Antenna device and partial discharge sensor

Abstract

This antenna device and partial discharge sensor comprise: a ground conductor (2) having a flat plate-shaped upper surface; a conductor (3), which has three sides, being two sides connected to a base end (6) and an upper side (7) facing the base end (6), the base end (6) being connected to a feed point (10) provided to the ground conductor (2), and which is disposed perpendicular to the ground conductor (2); a conductor (4) of annular shape with the center disposed on the upper side (7), the conductor (4) being connected to the upper side (7); and a conductor (5) having an outer diameter shorter than the inner diameter of the conductor (4), the conductor (5) being disposed inside the conductor (4) and connected to the upper side (7).

Description

Antenna Device and Partial Discharge Sensor 【0001】 The present disclosure relates to an antenna device and a partial discharge sensor used for detecting partial discharge phenomena such as GIS (Gas Insulated Switchgear). 【0002】 Generally, sulfur hexafluoride (hereinafter, SF6 gas) is filled as an insulating gas in a GIS. In order to detect partial discharge in the GIS, it is necessary to receive high-frequency waves ranging from 500 MHz to 1500 MHz generated during partial discharge. As a conventional technique, there is a partial discharge sensor in which a cylindrical depression is formed in a cylindrical structure configured to surround a high-voltage wire, and a top-loading monopole antenna composed of a disk and a cylinder is installed in the cylindrical depression (Patent Document 1 below). The top-loading monopole antenna of Patent Document 1 receives high-frequency waves of 500 MHz to 1500 MHz by adjusting the resonance frequency by adjusting the dimensions within a limited antenna installation range. 【0003】 International Publication No. 2012 / 137254 【0004】 When dry air is used instead of SF6 gas that has been conventionally used, high-frequency waves due to partial discharge are generated over a range of 100 MHz to 1500 MHz. Therefore, the partial discharge sensor is required to have further broadband characteristics. However, the partial discharge sensor of Patent Document 1 becomes an antenna that receives 100 MHz to 1500 MHz by increasing the dimensions. However, when there are restrictions on the antenna installation range inside the cylindrical depression, the dimensions cannot be increased sufficiently, and there is a problem that the reception characteristics on the low-frequency side (near 500 MHz and the lower frequency side thereof) of the operating frequency band (hereinafter, the operating frequency band) are insufficient. 【0005】 The present disclosure has been made to solve the above problems, and an object thereof is to obtain an antenna device and a partial discharge sensor that can be arranged within a limited antenna installation range, receive a wide band of 100 MHz to 1500 MHz, and improve the reception characteristics on the low-frequency side of the operating frequency band. 【0006】The antenna device according to this disclosure comprises a ground conductor with a flat top surface, a first conductor having three sides (two sides connected to the base end and an upper side opposite to the base end), the base end of which is connected to a feed point provided on the ground conductor and positioned perpendicular to the ground conductor, a second conductor having an annular shape with its center positioned on the upper side and connected to the upper side, and a third conductor having an outer diameter shorter than the inner diameter of the second conductor, positioned inside the second conductor and connected to the upper side. 【0007】 The partial discharge sensor according to this disclosure comprises an antenna device having a structure composed of a cylindrical conductor whose upper part is connected to a ground conductor and a ring connected to the outside of the bottom of the cylindrical conductor, and a moisture-absorbing material provided inside the structure. 【0008】 According to this disclosure, it is possible to obtain an antenna device and a partial discharge sensor that can receive a wide bandwidth from 100 MHz to 1500 MHz and have good reception characteristics on the lower end of the operating frequency band. 