CONDUCTOR

Technical Field

The invention relates to the field of insulated conductors for electrical power equipment, such as electric motors, in particular to electrical conductors being insulated with mica and resin. The invention further relates to a method for preparing an electrical insulation for an electrical conductor, especially for producing an electrical insulation with mica and resin. Background Art

Electrical conductors, such as coils, Roebel bars, or simpler geometries like wires and cables and the like are insulated, e.g. for insulation of voltage to ground, but also for avoiding contact between single windings of coils, if the windings are on different potentials. In some examples, conductors may be insulated for avoiding a short circuit between a HV (high voltage) component to ground in an electric motor, for example the stator of the electric motor.

For producing an insulated conductor, lapped insulation via winding / lapping of tapes (such as Mica tape) is usually applied. After winding the tape around the conductor, the conductor may be impregnated with a resin mixture. A vacuum pressure impregnation (VPI) is a known method for providing an electrical conductor with sufficient insulation. Examples are conductors for electrical machines (HV form-wound coils and Roebel bars) where mica tapes are used for insulation which are impregnated with a thermosetting resin and consequent heat curing. The resin mixture used for impregnation is desired to fulfill different requirements, e.g. regarding the viscosity for good flow and impregnation results, regarding the usability of the resin mixture over a certain time-period, regarding low waste of material and, consequently, a high material efficiency, regarding good and desired electrical insulation properties, in particular in the field of HV applications, and so on.

Additionally, in particular in the case of impregnation applications, for example for impregnating mica tape wound coils for electrical machines, it is desirable that the curable epoxy resin composition has both a long pot life, i.e. slow curing speed at environmental temperature, and a short gel time, i.e. fast cross-linking reaction resp. polymerization reaction, at curing temperature.

In order to decrease the gel time of resin mixtures (such as epoxy resin mixtures used inside impregnated machine coils), one would either accelerate the reaction by adding more catalyst / initiator in the resin mixture or by applying higher curing temperature of the oven. Shortened gel time benefits in higher material quality of the cured resin-mica composite by less drainage of the resin mixture from the electrical conductor (e.g. coils) after impregnation and limited formation of voids. However, increase of oven temperature is often limited bearing other risks. Adding more catalyst / initiator on the other hand usually leads to decreased pot life by slow polymerization even at storage conditions (low temperature) and thus, faster resin ageing. In addition, the risk of precipitation during storage is very much increased since the solubility of the additives in the resin mixture is also limited. This is relevant especially if a homopolymerized epoxy as VPI resin is used where no diluent or anhydride participates. In this case, the resin formulation would be used at elevated temperature, e.g. at 50 °C, in order to lower the viscosity for good impregnation quality. Here, the balance of gel time and pot life is also a relevant parameter. Adding higher amount of initiator into the resin mixture directly to force faster gelling has also downsides: decreased pot life and faster resin ageing as well as much increased risk of precipitation during storage of the resin mixture.

Documents US4296018A and US4356417A both describe a catechol or pyrogallol containing flexible insulating tape. In particular, a mica tape is described in these documents, which is prepared from a composition of an epoxy resin, an organotin salt, and catechol or pyrogallol. A conductor is wound with the tape and is impregnated with an impregnating resin using vacuum-pressure impregnation.

EP2418079A1 also addresses a dry mica tape, insulation coils, a stator coil, and rotating machines fitted with such insulation coils or stator coils. Said publication discloses a conductor arrangement for insulating an electrical conductor with a mica tape and a resin mixture, wherein the conductor arrangement comprises an electrical conductor, an insulation being provided around the electrical conductor as well as at least one mica tape layer (i.e. a dry mica tape plus a resin layer A plus a mica paper layer). Moreover, it discloses the presence of at least one impregnation resin layer (referred to as resin layer B). The at least one mica tape layer and the at least one impregnation layer contain a resin mixture, wherein the insulation comprises a catalyst (e.g. imidazole or metal acetylacetonate) for curing the resin mixture. WO2013/017149A1 and EP1881033A1 disclose a coil insulation material comprising a polymerization catalyst such as boron trichloride-amine complexes as well as a catalystactivating agent such as a cycloaliphatic diglycidyl ether, for example. Moreover, WO2013/017149A1 reveals that in case of impregnation applications, for example for impregnating mica tape wound coils for electrical machines or for the impregnation of paper wound conductors for bushings, or for filament wet winding applications, it is substantial that the curable epoxy resin composition has a long pot life, i.e. slow curing speed at processing temperature and a short gel time, i.e. fast cross-linking reaction resp. polymerization reaction, at curing temperature.

US3254150A refers to a mica tape for insulating an electrical conductor such as a wound coil, for example, with a resin mixture, comprising a support material for supporting mica. The mica material is provided on or in the support material. The mica tape comprises substantially no catalyst for curing the resin.

In view of the above, a mica tape, a conductor arrangement and a method for insulating an electrical conductor are provided that overcome at least some of the problems in the art. Brief Summary of the Invention

In view of the above, a mica tape for insulating an electrical conductor with a resin mixture, a conductor arrangement for insulating an electrical conductor, an electric machine with such a mica tape, and a method for preparing an electrical insulation are provided. Further aspects, advantages, and features of the present invention are apparent from the dependent claims, the description, and the accompanying drawings.

