Dielectric heating method for moisture extraction from an active part of a transformer

Abstract

A dielectric heating method for moisture extraction from an active part (10) of a transformer (1) is provided. The method comprises a step of configuring a system including at least one an apparatus (2) configured to generate electric fields alternating at radio frequencies, wherein the electric fields penetrate at least part of regions between freely selectable electrodes (3). The method further comprises a step of operating the at least one apparatus (2) for drying at least one moist region (7) of the active part (10) of the transformer (1), wherein the at least one moist region (7) is located at least partially between the freely selectable electrodes ( 3 ), so that the at least one moist region (7) is exposed to the generated alternating electric fields, resulting in heat generation within the at least one moist region ( 7 ).

Description

[0001]P2023,1512 WO N / P220353WO01 October29,2024 -1 - Description DIELECTRIC HEATING METHOD FOR MOISTURE EXTRACTION FROM AN ACTIVE PART OF A TRANSFORMERThe present disclosure relates to a dielectric heat ing methodfor moisture extraction from an active part of a tr ansformer.This dielectric heating method deals with high freq uencyelectromagnetic heating for moisture extraction fro m adielectric material for instance during the product ion orassemblyofa transformerorduring the production ofanactive part of a transformer. It is also possible t o applysuch method forthe moisture extraction from used transformers.Conventionally, the transformer’s active part conta iningdielectric or insulation material is subjected to a heatingprocess inside an oven multiple times during the pr oductionof the transformer. The heating process can be carr ied out toremove the moisture from the cellulose insulation s o that thewinding / s and supporting structure / s of the transfo rmer canbe shaped to the finaldimensionsand the clamping pressure / scan be adjusted. Conventionally, the heating proces s tofinally dry for instance the cellulose based dielec tricmaterials is mediated by kerosene vapor. These heat ingprocesses, however, are time-intensive and energy c onsuming.US 5424513 A, DE 2155524 A1 and US 2012 / 1248 55 A1describe transformers and different drying techniqu es.Embodiments of the present disclosure address the a boveshortcomings in whole or in part. The embodiments o f themethod for moisture extraction for instance from an active P2023,1512 WO N / P220353WO01 October29,2024 -2 - partofthe transformerare subjectmattersofthe independentand dependentclaims.The present disclosure proposes a new drying techni que thattargetsthe moisture inside the active partofthetransformer. The active part of the transformer can be theworking part of the transformer without the tank an d oil. Theactive part of the transformer may be seen as an as semblycomprising for instance a core, a plurality of wind ings andinsulation regions within the transformer. The acti ve partcan comprise a press-ring and / or other integral par ts. Forinstance,cellulose-based materialsmaybe used in theinsulation regions. The insulation regions may be l ocatedaround the core and / or the winding / s, between neigh boringwindings, between the core and one winding and / or b etween thecore and several windings of the transformer. The i nsulationregionsmaycomprise the press-ring.The idea of the new drying technique utilizes the h eatproduced from interactions between a high-frequencyalternating electricfield and watermolecules,to conductthe drying process in a significantly faster and mo re energy-efficient manner. The electric field is alternating attypical radio frequencies, but this method does not useradiation in the form of radio-waves or microwaves.Internal and / or external electrodes, which are free lyselectable,can be utilized aselectrodeswhen the electricfield is generated and alternated at high frequenci es, forinstance at radio frequencies. Integral part / s of t hetransformer, for instance integral part / s of the ac tive partof the transformer, can be utilized as freely selec tableelectrode / s during the process of generating heat w ithin the P2023,1512 WO N / P220353WO01 October29,2024 -3 -insulation regions, for example, within the cellulo se-basedinsulation regions. According to an embodimentofa dielectricheating method formoisture extraction from an active part of a transf ormer, themethod comprises a step of configuring a system inc luding atleast one apparatus which is configured to generate electricfields alternating at radio frequencies, wherein th e electricfields penetrate at least part of regions between f reelyselectable electrodes. The apparatus is operated fo r dryingat least one moist region of the active part of thetransformer,wherein the atleastone moistregion islocatedat least partially or entirely between the freely s electableelectrodes, so that the at least one moist region i s exposedto the generated alternating electric fields, resul ting inheat generation within the at least one moist regio n.In contrast to conventional heating method using ke rosenevapor and / or hot air, the dielectric heating genera tes heatdirectlyinside the moistregion which ismade for instancefrom a dielectric material. Here, the electric ener gy isconverted into heat due to dielectric losses in thedielectric material in the moist region. The dielec tricheating thus depends on interactions between molecu les in themoist region and the alternating