Power transmission device and power transmission system

Abstract

This power transmission device comprises: a first conductor to which a positive voltage of DC power is applied; a second conductor to which a negative voltage of DC power is applied; a second spacer and a first spacer of an insulator separating the first and second conductors; and a conduit, wherein the first spacer has first and second surfaces, the first surface facing the first conductor and having a plurality of first raised portions and a plurality of first recessed portions, the second surface facing the second conductor and having a plurality of second raised portions and a plurality of second recessed portions, each first recessed portion is disposed so as to include a respective position where a respective line penetrates the first surface, said line connecting by a minimum distance a respective point of contact between the second conductor and a respective second raised portion with the first conductor, and each second recessed portion is disposed so as to include a respective position where a respective line penetrates the second surface, said line connecting by a minimum distance a respective point of contact between the first conductor and a respective first raised portion with the second conductor.

Description

Power transmission device and power transmission system

[0001] This application claims priority to Japanese Patent Application No. 2023-222687, filed on December 28, 2023, the contents of which are incorporated herein by reference.

[0002] Patent Documents 1 and 2 show examples of the configuration of a cable for power transmission. The cables described in Patent Documents 1 and 2 include a conductor defining a hollow interior, a casing surrounding the conductor, an electrical insulator disposed between the conductor and the casing, and a fluid disposed within the hollow interior of the conductor. In this configuration, the electrical insulator disposed between the conductor and the casing is a pressurized fluid, a solid, or the like.

[0003] US Patent Application Publication No. 2023 / 0046156 US Patent Application Publication No. 2023 / 0048950

[0004] However, in the cables described in Patent Documents 1 and 2, when the electrical insulator is a pressurized fluid, there is a problem in that if the pressurized state cannot be maintained under high altitude conditions, for example, due to leakage from the casing, there is a risk of insulation breakdown.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a power transfer device and a power transfer system that can suppress the occurrence of dielectric breakdown.

[0006] In order to solve the above problem, a power transmission device according to the present disclosure includes: a first conductor to which a positive voltage of DC power is applied; a second conductor to which a negative voltage of the DC power is applied; a first spacer made of an insulator that separates the first conductor and the second conductor; a second spacer made of an insulator that has a hollow portion and that encloses the first conductor, the second conductor, and the first spacer in the hollow portion; and a conduit for a conductor that encloses the second spacer, wherein the first spacer has a first surface facing the first conductor and a second surface facing the second conductor. and a second surface facing the second conductor, the first surface having a plurality of first convex portions and a plurality of first concave portions, the second surface having a plurality of second convex portions and a plurality of second concave portions, each of the first concave portions being arranged so as to include each position where each line connecting the first conductor and each contact point between the second conductor and each of the second convex portions over the shortest distance passes through the first surface, and each of the second concave portions being arranged so as to include each position where each line connecting the second conductor and each contact point between the first conductor and each of the first convex portions over the shortest distance passes through the second surface.

[0007] The power transmission system according to the present disclosure includes one or more of the above-described power transmission devices, an AC / DC power conversion device housed in a first housing that receives AC power, converts it into DC power, and outputs it to the power transmission device, an AC / DC power conversion device housed in a second housing that receives DC power from the power transmission device, converts it into AC power, and outputs it, a pressurizing unit that introduces pressurized fluid into one or more of the power transmission devices, the first housing, and the second housing, and an exhaust unit that exhausts the pressurized fluid from one or more of the power transmission devices, the first housing, and the second housing.

[0008] According to the power transfer device and power transfer system of the present disclosure, it is possible to suppress the occurrence of dielectric breakdown.

