Partial Discharge Detection Sensor

Abstract

The present invention provides a partial discharge detection sensor that can accurately detect partial discharge. [Solution] A partial discharge detection sensor according to a first aspect of the embodiment has an electrode. The electrode is formed in a plate shape and has a first surface which is the front surface and a second surface which is the back surface. The first surface of the electrode is attached to the surface of a box that houses the electric power device, and the current to be measured is output from the second surface. The electrode has a substrate and a coating that covers the substrate. The thickness of the coating is equal to or greater than the skin depth calculated from the frequency of the current.

Description

[Technical Field]

[0001] SUMMARY OF THE INVENTION An embodiment of the present invention relates to a partial discharge detection sensor. [Background technology]

[0002] Partial discharge detection sensors are used to detect partial discharges in power equipment such as switchgears and transformers. There is a demand for partial discharge detection sensors that can accurately detect partial discharges. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-82449 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a partial discharge detection sensor that can accurately detect partial discharge. [Means for solving the problem]

[0005] The partial discharge detection sensor of the first embodiment has an electrode. The electrode is formed in a plate shape and has a first surface which is the front surface and a second surface which is the back surface. The first surface of the electrode is attached to the surface of a box that houses the power device, and the current to be measured is output from the second surface. The electrode has a substrate and a coating that covers the substrate. The thickness of the coating is equal to or greater than the skin depth calculated from the frequency of the current.

[0006] A partial discharge detection sensor according to a fourth aspect of the embodiment is based on the partial discharge detection sensor according to the first aspect. The coating is made of a material having a higher electrical conductivity than the substrate.

[0007] A partial discharge detection sensor according to a second aspect of the embodiment is based on the partial discharge detection sensor according to the first or second aspect. The coating is made of a material having a skin depth greater than that of the substrate.

[0008] A partial discharge detection sensor according to a third aspect of the embodiment is based on the partial discharge detection sensor according to any one of the first to third aspects. The coating is made of a material having a lower relative magnetic permeability than the substrate.

[0009] A partial discharge detection sensor according to a fifth aspect of the embodiment is based on the partial discharge detection sensor according to any one of the first to fourth aspects. The coating is made of silver.

[0010] A partial discharge detection sensor according to a sixth aspect of the embodiment is based on the partial discharge detection sensor according to any one of the first to fifth aspects. The substrate is made of a resin material.

[0011] A partial discharge detection sensor according to a seventh aspect of the embodiment is based on the partial discharge detection sensor according to the sixth aspect. The electrode has a coating only on the second surface.

[0012] The partial discharge detection sensor of the eighth embodiment has an electrode. The electrode is formed in a plate shape and has a first surface which is the front surface and a second surface which is the back surface. The first surface of the electrode is attached to the surface of a box that houses the power device, and the current to be measured is output from the second surface. The thickness of the electrode is equal to or less than twice the skin depth calculated from the frequency of the current.

[0013] A partial discharge detection sensor according to a ninth aspect of the embodiment is based on the partial discharge detection sensor according to any one of aspects 1 to 8. The partial discharge detection sensor has a dielectric sheet attached to a first surface. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 2 is a side cross-sectional view of the partial discharge detection sensor according to the first embodiment. [Figure 2] FIG. 10 is a side cross-sectional view of a partial discharge detection sensor according to a second embodiment. [Figure 3]FIG. 10 is a side cross-sectional view of a partial discharge detection sensor according to a third embodiment. [Figure 4] FIG. 10 is a side cross-sectional view of a partial discharge detection sensor according to a fourth embodiment. [Figure 5] FIG. 10 is a side cross-sectional view of a partial discharge detection sensor according to a fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, a partial discharge detection sensor according to an embodiment will be described with reference to the drawings. (First embodiment) 1 is a side cross-sectional view of a partial discharge detection sensor 1 according to a first embodiment. The partial discharge detection sensor 1 is, for example, a transient earth voltage (TEV) sensor.

[0016] Electric power equipment such as switchgear and transformers transforms and cuts off the voltage of electric power. These electric power equipment have an insulator that molds the high-voltage section. If the insulator has a defect such as a void or peeling and the electric field at the defect becomes high, a partial discharge occurs. Partial discharge erodes the solid insulation, causing the breakdown of the electric power equipment. Detecting partial discharge is very important for the maintenance of electric power equipment.

