Power transmission system, partial discharge detection method, and power transmission device

Abstract

This power transmission system comprises: a power transmission device including a first conductor to which a positive voltage of direct current power is applied, a second conductor to which a negative voltage of direct current power is applied, and an insulating first spacer separating the first conductor and the second conductor, the first spacer including a discharge detection conductor at an intermediate part between the first conductor and the second conductor; a resistor having one end connected to the discharge detection conductor; and a detector for detecting a current flowing through the resistor.

Description

Power transmission system, partial discharge detection method, and power transmission device

[0001] This application claims priority to Japanese Patent Application No. 2023-215640, filed on December 21, 2023, the contents of which are incorporated herein by reference.

[0002] Patent Document 1 describes the following wire protection device. That is, the wire protection device described in Patent Document 1 detects whether an arc discharge has occurred based on a current flowing through a thin conductive film (thin metal film) covered with a resin insulating film contained in a thin film spacer inserted between multiple power supply wire groups, each group having the same potential. Here, the multiple power supply wire groups are, for example, AC power supply wire groups for each phase of a three-phase AC, and each wire group is bundled with a string-type tape. Furthermore, the potential of the thin conductive film is ground potential.

[0003] U.S. Patent No. 9,953,748

[0004] In a thin film spacer that separates groups of electric wires bundled with tape, if it does not include a conductive thin film, the potential inside the thin film spacer will be at various levels depending on the distance between the groups of electric wires. On the other hand, if it includes a conductive thin film, the potential inside the conductive thin film will be the same, so the potential inside the thin film spacer will be different depending on whether it includes a conductive thin film or not. In other words, if a conductive thin film is provided on a thin film spacer, the potential distribution will change, and in some cases, the presence of the conductive thin film may make partial discharges more likely to occur.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a power transmission system, a partial discharge detection method, and a power transmission device that can prevent changes in the potential distribution caused by a discharge detection conductor when the discharge detection conductor is included in a spacer between conductors.

[0006] The power transmission system of the present disclosure comprises a power transmission device including 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, and a first spacer made of an insulator that separates the first conductor and the second conductor and includes a discharge detection conductor in an intermediate portion between the first conductor and the second conductor, a resistor having one end connected to the discharge detection conductor, and a detector that detects the current flowing through the resistor.

[0007] The partial discharge detection method according to the present disclosure detects partial discharge occurring within the power transmission device using a power transmission device including 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, and a first spacer made of an insulator that separates the first conductor and the second conductor and includes a discharge detection conductor in an intermediate portion between the first conductor and the second conductor, a resistor having one end connected to the discharge detection conductor, and a detector that detects the current flowing through the resistor.

[0008] The power transmission device according to the present disclosure comprises 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, and a first spacer made of an insulator that separates the first conductor and the second conductor and includes a conductor for detecting discharge in an intermediate portion between the first conductor and the second conductor.

[0009] According to the power transmission system, partial discharge detection method, and power transmission device of the present disclosure, it is possible to prevent changes in the potential distribution caused by the discharge detection conductor.

[0010] FIG. 1 is a configuration diagram of a power transmission system 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 block diagram of a power transmission system according to a first embodiment of the present disclosure. FIG. 5 is a configuration diagram of a power transmission system according to a first embodiment of the present disclosure. FIG. 6 is a diagram showing an example of potential distribution in a power transmission device according to a first embodiment of the present disclosure. FIG. 7 is a diagram showing a comparative example of potential distribution in a power transmission device according to a first embodiment of the present disclosure (when a discharge detection conductor is not present). FIG. 8 is a configuration diagram of a power transmission system according to a second embodiment of the present disclosure. FIG. 9 is a configuration diagram of a power transmission system according to a second embodiment of the present disclosure. FIG. 10 is a configuration diagram of a power transmission system according to a third embodiment of the present disclosure.

