Sensor and Partial Discharge Measuring Device

Abstract

To provide a sensor capable of detecting current (partial discharge signal) flowing to a metal wall by a partial discharge occurring inside the metal wall, and a partial discharge measuring device having the sensor.SOLUTION: A sensor for detecting current flowing to a metal wall by a partial discharge occurring inside the metal wall includes: an electrode for forming capacitance between an outer surface and itself by approaching an outer surface of the metal wall; a connector electrically connected to the electrode; an attachment for detachably attaching the sensor to an outer surface of the metal wall such that the electrode approaches the outer surface of the metal wall; and an adjustment mechanism for adjusting the capacitance. A partial discharge measuring device includes: the sensor; and a measuring instrument for measuring the partial discharge on the basis of a sensor signal outputted from the connector.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a sensor and a partial discharge measuring device.

Background Art

[0002] In high-voltage electrical equipment (such as transformers, circuit breakers, switchboards, etc.) surrounded by a metal enclosure, the electric field may be locally concentrated inside, and partial discharge may occur. If partial discharge continues to occur, there is a risk of dielectric breakdown. Therefore, a technique for measuring partial discharge, which is a precursor phenomenon of dielectric breakdown, is required.

[0003] Partial discharge is a minute discharge that occurs locally inside a device due to causes such as concentration of electric field stress. Partial discharge progresses the corrosion of the surrounding insulation structure, deteriorates the insulation performance of the device, and may lead to dielectric breakdown.

[0004] As a technique for measuring such partial discharge, a method is known in which a capacitance sensor is attached to the wall surface of the container of electrical equipment and the potential of the wall surface is measured to measure the partial discharge occurring inside the container (see, for example, Patent Document 1). This capacitance sensor includes a counter electrode that forms a capacitance with the wall surface of the container of electrical equipment, and an impedance element connected between the counter electrode and the ground potential portion. When a pulse current flowing to the wall surface due to partial discharge occurring inside the container flows through the above capacitance to the impedance element, a pulse voltage is generated at both ends of the impedance element. The conventional measurement method measures the partial discharge occurring inside the container by measuring this pulse voltage.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] When noise is superimposed on the current flowing through the metal wall due to partial discharge occurring inside the metal wall (hereinafter also referred to as "partial discharge signal"), the signal-to-noise ratio (SN ratio) of the partial discharge signal decreases, resulting in a decrease in the detection accuracy of the partial discharge signal.

[0007] The present disclosure provides a sensor capable of detecting a partial discharge signal with a high SN ratio and a partial discharge measuring device including the sensor.

Means for Solving the Problem

[0008] The present disclosure is a sensor for detecting a current flowing through a metal wall due to partial discharge occurring inside the metal wall, an electrode that forms a capacitance with the outer surface of the metal wall by being close to the outer surface of the metal wall, a connector electrically connected to the electrode, a fixture for detachably attaching the sensor to the outer surface of the metal wall so that the electrode is close to the outer surface of the metal wall, and an adjustment mechanism for adjusting the capacitance.

[0009] The present disclosure also provides a partial discharge measuring device including the sensor and a measuring instrument that measures the partial discharge based on a sensor signal output from the connector.

Advantages of the Invention

[0010] According to the technology of the present disclosure, a current (partial discharge signal) flowing through a metal wall due to partial discharge occurring inside the metal wall can be detected with a high SN ratio.

Brief Description of the Drawings

[0011]

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Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments according to the present disclosure will be described with reference to the drawings.

[0013] FIG. 1 is a diagram showing a configuration example of a partial discharge measurement device according to an embodiment. The partial discharge measurement device 100 shown in FIG. 1 is a device that measures partial discharge generated by a generation source 12 inside a high-voltage device 11 surrounded by a grounded metal housing. The partial discharge measurement device 100 includes a sensor 17 that detects a partial discharge signal such as a pulse current flowing on the surface of the metal housing due to partial discharge, and a measuring instrument 18 that measures the magnitude of the partial discharge and the like based on the sensor signal output from the sensor 17.

