JP7697237B2 - Sensor and partial discharge measuring device - Google Patents

Description

This disclosure relates to a sensor and a partial discharge measuring device.

In high-voltage power equipment (e.g., transformers, circuit breakers, switchboards, etc.) enclosed in a metal housing, electric fields can concentrate locally inside the equipment, causing partial discharges. If partial discharges continue to occur, it may lead to insulation breakdown, so there is a demand for technology to measure partial discharges that occur as a precursor to insulation breakdown.

Partial discharges are tiny discharges that occur locally inside equipment due to factors such as the concentration of electric field stress. Partial discharges accelerate the corrosion of the surrounding insulation structure, reducing the insulation performance of the equipment and potentially leading to dielectric breakdown.

As a technique for measuring such partial discharges, a method is known in which a capacitance sensor is attached to the wall surface of the container of the electric power equipment and the potential of the wall surface is measured to measure partial discharges occurring within the container (see, for example, Patent Document 1). This capacitance sensor has a counter electrode that forms a capacitance with the wall surface of the container of the electric power equipment, and an impedance element connected between the counter electrode and a ground potential portion. When a pulse current that flows on the wall surface due to partial discharges occurring within the container flows through the impedance element via the above-mentioned capacitance, a pulse voltage is generated across both ends of the impedance element. Conventional measurement methods measure partial discharges occurring within the container by measuring this pulse voltage.

JP 2011-149896 A

Some noise may be superimposed on the current (hereinafter referred to as the "partial discharge signal") that flows through a metal wall due to partial discharges that occur inside the metal wall. If the frequency of the noise superimposed on the partial discharge signal is included in the detection band of the sensor, the ratio of the partial discharge signal to noise (signal-to-noise ratio) decreases, and the detection accuracy of the partial discharge signal decreases.

This disclosure provides a sensor capable of detecting partial discharge signals with a high signal-to-noise ratio and a partial discharge measuring device equipped with the sensor.

The present disclosure relates to
A sensor for detecting a current flowing through a metal wall due to a partial discharge occurring inside the metal wall,
an electrode that is in close proximity to an outer surface of the metal wall to form a capacitance between the electrode and the outer surface;
a connector electrically connected to the electrode;
a mounting tool for removably mounting the sensor to the outer surface of the metal wall so that the electrode is proximate to the outer surface of the metal wall;
and an adjustment mechanism for adjusting the capacitance.

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

The technology disclosed herein makes it possible to detect with a high signal-to-noise ratio the current (partial discharge signal) that flows through a metal wall due to partial discharges that occur inside the metal wall.

FIG. 1 is a diagram illustrating an example of the configuration of a partial discharge measuring device according to an embodiment. 11A and 11B are diagrams for explaining adjustment of the detection band of the sensor by adjusting the capacitance. FIG. 2 is a cross-sectional view showing a configuration example of a sensor according to the first embodiment. 5A to 5C are diagrams illustrating an example of the configuration of a capacitance adjustment mechanism in the sensor according to the first embodiment. 11A to 11C are diagrams illustrating an example of an adjustment operation of the capacitance in the adjustment mechanism. 11 is a diagram illustrating an example of the relationship between the rotation angle of the movable electrode and the electrostatic capacitance. FIG. 11 is a cross-sectional view showing an example of the configuration of a sensor according to a second embodiment. 11A and 11B are diagrams illustrating combinations of on and off states of a plurality of switch elements in each switch element state. 5 is a diagram illustrating an example of the relationship between the state of each switch element and capacitance. FIG. FIG. 11 is a cross-sectional view showing an example of the configuration of a sensor according to a third embodiment. 13A to 13C are diagrams illustrating an example of the operation of the capacitance adjustment mechanism in the sensor according to the third embodiment. 10 is a diagram illustrating an example of the relationship between the distance between an electrode and a dielectric and the capacitance.

Embodiments of the present disclosure will be described below with reference to the drawings.

Figure 1 is a diagram showing an example of the configuration of a partial discharge measuring device according to one embodiment. The partial discharge measuring device 100 shown in Figure 1 is a device that measures partial discharges that occur at a source 12 inside a high-voltage device 11 that is surrounded by a grounded metal housing. The partial discharge measuring device 100 includes a sensor 17 that detects partial discharge signals such as a pulse current that flows on the surface of the metal housing due to partial discharge, and a measuring device 18 that measures the magnitude of the partial discharge based on the sensor signal output from the sensor 17.

