wherein the main part (112) and the outer cover (150) are fixed to each other by a chemical bond.

Description

[0001] P2024,0265 WO N / P230255WO01 February26,2025 -1 - Description Bushing,electricalapparatusand methodThe present disclosure relates to a bushing and a l iquidinsulated electrical apparatus comprising the bushi ng. Theelectrical apparatus may be a transformer or a swit chgear,for example. The present disclosure further relates to amethod for manufacturing a bushing, in particular a methodformanufacturing the bushing described herein.A bushing, for example, enables a conductor to pass through awall of an electrical apparatus, providing electric alinsulation between the conductorand the wall.EP 1014388 A2 relates to a bushing insulator, whi chcomprises an insulating and supporting body which i nternallyaccommodates at least one conductor, a set of sheds beingprovided externally to the insulating and a support ing bodywhich ismade ofpolymericmaterial.CN 212694914 U relates to a bushing, which compri ses acopper rod, an inner rigid insulating layer, a grad ing ringand an insulating umbrella skirt, the inner rigid i nsulatinglayer is formed on the outer side of the copper rod in aninjection molding mode through thermoplastic or the rmosettingmaterials.SE 506172 C2 relates to an insulator. The insulato r consistsof a tube which is made from a thermoplastic weldab lematerial. A number of pre-fabricated bushings are a ppliedabout the tube. The bushings are made from a rubber -likematerial,such ase.g.silicone rubber. P2024,0265 WO N / P230255WO01 February26,2025 -2 - JP H09161576 A relatesto an insulatorofpolymer which iscomposed of a core part, a body in the form of a co pingprotruding from the core, and a rubber sheath layer having acertain thickness.GB 1281583 A relates to a polymeric electric insu latorsleeve,which comprisessintered particlesofpolytetrafluoroethylene, or neoprene, butyl or sili conerubber. Itisdesirable to provide a bushing thatprovides a reliableoperation. It is further desirable to provide a met hod formanufacturing a bushing that is reliable and cost-e ffective.Embodimentsofthe disclosure relate to a bushing. In particular,the bushing isconfigured fora liquid insulatedelectrical apparatus. Further embodiments of the di sclosurerelate to a liquid insulated electrical apparatus c omprisingthe bushing.Furtherembodimentsofthe disclosure relate toa method for manufacturing a bushing, in particular a bushingof at least one of the embodiments described herein . Everyfeature described with respectto the bushing,the apparatus,and the method is also disclosed herein with respec t to theother ones of the bushing, the apparatus, and the m ethod,even if the respective feature is not explicitly me ntioned inthe contextofthe specificaspect. The bushing comprisesan electricalconductor.The bushingcomprises an insulator body. The electrical conduct or extendsthrough the insulator body. The insulator body comp rises amain part. The main part can also be referred to as"insulator core". For example, the main part compri ses a P2024,0265 WO N / P230255WO01 February26,2025 -3 -hollow cylinder shape. The conductor extends throug h thishollow cylinder. In particular, the main part compr ises onesingle hollow cylinder.Forexample,the insulator bodyisarranged at a distance from the electrical conducto r and isnot in direct contact with the electrical conductor .For example, the main part is completely arranged a t adistance from the electrical conductor and is not i n directcontact with the electrical conductor. For example, the mainpart is arranged at least for the most part at a di stancefrom the electricalconductorand isnotin direct contactwith the electrical conductor. For example, a propo rtion of10% or less of the main part is in direct contact w ith theelectrical conductor along the longitudinal axis. F orexample,a portion of90% ormore ofthe main part isspacedfrom the electrical conductor along the longitudina l axis.According to some embodiments, a free space is betw een theelectrical conductor and the insulator body, in par ticularbetween the main part and the electrical conductor. The freespace is configured such that in an operational con dition oilor another liquid can circulate between the electri calconductor and the insulator body, in particular bet ween themain part and the electrical conductor. For example , duringuse, the oil is in direct contact with the electric alconductor and the main part. The oil is used for co oling, forexample. The free space enables a sufficiently goodcirculation of the oil between the electrical condu ctor andthe insulator body and thus enables an improved hea texchange.The insulator body comprises an outer cover. The ou ter covercovers the main part at least in a middle part area . The P2024,0265 WO N / P230255WO01 February26,2025 -4 -cover covers the outward facing portions of the mai n part. Inparticular, an inner side facing the conductor is n ot coveredby the cover. The middle part area, for example, is the areabetween axial end sides of the main part. Axial end sides,for example, are not covered by the cover. For exam ple, amajorityofthe outward facing portion ofthe main partiscovered by the cover, for example more than 75%, mo re than80%, more than 90% or more than 95% of the outer su rface ofthe main part exposed to air and / or arranged outsid e theapparatusiscovered bythe cover.Anotherpartof thesurface of the main part which is exposed to the in sulatingliquid inside the apparatusisalso notcovered by the cover.The outer cover is fixed to the main part. The oute r cover isfixed to the main part. The outer cover adheres fir mly to