Corona shielding tape for rotating high-voltage motors, its uses, and motors

Abstract

The present invention relates to a corona shielding tape for a rotating high-voltage electric machine, in particular a reactive corona shielding tape, the electric machine comprising an insulation system which can be made by the vacuum pressure impregnation "VPI" process, in which, due to concerns about the sensitizing effect of acid anhydrides on the respiratory tract, the impregnating agent for impregnating the corona shielding tape in the VPI process is preferably present in an acid anhydride-free form. Based on a new generation of insulation systems which can be made by impregnating with an acid anhydride-free impregnating agent, a corona shielding tape is disclosed for the first time by the present invention, in which a tape accelerator for rapid initiation of homopolymerization can be placed. The tape accelerator is present in the form of a superstrong acid salt and is stably stored for up to 6 months in a corona shielding tape which at least partly comprises polyvinyl alcohol as a polymer matrix.

Description

[0001] The present invention relates to a corona shielding tape for rotating high-voltage electrical machines, in particular a reactive corona shielding tape, the electrical machine comprising an insulation system which can be produced by a vacuum pressure impregnation process (VPI process), wherein, due to concerns about the sensitizing effect of acid anhydrides on the respiratory tract, the impregnating agent in the VPI process is preferably present in an acid anhydride-free form. In addition, the present invention also relates to the use of such a corona shielding tape and an electrical machine having an insulation system which can be produced by using the corona shielding tape.

[0002] Depending on the rated voltage of the rotating electrical machine, different combinations of insulation system components are used in the production of the insulation system. For example, in electrical machines with a rated voltage of approximately more than 2 kV, a conductive layer for field equalization, i.e. an external corona shield, AGS, is provided at the slot exit position. Starting from a rated voltage of approximately 6 kV, the AGS is usually reinforced at the ends by an end corona shield EGS, and starting from a rated voltage of approximately 12 kV, the insulation system is also reinforced at the main insulator by an internal potential control IPS.

[0003] Due to physiological concerns about the acid anhydride-containing crosslinking agents which have hitherto generally been used in the impregnating agents of insulation systems, in particular insulation systems which can be produced by VPI, the acid anhydrides are increasingly being replaced by acid anhydride-free impregnating agents. This replacement has brought about a series of adjustment problems, since the winding tapes and / or corona shielding tapes which themselves contain organic binders, such as tape adhesives, polymer-based matrix materials and, precisely in the case of reactive corona shielding tapes, curing catalysts, should be adapted to the newly used acid anhydride-free impregnating agent.

[0004] There has hitherto been no formulation for an insulation system having AGS, EGS and / or IPS and comprising a corona shielding tape and some of its sensitive components, such as tape adhesives, polymer matrices, fillers, their coatings and an acid anhydride-free impregnating agent, which can be processed into a usable insulation system in a common VPI process.

[0005] The conductive layers of the IPS and AGS usually consist of a composite material containing carbon black and / or graphite and based on a polymer matrix. None of the components of the composite material, i.e. the carbon black / graphite and the polymer matrix, is resistant to partial discharges. If a partial discharge hits the conductive layer, for example the carbon black reacts with the surrounding oxygen to form CO 2 . The same applies to the polymer matrix.

[0006] The main insulator or the AGS, EGS and IPS are usually formed by winding mica tapes or corona shielding tapes impregnated with an impregnating agent. Here, the mica tapes of the main insulator usually contain barrier materials, such as insulating mica, while the corona shielding tapes contain conductive or partially conductive fillers, such as carbon black and the like. In the case of full VPI, compared to single VPI, the IPS, AGS and / or EGS are usually applied as tapes, preferably on the yet unimpregnated coils / rods, and subsequently - particularly preferably - impregnated with the impregnating agent during the impregnation process.

[0007] In particular, the tertiary amines and / or organic zinc salts which have hitherto been common and which are most suitable for anhydride-containing impregnating agents can no longer be used as so-called promoters for the novel anhydride-free impregnating agents, since they crosslink only inadequately under the conditions of the VPI process. This ultimately results in uncured soft regions and / or polymers with a low glass transition temperature in components of the AGS, EGS, IPS and / or the main insulator. Locally, a low glass transition temperature should also be avoided, since the mechanical and electrical properties of these regions are insufficient and lead to significantly premature degradation. During operation, rapid thermal and electrical property degradation or destruction occurs in these poorly tolerant regions.

[0008] Corona shielding tapes are used as components of the insulation system in rotating high-voltage machines. Rotating high-voltage machines are, for example, engines or generators for generating electrical energy in power plants. Such rotating high-voltage machines in particular have stator windings which are subject to particularly high requirements with regard to strength and reliability. In particular, at the interface between the main insulator of the stator winding and the laminated core, especially in the case of rotating machines starting from a rated voltage of approximately 2 kV, the insulation system of the stator winding is subject to high thermal, thermo-mechanical, dynamic and electromechanical operating loads, as a result of which the insulation system of the stator winding has a high risk of being damaged by partial discharges.