According to an aspect of the invention, a mica tape for insulating an electrical conductor with a resin mixture is provided. The mica tape includes a support material for supporting mica and mica being provided on or in the support material. The mica tape according to embodiments further includes a catalyst-activating agent for activating a catalyst for curing a resin in the resin mixture, wherein the catalyst-activating agent does substantially not cure the resin in the resin mixture. The mica tape according to embodiments described herein does substantially not include a catalyst for curing the resin.

According to a further aspect, an electrical conductor arrangement for insulating an electrical conductor with a mica tape and a resin mixture is provided. The electrical conductor arrangement includes an electrical conductor and an insulation being at least partially provided around the electrical conductor. The insulation includes a first mica tape layer, a second mica tape layer and at least one impregnation resin layer, wherein the first mica tape layer, the second mica tape layer and the at least one impregnation layer contain a resin mixture. The insulation includes a catalyst for curing (and having cured, respectively) the resin mixture and a catalyst-activating agent activating (and having activated, respectively) the catalyst. According to embodiments described herein, the concentration of the catalyst-activating agent is greater in the first mica tape layer and the second mica tape layer than in the impregnation resin layer. Further, the concentration of the catalyst per resin unit of the respective layer is substantially the same in the first mica tape layer, the second mica tape layer and in the impregnation resin layer. The at least one impregnation resin layer is provided between the first mica tape layer and the second mica tape layer.

According to a still further aspect, an electric machine, in particular an electric motor, having at least one electrical conductor comprising a mica tape according to embodiments described herein is provided.

According to embodiments described herein, the catalyst-free mica tape being provided with a catalyst-activating agent and the resulting gradient of the catalyst-activating agent in the insulation of the electrical conductor arrangement offers several beneficial effects. For instance, the electrical conductor arrangement and the mica tape according to embodiments described herein allows for having a shorter gel time of the resin mixture (especially with an anhydride- free epoxy resin and/or diluent-free resin, such as a homopolymerized resin). Also, the material quality of the insulation is increased in the electrical conductor arrangement according to embodiments described herein (e.g. by less drainage and less possible voids), in particular when using the mica tape according to embodiments described herein. At the same time, the resin mixture with a catalyst and substantially no catalyst-activating agent and the mica tape including the catalyst-activating agent and having substantially no catalyst according to embodiments described herein allow for having a longer pot life of the resin mixture due to lower amount of the catalyst-activating agent (such as e.g. catechol) in the liquid resin mixture and due to decelerated ageing of the resin mixture during storage. The resin mixture with catalyst according to embodiments described herein may especially be non-reactive up to certain temperature allowing long pot life. Other resin mixture are thinkable with a reactive catalyst that might still have a short pot life. The longer pot-life of the resin mixture and the decelerated ageing reduce material waste. Also, the mica tape according to embodiments described herein having a catalyst-activating agent and substantially no catalyst is subjected to less ageing effects than known mica tapes. The waste of mica tape is reduced by using embodiments described herein, too.

Further, embodiments described herein enable the use of homopolymerized epoxy resin mixtures (such as anhydride- and styrene-free epoxy resin mixtures). A high performance of the resin is maintained. The embodiments described herein allow for a long pot life of a homopolymerized epoxy resin mixture, in particular even if the resin mixture is frequently used at 50 °C for impregnation (lower viscosity).

According to a further aspect of the invention, a method for preparing an electrical insulation for an electrical conductor is provided. The electrical insulation includes a mica tape and a reactive resin mixture. The method includes mixing a reactive resin mixture including a catalyst for curing the reactive resin mixture; and arranging a mica tape around an electrical conductor, wherein the mica tape includes mica and a support material, on which the mica is placed. According to embodiments described herein, the mica tape provides a catalyst-activating agent for activating the catalyst in the reactive resin mixture. The catalyst-activating agent does substantially not cure the reactive resin mixture. Further, the mica tape is substantially free of the catalyst for curing the reactive resin mixture.

Embodiments described herein allow for increasing the storage time of a resin mixture and a mica tape, for increasing the insulation properties and for using a homopolymerized epoxy resin mixture with the aforementioned beneficial effects. The costs for the production of an insulated conductor arrangement can be decreased due to less material waste. The reduced material waste also helps saving the environment. Brief Description of the Drawings

The subject matter of the invention will be explained in more detail in the following text with reference to preferred exemplary embodiments which are illustrated in the drawings, in which:

Figure 1 is a schematic drawing of an electrical conductor arrangement provided with insulation according to embodiments described herein;

Figures 2a and 2b are a schematic sectional views of an electrical conductor arrangement provided with insulation according to embodiments described herein;

Figures 3a-3e show schematic distributions of a catalyst-activating agent through a sectional view of an electrical conductor arrangement provided with insulation according to embodiments described herein;

Figure 4 shows a schematic distribution of a catalyst per resin unit through a sectional view of an electrical conductor arrangement provided with insulation according to embodiments described herein;

Figures 5 a to 5 c show a schematic drawing of mica tapes according to embodiments described herein; and

Figure 6 shows a flow chart of a method for preparing an electrical insulation for an electrical conductor according to embodiments described herein.

The reference symbols used in the drawings, and their meanings, are listed in summary form in the list of reference symbols. In principle, identical parts are provided with the same reference symbols in the figures.

Preferred Embodiments of the Invention

According to embodiments described herein, an electrical conductor arrangement and a mica tape are provided, which in particular can be used in electrical power equipment, in particular rotating machines. For instance, the electrical conductor arrangement according to embodiments described herein may be used in electric motors, generators, and/or transformers.

