Solid crystal structure used as a filler in UV-curable thermosetting resins to enhance the electrical insulation of high-voltage conductor bars

Abstract

An electrically insulating mixture for forming a layer on a conductor surface is provided. The mixture includes a UV-curable thermosetting resin and a filler. The filler includes a UV-transparent crystal structure made of a crystal structure material. UV transparency is given for light in the wavelength range between 300 nm and 420 nm. Further, a method for electrically insulating a metal conductor is provided. The method includes: obtaining an electrically insulating mixture; forming a sheath on the surface of the metal conductor using the thus obtained mixture; and exposing the mixture to ultraviolet radiation to cure the mixture, thereby forming an electrically insulating layer on the surface of the metal conductor by the sheath. A metal conductor with an electrically insulating layer can be obtained by using the electrically insulating mixture.

Description

Technical Field

[0001] Various embodiments of the present disclosure generally relate to UV-curable mixtures for forming electrically insulating layers of electrical conductors. Background Art

[0002] Electrical conductors at different potentials need electrical insulation to prevent short circuits and / or avoid hazards. The electrical conductor can be, for example, a Roebel bar formed by multiple conductor strands, and insulation can prevent short circuits between different strands of the Roebel bar. For example, when compared with the same section of conductor formed by only one conductor strand (i.e., a single wire), a Roebel bar arrangement formed by multiple mutually insulated conductor strands can reduce the total resistance. Electrical conductors (e.g., Roebel bars) also need to be electrically insulated from ground and / or other conductors. Therefore, ground wall insulation is required. Similarly, for coil wires, stator windings, etc., different windings and / or coil turns need to be insulated from each other and need to be insulated from the body at ground potential and / or other conductors.

[0003] The electrical conductor can be, for example, a coil formed by one or more wires forming one or more windings (typically, multiple windings). Short circuits between different windings and / or different parts of the electrical conductor must be prevented to ensure uniform current flow along the entire conductor. For example, to maximize the magnetic field induced by the current flowing in the conductor. Therefore, for example, different windings need to be insulated from each other.

[0004] The electrical conductor can be part of a stator winding.

[0005] Furthermore, the electrical conductor may need insulation to ensure safety, for example, to avoid short circuits and / or the risk of electrocuting humans and / or animals.

[0006] Traditionally, mica tapes and / or resin impregnation are used to form electrical insulation. Resin impregnation can include a curing process.

[0007] Using mica tapes and / or cured resins to form electrical insulation is time-consuming and energy-consuming, and may result in the formation of voids, which cause non-uniform insulation of the electrical conductor.

[0008] In particular, for Roebel bars and / or coil wires, using mica tapes and / or curable resins for resin impregnation may result in non-uniform insulation, for example, causing non-uniform inter-strand and / or ground wall insulation. The non-uniform insulation layer can be caused, for example, by the presence of voids and / or by the non-uniform thickness and / or geometry of the mica tape winding of the conductor and / or conductor strands to be insulated.

[0009] Furthermore, the insulation properties of the resin (e.g., breakdown voltage and / or dielectric strength) may be poor.

[0010] Mica tapes and resin impregnations are also time-consuming and energy-consuming, resulting in a considerable amount of effort and cost.

[0011] To obtain more uniform insulation and / or better insulation, characterized for example by an increased breakdown voltage and dielectric strength, while also simplifying and improving the insulation process, other improvements are needed that overcome the disadvantages of using mica tapes and curable resins. Summary of the Invention

[0012] According to one aspect, there is provided an electrically insulating mixture for forming a layer on a conductor surface. The mixture comprises a UV-curable thermosetting resin and a filler. The filler comprises a UV-transparent crystal structure made of a crystalline structure material. As used herein, UV transparency is defined for light in the wavelength range between 300 nm and 420 nm.

[0013] According to the present disclosure, a material is UV-transparent if its transparency in the wavelength range between 300 nm and 420 nm is substantially similar to or higher than that of synthetic fluorophlogopite (synmica) (also known as fluorophlogopite). Herein, "substantially similar" is defined with a tolerance of 10% transparency. For example, in the said wavelength range, the transmittance of a UV-transparent material in the wavelength range between 300 nm and 420 nm can be, for example, equal to or higher than 90% of the transmittance of synmica. Preferably, the transparency can be the same as or higher than the transmittance of synmica.

[0014] According to another aspect, there is provided a method for electrically insulating a metal conductor. The method comprises: providing a metal conductor; obtaining an electrically insulating mixture as disclosed herein; forming a sheath on the surface of the metal conductor using the thus obtained mixture; and exposing the mixture to ultraviolet radiation to cure the mixture, thereby forming an electrically insulating layer on the surface of the metal conductor by the sheath.

[0015] According to yet another aspect, there is provided a metal conductor having an electrically insulating layer obtained by curing an electrically insulating mixture as disclosed herein, optionally obtained using the method as disclosed herein. Brief Description of the Drawings

[0016] The embodiments of the present disclosure are described in more detail with reference to the accompanying drawings, wherein:

[0017] Figure 1 Schematically shows an electrically insulating layer of a conductor according to an embodiment of the present disclosure.

[0018] Figure 2 Shows details of an electrically insulating layer of a conductor according to an embodiment of the present disclosure.