themain part.The outercovercoversthe main partat leastpartly. The outer cover houses the main part at lea st partly.The cover can also be referred to as housing or ins ulatorhousing. In particular, the cover covers a creepage length ofthe bushing when installed on the electrical appara tus.The main part is made of thermoplastic. In particul ar, thethermoplastic material comprises a high elastic mod ulus andmechanical strength, even at elevated temperatures, and isresistant to thermal degradation. It is also resist ant tochemical degradation, in particular by electric ins ulationliquids, for example by transformer oil and natural orsyntheticesters.For example, the thermoplastic material is at least one ofpolyether ether ketone (PEEK), polyphenylene sulfid e (PPS),polyphthalamide (PPA), polyethersulfone (PES), poly etherimide(PEI), polyamide (PA), and semi-aromatic polyamide. For P2024,0265 WO N / P230255WO01 February26,2025 -5 -example, the main part and / or the projecting ribs c omprise aglassfiberreinforcement.Thus,the thermoplastic materialis reinforced by the glass fiber filler. For exampl e, thethermoplastic material is one of the listed polymer icmaterialsfilled with glassfibers.In particular, ceramicmaterials can be omitted. The thermoplastic materia l enablesthe avoidance ofceramicsforthe main part.The outer cover is made of elastomeric material. Inparticular, the elastomeric material is a rubber or comprisesrubber. The elastomeric material is a self-adhesive siliconerubber or comprises a self-adhesive silicone rubber . Forexample, the outer cover provides a hydrophobic sur face. Theouter surface of the outer cover does not easily co llectcontamination and is efficiently cleaned by rainwat er duringoperation orin a cleaning procedure provided when servicing the bushing.The elastomeric material for example is one of mold able orextrudable liquid silicone rubber, high consistency rubber,and high temperature vulcanization silicone rubber. The coveris made of silicone elastomer material resistant todegradation in outdoor environment. The elastomeric materialis resistant to electric arc and to tracking and er osion andhas a hydrophobic surface. The elastomeric material featuresthe hydrophobicity recovery and hydrophobicity tran sferproperties, which minimizes leakage currents runnin g alongthe surface of the insulator body in wet and pollut edenvironments and reduce probability of surface disc harges orelectricalbreakdown.The bushing comprises a chemical bond which fixes t he coverand the main part together. The elastomer cover per manently P2024,0265 WO N / P230255WO01 February26,2025 -6 -adheres to the thermoplastic main part by the chemi cal bond,thus limiting possibility of water penetrating into theinterface and reducing probability of electrical br eakdownalong the interface.The chemicalbond isrealized betweenthe outer cover and the main part to connect the ou ter coverand the main part together. For example, the chemic al bond isformed during curing of the elastomeric material du ringproduction. For example, silane-based agents that a rechemicallyreactive both with the surface ofthethermoplastic material and with the other component s of theelastomeric material, in particular the silicone ru bbermixture and / or other constituents of the curable el astomercomposition forming the elastomeric material, in pa rticularthe curable silicone elastomer composition, are pro vided toestablish the chemical bond. The chemical bond conn ects thecover and the main part together, such that the cov er and themain part cannot be detached from each other withou t beingdestroyed. The chemical bond is a cohesive bond bet ween thesurfacesofthe coverand the main part.The combination of the use of the thermoplastic for the mainpart, the elastomeric material for the cover and th e chemicalbond to fix the main part and the cover to each oth er, forexample makesthe manufacturing processeasierand faster.Inparticular, the thermoplastic has desired and prese t surfacepropertiesdirectlyafterthe molding process.Self-adhesive elastomeric material in particular is suitablefor low voltage usage. Faster manufacturing and low costs arerealized to create a bond between the elastomeric m aterialand the thermoplastic.Forexample,the bond might notbe asstrong as with the use of a separate primer but str ong enoughfor the requirements and needs by a low voltage usa ge. In P2024,0265 WO N / P230255WO01 February26,2025 -7 -particular, the use of thermoplastic for the main p art allowsthe use of self-adhesive elastomeric material, beca use thesetwo materials bond together even without a separate primer.The elastomericmaterialcomprisesa self-adhesive siliconerubber or consists of a self-adhesive silicone rubb er. Forexample, the outer cover is made of a so-called cur ableliquid silicone rubber, in particular a self-adhesi vesilicone rubber containing chemical coupling agents able toform the chemicalbond between the surface ofthethermoplastic material and the cross-linked silicon e rubbermaterial. In particular, the elastomeric material i s asolidified liquid silicone rubber or a self-adhesiv e liquidsilicone rubbercured to the solid state.In the case of self-adhesive silicone rubber, no ad ditionalprimer or other auxiliary materials are necessary t o form thechemicalbond between the outercoverand the main bond.The chemicalcoupling agentispartofthe elastomeric materialand forms the chemical bond to the main part, in pa rticularto the thermoplastic material of the main part. Thu s, it issufficient to apply the curable elastomeric materia lincluding the chemical coupling agent in a liquid s tate onthe main part. The chemical bond