Figure 1 shows an example of the electrical conductor arrangement 100 including insulation for electrically insulating the conductor. The example of Figure 1 shows a longitudinal conductor, of which a section is drawn. The insulation typically includes a mica tape layer 110 and an impregnation resin layer 120. In the shown example of Figure 1, the mica tape layer 110 is provided by a mica tape wound around the conductor 101. According to some embodiments, the mica tape may helically be wound around the conductor (e.g. with overlapping portions). The impregnation resin layer 120 may be provided on the mica tape layer.

According to embodiments described herein, the mica tape layer 110 and the impregnation resin layer 120 contain a resin mixture, e.g. in different amounts, especially in different weight portions. For instance, the electrical conductor and the mica tape wound around the electrical conductor may be immersed or doused in or with a (reactive) resin mixture. As a first result, the mica tape may include the resin mixture. As a second result, the impregnation resin layer may build up on the mica tape layer containing the resin mixture. According to some embodiments, the mica tape layer may include mica and the resin mixture. The impregnation resin layer may consist of the resin mixture with substantially no mica. In some embodiments, the impregnation resin layer may substantially consist of the resin mixture only. The mica tape layer 110 and the impregnation resin layer 120 may form the insulation of the electrical conductor arrangement.

The resin mixture, or reactive resin mixture as used in embodiments described herein may include a resin and a catalyst for curing the resin or for curing the resin mixture. According to some embodiments, the resin may be a VPI (vacuum pressure impregnation) resin for HV electrical machine insulation. For instance, the resin may be an epoxy resin. In some embodiments, a homopolymerized resin and/or a resin without anhydrides as hardeners but reactive diluent may be used.

In some embodiments, the resin mixture may further include additives selected from filler materials, wetting/dispersing agents, plasticizers, antioxidants, light absorbers, as well as further additives used in electrical applications, such as electric machine (e.g. electric motors, generators, transformers and the like). The insulation of the electrical conductor arrangement 100 according to embodiments described herein, and especially the resin mixture of the insulation, includes a catalyst for curing the resin mixture. According to some embodiments, the catalyst may be described as being pre-dispersed in the resin mixture (e.g. a VPI resin mixture). For instance, the catalyst being present in the resin mixture, and, consequently, in the mica tape layer and the impregnation resin layer, may include organotin compounds, and/or Lewis acids, such as boron trichloride and derivatives (in particular amine complexes and imidazoles) and/or enolates, in particular acetylacetonate, in particular metal acetylacetonates. In particular, the catalyst for curing the resin mixture may include aluminum acetylacetonate, zirconium acetylacetonate, iron acetylacetonate, and/or combinations thereof.

Additionally, the insulation of the electrical conductor arrangement 100 according to embodiments described herein, and especially the mica tape layer 110 of the insulation includes a catalyst-activating agent activating the catalyst.

A catalyst-activating agent as described herein may be an agent activating the catalyst (especially the catalyst being present in the resin mixture) for curing the resin. Activating in this context may mean that the energy, in particular heat, required by the catalyst for curing the resin may be decreased by aid of the catalyst-activating agent. For instance, activating may mean that the catalyst-activating agent allows lowering the start reaction temperature (onset or reaction enthalpy in DSC) by certain degree °C, such as typically by at least 20°C, more typically by at least 40°C, and even more typically by at least 70°C. In one example, the lowered start reaction temperature may refer to a situation of heating up the resin mixture at a rate of 2°C/min starting from about 20°C. According to some embodiments, the activation may refer to the acceleration of the reaction time at a fixed temperature (in addition to the onset temperature of reaction). For instance, at a temperature of at least 160°C (or more), the acceleration of the reaction time may be between about 20 minutes and about 60 minutes, more typically between about 25 minutes and about 50 minutes, and even more typically between about 25 minutes and 40 minutes (in particular when compared to known mica tapes and known rein mixtures). In one example, the acceleration of the reaction at 160°C is about 30 minutes according to embodiments described herein. . According to some embodiments, the catalyst-activating agent may mainly have two functions: the first function is to act as a kind of co-catalyst for the catalyst. The second function of the catalyst-activating agent may be to act as an active binder for the resin. According to some embodiments, the catalyst-activating agent as referred to herein may describe the catalyst-activating agent before the reaction with the catalyst in the resin mixture and the catalyst-activating agent after the reaction with the catalyst and after curing of the resin in the resin mixture. For instance, the catalyst-activating agent may be present in a changed shape (such as the physical shape and/or chemical formation) after the reaction. In one example, the catalyst-activating agent may include a hydroxyl group before the reaction and the curing, but may be present as an ether compound after the reaction and the curing. Either shapes or formations may be described herein with the term "catalyst-activating agent." In some embodiments, the catalyst-activating agent may be described as an agent substantially not curing the resin mixture. This may mean that the catalyst-activating agent alone (i.e. without the catalyst) is not able to cure the resin in the resin mixture. For instance, the catalyst-activating agent not curing the resin may mean that the reaction enthalpy is less than < 1 J/g for up to 350 °C in DSC (Differential Scanning Calorimetry) with a rate of 2 °C/min starting from 20 °C.