【0009】This is a perspective view of an antenna device according to Embodiment 1. This is a top view of an antenna device according to Embodiment 1. This is a side view of an antenna device according to Embodiment 1. This is a diagram showing equivalent models of conductor 3 and conductor 4. This is a diagram showing the operating principles of conductor 3 and conductor 4. This is a diagram showing the reflection characteristics of an antenna device according to Embodiment 1. This is a diagram showing the directivity gain of an antenna device according to Embodiment 1. This is a perspective view of an antenna device using a conductor 3 with two straight sides. This is a perspective view of an antenna device in which the conductor 4 is divided into two parts. This is a top view of an antenna device in which the conductor 4 is divided into two parts. This is a side view of an antenna device in which the conductor 4 is divided into two parts, viewed from the +X direction. This is a diagram showing the current path in an antenna device using conductors 11 and 12. This is a schematic cross-sectional view of a partial discharge sensor according to Embodiment 2. This is a perspective view of a partial discharge sensor according to Embodiment 2. This is a top view of a partial discharge sensor according to Embodiment 2. This is a side view of a partial discharge sensor according to Embodiment 2, viewed from the +X direction. This is a cross-sectional view of an example in which a shield is added to a partial discharge sensor according to Embodiment 2. This is a perspective view of an example in which a shield is added to a partial discharge sensor according to Embodiment 2. This is a top view of an example in which a shield is added to a partial discharge sensor according to Embodiment 2. This is a side view from the +X direction of an example in which a shield has been added to the partial discharge sensor according to Embodiment 2. This is a schematic cross-sectional view of the partial discharge sensor according to Embodiment 3. This is a perspective view of the partial discharge sensor according to Embodiment 3. This is a top view of the partial discharge sensor according to Embodiment 3. This is a side view of the partial discharge sensor according to Embodiment 3 from the +X direction. This is a diagram showing the radiation efficiency of the partial discharge sensor according to Embodiment 3. 【0010】 Hereinafter, in order to describe the present invention in more detail, embodiments for carrying out the present invention will be described with reference to the attached drawings. Embodiment 1. Figure 1 is a perspective view of the antenna device according to Embodiment 1. Figure 2 is a top view of the antenna device according to Embodiment 1. Figure 3 is a side view of the antenna device according to Embodiment 1. 【0011】 The antenna device 1 according to Embodiment 1 comprises a ground conductor 2, a first conductor 3, a second conductor 4, a third conductor 5, and a feed point 10. 【0012】 The ground conductors 2, 3, 4, and 5 are plate-shaped conductors. The ground conductors 2, 4, and 5 are arranged on planes parallel to the X-Y plane of the XYZ coordinate system shown in Figures 1, 2, and 3. Conductor 3 is arranged on a plane parallel to the Y-Z plane. 【0013】 The conductor 3 has a shape with three sides: two sides of equal length and an upper side 7. The two sides are in the shape of an isosceles triangle with both hypotenuses of equal length bulging outwards. The width of the conductor widens from the base end 6, which is sandwiched between the two sides, towards the upper side 7. The conductor 3 is connected at the base end 6 to a feed point 10 provided on the ground conductor 2. The feed point 10 is the position where the antenna device 1 receives high frequencies. The conductor 3 is positioned perpendicular to the ground conductor 2, with the upper side 7 parallel to the ground conductor 2. 【0014】 The conductor 4 is a ring, and the outer diameter of the ring is the same as the length of the upper side 7. The conductor 4 is positioned parallel to the ground conductor 2. The center of the conductor 4 is positioned so that it coincides with the midpoint of the upper side 7, and it is connected to both ends of the upper side 7. 【0015】 Conductor 5 is a disc with a diameter shorter than the inner diameter of conductor 4. Conductor 5 is positioned parallel to ground conductor 2, with its center coinciding with the center of conductor 4. Therefore, conductors 4 and 5 are concentric circles centered on the midpoint of the upper edge 7, and conductors 4 and 5 are not in contact. 【0016】 To improve reception characteristics in the 100 MHz band, the two sides of conductor 3 are adjusted to bulge outwards so that the sum of the length of one of the two equal-length sides of conductor 3 and the length of 1 / 4 of the outer circumference of conductor 4 is approximately 1 / 4 of the free-space wavelength λ at the lower limit frequency of the operating frequency band (100 MHz). 【0017】 Next, I will explain how it works. 【0018】 Antenna device 1 receives incoming high-frequency signals through conductors 3, 4, and 5, and transmits the high-frequency signals to the outside from the feed point 10. 【0019】 First, let's explain the operation of conductor 3 and conductor 4. 