is formed during c uring ofthe elastomericmaterialto the solid state.According to an embodiment, the cover comprises a p lanarexpansion. The cover comprises a thickness perpendi cular tothe planar expansion. The thickness is substantiall y uniformbetween end portions. For example, the thickness is uniformwithin a tolerance of5%,25% or30%.Forexample, thethickness is constant and the same in most of the c over, forexample in more than 75%,more than 80%,more than 90% or P2024,0265 WO N / P230255WO01 February26,2025 -8 -more than 95% of the cover. In particular, a thickn ess of thecovertransverse to an outerside ofthe main part isbetween0.5 mm and 5 mm. At the end portions and / or in corn ers, thethicknessmaybe different.Forexample,the cover isobliquely flanked at the end portions and / or thicke ned incornerportions.In particular,the coveristhick enough tocover the main part and provide the desired surfaceproperties. In particular, the cover is not extra t hick inspecific places to form special elements, in partic ular thecover does not thicken to build a weather shed made of theelastomericmaterialalone.According to an embodiment, a wall thickness of the main partis 10 mm or less. In particular, the wall thickness in mostparts of the main part is 10 mm or less, for exampl e 6 mm orless,transverse to the main extension ofthe main partwhichis axial in most parts and radial or inclined at th eprojecting part. A thin-walled, material-saving and quick-to-produce main partisrealized.According to an embodiment, the insulator body comp rises aweather shed. For example, the weather shed is form ed by aprojecting part of the main part which is covered b y thecover.The weather shed increases the creepage length duri ngoperation. It also may reduce contamination of unde rlyingparts during operation. The weather shed is made wi th thethermoplastic material of the main part and the ela stomericmaterial of the cover. The cover is fixed to the ma in partsuch that firm adhesion is realized. Thus, during o peration,an arcrunning between the coverand the main part can be avoided.The riskofa flashovermaking a shortcut to the P2024,0265 WO N / P230255WO01 February26,2025 -9 -long creepage length is reduced. A short and cost-e fficientmanufacturing process with a low material consumpti on can berealized. A thin wall structure of the thermoplasti c materialcan be realized due to the material properties of t hethermoplasticmaterial.The thin wallstructure of thethermoplastic material makes the time needed for he attransfer through the wall thickness short, in parti cular thetime needed to cool down the molten thermoplastic m aterialuntil it solidifies in the mold. The projecting par t of themain partstabilizesthe weathershed.The weather shed is in particular not fully made ou t ofelastomeric material but made out of the combinatio n ofthermoplastic material and elastomeric material. Th e shape ofthe weather shed is defined by the shape of the pro jectingpart. In particular, the projecting part provides t hemechanical characteristics the weather shed and the covercovers the surface of the insulator body exposed to theoutdoor environment. The cover serves to provide de siredproperties to the surface of the weather shed expos ed to anoutdoor environment, for example a smooth outer sur face, aresistance to tracking and erosion, a resistance to UVradiation, and / or a hydrophobic property of its sur face.The thin wall structure of the main part and the we ather shedmakes the creepage length large. A significant part of thecreepage length runs in an area which is located be low theweather shed and is therefore hardly accessible for rain ormist water, such that electrical insulation is impr oved.According to an embodiment,the projecting partof the mainpart is substantially covered by the cover on two o pposingmain sides. In particular, the projecting part comp rises an P2024,0265 WO N / P230255WO01 February26,2025 -10 -upward-facing main side and an opposite downward-fa cing mainside. Both main sides, as well as a connecting side thatconnects the two main sides, are covered by the cov er.According to an embodiment, the main part comprises two ormore separate parts. The separate parts are stacked along alongitudinal axis of the conductor. It is also poss ible toprovide the main part in one single piece. By provi ding themain part in one single piece, manufacturing and mo unting ofthe bushing can be quick and easy. Providing the ma in partwith two or more separate parts, for example, enabl es agreater freedom of design. Different functionalitie s can berealized in different parts of the two or more sepa rateparts.According to an embodiment, an upper part of the tw o parts isformed inclined downwards to overlap a lower part o f the twoparts, at least in part. For example, the weather s hed isrealized by the upper part. The upper part forms th e weathershed which overlaps the lower part, such that the l ower partisprotected againstrain and othercontamination. The two or more separate partsofthe main partare made ofthermoplastic and covered with the cover made of el astomericmaterial. For example, all of the separate parts of the mainpart are made of thermoplastic and covered by the e lastomericmaterial. For example, the main part is an injectio n moldedbody. For example, the two or more separate parts a re eachinjection molded bodies. Injection molding realizes a simple,cost-effective and material-saving production of th e mainpart.According to embodiments, the insulator body compri ses anouter flange. The outer flange projects outwards fr om the P2024,0265 WO N / P230255WO01 February26,2025 -11 -main part for a coupling with