[0019] Figure 3 A flowchart of a method for electrically insulating a metal conductor according to an embodiment of the present disclosure is shown.

[0020] Figure 4 The chemical structures of natural phlogopite and synthetic fluorphlogopite are illustrated in comparison.

[0021] Figure 5 The relationship between the maximum sheath speed and the percentage of mica added to the epoxy resin, which is related to an embodiment of the present disclosure, is shown as a function.

[0022] Figure 6 The values of the scale parameters and breakdown strength of the insulating layer, which are related to an embodiment of the present disclosure, are shown.

[0023] Figure 7 The values of the shape parameters and breakdown strength of the failure probability, which are related to an embodiment of the present disclosure, are shown. Detailed Description

[0024] Since it is difficult to form a uniform mica tape winding, mica tape is not conducive to forming electrical insulation. The resin used to form the insulating impregnation may be characterized by poor insulation performance, such as, for example, low dielectric strength.

[0025] To overcome the above-mentioned drawbacks, the present disclosure describes a UV-curable mixture for forming an electrical insulating layer of a conductor, wherein the mixture comprises a UV-curable thermosetting resin and a filler, and the filler is formed of a UV-transparent solid crystal structure. In particular, the UV-transparent solid crystal structure may be a synthetic fluorphlogopite crystal structure.

[0026] In the present disclosure, the solid crystal structure is used as a filler in the UV-curable thermosetting resin to enhance the electrical insulation of the high-voltage conductor bar.

[0027] Mica tapes commercially available as insulating materials for high-voltage applications are generally composed of natural mica, such as muscovite with a dielectric strength of 120 kV / mm to 200 kV / mm or phlogopite with a dielectric strength of 115 kV / mm to 140 kV / mm. However, such natural mica is a strong absorber of energy in the ultraviolet range, making it impossible to use such mineral fillers for processing insulating materials using UV-curable thermosetting materials.

[0028] Laboratory tests have confirmed that the presence of even a small amount of mineral mica has a great impact on the curing speed of UV-curable thermosetting materials. For example, the presence of 5% by weight of muscovite will cause a 50% reduction in the curing speed of the UV epoxy resin.

[0029] Synthetic fluorophlogopite (synmica) (also known as fluorphlogopite) with a dielectric strength of approximately 180 kV / mm provides a solution for improving electrical insulation. Due to a minor change in the chemical structure compared to natural mica where the hydroxyl groups are replaced by fluorine atoms, synthetic mica (hereinafter also referred to as synmica) is presented as UV transparent: synmica does not absorb electromagnetic radiation in the ultraviolet range of the spectrum, thus allowing the curing reaction to maintain the same reaction rate as in the case of processing a pure thermosetting material that may not contain any filler material.

[0030] Synmica does not compete with the photoinitiator of the UV curable thermosetting material, thus allowing the curing reaction to maintain the same reaction rate as in the case of processing a pure thermosetting material that may not contain any filler material. Experiments have confirmed that adding up to 20% by weight of synmica does not result in any reduction in the curing speed of the UV curable thermosetting material.

[0031] By means of AC breakdown strength measurements in oil performed by testing according to Part 1 of IEC 60243-1 Electrical strength of insulating materials - Test methods at power frequency, experiments have demonstrated that adding synmica enhances the insulating properties of the UV curable thermosetting material.

[0032] This part of IEC 60243 provides a test method for determining the short-time electrical strength of solid insulating materials at power frequencies between 48 Hz and 62 Hz. Measurements are made using a pair of spherical metal electrodes of equal diameter, with each electrode having a diameter of 20 mm. The surrounding medium used to prevent flashovers during the test is transformer oil (Diala S4 ZX-1). The rate of voltage increase used is 2000 V / s.

[0033] This test measures the breakdown strength of the material, expressed in kV of the applied voltage, normalized by the thickness of the sample in mm. A series of measurements were performed, and the breakdown strength data was analyzed using a two-parameter Weibull cumulative distribution of the following form:

[0034]

[0035] where σ is the experimentally obtained breakdown strength value, i.e., the breakdown strength values that form a random variable, α is the scale parameter corresponding to the 63.2% cumulative probability of breakdown strength, and β is the shape parameter indicating the scatter of the statistical distribution: the higher the β value, the less the scatter of the breakdown strength values, and the stronger the insulation of the material. F σ (t) indicates the cumulative distribution function of the random variable σ and is defined as follows:

[0036] F σF(t) = P(σ ≤ t)

[0037] That is, F σ (t) indicates the probability that σ ≤ t (i.e., the random variable σ is less than or equal to the value t).

[0038] Adding 5% to 15% of synmica first reduces the average breakdown strength and the scale parameter α, while when 20% of synmica is used, these properties are significantly improved. Further, adding 15% of synmica to the UV - curable thermosetting material causes β to increase from 8.2 (for pure epoxy resin) to 17.3, and the breakdown strength at 0.01% failure increases from 13.7 kV / mm to 22.5 kV / mm. Measurements show that adding synmica to the UV - curable thermosetting material makes the resin a significantly more robust electrical insulator, and since its curing reaction rate is not reduced, it does not affect its processability.