In some embodiments, the catalyst-activating agent may be chosen from multifunctional hydroxyl, amino and/or thiol terminated aromatic, aliphatic or cyclic, compounds. In particular, the catalyst-activating agent may be is chosen from 1 ,2-dihydroxybenzene (catechol), 1,3-dihydroxybenzene (resorcinol), 1 ,4-dihydroxybenzene (hydroquinone), 1,2,3-trihydroxybenzene (pyrogallol), 1,2,4-trihydroxybenzene and/or a mixture of these compounds.

According to embodiments described herein, the concentration of the catalyst-activating agent is greater in the mica tape layer than in the impregnation resin layer, as will be explained in detail below with respect to Figures 3 a to 3e. In some embodiments, the concentration of the catalyst-activating agent in the mica tape layer is at least 2x, more typically 4x larger than in the impregnation resin layer, such as 5x larger, 8x larger or even more than 8x larger, such as lOx larger, or even more than lOx larger. Further, the concentration of the catalyst per resin unit of the respective layer is substantially the same in the mica tape layer and in the impregnation resin layer, as will be explained in detail with respect to Figure 4. In some embodiments, the concentration of the catalyst per resin unit being substantially the same in the mica tape layer and in the impregnation resin layer may include a deviation of the catalyst concentration in the mica tape layer of less than 20% of the catalyst concentration in the impregnation resin layer. For instance, the catalyst concentration per resin mixture unit in the mica tape layer may deviate less than 20%, such as about 15%, or about 10%, or even less than 10% from the catalyst concentration in the impregnation resin layer. According to some embodiments, the catalyst concentration may typically be between about 0.02wt% and 3wt%, more typically between about 0.05wt% and about 2wt%, and even more typically between about 0.1 wt% and about 2wt% of a resin unit.

In some embodiments, the concentration of the catalyst-activating agent in the insulation of the electrical conductor may be described as providing a gradient throughout the insulation. The concentration of the catalyst may be described as being substantially constant per resin mixture unit throughout the insulation.

The term "substantially" as used herein may mean that there may be a certain deviation from the characteristic denoted with "substantially." For instance, the term "substantially constant" refers to a concentration which may have certain deviations from the exact constant concentration, such as a deviation of up to 20% of the concentration in one layer. According to a further example, the term a layer containing "substantially only a first component" may refer to a layer consisting mainly of the first component, but may include further second components typically up to 15%, more typically up to 10% and even more typically up to 5% by weight or volume of the layer. In some embodiments, the term "substantially rectangular" may include a rectangular shape with one or more rounded corners.

A resin unit as used herein may be understood as a defined amount of the resin. As described above, both the mica tape layer and the impregnation resin layer include resin mixture. However, since the mica tape layer includes mica being immersed or soaked with the resin mixture and the impregnation resin layer consists substantially of the resin mixture, both layers contain different portions by weight or volume of the resin mixture. For instance, the impregnation resin layer may include about 100% by weight or by volume resin mixture. The mica tape layer may typically have only a portion of resin mixture of the total weight. The amount of catalyst is therefore given per resin unit, which may for instance be a weight unit, such as one gram resin mixture, or a volume unit, such as one mm ³ . According to some embodiments, and speaking in absolute terms, the concentration of the catalyst in the mica tape layer may be less than in the impregnation resin layer.

According to some embodiments, the concentration distribution of the catalyst-activating agent and the catalyst in the insulation of the electrical conductor arrangement may also be described as the changing relation of the catalyst-activating agent and the catalyst throughout the insulation of the electrical conductor arrangement. In particular, the relation of catalyst-activating agent to catalyst is larger in the mica tape layer than in the impregnation resin layer, in particular larger by at least the factor four.

Figures 2a and 2b show examples of electrical conductor arrangements 100 including an electrical conductor 101 being surrounded by two mica tape layers 110-1 (first mica tape layer) and 110-2 (second mica tape layer) and two impregnation resin layers 120-1 (first impregnation resin layer) and 120-2 (second impregnation resin layer) according to some embodiments described herein. As can be seen in the embodiments shown in Figures 2a and 2b, the mica tape layers 110-1 and 110-2 and the impregnation resin layers 120-1 and 120-2 (each containing the resin mixture) are arranged on the electrical conductor 101 alternately. Figures 2a and 2b are schematic simplified views. For instance, if the mica tape has overlapping portions (e.g. due to the winding process), there may be two mica tapes on top of each other. For the sake of simplification, the two overlapping portions of mica tape may be considered as one mica tape layer having a different thickness. In some examples, the resin mixture may penetrate in-between the overlapping portions of the mica tape so that a small (or thin) impregnation resin layer is formed between the overlapping portions of the mica tape.

Although only two mica tape layers and two impregnation resin layers are shown in Figures 2a and 2b, the number of the respective layers may be larger than two, such as four, five, or even ten of each layer. According to some embodiments, the number of the layers may be adapted to any suitable number (e.g. suitable for avoiding partial discharge in an electric motor). In some embodiments, the number of the layers may be a compromise between good insulation properties and material costs.

The thickness of the mica tape layers 110-1 and 110-2 and the impregnation resin layers 120-1 and 120-2 are exemplarily shown substantially equal in Figures 2a and 2b. However, the thickness of the mica tape layer and the impregnation resin layer may vary and be different from each other. For instance, the thickness of the impregnation resin layer may depend (or may be chosen dependent on) the intended application of the electrical conductor, the strength of an electrical machine, for which the electrical conductor is to be used, the material mixture of the resin mixture and the like. The example of Figures 2a and 2b shows a substantially rectangular shape of the conductor 101. The conductor 101 of Figures 2a and 2b have rounded corners. The electrical conductor according to embodiments described herein may also be provided by a conductor bundle for the conductor arrangement.