[0011] First Embodiment A power transmission system, a partial discharge detection method, and a power transmission device according to a first embodiment of the present disclosure will be described with reference to FIGS. 1 to 7 . FIG. 1 is a configuration diagram of a power transmission system 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 block diagram of a power transmission system according to a first embodiment of the present disclosure. FIG. 5 is a configuration diagram of a power transmission system according to a first embodiment of the present disclosure. FIG. 6 is a diagram illustrating an example of potential distribution in a power transmission device according to a first embodiment of the present disclosure. FIG. 7 is a diagram illustrating a comparative example of potential distribution in a power transmission device according to a first embodiment of the present disclosure (when a discharge detection conductor is not provided). Note that the same or corresponding components in each drawing are designated by the same reference numerals, and descriptions thereof will be omitted as appropriate. Furthermore, the terms “first,” “second,” and “third” used in this specification are used interchangeably to distinguish one component from another.

[0012] As shown in Fig. 1 , a power transmission system 100 according to a first embodiment of the present disclosure includes a power transmission device 1, a resistor 101, and a partial discharge detector 102. The power transmission system 100 is a system for detecting partial discharge that occurs within the power transmission device 1 that transmits DC power. Note that Fig. 1 shows a cross-sectional shape of the power transmission device 1.

[0013] As shown in Figures 1 to 3, the power transmission device 1 according to the first embodiment of the present disclosure comprises a first conductor 11, a second conductor 12, a first spacer 13, a second spacer 14, an electrical conduit 15, and a discharge detection conductor 17 provided (embedded) within the first spacer 13.

[0014] The first conductor 11 and the second conductor 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.

[0015] The first spacer 13 is an insulator that separates the first conductor 11 and the second conductor 12, and includes a discharge detection conductor 17 in the intermediate portion between the first conductor 11 and the second conductor 12. The discharge detection conductor 17 is, for example, a thin metal film, and extends in the direction of DC power transmission as shown in FIG. 2 . In this embodiment, the insulator is an object through which electricity flows very little. The intermediate portion refers to a region that is equidistant (almost equidistant) from the first conductor 11 and the second conductor 12.

[0016] 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 conduit 15. The conduit 15 is a conductor enclosing the second spacer 14. The conduit 15 is formed of a metal such as aluminum. The conduit 15 can also be referred to as a metal conduit. A fluid 16, such as a fluid such as air at atmospheric pressure, a pressurized gas, or a pressurized fluid such as a liquid, is introduced into the 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.

[0017] 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.

[0018] As shown in Fig. 3, the first conductor 11 has a first portion B11 forming a plane, and the second conductor 12 has a second portion B12 forming a plane opposite to the first portion B11. The first spacer 13 has a flat plate shape with a planar portion 131 facing the first portion B11 and the second portion B12. As shown in Fig. 2, the first conductor 11 has one or more plate-like portions B21 extending from the first portion B11 as a base end toward the second spacer 14. The second conductor 12 has one or more plate-like portions B22 extending from the second portion B12 as a base end toward the second spacer 14. This configuration achieves a good balance between improved cooling efficiency (increased surface area, reduced resistance, etc.) and weight reduction.

[0019] As shown in FIG. 4 , in the power transmission system 100 of this embodiment, for example, a positive voltage of DC power output by the converter 51 is applied to the first conductor 11 of the power transmission device 1, and a negative voltage of DC power output by the converter 51 is applied to the first conductor 11. The conduit 15 is connected to a neutral point N of the DC power output by the converter 51. The converter 51 receives AC output from a generator 22, such as a three-phase AC generator, converts it into DC power, and outputs it. In the example shown in FIG. 4 , two capacitors C are connected in series between the positive and negative output terminals of the converter 51, and the connection point between the two capacitors C is the neutral point N, which is at ground potential. However, the neutral point N of the DC power may be, for example, the neutral point of the generator 22. The conduit 15 of the power transmission device 1 is connected to the neutral point N (ground potential). The DC power output by the converter 51 is supplied to a DC load 23 through the power transmission device 1.