[0017] Partial discharge measuring equipment includes CTs that measure partial discharge currents and antennas that measure partial discharge electromagnetic waves. However, in order to measure partial discharges with these measuring equipment, it is necessary to temporarily suspend the operation of the power equipment. Stopping the operation of power equipment causes a power outage in the downstream system, placing a great burden on the system.

[0018] On the other hand, TEV sensors measure the transient ground potential generated by partial discharges. The metal box (panel) that covers the power equipment is grounded. High-frequency energy emitted by partial discharges propagates to the power equipment box, generating a transient ground potential due to induced current. TEV sensors are attached to the surface of the box and detect the occurrence of partial discharges by measuring the current in the box (sometimes called partial discharge current). TEV sensors can detect partial discharges while the power equipment is operating.

[0019] 1, the partial discharge detection sensor 1 is formed in a cylindrical shape and includes an electrode 10, a core wire 2, a connection terminal 3, and a case 6. In this application, the Z direction and R direction of the cylindrical coordinate system are defined as follows: The Z direction is the axial direction of the partial discharge detection sensor 1. The -Z side is the side of the core wire 2 of the electrode 10. The +Z side is the opposite side to the -Z side. The R direction is the radial direction of the partial discharge detection sensor 1. The +R side is the outer side of the R direction, and the -R side is the inner side of the R direction.

[0020] The electrode 10 is formed in a circular plate shape (disk shape). The electrode 10 is arranged coaxially with the partial discharge detection sensor 1. The electrode 10 is arranged at the end of the partial discharge detection sensor 1 on the +Z side. The electrode 10 has a first surface 11 on the +Z side, which is the front surface, and a second surface 12 on the -Z side, which is the back surface. The first surface 11 is exposed to the outside of the partial discharge detection sensor 1. The electrode 10 will be described in detail later.

[0021] The core wire 2 is a conductive wire. The end on the +Z side of the core wire 2 is connected to the center of the second surface 12 of the electrode 10. The end on the −Z side of the core wire 2 is connected to the connection terminal 3. The connection terminal 3 is, for example, a rotary lock type BNC connector. The connection terminal 3 is arranged at the end of the partial discharge detection sensor 1 on the -Z side. A cable 4 is connected to the connection terminal 3. The cable 4 is connected to a transient ground potential measuring device (not shown).

[0022] The case 6 is made of an electrically insulating resin material or the like. The case 6 is formed in a cylindrical shape. The core wire 2 and the connection terminal 3 are housed on the -R side of the case 6. An electrode 10 is attached to the end of the case 6 on the +Z side. A first surface 11 of the electrode 10 is attached to the surface of a box body (not shown) of the electric power equipment. A permanent magnet is embedded inside the case 6. The permanent magnet allows the partial discharge detection sensor 1 to be attached to and detached from the box body of the electric power equipment.

[0023] The partial discharge detection sensor 1 takes in the partial discharge current C to be measured from the first surface 11 of the electrode 10. The partial discharge detection sensor 1 outputs the current from the second surface 12 of the electrode 10 via the core wire 2 and the connection terminal 3. The current is input to the measuring instrument from the cable 4, and the measuring instrument detects the occurrence of partial discharge.

[0024] A noise current is superimposed on the partial discharge current C generated in the box of the power equipment. The electrode 10 of the partial discharge detection sensor 1 measures the partial discharge current C in a state where the noise current is superimposed on it. If the partial discharge current C becomes latent compared to the noise current, it becomes difficult to detect the partial discharge. The electrode 10 of the partial discharge detection sensor 1 is required to have improved measurement sensitivity for the partial discharge current C.

[0025] The partial discharge current C is a high-frequency current whose magnitude changes over time. This partial discharge current C flows mainly along the surface of the electrode 10 due to the so-called skin effect. In other words, the current density of the partial discharge current C decreases the deeper it goes from the surface of the electrode 10. In general, the current flowing at a skin depth d from the surface of the conductor is 1 / e times (e is the base of the natural logarithm) the current flowing on the surface of the conductor. The skin depth d is expressed by the following equation 1.

