EP4208882A1 - Corona shielding strip for a high-voltage rotating electric machine, use thereof, and electric machine - Google Patents

Abstract

The invention relates to a corona shielding strip, in particular a reactive corona shielding strip, for a high-voltage rotating electric machine, comprising an insulation system that can be produced by means of a vacuum pressure impregnation (VPI) process, wherein, owing to concerns about the sensitising effect of anhydrides on the respiratory tract, the impregnation agent for impregnating the corona shielding strip in the VPI process is preferably anhydride-free. Based on the new generation of insulation systems, which can be produced by impregnation with anhydride-free impregnation agents, the present invention discloses for the first time a corona shielding strip in which a strip accelerator that initiates homopolymerisation quickly can be placed. The strip accelerator is in the form of a salt of a superacid and is storage-stable for up to 6 months in a corona shielding strip that contains, at least in part, polyvinyl alcohol as a polymer matrix.

Description

description

Corona protection strip for rotating electrical high-voltage machine, use therefor and electrical machine

The invention relates to a corona protection band, in particular a reactive corona protection band, for a rotating electrical high-voltage machine with an insulation system that can be produced by vacuum pressure impregnation process (VPI process), the impregnation agent in the VPI process being used for concerns about the airway sensitizing effect of the Anhydrides de, preferably anhydride-free. The invention also relates to the use of such a corona protection strip and an electrical machine with an insulation system that can be produced using the corona protection strip.

Depending on the rated voltage of the rotating electrical machine, different combinations of components of an insulation system are used when producing an insulation system . For example, in motors with a rated voltage of approximately more than 2kV, there is a conductive layer at the slot exit point to equalize the field, the external corona protection, AGS. From an approximate rated voltage of 6kV, an AGS is usually reinforced at the ends by end corona protection EGS and from a rated voltage of approx . 12kV, the insulation system on the main insulation is reinforced by an IPS internal potential control.

Because of physiological concerns about the hitherto customary use of anhydride-containing crosslinkers in the impregnating agents of the insulation system, in particular the insulation systems that can be produced by VPI, the anhydride is increasingly being replaced by anhydride-free impregnating agents. This substitution entails a whole range of adjustment problems, since the winding tapes and/or corona protection tapes, which in turn contain organic binders such as the tape adhesive, polymer-based matrix materials and, in the case of reactive corona protective tapes also include curing catalysts, to which the newly used anhydride-free impregnating agents must be matched.

So far, there has been no formulation for an insulation system with AGS, EGS and/or IPS that includes a corona protection tape, a number of sensitive components such as the tape adhesive, the polymer matrix, the fillers, their coatings and an anhydride-free impregnating agent, which in one common VPI process into a usable isolation system.

The conductive layers of the IPS and the AGS usually consist of a composite material containing carbon black and/or graphite and based on a polymer matrix. No component of the composite material, neither the carbon black/graphite nor the polymeric matrix are resistant to partial discharges. If a partial discharge hits the conductive layer, the soot reacts with the surrounding oxygen to form CO ₂ . The same applies to the polymeric matrix.

Main insulation or AGS, EGS and IPS are usually formed by winding mica tape or corona protection tape, which is impregnated with an impregnating agent. The mica tape of the main insulation usually includes a barrier material, such as mica for insulation, while the corona protection tape contains electrically conductive or partially conductive fillers, such as carbon black, etc. includes . In the case of Global-VPI, in contrast to Single-VPI, IPS, AGS and/or EGS are generally applied as tapes, preferably to coils/rods that have not yet been impregnated and subsequently—particularly preferably—impregnated in an impregnation process with an impregnating agent.

In particular, the tertiary amines and/or organic zinc salts that have been customary up to now and are ideally suited for anhydride-containing impregnating agents can no longer be used as so-called belt accelerators for the new, anhydride-free impregnating agents because they can no longer be used under the conditions of the Inadequate networking of the VPI process. This ultimately results in uncured, soft areas in parts of the AGS, EGS, IPS and/or main insulation and/or to polymers with low glass transition temperature. A low glass transition temperature should also be avoided locally, since these areas have insufficient mechanical and electrical properties and lead to significantly premature degradation. During operation, these low-load areas are quickly thermally and electrically degraded or destroyed.

Corona protection tapes as part of the insulation system are used in rotating electrical high-voltage machines. Rotating high-voltage machines are, for example, motors or generators in a power plant for generating electrical energy. Such rotating high-voltage machines have, in particular, a stator winding which is subject to particularly high demands in terms of strength and reliability. In particular, the insulation system of the stator winding at the interface between the main insulation and the laminated core, especially in rotating electrical machines from approx. 2 kV rated voltage, the stator winding is heavily loaded by high thermal, thermomechanical, dynamic and electromechanical operating stress, which means that the risk of damage to the insulation system of the stator winding due to partial discharge is high.