The embodiment of Figure 2a shows a conductor arrangement 100, where the first inner layer (i.e. the layer being closest to the electrical conductor) is the first mica tape layer 110-1 covered or surrounded by the first impregnation resin layer 120-1. The embodiment of Figure 2b shows a conductor arrangement 100, where the first inner layer is the first impregnation resin layer 120-1 covered or surrounded by the first mica tape layer 110-1. Figure 2b further shows a third impregnation resin layer 120-3 being provided as outermost layer (i.e. the layer most distant from the electrical conductor).

Figures 3a to 3e show different concentration profiles of the catalyst-activating agent in a section through the electrical conductor and the insulation of the electrical conductor arrangement. In the Figures 3a to 3e, the abscissa shows the different zones of the section though the conductor arrangement according to embodiments described herein. The abscissa of Figures 3a to 3e shows the electrical conductor 101, the first mica tape layer 110-1, the first impregnation resin layers 120-1, the second mica tape layer 110-2, and the second impregnation resin layers 120-2 (as also shown in the sectional views of Figures 2a and 2b). The ordinate of the diagrams of Figures 3a to 3e show the concentration of the catalyst-activating agent. According to some embodiments, the concentration of the catalyst-activating agent may be measured in absolute terms or in relative terms. For instance, the concentration of the catalyst-activating agent of a layer may be measured in relation to the resin content of the layer or in relation to the total weight of the respective layer. Both measurement types are valid and may yield substantially the same schematic distribution as shown in Figures 3a to 3e. Figure 3a shows a concentration profile of a conductor arrangement 100 as shown in Figure 2a, i.e. with the first inner layer being the first mica tape layer. The electrical conductor 101 does not contain any catalyst-activating agent. The first mica tape layer 110- 1 provides a defined amount of the concentration of the catalyst-activating agent as indicated by the raising graph 130. The concentration of the catalyst-activating agent is shown as being substantially constant through the thickness of the first mica tape layer 110-1 as exemplarily shown in Figure 3 a. According to some embodiments described herein, the mica tape layer 110-1 and 110-2 as referred to in Figure 3 a may include a mica tape 200 as exemplarily shown in Figure 5a. Figure 5a shows a mica tape 200 including mica 210 and a catalyst-activating agent 230 distributed substantially uniform through the whole thickness of the mica tape 200, as a simplified example. The graph of the concentration of the catalyst-activating agent has a steep decrease within the first impregnation resin layer 120-1. According to some embodiments, the amount of catalyst-activating agent in the impregnation resin layer comes from the catalyst-activating agent of the mica tape layer diverging into the impregnation resin layer. The steepness of the graph 130 at the interface between mica tape layer and impregnation resin layer is drawn exemplarily and may vary depending on the materials used the curing temperature and the like.

After the steep decrease of the graph 130, the concentration of the catalyst-activating agent in the first impregnation resin layer 120-1 is zero. Approaching to the second mica tape layer 110-2, the graph 130 has a steep increase from zero to the concentration of catalyst- activating agent in the second mica tape layer 110-2. Similar to the first mica tape layer 110-1, the concentration of the catalyst-activating agent throughout the mica tape layer is substantially constant. After the interface between second mica tape layer 110-2 and second impregnation resin layer 120-2, the graph has a steep decrease to zero. In the simplified example of Figure 3a, the second interface layer 120-2 may be the outermost layer of the insulation of the electrical conductor arrangement. According to some embodiments, the outermost impregnation layer may have the largest difference in the catalyst-activating agent concentration to the mica tape layers. In some embodiments, the catalyst-activating agent diffused from the mica tape layers to the impregnation resin layers may yield a decrease of the graph 130 within the mica tape layer shortly before the interface of mica tape layer to impregnation resin layer.

As can be seen in Figure 3a, the concentration of catalyst-activating agent in any of the mica tape layers of the insulation is larger than in any of the impregnation resin layers. Figure 3b shows the concentration profile of the catalyst-activating agent in a conductor arrangement as shown in Figure 2b (i.e. the first inner layer being a resin impregnation layer). The electrical conductor 101 does not include a catalyst-activating agent. In the embodiment shown in Figure 3b, the first impregnation resin layer 120-1 does substantially not contain catalyst-activating agent. However, the first impregnation resin layer 120-1 shown in Figure 3b includes a small amount of catalyst-activating agent diffusing from the first mica tape layer 110-1 as can be seen at the interface between the first impregnation resin layer 120-1 and the first mica tape layer 110-1 by the steep slope of the graph 130. According to some embodiments, the second impregnation resin layer 120-2 may be described as being substantially free of catalyst-activating agent but may include small amount of catalyst-activating agent diffusing from the first mica tape layer 110-1 and the second mica tape layer 110-2. The third impregnation resin layer 120-3 does substantially not contain catalyst-activating agent except for small amounts diffusing from the second mica tape layer 110-2. Figure 3c shows a further example of a concentration of the catalyst-activating agent throughout the insulation of the conductor arrangement of Figure 2a according to embodiments described herein. As in Figure 3 a, the different layers provided on the electrical conductor 101 are shown in Figure 3c. The mica tape layers 110-1 and 110-2 as referred to in Figure 3c may be a mica tape as exemplarily shown in Figure 5b. The mica tape 200 shown in Figure 5b has a supporting film 220, on which the mica 210 and the catalyst-activating agent 230 distributed in the mica 210 are arranged. The mica tape 200, and thus, the mica tape layers as referred to in Figure 3c have a portion (i.e. the supporting film) being substantially free of the catalyst-activating agent, as can be seen by the graph 130 in Figure 3c having a steep raise of the catalyst-activating agent concentration within the mica tape layers 110-1 and 110-2. The remaining course of the graph 130 is similar to the graph shown in Figure 3 a. In particular, the catalyst-activating agent concentration has a steep decrease within the impregnation resin layers 120-1 and 120-2 (after the interface between mica tape layer and impregnation resin layer). According to some embodiments, the graph may also show some diffusing effects of the catalyst-activating agent within the mica tape layer, such as from the mica 210 to the supporting film 220 (as shown in Figure 5b).