electric field whi choscillates at high frequencies, for instance at rad iofrequencies.Such a dielectric heating method takes advantages o f the useof high-frequency electromagnetic drying which is u seful forfastand targeted heating.Such heating techniques are veryuseful for drying since the heat is directly genera ted withinthe bulk of the material in the moist region due to the P2023,1512 WO N / P220353WO01 October29,2024 -4 -interaction the alternating electric field for inst ance withdipolar water molecules. This method further provid esdistinct advantages over traditional heating proces ses, sinceheat is directly generated within the bulk of mater ial in themoist region as opposed to the heat flowing from ou tside themoistregion into the moistregion.Using this method, a reverse temperature gradient c an becreated, wherein the reverse temperature gradient m ay havehighesttemperature in the middle ofthe bulk,for instance in the centerofthe moistregion,and wherein thetemperature decreases from the center towards outer surfacesof the moist region. This is in sharp contrast comp ared tothe case of conventional heating, where the tempera turegradient is the exact opposite and shows highest te mperatureat outer surfaces and gradually decreases towards t he centerof the moist region. Such temperature gradient make s itdifficult to dry the center for instance of thick b locks ofpressboard material. This problem can be overcome b y usingthe dielectric heating method which can be self-reg ulating.This means that more heat is generated if more mois ture ispresent. Thus, it is possible to prevent overheatin g and savetime and energy.Using the dielectric heating method, useful spatial andtemporal variation of heat generation during the dr yingprocess can be realized due to the heat distributio ndescribed above. For instance, the spatial variatio n occursdue to higher heat generation at moist regions comp ared todrier ones. Moreover, the temporal variation is due to lessheatgeneration asthe heating processprogresses, sincethere would be less water molecules in the moist re gion or inthe bulk. Thus, compared to conventional heating pr ocesses P2023,1512 WO N / P220353WO01 October29,2024 -5 - using onlykerosene and / orhotair,the dielectric heatingprocess is significantly faster and more energy-eff icient.According to a further embodiment of the dielectric heatingmethod, the dielectric heating method is used for m oistureextraction from the active part of the transformer, whereinthe moistregion ofthe transformerisan integral dielectricpart of the active part of the transformer. The int egraldielectric part / s of the active part can be adjacen t toelectrically conducting integral parts of the trans former.The moist region or the integral dielectric part ca n belocated between the electrically conductive integra l parts ofthe active part of the transformer. During the proc ess ofdielectric heating, the electrically conductive int egralpart / s can be utilized as internal electrode / s to g enerateheat within the moist regions or within the dielect ric part / sof the active part or of the transformer in a targe tedmanner. The electrically conductive integral part / s of theactive part of the transformer can comprise a core, one partof the core, and different windings. The moist regi on or theintegraldielectricpartofthe active partofthetransformer can be any insulation regions between t hewindings, located between the core and the windings , aroundthe core oraround the windings.According to a further embodiment of the dielectric heatingmethod,the method isused formoisture extraction from a pluralityofdifferentmoistregionsin the active partofthe transformer. Different integral parts of the ac tive partofthe transformermaybe used asdifferentfreely selectable electrodesforthe purpose ofdrying the different moistregions in the active part of the transformer, in a targetedmanner. P2023,1512 WO N / P220353WO01 October29,2024 -6 -The integral parts being used as different freely s electableelectrodes are electrically conductive and can be m ade fromone metallic material or from several metallic mate rials. Theelectrically conductive integral part can be a core , one partof the core or a winding of the transformer. The mo istregions can be insulation regions which can be made fromdielectric materials, for instance based on cellulo se. Themoist region can be free of any electrically conduc tivematerial. It is also possible that the freely selec tableelectrodesare chosen in such a way,thatthere is noelectrically conductive material located between th e freelyselectable electrodes.Conventionally, during the process of manufacturing atransformer, the active part of the transformer sha ll beheated at least twice during the manufacturing proc ess: (i)while shaping the winding to adjust the clamping pr essure;and (ii) during a vapor phase drying to dry the cel lulosematerials within the active part of the transformer . Thetransformer may comprise thick blocks of pressboard , such aspress-rings, which are difficult to dry at their ce nter.Hence, it may take a long time and considerable ene rgyconsumption to reach the desired levelofdryness, forexample at 1 % or 0.5 % relative humidity. Moreover , it ispractically quite difficult to determine whether th e materialor the insulation region has reached 1 % or 0.5 % r elativehumidity at its center. By using the dielectric hea tingmethod described here, the process of drying the mo istregionsforinstance within the active partofthe