The stator winding has a conductor assembly that is electrically insulated from the main insulation and that is mounted in a slot that is arranged in the laminated core. When the rotating electrical machine is in operation, the stator is exposed to alternating thermal stress, as a result of which mechanical stresses are generated in the main insulation, caused by different thermal expansion rates and thermal conductivities of the conductor, the main insulation and the laminated core. As a result, localized detachment of the main insulation can occur, creating cavities between the main insulation and the sheet metal packets arise in which partial discharges can ignite. The partial discharges can lead to damage to the main insulation, which in the worst case can lead to an earth fault between the laminated core and the conductor, which means that the machine can no longer be operated . The conductor with its main insulation conventionally protrudes at the slot exits, where the interface between the conductor and the main insulation is arranged, which forms a sliding arrangement. This can be seen, for example, in FIG. 1 of EP 2362399B1, in which the section of the turbogenerator stand shown there corresponds schematically to the slot exit point dealt with here.

The main insulation of the winding against the laminated core is an electrically highly stressed system. During operation, high voltages arise, which must be dissipated in the insulating volume between the conductor bar and the laminated core, which is at ground potential. Field increases occur at the edges of the sheets in the laminated core, which in turn cause partial discharges and ultimately lead to premature aging and, in the worst case, to destruction of the insulation.

The exit point of the stator bars/coil legs from the laminated core, the slot exit point, is characterized by the meeting of two insulating materials, the gaseous and the solid, and the AGS and/or IPS or the laminated core. In this area, a boundary layer forms between the main insulation, which is solid in its aggregate state, and a gaseous medium, usually air or hydrogen . The resulting dielectric interface between the main insulation and the air creates a classic slip arrangement which, in addition to a purely radial field component E _rad , which is perpendicular to the conductor and which occurs in the area of the laminated core, also has a tangential field component E _{tan arising} along the conductor after AGS end has . The interfaces that are tangentially stressed as a result, for example between the main insulation and the air, represent particular weak points in an insulation arrangement. Due to the low electrical strength of the air, partial discharges can occur even with comparatively low voltages in this area of the triple point "laminated core insulation system-air" at the end of the external corona protection "AGS", caused by the local tangential field strength increase of approx. 0.5kV/mm with a clean surface, which can expand as the voltage increases to form creeping discharges along the insulating material surface up to an electrical breakdown, which is characterized by a conductor-earth short circuit.

In order to suppress these electrical creeping discharges, a resistive-capacitive field control in the form of an end corona protection "EGS" is connected to the AGS in addition to the external corona protection "AGS" for electrical rotating machines from a rated voltage of 6kV. When calculating and designing an end corona protection, it must be noted that the highest electro-thermal load on the system does not occur at the operating voltage, but rather when the insulation system is checked with an increased test voltage . The insulating material is destroyed in the long term by the formation of creeping discharges on the surface. Like the external corona protection, the end corona protection is a resistive coating directly on the surface of the main insulation. In contrast to the "AGS", the external corona protection, which has a surface resistance of around 1000 - 10,000 ohms, the "EGS", the end corona protection, has a significantly higher electrical surface resistance, which is non-linear and has a field strength of 100V/mm is around 5 x 10 ⁹ ohms. In general, the relevant resistance range of the EGS can be specified as 2x10 ⁸ ohms to 1x10 ¹³ ohms.

In particular, heating, electrical erosion and chemical degradation can destroy the EGS and thus damage the insulation system and ultimately flashover as a result of the destruction of the end corona protection. It can be due to local heat development an operating point shift in addition to disrupting the functioning of the insulation system and increasing the dielectric losses.

The AGS has a certain square resistance, which must not fall below or exceed a specific lower and upper limit. If the limit value is not reached, high circulating currents induced, which close via the ends of the laminated core and the external corona protection, can lead to high-current arcs between two laminated cores in the laminated core, resulting in high electrical losses . If the resistance is too high, high-voltage spark erosion can occur, in which case the AGS no longer acts like a field equalization, but like an insulation. Ideally, external corona protection has a pronounced anisotropy in the resistance behavior; the resistance in the tangential, i.e. axial, direction should be high and in the radial direction low.

In practice, however, this desired property of the AGS cannot be realized, so that hitherto the AGS has always had lower resistance in the tangential direction than in the radial direction. These phenomena can also be read in relevant specialist literature, for example in "High Voltage Technology" by A. Küchler, Springer Verlag, Vol 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, pp 927-932.

The object of the present invention is therefore to provide a corona protection strip for further processing in the VPI process, a carrier strip, at least one strip accelerator for the impregnating resin and at least one polymeric matrix material with an electrically conductive, optionally coated filler comprehensive, wherein the belt accelerator contained in the corona protection belt is suitable for curing-accelerating an anhydride-free impregnating agent, in particular based on epoxy resin, in the VPI process. The solution to this problem is provided by the subject matter of the present invention, as disclosed in the description, the claims and the figures.