a wall for the electr icalapparatus.The outerflange isan integralpartof the main part.The flange providesa mounting interface for thebushing to the electrical apparatus. For example, t he bushingis fixed to the electrical apparatus at the outer f lange.According to an embodiment, the outer flange is con figured tohold a gasket. This ensures that the gasket is reli ably heldin place during transport, installation and / or oper ation. Thegasket reliably seals the bushing and the electrica lapparatusagainstfluids.According to an embodiment, the liquid insulated el ectricalapparatus comprises the bushing according to one of theembodiments described herein or according to any co mbinationofthe described embodiments.The liquid insulated electrical apparatuscomprisesa wallin which the bushing is installed.The bushing enables the conductive path through the wall andprovides an electrical insulation between the condu ctor andthe wall.The electrical apparatus may be a low voltage appar atus, amedium voltage apparatus and / or a high voltage appa ratus. Asan example, the electrical apparatus is a transform er oranotherelectricalapparatus. The electricalapparatuscomprisesa tankin which one ormore electrical functional elements are located. Fo r example,a winding, such as a transformer winding, may be lo cated inthe tank. The tank is filled by an insulating liqui d.According to an embodiment, the method for manufact uring abushing comprises: P2024,0265 WO N / P230255WO01 February26,2025 -12 -- injecting thermoplastic into a first mold to form a mainpartofan insulatorforthe bushing,- applying an elastomeric material to an outer side of themain part, wherein the elastomeric material (151) c omprises aself-adhesive liquid silicone rubber or consists of a self-adhesive liquid silicone rubber,and thereby -forming a coverofthe main part,which isfixed to the main partbya chemicalbond.The main body is covered by the elastomeric materia l duringproduction to form the cover.Injection molding of thethermoplastic material enables a reliable, cost-eff ective andfast production of the main part. Forming the cover on themain partallowsa simple and reliable realization ofdesiredand / or preset surface properties like a smooth surf ace whichis weather-resistant, resistant against contaminati on and / orhydrophobic. The chemical bond realizes a stable an d reliableconnection between the elastomeric material and thethermoplastic. The connection is fast, simple and e fficientto manufacture.In particular, the thermoplastic is injected in mol ten stateand cooled to a temperature below its melting pointafterwards.Forexample,the coverisformed using a liquid,curable elastomeric material, also referred to as e lastomercomposition, which is applied onto the surface of t he mainpartand cured afterwardsto form the cover.According to an embodiment, applying the elastomeri c materialcomprises:- placing the main part into a second mold and inje cting theelastomeric material into the second mold such that theelastomeric material covers the outer side of the m ain part P2024,0265 WO N / P230255WO01 February26,2025 -13 -at least in part. Thus, the insulator body with the chemicalbond is manufactured with a two-component injection moldingprocess.According to an alternative embodiment, applying th eelastomericmaterialcomprises:- extruding the elastomeric material on the outer s ide of themain part such that the elastomeric material covers the outerside atleastin part.The elastomericmaterialis extrudedaround the surface of the main part to form the cov er.The method comprises applying the elastomeric mater ial whichcomprises a chemical coupling agent. The elastomeri c materialwhich comprises a liquid silicone rubber or consist s of aliquid silicone rubberisapplied.The elastomeric materialwhich comprises a self-adhesive liquid silicone rub ber orconsistsofa self-adhesive liquid silicone rubber isapplied. In this case, no additional primer is nece ssary. Aspart of the elastomeric material, the chemical coup ling agentformsthe chemicalbond to the main part.Thus,it issufficient to apply the elastomeric material includ ing thechemical coupling agent in a liquid state on the ma in part.The chemical bond is formed during curing of the el astomericmaterial to the solid state. An easy and fast produ ction ofthe insulatorbodyispossible.For example, after the thermoplastic has been injec ted intothe mold, it is cooled down below its melting tempe rature,which ishigh,typicallyhigherthan 150°C,before demolding and,according to embodiments,transferring to the second mold. P2024,0265 WO N / P230255WO01 February26,2025 -14 -For example, the liquid silicone rubber, in order t o initiateits curing, has to be heated up to an elevated temp erature,typically above 100°C. When the liquid silicone rub ber isinjected onto that hot thermoplastic, the heat is t ransferredfrom the thermoplastic to the silicone rubber, whic hsignificantlyreducesthe totalprocessing time.For example, the thickness of the silicone rubber c over issmall and uniform. This shortens the time of heat t ransfer tothe silicone rubber needed to heat it up to the cur ingtemperature. Hereinafter,the bushing,the electricalapparatus and themethod will be explained in more detail with refere nce to thedrawings on the basis of exemplary embodiments. Theaccompanying figures are included to provide a furt herunderstanding. In the figures, elements of the same structureand / or functionality may be referred to by the same referencesigns.Itisto be understood thatthe embodiments shown inthe figures are illustrative representations and ar e notnecessarilydrawn to scale.Insofaraselementsor componentscorrespond