[0039] Figure 1 Schematically shows an electrical insulation layer of a conductor according to an embodiment of the present disclosure. Specifically, Figure 1 Shows a conductor arrangement 10 with an insulation layer 20, in which a plurality of conductor strands 15 - 1, 15 - 2, 15 - 3, 15 - 4 are embedded.

[0040] The thickness of the insulation layer 20 may be between 0.5 mm and 2.0 mm.

[0041] The plurality of conductor strands 15 - 1, 15 - 2, 15 - 3, 15 - 4 form an integral electrical conductor, such as a Roebel bar, a coil wire and / or a coil turn, a stator winding, etc. Hereinafter, for simplicity, the conductor strands 15 - 1, 15 - 2, 15 - 3, 15 - 4 may be referred to as conductors.

[0042] For a Roebel bar, the conductor strands (the cross - section of which is shown in Figure 1 can be further intertwined and / or arranged along the longitudinal direction of the conductor so as to reduce the resistance in the presence of the skin effect.

[0043] A gap G is provided between different conductor strands, for example, in order to increase the total number of windings / turns of the coil and / or to avoid short - circuits between the conductor strands of the Roebel bar.

[0044] AC current flows in a direction substantially perpendicular to the Figure 1 plane. In Figure 1In it, the conductor arrangement 10 includes spatially adjacent conductors 15-1, 15-2, 15-3, 15-4, each conductor having a substantially rectangular cross-section with rounded corners. However, neither the cross-sectional shape nor the number of the conductors 15-1, 15-2, 15-3, 15-4 is limited to those shown in the drawings.

[0045] For example, there may be only one conductor 15-1, or two (15-1, 15-2), three (15-1, 15-2, 15-3) or any finite number n of conductors (15-1, 15-2, 15-3, ……, 15-n) may be arranged at multiple spatial positions. For example, one or more of the conductors may have different cross-sectional shapes, such as square, square with rounded corners, rectangular, circular, etc. In Figure 1 the example, each of the conductors 15-1, 15-2, 15-3, 15-4 is an enameled conductor, but is not limited thereto.

[0046] For example, dividing the conductor into multiple conductor strands 15-1, 15-2, 15-3, 15-4 allows increasing the windings / turns of the coil and / or allows reducing the total resistance of the conductor in the presence of the skin effect, particularly when the conductor strands are longitudinally intertwined and / or regularly arranged. The conductor strands must be kept insulated from each other to avoid short circuits, which may, for example, reduce the magnetic field generated in the coil and / or increase the resistance in the Roebel bar.

[0047] Furthermore, there is also a gap between the conductor and any body (not shown) that is grounded and / or at ground potential.

[0048] The insulating layer 20 insulates different conductor strands to avoid short circuits between the conductor strands. Thus, the insulating layer 20 can form interstrand insulation and / or ground wall insulation.

[0049] For example, the conductor formed by the conductor strands together with the insulating layer 20 forms the conductor arrangement 10, which can be used, for example, in an electric machine (such as, for example, a generator or a motor), thereby forming, for example, a coil.

[0050] For example, the conductor formed by the conductor strands together with the insulating layer 20 forms the conductor arrangement 10, which can be used, for example, to transfer electrical energy from a generator to a load in a circuit, thereby forming, for example, a Roebel bar arrangement.

[0051] According to the present disclosure, the insulating layer 20 includes an insulating material obtained by a curing process of a thermosetting material, wherein a solid electrical insulating element 25 such as a mica crystal structure is present inside the thermosetting material. Preferably, in the uncured state, the relationship (volume ratio) of the solid insulating element to the thermosetting material component of the insulating material is between (at least) 20:80 by volume, preferably between (at least) 25:75, and typically, about (at least) 30:70. Preferably, in the uncured state, the solid insulating element has at least 20% of the total volume of the insulating material, preferably at least 25%, and particularly preferably at least 30%, and the thermosetting material preferably substantially constitutes the remaining part of the volume. Thus, by volume, the volume of the thermosetting material is preferably at most 80%, preferably at most 75%, and typically, at most 70%.

[0052] A preferably upper limit of the volume of the solid insulating element is 40%, preferably 35%, and particularly preferably 30%. A preferably lower limit of the volume of the thermosetting material is 60%, preferably 65%, and particularly preferably 70%.

[0053] From another perspective, in the uncured state, by volume, the volume fraction of the solid insulating element to the thermosetting material component of the insulating material is between 20:80 (20% to 80%), preferably between 25:75 (25% to 75%), and typically, about 30:70 (30% to 70%). A particularly preferably upper limit of the crystal structure content is 50% by volume or even 40%. Such a crystal structure content is particularly preferably used to improve the electrical insulating mixture, thereby ensuring effective UV curing (e.g., by allowing sufficient UV light penetration for rapid and effective curing), while providing appropriate characteristics of the cured mixture and good dielectric strength.