[0009] The stator winding has a conductor assembly which is electrically insulated by a main insulator and is arranged in a slot in the laminated core. When the rotating machine is operating, the stator is exposed to alternating thermal loads, which are caused by the different thermal expansion rates and thermal conductivities of the conductor, the main insulator and the laminated core, as a result of which mechanical loads are generated in the main insulator. As a result, local limited detachment of the main insulator can occur, thereby forming a cavity between the main insulator and the laminated core, in which a local discharge can be initiated. The local discharge can cause damage to the main insulator, which in the worst case can lead to a ground connection between the laminated core and the conductor, as a result of which the machine can no longer operate. The conductor with its main insulator usually projects at the slot outlet, where the interface between the conductor and the main insulator is arranged, which forms a sliding arrangement. For example, this can be seen in Figure 1 EP 2362399 B1, where the local schematic of the turbine generator stator shown there corresponds approximately to the slot outlet position discussed here.

[0010] The winding is a high-load electrical system with respect to the main insulator of the laminated core. During operation, a high voltage is generated, which has to be dissipated in the insulation volume between the conductor bar and the laminated core at earth potential. Field enhancement occurs at the laminated edges of the laminated core, which itself causes partial discharges and ultimately leads to premature ageing and, in the worst case, destruction of the insulation.

[0011] The exit position of the stator bar / coil leg from the laminated core, i.e., the slot exit position, is characterized by the encounter of two insulating materials (gaseous and solid) and AGS and / or IPS or the laminated core. In this region, a boundary layer is formed between the main insulator in a solid polymerized state and the gaseous medium (usually air or hydrogen). Through the dielectric separation surface generated between the main insulator and air, a classical sliding arrangement is produced, which, in addition to the pure radial field component E perpendicular to the conductor and present in the laminated core region rad also has a tangential field component E generated along the conductor towards the end of AGS tan . Thus, the tangentially loaded interface, such as the interface between the main insulator and air, represents a special weakness in the insulation device.

[0012] Due to the low electrical strength of air, partial discharges occur even at relatively low voltages in the "laminated core - insulation system - air" triple - point region at the end of the external corona shield "AGS". In the case of a clean surface, this is caused by a local tangential field enhancement of about 0.5 kV / mm, which can spread to electrical breakdown during surface discharge along the insulation material surface when the voltage is further increased. The electrical breakdown is characterized by a short - circuit of the conductor to the ground.

[0013] To suppress electrical surface discharge, in the case of rotating machines, in addition to the external corona shield "AGS", a capacitive - resistive field control in the form of an end corona shield "EGS" is connected to the AGS starting from a rated voltage of 6 kV. When calculating and designing the end corona shield, it should be noted that the highest electro - thermal load on the system does not occur at the operating voltage, but rather when checking the insulation system with an increased test voltage. In the long term, the insulating material will be damaged due to the formation of surface discharge on the surface. Like the external corona shield, the end corona shield is a resistive coating directly on the surface of the main insulator. Compared with the external corona shield "AGS" with a surface resistance of about 1000 - 10000 ohms, the end corona shield "EGS" has a significantly higher surface resistance, which is designed to be non - linear and is about 5x10 9 ohms at a field strength of 100 V / mm. Generally, the relevant resistance range of EGS can be specified as 2x10 8 ohms to 1x10 13 ohms.

[0014] In particular, due to heating, electrical corrosion, and chemical degradation, the EGS will be damaged, thus damaging the insulation system and ultimately leading to flashover due to the failure of the end corona shield. Due to local heating, changes in the operating point will also cause interference in the function of the insulation system and an increase in dielectric losses.

[0015] The AGS has a certain sheet resistance, which must not be lower than or exceed certain lower and upper limits. When below the limit value, a high inductive circulating current closed through the end of the laminated core and the external corona shield will cause a strong current arc between two laminations in the laminated core, resulting in high electrical losses. When the resistance is too high, high-voltage spark erosion may occur, where the AGS no longer functions as a field equalizer but as an insulator. Ideally, the external corona shield has significant anisotropy in terms of resistance behavior; the resistance in the tangential, i.e., axial direction, should be high, while the resistance in the radial direction should be low.

[0016] However, in practice, this ideal performance of the AGS cannot be achieved, and thus the resistance of the AGS in the tangential direction has always been lower than that in the radial direction to date. These phenomena can also be read in relevant professional literature, such as "Hochspannungstechnik" by A. Küchler, Springer Verlag, Volume 15, 2009, ISBN 3-540-78412-8, and "Design Dependent Slot Discharge and Vibration Sparking on High Voltage Windings" by M. Liese and M. Brown, IEEE Trans DIE, August 2008, pages 927-932.

[0017] Therefore, the object of the present invention is to provide a corona shield tape for further processing in the VPI process, which includes a carrier tape, at least one tape promoter for impregnating resin, and at least one polymer matrix material with a conductive, optionally coated filler, wherein the tape promoter contained in the corona shield tape is suitable for promoting the curing of an acid anhydride-free impregnating agent, especially an epoxy resin-based impregnating agent, in the VPI process.

[0018] The object is achieved by the subject matter of the present invention as disclosed in the description, claims, and drawings.

[0019] Accordingly, the subject matter of the present invention is a corona shielding tape for further processing into an insulation system, which has a winding and a potential control by means of an external corona shielding and / or an internal potential control and / or an end corona shielding, the insulation system being made, for example, by VPI impregnation by impregnating the winding with an acid anhydride-free and resin-based impregnating agent at 45 °C to 85 °C and under vacuum, wherein the corona shielding tape comprises at least one carrier tape, a conductive or partially conductive filler in a polymer matrix and at least one tape promoter suitable for curing and / or gelling the impregnating agent, characterized in that the polymer matrix comprises at least one polyvinyl alcohol and / or polyvinyl alcohol copolymer, and the at least one tape promoter is selected from super strong acid salts, wherein it is suitable for promoting the cationic homopolymerization of the resin-based acid anhydride-free impregnating agent.