[0020] One end of the resistor 101 is connected to the discharge detection conductor 17, and the other end is connected to the neutral point N (ground potential). The partial discharge detector 102 includes, for example, a clamp-type current detector 1021 and a detection circuit 1022, and detects that a current equal to or greater than a predetermined value has flowed through the resistor 101.

[0021] In the power transmission system 100 of this embodiment, as shown in Fig. 5, a discharge detection conductor 17 is embedded, for example, as a conductive film, inside a first spacer 13 located between a first conductor 11 and a second conductor 12 that constitute the positive and negative transmission lines, and the occurrence of a partial discharge is detected by detecting, as a discharge current, an electric charge induced in the conductive film by a partial discharge that occurs between the transmission lines using an external partial discharge detector 102. Fig. 5 indicates multiple locations with a relatively high possibility of partial discharge occurrence using star marks 50 (hereinafter also referred to as occurrence locations 50). The discharge detection conductor 17 can effectively detect partial discharges within an area DB surrounded by a dashed line.

[0022] Since the discharge detection conductor 17 is provided in the middle between the first conductor 11 and the second conductor 12, the neutral potential (0 V (including almost 0 V)) of the DC power transmitted by the power transmission device 1 is applied to the discharge detection conductor 17 in a steady state (a state in which DC power is being transmitted and no partial discharge is occurring). In this embodiment, the first spacer 13 has a flat plate shape that faces a first portion B11 that forms a plane with the first conductor 11 and a second portion B12 that forms a plane with the second conductor 12. Therefore, the potential of the discharge detection conductor 17 can be set to 0 V over almost the entire area of ​​the first spacer 13 in a steady state.

[0023] Furthermore, although the placement of the discharge detection conductor 17 raises concerns about electrical disturbances inside the power transmission device 1 (such as partial discharges caused by the conductive film), if the discharge detection conductor 17 is inserted midway along the transmission line as shown in Fig. 6 , the internal potential distribution does not change (the potential distribution is equivalent to the potential distribution without the discharge detection conductor 17 shown in Fig. 7 ). Therefore, the power transmission system 100 of this embodiment makes it possible to detect partial discharges without causing electrical disturbances due to the conductive film.

[0024] As described above, the power transmission system, partial discharge detection method, and power transmission device of the present embodiment can prevent changes in the potential distribution caused by the discharge detection conductor.

[0025] Although the above describes an example in which the first spacer 13 includes one discharge detection conductor 17, there may be multiple discharge detection conductors 17. Alternatively, one power transmission device 1 may be provided with multiple first spacers 13 in the power transmission direction, each including one or more discharge detection conductors 17. In this case, the location of the partial discharge occurrence can be identified by identifying the location of the discharge detection conductor 17 that detected the current due to the partial discharge.

[0026] Second Embodiment Next, a power transmission system, a partial discharge detection method, and a power transmission device according to a second embodiment of the present disclosure will be described with reference to FIGS. 8 to 10 . A power transmission system 100A according to the second embodiment of the present disclosure includes a power transmission device 1A, a resistor 101, and a partial discharge detector 102 shown in FIG. 8 , as well as at least one of a partial discharge detector 103 shown in FIG. 9 and a partial discharge detector 104 shown in FIG. 10 . As shown in FIG. 8 , the power transmission device 1A includes one or more optical fibers 30 in a hollow portion 141. Each optical fiber 30 has one or more light-receiving units (or light-receiving surfaces) 31. The light-receiving units 31 receive and transmit partial discharges generated in a light-receiving direction 32 indicated by an arrow. The light-receiving units 31 may be, for example, a portion of a coated optical fiber where the coating has been removed, or a portion to which an optical component such as an optical fiber is further coupled. The light-receiving direction 32 is determined so that a partial discharge occurrence point 50 falls within the field of view of the light-receiving units 31.