[0054] Alternatively or additionally, in the uncured state, the volume of the crystal structure can be, for example, 20% of the volume of the electrical insulating mixture, and the volume of the thermosetting resin can be 80% of the volume of the electrical insulating mixture; or the volume of the crystal structure can be, for example, 25% of the volume of the electrical insulating mixture, and the volume of the thermosetting resin can be 75% of the volume of the electrical insulating mixture; or, the volume of the crystal structure can be, for example, 30% of the volume of the electrical insulating mixture, and the volume of the thermosetting resin can be 70% of the volume of the electrical insulating mixture. Alternatively, the volume of the crystal structure can be 20% or more of the volume of the electrical insulating mixture, and the remaining volume of the electrical insulating mixture is occupied by the thermosetting resin. In particular, the volume of the crystal structure can be 20% or more, or 25% or more, or 30% or more, and the remaining volume of the electrical insulating mixture is filled with the thermosetting resin.

[0055] The term "composition" generally refers to a mixture or compound of the materials involved. In particular, a composition of a thermosetting material and a mica element can be obtained by mixing an uncured thermosetting material and an insulating element. For example, the thermosetting material and the mica sheet are fed, typically in a gravimetric analysis manner, into a mixer that produces the composition. The composition can generally be a liquid resin compound filled with a mica crystal structure. The thermosetting material can be a UV-curable thermosetting resin. The insulating element can be mica particles having a predetermined average particle size, typically, mica sheets. The insulating material or its thermosetting material component is typically cured accordingly.

[0056] Figure 2 Details of an electrical insulation layer of a conductor according to an embodiment of the present disclosure are shown.

[0057] For example, Figure 2 shows Figure 1 Details of region E of the cross-section of. For example, region E can correspond to the upper left corner of a segment of the conductor strand 15-1.

[0058] As schematically shown, the conductor strand 15-1 can be insulated by the insulating layer 20, which forms ground wall insulation and / or interstrand insulation and / or insulates the conductor 15-1 from other conductors and / or windings and / or coil turns.

[0059] In some embodiments of the present disclosure, the insulating layer 20 can be formed from a UV-curable mixture comprising a UV-curable thermosetting resin and a filler, wherein the filler is formed by a UV-transparent solid crystal structure 25, for example, formed by a synthetic fluorophlogopite crystal structure.

[0060] According to an embodiment of the present disclosure, there is provided an electrical insulation mixture for forming a layer on a conductor surface, wherein the mixture comprises an ultraviolet (UV)-curable thermosetting resin and a filler, wherein the filler comprises a UV-transparent crystal structure made of a crystal structure material, wherein UV transparency is given for light in a wavelength range between 300 nm and 420 nm.

[0061] The crystal structure can have a substantially sheet-like shape, wherein its (average) thickness (in a direction perpendicular to the local sheet plane) is much smaller than its length and width (measured for the flattened sheet if the sheet is not completely flat). In one possible definition, for example, a crystal structure can be considered transparent if the radiation flux of the UV light incident on the local sheet plane is substantially transmitted through the entire crystal structure and passes through the entire crystal structure without significant attenuation. For example, the radiation flux transmitted through the thickness of the sheet and exiting the sheet can be, for example, 85% or more of the incident radiation flux incident on the sheet-like crystal structure.

[0062] The surface of the crystal structure may not reflect the UV light back, and the crystal structure material of the crystal structure may not dissipate or absorb the UV light to a greater extent than expressed by the above threshold.

[0063] The purpose of the UV radiation is to interact with the thermosetting resin to activate the photoinitiator, which catalyzes the crosslinking reaction of the thermosetting material. The interaction of the insulating mixture filled with the synmica crystal structure with the UV radiation is substantially the same as that of the insulating mixture composed of pure resin (i.e., without the synmica crystal structure). This can be achieved when the crystal structure is substantially UV transparent.

[0064] The UV light can be light with a wavelength between 380 nm and 420 nm, and can be generated, for example, by a source having an irradiance of 4 W / cm 2 at the UV emission window for an emission window of, for example, 300 mm × 20 mm. The total UV power of 240 W can be irradiated by a source such as a UV LED (e.g., a UV LED based on SLM technology).

[0065] For example, in the wavelength range between 0.38 μm and 0.42 μm, a transmittance of 85% or more through the synmica crystal structure can be obtained.

[0066] As long as the intensity does not increase, the constant value of the maximum depth of penetration of the UV beam into the non-transparent material will be limited. The maximum penetration depth can be the maximum depth at which the radiant flux of the UV light is higher than the radiant flux incident on the non-transparent material.

[0067] For the material interacting with the UV radiation beam, the intensity of the beam attenuates according to the penetrated depth.

[0068] For the present disclosure, the thickness of the insulating layer is significantly less than the maximum penetration depth, so there is basically no resin curing gradient from the surface to the insulating conductor interface; the degree of curing is the same throughout the thickness of the insulating layer.

[0069] For example, the transparency of the crystal structure can be measured by irradiating the surface of the crystal structure with UV light, e.g., emitting light propagating in a direction perpendicular to the local sheet plane, and measuring the radiation flux passing through the sheet plane that exits on the opposite side of the sheet as a part of the radiation flux incident on the sheet. In practice, the measurement can be carried out by focusing a UV light beam onto the surface of the crystal structure, measuring the radiation power of the beam incident on the sheet, and the radiation power of the UV light emitted through the sheet on the side opposite to the side where the beam is directed onto the sheet. For example, for wavelengths greater than 0.2 microns, e.g., 0.3 microns and / or less than 1.0 microns, e.g., less than 0.4 microns, the transmittance of the crystal structure having a sheet-like shape (i.e., the radiation power passing through the crystal structure / sheet and re-emitted by the crystal structure / sheet as a part of the incident power) may be 85% or more.