[0020] The basis of the resin-based impregnating agent is preferably an epoxy resin, in particular an epoxy resin mixture, for example an epoxy resin mixture comprising one or more alicyclic epoxy resins. Siloxanes can also be comprised in the mixture, for example, such that a thermosetting material having a main chain comprising -O-SiR 2 -O units is obtained upon curing of the impregnating agent.

[0021] According to an advantageous embodiment of the invention, the impregnating agent is a resin that is particularly free of phthalic anhydride or derivatives thereof, or a resin mixture based on epoxy resins, preferably comprising at least one alicyclic epoxy resin and an epoxy resin based on bisphenol A-diglycidyl ether and / or an epoxy resin based on bisphenol F-diglycidyl ether and / or an epoxy resin based on epoxy novolac. For example, there is an impregnating resin mixture based on an alicyclic epoxy resin and bisphenol A-diglycidyl ether with a mixing ratio of 50:50 to 90:10, in particular a mixing ratio of 80:20 (m / m).

[0022] For example, the polymer matrix comprises a tape adhesive and - at least in part - a tape promoter dissolved and / or finely dispersed therein, also referred to as a "tape catalyst". The tape promoter is used to gel a dilute liquid impregnating resin that acts, for example, on the corona shielding tape and the main insulator of the stator winding during vacuum pressure impregnation (VPI). This typically occurs at elevated temperatures of 45 °C to 85 °C. After impregnation, the stator winding in the stator stack core is also post-cured thermally.

[0023] The at least one tape promoter is preferably present in the polymer matrix comprising the filler. During impregnation, this at least partially mixes with the impregnating agent and / or can at least partially migrate into the impregnating agent and is thus used to gel the impregnating agent before curing in a subsequent tempering step of the impregnation process.

[0024] According to one embodiment of the present invention, the promoter, which is present, for example and preferably in the form of a superacid salt, is present in a finely dispersed and / or dissolved form in a polymer matrix or adhesive tape containing at least one polyvinyl alcohol.

[0025] Due to the required and desired storage stability of the corona shielding tape, it is advantageous that the promoter present in the corona shielding tape in the form of a superacid and / or superacid salt reacts only upon contact with the impregnating agent and at elevated temperatures of 45 °C to 85 °C. A prior reaction with the polymer matrix is not desired because the promoter would then be "consumed" and the impregnating agent would no longer be able to cure, gel or solidify. Thus, the key point of the present invention is that the promoter, although present in the form of a highly reactive superacid and / or its derivatives, does not react or reacts in an insignificant amount with the polymer matrix of the corona shielding tape at temperatures up to 70 °C.

[0026] The amount of promoter contained in the carrier tape is, for example, from 0.1 g / m 2 to 15 g / m 2 , in particular from 0.25 g / m 2 to 10 g / m 2 , with a preferred amount of from 0.5 g / m 2 to 5 g / m 2 .

[0027] Here, the promoter embedded in the components of the insulation system and the promoter concentration can be the same or different.

[0028] Particularly relevant "components of the insulation system" here are, for example,

[0029] - the windings of the main insulator - which have no conductive or partially conductive fillers since the main insulator is electrically insulating,

[0030] - the windings of the IPS, AGS and / or EGS, which have a graded conductivity or partial conductivity, as described above.

[0031] To avoid partial discharges, the main insulator of a winding bar / coil with internal and external conductive layers can be shielded against cavities and detachment, as described above also by means of internal potential control of the IPS and AGS. The EGS can be applied in connection with the AGS.

[0032] Corona shielding tapes are known from EP 2362399 and DE 19839285 C1, in which planar fillers are incorporated in the polymer matrix. The planar fillers consist of mica substrates coated with doped metal oxides, such as titanium oxide and / or tin oxide. In particular, such fillers are more resistant to partial discharges than carbon-based fillers.

[0033] In principle, in a polymer matrix filled with planar fillers, the resistance in the direction of the strip is significantly lower than the resistance perpendicular to the strip, which in turn reduces the conductivity in the radial direction. By adding circular fillers based on quartz material or quartz powder, which are in turn also coated with a doped metal oxide, the radial resistance can be reduced.

[0034] According to a preferred embodiment, the conductive and / or partially conductive filler has at least one component selected from carbon black, graphite, carbon nanotubes - CNT, antimony-doped tin oxide, silicon carbide, and / or aluminum-doped silicon carbide, where the respective components can be present in doped or undoped, coated or uncoated, doped and coated or undoped but coated form.

[0035] To reduce the increase in field strength in the end region of the external corona shield, capacitive-resistive field control is used. The capacitive control is achieved through the main insulator, while the resistive control is achieved through the end corona shield (EGS). These are conductive surface coatings with a sheet resistance of approximately 10 8 to 10 10 ohms at a field strength of 100 V / mm. By means of the strong non-linearity of the resistance of the material used in the EGS, an attempt is made to shift the electric field away from the high-field-strength region. The reason is that as the electric field strength increases, the specific resistance decreases.