[0014] The high-voltage device 11 has a bushing 13 that is electrically connected to a high-voltage power supply 14 via a lead wire 15. The bushing 13 is an example of a high-voltage introduction unit that introduces the high voltage HV supplied from the high-voltage power supply 14 into the high-voltage device 11. The high-voltage device 11 has an internal conductor to which the high voltage HV introduced via the bushing 13 is applied. The high-voltage device 11 is a power device that handles high power, and specific examples thereof include a switchboard, a transformer, a circuit breaker, and the like. The high-voltage device 11 is not limited to these specific examples.

[0015] The high-voltage device 11 has a metal wall 1. The metal wall 1 is a part of the metal housing of the high-voltage device 11. The metal wall 1 is not limited to the wall of the metal housing, and may be the wall of a metal door or the like. The metal wall 1 may have a dielectric coating film.

[0016] The sensor 17 is a detection device that is attached and used on the outer surface 1a of the grounded metal wall 1. The sensor 17 detects partial discharge signals such as pulse currents flowing through the metal wall 1 due to partial discharges occurring inside the metal wall 1 by an electrostatic coupling method, and outputs a sensor signal representing the detection result to a measuring instrument 18. The sensor 17 is also referred to as a TEV (Transient Earth Voltage) sensor. The attachment location of the sensor 17 may be any location on the outer surface 1a of the metal wall 1.

[0017] The sensor 17 includes an electrode 3 that forms a capacitance C with the outer surface 1a by being close to the outer surface 1a of the metal wall 1, a connector 5 electrically connected to the electrode 3, and a fixture 40 that detachably attaches the sensor 17 to the outer surface 1a of the metal wall 1 with a magnet or the like so that the electrode 3 is close to the outer surface 1a of the metal wall 1. The dielectric interposed between the outer surface 1a and the electrode 3 may be a solid such as resin or a gas such as air. Both solid and gas dielectrics may be interposed (for example, when there is a gap between at least one of the outer surface 1a and the electrode 3 and the solid dielectric).

[0018] The sensor 17 detects a partial discharge signal such as a pulse current flowing through the metal wall 1 due to partial discharge by means of the capacitance C, and outputs the partial discharge signal detected by the capacitance C from the connector 5 to the measuring instrument 18 as a sensor signal.

[0019] Based on the sensor signal output from the connector 5 of the sensor 17, the measuring instrument 18 measures the magnitude of partial discharge generated inside the metal wall 1 and the like. The measuring instrument 18 outputs the measurement result of the magnitude of partial discharge and the like to the outside. Thereby, the user can grasp the measurement result. The measuring instrument 18 may output an alarm for notifying deterioration due to partial discharge, for example, when a sensor signal exceeding a predetermined level is detected a predetermined number of times or more. Thereby, the user can take preventive measures such as component replacement before actual insulation breakdown occurs. The measuring instrument 18 may be a measuring instrument itself such as a data logger or an oscilloscope, or a control device equipped with a measuring instrument.

[0020] The measuring instrument 18 has, for example, a memory and a processor (for example, a CPU (Central Processing Unit)). The function of the measuring instrument 18 is realized by the operation of the processor according to a program stored in the memory.

[0021] By the way, the partial discharge signal propagating through the metal wall 1 includes a ground current of a low-frequency component (for example, less than 100 MHz) flowing from the source 12 to the metal wall 1 via the ground wire 16, and a current of a high-frequency component (for example, 100 MHz or more) derived from electromagnetic waves radiated from the source 12 and the like. Also, in the field where the high-voltage device 11 operates, environmental noise such as broadcast waves, inverter surges, and switching surges may occur. Such environmental noise induces a noise current of a low-frequency component (for example, several tens of MHz or less) in the metal wall 1.

[0022] Therefore, as shown in FIG. 2, in a frequency band of several 10 MHz or less, environmental noise such as noise current may be superimposed on the partial discharge signal. If the frequency of the environmental noise superimposed on the partial discharge signal is included in the detection band of the sensor, the sensor will also detect the environmental noise superimposed on the partial discharge signal, resulting in a decrease in the signal-to-noise ratio.

