Galvanic isolation transformer

Abstract

The invention relates to a galvanic isolation transformer (400) comprising: - a magnetic core (102); and - a primary winding (104A-C) and a secondary winding (106A-C), wound around the magnetic core (102) in order to be magnetically coupled to each other. It further comprises two electrical insulating shields (112, 114, 502, 504) inserted between the primary winding (104A-C) and the secondary winding (106A-C), the two electrical insulating shields (112, 114, 502, 504) being respectively made of two materials, which are such that the first material has a value of a first property that is at least 10% higher, preferably 20% higher, than that of the second material, and which are such that the second material has a value of a second property that is at least 10% higher, preferably 20% higher, than that of the first material, the first and second properties being selected from: a temperature of use range, a dielectric strength, an inverse of the dielectric constant, a volume resistivity, a chemical resistance, mechanical properties, a flame retardancy, a heat capacity, an aging, and a thermal conductivity.

Description

Description TITLE: GALVANIC INSULATION TRANSFORMER Technical field of the invention

[0001] The present invention relates to a galvanic isolation transformer, and an aircraft comprising such a galvanic isolation transformer.

[0002] The present invention finds application particularly in the field of electrical power conversion, and more specifically in aircraft, both for electrical generation in an onboard network and for electric propulsion. Technological background

[0003] Climate change is a major concern for many legislative and regulatory bodies worldwide. Indeed, various restrictions on carbon emissions have been, are being, or will be adopted by different countries. In particular, an ambitious standard applies to both new types of aircraft and those already in operation, requiring the implementation of technological solutions to bring them into compliance with current regulations. Civil aviation has been actively working for several years now to contribute to the fight against climate change.

[0004] Technological research efforts have already led to very significant improvements in the environmental performance of aircraft. The Applicant takes into account the factors impacting all phases of design and development in order to obtain less energy-intensive and more environmentally friendly aeronautical components and products whose integration and use in civil aviation have moderate environmental impacts, with the aim of improving the energy efficiency of aircraft.

[0005] Consequently, the Applicant is constantly working to reduce its climate impact by using methods and operating virtuous development and manufacturing processes that minimize greenhouse gas emissions to the minimum possible in order to reduce the environmental footprint of its activity.

[0006] This sustained research and development work focuses on new generations of aircraft engines, the weight reduction of aircraft, particularly through the materials used and lighter on-board equipment, the development of the use of electrical technologies to provide propulsion, and, as essential complements to technological progress, aviation biofuels.

[0007] Galvanic isolation of electrical networks can be achieved using a low-frequency or high-frequency transformer. The use of galvanically isolated transformers ensures segregation between the two sides of the transformer, generally referred to as the "primary" and "secondary" windings.

[0008] With the concept of the more electric aircraft, new power sources and loads have emerged. Fault propagation between these is not permitted. This requirement to prevent fault propagation necessitates a redesigned sizing and engineering of galvanically isolated transformers.

[0009] As is known in itself, a galvanic isolation transformer comprises a magnetic core (also called a "magnetic body") and at least two windings, for example of copper or aluminum, forming respectively a primary winding and a secondary winding of the galvanic isolation transformer.

[0010] To ensure minimal galvanic isolation, the turns of the primary and secondary windings are electrically isolated from each other using an insulating material.

[0011] Thus, we know from the state of the art a galvanic isolation transformer comprising: - a magnetic core; and - a primary winding and a secondary winding, wound around the magnetic core so as to be magnetically coupled to each other.

[0012] In such a galvanically isolated transformer, the primary and secondary windings are often superimposed or interleaved, so that the primary and secondary windings are always close to each other, which always represents a risk of galvanic isolation failure. Indeed, in the event of a problem with one of the windings, such as a short circuit, the melting of the winding and Insulators can lead to direct electrical contact between the primary and secondary, thus breaking the galvanic isolation.

[0013] This risk also exists when the primary and secondary windings are not overlapped or interleaved. If, for example, the insulation between one winding and the magnetic core melts or degrades, the fault can then propagate and be located next to the other winding, resulting in a potentially high risk of galvanic insulation failure, which is particularly dangerous for the aircraft's electric propulsion or onboard electrical system.