[0036] The ohmic surface coating can be made by coating with a dry and / or curable resin that is directly applied to the surface of the insulating material and / or in conjunction with the manufacture of the wound main insulator (but which is then wound as a tape before the manufacture or impregnation of the main insulator) in the form of a prepreg or a cured porous tape.

[0037] Then the main insulator of the winding is impregnated with an impregnating resin and, for example, by the vacuum pressure impregnation process (VPI process) stated hereby. Here, generally, i.e., according to the prior art, epoxy resins and / or mixtures of epoxy resins and acid anhydrides are particularly used as curing agents. Due to the sensitizing effect on the respiratory tract and the corresponding concerns regarding the unrestricted use of acid anhydrides, especially phthalic anhydride or and / or phthalic anhydride derivatives as curing agents, only anhydride-free, especially phthalic anhydride-free or phthalic anhydride derivative-free impregnating agents are used here. For example, an epoxy resin-based insulating system containing a homopolymerizable anhydride-free impregnating agent is known from WO2016 / 124387.

[0038] Thus, the reactive corona shield tape comprises a conductive and / or semiconductive or partially conductive material applied on a flexible carrier, such as a film, non-woven fabric, and / or fabric (referred to here as the "carrier tape"), which is connected to the carrier tape and optionally joined to the final covering layer and / or another layer by means of a tape adhesive, which represents the polymer matrix and / or contains a polymer matrix.

[0039] As a conductive and / or semiconductive or partially conductive material, for example, ceramic materials using carbon-based fillers and / or having a partially conductive coating, in particular a conductive coating achieved by doping (which is made of, for example, titanium oxide and / or tin oxide and / or silicon carbide doped and undoped with aluminum), especially mica-based materials, are used. On the other hand, as an alternative or supplement, the mentioned conductive and / or semiconductive or partially conductive materials, such as doped titanium oxide and / or tin oxide and / or silicon carbide doped and undoped with aluminum, can also exist as fillers without the form of a substrate (such as mica).

[0040] The tape for manufacturing an external corona shielding winding contains at least one binder, usually a polymer, and a mixture of planar and / or spherical and / or tubular conductive and / or partially conductive fillers, which optionally have a possibly doped coating.

[0041] According to an advantageous embodiment of the present invention, the polymer matrix contains various polyvinyl alcohols. In principle, the polyvinyl alcohol according to the present invention can be used as the polymer matrix of the corona shielding tape or a part of the polymer matrix, but some particularly suitable polyvinyl alcohols that can be used alone or in combination are mentioned below for example.

[0042] The polyvinyl alcohol with CAS number 9002-89-5 and the molecular general formula of the repeating unit (-C 2 H 4 O-) n is a thermoplastic material and is commonly commercially available as a crystalline, white to light yellow water-soluble plastic.

[0043] Different from most vinyl polymers, polyvinyl alcohol cannot be manufactured by the simple polymerization of the corresponding monomer. The necessary monomer vinyl alcohol only exists as acetaldehyde in its tautomeric form. Polyvinyl alcohol is obtained by the transesterification and / or alkaline saponification of polyvinyl acetate. The hydrolysis is easily controlled. There are polyvinyl alcohol copolymers and various derivatives, in which a part of the hydroxyl groups are replaced by chemically similar reactive groups such as siloxanes.

[0044] Suitable polyvinyl alcohols have, for example, a degree of hydrolysis greater than 70 mol%. Advantageously, fewer or more hydroxyl groups are replaced by silicon-containing compounds.

[0045] According to an advantageous embodiment of the present invention, the polymer matrix in the tape contains polyvinyl alcohol with crosslinked parts. To what extent?

[0046] According to an advantageous embodiment, the polymer matrix in the tape contains one or more polyvinyl alcohols modified with aldehydes and / or crosslinked with melamine.

[0047] According to an advantageous embodiment of the invention, the polymer matrix comprises at least one polymer binder which is polyvinyl alcohol having a degree of hydrolysis of at least 70 mol%, in particular at least 85 mol%, preferably at least 87 mol% or more.

[0048] According to another advantageous embodiment of the invention, the polymer matrix comprises at least one polyvinyl alcohol, wherein the hydroxyl groups of the polyvinyl alcohol are at least partially substituted by siloxane groups and / or silanol groups.

[0049] For the detection of the composition of the corona shielding tape according to an embodiment of the invention, in particular in a finished insulation system, detection methods such as IR, UV and / or VIS spectroscopic methods and / or scanning electron research methods, in particular X-ray spectroscopy, such as EDX, are suitable.

[0050] According to an advantageous embodiment of the invention, the conductive filler mainly comprises a carbon-based component, such as a carbon modifier - preferably carbon black, graphite and / or carbon nanotubes.

[0051] According to another advantageous embodiment of the invention, the conductive filler comprises silicon carbide, undoped and / or doped silicon carbide.

[0052] According to another advantageous embodiment of the invention, the conductive filler comprises particles made at least in part of metal oxides, in particular mixed oxides.

[0053] Herein, a compound between a metal and oxygen is called a metal oxide, wherein the oxygen in the compound formally, i.e., simplifiedly has a 2-fold negative charge. In principle, the oxygen in the compound is an electronegative ligand. Hence it is called an "oxide".