[0023] The sensor 17 according to the present embodiment shown in FIG. 1 includes an adjustment mechanism 19 for automatically or manually adjusting the capacitance C. The adjustment mechanism 19 adjusts the capacitance C by changing at least one of, for example, the area S of the electrode 3 facing the outer surface 1a, the thickness d of the dielectric between the electrode 3 and the outer surface 1a (the distance between the electrode 3 and the outer surface 1a), and the dielectric constant ε of the dielectric.

[0024] By decreasing the capacitance C, the adjustment mechanism 19 can adjust the detection band of the sensor 17 to a frequency band higher than the low-frequency band including the frequency of the environmental noise (see FIG. 2). As a result, the sensor 17 can detect the partial discharge signal with a high signal-to-noise ratio. Consequently, the accuracy of detecting the partial discharge signal by the sensor 17 is improved, and the accuracy of measuring the partial discharge by the measuring instrument 18 is also improved.

[0025] By adjusting the capacitance C, the adjustment mechanism 19 has a wider range for adjusting the detection band of the sensor 17 to the high-frequency side compared to a mechanism (not shown) for adjusting the inductance of the signal line electrically connecting between the outer surface 1a and the connector 5. In the mechanism for adjusting the inductance of the signal line electrically connecting between the outer surface 1a and the connector 5, since the inductance for adjustment increases, it is difficult to shift the detection band of the sensor to the high-frequency region side. In contrast, since the sensor 17 is provided with the adjustment mechanism 19 for adjusting the capacitance C, it can avoid the low-frequency band including the frequency of the environmental noise and extract the high-frequency partial discharge signal with a high signal-to-noise ratio.

[0026] Next, several embodiments of the sensor 17 will be described.

[0027] FIG. 3 is a cross-sectional view showing a configuration example of the sensor according to the first embodiment. The sensor 17A shown in FIG. 3 is an example of the above-described sensor 17. The sensor 17A is attached to the outer surface 1a of the grounded metal wall 1, and detects a partial discharge signal generated in the metal wall 1 due to partial discharge occurring inside the metal wall 1 (on the side opposite to the outer surface 1a).

[0028] The sensor 17A includes an electrode 3, a connector 5, a case 2, a magnet 8, a dielectric 7, and an adjustment mechanism 19A.

[0029] The electrode 3 forms a capacitance C with the outer surface 1a by approaching the outer surface 1a of the metal wall 1. The electrode 3 is, for example, a flat conductor.

[0030] The connector 5 is electrically connected to the electrode 3. In this example, the connector 5 is electrically connected to the electrode 3 via a conducting wire 6. The connector 5 has, for example, one end of a coaxial cable connected thereto, and the other end of the coaxial cable is connected to the above-described measuring instrument 18 (FIG. 1). The signal line of the coaxial cable is electrically connected to the electrode 3 via the conducting wire 6, and the shield wire of the coaxial cable is electrically connected to the case 2.

[0031] The case 2 is a conductive container that houses the electrode 3 and the conducting wire 6 and supports the connector 5. The case 2 functions as a shield case for suppressing external noise.

[0032] The dielectric 7 is a plate-like member that forms the bottom wall of the sensor 17A. The dielectric 7 may be a part of the housing of the sensor 17A or a substrate assembled to the case 2. The electrode 3 contacts the upper surface of the dielectric 7. Thereby, variations in the capacitance C are suppressed, and the detection accuracy of the partial discharge signal is improved. Further, since the case 2 and the electrode 3 are electrically insulated by the dielectric 7, the dielectric 7 can prevent the partial discharge signal passing through the electrode 3 from leaking into the case 2.

[0033] The magnet 8 is an example of the above-mentioned fixture 40 (Fig. 1). The magnet 8 detachably attaches the sensor 17A to the outer surface 1a such that the dielectric 7 is interposed between the electrode 3 and the outer surface 1a. Thereby, compared with the form in which the dielectric between the outer surface 1a and the electrode 3 is a gas such as air, the variation in the capacitance C is suppressed, so that the detection accuracy of the partial discharge signal is improved.