【0020】Because conductor 3 has a shape in which two sides bulge outward from the base end 6 towards the top edge 7, good reflection characteristics can be obtained over a wide bandwidth. Figure 4 shows an equivalent model of conductor 3 and conductor 4. Conductors 3 and conductor 4 exhibit electrically equivalent operation to when two sets of bifurcated λ / 4 inverted L antennas are placed opposite each other and excited with equal amplitude and in phase, and a long current path can be secured between conductors 3 and conductor 4. As a result, conductors 3 and conductor 4 can obtain good reflection characteristics in the lower end of the operating frequency band where a long current path is required, even when the antenna installation range is restricted. 【0021】 Figure 5 shows the operating principle of conductors 3 and 4. The solid arrows in Figure 5 indicate the current path. A high-frequency signal is applied to conductor 3 from the feed point 10. The current applied to conductor 3 propagates within conductor 3 in the direction from the base end 6 toward the upper edge 7, and is applied to conductor 4 from both ends of the upper edge 7. 【0022】 The current applied to conductor 4 propagates within conductor 4 along a ring. When the current on conductor 4 is decomposed into a current component in the X direction and a current component in the Y direction, the currents in both directions cancel each other out and therefore do not contribute to the radiation pattern. On the other hand, when the current flowing through conductor 3 is decomposed into a current component in the Y direction and a current component in the Z direction, the current component in the Y direction cancels each other out and does not contribute to the radiation pattern, but only the current component in the Z direction remains, so the radiation pattern becomes omnidirectional in the X-Y plane. As a result, both conductor 3 and conductor 4 have only a current component in the Z direction, resulting in an omnidirectional radiation pattern in the X-Y plane. 【0023】 Next, we will explain the operation of conductor 3 and conductor 5. 【0024】 Since a circular conductor 5 is connected to the upper edge 7 of conductor 3, conductors 3 and 5 operate as a top-loading monopole antenna. Because the current path of conductor 5 is shorter than that of conductor 4, conductors 3 and 5 resonate at specific frequencies within the operating frequency band, resulting in good reflection characteristics. Furthermore, by making conductor 5 circular, conductors 3 and 5 produce an omnidirectional radiation pattern in the X-Y plane. 【0025】From the above, the antenna device 1 secures a long current path by conductors 3 and 4 in the low-frequency range of the operating frequency band, thereby obtaining good reflection characteristics, and the radiation pattern of the antenna device as a whole is omnidirectional in the X-Y plane. 【0026】 Figure 6 shows the reflection characteristics of the antenna device according to Embodiment 1. In Figure 6, characteristic A1 shows the reflection characteristics of antenna device 1, and characteristic A2 shows the reflection characteristics of the antenna device based on Patent Document 1. The antenna installation range was set to a height of 39 mm (0.013λ in terms of wavelength at 100 MHz) and a cylindrical diameter of 159 mm (0.053λ). The height of conductor 3 is 0.013λ, and the length of the upper side 7 of conductor 3 is 0.053λ. The diameter of conductor 5 was set to a dimension that generates resonance on the high-frequency side (higher than 1000 MHz) of the operating frequency band. The height of the antenna device based on Patent Document 1 was the same as the height of conductor 3, and the diameter of the disc was the same as the length of the upper side 7 of conductor 3. 【0027】 In Figure 6, characteristic A1 exhibits better reflection characteristics than characteristic A2 below 500 MHz. Thus, the antenna device 1 can obtain good reflection characteristics at the low end of the operating frequency band. Furthermore, characteristic A1 also exhibits better reflection characteristics than characteristic A2 at the high end of the operating frequency band. 【0028】 Figure 7 shows the directional gain of the antenna device according to Embodiment 1. The directional gain is the gain in the X-Y plane, and the frequencies are 100 MHz, 500 MHz, 750 MHz, and 1500 MHz. It exhibits omnidirectional characteristics at all frequencies and can receive signals with high sensitivity over a wide bandwidth. 【0029】 Note that the dimensions of each conductor are not limited to these and may be adjusted according to the surrounding environment. 【0030】As described above, the antenna device 1 according to Embodiment 1 can improve the reception characteristics on the lower end of the operating frequency band by connecting a conductor 3 having a shape with two sides bulging outwards and a ring-shaped conductor 4 to form a current path necessary on the lower end of the operating frequency band. Furthermore, by connecting the conductor 3 and the disc-shaped conductor 5 to generate resonance at a specific frequency in the operating frequency band, an antenna device capable of receiving high frequencies with high sensitivity over a wide bandwidth can be obtained. 