to one another in terms of their functio n indifferent figures, the description thereof is not n ecessarilyrepeated foreach ofthe following figures.Figures 1 and 2 schematically show different embodi ments of abushing and an electricalapparatus,andFigure 3 shows a flowchart of a method according to anembodiment.The embodiment of Figure 1 in particular is applica ble forlow voltage bushings100.The embodimentofFigure 2 in P2024,0265 WO N / P230255WO01 February26,2025 -15 -particular is applicable for medium voltage bushing s 100.Ratings may cover AC or DC voltages. For example, a rangefrom 0.1kV to 72.5kV, in particular from 1kV to 3.6 kV, isreferred to as low voltage. For example, a range fr om 3kV to72.5kV is referred to as medium voltage (MV), in pa rticularlager than 3.6 kV. For example, current rating is f rom 100 Ato 10000 A. Figures1 and 2 each schematicallyshow a vertical section ofthe bushing 100 according to different embodiments. Inparticular, the bushing 100 comprises a rotationall ysymmetricaland / ormirror-symmetricalshape.The bushing 100 is shown installed in a wall 201 of anelectricalapparatus200.The electricalapparatus 200 for example isa liquid insulated electricalapparatus like a transformerora reactor.An insulating liquid 103 isarranged in a tank which is bonded by a wall 201. T he liquid103 for example is a transformer oil 195 or a natur al or asyntheticester.The bushing 100 provides an electrical connection o f theelectricalapparatus200 through the wall201 from an outsideto an inside. The wall 201 may be on earth potentia l or atleast on an electrical potential that is potentiall ydifferentfrom the potentialofa conductor101 of thebushing 100. An insulator body 110 of the bushing 1 00providesan electricalinsulation between the wall 201 and the electricalconductor101.The insulator body 110 surrounds the electrical con ductor101. The electrical conductor 101 extends elongated throughthe insulator body 110 along a longitudinal axis 10 2. A part P2024,0265 WO N / P230255WO01 February26,2025 -16 -of the insulator body 110 is exposed to the air env ironment,typicallyoutdoorenvironment,and anotherpartof theinsulator body 110 is immersed in the insulating li quid 103ofthe apparatus200.The insulator body 110 comprises a main part 112. T he mainpart112 comprisesa hollow cylindershape 113,at leastin a part.The main part112 iscoaxiallyarranged with the electricalconductor101.Forexample,a centerof the hollow cylindershape 113 isthe longitudinalaxis102. The insulatorbody110 comprisesan innerside 114 which facesthe electricalconductor101.The innerside 114 extendsalong the longitudinalaxis102.The inner side 114 is arranged at a distance to theelectrical conductor 101, such that a free space 19 0 isprovided between the insulator body 110 and the ele ctricalconductor101.The innerside 114,which facesthe electricalconductor 101, is arranged spaced apart from the el ectricalconductor 101. The inner side 114 and the electrica lconductor 101 are not in direct contact with each o ther. Inparticular,the free space 190 isprovided between the main part112 and the electricalconductor101.The oil 195 oranother liquid 103 which is provided inside the ele ctricalapparatus 200 for cooling and / or insulation can cir culatebetween the insulator body 110 and the electrical c onductor101 in the free space 190, in particular between th e innerside 114 and the electrical conductor 101. The free space 190allows good heat exchange between the conductor 101 and theoil 195 as the oil 195 can circulate around the ele ctricalconductor101 in the free space 190. P2024,0265 WO N / P230255WO01 February26,2025 -17 -The insulator body 110 comprises an outer side 129. The outerside 129 is arranged radially opposite the inner si de 114.Forexample,the innerside 114 isin contactwith the liquid103 and the outer side 129 is not in contact with t he liquid103.The main part 112 is made of a thermoplastic materi al 115.The main part 112 with the hollow cylinder shape 11 3 is, forexample, manufactured by an injection molding proce ss.In particular, the insulator body 110 comprises one singlehollow cylindrical sleeve 113. For example, the ins ulatorbody 110 comprises no additional second sleeve whic h is madefrom thermoplastic,which iscoaxiallyarranged to the sleeve113. In particular, the main part 112 comprises one singlehollow cylindrical sleeve 113 made from thermoplast ic 115.The insulator body 110 comprises an outer cover 150 . Theouter cover 150 comprises an elastomeric material 1 51 orconsists of the elastomeric material 151. For examp le, theelastomeric material 151 is silicone rubber which p rovides ahydrophobicsurface forthe insulatorbody110.The elastomeric material 151 is chemically bonded t o thethermoplastic material 115 of the main part 112. Th e chemicalbond provides a cohesive connection between the ela stomericmaterial 151 of the cover 150 and the thermoplastic material115 of the main part 112. In particular, the connec tioncannotbe detached non-destructively.The elastomeric material 151 and the outer cover 15 0 providesa hydrophobicity recovery and hydrophobicity transf erproperties, which make the hydrophobic nature of it s surface P2024,0265 WO N / P230255WO01 February26,2025 -18 -persist during most of the time of operation of the bushing,also in polluted environments, thus minimizing leak agecurrents running along the surface of the main part 112 inwetconditions.Thus,the probabilityofa surface dischargeand / or electrical breakdown is reduced by the cover 150. Theprocessofhydrophobicityrecovery,afteran event renderingthe silicone rubber surface less hydrophobic or eve nhydrophilic, such as activity of