[0034] The magnet 8 detachably attaches the sensor 17A to the outer surface 1a of the metal wall 1 such that the dielectric 7 contacts the outer surface 1a of the metal wall 1. Due to the contact between the dielectric 7 and the outer surface 1a, the variation in the capacitance C is suppressed, so that the detection accuracy of the partial discharge signal is improved.

[0035] In the example shown in Fig. 3, in order to attach the sensor 17A to the metal wall 1, the magnet 8 is embedded in a hole formed in the dielectric 7 of the sensor 17A. The hole formed in the dielectric 7 may penetrate the dielectric 7 or may have a bottom so as not to penetrate the dielectric 7. Since the position of the magnet 8 is fixed at the bottom of the hole, the attachment of the magnet 8 becomes easy.

[0036] In the example shown in Fig. 3, the sensor 17A adheres to the outer surface 1a of the metal wall 1 by utilizing the attractive force of the magnet 8, and the bottom surface of the dielectric 7 contacts the outer surface 1a. The upper surface of the dielectric 7 contacts the electrode 3. That is, a capacitor structure in which the dielectric 7 is interposed between the electrode 3 and the outer surface 1a is obtained. The sensor 17A detects a partial discharge signal by this capacitor structure, and transmits the detected partial discharge signal to the measuring instrument 18 via the lead wire 6 and the connector 5.

[0037] The adjustment mechanism 19A is an example of the above-mentioned adjustment mechanism 19 (Fig. 1) for adjusting the capacitance C. The adjustment mechanism 19A changes the area S of the surface of the electrode 3 facing the outer surface 1a through the dielectric 7 to adjust the capacitance C. In the example shown in Fig. 3, the electrode 3 includes a fixed electrode 9 and a movable electrode 10. The fixed electrode 9 is an example of the first electrode, and the movable electrode 10 is an example of the second electrode.

[0038] FIG. 4 is a diagram showing a configuration example of the adjustment mechanism 19A. FIG. 4(a) is a schematic diagram showing the adjustment mechanism 19A in a plan view. FIG. 4(b) is a schematic diagram showing the adjustment mechanism 19A in a side view. The adjustment mechanism 19A changes the area S of the opposing surfaces of the fixed electrode 9 and the movable electrode 10 with respect to the outer surface 1a of the metal wall 1 via the dielectric 7 by moving the movable electrode 10, and adjusts the capacitance C.

[0039] In this example, the adjustment mechanism 19A has a rotating shaft 4 for rotating the movable electrode 10. The adjustment mechanism 19A rotates the movable electrode 10 by rotating the rotating shaft 4 manually or by a motor. The adjustment mechanism 19A changes the area S of the opposing surfaces of the fixed electrode 9 and the movable electrode 10 with respect to the outer surface 1a of the metal wall 1 via the dielectric 7 by rotating the movable electrode 10, and adjusts the capacitance C.

[0040] In the plan view of the fixed electrode 9 and the movable electrode 10, the adjustment mechanism 19A changes the area S of the opposing surfaces of the fixed electrode 9 and the movable electrode 10 with respect to the outer surface 1a of the metal wall 1 via the dielectric 7 by overlapping the fixed electrode 9 and the movable electrode 10, and adjusts the capacitance C. By overlapping the fixed electrode 9 and the movable electrode 10, the adjustment mechanism 19A can be miniaturized.

[0041] The fixed electrode 9 is fixed to the upper surface of the dielectric 7 with an adhesive or the like. The fixed electrode 9 and the movable electrode 10 have the same semi-circular shape, and the rotating shaft 4 is fixed to the center of the diameter of the movable electrode 10 with an adhesive or the like. The conducting wire 6 is fixed to the fixed electrode 9 with solder or the like, and is fixed to the outer edge of the fixed electrode 9, for example, as shown in FIG. 5.

[0042] FIG. 5 is a diagram illustrating the capacitance adjustment operation in the adjustment mechanism. When the rotating shaft 4 protruding outside the sensor 17A is rotated clockwise in a plan view, the effective area of the electrode 3 can be changed, and the capacitance C of the capacitor structure described above can be adjusted.