[0014] This problem persists even when the magnetic core is made of ferrite, because this material does not necessarily guarantee adequate insulation against the high voltages required.

[0015] One possible solution to improve galvanic isolation would be to duplicate it, that is, to use two galvanic isolation transformers, one behind the other. However, such a solution would increase the weight and size of the system.

[0016] Furthermore, the patent application published under number US 4,649,640 A describes a transformer with a primary winding, a secondary winding and three insulating layers which can be made respectively of rock wool, pre-impregnated epoxy glass and glass tape pre-coated with a polymerization accelerator.

[0017] To this end, the invention is the result of technological research aimed at significantly improving aircraft performance and, in this sense, contributes to reducing the environmental impact of aircraft. Summary of the invention

[0018] Therefore, a galvanic isolation transformer is proposed comprising: - a magnetic core; - a primary winding and a secondary winding, wound around the magnetic core so as to be magnetically coupled to each other; characterized in that it further comprises two electrically insulating screens interposed between the primary winding and the secondary winding, the two electrically insulating screens being made of two different materials respectively, such that the first material has a first property value at least 10% higher. preferably 20%, than the second material, and such that the second material has a value of a second property that is at least 10%, preferably 20%, higher than the first material, the first and second properties being taken from: range of temperature range of use, dielectric strength, inverse dielectric constant, volume resistance, chemical resistance, mechanical properties, non-flammability, heat capacity, aging, and thermal conductivity.

[0019] The advantage of using different materials lies in their ability to react differently under electrical and / or mechanical stresses. This diversity of reactions helps to limit the propagation of electrical faults.

[0020] In summary, this approach strengthens electrical insulation by multiplying the layers of protection and exploiting the distinct properties of the materials used, which limits the propagation of electrical faults.

[0021] The invention may further include one or more of the following optional features, in any technically feasible combination.

[0022] Optionally, the two electrical insulating screens are sized and arranged so that any line from the primary winding to the secondary winding passes through both electrical insulating screens.

[0023] Optionally, the secondary winding is also wound around the primary winding, and each of the first and second electrical insulating screens is in the form of a cylinder, with the cylinder forming the first electrical insulating screen surrounded by the cylinder forming the second electrical insulating screen.

[0024] Optionally, the secondary winding follows the primary winding along the magnetic core, and each of the electrically insulating screens has a central opening through which the magnetic core passes.

[0025] Optionally, the galvanic isolation transformer also includes an electrical conductor interposed between the primary and secondary windings.

[0026] Optionally, at least one of the two electrically insulating screens is in one of the following: Kapton, Nomex, Mylar, Teflon, and Mica.

[0027] It is also proposed that an aircraft includes a galvanic isolation transformer according to the invention. Brief description of the figures

[0028] The invention will be better understood with the aid of the following description, given solely by way of example and with reference to the accompanying drawings, in which: - Figure 1 is a cross-sectional view of a first galvanic isolation transformer according to the invention, - Figure 2 is a cross-sectional view of a second galvanic isolation transformer according to the invention, - Figure 3 is a cross-sectional view of a third galvanic isolation transformer according to the invention, - Figure 4 is a perspective view of a fourth galvanic isolation transformer according to the invention, and - Figure 5 is a cross-sectional view of the fourth galvanic isolation transformer according to the invention. Detailed description of the invention

[0029] With reference to Figure 1, a first galvanic isolation transformer 100 according to the invention will now be described.

[0030] The galvanic isolation transformer 100 comprises a magnetic core 102, as well as a primary winding 104 and a secondary winding 106. Generally, either of the two windings can be referred to as "primary", the other being referred to as "secondary".

[0031] Each of the primary winding 104 and the secondary winding 106 comprises an electrical cable with a central conductor 108 surrounded by an insulating sheath 110.