[0054] A mixed oxide - abbreviated as MOX - correspondingly denotes a substance in which more than one metal cation is present in the oxidation compound, such as titanium-aluminum oxide or iron-nickel oxide, etc.

[0055] According to an advantageous embodiment of the invention, a coating made of doped tin oxide and / or doped titanium oxide and / or a filler composed of doped tin oxide and / or titanium oxide is used.

[0056] The filler particles can exist as hollow bodies, solid particles, coated particles and / or core-shell particles.

[0057] On the carrier tape, at least a part, but preferably not necessarily only sheet-like particles are applied, which are held together by the polymer matrix, i.e., the binder, and thus form a corona shielding tape. In order to adjust the resistance, it may be advantageous here to supplement that part of the sheet-like filler particles with spherical, i.e., globular, filler particles.

[0058] According to an advantageous embodiment of the invention, the corona shielding tape has a basis weight of < 150 g / m 2 , preferably less than 100 g / m 2 per unit area.

[0059] According to an advantageous embodiment, the carrier tape comprises reinforcing fibers, for example in the form of a fabric and / or a fiber composite, incorporated into and / or on and / or adhesively bonded to a polymer matrix containing a conductive filler.

[0060] The carrier tape preferably has a basis weight of 30 - 60 g / m 2 per unit area.

[0061] These reinforcing fibers are, for example, glass fibers and / or polyethylene terephthalate - PET fibers.

[0062] According to an advantageous embodiment, the carrier tape is coated with a primer. Particularly advantageously, the carrier tape is coated with up to 5 g / m 2 of primer.

[0063] Particularly proven to be advantageous is that the primer of the carrier tape comprises polyvinyl alcohol, epoxy functional groups and / or amine functional groups.

[0064] Here, the primer represents a base coat by which the cut resistance of the reinforcing fibers and / or the carrier tape, carrier fabric is improved and prepared for wetting with and bonding to the polymer matrix.

[0065] According to an advantageous embodiment of the invention, the amount of the carrier tape coated with a polymer matrix containing at least a part of the conductive filler and / or optionally also at least one promoter is 20 g / m 2 to 100 g / m 2 , in particular 20 g / m 2 to 60 g / m 2 , particularly preferably 30 g / m 2 to 45 g / m 2 .

[0066] According to the invention, the corona shielding tape is used for manufacturing an external corona shielding system and / or an internal potential control system and / or an end corona shielding system.

[0067] Advantageously here, the sheet resistance and / or surface resistance of the external corona shielding system and / or the internal potential control system made of the corona shielding tape according to the invention is 0.01 kΩ to 100 kΩ, measured at a field strength of 1 V / mm.

[0068] In particular, the sheet resistance and / or surface resistance value controlled by this internal potential is preferably from 0.01 kΩ to 10 kΩ, more preferably from 0.01 to 5 kΩ, particularly preferably from 0.05 to 1 kΩ, and / or the sheet resistance value of this external corona shield is from 0.1 to 100 kΩ, especially from 0.1 kΩ to 50 kΩ, particularly preferably from 1 kΩ to 10 kΩ, measured at an electric field strength of 1 V / mm respectively.

[0069] In the case of manufacturing an end corona shield with a corona shield tape according to the invention, it is advantageous that at an electric field strength of 100 V / mm there is a surface resistance of 1×10 8 to 1×10 12 ohms, especially 1×10 8 to 1×10 12 ohms.

[0070] The present invention relates to a corona shield tape for high-voltage motors, which comprises an epoxy resin without acid anhydride, especially without phthalic anhydride derivatives. The corona shield tape introduced here for the first time is adjusted to a novel epoxy resin-based VPI impregnating resin without alkyl phthalic anhydride derivatives, etc. through its components, especially the adhesive polymer matrix and the embedded cationic tape accelerator.

[0071] The tape accelerator is preferably a compound structured from an ion source of one or more sulfonium cations and one or more anions, especially complex-structured anions such as hexafluoroantimonate anions, which are respectively suitable for the VPI process of manufacturing an insulating system with an acid anhydride-free impregnating agent.

[0072] The tape accelerator is a cationic tape accelerator, so it is preferably structured from an ion source. In particular, the tape accelerator has a sulfonium cation.

[0073] For example, suitable cationic tape accelerators are chemical compounds belonging to one of the structural formulas I, II or III:

[0074] Super strong acid salts having a sulfonium cation structure I

[0075]

[0076] Cation structure II

[0077]

[0078] Cation structure III

[0079]

[0080] The sulfonium cations I, II and III shown here and complex anions such as BF 4 - 、PF6 - , SbF 6 - , AsF 6 - , SbF 5 (OH) - , ASF 5 (OH) - , Al[OC(CF 3 ) 3 4 - Form the corresponding superacid salts, which can be used herein as promoters.

[0081] "Superacid" means an acid stronger than 100% sulfuric acid with a pKa value = -3. Examples are fluorosulfonic acid, fluoroantimonic acid, perhalocarboranes, etc.

[0082] Herein, the structural formula "Structure I" represents the cationic part of the promoter-containing according to a preferred embodiment of the present invention.

[0083] "Cationic promoter" means a promoter constructed from an ion source, the cation of which initiates the cationic polymerization, especially cationic homopolymerization, of a pre-placed impregnating resin in a liquid impregnating agent.