Accordingly, the subject of the present invention is a corona protection tape for further processing into an insulation system with winding and potential control through external corona protection and/or internal potential control and/or end corona protection, the insulation system by impregnating the winding with an anhydride-free and resin-based Impregnating agent at 45 ° C to 85 ° C and under vacuum, for example by means of VPI impregnation, can be produced, the corona protection tape at least one carrier tape an electrically conductive or partially conductive filler in a polymer matrix and at least one tape accelerator suitable for Hardening and/or gelling of the impregnating agent, characterized in that the polymer matrix contains at least one polyvinyl alcohol and/or a polyvinyl alcohol copolymer and that the at least one belt accelerator is selected from the group of super acid salts , using it to speed up a katio African homopolymerization of the resin-based anhydride-free impregnating agent is suitable.

The basis of the resin-based impregnating agent is preferably an epoxy resin, in particular also an epoxy resin mixture, for example an epoxy resin mixture comprising one or more cycloaliphatic epoxy resins. This mixture can also contain siloxane, for example, so that when the impregnating agent cures, a duromer with a backbone comprising —O—SiR ₂ —O— units is obtained.

According to an advantageous embodiment of the invention, the impregnating agent is in particular a phthalic anhydride or phthalic anhydride derivative-free resin or a resin mixture based on epoxy, preferably at least one cycloaliphatic epoxy resin and an epoxy resin based on bisphenol A and/or bisphenol F diglycidyl ether. and/or epoxy volak base comprehensive . For example, there is an impregnating resin mixture based on cycloaliphatic epoxy resin and bisphenol A diglycidyl ether in a mixing ratio in the range from 50:50 to 90:10, in particular in a mixing ratio of 80:20 (m/m).

For example, the polymer matrix includes the tape adhesive and - at least partially - the tape accelerator dissolved and/or finely distributed in it, also called "tape catalyst". -Pressure impregnation (VPI) acts on the corona protection strip and the main insulation of the stator winding.This usually happens at elevated temperatures, 45 °C to 85 °C.After impregnation, the stator windings in the stator core are thermally post-hardened.

The at least one belt accelerator is preferably present in the polymeric matrix with the fillers. During impregnation, this mixes at least partially with the impregnating agent and/or can at least partially migrate into the impregnating agent and thus serves to gel the impregnating agent before it hardens in the subsequent tempering step of the impregnating process.

According to one embodiment of the invention, the tape accelerator, which is present for example and preferably in the form of a superacid salt, is present in the polymer matrix or the tape adhesive, ie comprising at least one polyvinyl alcohol, very finely distributed and/or dissolved.

Because of the required and desired storage stability of the corona protection tape, it is advantageous if the tape accelerator present in the corona protection tape in the form of a super acid and/or a super acid salt only reacts on contact with the impregnating agent and at elevated temperatures of 45° C. to 85° C . A prior reaction with the polymeric matrix is undesirable because the belt accelerator is then “loaded”. would be needed" and the impregnating agent could no longer harden, gel or harden. Therefore, a critical point of the present invention is that the belt accelerator is in the form of the extremely reactive super acid and/or a derivative thereof, with the polymer matrix of the corona protection strip does not react or reacts to an insignificant extent under conditions of up to 70 °C.

The accelerator in the carrier tape is, for example, in an amount in the range from 0.1 g/m ² to 15 g/m ² , in particular from 0.25 g/m ² to 10 g/m ² , preferably in an amount of 0. 5 g/m ² to 5 g/m ² included.

The embedded belt accelerators and belt accelerator concentrations in the components of the insulation system can be the same or different.

The "components of the insulation system" that are primarily affected here are, for example

- the winding of the main insulation - without conductive or partially conductive fillers, since the main insulation is electrically insulating,

- the winding of the IPS , AGS and/or EGS , which have graded electrical conductivity or partial conductivity, see above .

In order to avoid partial discharges, the main insulation of winding bars/coils can be shielded against cavities and detachments with an inner and an outer conductive layer, precisely by means of internal potential control IPS and AGS, as explained above. An EGS can then be applied to the AGS.

Corona protection tapes are known from EP 2362399 and DE 19839285 G1, in which a planar filler is bound in a polymeric matrix. The planar filler described consists of a mica substrate with doped metal oxide, for example titanium oxide and/or tin oxide, is coated. In particular, this filler is more resistant to partial discharges than the carbon-based fillers.

In principle, the electrical resistance in the direction of the strip in the polymer matrices filled with planar fillers is significantly lower than that perpendicular through the strip, which in turn reduces the electrical conductivity in the radial direction. The radial resistance can be reduced by the addition of round fillers, in which quartz material or powdered quartz serves as the substrate, which in turn has also been coated with doped metal oxide.

According to a preferred embodiment, the electrically conductive and/or partially conductive filler has at least one component selected from the group consisting of carbon black, graphite, carbon nanotubes—CNTs—, antimony-doped tin oxide, silicon carbide and/or aluminum-doped silicon carbide, with the respective component being doped or undoped, coated or uncoated, doped coated or undoped coated.