[0027] FIG. 9 shows an example of the configuration of the optical fibers 30 and the partial discharge detector 103. In the example shown in FIG. 9, the light receiving units 31 of the multiple optical fibers 30 are provided at different positions relative to the transmission direction of the DC power. The interval L1 can be, for example, approximately several tens of centimeters. However, the interval L1 is not limited to this example. The partial discharge detector 103 includes a photoelectric conversion unit 1031 that converts the light output from each optical fiber 30 into electricity, and a partial discharge detector 1032 that detects the generation of an electrical signal corresponding to light of a predetermined intensity or greater. The partial discharge detector 1032 can identify the optical fiber 30 that has received light of a predetermined intensity or greater, thereby identifying the location of the partial discharge. This configuration can simplify the configuration of the partial discharge detector 103.

[0028] FIG. 10 shows a configuration example of an optical fiber 30 and a partial discharge detector 104. In the example shown in FIG. 10, one optical fiber 30 has multiple light-receiving units 31, and the light-receiving units 31 are located at different positions relative to the transmission direction of DC power. The intervals L1 between the light-receiving units 31 may be equal or unequal. The partial discharge detector 104 includes a photoelectric conversion unit 1041 that converts light output from one end of the optical fiber 30 into electricity, a photoelectric conversion unit 1042 that converts light output from the other end of the optical fiber 30 into electricity, and a time difference detection and partial discharge detector 1043 that detects the generation of an electrical signal corresponding to light of a predetermined intensity or greater and detects the time difference between the arrival times of the light (the time difference between the detection time by the photoelectric conversion unit 1041 and the detection time by the photoelectric conversion unit 1042). When light of a predetermined intensity or greater is received, the time difference detection and partial discharge detector 1043 can identify the location of a partial discharge based on the time difference between the arrival times of the light. According to this configuration, the number of optical fibers 30 can be reduced, and therefore the cooling space within the power transfer device 1A can be increased.

[0029] The configuration shown in FIG. 9 and the configuration shown in FIG. 10 can be combined as appropriate.

[0030] According to this embodiment, the partial discharge detector 102 can detect with high sensitivity the partial discharge that occurs between the conductor 11 and the conductor 12, and the partial discharge detector 103 or the partial discharge detector 104 can detect with high sensitivity the partial discharge that occurs between the conductor 11 or the conductor 12 and the electric conduit 15.

[0031] Third Embodiment Next, a power transfer system, a partial discharge detection method, and a power transfer device according to a third embodiment of the present disclosure will be described with reference to FIG. 11 . A power transfer system 100B according to the third embodiment of the present disclosure includes a power transfer device 1B, a resistor 101, a partial discharge detector 102, and a partial discharge detector 105. As shown in FIG. 11 , the power transfer device 1B includes one or more electromagnetic wave antennas 60 that are closely attached to or near the inner wall of the electrical conduit 15 at predetermined intervals in the circumferential direction. The electromagnetic wave antennas 60 may be concentrated near a partial discharge occurrence point 50. A thin and flexible structure is desirable for the electromagnetic wave antenna 60, taking into consideration its close contact with the inner wall of the electrical conduit 15. A suitable electromagnetic wave antenna 60 is, for example, a structure in which a patch antenna is embedded in a film made of PEN (polyethylene naphthalate), PI (polyimide), or the like.

[0032] The partial discharge detector 105 detects that each electromagnetic wave antenna 60 has received an electromagnetic wave of a predetermined intensity or more. The partial discharge detector 105 can also identify the location of a partial discharge by identifying the electromagnetic wave antenna 60 that has received an electromagnetic wave of a predetermined intensity or more.

[0033] According to this embodiment, the partial discharge detector 102 can detect with high sensitivity partial discharges occurring between the conductors 11 and 12, and the partial discharge detector 105 can detect with high sensitivity partial discharges occurring between the conductors 11 or 12 and the electrical conduit 15.