【0031】 In the first embodiment, conductors 3, 4, and 5 are plate-shaped conductors, but the plate-shaped conductors may also be mesh-shaped, formed by assembling linear conductors in a grid pattern. By using a mesh-like structure, the antenna device can be made lighter. 【0032】 Although conductor 3 is a single plate-shaped conductor, it may also be composed of two plate-shaped conductors, in which case the plate-shaped conductors should be arranged perpendicularly in a cross shape. Furthermore, the number of conductors can be increased to three or more plate-shaped conductors that intersect. By composing conductor 3 with multiple plate-shaped conductors, the antenna device can be made less likely to tip over. 【0033】 The conductor 3 has a shape in which two sides bulge outward, but the two sides may also be straight. Figure 8 is a perspective view of an antenna device using a conductor 3 with two straight sides. The conductor 3 may also have a shape in which two sides are recessed inward from the two equally sized hypotenuses of an isosceles triangle. If it is recessed, the area of ​​the conductor will be smaller than that of the conductor 3 in Figure 1, thus reducing the cost of the antenna device. The two sides of the conductor 3 may also be of different lengths. In this case, the difference in length may be due to manufacturing tolerances. Even if the lengths differ to some extent, the effects of this embodiment can still be achieved. The upper side 7 is positioned parallel to the ground conductor 2, but it does not have to be parallel. In this case, the reason for not being parallel may be due to manufacturing tolerances. Even if it is not parallel to some extent, the effects of this embodiment can still be achieved. 【0034】Although the conductor 4 is an annular shape, it may be any shape that is symmetrical with respect to the X-Z plane passing through the power supply point 10, and may be a polygon. Making it a polygon improves the manufacturability of the conductor 4. Although the conductor 4 has an outer diameter the same as the length of the top side 7, it may have a different length. In this case, the reason for the different length may include manufacturing errors. Even if the length differs to some extent, the effects of this embodiment can be achieved. The conductor 4 is positioned parallel to the ground conductor 2, but it does not have to be parallel. In this case, the reason for the non-parallel position may include manufacturing errors. Even if the position is not parallel to some extent, the effects of this embodiment can be achieved. The conductor 4 is positioned so that its center coincides with the midpoint of the top side 7, but it may be positioned on the top side 7 at a different position from the midpoint. In this case, the reason for the position being different from the midpoint may include manufacturing errors. Even if the position differs to some extent, the effects of this embodiment can be achieved. Although the conductor 4 is configured to connect to both ends of the upper edge 7, it may also be configured to connect to a different position on the upper edge 7. In this case, the difference in connection position may include manufacturing tolerances. Even if the connection position differs to some extent, the effects of this embodiment can still be achieved. 【0035】 The conductor 4 may be configured to be divided into two parts. Figures 9, 10, and 11 show a perspective view, a top view, and a side view from the +X direction of an antenna device in which the conductor 4 is divided into two parts. Conductors 11 and 12 are arranged in place of conductor 4. Conductors 11 and 12 are formed symmetrically with respect to a plane passing through the base end 6 and perpendicular to conductor 3. Figure 12 shows the current path in an antenna device using conductors 11 and 12. Comparing Figure 12 with Figure 5, the current path flowing through conductors 11 and 12 is the same as that of conductor 4, so the antenna device in which the conductor 4 is divided into two parts can achieve the same effect as antenna device 1. 【0036】Although conductor 5 is arranged parallel to ground conductor 2, it does not have to be parallel. In this case, the reason for the non-parallel position may include manufacturing tolerances. Even if it is not parallel to some extent, the effects of this embodiment can still be achieved. Although conductor 5 is circular, it may also be polygonal. By making it polygonal, the manufacturability of conductor 5 can be improved. Conductor 5 may also be annular. By making it annular, the area of ​​the conductor is reduced, thus lowering the cost of the antenna device. Although conductor 5 is arranged concentrically with conductor 4, the position of the center of conductor 5 may be moved to a position different from the midpoint on the upper edge 7, as long as conductors 4 and conductor 5 do not come into contact. Since the position of conductor 5 can be adjusted, the reflection characteristics of the antenna device can be adjusted according to changes in the surrounding environment. 