A capacitive-resistive field control is used to reduce the field strength increase in the area of the end of the external corona protection. The capacitive control is realized through the main insulation, while the resistive control takes place through the end corona protection (EGS). These are conductive surface coatings that have a square resistance of approx. 10 ⁸ to 10 ¹⁰ ohms at a field strength of 100 V/mm. With the help of the strong non-linearity of the resistance of the materials used in the EGS, an attempt is made to displace the electric field from the areas of high field strength. This is due to the reduction in specific resistance as the electrical field strength increases. The ohmic surface coatings can be applied either by painting from drying and/or hardenable resins, which are applied directly to the surface of the insulating material and/or together with the production of the wound main insulation, which is then applied before production or respectively Impregnation of the main insulation are wound up as tapes, either in the form of a prepreg or an already cured, porous tape.

The main insulation of the winding is then impregnated with an impregnating resin and, for example, by means of a vacuum pressure impregnation process (VPI process) carried out therewith. Conventionally, that is to say according to the state of the art, epoxy resins and/or epoxy resin mixtures with anhydrides in particular are used as hardeners. Because of the sensitizing effect on the respiratory tract and corresponding concerns about the unrestricted use of anhydrides as hardeners, in particular phthalic anhydrides, or and/or phthalic anhydride derivatives, only anhydride-free, in particular phthalic anhydride or Phthalic anhydride derivative-free impregnating agent used. From the

For example, WO2016/124387 discloses an insulation system based on an epoxy resin with an anhydride-free impregnating agent that can be homopolymerized.

Accordingly, a reactive corona protection band comprises an electrically conductive and/or semi- or partially conductive material applied to a flexible carrier such as film, fleece and/or fabric, which is referred to here as "carrier tape", which is connected to the carrier tape with one another and is optionally connected to a final cover layer and/or a further layer by means of a tape adhesive which represents the polymer matrix and/or comprises the polymer matrix.

As an electrically conductive and / or semi- or partially conductive material z. B. Carbon-based fillers and/or ceramic, in particular mica based material with a partially conductive coating, in particular a conductive coating obtained by doping, for example made of titanium oxide and/or tin oxide, and/or silicon carbide doped with and without aluminum. On the other hand, as an alternative or in addition, the mentioned electrically conductive and/or semi- or partially conductive materials such as doped titanium oxide and/or tin oxide and/or silicon carbide doped with and without aluminum can also be used without a substrate, such as mica Filler present.

The tape that is used to produce the external corona protection winding comprises at least one binder, usually a polymer and a mixture of planar and/or globular and/or tubular electrically conductive and/or partially conductive fillers, which optionally have a u. U. have doped coating.

According to an advantageous embodiment of the invention, the polymeric matrix comprises several polyvinyl alcohols. In principle, polyvinyl alcohols according to the invention can be used as the polymer matrix or part of the polymer matrix of the corona shielding strip, but some particularly suitable polyvinyl alcohols, which can be used alone or in combination, are mentioned below, for example.

Polyvinyl alcohol with the GAS number 9002-89-5 and the molecular formula (-C ₂ H ₄ O-) _n the repeating unit is a thermoplastic and is commercially available as a crystalline, white to yellowish, water-soluble plastic.

Unlike most vinyl polymers, polyvinyl alcohol cannot be produced by simply polymerizing the corresponding monomer. The necessary monomer ethenol only exists in its tautomeric form as acetaldehyde. Polyvinyl alcohols are obtained by transesterification and/or alkaline saponification of polyvinyl acetate. The hydrolysis is easily controllable. There are polyvinyl alcohol copolymers and various derivatives in which a Some of the hydroxyl groups are replaced by chemically similar reactive groups such as siloxanes.

Suitable polyvinyl alcohols have, for example, a degree of hydrolysis of more than 70 mol%. Advantageously, few or more hydroxyl groups are substituted by silicon-containing compounds.

According to an advantageous embodiment of the invention, the polymeric matrix in the strip comprises polyvinyl alcohol with cross-linked portions. To what degree?

According to an advantageous embodiment, the polymeric matrix in the tape comprises one or more polyvinyl alcohol(s) modified with an aldehyde and/or crosslinked with melamine.

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

According to a further advantageous embodiment of the invention, the polymeric matrix comprises at least one polyvinyl alcohol in which the hydroxyl groups of the polyvinyl alcohol are at least partially substituted by siloxane and/or silanol groups.

Investigation methods such as IR, UV, and/or VIS spectroscopic methods and/or scanning electronic investigation methods, including X-ray spectroscopy, for example, are used to detect the components of a corona protective strip according to one embodiment of the invention, in particular also in a finished insulation system EDX, suitable .

According to an advantageous embodiment of the invention, the electrically conductive filler mainly comprises carbon Lenstoff-based components such as a carbon modification material - preferably carbon black, graphite and / or carbon nanotubes.

According to a further advantageous embodiment of the invention, the electrically conductive filler comprises a silicon carbide, undoped and/or doped silicon carbide.

According to a further advantageous embodiment of the invention, the electrically conductive filler comprises particles which are at least partly made of metal oxide, in particular a mixed oxide.

In the present case, a compound between a metal and oxygen is referred to as a metal oxide, the oxygen in the compound formally, ie in simplified terms, having a 2-fold negative charge. Basically, the oxygen in the compound is the electronegative partner. Hence the name "oxide".