[0032] The primary winding 104 and the secondary winding 106 are wound around the magnetic core 102 so as to be magnetically coupled to each other. To enhance the magnetic coupling, the primary winding 104 and the secondary winding 106 are preferably close to each other, for example, separated by a distance less than the breakdown distance in air. For example, this distance between the windings 104 and 106 is less than or equal to 5 millimeters, preferably less than or equal to 1 millimeter.

[0033] For example, as in the example illustrated in Figure 1, the secondary winding 106 is wound around the primary winding 104.

[0034] The galvanic isolation transformer 100 further comprises first and second electrical insulating screens 112, 114, having, for example, an electrical resistance greater than 10 8Ω·m, interposed between the primary winding 104 and the secondary winding 106. For example, the electrical insulating screens are dimensioned and arranged so that any straight line segment from the primary winding 104 to the secondary winding 106 passes successively through the first and second electrical insulating screens 112, 114. For example, as in the example illustrated in Figure 1, the first and second electrical insulating screens 112, 114 are placed side by side.

[0035] For example, as illustrated in Figure 1, each of the first and second electrical insulating screens 112, 114 is cylindrical, with the cylinder forming the first electrical insulating screen 112 surrounded by the cylinder forming the second electrical insulating screen 114. The cylinders forming the first and second electrical insulating screens 112, 114 are thus, for example, coaxial. These cylinders can generally have a round or rectangular cross-section, depending on the shape of the first and second windings 104, 106.

[0036] The first and second electrical screens 112, 114 are made of first and second materials respectively, which are different from each other. These two materials are chosen such that the first material has a value of a first property that is at least 10%, preferably 20%, higher than the second material, and such that the second material has a value of a second property that is at least 10%, preferably 20%, higher than the first material.

[0037] Put another way, by noting P1 and P2 the values ​​of the first and second properties, we obtain: P1material1 > 1.1 x P1material2 and P2material2 > 1.1 x P2material1.

[0038] The first and second properties are chosen from: - a range of operating temperature, - a dielectric strength, for example measured according to ASTM D149 (Standard Method for the Measurement of Dielectric Strength and Dielectric Breaking Strength of Solid Electrical Insulating Materials), - an inverse of the dielectric constant, the dielectric constant being measured, for example, according to ASTM D150 (Standard Method for the dielectric properties of solid insulating materials at alternating frequencies), - volume resistance, for example measured according to ASTM D257 and IEC 60993 (Standard method for resistance and resistivity of electrical insulating materials), - chemical resistance, for example measured according to ASTM D543 (Standard method for chemical resistance of plastics), - mechanical properties, for example measured according to ASTM D882 (Standard method for tensile properties of thin plastic films), - non-flammability, for example measured according to UL 94 (Standard for testing the flammability of plastic materials for parts in electronic devices and applications), - thermal capacity, for example measured according to ASTM E1269 (Standard method for determining specific heat capacity by differential scanning calorimetry), - aging,for example, measured according to the ASTM D3045 method (Standard method for measuring resistance to thermal aging of plastic materials), and - a thermal conductivity.

[0039] These properties are evaluated for example for a thickness of 50 µm at 23°C (73°F) and 50% relative humidity. The thickness is measured for example according to the ASTM D374 method (Standard method for determining the thickness of materials).

[0040] Mechanical, chemical resistance, and aging properties are sometimes expressed qualitatively (very good, excellent, etc.). In this case, they are quantified (resistance in pascals, aging in time, etc.) to be compared from one material to another.