[0070] The length / size of the sheet-like crystal structure made of synmica (fluorphlogopite) may be from 3.2 μm to 14.3 μm. The thickness of the crystal structure can be between 0.30 μm and 0.35 μm. The aspect ratio of the synmica crystal structure may be 3.2 / 0.35 = 9 to 14.3 / 0.30 = 48.

[0071] The UV-transparent light does not reflect back from the surface of the crystal structure and effectively penetrates the crystal structure material and the electrically insulating mixture.

[0072] Moreover, due to the transparency of the crystal structure material, the UV light absorbed by the surface of the crystal structure material further propagates in the crystal structure material. The UV radiation transmitted through the surface of the crystal structure material further propagates in the crystal structure material to a depth corresponding at least to the maximum diameter / size d of the crystal structure.

[0073] According to the present disclosure, if the material of the crystal structure is UV-transparent in the wavelength range between 300 nm and 420 nm, the transparency of the material of the crystal structure is substantially similar to (i.e., at least substantially the same, with a tolerance of, for example, about 10%) the transparency of synthetic fluorophlogopite (synmica) (also known as fluorophlogopite mica). If the transmittance of the crystal structure material is substantially similar to the transmittance of synmica, the crystal structure material may be considered UV-transparent. For example, the transmittance of the UV-transparent material of the crystal structure in the wavelength range between 300 nm and 420 nm may be similar to the transmittance of synmica in this wavelength range, for example, 90% or more of the transmittance of synmica. The transmittance may be the transmittance relative to the maximum diameter / size of the crystal structure. The transmittance may be a function of the wavelength. For each wavelength in the range between 300 nm and 420 nm, the transmittance of a layer of the crystal structure material with a thickness of d is at least 90% of the transmittance of a layer of synmica with a thickness of d for the same wavelength and for any thickness d (e.g., the maximum thickness / size or the average thickness / size of the crystal structure).

[0074] As used herein, "substantially similar" is defined with a 10% transparency tolerance. For example, in the said wavelength range, the transmittance of the UV-transparent material in the wavelength range between 300 nm and 420 nm may be, for example, equal to or higher than 90% of the transmittance of synmica. Preferably, the transparency may be the same as or higher than the transmittance of synmica.

[0075] Thus, if for each wavelength in the range between 300 nm and 420 nm, the transmittance of a layer of the crystal structure material with a thickness of d is at least 90% of the transmittance of a layer of synmica with a thickness of d for the same wavelength and for any thickness d (e.g., the maximum or average thickness / size of the crystal structure), the crystal structure and / or the crystal structure material is considered UV-transparent.

[0076] For example, if for each wavelength in the range between 200 nm and 420 nm, the transmittance of a layer of the crystal structure material with a thickness of d is at least 90% of the transmittance of a layer of synmica with a thickness of d for the same wavelength and for any thickness d (e.g., the maximum thickness or the average thickness), the crystal structure and / or the crystal structure material is considered UV-transparent.

[0077] In some embodiments, the crystal structure material is further characterized in that the dielectric strength is substantially the same as the dielectric strength of synmica, for example, 90% or greater than the dielectric strength of synmica.

[0078] The crystal structure does not need to be made of a pure crystal structure material and / or the crystal structure does not need to be made of pure synmica. As long as the light transmittance / transmissivity and / or the dielectric strength are not substantially affected, for example, as long as the transmissivity is 90% or greater than the transmissivity of pure synmica and the dielectric strength is 90% or greater than the dielectric strength of pure synmica, the crystal structure material and / or synmica can contain impurities.

[0079] For example, the dielectric strength of the crystal structure material may be between 115 kV / mm and 180 kV / mm, for example, 140 kV / mm.

[0080] The crystal structure material can be synmica or can be a material having substantially similar properties to synmica.

[0081] The UV-transparent solid crystal structure 25 ensures that less UV light is absorbed by the mixture including the UV-curable thermosetting resin and the filler including the UV-transparent crystal structure. Thus, the electrically insulating mixture can be advantageously cured by UV light, and in particular, an elevated curing speed can be maintained to form an insulating layer, and additionally, the dielectric strength of the insulating layer is increased.

[0082] In particular, the UV-transparent solid crystal structure 25 can include a synthetic fluorophlogopite crystal structure. Due to the insulating properties of synthetic fluorophlogopite, the UV-transparent solid crystal structure 25 improves the dielectric strength of the electrically insulating mixture; and due to the UV transparency of the solid crystal structure 25, it further allows the UV-curable thermosetting resin in the mixture to cure rapidly. In particular, a substantially UV-transparent synthetic fluorophlogopite crystal structure ensures effective penetration of UV light through the mixture of the UV-curable thermosetting resin of the curing mixture. A UV-opaque crystal structure formed of natural mica, for example, can still improve the dielectric strength, but absorption of UV light may prevent the UV-curable thermosetting resin from curing effectively and rapidly to quickly form an insulating layer of an electrical conductor.