transformercan be simplified,notonlyduring the processofmanufacturing a new transformer but also during the processofextracting moisture from a used transformer. P2023,1512 WO N / P220353WO01 October29,2024 -7 -According to a further embodiment of the dielectric heatingmethod,the moistregion isa dielectricregion of thetransformer and is at least one of: a press-ring of thetransformer; an insulation region between two neigh boringwindings of the transformer; and an insulation regi on betweenone winding and a core ofthe transformer.Depending on which dielectric region of the transfo rmer shallbe dried, internal and / or external electrodes can b e used asthe freely selectable electrodes during the process ofextracting moisture from the dielectric region in q uestion.Itispossible thatonlyexternalelectrodes,only internalelectrodes, or a combination of external and intern alelectrodes are used. The to be dried dielectric reg ion, i.e.the moistregion,islocated atleastpartiallyor entirely between the freelyselectable electrodes.According to a further embodiment of the dielectric heatingmethod, the apparatus is configured to generate ele ctricfields,alternating atfrequenciesin a range from 1 MHzto50 MHz, for instance in a range from 1 MHz to 41 MH z, from 3MHz to 41 MHz,from 3 MHzto 30 MHz,from 4 MHzto 41 MHz, from 5 MHzto 41 MHz,orfrom 13 MHzto 41 MHz.The potential, i.e. the voltage, between the freelyselectable electrodes can be chosen in a range from 0.5 kV to100 kV, for instance from 0.5 kV to 90 kV, from 0.5 kV to 80kV, from 0.5 kV to 70 kV, from 5 kV to 100 kV, from 10 kV to100 kV, from 15 kV to 100 kV or from 1 kV to 60 kV, from 5 kVto 50 kV, from 10 kV to 50 kV or from 15 kV to 45 k V. P2023,1512 WO N / P220353WO01 October29,2024 -8 -According to a further embodiment of the dielectric heatingmethod, at least one of the freely selectable elect rodescomprises one integral part of the transformer bein g used asone internal electrode. The integral part of the tr ansformercan be a core or any winding of the transformer. Th e otherfreely selectable electrode can be an external elec trode oranotherintegralpartofthe active partorofthetransformer. The other integral part can be the cor e oranotherwinding.According to a further embodiment of the dielectric heatingmethod,one integralpartofthe transformerbeing used asone internal electrode of the freely selectable ele ctrodes isa winding ofthe transformer.The winding can be a low-voltage or a high-voltage winding of the transforme r. Theother freely selectable electrode can be an externa lelectrode or the core or another winding of the tra nsformer.According to a further embodiment of the dielectric heatingmethod,one integralpartofthe transformerbeing used asone internal electrode of the freely selectable ele ctrodes isthe core of the transformer. Further freely selecta bleelectrode / s can be external electrodes or further w inding / sof the transformer. The moist region can be located betweenthe core and the further freely selectable electrod e / s.According to a further embodiment of the dielectric heatingmethod, the freely selectable electrodes comprise t wodifferent integral parts of the transformer being u sed as twodifferent internal electrodes. The two different in tegralparts can be two neighboring windings of the transf ormer. Itis also possible that the two different integral pa rts arethe core and one winding ofthe transformer. P2023,1512 WO N / P220353WO01 October29,2024 -9 -According to a further embodiment of the dielectric heatingmethod, the two different integral parts of the tra nsformerbeing used as the two different internal electrodes are twodifferent windings of the transformer. It is possib le thatthe two different windings are arranged next to eac h otherand do not surround each other. It is also possible that thetwo different windings are arranged next to each ot her,wherein one of the windings is surrounded by anothe r winding.The moist region can be located between the two dif ferentwindingsused asthe freelyselectable electrodes.For example, the two different integral parts of th etransformer being used as the freely selectable ele ctrodesare a low-voltage winding and a high-voltage windin g of thetransformer.Furthermore,itisalso possible that the twodifferent integral parts being used as the freely s electableelectrodes are two neighboring high-voltage winding s or twoneighboring low-voltage windings.According to a further embodiment of the dielectric heatingmethod, the two different integral parts of the tra nsformerbeing used as the two different internal electrodes comprisea core and at least one winding of the transformer. In thiscase the moist region is located between the core a nd the onewinding.According to a further embodiment of the dielectric heatingmethod, at least one of the freely selectable elect rodes isan external electrode which is not an integral part of thetransformer or of the active part of the transforme r. Forinstance, the external electrode is located outside a press-ring.Itispossible to use more than one external P2023,1512 WO N / P220353WO01 October29,2024 -10 -electrodes. Furthermore, it is also possible to use acombination ofone ormore externalelectrodesand one ormore internal electrodes. The internal electrode ca n comprisethe core, one part of the core, one winding or seve ralwindings of the transformer. The moist region can b e thepress-ring or an outer block or ring of the transfo rmer.According to a further embodiment of the dielectric