[0034] (Effects) In the power transmission system, partial discharge detection method, and power transmission device configured as described above, the power transmission device 1 is used, which 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 DC power is applied; a first spacer 13 made of an insulator separating the first conductor 11 and the second conductor 12, the first spacer 13 including a discharge detection conductor 17 in an intermediate portion between the first conductor 11 and the second conductor 12; a second spacer 14 made of 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; and a conductor conduit 15 enclosing the second spacer 14, and partial discharge is detected by detecting a current flowing through a resistor 101 having one end connected to the discharge detection conductor 17. According to this configuration, the discharge detection conductor 17 is provided in the middle between the first conductor 11 and the second conductor 12, which are originally at a constant potential (0 V; neutral point potential) (when the discharge detection conductor 17 is not present), so there is no change in the potential distribution due to the discharge detection conductor 17. Furthermore, the provision of the discharge detection conductor 17 does not make partial discharges more likely to occur.

[0035] (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 present disclosure. In the above embodiment, a metal thin film is used as the discharge detection conductor 17, but the shape is not limited thereto. For example, the conductor 17 may be a single electric wire, an array of multiple electric wires, or a mesh-like array of multiple electric wires. Furthermore, the configurations of the second and third embodiments may be used in combination.

[0036] Note that partial discharge detector 102 is an example of a "detector" according to the present disclosure, partial discharge detectors 103 and 104 are examples of a "second detector" according to the present disclosure, and partial discharge detector 105 is an example of a "third detector" according to the present disclosure.

[0037] <Additional Notes> The power transfer system 100, 100A, or 100B described in each embodiment can be understood, for example, as follows.

[0038] (1) A power transmission system 100, 100A, or 100B according to a first aspect includes a power transmission device 1, 1A, or 1B including 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 separating the first conductor and the second conductor, the first spacer including a discharge detection conductor 17 in an intermediate portion between the first conductor and the second conductor, a resistor 101 having one end connected to the discharge detection conductor, and a detector (partial discharge detector 102) that detects a current flowing through the resistor. According to this aspect and the following aspects, it is possible to prevent a change in the potential distribution caused by the discharge detection conductor.

[0039] (2) Power transmission systems 100, 100A, and 100B according to a second aspect are the power transmission systems of (1), in which the first conductor has a first portion B11 forming a plane, the second conductor has a second portion B12 forming a plane facing the first portion, and the first spacer has a flat plate shape with a flat portion 131 facing the first portion and the second portion. According to this aspect, the potential of a relatively wide area, such as the entire area, can be kept constant, and the area of ​​the discharge detection conductor can be increased, for example.

[0040] (3) The power transmission systems 100, 100A, and 100B according to a third aspect are the power transmission systems of (1), in which the other end of the resistor 101 is connected to the neutral point of the DC power. According to this aspect, the potential of the discharge detection conductor can be stabilized at the neutral point potential (0 V) of the DC power.

[0041] (4) A power transmission system 100A according to a fourth aspect is the power transmission system of any one of (1) to (3), in which the power transmission device 1A has a hollow portion 141 and further includes a second spacer 14 made of an insulator that encloses the first conductor, the second conductor, and the first spacer in the hollow portion, and further includes one or more optical fibers 30 laid in the hollow portion 141 and a second detector (partial discharge detectors 103 and 104) that detects that the one or more optical fibers have received light in the hollow portion. According to this aspect, partial discharges occurring at locations where the detection sensitivity of the detector (partial discharge detector 102) is reduced can be detected with better sensitivity than when this configuration is not used.

[0042] (5) A power transmission system 100A according to a fifth aspect is the power transmission system of (4), wherein the optical fiber is plural, and the light receiving units 31 of the plural optical fibers are provided at different positions relative to the transmission direction of the DC power. According to this aspect, it is possible to identify the location of the partial discharge.