Figure 3d shows a further example of a concentration of the catalyst-activating agent throughout the insulation of the conductor arrangement of Figure 2a according to embodiments described herein. As in Figure 3 a, the different layers provided on the electrical conductor 101 are shown in Figure 3d. The mica tape layers 110-1 and 110-2 as referred to in Figure 3d may be a mica tape as exemplarily shown in Figure 5c, i.e. the supporting material 220 is provided with mica 210 and the catalyst-activating agent 230 on both sides of the supporting material 220. The concentration profile of Figure 3d shows that the supporting material (similar to the embodiment shown in Figure 3 c) does substantially not contain catalyst-activating agent. The slope of the concentration of the catalyst-activating agent within the first mica tape layer 110-1 and the second mica tape layer 110-2 refers to a diffusion of the catalyst-activating agent into the supporting material.

In other embodiments, the supporting material (such as the supporting material exemplarily shown and described in Figures 3c, 3d, 5b and 5c) may include catalyst-activating agent, for instance in a similar concentration as the mica, or in a lower concentration.

Figure 3e corresponds substantially to the situation in Figure 3 a. However, the decrease in the catalyst-activating agent concentration within the impregnation resin layers 120-1 and 120-2 is steeper than in Figure 3 a. According to some embodiments, the impregnation resin layers as exemplarily shown in Figure 3e may be described as being substantially free of catalyst-activating agent.

According to some embodiments described herein, a layer or mixture containing substantially no or being substantially free of a material (such as free of the catalyst- activating agent or free of the catalyst) may be understood in that the layer or mixture may include small amounts of the material, such as typically up to 5% by weight or less of the material, more typically less than 3% by weight, and even more typically less than 1% by weight. It may be understood that the configuration shown in Figures 3c, 3d, and 3e (referring to a conductor arrangement as shown in Figure 2a) may also be provided in a conductor arrangement as shown in Figure 2b. For instance, either of the herein described mica tapes may be used in the conductor arrangements of Figures 2a and 2b.

Figure 4 shows a schematic diagram of the concentration of the catalyst per resin unit throughout the insulation of the conductor arrangement according to embodiments described herein. The abscissa shows the amount of catalyst per resin unit (as explained in detail above) and the ordinate shows the electrical conductor and the different layers of the insulation. Figure 4 shows a substantial constant concentration of the catalyst per resin unit through the first mica tape layer 110-1, the first impregnation layer 120-1, the second mica tape layer 110-2, and the second impregnation layer 120-2. Figures 5 a to 5 c show examples of mica tapes according to embodiments described herein. The mica tape 200 of Figure 5a to 5c each include mica 210 and a catalyst-activating agent 230 for activating a catalyst for curing a resin in the resin mixture of the insulation of the conductor arrangement. According to some embodiments, the catalyst-activating agent may be a catalyst-activating agent as described in embodiments above. In particular, the catalyst-activating agent does substantially not cure the resin in the resin mixture.

According to embodiments described herein, the mica tape does substantially not include or is free of catalyst for curing the resin. Typically, the mica tape according to embodiments described herein is not able to cure the resin in the resin mixture, unless the resin mixture contains a catalyst. Figure 5 a shows an embodiment, where the mica 210 is solved or mixed in a supporting material (not shown in Figure 5a) for the mica. Figure 5b shows an embodiment, where the mica 210 is arranged on the supporting material 220. The supporting material 220 of Figure 5b is shown as a film or tape, on which the mica 210 is placed. Figure 5c shows an example, where the supporting material 220 has on both sides mica 210 with the catalyst- activating agent 230.