[0084] A compound constructed as an "ion source" means a heteropolar compound, the chemical reactivity of which is determined by the cations and anions present in the compound. Classic compounds in which an "ion source" exists are salts. However, complex structures having cationic and anionic characteristics are also referred to herein as compounds constructed as an "ion source".

[0085] "Sulfonium cation" is a cation that contains, in addition to the one or more anions in the molecule, a unit that can be represented by the simple positively charged structure II or III or by the empirical formula [SR 3 + .

[0086] "Alkyl-aryl-sulfonium" or "dialkyl-aryl-sulfonium" herein means a sulfonium cation in which one or two of the three "R" groups on the sulfur atom in the sulfonium cation are alkyl groups. An alkyl group is a molecular moiety consisting of interconnected carbon and hydrogen atoms. In the context of the present invention, preferred alkyl groups are those having 1 to 12 carbon atoms, which may be branched or linear. The alkyl group is monovalently connected to the central sulfur atom herein.

[0087] According to the present invention, one or two alkyl groups may be present in the dialkyl-aryl-sulfonium cation, which may be the same or different from each other.

[0088] ​​"Aryl-alkyl-sulfonium or diaryl-alkyl-sulfonium" herein denotes a sulfonium cation in which one or two of the three "R" groups on the sulfur atom of the sulfonium cation are aryl groups. An aryl group is a molecular moiety that is monovalently or attached via a single bond to a carbon skeleton or a sulfur atom and has at least one aromatic ring that may be partially or fully substituted or unsubstituted.

[0089] According to the present invention, one or two aryl groups may be present in the aryl-alkyl-sulfonium cation, which may be the same or different from each other.

[0090] The third group may be arbitrary here, i.e., it may be an alkyl or aryl group, which is fully or partially substituted or unsubstituted.

[0091] An aryl group is an organic chemical group having an aromatic skeleton. It is the name of a monovalent atomic group derived from an aromatic hydrocarbon by removing a hydrogen atom bonded to the ring. Most aryl groups are derived from benzene, and the simplest aryl group is the phenyl group.

[0092] According to a preferred embodiment, at least one aryl group is present in the sulfonium cation.

[0093] Preferably here, there is at least one monocyclic aryl group, i.e., for example, an aryl group having an aryl structure derived from benzene, such as a phenyl group or a benzyl group.

[0094] Particularly preferably, there is at least one substituent on the monocyclic aromatic group of the aryl group in the sulfonium cation, i.e., a hydrogen on the aromatic ring is substituted, for example, by a functional group or an alkyl group.

[0095] The functional group may be present here in the form with or without heteroatoms, such as oxygen, nitrogen, sulfur, phosphorus.

[0096] Particularly preferred is an aryl group in which the hydrogen on the aromatic ring is substituted by an acetoxy group.

[0097] Furthermore, particularly preferably, a sulfonium cation combined with a hexafluoroantimonate anion is present as a corona shielding belt promoter.

[0098] The corona shielding belt promoter may be present as a mixture of at least two cationic belt promoters, the two cationic belt promoters having different sulfonium cations respectively. The anions may be the same or different, particularly hexafluoroantimonate as the anion.

[0099] The corona shielding belt promoter, whether present as a single compound or as a mixture, preferably has a melting point in the range of 145 °C to 165 °C, particularly preferably a melting point in the range of 150 °C to 160 °C.

[0100] The subject matter of the present invention is also the use of a reactive corona shielding tape for producing an acid anhydride-free insulation system by impregnating a solid corona shielding tape with an impregnating agent, where the impregnating agent contains an acid anhydride-free and epoxy group-containing aromatic and / or cycloaliphatic impregnating resin.

[0101] In particular, anions of complexed structure, such as hexafluoroantimonate anions, are suitable as anions of the cationic tape promoter, and thus, for example, 4-acetoxyphenyl-dimethylsulfonium hexafluoroantimonate - CAS No. 135691-31-5 - of structure I is present as a tape promoter.

[0102] The present invention is explained in more detail below by means of application examples which describe embodiments of the invention:

[0103] By using the sulfonium superacid derivative 4-acetoxyphenyl-dimethylsulfonium hexafluoroantimonate mentioned in structure I, polyvinyl alcohol preferably modified with silanol groups, and a doped flaky filler, such as tin oxide, which has been adjusted to be partially conductive, and an aqueous mixture of an organic solvent, such as 2-butanone and water, a paint can be prepared which can be impregnated / applied to a polymer and / or glass fabric carrier and is used to form, after drying, a layer on the polymer and / or glass fabric carrier which has the required conductivity according to the invention, i.e., has a sheet resistance in ohms in the temperature range from 20 to 150 °C.

[0104] By using the sulfonium superacid derivative as a crosslinking promoter, this novel corona shielding tape is suitable for curing traditional epoxy resin-phthalic anhydride mixtures as well as novel, i.e., acid anhydride-free, epoxy resin-containing impregnating agents (which are especially combined with cycloaliphatic epoxy resins). Such a (one or more) sulfonium superacid derivative can gel and cure bisphenol A-diglycidyl ether, bisphenol F-diglycidyl ether, glycidyl esters, aliphatic and / or cycloaliphatic epoxy resins (separately alone and in any combination). Successful tests have been carried out on cycloaliphatic epoxy resins mixed with BADGE (bisphenol A-diglycidyl ether).