[0026]

number

[0027] On the other hand, the larger the resistance value R of the electrode 10 with respect to the partial discharge current C, the greater the attenuation of the partial discharge current C when the partial discharge current C flows through the electrode 10. Generally, the resistance value R of a conductor is expressed by the following equation 2.

[0028]

number

[0029] The larger the skin depth d of the electrode 10 relative to the partial discharge current C, the larger the flow path cross-sectional area S of the partial discharge current C. This reduces the resistance value R of the electrode 10, and the attenuation of the partial discharge current C. As a result, the partial discharge current C becomes more apparent compared to the noise current, making it easier to detect partial discharges. Therefore, the larger the skin depth d of the electrode 10, the better the measurement sensitivity of the partial discharge current C.

[0030] In Equations 1 and 2, the reciprocal of the conductivity σ is the resistivity ρ. In Equation 1, the skin depth d is proportional to the square root of the resistivity ρ. As described above, the larger the skin depth d, the larger the flow path cross-sectional area S in Equation 2. In Equation 2, the resistance value R of the conductor is inversely proportional to the flow path cross-sectional area S. That is, the resistance value R of the conductor is inversely proportional to the square root of the resistivity ρ. In Equation 2, the resistance value R of the conductor is proportional to the resistivity ρ. As described above, the larger the resistivity ρ, the larger the resistance value R of the conductor. Conversely, the larger the conductivity σ, the smaller the resistance value R of the conductor. As described above, if the resistance value R of the electrode 10 is small, the attenuation of the partial discharge current C is reduced. As a result, the partial discharge current C becomes more apparent compared to the noise current, making it easier to detect partial discharges. Therefore, the larger the conductivity σ of the electrode 10, the better the measurement sensitivity of the partial discharge current C.

[0031] The electrode 10 of the first embodiment shown in FIG. The substrate 14 is made of a metal material having electrical conductivity. The substrate 14 is made of, for example, copper or iron. If the substrate 14 is made of inexpensive iron, the cost of the partial discharge detection sensor 1 can be reduced.

[0032] The coating 15 covers the substrate 14. The coating 15 is formed on the entire first surface 11 and second surface 12 of the electrode 10, as well as on the +R side surface. The core wire 2 is connected to the coating 15 formed on the second surface 12 of the electrode 10. The coating 15 may be formed on part of the first surface 11 and second surface 12 of the electrode 10, as well as on part of the +R side surface. The coating 15 only needs to be continuous from the first surface 11 of the electrode 10 to the connection portion with the core wire 2.

[0033] The coating 15 is formed by plating such as electrolytic plating or electroless plating. The coating 15 may also be formed by coating, vapor deposition, or the like. The coating 15 is made of a metal material having electrical conductivity. The coating 15 is made of, for example, silver. The electrical conductivity of silver is approximately 6.29×10 7 S / m and the magnetic permeability is approximately 1.26 μH / m.

[0034] The thickness of coating 15 is larger than the skin depth d calculated from the frequency of partial discharge current C. When the power equipment is a switchgear or a transformer, the frequency of partial discharge current C is 10 to 30 MHz. When the power equipment is a generator, the frequency of partial discharge current C is 1 to 5 MHz. For example, when the frequency of partial discharge current C is 20 MHz, the skin depth d of silver, which is an example material of coating 15, is approximately 14.1 μm. In this case, the thickness of coating 15 is set to be 14.1 μm or more, which is equal to or larger than the skin depth d.

[0035] The minimum frequency of partial discharge current C is 1 MHz. When the frequency of partial discharge current C is 1 MHz, the skin depth d of silver, an example material of coating 15, is approximately 63.1 μm. Therefore, it is desirable to set the thickness of coating 15 to 63.1 μm or more, which is equal to or greater than the skin depth d corresponding to the minimum frequency of partial discharge current C.

[0036] The conductivity of the coating 15 is greater than the conductivity of the substrate 14. The conductivity of silver, an example material of the coating 15, is approximately 6.29×10 7 S / m, which is greater than the conductivity of copper or iron, which are examples of materials for the substrate 14. This reduces the resistance value R of the electrode 10 and reduces the attenuation of the partial discharge current C. Therefore, the measurement sensitivity of the partial discharge current C at the electrode 10 is improved.