plasma generated b yneighboring electricarcoran extreme rainfallof longduration, is described, for example, in D. Bodas an d C. Khan-Malek, Sens. Actuators B: Chem. vol. 123, p. 368 (2 007). Theprocess of hydrophobicity transfer, i.e., transferr ing thehydrophobicpropertiesofthe silicone rubberonto thepollution layers accumulating on its surface during serviceofthe insulator,isdescribed,forexample,in A. Hergert, etal.,IEEE Trans.Dielectr.Electr.Insul.,vol. 24,no.2, p.1057 (2017). The elastomericmaterial151 forexample isone of moldableor extrudable liquid silicone rubber, high consiste ncyrubber, and high temperature vulcanization silicone rubber.For example, the curable elastomeric material 151 i s appliedin liquid form and then hardens to form the cover 1 50.Self-adhesive silicone rubber can be used to produc e theouter cover 150. Without being bound to it, example s forself-adhesive silicone rubber are described in EP 0 497349,US 4,742,103,EP 0493791 A1,EP 0497349 B1,US 5,595,826,EP 0875536 B1, US 6,743,515 B1, US 2003 / 0236380 A 1, and US2005 / 0089696A1, the contents of which are hereby in corporatedby reference. Other examples include SILASTIC™ SA 9 940compositions from Dow Chemical Company, Silopren™ L SR 2740from Momentive Performance Materials Inc., or ELAST OSIL® LR P2024,0265 WO N / P230255WO01 February26,2025 -19 -3070 grades from Wacker Chemie AG. The self-adhesiv e siliconerubber contains chemical coupling agents to form th e chemicalbond between the outer side 129 of the thermoplasti c material115 of the main part 112 and the solidified silicon e rubber.In particular, silane-based agents chemically react ive bothwith the surface ofthe thermoplasticmaterial115 and withthe other components of the elastomeric material 15 1, inparticular the silicone rubber mixture and / or otherconstituents of the curable elastomer composition f orming theelastomeric material, in particular the curable sil iconeelastomer composition, are provided to establish th e chemicalbond.At least a middle part area 180 of the outer side 1 29 of themain part 112 is covered by the cover 150. The midd le partarea 180 in particular comprises the outer side 129 between avertical upward end at a holder 126 and the wall 20 1. Partsof the outer side 129 which could come in contact w ith theenvironment without the cover 150 are covered by th e cover150. In particular, the cover 150 is arranged at th e outerside 129 in areas, where a creepage length 187 exte ndsbetween the holder 126 and the wall 201. For exampl e, theinner side 114 of the main part 112 which is in con tact withthe liquid 103 isnotcovered bythe cover150.The holder 126 of the upper part 121 serves as a co mpressionmeans for the conductor seal 140, while the externa l part ofthe upper part 121 serves as the weather shed 116 o f theinsulatorbody110.The main part 112 comprises a projecting part 181 o r aplurality of projecting parts 181. The projecting p arts 181ofthe main part112 are covered bythe cover150. P2024,0265 WO N / P230255WO01 February26,2025 -20 - The projecting part181 with the cover150 thereon form aweather shed 116. The weather shed elongates the cr eepagelength 187 and protects other parts of the insulato r body 110againstcontamination.The cover 150 comprises a thickness 182 perpendicul ar to theouterside 129.The cover150 coversthe main part 112 in aplanar manner and the thickness 182 is perpendicula r to theplanar extension of the cover 150. The cover 150 co mprises inmost parts the same thickness 182 within normal tol erances offorexample 5% orless.Forexample,the thickness 182 isconstant and the same in most of the cover 150. For example,the thickness 182 of the cover 150 transverse to th e outerside 129 isbetween 0.5 mm and 5 mm.The thickness maybedifferent in the corners, for example as connection 119 wherean outer flange 118 is connected or at end portions 183, 184ofthe cover150.Forexample,the end portion 183 isthevertical end adjacent to the holder 126 and the sec ond endportion 184 isthe end adjacentto the wall201.To form the weather shed 116, the projecting part 1 81 iscovered by the cover 150 on a first main side 185 w hich isfacing awayfrom the wall201.The projecting part 181 isalso covered by the cover 150 on a second main side 186 whichisfacing the wall201.The design and material of the insulator body 110 w ith themain part 112 allows a thin wall structure of the m ain partwith a reduced wall thickness 124. For example, the wallthickness 124 comprises a value of 10 mm or less, f or example6 mm orless. P2024,0265 WO N / P230255WO01 February26,2025 -21 -The insulator body 110 comprises the flange 118 whi chradiallyprojectsoutwardsfrom the outerside 129 ofthemain part 112. The flange 118 is configured to prov ide amounting of the bushing 100 to the wall 201. A gask et 160 isarranged between the flange 118 and the wall 201 to provide afluid-tightconnection.As shown in Figure 1, the main part 112 is provided by anupper part 121 and a separate lower part 122 accord ing toembodiments. The lower part 122 comprises the hollo w cylindershape 113 and the flange 118. The upper part 121 is arrangedon an end of the lower part 122 facing away from th e wall 201along the longitudinalaxis102. The upperpart121 isinclined with respectto thelongitudinal axis 102 and overlaps the lower part 1 22 inpart. The upper part 121 forms the weather shed 116 . Thecover 150 covers the first main side 185 which face s awayfrom the conductor 101 as well as the second main s ide 186which faces the conductor 101. For example, areas o f theupperpart121 directlyadjacentto the lowerpart 122 ortoa conductor seal 140 are not covered by the cover 1 50. Inparticular, those