[0043] When the shapes of the fixed electrode 9 and the movable electrode 10 in plan view are semi-circular and the area of the semi-circle is S1, when the rotation axis 4 rotates by about 180°, the effective area of the electrode 3 becomes about 2×S1. As a result, the capacitance C of the capacitor structure is doubled, and the signal detection band of the sensor 17 can be adjusted. Note that the shapes of the fixed electrode 9 and the movable electrode 10 are not limited to semi-circular shapes.

[0044] FIG. 6 is a diagram illustrating the relationship between the rotation angle of the movable electrode 10 and the capacitance C. The adjustment mechanism 19A increases the rotation angle of the movable electrode 10, so that the effective area of the electrode 3 becomes wider, and thus the capacitance C increases.

[0045] Note that the adjustment mechanism 19A adjusts the capacitance C by moving one of the pair of electrodes (in this example, the movable electrode 10), but the capacitance C may also be adjusted by moving both electrodes.

[0046] FIG. 7 is a cross-sectional view showing a configuration example of the sensor according to the second embodiment. The sensor 17B shown in FIG. 7 is an example of the above-described sensor 17. The sensor 17B is attached to the outer surface 1a of the grounded metal wall 1 and detects a partial discharge signal generated in the metal wall 1 due to partial discharge occurring inside the metal wall 1 (on the side opposite to the outer surface 1a). In the second embodiment, the description of the same configuration as in the above-described embodiment is omitted by referring to the above description.

[0047] The sensor 17B includes an electrode 3, a connector 5, a case 2, a magnet 8, a dielectric 7, and an adjustment mechanism 19B.

[0048] The adjustment mechanism 19B is an example of the above-described adjustment mechanism 19 (FIG. 1) that adjusts the capacitance C. The adjustment mechanism 19A adjusts the capacitance C by changing the effective area S in which the electrode 3 faces the outer surface 1a via the dielectric 7. In the example shown in FIG. 7, the electrode 3 includes a plurality of partial electrodes 31 to 35.

[0049] The plurality of partial electrodes 31 to 36 are fixed to the upper surface of the dielectric 7 with an adhesive or the like in a state where they are spaced apart from each other and do not contact. In the example shown in FIG. 7, the electrode 3 includes six partial electrodes 31 to 36 having the same shape. The number of partial electrodes may be plural and is not limited to six.

[0050] The adjustment mechanism 19B has at least one switch element (in this example, five switch elements 21 to 25, which is one less than the number of partial electrodes 31 to 36) for switching between conduction and non-conduction between the plurality of partial electrodes 31 to 36. The adjustment mechanism 19B changes the effective area S in which the plurality of partial electrodes 31 to 36 face the outer surface 1a via the dielectric 7 by turning on or off each of the plurality of switch elements 21 to 25, and adjusts the capacitance C.

[0051] In this example, adjacent partial electrodes among the plurality of partial electrodes 31 to 36 are connected in parallel via the conducting wire 6 and the switch elements 21 to 25. The switch elements 21 to 25 are provided in the case 2 and are independently turned on or off by a manual or a driving circuit (not shown).

[0052] FIG. 8 is a diagram illustrating combinations of on or off states of the plurality of switch elements 21 to 25 in each switch element state S1 to S6. FIG. 9 is a diagram illustrating the relationship between each switch element state S1 to S6 and the capacitance C. When all of the switch elements 21 to 25 are in the off state, the effective area S of the sensor 17B becomes the area s1 of one partial electrode 31. When the switch elements 21 to 25 in the all-off state are turned on in ascending order, the effective area S expands by s1 each time, and the capacitance C increases. When the switch elements 21 to 25 in the all-on state are turned off in descending order, the effective area S shrinks by s1 each time, and the capacitance C decreases.

[0053] FIG. 10 is a cross-sectional view showing a configuration example of a sensor according to the third embodiment. The sensor 17C shown in FIG. 10 is an example of the above-described sensor 17. The sensor 17C is attached to the outer surface 1a of the grounded metal wall 1, and detects a partial discharge signal generated in the metal wall 1 due to partial discharge occurring inside the metal wall 1 (on the side opposite to the outer surface 1a). In the third embodiment, the description of the same configuration as that in the above-described embodiment is omitted by referring to the above description.