[0041] For example, each of the first and second electrical screens 112, 114 is made of one of the following: a polyimide film (e.g., Kapton (registered trademark)), a polyethylene terephthalate film (e.g., Mylar (registered trademark)). These materials exhibit, for example, the following properties for a thickness of 50 µm at 23°C and 50% relative humidity: Property Kapton Mylar Nomex Teflon Mica Polypropylene Type Polyimide Polyethylene Paper Polytetrafluoroethylene Phyllosilicate Polypropylene Material Terephthalate Aramid Polyethylene Mineral (PP) (PET) (PTFE) Operating Temperature -269°C to -70°C to -196°C to -200°C to -100°C to -20°C to 400°C 150°C 300°C 260°C 500°C 100°C Dielectric Strength 200 kV / mm 150 kV / mm 20 kV / mm 60 kV / mm 120 kV / mm 30 kV / mm Dielectric Constant 3.5 3.1 1.6 2.1 5.4 2.2 Dielectric Resistance 10^17 10^15 10^14 10^18 10^12 10^16 volumetric ohm·cm ohm·cm ohm·cm ohm·cm ohm·cm ohm·cm Resistance Excellent Good Good Excellent Excellent Good chemical resistance resistance resistance resistance resistance to resistance resistance to products to products to oils, almost all chemical, to chemicals, chemicals, hydrocarbon products except chemical acids, solvents, limited against s, chemical solvents hydrofluoric less good oils, bases weak solvents;against acids and strong acids limited against solvents and strong acids strong acids and strong alkalis Properties High Good Good Low Good Good mechanical resistance resistance resistance resistance resistance resistance resistance resistance resistance resistance resistance Inflammabili Inflammabili Flammable Self-extinguishing Inflammable Inflammable Flammable Self-extinguishing Capacity 1.09 J / g·K 1.30 J / g·K 1.38 J / g·K 1.00 J / g·K 0.88 J / g·K 1.80 J / g·K thermal Aging Excellent Good Very good Excellent Excellent Resistance to moderate aging resistance to thermal aging and degradation, and possible environmental degradation to UV;

[0042] Thus, by taking the first screen in Kapton and the second screen in Mylar, it is possible to obtain both good thermal conductivity thanks to the Mylar (1.155 > 1.2 x 1.120) and a good temperature range thanks to the Kapton (852 > 1.2 x 394).

[0043] With reference to Figure 2, a second galvanic isolation transformer 200 according to the invention will now be described.

[0044] The second galvanic isolation transformer 200 is identical to the first galvanic isolation transformer 100, except for one conductor, having for example a conductivity greater than 10 4S / m is interposed between the first and second electrically insulating screens 112 and 114. Conductor 202 thus forms an electrostatic screen, enhancing galvanic isolation. Preferably, conductor 202 is connected to an electrical ground to prevent direct arcing between the primary winding 112 and the secondary winding 114.

[0045] The conductor 202 for example is dimensioned and arranged so that any straight segment going from the primary winding 104 and arriving at the secondary winding 106 passes successively through the first electrical insulating screen 112, then the conductor 202, then the second electrical insulating screen 114.

[0046] For example, as in the example illustrated in Figure 2, the conductor 202 is in the form of a cylinder, surrounding the cylinder forming the first electrical insulating screen 112 and surrounded by the cylinder forming the second electrical insulating screen 114.

[0047] With reference to Figure 3, a third galvanic isolation transformer 300 according to the invention will now be described.

[0048] The third galvanic isolation transformer 300 is identical to the second galvanic isolation transformer 200, except that the second winding 106 follows the first winding 104 along the magnetic core 102, so that the first and second windings 104 and 106 are side by side. Furthermore, the first and second electrical insulating screens 112 and 114 are located between the first and second windings 104 and 106 along the magnetic core 102. For example, as in the illustration in Figure 3, each of the electrical insulating screens 112 and 114 has a central opening 302 through which the magnetic core 102 passes.

[0049] With reference to Figure 4 and Figure 5, a fourth galvanic isolation transformer 400 according to the invention will now be described.

[0050] In this fourth galvanic isolation transformer 400, the core 102 has several legs, specifically three in the illustrated example, labeled 102A, 102B, and 102C. The fourth galvanic isolation transformer 400 comprises then, around each leg 102A-C, a primary winding 104A-C and a secondary winding 106A-C wound around each other as in figure 1.