[0037] The skin depth d of the coating 15 is greater than the skin depth d of the substrate 14. For example, when the frequency of the partial discharge current C is 20 MHz, the skin depth d of silver, an example material of the coating 15, is approximately 14.1 μm, which is greater than the skin depth d of iron, an example material of the substrate 14. This reduces the resistance value R of the electrode 10 and reduces the attenuation of the partial discharge current C. This improves the measurement sensitivity of the partial discharge current C at the electrode 10.

[0038] The relative magnetic permeability of the coating 15 (ratio to the magnetic permeability of a vacuum) is smaller than that of the substrate 14. The relative magnetic permeability of silver, an example material of the coating 15, is approximately 1.0, which is smaller than that of iron, an example material of the substrate 14. According to Equation 1, the smaller the magnetic permeability μ, the larger the skin depth d. This improves the measurement sensitivity of the partial discharge current C at the electrode 10.

[0039] According to Equation 2, the smaller the current flow path length l, the smaller the resistance value R of the conductor. Due to the skin effect, the partial discharge current C flows mainly along the surface of the electrode 10. The smaller the diameter of the electrode 10 in the R direction and the smaller the thickness of the electrode 10 in the Z direction, the smaller the flow path length l of the partial discharge current C. This reduces the resistance value R of the electrode 10 (coating 15), improving the measurement sensitivity of the partial discharge current C at the electrode 10.

[0040] As described above in detail, the partial discharge detection sensor 1 of the first embodiment has the electrode 10. The electrode 10 is formed in a plate shape and has a first surface 11 which is the front surface and a second surface 12 which is the back surface. The first surface 11 of the electrode 10 is attached to the surface of a box that houses the electric power equipment, and the partial discharge current C to be measured is output from the second surface 12. The electrode 10 has a substrate 14 and a coating 15 that covers the substrate 14. The thickness of the coating 15 is equal to or greater than the skin depth d calculated from the frequency f of the partial discharge current C.

[0041] This configuration ensures a sufficient flow path cross-sectional area S for the partial discharge current C in the coating 15. This reduces the resistance value R of the coating 15 and reduces the attenuation of the partial discharge current C. Since the partial discharge current C becomes apparent compared to the noise current, the measurement sensitivity of the partial discharge current C in the electrode 10 improves. Therefore, the partial discharge detection sensor 1 can detect partial discharges with high accuracy.

[0042] The coating 15 is formed of a material having a conductivity σ greater than that of the substrate 14 . The coating 15 is formed of a material having a skin depth d greater than that of the substrate 14 . The coating 15 is made of a material having a smaller relative magnetic permeability than the substrate 14 . As a result, the resistance value R of the electrode 10 is smaller than when the electrode 10 is made up of only the substrate 14. Therefore, the partial discharge detection sensor 1 can detect partial discharges with high accuracy.

[0043] The coating 15 is made of silver. Silver has a high electrical conductivity σ, a large skin depth d, and a low relative permeability, which reduces the resistance R of the coating 15. Therefore, the partial discharge detection sensor 1 can accurately detect partial discharges.

[0044] (Second embodiment) 2 is a side cross-sectional view of a partial discharge detection sensor 1 of a second embodiment. The partial discharge detection sensor 1 of the second embodiment differs from the first embodiment in that the base material 14 of the electrode 10 is formed of a resin material. Explanation of the second embodiment in respect to the same points as the first embodiment may be omitted.

[0045] The substrate 14 is made of a resin material, which is a dielectric. The substrate 14 is made of, for example, a fluororesin or an epoxy fiber reinforced resin. If the substrate 14 is made of an inexpensive resin material, the cost of the partial discharge detection sensor 1 can be reduced. The resin material of the film 15 is formed by electroless plating, coating, vapor deposition, or the like.

[0046] The resin material, which is a dielectric, functions as a high-pass filter. As described above, the partial discharge current C has a high frequency of 1 MHz or more. The partial discharge current C flows through the coating 15 and penetrates the dielectric substrate 14 in the Z direction. On the other hand, low-frequency noise currents less than 1 MHz are blocked by the dielectric substrate 14 and do not penetrate the substrate 14 in the Z direction. This makes the partial discharge current C more apparent than the noise current. This improves the measurement sensitivity of the partial discharge current C in the electrode 10. The thickness of the substrate 14 in the Z direction is preferably 10 mm or less. This improves the measurement sensitivity of the partial discharge current C.