【0037】 Conductor 3 may be three-dimensional in shape. For example, conductor 3 may be a hemisphere or a cone. This makes the antenna device less likely to tip over. If conductor 3 is three-dimensional, conductors 4 and 5 should also be three-dimensional. Conductor 4 should be a donut shape with a circular cross-section in the Y-Z plane. The cross-section may also be a square or rectangle. Conductor 5 may be a sphere or the like. By making conductors 4 and 5 three-dimensional, the adjustable dimensions increase, increasing the degree of design freedom, and thus improving the reflection characteristics of the antenna device. 【0038】 When conductors 3, 4, and 5 are plate-shaped conductors, they may be formed on a dielectric substrate. In this case, the dielectric substrate on which conductor 3 is formed and the dielectric substrate on which conductor 4 is formed are bonded together, and the respective conductor portions are connected electrically. Furthermore, the dielectric substrate on which conductor 3 is formed and the dielectric substrate on which conductor 5 is formed are bonded together, and the respective conductor portions are connected electrically. Forming them on a dielectric substrate improves manufacturability and increases rigidity and strength. Since conductors 4 and 5 are arranged on the same plane, they may be formed on a single dielectric substrate. Forming them on a single dielectric substrate improves manufacturability. 【0039】 Embodiment 2. Embodiment 2 describes a partial discharge sensor in which the antenna device of Embodiment 1 is installed inside a cylindrical branch pipe of a GIS. 【0040】FIG. 13 is a cross-sectional view showing an outline of the partial discharge sensor according to Embodiment 2. FIG. 14 is a perspective view of the partial discharge sensor according to Embodiment 2. FIG. 15 is a top view of the partial discharge sensor according to Embodiment 2. FIG. 16 is a side view of the partial discharge sensor according to Embodiment 2, showing a view seen from the +X direction. 【0041】 In FIGS. 13 to 16, the same reference numerals as those in FIGS. 1 to 3 denote the same or corresponding parts, and thus the description thereof will be omitted. 【0042】 First, the partial discharge sensor will be described. In the partial discharge sensor 1A, the upper surface of the structure 20 corresponds to the ground conductor 2 of the antenna device 1. 【0043】 The structure 20 is composed of an upper surface which is a flat ground conductor 2, a side surface which is cylindrical with the upper part connected to the ground conductor 2, and an annular ring connected to the outside of the bottom of the side surface. The upper surface, the side surface, and the annular ring are conductors. A plurality of holes for ventilation are formed in the upper surface and the side surface of the structure 20. 【0044】 A conductor 3 is connected so as to be orthogonal to the upper surface of the structure 20, and a high-frequency signal is transmitted from the power supply point 10 which is the connection point. 【0045】 Next, the surrounding structure of the partial discharge sensor will be described. In FIG. 13, the tank body 30 has a cylindrical closed space so as to surround the high-voltage electric wire 31. 【0046】 The surface of the tank body 30 is set to the ground potential, and the closed space is filled with dry air. A moisture absorbent (not shown) is disposed inside the structure 20 to keep the closed space dry. The branch pipe 33 is formed in a cylindrical shape, one end thereof is connected to the tank body 30, and the other end is blocked by a lid member 34 having an opening. 【0047】The partial discharge sensor 1A is provided inside the branch pipe 33 so as to be in contact with the lid member 34 and block the opening of the lid member 34, and the upper side 7 of the conductor 4 of the partial discharge sensor 1A is arranged to be located at the joint of the tank body 30 and the branch pipe 33. When the conductors 3, 4, and 5 of the partial discharge sensor 1A are in a three-dimensional shape, the upper surface of the conductor 3 is arranged to be located at the joint of the tank body 30 and the branch pipe 33. The structure 20 is electrically connected to the tank body 30 through the lid member 34 and is set to the ground potential similar to the tank body 30. 【0048】 Next, the operation will be described. 【0049】 The closed space in the tank body 30 is filled with dry air. However, when a high voltage is applied to the high-voltage wire 31, partial discharge may occur between the high-voltage wire 31 and the metal parts existing inside the tank body 30. When partial discharge occurs, a high frequency is generated according to the partial discharge. In the case of dry air, a high frequency of 100 MHz to 1500 MHz is generated, and the high frequency propagates in the axial direction (±Y direction in FIG. 13) inside the tank body 30. 