[0009] 1 is a cross-sectional view of a power transmission device according to a first embodiment of the present disclosure. FIG. 2 is a perspective view of a power transmission device according to a first embodiment of the present disclosure. FIG. 3 is a perspective view of a conductor and a spacer according to a first embodiment of the present disclosure. FIG. 4 is a perspective view of a spacer according to a first embodiment of the present disclosure. FIG. 5 is a perspective view of a conduit according to a first embodiment of the present disclosure. FIG. 6 is a cross-sectional view of a power transmission device according to a first embodiment of the present disclosure. FIG. 7 is a perspective view of another example of a spacer according to a first embodiment of the present disclosure. FIG. 8 is a partially enlarged cross-sectional view of a spacer and a conductor according to a first embodiment of the present disclosure. FIG. 9 is a diagram showing an example of a relationship between a gap length between a conductor and a spacer according to a first embodiment of the present disclosure and a gap field conductor. FIG. 10 is a diagram showing an example of a creepage distance between conductors according to a first embodiment of the present disclosure. FIG. 11 is a diagram showing an example of a creepage distance between conductors according to a first embodiment of the present disclosure. FIG. 12 is a diagram showing an example of specifications of a power transmission device according to a second embodiment of the present disclosure. FIG. 13 is a schematic diagram showing an example of a configuration of a power transmission system according to a third embodiment of the present disclosure. FIG. 14 is a schematic diagram showing an example of a configuration of a power transmission system according to a third embodiment of the present disclosure. FIG. 15 is a schematic diagram showing an example of a configuration of a power transmission system according to a third embodiment of the present disclosure. FIG. 16 is a schematic diagram showing an example of a configuration of a power transmission system according to a fourth embodiment of the present disclosure. FIG. 17 is a schematic diagram showing an example of a configuration of a power transmission system according to a fourth embodiment of the present disclosure.

[0010] First Embodiment A power transmission device according to a first embodiment of the present disclosure will be described with reference to FIGS. 1 to 11 . FIG. 1 is a cross-sectional view of the power transmission device according to the first embodiment of the present disclosure. FIG. 2 is a perspective view of the power transmission device according to the first embodiment of the present disclosure. FIG. 3 is a perspective view of a conductor and a spacer according to the first embodiment of the present disclosure. FIG. 4 is a perspective view of a spacer according to the first embodiment of the present disclosure. FIG. 5 is a perspective view of a conduit according to the first embodiment of the present disclosure. Note that the same or corresponding components in each drawing are denoted by the same reference numerals, and descriptions thereof will be omitted as appropriate. Furthermore, the terms "first," "second," "third," and "fourth" used in this specification are used interchangeably to distinguish one component from another.

[0011] 1 to 5 , a power transfer device 1 according to a first embodiment of the present disclosure includes a first conductor 11, a second conductor 12, a first spacer 13, a second spacer 14, and a conduit 15. The power transfer device 1 is a device for transferring DC power.

[0012] The first conductor 11 and the second conductor 12 are electric wires that constitute the main line of the DC power circuit, and a positive voltage (positive pole) of the DC power is applied to the first conductor 11, and a negative voltage (negative pole) of the DC power is applied to the second conductor 12. In this embodiment, the conductor is a material with a relatively high electrical conductivity, and can be made of, for example, copper, aluminum, or other metals.

[0013] The first spacer 13 is an insulator that separates the first conductor 11 and the second conductor 12. In this embodiment, an insulator is an object through which electric current hardly flows. The second spacer 14 is an insulator having a hollow portion 141 and enclosing the first conductor 11, the second conductor 12, and the first spacer 13 in the hollow portion 141. The second spacer 14 separates the first conductor 11 and the second conductor 12 from the electrical conduit 15. The electrical conduit 15 is a conductor that encloses the second spacer 14. The electrical conduit 15 is formed of a metal such as aluminum. The electrical conduit 15 can also be referred to as a metal conduit. A fluid 16, such as air at atmospheric pressure, a pressurized gas, or a pressurized fluid such as liquid, is introduced into the electrical conduit 15. The fluid 16 forms an insulating layer and also functions as a cooling medium for air- or water-cooling the first conductor 11, the second conductor 12, etc. Also, the conduit 15 may be grounded, for example.

[0014] The first conductor 11 and the second conductor 12 and the first spacer 13, the first conductor 11 and the second conductor 12 and the second spacer 14, and the second spacer 14 and the conduit 15 are assembled in contact with each other or with a certain gap between them, and are not fixed to each other. However, each component may be fixed as appropriate. For example, the contact state or gap between the first conductor 11 and the second conductor 12 and the first spacer 13, between the first conductor 11 and the second conductor 12 and the second spacer 14, and between the second spacer 14 and the conduit 15 changes depending on, for example, temperature conditions and the magnitude of the repulsive force acting between the first conductor 11 and the second conductor 12 due to electromagnetic force.

[0015] The first spacer 13 has a first surface 131 facing the first conductor 11 and a second surface 132 facing the second conductor 12, the first surface 131 having a plurality of first convex portions 133 and a plurality of first concave portions 134, and the second surface 132 having a plurality of second convex portions 135 and a plurality of second concave portions 136. As shown in Fig. 6, each first concave portion 134 is arranged so as to include each position PA where each line LA connecting, over the shortest distance, each contact point 137 between the second conductor 12 and each second convex portion 135 and the first conductor 11 passes through the first surface 131. Furthermore, each second concave portion 136 is arranged so as to include each position PB where each line LB connecting, over the shortest distance, each contact point 138 between the first conductor 11 and each first convex portion 133 and the second conductor 12 passes through the second surface 132.