[0051] As illustrated more precisely in Figure 5, the fourth galvanic isolation transformer 400 comprises, for each pair of first and second windings 104A-C, 106A-C, the electrostatic screen 202 and the first and second electrical insulating screens 112, 114 as shown in Figure 2. Furthermore, the fourth galvanic isolation transformer 400 comprises, for each pair of first and second windings 104A-C, 106A-C, third and fourth electrical insulating screens 502, 504 on either side of the first and second electrical insulators 112, 114. Of these four electrical insulators, at least two are made of different materials. For example, the electrostatic screens are generally manufactured directly covered with the electrical insulators 112, 114 of the same material. Thus, the third and fourth electrical insulating screens 502, 504 can for example be made of the same material, but different from that of the electrical insulators 112, 114.

[0052] In conclusion, it is clear that a galvanic isolation transformer such as those described above makes it possible to strengthen galvanic isolation, in particular by making it more robust to mechanical and / or voltage and / or temperature stresses.

[0053] It should also be noted that the invention is not limited to the embodiments described above. Indeed, it will be apparent to those skilled in the art that various modifications can be made to the embodiments described above, in light of the information just disclosed to them.

[0054] In particular, the invention is not limited to a particular number of insulators made of different materials.

[0055] Furthermore, it will be appreciated that the invention can be applied to different types of transformers: conventional single-phase, three-phase, or polyphase, or planar, as well as to different types of windings (strip, copper flat, Litz, etc.). In addition, a galvanic isolation transformer according to the invention can be used at both low and high frequencies.

[0056] In the detailed presentation of the invention given above, the terms used should not be interpreted as limiting the invention to the embodiments set forth in this description, but should be interpreted to include all equivalents whose prediction is within the reach of the person skilled in the art by applying their general knowledge to the implementation of the teaching that has just been disclosed to them.

Claims

Claims [1] Galvanic isolation transformer (100; 200; 300; 400) comprising: - a magnetic core (102); and - a primary winding (104; 104A-C) and a secondary winding (106; 106A-C), wound around the magnetic core (102) so as to be magnetically coupled to each other; characterized in that it further comprises two electrical insulating screens (112, 114, 502, 504) interposed between the primary winding (104; 104A-C) and the secondary winding (106;106A-C), the two electrical insulating screens (112, 114, 502, 504) being respectively in two materials, such that the first material has a value of a first property higher by at least 10%, preferably 20%, than the second material, and such that the second material has a value of a second property higher by at least 10%, preferably 20%, than the first material, the first and second properties being taken from: operating temperature range, dielectric strength, inverse dielectric constant, volume resistance, chemical resistance, mechanical properties, non-flammability, heat capacity, aging, and thermal conductivity. [2] Galvanic isolation transformer (100; 200; 300; 400) according to claim 1, wherein the two electrical insulating screens (112, 114, 502, 504) are dimensioned and arranged so that any line from the primary winding (104;104A-C) and arriving at the secondary winding (106; 106A-C) passes through the two electrical insulating screens (112, 114, 502, 504). [3] Galvanic isolation transformer (100; 200; 400) according to claim 1 or 2, in which the secondary winding (106) is wound around the primary winding (104), and in which each of the first and second electrical insulating screens (112, 114, 502, 504) is in the form of a cylinder, with the cylinder forming the first electrical insulating screen (112, 114, 502, 504) surrounded by the cylinder forming the second electrical insulating screen (112, 114, 502, 504). [4] Galvanic isolation transformer (300) according to claim 1 or 2, wherein the secondary winding (106) follows the primary winding (104) along the magnetic core (102), and wherein each of the electrical insulating screens (112, 114); has a central opening (302) through which the magnetic core (102) passes. [5] Galvanic isolation transformer (200; 400) according to any one of claims 1 to 4, further comprising an electrical conductor (202) interposed between the primary winding (104; 104A-C) and the secondary winding (106; 106A-C). [6] Galvanic isolation transformer (100; 200; 300; 400) according to any one of claims 1 to 5, wherein at least one of the two electrical insulating screens (112, 114, 502, 504) is made of one of: Kapton, Nomex, Mylar, Teflon, and Mica. [7] Aircraft includes a galvanic isolation transformer (100; 200; 300; 400) according to any one of claims 1 to 6.

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