[0105] Surprisingly, it has been shown that, in the sense of tape stability with respect to the conductivity of the layer, a shaping crosslinking agent can also be additionally applied, but the tape also has sufficient stability for winding without a shaping crosslinking agent.

[0106] The corona shielding tape thus produced by subsequent hot air drying shows only slightly adverse swelling behavior when hot impregnated at 70 °C and subsequently hot cured at 140 °C using an anhydride-free epoxy resin or a favorable mixture of about 80 wt% alicyclic epoxy resin and about 20 wt% distilled bisphenol A-diglycidyl ether according to the invention. Thus, the sheet resistance initially set on the corona shielding tape also remains anhydride-free during and after curing with the liquid epoxy resin, most preferably mainly, but not exclusively, of alicyclic structure, and thus retains its partially conductive properties when the corona shielding tape is applied in an electric machine to reduce the high electric field strength in the stator winding.

[0107] According to the invention, then, for the preparation of the paint, 20.0 g of 4-acetoxyphenyl-dimethylsulfonium hexafluoroantimonate are dissolved in 200.0 g of ethyl methyl ketone. This clear organic solution is slowly added dropwise with stirring at room temperature to a suspension of 590.0 g of Iriotec 7320 (company Merck KGaA, Darmstadt) and 108.7 g of Poval TM 25-98R (company Kuraray Europe GmbH, Hattersheim am Main) in 2400.0 g of distilled water and stirred for a further 30 minutes at room temperature, for example by means of a dissolver with a toothed dispersing disk, in order to chop up possible agglomerates by shear in the vicinity of the disk.

[0108] This turquoise-colored shiny paint suspension is then applied by dip coating in a base coater belt impregnating device (company COATEMA Coating Machinery GmbH, Dormagen) to a 200 mm wide glass / polyester-mixture fabric (company Krempel GmbH, Vaihingen / Enz) with a unit area weight of 44.7 g / m 2 and dried vertically in a hot air fan oven at a belt surface temperature of about 120 °C over a length of 1.5 m at a belt speed of 0.8 m / min. The result on the belt is a dry total applied amount of 27.48 g / m 2 , where 0.77 g / m 2 of 4-acetoxyphenyl-dimethylsulfonium hexafluoroantimonate as promoter substance, 22.56 g / m 2 of Iriotec 7320 as field-controlling partially conductive material and 4.16 g / m 2 Poval TM 25-98R as binder. Overall, the tape thus has a specific total unit area weight of about 72 g / m 2 .

[0109] A corona shielding tape with excellent touch feel, very easy to wind, non-sticky, low odor, turquoise color, strong and novel has a sheet resistance at 20 - 23 °C ohms, using a 10 cm 2 high-ohm spring tongue electrode 3501FE is measured according to DIN53482 or DIN EN 62631-3-2 (company name H.-P.Fischer Elektronik GmbH&Co., Mittenwalde).

[0110] To study the critical swelling behavior of the novel corona shielding tape in the epoxy resin of a phthalic anhydride-free mixture based on alicyclic epoxy resin and glycidyl ether epoxy resin according to the present invention during the VPI impregnation process and the heat curing process, two strips of corona shielding tape with dimensions of 12 cm × 2.5 cm are prepared, and commercially available conductive silver paint is applied on both sides at the ends with a width of 1 cm each to obtain two electrically contactable strips of corona shielding tape with dimensions of 10 cm × 2.5 cm. These strips are in contact with heat-resistant alligator clips at the conductive silver paint contacts and are connected to a multi-channel precision measuring device 2890-9 (company name Ahlborn Mess-und Regeltechnik GmbH, Holzkirchen) for continuous resistance recording.

[0111] Then, the strips of corona tape are placed under tension due to their weight in the center respectively, transferred to a circulating air oven, and completely immersed in a 70 °C hot phthalic anhydride-free epoxy resin mixture for 4 hours. This mixture consists of 80% by weight of 3,4-epoxycyclohexylmethyl 3',4'-epoxycyclohexanecarboxylate (Cel-loxide TM C202 1P, company name Daicel Corporation, Tokyo; CAS number 2386-87-0) type alicyclic epoxy resin and 20% by weight of distilled bisphenol A-diglycidyl ether (Epikote TM Resin 162, company name Hexion GmbH, Iser-lohn; CAS number 1675-54-3).

[0112] After a period of 4 hours following the 70 °C VPI impregnation stage, the corona shield strip of the electrical contact is removed from the resin and thermally cured in an oven at 145 °C for 10 hours, and then cooled to room temperature. The resistance is continuously recorded during this time. By converting the resistance recorded over time into a sheet resistance value (10 cm * 2.5 cm), it was surprisingly found that the ideal resistance characteristics of the novel corona shield strip remained at 1 - 10 kΩ over the full temperature range of 20 - 145 - 20 °C, and thus it is most suitable for controlling the electric field at the windings in motors and generators impregnated with non - anhydride, VPI epoxy resin.