A mixed oxide - MOX for short - is accordingly a substance in which more than one metal cation is present in an oxidic compound, for example titanium-aluminum oxide or iron-nickel oxide or the like.

According to an advantageous embodiment of the invention, a filler is used which has a coating of a doped tin oxide and/or a doped titanium oxide and/or consists of a doped tin oxide and/or titanium oxide.

The filler particles can be in the form of hollow bodies, solid particles, coated particles and/or core-shell particles.

At least one fraction, preferably but not necessarily exclusively, of platelet-shaped particles is applied to the carrier tape, which are held together by a polymer matrix, i.e. the binder, and thus the glow form a protective band. In order to adjust the electrical resistance, it can be advantageous to supplement the fraction of platelet-shaped filler particles with spherical, ie globular, filler particles.

According to an advantageous embodiment of the invention, the corona protection strip has a basis weight of <150 g/m ² , preferably less than 100 g/m ² .

According to an advantageous embodiment, the carrier tape comprises reinforcing fibers, for example in the form of a fabric and/or a fiber composite, in and/or on which the polymeric matrix with the electrically conductive filler is introduced and/or with which it is connected through the binder is bonded.

The carrier tape preferably has a basis weight of 30-60 g/m ² .

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

According to an advantageous embodiment, the carrier tape is coated with a primer. It is particularly advantageous if the carrier tape is coated with a primer of up to 5 g/m ² .

In particular, it has proven to be advantageous if the priming of the carrier tape comprises polyvinyl alcohol, epoxy and/or amine functionalities.

In the present case, priming refers to a priming coating through which the cut resistance of the reinforcing fibers and/or the carrier tape or fabric is improved and prepared for wetting and bonding with the polymeric matrix. According to an advantageous embodiment of the invention, the amount of coating of the carrier tape with the polymeric matrix, which contains the at least one fraction of electrically conductive filler and/or possibly also the at least one tape accelerator, is in the range from 20 g/m ² to 100 g/m ² , in particular in the range from 20 g/m ² to 60 g/m ² , particularly preferably in the range from 30 g/m ² to 45 g/m ² .

According to the invention, the corona protection strip is used to produce an external corona protection system and/or an internal potential control system and/or an end corona protection system.

It is advantageous if the square and/or surface resistance of an external corona protection system produced by a corona protection strip according to the present invention and/or an internal potential control system is in the range from 0.01 kOhm to 100 kOhm, measured at a field strength of 1 V /mm lies .

In particular, the square and/or sheet resistance values of such an internal potential control are preferably in the range from 0.01 kOhm to 10 kOhm, preferably in the range from 0.01 to 5 kOhm and particularly preferably in the range from 0.05 to 1 kOhm and/or or the square resistance values of such external corona protection in the range from 0.1 to 100 kOhm, in particular from 0.1 kOhm to 50 kOhm and particularly preferably in the range from 1 kOhm to 10 kOhm, each measured at a field strength of 1 V/mm.

When producing an end corona protection using a corona protection band according to the present invention, it is advantageous if a surface resistance in the range from Ixl O ⁸ to 1 x 10 ¹² ohms, in particular in the range from Ixl O ⁸ to Ixl O ¹² ohms, at a field strength of 100 V /mm is present.

The invention relates to a corona protection strip for an electrical high-voltage machine with anhydride-free, in particular Epoxy resins free of phthalic anhydride derivatives. The corona protection tape presented here for the first time is adjusted with its components, in particular the connecting polymeric matrix and the embedded cationic tape accelerator, to the new epoxy resin-based VPI impregnation resins, which are also free of alkyl phthalic anhydride derivatives, for example.

The belt accelerator is preferably an ionic compound composed of one or more sulfonium-containing cation(s) with one or more anions, in particular complex anions, such as hexafluoroantimonate anion(s), each suitable for use in a VPI Process for manufacturing an insulation system with an anhydride-free impregnating agent. .

The belt accelerator is a cationic belt accelerator and is therefore preferably constructed ionogenically. In particular, the ribbon accelerator has a sulfonium-containing cation.

For example, a suitable cationic belt accelerator is a chemical compound that falls under one of structural formulas I, II, or III:

Superacid salt with sulfonium cation Structure I

Structure I

cation structure II

Di-aryl-alkyl-sulfonium cation 15

cation structure III

Di-alkyl-aryl-sulfonium cation The sulfonium cations I, II and III shown here form with complex anions such as BF ₄ -, PF ₆ -, SbF ₆ -, AsF ₆ -, SbF ₅ (OH)-, ASF ₅ (OH)Al[OC(CF ₃ ) ₃ ] ₄ - the corresponding superacid salts useful herein as line accelerators.

"Superacids" are acids that are stronger than concentrated 100% sulfuric acid with a pKa value of -3. Examples are fluorosulfonic acid, fluoroantimonic acid, per-halogenated carboranes, and others.

The structural formula "Structure I" shows the cationic part of a belt accelerator according to a preferred embodiment of the present invention.

A "cationic belt accelerator" is a belt accelerator which is ionic and whose cation initiates the cationic polymerization, in particular the cationic homopolymerization, of an impregnating resin in a liquid impregnating agent.