Generally, the film or tape may include a wide range of insulation materials. For instance, the film may include from commodities to high performance thermoplastics resisting high temperatures and electric fields, filled (silica, alumina or mica) and fiber- (e.g. basalt or glass) or fabric-reinforced (e.g. glass cloth) materials for optimized mechanical properties and the like. In some embodiments, thermoplastic materials, such as high performance thermoplastics such as PES, PESU, PBT, PP, PEEK or PSU, may be used. Furthermore, in some embodiments, fiber-free tapes may typically be used for having better material interfaces and less voids as well as lower material costs. In other examples, thermosetting materials in combination with glass fibers may be used. In some embodiments, a glass cloth, PET or polyimide may be used as a film for supporting the mica. The simplified and schematic drawings of Figures 5a and 5b each show a uniform distribution of the catalyst-activating agent 230 in the mica. In some embodiments, the catalyst-activating agent may be arranged within the mica in an irregular distribution. According to some embodiments, the catalyst-activating agent may be provided only on top of the mica, or between mica flakes. For instance, the catalyst-activating agent may be provided in or on the mica tape by coating, painting, impregnating, gluing and/or spraying on the mica tape. In some embodiments, solvents may be used for bringing the catalyst- activating agent to the mica tape. The catalyst-activating agent may be either physically attached on the mica tape or provided between the mica flakes or provided between the mica flakes and other components in the tape (such as between the film or tape and the mica). In some embodiments, the catalyst-activating agent may be chemically bonded in or on the mica tape. For instance, the catalyst-activating agent being chemically bonded to the mica tape may result in less catalyst-activating agent dispersing into the resin mixture, as for instance shown in Figure 3e. The concentrations of the catalyst-activating agent can also vary and may in particular be adjusted to the technical requirements and/or the resin mixture used.

According to some embodiments, the catalyst-activating agent enables a local reaction with the catalyst of the resin mixture, when the mica tape as described herein is immersed or covered by the resin mixture. The mica tape being provided with the catalyst-activating agent for the "local" reaction may enable a reaction of the catalyst-activating agent of the mica tape and the catalyst of the resin mixture at the mica tape (upon contact of the mica tape and the resin mixture). The local reaction of the catalyst-activating agent and the catalyst of the resin mixture allow the resin to cure at decreased process temperature. Also, less catalyst-activating agent (compared to a catalyst-activating agent being pre-dissolved in the resin) can be used due to the local (and thus effective) reaction, which decreases the costs for production of a conductor arrangement.

Typically, the catalyst-activating agent may be described by "multifunctional hydroxyl terminated aromatic or cyclic compounds", and in particular catechol or pyrogallol and their derivatives may be used. According to some embodiments, a method for preparing an electrical insulation for an electrical conductor is provided. Figure 6 shows a flow chart 300 of the method according to embodiments described herein. The electrical insulation to be provided for an electrical conductor includes a mica tape and a reactive resin mixture.

According to some embodiments, which may be combined with other embodiments described herein, the electrical conductor may be a longitudinal conductor, like a cable, a coil, a bar, or the like, for instance an electrical conductor for an electric motor. In one example, the conductor may be made of copper, or may include copper to a large extent. In some embodiments, a conductor as referred to herein may be understood as a material having the property of transmitting electricity. Typically, a conductor as referred to herein may have a conductivity value equal to or greater than 10 ³ S/m at 20°C. In some embodiments, the conductor as referred to herein may also be a bundle of several conductors. In some embodiments, the conductor may be a wound conductor. For instance, the conductor including a bundle of small conductors may be provided in the form of a wound conductor, such as a coil or a Roebel bar.

The method according to embodiments described herein includes in box 310 mixing a reactive resin mixture including a resin and a catalyst for curing the reactive resin mixture. In some embodiments, the resin may be a homopolymerization resin. In particular, the resin mixture may include an anhydride-free epoxy resin. The catalyst may be a catalyst as described above including, for instance, organotin compounds, Lewis acids, such as boron trichloride and derivatives, in particular amine complexes, imidazoles, and a metal acetylacetonate, in particular chosen from the group consisting of aluminum acetylacetonate, zirconium acetylacetonate, iron acetylacetonate, or combinations thereof.

In box 320, the method includes arranging a mica tape around the electrical conductor. Typically, the mica tape includes mica and a support material, on or in which the mica is placed. According to some embodiments, the mica tape arranged in box 320 may be a mica tape as described in embodiments above, e.g. with respect to Figures 5a and 5b. The mica tape may be arranged around the electrical conductor by being wound around the conductor. In some embodiments, the mica tape may be provided by a shrinkable tube around the conductor.

The mica tape provides a catalyst-activating agent for activating the catalyst in the reactive resin mixture. The catalyst-activating agent may be provided to the mica tape by being physically attached to the mica tape, being chemically attached to the mica tape, being provided on the mica tape, being provided between mica flakes of the mica of the mica tape; being provided between the mica and other components of the mica tape (such as between the mica and the support material), and/or being chemically bonded to the mica tape. Typically, the catalyst-activating agent may be a catalyst-activating agent as described in embodiments above. In particular, the catalyst-activating agent does substantially not cure the reactive resin mixture.

According to embodiments described herein, the mica tape arranged around the electrical conductor is substantially free of the catalyst for curing the reactive resin mixture. In some embodiments, which may be combined with other embodiments described herein, the reactive resin mixture contains substantially no catalyst-activating agent for the catalyst for curing the reactive resin mixture. Further, according to some further embodiments, which may be combined with other embodiments described herein, the catalyst-activating agent is chosen from the class of multifunctional hydroxyl terminated aromatic, aliphatic and cyclic compounds. In the following, some examples and tests are given for embodiments described herein. A specific resin and other formulations were prepared by first mixing the epoxy resins EP158 (bisphenol F epoxy) and/or MY790 (bisphenol A epoxy) resins at ca. 50 °C with a mechanical stirrer. A phenolic accelerator and aluminum acetylacetonate were added and the whole mixture is mixed in an ultrasonic bath. After cooling to room temperature, styrene was optionally added and mixed.