[0113] A so - called resin infection experiment or promoter availability test was also carried out to check for the elution of the promoter from the novel corona shield strip. For this purpose, two corona shield strips with dimensions of 2.5 cm x 4.8 cm (12 cm 2 ) were prepared and stored in 30 g each of the above - mentioned (alkyl) phthalic anhydride - free epoxy resin (80 wt% 3′,4′ - epoxycyclohexanecarboxylic acid 3,4 - epoxycyclohexylmethyl ester / 20 wt% distilled bisphenol A - diglycidyl ether) at 70 °C for 4 hours. Then the impregnated corona shield strips were removed from the liquid, and the remaining epoxy resin mixture was stored at 100 °C for another 20 hours. After cooling to 70 °C, the dynamic viscosities (η 样品1，20小时 / 100℃，η样品2，20小时 / 100℃ ) were measured respectively. The following values and properties were obtained after subtracting the resin blank value (η BW，20小时 / 100℃ ) without the corona shield strip:

[0114] η BW，20小时 / 100℃ = 24.87 mPa·s

[0115] η 样品1，20小时 / 100℃ = 43.78 mPa·s

[0116] η 样品2，20小时 / 100℃ = 56.93 mPa·s

[0117] Appearance 样品1&2，20小时 / 100℃ = The corona strip is hard and non - sticky

[0118] Promoter availability 样品1，20小时 / 100℃ = 43.78 mPa·s - 24.87 mPa·s = 18.91 mPa·s

[0119] Promoter availability 样品2，20小时 / 100℃ = 56.93 mPa·s - 24.87 mPa·s = 32.06 mPa·s

[0120] Furthermore, after storage at room temperature for up to 4 weeks, the reactivity of the novel corona shielding tape was examined. For this purpose, punched samples were taken from the corona shielding tape, wetted in a DSG crucible with an acid anhydride-free epoxy resin (80 wt% 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate / 20 wt% distilled bisphenol A-diglycidyl ether), and the reaction enthalpy was determined at 10 K / min by dynamic differential scanning calorimetry (Netzsch-Devicebau GmbH, Selb; DSC Phoenix Fl) (see Figure 5). With the help of a rather constant reaction enthalpy (about 300 - 400 joules per gram of epoxy resin mixture), the stability of the novel corona shielding tape could be demonstrated.

[0121] Based on a new generation of insulation systems that can be made by impregnating with an anhydride-free impregnating agent, the present invention for the first time discloses a corona shielding tape in which a very suitable tape accelerator for rapid initiation of homopolymerization can be placed. The tape accelerator is present in the form of a super strong acid salt and is stably stored for up to 6 months at a temperature of +6 °C to 23 °C in a corona shielding tape that at least partially contains polyvinyl alcohol as a polymer matrix.

Claims

1. A corona shielding tape for further processing into an insulation system, said insulation system comprising an impregnated winding having potential control by means of an external corona shield "AGS" and / or an internal potential control "IPS" and / or an end corona shield "EGS", said insulation system being made by impregnating the winding with an acid anhydride-free and resin-based impregnating agent at 45 - 85 °C and under vacuum, wherein said corona shielding tape comprises at least one carrier tape, a conductive and / or partially conductive filler in a polymer matrix, and at least one tape promoter suitable for curing and / or gelling the impregnating agent, characterized in that, said polymer matrix comprises at least one polyvinyl alcohol and / or a polyvinyl alcohol copolymer, and said at least one tape promoter is selected from superacids salts which are suitable for promoting the cationic homopolymerization of said resin-based acid anhydride-free impregnating agent, wherein the basis of said resin-based impregnating agent is an acid anhydride-free epoxy resin, and wherein at least one ion of the superacid salt which is at least part of the tape promoter is a sulfonium cation having an aryl group.

2. The corona shielding tape according to claim 1, wherein a plurality of tape promoters are present in combination.

3. The corona shielding tape according to claim 1, wherein the sulfonium cation is present in the form of an aryl-alkyl-sulfonium cation.

4. The corona shielding tape according to claim 1, wherein at least one dialkyl-aryl-sulfonium cation is present.

5. The corona shielding tape according to claim 1, wherein at least one diaryl-alkyl-sulfonium cation is present.

6. The corona shielding tape according to any one of claims 1 to 5, wherein the aryl group of the sulfonium cation is present in a substituted form.

7. The corona shielding tape according to any one of claims 1 to 5, wherein a tape promoter comprising a sulfonium cation having an aryl group is present, said aryl group comprising a phenyl group substituted with an acetoxy group.

8. The corona shielding tape according to any one of claims 1 to 5, which comprises a superacid salt having the following chemical structure as a tape promoter:

9. The corona shielding tape according to any one of claims 1 to 5, wherein said polymer matrix comprises a plurality of polyvinyl alcohols.

10. The corona shielding tape according to any one of claims 1 to 5, wherein said polymer matrix comprises at least one polyvinyl alcohol having a crosslinked portion.

11. The corona shielding tape according to any one of claims 1 to 5, wherein said conductive and / or partially conductive filler may comprise at least one component selected from carbon black, graphite, carbon nanotubes CNT, antimony-doped tin oxide, silicon carbide, and / or aluminum-doped silicon carbide, said respective components being present in doped or undoped, coated or uncoated, doped and coated or undoped but coated form.

12. Use of the corona shielding tape according to any one of the preceding claims 1 to 11 for manufacturing an insulation system having AGS, IPS, and / or EGS.

13. A rotating electrical machine having an insulation system obtainable by the use according to claim 12.

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