heatingmethod, at least one of the freely selectable elect rodescomprises one integral part of the transformer bein g used asone internalelectrode.Atleastone ofthe freely selectableelectrodes can be an external electrode which is no t anintegral part of the transformer. For instance, the core orone part of the core of the active part forms one f reelyselectable electrode.Itisalso possible to use a combination oftwo ormore externalelectrodesand the core asthe freelyselectable electrodes.According to a further embodiment of the dielectric heatingmethod, the freely selectable electrodes comprise e xternalelectrodes which are not integral parts of the tran sformer.The number of external electrodes can be at least t wo, threeor four. For example, the active part of the transf ormer ispartiallyorcompletelysurrounded bythe external electrode / s.In all embodiments, the apparatus configured to gen erate theelectric field alternating for instance at radio fr equenciescan comprise at least a source unit, for instance a voltagesupply unit. The apparatus is thus not configured t o generateelectromagneticradiation in the narrow sense.The apparatusis configured to generate alternating electric fiel dsoscillating forinstance atradio frequencies.The external P2023,1512 WO N / P220353WO01 October29,2024 -11 -electrodes can be integral parts of the apparatus o r not beintegral parts of the apparatus. The internal elect rodes arenot integral parts of the apparatus but are integra l parts ofthe transformer, for instance of the active part of thetransformer. It is possible to use electrical conne ction / s toelectrically connect the internal electrode / s to th e voltagesupply unit. The electrical connection / s can be par ts of theapparatus or of the system comprising the apparatus . Theelectrical connection / s can be used for grounding p urposes.The method described here can be realized byusing externalelectrode / s and / or internal electrode / s such as the windingsand the core for high-frequency electromagnetic hea ting.Different terminals configurations of the freely se lectableelectrodes, for instance of the windings and the co re, couldbe used to emphasize heating in strategic areas. It is alsopossible to place electrodes inside a drying chambe r andplace the cellulose-based insulation between these. Thismethod may fully or partially replace the conventio nalheating. For instance, the method may be utilized e ither withorwithoutuse ofKerosene.The present disclosure comprises several embodiment s of thedielectricheating method.Everyfeature described withrespect to one of the embodiments is also disclosed hereinwith respectto the otherembodiments,even ifthe respective feature isnotexplicitlymentioned in the context ofthe specificembodiment. The accompanying figuresare included to provide a furtherunderstanding. In the figures, elements of the same structureand / orfunctionalitymaybe referenced bythe same reference signs.Itisto be understood thatthe embodiments shown in P2023,1512 WO N / P220353WO01 October29,2024 -12 -the figures are illustrative representations and ar e notnecessarilydrawn to scale.While the disclosure is amenable to various modific ations andalternative forms, specifics thereof are shown by w ay ofexample in the figures and will be described in det ail. Itshould be understood, however, that the intention i s not tolimit the disclosure to the particular described em bodimentsand examples. The accompanying figuresare included to provide a furtherunderstanding of the heating method. In the figures , elementsof the same structure and / or functionality may be a ssigned tothe same reference signs. It is to be understood th at theexamplesshown in the figuresare illustrativerepresentations and are not necessarily true to sca le.Figure 1 shows a general concept of a dielectric he atingmethod for moisture extraction from a moist region.Figure 2 shows an example of the dielectric heating methodformoisture extraction from a moistregion ofthe active partofthe transformer.Figures 3A, 3B, 4A, 4B, 5A and 5B show further exam ples ofthe dielectric heating method for moisture extracti on fromdifferentmoistregionsofthe active partofthe transformer.Figure 1 schematically shows an active part of a tr ansformercomprising a region 7 which is for instance a moist region 7.The region 7 can be partially or entirely electrica llyinsulating. The region 7 comprises for instance one P2023,1512 WO N / P220353WO01 October29,2024 -13 -dielectric material or several dielectric materials . Thedielectric material can be a cellulose based dielec tricmaterial.For moisture extraction from the region 7, an appar atus 2 canbe used to generate electricfieldsalternating at highfrequencies, for instance at radio frequencies. The electricfieldspenetrate regionsbetween freelyselectable electrodes 3.In Figure 1,two freelyselectable electrodes3 are shown,wherein the moist region 7 is located between the t woselectable electrodes 3. Thus, during the operation of theapparatus 2, the moist region 7 is exposed to the a lternatingelectric field / s. Since water molecules are electri c dipoles,they move or rotate as they try to align themselves with thealternating electric field. These molecular movemen ts of thewater molecules create heat by friction as the rota tingmolecules collide with other molecules in the moist region 7,for instance with the molecules of the dielectric m aterial,and force these other molecules into motion, result ing ingeneration ofheatwithin the moistregion 7.This kind of