【0050】 The propagated high frequency is received by the partial discharge sensor 1A, transmitted as a high-frequency signal from the power supply point 10 of the partial discharge sensor 1A to the outside, and it is detected by the measuring instrument that partial discharge has occurred inside the tank body 30. 【0051】 As described above, in the partial discharge sensor according to the second embodiment, since the upper side 7 of the conductor 4 of the partial discharge sensor 1A is arranged in the branch pipe 33 so as to be located at the joint of the tank body 30 and the branch pipe 33, the same effects as those of the first embodiment can be achieved. 【0052】 Next, an example in which a shield is added to the partial discharge sensor will be described. 【0053】 FIGS. 17, 18, 19, and 20 are a cross-sectional view, a perspective view, a top view, and a side view seen from the +X direction of an example in which a shield is added to the partial discharge sensor according to the second embodiment. In FIGS. 17 to 20, the same reference numerals as those in FIGS. 13 to 16 denote the same or corresponding parts, and thus the description thereof will be omitted. 【0054】An example of adding a shield to a partial discharge sensor includes a partial discharge sensor 1A and a shield 42. The shield 42 is composed of a shield conductor 40 and a support conductor 41. 【0055】 The shield conductor 40 is an annular conductor, with an inner diameter larger than the outer diameter of the conductor 4, and an outer diameter smaller than the outer diameter of the upper surface of the structure 20, and it is not connected to the conductor 4. The upper surface of the shield conductor 40 is positioned to be approximately flush with the conductor 4 by the support conductor 41. The support conductor 41 is columnar and supports the shield conductor 40 on the structure 20. 【0056】 The shield conductor 40 is electrically connected to the structure 20 through the support conductor 41. 【0057】 Next, we will describe the operation of an example where a shield has been added to a partial discharge sensor. 【0058】 A high voltage is induced by the current flowing through the high-voltage wire 31, and when the induced voltage exceeds the allowable voltage, a discharge occurs between the metal parts inside the tank body 30 and the high-voltage wire 31. The discharge is applied not only to the partial discharge sensor 1A but also to the shield 42, so the shield 42 functions as an electric field mitigation shield. 【0059】 The maximum value of the electric field induced in the partial discharge sensor 1A from the high-voltage power line 31 is compared with and without shielding. The dimensions of the partial discharge sensor 1A are the same as those of Embodiment 1. The maximum electric field value was 16.6 kV / mm when no shielding was installed, while it was 6.6 kV / mm when shielding 42 was installed. By installing shielding 42, the voltage induced in the partial discharge sensor 1A can be reduced by 10 kV / mm. 【0060】 As described above, by loading the shield 42 onto the partial discharge sensor according to Embodiment 2, the voltage due to discharge applied to the partial discharge sensor 1A can be reduced. 【0061】 Embodiment 3. Embodiment 3 describes an example in which a shield divided into two parts is added to a partial discharge sensor. 【0062】Figure 21 is a schematic cross-sectional view of the partial discharge sensor according to Embodiment 3. Figure 22 is a perspective view of the partial discharge sensor according to Embodiment 3. Figure 23 is a top view of the partial discharge sensor according to Embodiment 3. Figure 24 is a side view of the partial discharge sensor according to Embodiment 3, shown from the +X direction. 【0063】 In Figures 21 to 24, the same reference numerals as in Figures 17 to 20 indicate the same or corresponding parts, so their explanation is omitted. 【0064】 The shield 52 is composed of a first shield conductor, a shield conductor 50, a second shield conductor, a shield conductor 51, and a support conductor 41. 【0065】 The shield conductors 50 and 51 are constructed by dividing the shield conductor 40 into multiple parts, specifically in the case where it is divided into two parts. The shield conductors 50 and 51 are formed rotationally symmetric with respect to the center of the annular shield conductor 40 in a plane parallel to the upper surface of the structure 20 and containing the conductor 4. The upper surfaces of the shield conductors 50 and 51 are positioned to be approximately flush with the conductor 4 by columnar support conductors 41. The shield conductors 50 and 51 are electrically connected to the structure 20 through the support conductors 41. 