"Ionogenic" compounds are heteropolar compounds whose chemical reactivity is characterized by the presence of a cation and an anion in the compound. Classic "ionogenic" compounds are salts. ze . However, complex structures with a cationic and anionic character are also referred to here as “ionogenic” compounds.

A “sulfonium-containing cation” is a cation which, in addition to the anion or anions, includes a unit in the molecule which can be described by the simply positively charged structures II or III or by the molecular formula [SR ₃ ] ⁺ .

A sulfonium-containing cation is referred to as “alkyl-aryl-sulfonium” or “di-alkyl-aryl-sulfonium” in which one or two of the three radicals “R” on the sulfur atom in the sulfonium cation are alkyl groups Alkyl groups are parts of a molecule consisting of carbon and hydrogen atoms bonded to one another.In the context of the invention, preferred alkyl radicals are those having 1 to 12 carbon atoms, which can be branched or linear thereby monovalently bonded to the central sulfur atom.

According to the invention, a di-alkyl-aryl-sulfonium cation can have one or two alkyl radicals, which in turn can be identical or different.

A sulfonium-containing cation in which one or two of the three radicals “R” on the sulfur atom in the sulfonium cation are aryl groups is referred to as “aryl-alkyl-sulfonium or di-aryl-alkyl-sulfonium”. Aryl groups are parts of a molecule that are monovalent or are attached by a single bond to the carbon skeleton, or to the sulfur atom, and have at least one aromatic nucleus, which can be partially or fully substituted or unsubstituted.

According to the invention, an aryl-alkyl-sulfonium cation can have one or two aryl radicals, which in turn can be identical or different. The third radical can be anything, ie also an alkyl group or an aryl group, fully or partially substituted or not.

An aryl group is an organic chemical radical with an aromatic backbone. It is the designation for a monovalent atomic group derived from aromatic hydrocarbons by removing a hydrogen atom attached to the ring. Most aryl groups are derived from benzene, the simplest aryl group being the phenyl group.

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

It is preferred if at least one mononuclear aryl group, for example an aryl group with an aryl structure derived from benzene, such as phenyl or benzyl, is present.

In particular, it is also preferred if there is at least one substitution on a mononuclear aromatic radical of the aryl group of the sulfonium-containing cation, ie a hydrogen on the aromatic nucleus is replaced, for example by a functional group or an alkyl group.

The functional group can be present with or without a heteroatom such as oxygen, nitrogen, sulfur or phosphorus.

An aryl group in which a hydrogen on the aromatic nucleus is replaced by an acetyloxy group is particularly preferred.

Furthermore, it is particularly preferred that a sulfonium-containing cation combined with a hexafluoroantimonate anion is present as the belt accelerator.

The corona protection belt accelerator can be a mixture of at least two cationic belt accelerators, each of which has a different have res sulfonium cation, are present. The anions can be the same or different, in particular as an anion hexafluoro-antimonate.

The corona protection strip accelerator, regardless of whether it is present as an individual compound or as a mixture, preferably has a melting point in the range from 145.degree. C. to 165.degree. C., particularly preferably in the range from 150.degree. C. to 160.degree.

The invention also relates to the use of the reactive corona protection tape for producing an anhydride-free insulation system by impregnating the solid corona protection tape with an impregnation agent, the impregnation agent comprising an aromatic and/or cycloaliphatic impregnation resin, the anhydride - is free and contains epoxy groups.

Anions with a complex structure, such as the hexafluoro-antimonate anion, are particularly suitable as the anions of the cationic belt accelerator, so that, for example, the 4-acetyloxyphenyldimethylsulphonium hexafluoroantimonate - CAS no. 135691-31-5 - Structure I .

The invention is explained in more detail below using an application example that describes an embodiment of the invention:

By using the sulphonium superacid derivative 4-acetyloxyphenyl-dimethylsulfonium-hexafluoroantimonate mentioned in structure I in an aqueous mixture with preferably silanol-group-modified polyvinyl alcohol and flake-form filler which has been made partially conductive with tin oxide, for example doped, and organic solvents, such as e.g . B. 2-butanone, and water can be prepared a paint that is capable of impregnating/applying to polymer and/or glass fabric carriers and with which, after drying, a layer of the desired conductivity according to the invention, d. H . with square resistances in the range of R =1- 10 kOhm over a temperature range of 20-150 °C, can be set on the polymer and/or glass fabric carrier.

By using a sulphonium superacid derivative as a crosslinking accelerator, this novel corona protection tape is suitable for curing conventional epoxy resin-phthalic anhydride mixtures as well as novel, i.e. anhydride-free, impregnating agents with epoxy resins, particularly in combination with cycloaliphatic epoxy resins. Such sulphonium superacid derivative(s), bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, glycidyl ester, aliphatic and/or cycloaliphatic epoxy resins can gel and cure alone, but also in any combination. Successful tests have already been carried out with cycloaliphatic epoxy resins mixed with BADGE (bisphenol A diglycidyl ether) .