[0047] As described above in detail, the base material 14 of the second embodiment is made of a resin material. The resin material, which is a dielectric, functions as a high-pass filter, so that the partial discharge current C becomes apparent compared to the noise current. Therefore, the partial discharge detection sensor 1 can detect partial discharge with high accuracy.

[0048] (Third embodiment) 3 is a side cross-sectional view of a partial discharge detection sensor 1 of a third embodiment. The partial discharge detection sensor 1 of the third embodiment differs from the second embodiment in that the partial discharge detection sensor 1 has a coating 15 only on the second surface 12 of the electrode 10. Explanation of the third embodiment in respect to the same points as the second embodiment may be omitted.

[0049] The electrode 10 has a coating 15 only on the second surface 12. The coating 15 is formed only on the second surface 12 of the electrode 10, and is not formed on the first surface 11 or the side surface on the +R side. The method for manufacturing the coating 15 is as follows. The first surface 11 and side surfaces of the electrode 10 are covered with a mask material. The coating 15 is formed on the second surface 12 of the electrode 10 by plating or the like. The mask material covering the first surface 11 and side surfaces of the electrode 10 is removed. As a result, the coating 15 is formed only on the second surface 12 of the electrode 10.

[0050] The substrate 14 is exposed on the first surface 11 of the electrode 10. The +Z side surface of the substrate 14 is attached to the surface of the housing of the power equipment. The substrate 14 is made of a resin material. The resin material, which is a dielectric, functions as a high-pass filter. A partial discharge current C generated in the housing of the power equipment passes through the substrate 14 in the Z direction. The partial discharge current C that passes through the substrate 14 flows into the coating 15 formed on the second surface 12 of the electrode 10 and is output to the core wire 2. On the other hand, low-frequency noise currents below 1 MHz are blocked by the substrate 14 and do not pass through the substrate 14 in the Z direction. As a result, the partial discharge current C is output from the electrode 10 in a state where it is apparent relative to the noise current. The thickness of the substrate 14 in the Z direction is preferably 10 mm or less. This improves the measurement sensitivity of the partial discharge current C.

[0051] As detailed above, the electrode 10 of the third embodiment has the coating 15 on the second surface 12 only. The substrate 14 is exposed on the first surface 11 of the electrode 10. The substrate 14 is made of a resin material. The resin material, which is a dielectric, functions as a high-pass filter, making the partial discharge current C apparent compared to the noise current. Therefore, the partial discharge detection sensor 1 can detect partial discharges with high accuracy.

[0052] (Fourth embodiment) 4 is a side cross-sectional view of a partial discharge detection sensor 1 of a fourth embodiment. The partial discharge detection sensor 1 of the fourth embodiment differs from the first embodiment in that it has a dielectric sheet 16 on the first surface 11 of the electrode 10. Description of the fourth embodiment that is similar to the first embodiment may be omitted.

[0053] The partial discharge detection sensor 1 has a dielectric sheet 16 on the first surface 11 of the electrode 10. The dielectric sheet 16 is formed of a resin material such as fluororesin or epoxy fiber reinforced resin. The thickness of the dielectric sheet 16 in the Z direction is approximately 1 to 2 mm. The dielectric sheet 16 covers all or part of the first surface 11 of the electrode 10. The surface on the +Z side of the dielectric sheet 16 is attached to the surface of the box of the power equipment.

[0054] The dielectric sheet 16 functions as a high-pass filter. A partial discharge current C generated in the housing of the power equipment passes through the dielectric sheet 16 in the Z direction and flows into the electrode 10. On the other hand, a low-frequency noise current of less than 1 MHz is blocked by the dielectric sheet 16 and does not pass through the dielectric sheet 16 in the Z direction. As a result, the partial discharge current C is output from the electrode 10 in a state where it is apparent relative to the noise current. The thickness of the dielectric sheet 16 in the Z direction is preferably 10 mm or less. This improves the measurement sensitivity of the partial discharge current C.