【0066】 Next, I will explain how it works. 【0067】 The discharge generated between the metal parts inside the tank body 30 and the high-voltage wire 31 is applied not only to the partial discharge sensor 1A but also to the shield 52, so the shield 52 functions as an electric field mitigation shield. 【0068】 On the other hand, some of the high-frequency currents caused by partial discharge are also induced in the shield 52. This effect will be explained below. 【0069】If the shield conductor 40 is annular, as in Embodiment 2, the shield conductor 40 added to the partial discharge sensor 1A, which follows the dimensions of Embodiment 1, will have an outer circumference approximately the same length as the free-space wavelength at approximately 500 MHz. Therefore, the shield conductor 40 will operate as an unexcited one-wavelength loop antenna, degrading the reception characteristics at approximately 500 MHz. In contrast, the shield conductors 50 and 51, which are divided into two parts, have an outer circumference shorter than that of the shield conductor 40. As a result, by using the shield conductors 50 and 51, they will no longer operate as an unexcited one-wavelength loop antenna at approximately 500 MHz, thus suppressing the degradation of reception characteristics at approximately 500 MHz. 【0070】 The effect of the electric field mitigation shield on the characteristics of the partial discharge sensor is confirmed. Figure 25 shows the radiation efficiency of the partial discharge sensor calculated by electromagnetic field simulation. The dimensions of the partial discharge sensor 1A are the same as those of Embodiment 1. Radiation efficiency is the ratio of total radiated power to input power, and total radiated power is calculated taking into account conductor losses. 【0071】 Characteristic B1 shows the radiation efficiency of the partial discharge sensor 1A without a shield, characteristic B2 shows the radiation efficiency when the shield 42 is installed, and characteristic B3 shows the radiation efficiency when the shield 52 is installed. 【0072】 It can be seen that characteristic B2 shows a 4 dB degradation in radiation efficiency at approximately 500 MHz compared to characteristic B1, while characteristic B3 shows an improvement of approximately 2 dB in radiation efficiency at approximately 500 MHz compared to characteristic B2. Therefore, when shield 42 is installed, the number of components in the conductor can be reduced, but the radiation efficiency decreases. By installing shield 52, the number of components in the conductor increases, but the decrease in radiation efficiency can be suppressed. 【0073】 Next, the maximum value of the electric field induced from the high-voltage power line 31 is compared with and without shielding. The dimensions of the partial discharge sensor 1A are the same as those of Embodiment 1. 【0074】The maximum electric field value is 6.3 kV / mm when the shield 52 is installed, and by installing the shield 52, the voltage induced in the partial discharge sensor 1A can be reduced by 10.3 kV / mm. 【0075】 As described above, in the partial discharge sensor according to Embodiment 3, since the shield 52 functions as an electric field mitigation shield, it is possible to reduce the voltage applied to the partial discharge sensor while suppressing deterioration of the receiving characteristics. 【0076】 Furthermore, within the scope of the present invention, it is possible to freely combine each embodiment, modify any component of each embodiment, or omit any component in each embodiment. 【0077】 The antenna device and partial discharge sensor according to this invention comprises a ground conductor with a flat top surface, a first conductor having three sides (two sides connected to the base end and an upper side opposite the base end), the base end of which is connected to a feed point provided on the ground conductor and positioned perpendicular to the ground conductor, a second conductor having an annular shape with its center positioned on the upper side and connected to the upper side, and a third conductor having an outer diameter shorter than the inner diameter of the second conductor, positioned inside the second conductor and connected to the upper side. This makes it possible to obtain an antenna device and partial discharge sensor that can receive a wide band from 100 MHz to 1500 MHz and have good reception characteristics on the lower end of the operating frequency band, and is suitable for use as an antenna device and partial discharge sensor for detecting partial discharge phenomena such as GIS. 【0078】 1 Antenna device 1A Partial discharge sensor 2 Ground conductor 3 First conductor 4 Second conductor 5 Third conductor 6 Base end 7 Top edge 10 Feed point 11, 12 Conductors 20 Structure 40 Shield conductor 41 Support conductors 42, 52 Shield 50 First shield conductor 51 Second shield conductor