It has also surprisingly turned out that in terms of tape stability with regard to the electrical conductivity of the layer, a shaping crosslinker can also be applied, but the tape also has sufficient stability for winding without a shaping crosslinker.

The corona protection tape produced in this way via subsequent hot-air drying shows, with heat impregnation according to the invention at 70° C. and subsequent hot curing at 140° C. with anhydride-free epoxy resin or an advantageous mixture of approx. 80 wt. -% cycloaliphatic epoxy resin and approx. 20 wt. -% distilled bisphenol A diglycidyl ether, only slight, disadvantageous swelling behavior, so that the square resistance originally set on the corona protection tape also during and after curing with liquid epoxy resin, anhydride-free nature, most preferably mainly, but not exclusively cycloaliphatic structure, is retained and so the partially conductive characteristic is preserved when the corona protection tape is applied in an electrical machine to reduce high electrical field strengths in the stator windings. According to the invention, 20.0 g of 4-acetyloxyphenyldimethylsulfonium hexafluoroantimonate were dissolved in 200.0 g of ethyl methyl ketone to produce the lacquer. This clear, organic solution was slowly stirred at room temperature to form a suspension of 590.0 g of Iriotec 7320 (Merck KGaA, Darmstadt) and 108.7 g of Poval™ 25-98 R (Kuraray Europe GmbH, Hattersheim am Main ) was added dropwise to 2400.0 g distilled water and stirred for a further 30 minutes at room temperature, eg using a dissolver with a toothed dispersing disc in order to break up any agglomerates by shearing in the vicinity of the disc.

This turquoise shimmering paint suspension was then applied to a 200 mm wide glass/polyester blended fabric with a basis weight of 44.7 g/m ² (Krempel GmbH, Vaihingen/Enz) by means of dip application in a base coater belt impregnation system (COATEMA Coating Machinery GmbH, Dormagen) and dried at a strip surface temperature of around 120°C in a hot-air fan oven vertically with a strip running at 0.8 meters/minute over a length of 1.5 m. The result on the belt was a total dry application of 27.48 g/m ² , with 0.77 g/m ² of 4-acetyloxyphenyl dimethyl sulfonium hexafluoroantimonate as an accelerator substance, 22.56 g/m ² of Iriotec 7320 as a partially conductive material for field control and 4.16 g/m ² Poval™ 25-98 R as a binder. In total, the tape had a specific total area weight of approx. 72 g/m ² .

The tactile, excellent, very easy to wind, non-tacky, low-odour, turquoise, robust and innovative corona protection tape had a square resistance Rrj=6.5 kOhm at 20-23°C, measured using a 10cm ² high-ohm spring tongue electrode 3501FE according to DIN 53482 or DIN EN 62631-3-2 (H.-P. Fischer Elektronik GmbH & Co., Mittenwalde).

To investigate the critical swelling behavior of the novel corona protection strip during VPI impregnation and during hot curing in the phthalic anhydride-free epoxy resin according to the invention based on mixtures of cyclic loaliphatic epoxy resin and glycidyl ether epoxy resin, two corona protection tape strips measuring 12 cm x 2.5 cm were prepared and the ends, each one centimeter wide, were provided with commercially available conductive silver paint on both sides, so that two electrically contactable corona protection tape strips measuring 10 cm x 2.5 cm were obtained. These strips were contacted with heat-resistant crocodile clips at the conductive silver paint contact and connected to a multi-channel precession measuring device Almemo® 2890-9 (from Ahlborn Mess- und Regeltechnik GmbH, Holzkirchen) for continuous resistance recording.

The glow strip strips were then placed in the center by weights under tension, transferred to a convection oven and immersed completely for four hours in a phthalic anhydride-free epoxy resin mixture at 70° C., consisting of 80% by weight of cycloaliphatic epoxy resin of the 3,4- Epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate (Celloxide™ C2021P, Daicel Corporation, Tokyo; CAS No. 2386-87-0) and 20% by weight distilled bisphenol A diglycidyl ether (Epikote™ Resin 162 , Hexion GmbH, Iserlohn; CAS No. 1675-54-3) , immersed.

After this four-hour period of time, following the 70 °C VPI impregnation phase, the electrically contacted corona protective tape strips were lifted out of the resin, heat-cured in the oven at 145 °C for ten hours and then cooled to room temperature. During this time the electrical resistance was continuously recorded. By converting the resistance recorded over time into the square resistance (10 cm * 2.5 cm), it was surprisingly found that the ideal resistance characteristics of the novel corona protection tape in the range of 1-10 kOhm are retained in the full temperature range of 20-145 °C and is therefore ideally suited for deflecting electrical fields on windings in anhydride-free, VPI epoxy resin-impregnated electrical machines and generators. A so-called resin infection test or accelerator availability test was also carried out to check how the accelerator was washed out of the new corona protection tape. For this purpose, two corona protection tape strips measuring 2.5 cm x 4.8 cm (12 cm ² ) were prepared and each 30 g of the abovementioned (alkyl) phthalic anhydride-free epoxy resin (80% by weight of 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexane carboxylate/ 20