heating is self-regulating, since more heat willbe generated if there are more water molecules pres ent, i.e.more moisture. Possible overheating can thus be pre vented.Moreover, the self-regulating heating process is re flected bythe temporal and spatial variations of the heat gen eration,since more heat is generated at humid regions compa red todrier ones. The temperature gradient may have highe sttemperature in the center of the moist region havin g thehighest humidity, wherein the temperature decreases from thecenter towards outer regions having lower humidity. Thus moreheat is generated at the most humid region resultin g inrealizing a targeted and efficientheating method. P2023,1512 WO N / P220353WO01 October29,2024 -14 -The targeted heating method is also reflected by th e factthat the electrodes 3 are freely selectable. Hence, dependingon the arrangements or configurations of the electr odes 3,individual moist regions 7 can be dried in a target ed manner.The electrodes3 shown in Figure 1 can be externalelectrodes, internal electrodes or a combination of at leastone internalelectrode and one externalelectrode. An externalelectrode can be understood to mean anelectrically conductive structure which is not an i ntegralpartofthe transformer1 orofthe active part10 ofthetransformer 1. The external electrode can be part o f theapparatus 2. An internal electrode can be understoo d to meanan electrically conductive structure which is an in tegralpartofthe transformer1 orofthe active part10 ofthetransformer 1. The integral part of the transformer 1 or ofthe active part 10 can be an electrically conductiv estructure, for example, a winding structure or a co restructure ofthe transformer1.The apparatus 2 comprises a source unit for generat ing analternating electric field. For instance, the appar atus 2 cancomprise a voltage supply unit. It is also possible that theapparatus 2 comprises electrical connection / s which can beused to electrically connect the voltage supply uni t with thefreely selectable electrodes 3. The electrical conn ection / scan also be used for grounding purposes as schemati callyshown in Figure 1.The dielectric heating method for moisture extracti on from anactive partofa transformerthuscomprisesa step ofconfiguring a system including at least one apparat us which P2023,1512 WO N / P220353WO01 October29,2024 -15 -is configured to generate electric fields alternati ng atradio frequencies. The system can further include t he freelyselectable electrodes 3. The freely selectable elec trodes 3may be integralpartsornotintegralpartsofthetransformer 1. It is possible that the system inclu desfurtherelectricalconnections.Figure 2 shows a concrete example of the dielectric heatingmethod for moisture extraction from a transformer 1 , forinstance from the active part 10 of the transformer 1.The active part 10 comprises a press-ring 70. The p ress-ring70 can be a pressboard formed from a dielectric mat erial. Thedielectric material can be based on cellulose. It i s possiblethat the press-ring 70 form an outermost layer of t he activepart10.The active part 10 comprises a core 4 and winding / s 5 aroundthe core 4 oraround some partsofthe core 4.The winding 5can be separated from the core 4 by an insulation r egion 73.The insulation region 73 can be made from a dielect ricmaterial which can be based on cellulose. As schema ticallyshown in Figure 2,the moistregion 7 can comprise the press- ring 70 and / orthe insulation region 73.The press-ring 70 and / or the insulation region 73 c an besubjected to electric field alternating at high fre quencies,forinstance atradio frequencyasshown in Figure 2.Herethe core 4 or part of the core 4 could be used as o ne freelyselectable electrode 3 which is an internal electro de 30. Forinstance, the core 4 can be grounded. As shown in F igure 2,further external electrode / s 31 can be used as furt her freelyselectable electrode / s3.The externalelectrode / s 31 can be P2023,1512 WO N / P220353WO01 October29,2024 -16 -electrically connected to a voltage source which is used togenerate the alternating electricfields. In Figure 2,there are two externalelectrodes31. Theexternal electrodes 31 are arranged outside the act ive part10 of the transformer 1. The geometries of the exte rnalelectrodes 31 can be adapted to the geometries of t he press-ring 70, the insulation region 73 and / or of the cor e 4. Asshown in Figure 2, the external electrodes 31 can h ave acurved shape orcan be ofa ring-shaped structure. Itispossible that only one external electrode 31 is use d. Theonly one external electrode 31 can be curved or rin g-shaped.Furthermore, it is possible that two or more extern alelectrodes 31 are used simultaneously. It is also p ossiblethat only the external electrodes 31, i.e no intern alelectrodes, are used. In the latter case, none of t heintegral parts of the active part 10 of the transfo rmer isused asa freelyselectable electrode.Since the press-ring 70 and / or the insulation regio n 73 areexposed to the alternating electric field, water mo leculeswithin in the press-ring 70 and / or the insulation r egion 73are excited orforced to move orrotate.The water moleculeswill collide with further molecules of the dielectr icmaterial / s in the press-ring 70 and / or the insulati on region73 resulting in generation of heat within the press -ring 70and / orwithin the insulation region 73.According to Figures 3A to 5B, integral parts of th e activepart 10 of the transformer 10 can be used as electr odes 3,namely as