[0016] With this configuration, an insulating material layer made of first spacer 13 and a fluid layer such as an air layer made of fluid 16 such as air are always arranged in series between the portions of first conductor 11 and second conductor 12 where a potential difference occurs. Therefore, with this configuration, even if a dielectric breakdown occurs in the fluid layer, the dielectric breakdown can be prevented by the insulating material layer, and therefore, the occurrence of a dielectric breakdown between first conductor 11 and second conductor 12 can be suppressed.

[0017] 4 and 6, the second spacer 14 has a third surface 142 facing the conduit 15. The third surface 142 has a plurality of third recesses 143. As shown in FIG. 6, the third recesses 143 are arranged so as to encompass positions PC at which lines LC passing through the third surface 142 connect, over the shortest distance, contact points 145 between the fourth surface 144 of the second spacer 14 forming the hollow portion 141 and the first conductor 11 or the second conductor 12 and the conduit 15.

[0018] With this configuration, an insulating material layer made of second spacer 14 and a fluid layer such as an air layer made of fluid 16 such as air are always arranged in series between first conductor 11 and second conductor 12 and the portion of conduit 15 where a potential difference occurs. Therefore, with this configuration, even if a dielectric breakdown occurs in the fluid layer, the dielectric breakdown can be prevented by the insulating material layer, and therefore, the occurrence of a dielectric breakdown between first conductor 11 and second conductor 12 and conduit 15 can be suppressed.

[0019] 1 , the first conductor 11 and the second conductor 12 each include a first plate-shaped portion B1 that faces the first spacer 13 and extends in the direction of DC power transmission, and one or more second plate-shaped portions B2 that extend from the first plate-shaped portion B1 as a base end B11 toward the fourth surface 144. The one or more second plate-shaped portions B2 each include a plate-shaped portion B21 that extends perpendicularly from the plate surface B12 of the first plate-shaped portion B1. This configuration achieves a good balance between improved cooling efficiency (increased surface area, reduced resistance, etc.) and weight reduction.

[0020] The shapes of the first spacer 13 and the second spacer 14 are not limited to those described above, and the first convex portion 133, the first concave portion 134, the second convex portion 135, and the second concave portion 136 may be discontinuous in the direction of transmission of DC power, as in the first spacer 13a shown in Fig. 7. Fig. 7 is a perspective view of another example (first spacer 13a) of the first spacer 13 according to the first embodiment of the present disclosure.

[0021] Next, examples of setting the shape of each part will be described with reference to FIGS. 8 to 11 . FIG. 8 is a partially enlarged cross-sectional view of a spacer and a conductor according to the first embodiment of the present disclosure. FIG. 9 is a diagram showing an example of the relationship (logarithmic scale) between the gap length g and the gap electric field Eg between the conductor and the spacer according to the first embodiment of the present disclosure. FIGS. 10 and 11 are diagrams showing examples of the creepage distance between the conductors according to the first embodiment of the present disclosure. FIG. 8 shows a partially enlarged view of the contact portion between the first conductor 11 and the second spacer 14. The first conductor 11 and the second conductor 12 have a curved shape at the portion CP that contacts the fourth surface 144. The curved shape of the portion CP was determined by performing a simulation using the finite element method or the like to determine the relationship between the gap length g and the gap electric field Eg shown in FIG. 9 and to avoid the discharge region. Furthermore, as shown in Figures 10 and 11, the shapes of the first conductor 11, the second conductor 12, and the first spacer 13 are set so that the necessary creepage distances can be secured for the creepage distance CP1 of the first spacer 13 between the first conductor 11 and the second conductor 12, and the creepage distance CP2 of the second spacer 14 between the first conductor 11 and the second conductor 12.

[0022] As described above, according to this embodiment, the occurrence of dielectric breakdown can be suppressed by arranging a fluid layer such as an air layer and an insulating material layer in series between the first conductor 11 and the second conductor 12 where a potential difference occurs, and between the first conductor 11 and the second conductor 12 and the conduit 15. Furthermore, the shapes of the conductor and insulating material are adopted such that the creepage distance of the insulating material, where a high voltage occurs, is equal to or greater than the insulation distance, thereby improving the resistance to insulation.