parts of the upper part 121 where thecreepage length 187 extends are covered by the cove r 150.The outer side 129 facing away from the conductor 1 01 of thelower part 122 is covered by the cover 150. In addi tion, theflange 118, in particular on those parts facing awa y from thewall 201 and facing away from the conductor 101, is coveredbythe cover150.Thus,the whole extension ofthe creepage length 187 between the holder126 and the wall201 iscovered bythe cover150,exceptpossiblya narrow gap 109 between the upperpart121 and the lowerpart122.The gap 109 is P2024,0265 WO N / P230255WO01 February26,2025 -22 -small enough such that the creepage length 187 does notextend through the gap 109.The upper part 121 is fixed to the conductor 101 by theholder 126. During manufacturing, the lower part 12 2 isarranged on the wall 201 such that the flange 118 i ssupported on the wall 201. Inside the tank, the con ductor 101is supported via an insulating support 107 at the w all 201.The conductor seal 140 is arranged on the conductor 101 andpressed verticallyalong the longitudinalaxis102 againstaseal seat 125 of the lower part 122 by the upper pa rt 121.Thiscompression force ismaintained byfixing the upperpart 121 with the holder126 atthe conductor101.The transition between the upper part 121 and the l ower part122 at the gap 109 is sealed via the conductor seal 140.Figure 2 schematically shows an embodiment with the main part112 formed of one single piece. The main part 112 c omprisestwo projecting parts 181 covered with the cover 150 to formtwo weather sheds 116. According to further embodim ents, morethan two weather sheds 216 or just one single weath er shed116 are provided. A hood 128 isprovided to pressthe conductorseal 140 againstthe sealseat125 ofthe main part112 and againstthe conductor 101. The hood 128 is fixed to the con ductor101. For example, the hood 128 comprises an electri callyconductive material like a metal. Thus, the creepag e length187 extends between the hood 128 and the wall 201 o r, asshown in Figure 2, a flange clamp 111 which is elec tricallyconductive. P2024,0265 WO N / P230255WO01 February26,2025 -23 - The insulatorbody110 isfixed to the wall201 by the flangeclamp 111. The flange clamp is a separate part whic h is fixedto the wall201,forexample bya screw connection with themounting element 123, and exerts a force on the fla nge 118.The flange 118 is fixed between the flange clamp 11 1 and thewall201.The mounting element123,forexample is a threadedstud welded to the wall of the electrical apparatus andextending through the opening and a nut threaded on the studholdsthe flange in place.In the embodiment shown in Figure 2, the electrical conductor101 extends only partly along the main part 112. Anelectricallyconductive conductorextension 108 iselectrically and mechanically connected with the co nductor101 and extends further longitudinally across the w all 201.For example, the conductor 108 is made from an elec tricallyconductive metal. It is possible that a longer elec tricalconductor 101 which extends further across the wall 201 isprovided and that the conductor extension 108 is om itted.Figure 3 shows a flowchart of a method for manufact uring thebushing 100 according to an embodiment.In a first step 301,the molten thermoplastic material 115 is injected i nto afirst mold to form the main part 112. In particular , the moldis designed such that the projecting part 181 is fo rmed atthe main part 112. It is also possible that the mai n part isformed by the injection molding process without theprojecting part181. To form the bushing according to the embodimentof Figure 1,the step 301 comprises a plurality of first molds t o form theupper part 121 and the lower part 122 of the main p art 112separately. P2024,0265 WO N / P230255WO01 February26,2025 -24 -In a step 302, the curable elastomeric material 151 isapplied to the outer side 129 of the main part 112, inparticularto atleastthe middle partarea 180 of the outerside 129. The curable elastomeric material is appli ed to theprojecting part 181. In other words, a curable elas tomercomposition isapplied,which,aftercuring to the solid state,formsthe elastomericmaterial151.In particular, the main part is cooled below a give ntemperature value before step 302.In a step 303, the cover 150 is formed by the elast omericmaterial 151 applied in step 302, for example by cu ring theelastomeric material to the solid state. For exampl e, thecover 150 is fixed to the main part 112 by a chemic al bondwhich isformed during step 303.According to embodiments, step 302 comprises placin g the mainpart 112 into a second mold and injecting the curab leelastomericmaterial151 into the second mold such thatthecurable elastomeric material 151 covers the outer s ide 129 atleast in part. Thus, the cover 150 is made by an in jectionmolding process. The insulator body 110 is manufact ured witha two-componentinjection molding process.Alternatively, step 302 comprises an extrusion of t he curableelastomeric material 151 on the outer side 129 such that thecurable elastomeric material 151 covers the outer s ide 129 atleastin part. Forexample,the step 302 comprisesan application ofthe curable elastomericmaterial151 which comprisesa chemical P2024,0265 WO N / P230255WO01 February26,2025 -25 -coupling agent. The chemical coupling agent is prov ided toform the chemicalbond during step 303 between thethermoplastic 115 and the elastomeric material 151.For example, a so-called self-adhesive silicone rub ber isapplied during the step 302. The curable elastomeri c material151 applied during step 302, for example, is a so-c alledliquid silicone rubber containing the chemical