Claims

1. An antenna device comprising: a ground conductor with a flat top surface; a first conductor having three sides, two sides connected to the base end and an upper side opposite the base end, the base end of which is connected to a feed point provided on the ground conductor and positioned perpendicular to the ground conductor; a second conductor having an annular shape, with its center positioned on the upper side and connected to the upper side; and a third conductor having an outer diameter shorter than the inner diameter of the second conductor, positioned inside the second conductor and connected to the upper side.

2. The antenna device according to claim 1, wherein the first conductor, the second conductor, and the third conductor are plate-shaped conductors.

3. The antenna device according to claim 1 or claim 2, wherein the first conductor is formed by crossing a plurality of plate-shaped conductors.

4. The antenna device according to any one of claims 1 to 3, wherein the first conductor is positioned such that the lengths of the two sides are equal and the upper side is parallel to the ground conductor.

5. The antenna device according to any one of claims 1 to 4, wherein the second conductor is a ring connected to both ends of the upper edge, and is positioned parallel to the ground conductor, with its center coinciding with the midpoint of the upper edge.

6. The antenna device according to any one of claims 1 to 5, wherein the second conductor is a polygon connected to both ends of the upper edge, and is positioned parallel to the ground conductor, with its center coinciding with the midpoint of the upper edge.

7. The antenna device according to any one of claims 1 to 6, wherein the second conductor is composed of a conductor divided into two parts.

8. The antenna device according to any one of claims 1 to 7, wherein the third conductor is a disc arranged parallel to the ground conductor.

9. The antenna device according to any one of claims 1 to 8, wherein the third conductor is a polygon arranged parallel to the ground conductor.

10. The antenna device according to any one of claims 1 to 9, wherein the third conductor is a ring arranged parallel to the ground conductor.

11. The antenna device according to any one of claims 1 to 10, wherein the center of the third conductor is located at a position coinciding with the center of the second conductor.

12. The antenna device according to any one of claims 1 to 11, wherein the first conductor, the second conductor, and the third conductor are formed on a dielectric substrate.

13. The antenna device according to any one of claims 1 to 12, wherein the sum of the length of one of the two sides and the length of one-quarter of the outer circumference of the second conductor is one-quarter of the length of the free-space wavelength at the lower limit frequency of the operating frequency band.

14. The antenna device according to claim 1, wherein the first conductor is a hemisphere or a cone, the second conductor is a donut shape having a circular, square, or rectangular cross-sectional shape perpendicular to the ground conductor, and the third conductor is a sphere.

15. The antenna device according to any one of claims 1 to 13, wherein the first conductor has a shape in which the two sides are equal in length and the two hypotenuses bulge outwards.

16. The antenna device according to any one of claims 1 to 13, wherein the first conductor has two straight sides.

17. The antenna device according to any one of claims 1 to 13, wherein the first conductor has a shape in which the two sides are equal in length and the two hypotenuses of an isosceles triangle are concave inward.

18. An antenna device according to any one of claims 1 to 17, comprising a structure comprising a cylindrical conductor whose upper part is connected to the ground conductor and a ring connected to the outside of the bottom of the cylindrical conductor, and a partial discharge sensor comprising a moisture-absorbing material provided inside the structure.

19. The partial discharge sensor according to claim 18, comprising: a shield conductor which is an annular conductor whose inner diameter is larger than the outer diameter of the second conductor and whose outer diameter is smaller than the outer diameter of the upper surface of the structure, and which is positioned to be flush with the second conductor; and a support conductor which supports the shield conductor on the structure.

20. The partial discharge sensor according to claim 19, wherein the shield conductor is composed of conductors obtained by dividing a ring into multiple parts, each of which is supported by the support conductor.

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