[0023] In addition, in this embodiment, since the round-trip current path is placed inside a metal tube, it is easier to reduce weight compared to when the outgoing and return paths are configured using separate cables. Furthermore, since the positive and negative conductors face each other, Coulomb force can be increased to suppress radiation, thereby reducing electromagnetic radiation.

[0024] Second Embodiment Next, as a second embodiment, material selection according to a concept will be described. In this embodiment, a highly heat-resistant material is selected for the insulating material in contact with the transmission line (conductor), significantly improving the cooling margin. Furthermore, materials can be selected according to the concept, while satisfying the conditions for electric field, cooling, and strength. For example, multiple specifications are available, allowing for aluminum as the conductor material if weight is a priority, and copper if transmission efficiency is a priority. FIG. 12 shows an example of material specification settings. Using a highly heat-resistant material such as fluororesin for the insulating material raises the upper limit of the heat generation temperature of the transmission line, thereby enabling the cooling flow rate (flow velocity) to be reduced, resulting in a realistic solution. Furthermore, we confirmed that selecting copper or aluminum as the material for the transmission line can be reflected in designs that prioritize weight (lightweight: aluminum) or efficiency (low loss: copper).

[0025] Third Embodiment Next, a third embodiment will be described with reference to FIGS. 13 to 15 , in which the power transfer device 1 of the first embodiment is applied to an aircraft. FIGS. 13 to 15 are schematic diagrams illustrating a configuration example of a power transfer system according to a third embodiment of the present disclosure. The aircraft 20 shown in FIG. 13 is an electric aircraft in which electric power generated by a generator 22 driven by an aircraft engine 21 is transmitted as DC power via a transmission line 102 to drive a boundary layer ingestion (BLI) fan 23 provided at the rear. The transmission line 102 is configured using a plurality of power transfer devices 1 of the first embodiment. However, the transmission line 102 may be configured using a single power transfer device 1. The power transmission system 100 includes a generator 22, a converter (AC / DC power conversion device) 101 that receives AC power generated by the generator 22, converts it into DC power, and outputs it to the power transmission device 1, a transmission path 102, and an inverter (AC / DC power conversion device) 103 that receives DC power from the power transmission device 1, converts it into AC power, and outputs it.

[0026] 14, the power transmission system 100 includes a transmission path 102 (one or more power transmission devices 1), a converter 101 housed in a first housing 104-1, an inverter 103 housed in a second housing 104-2, a pressurizing unit 105 such as a pump that introduces pressurized fluid such as air into the transmission path 102, the first housing 104-1, and the second housing 104-2, and an exhaust unit 106 that exhausts the pressurized fluid from the transmission path 102, the first housing 104-1, and the second housing 104-2 while maintaining the pressurized state. The conduit 15 of the power transmission device 1 is electrically connected to the first housing 104-1 and the second housing 104-2 by a connection unit 111, and the power transmission device 1, the first housing 104-1, and the second housing 104-2 are sealed so as to integrally form a pressurized space.

[0027] FIG. 15 shows another example configuration of the power transfer system 100 shown in FIG. 13 as a power transfer system 100B. In the power transfer system 100B shown in FIG. 15, the transmission path 102 (power transfer device 1), the first housing 104-1, and the second housing 104-2 each form a pressurized space. The conduit 15 of the power transfer device 1 has flanges 112-1 and 112-2 at both ends, and the conduit 15 and the flanges 112-1 and 112-2 form an enclosed space. In this case, the pressurizing unit 105 includes a pressurizing unit 105-1 that introduces pressurized fluid into the power transfer device 1, a pressurizing unit 105-2 that introduces pressurized fluid into the first housing 104-1, and a pressurizing unit 105-3 that introduces pressurized fluid into the second housing 104-2. The exhaust unit 106 includes an exhaust unit 106-1 that exhausts the pressurized fluid from the power transfer device 1, an exhaust unit 106-2 that exhausts the pressurized fluid from the first housing 104-1, and an exhaust unit 106-3 that exhausts the pressurized fluid from the second housing 104-2. The power transmission paths between the power transfer device 1 and the first and second housings 104-1 and 104-2 pass through the non-preload area, and therefore transmit power using, for example, a thick, insulated wire CW.

[0028] According to this embodiment, the breakdown voltage of a fluid layer such as air can be increased by applying pressure, so that the occurrence of dielectric breakdown in the transmission line 102, converter 101, and inverter 103 can be suppressed.