coup ling agentable to form the chemicalbond between the surface ofthethermoplastic material 115 and the cross-linked sil iconerubber material of the elastomeric material 151. In thiscase, no additional primer is necessary. As part of theelastomeric material 151, the chemical coupling age nt formsthe chemical bond to the main part. Thus, it is suf ficient toapply the elastomeric material including the chemic alcoupling agent in a liquid state on the main part 1 12. Thechemical bond is formed during curing of the elasto mericmaterial 151, in particular during curing of the cu rableelastomercomposition to the solid state.Alternatively, a primer is applied onto the outer s ide 129during step 302 before applying the uncured elastom ericmaterial 151. The elastomeric material 151 is appli ed ontothe primer. The primer establishes the permanent ch emicalbonding between the thermoplasticmaterial115 and theelastomeric material 151. For example, the primer c omprisesconstituents able to chemically react with the oute r surface129 ofthe thermoplasticmaterial115 and with theconstituents of the reactive liquid silicone rubber mixtureforming the cover150.The different features of the different embodiments accordingto Figures 1 to 3 can be combined with each other i n any P2024,0265 WO N / P230255WO01 February26,2025 -26 -combination. The bushing 100 according to the diffe rentembodiments and the method for manufacturing the bu shing 100each provide a bushing 100 which is easy to manufac ture,cost-effective and providesa reliable insulation. A shortmanufacturing process time and low material consump tion ispossible. The elastomeric material 151, in particul ar thecured self-adhesive silicone rubber, provides a des iredsmooth surface. A long creepage length 187 is reali zed by theweather shed 116 with a thermoplastic core formed b y theprojecting part 181 and the silicone housing formed by thecover 150. The self-adhesive liquid silicone rubber materialprovides a permanent chemical bond between the main part 112and the cover150.Thus,a reliable bushing 100 is provided.

[0002] P2024,0265 WO N / P230255WO01 February26,2025 -27 - Reference Signs 100 bushing 101 electricalconductor 102 longitudinalaxis 103 liquid 107 support 108 conductorextension 109 gap 110 insulatorbody 111 flange clamp 112 main part 113 hollow cylindershape 114 innerside 115 thermoplasticmaterial 116 weathershed 118 outerflange 119 connection 121 upperpart 122 lowerpart 123 mounting element 124 wallthickness 125 sealseat 126 holder 128 hood 129 outerside 140 conductorseal 150 outercover 151 elastomericmaterial 160 gasket 180 middle partarea 181 projecting part 182 thickness P2024,0265 WO N / P230255WO01 February26,2025 -28 - 183 firstend portion 184 second end portion 185 firstmain side 186 second main side 187 creepage length 190 free space 195 oil 200 electricalapparatus 201 wall 301-303 method steps

Claims

P2024,0265 WO N / P230255WO01 February26,2025 -29 - Claims1. A bushing (100) for a liquid-insulated electrica lapparatus(200),the bushing (100)comprisingan electrical conductor (101) and an insulator body (110)through which the electrical conductor (101) extend s, whereinthe insulator body (110) comprises a main part (112 ) and anouter cover (150), the outer cover (150) covering t he mainpart (112) at least in part, the main part (122) is made ofthermoplastic (115) and the external cover (150) is made ofelastomeric material (151), wherein the elastomeric material(151)comprisesa self-adhesive silicone rubberor consistsof a self-adhesive silicone rubber, and wherein the main part(112) and the outer cover (150) are fixed to each o ther by achemicalbond. 2.The bushing ofthe preceding claim,wherein the cover (150)comprisesa planarexpansion and a thickness (182)perpendicular to the planar expansion, the thicknes s (182)being substantially uniform between end portions (1 83, 184).

3. The bushing of any of the preceding claims, wher ein theinsulator body (110) comprises a weather shed (116) , theweather shed (116) being formed by a projecting par t (181) ofthe main part (112) which is covered by the cover ( 150).

4. The bushing of any of the preceding claims, wher ein themain part (112) comprises two or more separate part s (121,122) stacked along a longitudinal axis (102) of the conductor(108), wherein the two or more parts (121, 122) are coveredbythe cover(150)atleastin part.P2024,0265 WO N / P230255WO01 February26,2025 -30 -5. A liquid-insulated electrical apparatus (200) co mprisingthe bushing (100) according to any one of the prece dingclaimsand a wall(201)in which the bushing (100) is installed.

6. A method for manufacturing a bushing (100), comp rising:- injecting thermoplastic (115) into a first mold t o form amain part (112) of an insulator for the bushing (10 0),- applying an elastomeric material (151) to an oute r side(129) of the main part (112), wherein the elastomer icmaterial (151) comprises a self-adhesive liquid sil iconerubber or consists of a self-adhesive liquid silico ne rubber,and thereby- forming a cover (150) of the main part (112), whi ch isfixed to the main part(112)bya chemicalbond.

7. The method of claim 6, wherein applying the elas tomericmaterial(151)comprises:- placing the main part (112) into a second mold an dinjecting the elastomeric material (151) into the s econd moldsuch that the elastomeric material (151) covers the outerside (129) of the main part (112) at least in part, or- extruding the elastomeric material (151) on the o uter side(129) of the main part (112) such that the elastome ricmaterial (151) covers the outer side (129) at least in part.

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