internal electrodes 30. Thus, the dielect richeating method or the electromagnetic drying can befacilitated without resorting to external electrode s 31. P2023,1512 WO N / P220353WO01 October29,2024 -17 -According to Figures 3A to 5B, basically two galvan icallyisolated metallic parts in the active part 10 of th etransformer 1 can be utilized as the freely selecta bleelectrodes3,in particularasinternalelectrodes 30.Theexcitation can be connected either from line-end te rminals,neutral-end terminals,ortap-winding terminals.Figure 3A shows a further concrete example of the d ielectricheating method for moisture extraction from the act ive part10 of the transformer 1. The active part 10 compris es a core4 and a plurality of windings 5. The core 4 can com priselateral parts 41 and vertical parts 42. The lateral parts 41and verticalparts42 can be connected directlyto eachother. The plurality of windings 5 comprise first w indings 51and second windings52.The second windings52 can be high-voltage windings. The first windings 51 can be low- voltagewindings. The first winding 51 is for instance an i nnerwinding 51 surrounding one verticalpart42 ofthe core 4.The second winding 52 is for instance an outer wind ingsurrounding both the inner winding 51 and the one v erticalpart42 ofthe core 4.For instance, the active part 10 of the transformer 1comprises a plurality of pairs of windings 5, where in eachpair of windings 5 comprises one first winding 51 a nd onesecond winding 52. As shown in Figure 3A, the first winding51 and the second winding 52 of the same pair are a rrangedaround one common vertical part 42 of the core 4. I n otherwords, both the first winding 51 and the second win ding 52laterally surround one common vertical part 42 of t he core 4.The first winding 51 is located between the vertica l part 42ofthe core 4 and the second winding 52.The first winding 51 can enclose the associated verticalpart42 ofthe core 4. P2023,1512 WO N / P220353WO01 October29,2024 -18 -The second winding 52 can enclose both the associat ed firstwinding 51 and the associated vertical part 42 of t he core 4.As shown in Figure 3A, the active part 10 can compr ise afirst insulation region 71 located between the firs t winding51 and the second winding 52 of the same pair of wi ndings 5.The active part 10 can comprise a second insulation region 72located between the two neighboring second windings 52 of twoneighboring pairs of windings 5. The active part 10 cancomprise a third insulation region 73 located betwe en thefirst winding 51 and its associated vertical part 4 2 of thecore 4. Any of the vertical part 42 of the core 4 c an belaterally surrounded by the first insulation region 71 and / orby the third insulation region 73. At least some of verticalparts 42, for instance inner vertical parts 42 of t he core 4can be laterally surrounded by the second insulatio n region72.In Figure 3A, three vertical parts 42 of the core 4 and threepairs of windings 5 are shown. It is, however, poss ible thatthe active part 10 of the transformer 1 comprises m ore thanthree vertical parts 42 of the core 4 and thus more thanthree pairs of windings 5. Any of the first insulat ion region71, the second insulation region 72 and the third i nsulationregion 73 can be formed from a dielectric material, forinstance from a material based on cellulose. Any of the firstinsulation region 71,the second insulation region 72 and the third insulation region 73 can be a moistregion 7 ofthe active part10 ofthe transformer1.The core 4,a partofthe core 4 and / or any of the windings 5 can be used aselectrode / s 3, for instance as internal electrode / s 30 forperforming the dielectric heating method for moistu reextraction from anyofthe firstinsulation region 71,second P2023,1512 WO N / P220353WO01 October29,2024 -19 -insulation region 72 and third insulation region 73 in atargeted manner.According to Figure 3A, the first winding 51 and th e secondwinding 52 ofthe same pairofwindings5 are used astheinternal electrodes 30 for extracting moisture from the firstinsulation region 71.Using a firstconnection 61, the firstwinding 51 can be grounded. The second winding 52 c an beelectrically connected to a source unit 20, for exa mple via asecond connection 62. The source unit 20 is part of theapparatus 2. For example, the source unit 20 compri ses avoltage supply unit configured for generating an el ectricfield alternating atradio frequencies.The source unit20can also be grounded, for example, via the second c onnection62.In Figure 3A, only the windings 51 and 52 of one le ft pair ofwindings 5 are used as internal electrodes 30 for h eating thefirst insulation region 71 located between the firs t winding51 and the second winding 52. In this way, moisture can beextracted from the first insulation region 71 being the moistregion 7 in a targeted manner. Any pair of the wind ings 5 canbe used as internal electrodes 30 for extracting th e moisturefrom the associated firstinsulation region 71.The dielectric heating method for moisture extracti on shownin Figure 3B is basically identical to dielectric h eatingmethod shown in Figure 3A, except that the second w inding 52isgrounded forinstance via the second connection 62.Thefirst winding 51 can be electrically connected to t he sourceunit20 via the firstconnection 61. P2023,1512 WO N / P220353WO01 October29,2024 -20 -The dielectric heating method for moisture extracti on shownin Figure 4A is basically identical to dielectric h eatingmethod shown in Figure 3A, except that two