[0054] The sensor 17C includes an electrode 3, a connector 5, a case 2, a magnet 8, a dielectric 7, and an adjustment mechanism 19C.

[0055] The adjustment mechanism 19C is an example of the above-described adjustment mechanism 19 (FIG. 1) that adjusts the capacitance C. The adjustment mechanism 19C adjusts the capacitance C by changing the distance d at which the electrode 3 faces the outer surface 1a via the dielectric 7. For example, the adjustment mechanism 19C changes the distance d by moving the electrode 3.

[0056] In the example shown in FIG. 10, the adjustment mechanism 19C has a moving mechanism 43 that moves the electrode 3 in the direction in which the distance d changes. The moving mechanism 43 includes a rod 42 that moves in the direction in which the distance d changes, a support portion 44 that supports the rod 42, and a screw 41 that fixes the rod 42 to the support portion 44. The rod 42 is a member for adjusting the height of the electrode 3 from the dielectric 7. The tip of the rod 42 is fixed to the main surface of the electrode 3 with an adhesive or the like. The support portion 44 is a cylindrical portion fixed to the outside of the case 2. The middle portion of the rod 42 passing through the case 2 passes through the hollow portion of the cylindrical support portion 44 and is fixed to the inner wall of the support portion 44 by a screw 41 that enters from the side surface of the support portion 44 into the hollow portion. By loosening the screw 41, the rod 42 can move in the direction in which the distance d changes. When the rod 42 moves in the vertical direction, the distance d changes.

[0057] The adjustment mechanism 19C moves the rod 42 manually or by a motor in the vertical direction with the screw 41 loosened, thereby moving the electrode 3 in the vertical direction (see FIG. 11). By moving the electrode 3 in the vertical direction, the adjustment mechanism 19C changes the distance d1 between the electrode 3 and the dielectric 7 and adjusts the capacitance C. The adjustment mechanism 19C stops the vertical movement of the rod 42 in a state where the target capacitance C is obtained at the distance d (distance d1), and fixes the rod 42 to the support portion 44 by tightening the screw 41.

[0058] FIG. 12 is a diagram illustrating the relationship between the distance d1 and the capacitance C. As the distance d1 increases, the distance d between the electrode 3 and the outer surface 1a increases, so the capacitance C decreases.

[0059] Although the embodiments have been described above, the technology of the present disclosure is not limited to the above embodiments. Various modifications and improvements such as combinations and substitutions with some or all of other embodiments are possible.

Explanation of Reference Numerals

[0060] 1 Metal wall 1a Outer surface 2 Case 3 Electrode 4 Rotating shaft 5 Connector 6 Conductive wire 7 Dielectric 8 Magnet 9 Fixed electrode 10 Movable electrode 11 High-voltage device 12 Generation source 13 Bushings 14 High-voltage power supply 15 Lead wire 16 Ground wire 17, 17B, 17C Sensors 18 Measuring instrument 19, 19A, 19B, 19C Adjustment mechanisms 21, 22, 23, 24, 25 Switch elements 31, 32, 33, 34, 35 Partial electrodes 40 Fixture 41 Screw 42 Rod 43 Moving mechanism 44 Support part 100 Partial discharge measurement device

Claims

1. A sensor for detecting a current flowing through a metal wall due to partial discharge occurring inside the metal wall, comprising: an electrode that forms a capacitance with the outer surface of the metal wall by being close to the outer surface of the metal wall; a connector electrically connected to the electrode; a fixture for removably attaching the sensor to the outer surface of the metal wall such that the electrode is close to the outer surface of the metal wall; an adjustment mechanism for adjusting the capacitance; a dielectric; a conductive case for housing the electrode, wherein the case and the electrode are electrically insulated by the dielectric, and the fixture removably attaches the sensor to the outer surface of the metal wall such that the dielectric is interposed between the electrode and the outer surface of the metal wall.