% by weight of distilled bisphenol A diglycidyl ether) aged at 70° C. for four hours. The impregnated corona protection tape strips were then removed from the liquid and this remaining epoxy resin mixture was stored at 100° C. for a further 20 hours. After cooling to 70° C., the dynamic viscosity (η _{sample 1, 20 h/100° C.} , η _{sample 2, 20 h/100° C.} ) was determined in each case. Subtracting a glow shield band-free resin blank value (η _BW , _20h/100°C ) resulted in the following values or properties: η _BW , _20h/100°C ⁼ 24.87 mPa s η _Sample1 , _20h/100°C = 43.78 mPa s η _Sample2 , _20h/100°C ⁼ 56.93 mPa s

Appearance _Sample1&2 , _20h/100°C = glow strips are stiff, no tack Accelerator _{availability Sample1} , _20h/100°C = 43.78 mPa s - 24.87 mPa s = 18.91 mPa s

Accelerator _{availability Sample2} , _20h/100°C = 56.93 mPa s - 24.87 mPa s = 32.06 mPa s

Furthermore, the reactivity of the novel corona protection tape was examined after storage at room temperature for up to four weeks. For this purpose, punched samples were taken from the corona protection tape, wetted with anhydride-free epoxy resin (80% by weight of 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate/20% by weight of distilled bisphenol A diglycidyl ether) in a DSG crucible and the reaction enthalpy was determined at 10 K/min by differential scanning calorimetry (Netzsch-Devicebau GmbH, Selb; DSC Phoenix Fl) (cf. Fig. 5). The stability of the novel corona protection tape could be demonstrated using fairly constant reaction enthalpies (approx. 300-400 joules per gram of epoxy resin mixture). Based on the new generation of insulation systems that can be produced by impregnation with anhydride-free impregnating agents, the present invention discloses a corona protection strip for the first time, in which a well-suited strip accelerator that quickly initiates homopolymerization can be deposited. The tape accelerator is in the form of a salt of a superacid and is storage-stable for up to 6 months at a temperature of +6 °C to 23 °C in a corona protection tape that at least partially contains polyvinyl alcohol as the polymer matrix.

Claims

patent claims

1 . Corona protection tape for further processing into an insulation system, comprising an impregnated winding with potential control through external corona protection "AGS" and/or internal potential control "IPS" and/or end corona protection "EGS", the insulation system by impregnating the winding with a Anhydride-free and resin-based impregnation agent can be produced at 45 - 85 °C and in a vacuum, with the corona protection tape having at least one carrier tape, an electrically conductive and/or partially conductive filler in a polymer matrix and at least one tape accelerator, suitable for hardening and/or gelling the impregnating agent, characterized in that the polymer matrix contains at least one polyvinyl alcohol and/or a polyvinyl alcohol copolymer and that the at least one belt accelerator is selected from the group of super acids and/or super acid salts , which is based on accelerating a cationic homopolymerization of the resin Anhydride-free impregnating agent is suitable.

2 . Corona protection tape according to claim 1, wherein the base of the resin-based impregnating agent is an anhydride epoxy resin.

3 . Corona protection tape according to one of Claims 1 or 2, in which at least one ion of a super acid salt which is at least part of the tape accelerator is a sulfonium cation.

4 . Corona protection tape according to one of Claims 1 or 2, in which at least one ion of a superacid salt which is at least part of the tape accelerator is a sulfonium cation with an aryl radical.

5. Corona protection belt according to one of the preceding claims, in which several belt accelerators are present in combination.

6. Corona protection band according to one of claims 3 or 4, in which a sulfonium cation is present in the form of an aryl-alkyl-sulfonium cation.

7. Corona protection band according to one of the preceding claims, in which at least one di-alkyl-aryl-sulfonium cation is present.

8. Corona protection band according to one of the preceding claims, in which at least one di-aryl-alkyl-sulfonium cation is present.

9. Corona protection band according to one of the preceding claims 3 to 8, in which an aryl radical of a sulfonium cation is substituted.

10. Corona protective tape according to one of the preceding claims, in which a tape accelerator with a sulfonium cation with an aryl radical comprising a phenyl radical which is acetyloxy- is present.

11. Corona protection band according to one of the preceding claims, which comprises a superacid salt with the following chemical structure as the band accelerator:

Corona protection band according to one of the preceding claims, wherein the polymer matrix comprises a plurality of polyvinyl alcohols.

13. Corona protection band according to one of the preceding claims, wherein the polymer matrix comprises at least one polyvinyl alcohol with crosslinked portions.

14. Corona protection band according to claim 1, wherein the electrically conductive and/or partially conductive filler material contains at least one component selected from the group consisting of carbon black, graphite, carbon nanotubes—CNTs—, antimony-doped tin oxide, silicon carbide, and/or aluminum Silicon carbide, the respective component can include doped or undoped, coated or uncoated, doped coated or undoped coated.

15. Use of a corona protection band according to one of the preceding claims 1 to 14 for producing an insulation system with AGS, IPS and/or EGS.

16. Electrical rotating machine with an insulation system, which is obtainable through a use according to claim 15.