[0055] As described above in detail, the partial discharge detection sensor 1 of the fourth embodiment has the dielectric sheet 16 attached to the first surface 11. Since the dielectric sheet 16 functions as a high-pass filter, the partial discharge current C becomes apparent compared to the noise current, and therefore the partial discharge detection sensor 1 can detect partial discharge with high accuracy.

[0056] (Fifth embodiment) 5 is a side cross-sectional view of a partial discharge detection sensor 1 of a fifth embodiment. In the partial discharge detection sensor 1 of the fifth embodiment, the thickness of the electrode 10 in the Z direction is thinner than that of the first embodiment. Description of the fifth embodiment that is similar to the first embodiment may be omitted.

[0057] The electrode 10 is composed of only a substrate and does not have a coating. The electrode 10 is formed of a conductive metal material. The electrode 10 is formed of, for example, silver or copper. The thickness of the electrode 10 in the Z direction is equal to or less than twice the skin depth d calculated from the frequency of the partial discharge current C. For example, when the frequency of the partial discharge current C is 20 MHz, the skin depth d of silver, an example material of the electrode 10, is approximately 14.1 μm. In this case, the thickness of the electrode 10 is set to 28.2 μm or less, which is equal to or less than twice the skin depth d. Furthermore, when the frequency of the partial discharge current C is 20 MHz, the skin depth d of copper, an example material of the electrode 10, is approximately 15.9 μm. In this case, the thickness of the electrode 10 is set to 31.8 μm or less, which is equal to or less than twice the skin depth d.

[0058] Since the thickness of the electrode 10 is equal to or less than twice the skin depth d, the partial discharge current C flows through the electrode 10 in the Z direction. In Equation 2, the flow path length l of the partial discharge current C becomes smaller, and the resistance value R of the electrode 10 becomes smaller. This reduces the attenuation of the partial discharge current C, improving the measurement sensitivity of the partial discharge current C at the electrode 10.

[0059] As described above in detail, the thickness of the electrode 10 of the fifth embodiment is equal to or less than twice the skin depth d calculated from the frequency f of the partial discharge current C. This improves the measurement sensitivity of the partial discharge current C at the electrode 10. Therefore, the partial discharge detection sensor 1 can detect partial discharge with high accuracy.

[0060] A dielectric sheet 16 similar to that of the fourth embodiment may be attached to the first surface 11 of the electrode 10 of the fifth embodiment. The dielectric sheet 16 functions as a high-pass filter, making the partial discharge current C more apparent than the noise current. Therefore, the partial discharge detection sensor 1 can accurately detect partial discharges.

[0061] At least one of the embodiments described above has the electrode 10 designed in relation to the skin depth d, which allows for accurate detection of partial discharge.

[0062] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention described in the claims and their equivalents. [Explanation of symbols]

[0063] 1...partial discharge detection sensor, 10...electrode, 11...first surface, 12...second surface, 14...substrate, 15...coating, 16...dielectric sheet

Claims

1. an electrode formed in a plate shape, having a first surface as a front surface and a second surface as a back surface, the first surface being attached to a surface of a box that accommodates an electric power device, and outputting a current to be measured from the second surface; The electrode has a substrate and a coating covering the substrate, The thickness of the coating is equal to or greater than a skin depth calculated from the frequency of the current. Partial discharge detection sensor.

2. The coating is formed of a material having a higher electrical conductivity than the substrate. The partial discharge detection sensor according to claim 1 .

3. the coating is formed of a material having a skin depth greater than that of the substrate; The partial discharge detection sensor according to claim 1 or 2.

4. the coating is formed of a material having a relative magnetic permeability smaller than that of the substrate; The partial discharge detection sensor according to claim 1 or 2.

5. The coating is formed of silver. The partial discharge detection sensor according to claim 1 or 2.

6. The substrate is formed of a resin material. The partial discharge detection sensor according to claim 1 or 2.

7. the electrode has the coating only on the second surface; The partial discharge detection sensor according to claim 6.

8. an electrode formed in a plate shape, having a first surface as a front surface and a second surface as a back surface, the first surface being attached to a surface of a box that accommodates an electric power device, and outputting a current to be measured from the second surface; The thickness of the electrode is equal to or less than twice the skin depth calculated from the frequency of the current. Partial discharge detection sensor.

9. a dielectric sheet attached to the first surface; The partial discharge detection sensor according to claim 1 or 8.

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