[0029] Fourth Embodiment Next, a fourth embodiment will be described with reference to FIGS. 16 and 17 . In this embodiment, a low-resistance electrical conduit 15 (metal conduit) functions as a current return path (power transmission return line). In power transmission systems 100C and 100D shown in FIGS. 16 and 17 , the electrical conduit 15 serves as an electrical connection that also serves as a current return path in the airframe structure, significantly reducing the number of current return paths. According to this embodiment, for example, lightning current can be passed by connecting both ends of the electrical conduit 15 to the airframe, which has the effect of significantly reducing the number of copper wire current return paths required in the airframe structure. For example, if the metal conduit resistance of the electric conduit 15 (Φ120 mm, thickness 2.5 mm, aluminum) is about 3 uΩ / m, and even if a total lightning current of 200 kA flows through a 10 m metal conduit, the voltage generated at both ends will be about 6 V (3E-6 x 200E3), and the impact on the system is tolerable. Note that the power transmission system 100C shown in FIG. 16 is a case of a monopole conductor return type power transmission system, and the power transmission system 100D shown in FIG. 17 is a case of a bipolar neutral conductor type power transmission system.

[0030] (Other Embodiments) Although the embodiments of the present disclosure have been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and design modifications and the like are also included within the scope of the gist of the present disclosure. For example, the shapes of the first conductors 11 and the second conductors 12 are not limited to those described above. For example, the number of second plate-shaped portions B2 is not limited to three, and may be two or less, or four or more. Furthermore, the second plate-shaped portions B2 may have a shape that extends radially from the first plate-shaped portion B1, for example.

[0031] <Additional Notes> The power transfer device 1 and the power transfer system 100 described in each embodiment can be understood, for example, as follows.

[0032] (1) A power transmission device 1 according to a first aspect includes: a first conductor 11 to which a positive voltage of DC power is applied; a second conductor 12 to which a negative voltage of the DC power is applied; a first spacer 13 made of an insulator that separates the first conductor 11 and the second conductor 12; a second spacer 14 made of an insulator that has a hollow portion 141 and encloses the first conductor 11, the second conductor 12, and the first spacer 13 in the hollow portion 141; and a conduit 15 made of a conductor that encloses the second spacer 14. The first spacer 13 has a first surface 131 facing the first conductor 11 and a second surface 132 facing the second conductor 12. The first surface 131 has a plurality of first convex portions 133 and a plurality of first concave portions 134, the second surface 132 has a plurality of second convex portions 135 and a plurality of second concave portions 136, each of the first concave portions 134 is arranged so as to include a position PA at which each line LA connecting, over the shortest distance, each contact point 137 between the second conductor 12 and each of the second convex portions 135 and the first conductor 11 passes through the first surface 131, and each of the second concave portions 136 is arranged so as to include a position PB at which each line LB connecting, over the shortest distance, each contact point 138 between the first conductor 11 and each of the first convex portions 133 and the second conductor 12 passes through the second surface 132. According to this aspect and the following aspects, it is possible to suppress the occurrence of dielectric breakdown.

[0033] (2) The power transmission device 1 according to the second aspect is the power transmission device 1 of (1), wherein the second spacer 14 has a third surface 142 facing the conduit 15, the third surface 142 having a plurality of third recesses 143, and each of the third recesses 143 is arranged so as to encompass each position PC at which each line LC connecting the fourth surface 144 of the second spacer forming the hollow portion 141 with each contact point 145 between the first conductor 11 or the second conductor 12 and the conduit 15 in the shortest distance passes through the third surface 142.

[0034] (3) The power transmission device 1 according to the third aspect is the power transmission device 1 of (1) or (2), wherein the first conductor 11 and the second conductor 12 have a first plate-shaped portion B1 facing the first spacer 13 and extending in the direction of transmission of DC power, and one or more second plate-shaped portions B2 extending in the direction of the fourth surface 144 with the first plate-shaped portion B1 as a base end B11.

[0035] (4) The power transmission device 1 according to the fourth aspect is the power transmission device 1 of (3), wherein one or more of the second plate-shaped portions B2 include a plate-shaped portion B21 extending vertically from the plate surface B12 of the first plate-shaped portion B1.

[0036] (5) The power transmission device 1 according to the fifth aspect is the power transmission device 1 of (2) to (4), in which the first conductor 11 and the second conductor 12 have a curved shape (part CP) at the portion in contact with the fourth surface 144.