[0083] The insulation thickness (i.e., the thickness of the insulating layer) can be, for example, between 0.5 mm and 2.0 mm.

[0084] By weight, the concentration of the crystal structure in the mixture can be from 0% to 20%.

[0085] Figure 3 A flowchart of a method 300 for electrically insulating a metal conductor according to an embodiment of the present disclosure is shown.

[0086] A method 300 for electrically insulating a metallic conductor begins at 1001. The method includes: obtaining 1002 an electrical insulation mixture that includes a UV curable thermosetting resin and a filler. The method further includes: forming 1003 a sheath on the surface of the conductor using the mixture obtained at 1002, and exposing the mixture to 1004 ultraviolet (UV) radiation to cure the mixture, thereby forming an electrical insulation layer 20 on the surface of the metallic conductor by the sheath.

[0087] In some embodiments, at least one of the following is repeated 1005 one or more times: obtaining 1002 the mixture; forming 1003 the sheath; and exposing the mixture to 1004 UV radiation until the entire surface of the conductor is electrically insulated. In particular, during the repetition, different longitudinal segments of the conductor can be electrically insulated. For example, during the repetition, the sheath unit can be translated along the longitudinal axis of the conductor, and for each longitudinal segment of the longitudinally extending conductor, forming 1003 the sheath and exposing the mixture to 1004 UV radiation are iteratively performed.

[0088] Similarly, the repetition 1005 can be performed along a wire or a group of wires that can form a coil and / or along the turns of wire that form a coil in an electric machine.

[0089] Figure 4 The chemical structure of natural phlogopite is illustrated on the left and that of synthetic fluorphlogopite is illustrated in the upper right. The hydroxyl groups in natural mica are replaced by fluorine atoms, thereby rendering synthetic fluorphlogopite UV transparent while maintaining good electrical insulation properties, e.g., the high dielectric strength of synthetic mica.

[0090] Then, Figure 4 the synthetic fluorphlogopite can be used in a method 300 for forming a UV transparent crystal structure 25 of the filler of the electrical insulation mixture obtained at 1002. The synthetic fluorphlogopite improves the dielectric strength while still allowing rapid UV curing of the mixture. The mixture is used to form an electrical insulation layer 20 according to method 300. In particular, the solid crystal structure 25 including synthetic fluorphlogopite improves the dielectric strength of the finally obtained electrical insulation layer 20 while allowing rapid curing when the mixture is exposed to 1004 UV radiation according to method 300.

[0091] Figure 5 The maximum sheath speed in mm / min is shown as a function of the percentage of mica added to an epoxy resin that is a UV curable thermosetting resin according to the present disclosure. If the mica added is natural mica, the maximum sheath speed decreases as the percentage of mica added to the epoxy resin increases. For example, for a thermosetting resin, e.g., an epoxy resin, in the absence of added mica, according to Figure 5, the maximum sheathing speed may be 800mm / min. When 5% mica is added to the thermosetting resin, the maximum sheathing speed has been reduced to 400mm / min. And for 20% mica added to the epoxy resin, the maximum sheathing speed may be only about 200mm / min. When synmica is used, the synmica does not interfere with the curing process. Therefore, the maximum sheathing speed remains approximately constant and equal to the maximum sheathing speed that the epoxy resin can obtain without the addition of any mica crystal structure. For example, for any percentage of mica in the range of 0% to 20% added to the epoxy resin, the maximum sheathing speed can remain approximately constant and equal to 800mm / min.

[0092] The maximum sheathing speed is defined as the maximum speed at which the insulation on the conductor has been sufficiently crosslinked by the curing reaction to consider the thermoset material to have hardened. The crosslinking reaction is driven by the photoinitiator present in the thermoset resin and the photoinitiator reacts only during its exposure to UV radiation.

[0093] For example, after curing is completed, the insulating layer is, for example, sufficiently regular and / or uniform, for example, without gaps and / or cracks and / or variations along the longitudinal axis of the conductor.

[0094] Figure 5 The effect of the presence of synmica compared to natural mica is illustrated merely exemplarily, showing that for synmica the maximum sheathing speed does not depend on the percentage of synmica added, whereas for natural mica the maximum sheathing speed decreases rapidly with the percentage of mica added to the epoxy.

[0095] Depending on parameters such as, for example, the geometry of the electrical conductor and / or the rate at which the thermosetting resin (e.g., epoxy) is provided and / or the power of the UV light during curing, the maximum sheathing speed may vary. However, when synmica is added, the maximum sheathing speed that varies with the percentage of synmica added to the UV-curable thermosetting resin remains substantially constant, and / or the decrease in the maximum sheathing speed that varies with the percentage of mica added to the epoxy resin is much lower than when natural mica is added.

[0096] therefore, Figure 5 The maximum sheathing speed obtainable when a mixture for forming an insulating layer on a conductor surface is exposed to ultraviolet (UV) radiation to cure the mixture according to an embodiment of the present disclosure is shown.

[0097] Once curing is complete, the breakdown strength σ of the insulating layer forms a cumulative distribution F of the form σ (t) is a real-valued nonnegative random variable:

[0098]

[0099] The cumulative distribution is a two-parameter Weibull cumulative distribution.