2. The sensor according to claim 1, wherein the dielectric forms a bottom wall of the sensor.

3. The sensor according to claim 2, wherein the dielectric is a plate-like member forming the bottom wall.

4. The sensor according to claim 1, wherein the dielectric is part of a housing of the sensor.

5. A sensor for detecting a current flowing through a metal wall due to partial discharge occurring inside the metal wall, comprising: an electrode that forms a capacitance with the outer surface of the metal wall by being close to the outer surface of the metal wall; a connector electrically connected to the electrode; a fixture for removably attaching the sensor to the outer surface of the metal wall such that the electrode is close to the outer surface of the metal wall; an adjustment mechanism for adjusting the capacitance; a substrate that is a dielectric, wherein the fixture removably attaches the sensor to the outer surface of the metal wall such that the dielectric is interposed between the electrode and the outer surface of the metal wall.

6. The sensor according to any one of claims 1 to 5, wherein the fixture removably attaches the sensor to the outer surface of the metal wall such that the dielectric contacts the outer surface of the metal wall.

7. The sensor according to any one of claims 1 to 6, wherein the electrode contacts the dielectric.

8. The sensor according to claim 7, wherein the electrode contacts an upper surface of the dielectric.

9. The case functions as a shield case, according to claim 1 of the sensor.

10. The sensor according to claim 1, wherein the case supports the connector.

11. The sensor according to any one of claims 1 to 10, wherein the adjustment mechanism adjusts the capacitance by changing the area of the electrode facing the outer surface.

12. The electrode includes a first electrode and a second electrode, The sensor according to claim 11, wherein the adjustment mechanism changes the area of the first electrode and the second electrode facing the outer surface by moving at least one of the movable electrodes of the first electrode and the second electrode, and adjusts the capacitance.

13. A sensor for detecting a current flowing through a metal wall due to partial discharge occurring inside the metal wall, An electrode that forms a capacitance with the outer surface by being close to the outer surface of the metal wall, A connector electrically connected to the electrode, A fixture for detachably attaching the sensor to the outer surface of the metal wall so that the electrode is close to the outer surface of the metal wall, An adjustment mechanism for adjusting the capacitance, The electrode includes a first electrode and a second electrode, The adjustment mechanism has a rotating shaft for rotating at least one of the movable electrodes of the first electrode and the second electrode, and by rotating the rotating shaft, the area of the first electrode and the second electrode facing the outer surface is changed, and the capacitance is adjusted. Sensor.

14. A sensor for detecting a current flowing through a metal wall due to partial discharge occurring inside the metal wall, An electrode that forms a capacitance with the outer surface by being close to the outer surface of the metal wall, A connector electrically connected to the electrode, A fixture for detachably attaching the sensor to the outer surface of the metal wall so that the electrode is close to the outer surface of the metal wall, An adjustment mechanism for adjusting the capacitance, The electrode includes a first electrode and a second electrode, At least one of the first electrode and the second electrode is a movable electrode, The adjustment mechanism changes the area of the first electrode and the second electrode facing the outer surface by overlapping the first electrode and the second electrode, and adjusts the capacitance. Sensor.

15. The first electrode is a fixed electrode, The sensor according to any one of claims 12 to 14, wherein the second electrode is a movable electrode.

16. The electrode includes a plurality of partial electrodes, The adjustment mechanism has at least one switch element for switching between conduction and non-conduction between the plurality of partial electrodes, and by turning on or off the switch element, the effective area of the plurality of partial electrodes facing the outer surface is changed to adjust the capacitance. The sensor according to claim 11.

17. The adjustment mechanism adjusts the capacitance by changing the distance at which the electrode faces the outer surface. The sensor according to any one of claims 1 to 10.

18. The adjustment mechanism changes the distance by moving the electrode. The sensor according to claim 17.

19. The adjustment mechanism has a rod fixed to the electrode and a moving mechanism for moving the rod to move the electrode. The sensor according to claim 18.

20. A sensor according to any one of claims 1 to 19, and a measuring instrument for measuring the partial discharge based on the sensor signal output from the connector. A partial discharge measuring device.

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