[0037] (6) A sixth aspect of the power transmission device 1 is the power transmission device 1 according to any one of (1) to (5), in which a pressurized fluid is introduced into the conduit 15.

[0038] (7) The power transmission device 1 according to the seventh aspect is the power transmission device 1 of (1) to (6), which is mounted on an aircraft and the conduit 15 is connected to a return line for power transmission.

[0039] (8) A power transmission system 100 (100A and 100B) according to an eighth aspect includes one or more power transmission devices 1 of (1) to (7), an AC / DC power conversion device (converter 101) housed in a first housing 104-1 that receives AC power, converts it into DC power, and outputs it to the power transmission device, an AC / DC power conversion device (inverter 103) housed in a second housing 104-2 that receives DC power from the power transmission device, converts it into AC power, and outputs it, a pressurizing unit that introduces pressurized fluid into one or more of the power transmission devices, the first housing, and the second housing, and an exhaust unit that exhausts the pressurized fluid from one or more of the power transmission devices, the first housing, and the second housing.

[0040] (9) A power transmission system 100A according to a ninth aspect is the power transmission system 100A of (8), in which one or more of the power transmission devices, the first housing, and the second housing integrally form a pressurized space.

[0041] According to the power transfer device and power transfer system of the present disclosure, it is possible to suppress the occurrence of dielectric breakdown.

[0042] REFERENCE SIGNS LIST 1... Power transmission device 100... Power transmission system 11... First conductor 12... Second conductor 13... First spacer 14... Second spacer 15... Electrical conduit 16... Fluid

Claims

1. A power transmission device, comprising: a first conductor to which a positive voltage of direct current power is applied; a second conductor to which a negative voltage of the direct current power is applied; a first spacer of an insulator that separates the first conductor and the second conductor; a second spacer of an insulator that has a hollow portion and encloses the first conductor, the second conductor, and the first spacer in the hollow portion; and an electric wire tube of a conductor that encloses the second spacer, wherein the first spacer has a first surface facing the first conductor and a second surface facing the second conductor, the first surface has a plurality of first convex portions and a plurality of first concave portions, the second surface has a plurality of second convex portions and a plurality of second concave portions, each of the first concave portions is arranged to include positions where lines connecting each contact point between the second conductor and each of the second convex portions and the first conductor penetrate the first surface at the shortest distance, and each of the second concave portions is arranged to include positions where lines connecting each contact point between the first conductor and each of the first convex portions and the second conductor penetrate the second surface at the shortest distance.

2. The power transmission device according to claim 1, wherein the second spacer has a third surface facing the electric wire tube, the third surface has a plurality of third concave portions, and each of the third concave portions is arranged to include positions where lines connecting each contact point between the fourth surface of the second spacer forming the hollow portion and the first conductor or the second conductor and the electric wire tube penetrate the third surface at the shortest distance.

3. The power transmission device according to claim 2, wherein the first conductor and the second conductor include a first plate-shaped portion that faces the first spacer and extends in the power transmission direction of the direct current power, and one or more second plate-shaped portions that extend in the direction of the fourth surface with the first plate-shaped portion as a base end portion.

4. The power transmission device according to claim 3, wherein one or more of the second plate-shaped portions include a plate-shaped portion that extends in a direction perpendicular to the plate surface of the first plate-shaped portion.

5. The power transmission device according to claim 4, wherein the first conductor and the second conductor have a curved surface shape at a portion in contact with the fourth surface.

6. The power transmission device according to claim 5, wherein a pressurized fluid is introduced into the electric wire tube.

7. The power transmission device according to any one of claims 1 to 6, which is mounted on an aircraft and the electric wire tube is connected to a return wire for power transmission.

8. The power transmission device according to one or more of claims 1, a AC-DC power conversion device housed in the first housing, which inputs AC power, converts it into DC power, and outputs the DC power to the power transmission device, a DC-AC power conversion device housed in the second housing, which inputs DC power from the power transmission device, converts it into AC power, and outputs the AC power, a pressurizing unit that introduces pressurized fluid into one or more of the power transmission devices, the first housing, and the second housing, and an exhaust unit that exhausts pressurized fluid from one or more of the power transmission devices, the first housing, and the second housing. A power transmission system comprising these components.

9. The power transmission system according to claim 8, wherein one or more of the power transmission devices, the first housing, and the second housing integrally form a pressurized space.

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