A differential scanning calorimetry (DSC) was performed. Heat release (exotherm) and onset temperatures of curing reactions were measured using Perkin Elmer DSC-7 and DSC-1 Differential Scanning Calorimeters. Uncured resin samples weighing approximately 5-10 mg, respectively, were loaded in vented aluminum pans. Heating ramps were performed at a rate of 2 °C/min in case of curing characterization.

The gel time was then determined. Gel time measurements were performed here in two different setups: 1. Gel time was determined by measuring viscosity using a Bohlin CVO rheometer with 40 mm parallel aluminum plates and a gap of 500 μιη. Such measurements were performed in single shear mode with a constant shear rate of 100/s. The resin was kept ca. 1 min between the plates (to adjust to the temperature) before starting the test. The onset of the rapid viscosity increase is used as gel time. 2. Samples of approximately 10 g of the formulation were prepared in an aluminum dish (5 cm diameter) and kept in an oven at a defined temperature (5 replicates per formulation). Gel time was detected by observation of the initial liquid by moving the dishes.

The results on homopolymerized epoxy (formulation of 100 phr EP158, x phr Al(acac)3 and y phr catechol): In the thermograms of DSC measurements as well as the gel time measurements one can see the large influence of the catechol. On the other hand, other properties such as glass transition temperature and dielectric properties of the finally cured resins are not impacted largely by varying the catechol concentration. In contrast, carrying or increasing the amount of aluminum acetylacetonate does not influence largely the reactivity.

According to some embodiments, the electrical conductor arrangement, the mica tape and the method for preparing an insulation for an electrical conductor may typically be used for high voltage (HV) electrical machines. Generally, an electrical machine as referred to herein may be an electrical machine for high voltages. For instance, the electrical machine and the electrical conductor arrangement according to embodiments described herein may be adapted for a rated voltage being typically larger than 1 kV, more typically larger than about 5 kV, and even more typically larger than about 10 kV. According to some embodiments, the rated voltage may be in a range between about 1 kV to about 14 kV.

Embodiments described herein mainly refer to the specific application for HV rotating machines for manufacturing electrical "main-wall" insulation on conductor coils and bars. Typically, the insulation provided in embodiments described herein is configured for providing the main insulation or main wall insulation of the electrical conductor.

The electrical conductor arrangement, the mica tape and the method for preparing insulation for an electrical conductor relate in particular to an application in or for HV rotating machines based on the mica tape including the catalyst-activating agent and substantially no catalyst. The mica tape according to embodiments described herein is especially compatible with impregnating epoxy based resins. In particular, the mica tape according to embodiments described herein improves the processibility of VPI resins - in particular based on homopolymerization or polymerization with a reactive diluent such as styrene The mica tape according to embodiments described herein provided with specific chemicals in order to boost the reaction with impregnating epoxy based resin results in a shorter gel time when curing the mica-tape-epoxy compound. In embodiments described herein, the chemical nature of such booster or catalyst-activating agent may be described by "multifunctional hydroxyl terminated aromatic or cyclic compounds", such as catechol or pyrogallol. The mica tape does substantially not include the catalyst for the resin. In some embodiments, e.g. in specific resin formulations, catechol is used as catalyst- activating agent - alongside with the catalyst aluminum acetylacetonate - for the homopolymerization of the epoxy functionalities and is, therefore, responsible for activating the catalyst for the gelling / curing of the full resin. Additionally, a reactive diluent may be used in the resin mixture in some embodiments. Inter alia, the reactivity - thus gel time - is largely affected by the amount of catechol. Another positive feature is the much longer lifetime compared to the conventional epoxy-anhydride systems used for HV insulation. In known systems, besides the epoxy resin, styrene as reactive diluent and aluminum acetylacetonate as catalyst is used in the resin mixture. Styrene may be used in order to lower the viscosity so that resin can be used at room temperature and a good impregnation quality can be ensured. In the specific resin, the amount of both catechol and aluminum acetylacetonate was adjusted to obtain a long pot life at storage temperatures between 7 and 25 °C in known systems. At the same time, gelling at elevated temperatures such as 140 or 160 °C is desired to be reached within a given short time frame. In addition, the level of catalyst system was kept as low as possible for cost reasons and risk of precipitation during long storage of the VPI resin formulation. Both initiator catechol and catalyst aluminum acetylacetonate are responsible for the polymerization, so gelling and curing, of the full resin. The overall reactivity - thus gel time - is dominantly affected by the amount of catechol. The electrical conductor arrangement, the mica tape and the method according to embodiments described herein allow separating the catalyst and the catalyst-activating agent (such as catechol) and help avoiding ageing of the resin mixture and the need of high process temperatures. Though the present invention has been described on the basis of some preferred embodiments, those skilled in the art should appreciate that those embodiments should by no way limit the scope of the present invention. Without departing from the spirit and concept of the present invention, any variations and modifications to the embodiments should be within the apprehension of those with ordinary knowledge and skills in the art, and therefore fall in the scope of the present invention which is defined by the accompanied claims.

Reference numerals

100 electrical conductor arrangement

101 electrical conductor 110, 110-1, 1 10-2 mica tape layer

120; 120-1 to 120-3 impregnation resin layer 130 graph

200 mica tape

210 mica

220 support material

230 catalyst-activating agent 300 flow chart

310, 320 boxes of the flow chart