neighbor ing secondwindings52 are used asinternalelectrodes30.In thisway,the dielectric heating method is configured for moi stureextraction from the second insulation region 72 bet ween thetwo neighboring second windings52. In Figures3A and 3B,the two differentwindings5 used asinternal electrodes 30, namely one first winding 51 and onesecond winding 52, are arranged next to each other, whereinthe first winding 51 is surrounded by the second wi nding 52.In Figure 4A, however, the two different windings 5 used asinternal electrodes 30, namely one second winding 5 2 and onefurther second winding 52, are arranged next to eac h otherand do not surround each other. The two different s econdwindings5 in Figure 4A enclose differentvertical parts42of the core 4. If the second insulation region 72 b etweenthese two neighboring second windings 52 is a moist region 7,the moist region 7 can be heated for moisture extra ction fromthissecond insulation region 72. Asshown in Figure 4A,an innersecond winding 52, i.e.themiddle second winding 52, being an internal electro de 30 isgrounded, for instance via the first connection 61. An outersecond winding 52, i.e. the left second winding 52, isanother internal electrode 30 and can be electrical lyconnected to the source unit 20 via the second conn ection 62.Using appropriate second windings 52 as internal el ectrodes30, any of the second insulation regions 72 between twoneighboring second windings 52 can be heated for mo istureextraction from thatsecond insulation region 72. P2023,1512 WO N / P220353WO01 October29,2024 -21 -The dielectric heating method for moisture extracti on shownin Figure 4B is basically identical to dielectric h eatingmethod shown in Figure 4A, except that the outer se condwinding 52 being used as an internal electrode 30 i sgrounded, for instance via the second connection 62 . Theinner second winding 52, i.e. the middle second win ding 52,is another internal electrode 30 and can be electri callyconnected to the source unit 20 via the first conne ction 61.The dielectric heating method for moisture extracti on shownin Figure 5A is basically identical to dielectric h eatingmethod shown in Figure 3B, except that the core 4 o r part ofthe core is used as a further internal electrode 30 . In thisway, the dielectric heating method is configured fo r moistureextraction from the third insulation region 73 betw een thefirst winding 51 and the core 4 or between the firs t winding51 and one verticalpart42 ofthe core 4.As shown in Figure 5A, the core 4 being an internal electrode30 is grounded, for instance via the second connect ion 62.The left first winding 51 is another internal elect rode 30and is electrically connected to the source unit 20 via thefirst connection 61. Using appropriate first windin gs 51 asinternal electrodes 30, any of the third insulation regions73 being a moist region 7 between the core 4 and an y of thefirst windings 51 can be heated for moisture extrac tion fromthat third insulation region 73 in a targeted manne r.The dielectric heating method for moisture extracti on shownin Figure 5B is basically identical to dielectric h eatingmethod shown in Figure 5A, except that the first wi nding 51being an internal electrode 30 is grounded, for ins tance viathe first connection 61. The core 4 is another inte rnal P2023,1512 WO N / P220353WO01 October29,2024 -22 -electrode 30 and is electrically connected to the s ource unit20 via the second connection 62.Forinstance,the secondconnection 62 is electrically connected to a latera l part 41of the core 4. It is, however, possible that the se condconnection 62 is electrically connected any part 41 or 42 ofthe core 4.Thus, different combinations of the freely selectab leelectrodes 3 can be utilized to target specific moi st regions7 between the freely selectable electrodes 3 for dr ying. Thefreely selectable electrodes 3 can comprise externa lelectrode / s 31 and / or internal electrode / s 30, wher ein theinternal electrode 30 can be any winding 5 or the c ore 4 ofthe active part 10 of the transformer 1. This resul ts in aheating process which is targeted, significantly fa st,efficient, and less time-consuming. Such a method c an beapplied not only during the production of new trans formers,for example of active parts of new transformers, bu t also forthe moisture extraction from used transformers, for instancefrom active partsofused transformers.The examples shown in the figures as stated represe ntexamples of the dielectric heating method for moist ureextraction from a transformer, for instance from an activepart of the transformer; therefore, they do not con stitute acomplete list of all examples according to the impr ovedheating method. Actual arrangements or implementati on of themethod mayvaryfrom the examplesdescribed above.This application claims the priority of the Europea n patentapplication EP 24153935.2, the disclosure content o f which isherebyincluded byreference. P2023,1512 WO N / P220353WO01 October29,2024 -23 - Reference signs 1 transformer 10 active partofthe transformer 2 apparatus 20 source unit / voltage supplyunit 3 electrode 30 internalelectrode 31 externalelectrode 4 core 41 lateralpartofthe core 42 verticalpartofthe core 5 winding 51 firstwinding / low-voltage winding 52 second winding / high-voltage winding 61 firstconnection 62 second connection 7 moistregion 70 press-ring 71 firstinsulation region between two windings 72 second insulation region between two windings 73 insulation region between winding and core