[0100] The breakdown strength σ is a real-valued non-negative random variable, so the cumulative distribution F σ (t) indicates the probability that σ ≤ t, so, F σ (t) = P(σ ≤ t).

[0101] The parameter α forms the scale parameter, while β forms the shape parameter.

[0102] Therefore, for t = α, Therefore, the scale parameter α corresponds to / identifies the cumulative probability 0.632 of the breakdown strength, i.e.,

[0103]

[0104] The shape parameter β indicates the spread of the statistical distribution F σ (t). When β increases, the cumulative distribution function F σ (t) becomes steeper. We observe that:

[0105]

[0106] Therefore, when β → +∞, according to the previous formula, the probability density function converges to the Dirac δ distribution centered at α, and converges to the unit step function centered at α and where is.

[0107] The breakdown strength σ can be measured, for example, in kV / mm.

[0108] Therefore, for the value β → +∞, the probability that the breakdown strength value is less than α is 0, while for any value ε > 0, the probability that the breakdown strength value is less than α + ε is 1.

[0109] This means that when an electric field strictly less than α is applied, no electrical breakdown occurs; while for any electric field strictly greater than α, electrical breakdown will definitely occur.

[0110] For a finite positive value of β, the transition of F σ (t) corresponding to α will have a finite positive slope, where the steepness increases with the increase of the β value.

[0111] Therefore, it is desirable to have as large a value of α as possible and as large a value of β as possible.

[0112] Figure 6Shows the values of the scaling parameter α in kV / mm for pure epoxy resin and epoxy resins with 5%, 10%, 15%, and 20% of synmica added respectively. Further, Figure 6 Shows the experimentally determined average breakdown strength in kV / mm. We observe that the average breakdown strength is centered around the scaling parameter α. Thus, Figure 6 Describes the scaling parameter and the average breakdown strength of the insulating layer according to an embodiment of the present disclosure. In particular, Figure 6 Shows the average breakdown strength and the scaling parameter of the electrical insulation formed from an electrically insulating mixture comprising a UV-curable thermosetting resin and a filler according to an embodiment of the present disclosure, the filler comprising a UV-transparent crystal structure comprising synthetic fluoromica (synmica).

[0113] Adding 5% to 15% of synmica may first result in a decrease in the average breakdown strength and / or the scaling parameter α, but when 20% of synmica is used, the breakdown strength and the scaling parameter α increase significantly.

[0114] Figure 6 Only exemplarily shows the dependence on the percentage of synmica according to an embodiment of the present disclosure.

[0115] Figure 7 Shows the value of the shape parameter β and the value of t in kV / mm 0.0001 , where P(σ ≤ t0. 0001 ) = 0.0001, that is, t0.0001 indicates the breakdown strength corresponding to the cumulative probability of 0.0001, or more informally, the breakdown strength at 0.01% failure. In Figure 7 , t 0.0001 Is indicated using "life at 0.01% failure".

[0116] For example, for adding 15% of synmica to the UV-curable thermosetting resin, compared with the shape parameter β of pure epoxy resin being only 8.2, the shape parameter β increases to 17.3. This results in a significant improvement in the steepness of the cumulative distribution F σ (t) and a reduction in the scatter around α.

[0117] Figure 7 Also shows that the breakdown strength at 0.01% failure (P(σ ≤ t0.0001) = 0.0001) indicated using "life at 0.01% failure" increases from 13.7 kV / mm in the case of pure epoxy resin to 22.5 kV / mm in the case of adding 15% of synmica.

[0118] Addition indicates that an electrical insulating mixture for forming a layer on a conductor surface, comprising a UV curable thermosetting resin and a filler, where the filler comprises a UV transparent crystal structure including synmica (synthetic fluorophlogopite) according to the present disclosure, is beneficial for improving electrical insulation, for increasing the shape parameter α of the 0.01% failure and / or breakdown strength, while maintaining an elevated maximum sheath speed as Figure 5 shown.

[0119] In some embodiments of the present disclosure, there is provided an electrical insulating mixture for forming a layer on a conductor surface, where the mixture comprises a UV curable thermosetting resin and a filler, where the filler comprises a UV transparent crystal structure made of a crystal structure material, and where UV transparency is given for light in the wavelength range between 300 nm and 420 nm.

[0120] In some embodiments, the UV transparent crystal structure comprises a solid crystal structure having a predominantly crystalline molecular structure with a density greater than 2 g / cm 3 .

[0121] In some embodiments, the crystal structure material of the UV transparent crystal structure comprises synthetic fluorophlogopite flakes.

[0122] In some embodiments, the relationship of the UV transparent crystal structure to the mixture is less than or equal to 25% by weight-%, optionally less than or equal to 20% by weight-% or less than or equal to 15% by weight-%.

[0123] In some embodiments, the crystal structure material has a dielectric strength of at least 180 kV / mm.

[0124] In some embodiments, for a 0.01% failure probability, the mixture has a dielectric strength greater than 17 kV / mm, optionally greater than 22 kV / mm or greater than 22.5 kV / mm.