[0043] (6) A power transmission system 100A according to a sixth aspect is the power transmission system of (4) or (5), wherein at least one of the optical fibers has a plurality of light receiving units 31 at different positions relative to the transmission direction of the DC power, and the second detector (partial discharge detector 104) further detects a time difference between the arrival times of light received by the optical fiber at both ends of the optical fiber. According to this aspect, it is possible to identify the location of a partial discharge using a small number of optical fibers.

[0044] (7) A power transmission system 100B according to a seventh aspect is the power transmission system of any one of (1) to (6), wherein the power transmission device 1B further includes a second spacer 14 made of an insulator having a hollow portion 141 and enclosing the first conductor, the second conductor, and the first spacer in the hollow portion, a conduit 15 of a conductor enclosing the second spacer, one or more antennas 60 installed in the conduit, and a third detector (partial discharge detector 105) that detects that the one or more antennas have received electromagnetic waves generated in the conduit. According to this aspect, partial discharges occurring at locations where the detection sensitivity of the detector (partial discharge detector 102) is reduced can be detected with better sensitivity than when this configuration is not used.

[0045] According to the power transmission system, partial discharge detection method, and power transmission device of the present disclosure, it is possible to prevent changes in the potential distribution caused by the discharge detection conductor.

[0046] REFERENCE SIGNS LIST 1... Power transmission device 100, 100A, 100B... Power transmission system 11... First conductor 12... Second conductor 13... First spacer 14... Second spacer 15... Conduit 16... Fluid 17... Discharge detection conductor 101... Resistor 102 to 105... Partial discharge detector 141... Hollow portion N... Neutral point

Claims

1. A power transmission device comprising: 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 separating the first conductor and the second conductor, the first spacer including a discharge detection conductor in an intermediate portion between the first conductor and the second conductor; a resistor having one end connected to the discharge detection conductor; and a detector for detecting a current flowing through the resistor.

2. The power transmission system described in claim 1, wherein the first conductor has a first portion forming a plane, the second conductor has a second portion forming a plane opposite to the first portion, and the first spacer has a flat plate shape having a planar portion opposite to the first portion and the second portion.

3. The power transmission system according to claim 2, wherein the other end of the resistor is connected to a neutral point of the DC power.

4. The power transmission system described in claim 3, further comprising a second spacer made of an insulator having a hollow portion and enclosing the first conductor, the second conductor and the first spacer in the hollow portion, one or more optical fibers laid in the hollow portion, and a second detector that detects that the one or more optical fibers have received light within the hollow portion.

5. The power transmission system according to claim 4, wherein the optical fiber is multiple, and the light receiving portions of the multiple optical fibers are provided at different positions relative to the transmission direction of the DC power.

6. The power transmission system according to claim 4, wherein at least one of the optical fibers has a plurality of light receiving units at different positions relative to the transmission direction of the DC power, and the second detector further detects a time difference between the times at which the light received by the optical fiber reaches both ends of the optical fiber.

7. The power transmission system described in any one of claims 1 to 6, further comprising: a second spacer made of an insulator having a hollow portion and enclosing the first conductor, the second conductor and the first spacer in the hollow portion; and a conduit of a conductor enclosing the second spacer; one or more antennas installed in the conduit; and a third detector that detects that the one or more antennas have received electromagnetic waves generated in the conduit.

8. A partial discharge detection method for detecting a partial discharge occurring within a power transmission device, comprising: 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; and a first spacer made of an insulator separating the first conductor and the second conductor, the first spacer including a discharge detection conductor in an intermediate portion between the first conductor and the second conductor; a resistor having one end connected to the discharge detection conductor; and a detector for detecting a current flowing through the resistor.

9. A power transmission device comprising: 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; and a first spacer made of an insulator separating the first conductor and the second conductor, the first spacer including a conductor for detecting discharge in an intermediate portion between the first conductor and the second conductor.

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