Claims

P2023,1512 WO N / P220353WO01 October29,2024 -24 - Claims1. A dielectric heating method for moisture extract ion froman active part (10) of a transformer (1), comprisin gfollowing steps:- configuring a system including at least one apparat us (2)configured to generate electricfieldsalternating at radio frequencies, wherein the electric fields pene trateatleastpartofregionsbetween freelyselectable electrodes(3);and- operating the at least one apparatus (2) for drying atleastone moistregion (7)ofthe active part(10) ofthe transformer (1), wherein the at least one moist reg ion (7)islocated atleastpartiallybetween the freely selectable electrodes (3), so that the at least one moistregion (7)isexposed to the generated alternating electric fields, resulting in heat generation withi n theatleastone moistregion (7).

2. The dielectric heating method according to claim 1 formoisture extraction from a plurality of different m oistregions (7) in the active part (10) of the transfor mer (1),wherein different integral parts of the active part (10) ofthe transformer (1) are used as different freely se lectableelectrodes (3) for the purpose of drying the differ ent moistregions (7) in the active part (10) of the transfor mer (1) ina targeted manner.

3. The dielectric heating method according to any o fpreceding claims, wherein the at least one moist re gion (7)is a dielectric region of the transformer (1) and i s at leastone of: − a press-ring (70)ofthe transformer(1),P2023,1512 WO N / P220353WO01 October29,2024 -25 - −an insulation region (71, 72) between two neighbori ngwindings(5)ofthe transformer(1),and −an insulation region (73) between one winding (5) a nd acore (4)ofthe transformer(1).

4. The dielectric heating method according to any o fpreceding claims, wherein the at least one apparatu s (2) isconfigured to generate electricfieldsalternating at frequenciesin a range from 1 MHzto 50 MHz.

5. The dielectric heating method according to any o fpreceding claims, wherein at least one of the freel yselectable electrodes (3) comprises one integral pa rt of thetransformer (1) being used as one internal electrod e (30).

6. The dielectric heating method according to any o f thepreceding claims,wherein one integralpartofthetransformer (1) being used as one internal electrod e (30) ofthe freely selectable electrodes (3) is a winding ( 5, 51, 52)ofthe transformer(1).

7. The dielectric heating method according to any o f thepreceding claims,wherein one integralpartofthetransformer (1) being used as one internal electrod e (30) ofthe freelyselectable electrodes(3)isa core (4) ofthe transformer(1).

8. The dielectric heating method according to any o f thepreceding claims, wherein the freely selectable ele ctrodes(3) comprise two different integral parts of the tr ansformer(1) being used as two different internal electrodes (30).P2023,1512 WO N / P220353WO01 October29,2024 -26 -9. The dielectric heating method according to claim 8,wherein the two different integral parts of the tra nsformer(1) being used as the two different internal electr odes (30)are two different windings (5, 51, 52) of the trans former(1).

10. The dielectric heating method according to clai m 9,wherein the two differentwindings(5,51,52)are arranged nextto each otherand do notsurround each other.

11. The dielectric heating method according to clai m 9,wherein the two differentwindings(5,51,52)are arrangednext to each other, and wherein one of the windings (5, 51)issurrounded byanotherwinding (5,52).

12. The dielectric heating method according to clai m 8,wherein the two different integral parts of the tra nsformer(1) being used as the two different internal electr odes (30)comprise a core (4) and at least one winding (5, 51 , 52) ofthe transformer(1). 13.The dielectricheating method according to any ofclaims1 to 7, wherein at least one of the freely selectab leelectrodes(3)isan externalelectrode (31)which isnotan integralpartofthe transformer(1). 14.The dielectricheating method according to any ofthe claims1 to 7,wherein −at least one of the freely selectable electrodes (3 )comprisesone integralpartofthe transformer(1) being used asone internalelectrode (30),andP2023,1512 WO N / P220353WO01 October29,2024 -27 - −at least one of the freely selectable electrodes (3 ) isan external electrode (31) which is not an integral partofthe transformer(1). 15.The dielectricheating method according to any oftheclaims 1 to 7, wherein the freely selectable electr odes (3)comprise external electrodes (31) which are not int egralpartsofthe transformer(1).

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