[0125] Some embodiments of the present disclosure are formed by a method for electrically insulating a metal conductor, the method comprising: obtaining the electrical insulating mixture according to any one of the preceding claims; using the mixture thus obtained to form a sheath on the surface of the metal conductor; exposing the mixture to ultraviolet radiation to cure the mixture, thereby forming an electrical insulating layer on the surface of the metal conductor by the sheath. The thickness of the insulating layer is not particularly limited. For example, the space between two strands can be completely filled by the insulating layer.

[0126] In particular, the crystal structure is transparent to ultraviolet radiation (i.e., at least for the main wavelength of the ultraviolet radiation and / or for at least 80% of the wavelength-dependent intensity of the ultraviolet radiation). Thus, the UV curing of the electrical insulating mixture is improved because the UV transparent crystal structure absorbs less UV light.

[0127] In some embodiments, the metal conductor comprises one or more conductor strands, and an electrical insulation layer is formed on each of the one or more conductor strands, optionally on each of the conductor strands.

[0128] In some embodiments, the electrical insulation layer is formed on each of at least two adjacent conductor strands to simultaneously provide inter-strand insulation and external ground-wall insulation of the metal conductor.

[0129] Some embodiments of the present disclosure are formed of a metal conductor having an electrical insulation layer obtained by curing an electrical insulation mixture.

[0130] In some embodiments, the metal conductor has electrical insulation obtained using the method of the present disclosure.

[0131] The techniques described in the present disclosure can contribute to improving electrical insulation mixtures and methods for electrically insulating metal conductors, as well as metal conductors having an electrical insulation layer. According to the present disclosure, the electrical insulation layer can be obtained by curing a mixture using UV radiation after forming a sheath on the surface of the conductor; sheathing at a sheathing speed that does not decrease with an increase in the percentage of UV-transparent synthetic mica flakes in the filler of the mixture; the UV-transparent synthetic mica flakes in the filler of the mixture allow for rapid sheathing and curing while providing good and improved properties of the electrical insulation layer, such as, for example, an increased shape parameter β and / or an increased breakdown strength, characterized by an increased breakdown strength of, for example, 0.01% failures and / or an increased scale parameter α of the cumulative distribution function F σ (t) of the breakdown strength σ and / or an increased average breakdown strength, for example, the measured average breakdown strength of the insulation layer.

Claims

1. An electrically insulating mixture for forming a layer on the surface of a conductor, wherein the mixture comprises a UV curable thermosetting resin and a filler, wherein the filler comprises a UV transparent crystal structure made of a crystal structure material, and wherein UV transparency is given for light in the wavelength range between 300 nm and 420 nm.

2. The mixture according to claim 1, wherein the UV-transparent crystal structure comprises a solid crystal structure having a predominantly crystalline molecular structure with a density greater than 2 g / cm 3 ³.

3. The mixture according to claim 1 or 2, wherein the crystal structure material of the UV transparent crystal structure comprises a synthetic fluorophlogopite crystal structure.

4. The mixture according to claim 1 or 2, wherein the relationship of the UV transparent crystal structure to the mixture is less than or equal to 25% by weight-%.

5. The mixture according to claim 1 or 2, wherein the relationship of the UV transparent crystal structure to the mixture is less than or equal to 20% by weight-%.

6. The mixture according to claim 1 or 2, wherein the relationship of the UV transparent crystal structure to the mixture is less than or equal to 15% by weight-%.

7. The mixture according to claim 1 or 2, wherein the crystal structure material has a dielectric strength of at least 180 kV / mm.

8. The mixture according to claim 1 or 2, wherein for a failure probability of 0.01%, the mixture has a dielectric strength greater than 17 kV / mm.

9. The mixture according to claim 1 or 2, wherein for a failure probability of 0.01%, the mixture has a dielectric strength greater than 22 kV / mm.

10. The mixture according to claim 1 or 2, wherein for a failure probability of 0.01%, the mixture has a dielectric strength greater than 22.5 kV / mm.

11. The mixture according to claim 1 or 2, wherein in the uncured state, the volume fraction of the crystal structure relative to the thermosetting resin is between 20% and 80%.

12. A method for electrically insulating a metal conductor, the method comprising: obtaining the electrically insulating mixture according to any one of the preceding claims; using the thus obtained mixture to form a sheath on the surface of the metal conductor; exposing the mixture to ultraviolet radiation to cure the mixture, thereby forming an electrically insulating layer on the surface of the metal conductor by the sheath.

13. The method according to claim 12, wherein the metal conductor comprises one or more conductor strands, and wherein the electrically insulating layer is formed on each of one or more of the conductor strands in the conductor strands.

14. The method according to claim 12, wherein the metal conductor comprises one or more conductor strands, and wherein the electrically insulating layer is formed on each of the conductor strands of the conductor strands.

15. The method according to claim 13 or 14, wherein the electrically insulating layer is formed on each of at least two adjacent conductor strands for simultaneously providing inter-strand insulation and outer wall insulation of the metal conductor.

16. The method according to any one of claims 12 to 14, wherein the crystal structure is transparent to the ultraviolet radiation.

17. A metal conductor having an electrically insulating layer, the electrically insulating layer being obtained by curing the electrically insulating mixture according to any one of claims 1 to 11.

18. A metal conductor having electrical insulation, the electrical insulation being obtained by using the method according to any one of claims 12 to 16.

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