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

The high-voltage equipment 11 has a metal wall 1. The metal wall 1 is part of the metal housing of the high-voltage equipment 11. The metal wall 1 is not limited to the wall of a metal housing, but may be the wall of a metal door, etc. The metal wall 1 may have a dielectric coating.

The sensor 17 is a detection device that is attached to the outer surface 1a of the grounded metal wall 1. The sensor 17 detects partial discharge signals, such as pulse currents that flow through the metal wall 1 due to partial discharges that occur inside the metal wall 1, using an electrostatic coupling method, and outputs a sensor signal that represents the detection result to the measuring instrument 18. The sensor 17 is also called a TEV (Transient Earth Voltage) sensor. The sensor 17 may be attached anywhere on the outer surface 1a of the metal wall 1.

The sensor 17 includes an electrode 3 that forms a capacitance C between itself and the outer surface 1a of the metal wall 1 by coming close to the outer surface 1a, a connector 5 electrically connected to the electrode 3, and a mounting fixture 40 that detachably mounts the sensor 17 to the outer surface 1a of the metal wall 1 with a magnet or the like so that the electrode 3 comes 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).

The sensor 17 detects partial discharge signals, such as a pulse current that flows through the metal wall 1 due to partial discharge, using capacitance C, and outputs the partial discharge signal detected by capacitance C from connector 5 to the measuring instrument 18 as a sensor signal.

The measuring device 18 measures the magnitude of partial discharges that have occurred inside the metal wall 1, etc., based on the sensor signal output from the connector 5 of the sensor 17. The measuring device 18 outputs the measurement results, such as the magnitude of partial discharges, to the outside. This allows the user to understand the measurement results. For example, if a sensor signal exceeding a predetermined level is detected a predetermined number of times or more, the measuring device 18 may output an alarm to notify of deterioration due to partial discharge. This allows the user to take preventive measures, such as replacing parts, before insulation breakdown actually occurs. The measuring device 18 may be a measuring device itself, such as a data logger or oscilloscope, or it may be a control device equipped with a measuring device.

The measuring device 18 has, for example, a memory and a processor (e.g., a CPU (Central Processing Unit)). The functions of the measuring device 18 are realized by the processor operating according to a program stored in the memory.

Incidentally, the partial discharge signal propagating through the metal wall 1 contains a ground current with low frequency components (e.g., less than 100 MHz) that flows from the source 12 through the ground wire 16 to the metal wall 1, and a current with high frequency components (e.g., 100 MHz or higher) that originate from electromagnetic waves radiated from the source 12. In addition, at the site where the high-voltage equipment 11 is in operation, environmental noise such as broadcast waves, inverter surges, and switching surges may occur. Such environmental noise induces a noise current with low frequency components (e.g., several tens of MHz or less) in the metal wall 1.

As a result, as shown in Figure 2, in frequency bands of several tens of MHz or less, environmental noise such as noise currents 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 reduced signal-to-noise ratio.

The sensor 17 according to this embodiment shown in FIG. 1 includes an adjustment mechanism 19 that automatically or manually adjusts the capacitance C. The adjustment mechanism 19 adjusts the capacitance C by, for example, changing at least one of 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.

By reducing 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 region that includes the frequencies of environmental noise (see FIG. 2). This allows the sensor 17 to detect partial discharge signals with a high signal-to-noise ratio. As a result, the accuracy of the detection of partial discharge signals by the sensor 17 is improved, and the accuracy of the measurement of partial discharges by the measuring device 18 is also improved.

By adjusting the capacitance C, the adjustment mechanism 19 adjusts the detection band of the sensor 17 to a wider range toward higher frequencies than a mechanism (not shown) that adjusts the inductance of the signal line that electrically connects the outer surface 1a and the connector 5. With a mechanism that adjusts the inductance of the signal line that electrically connects the outer surface 1a and the connector 5, the inductance required for the adjustment increases, making it difficult to shift the detection band of the sensor toward the higher frequency range. In contrast, the sensor 17 is equipped with an adjustment mechanism 19 that adjusts the capacitance C, and thus can extract high-frequency partial discharge signals with a high signal-to-noise ratio, avoiding the low-frequency range that includes the frequencies of environmental noise.

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

Figure 3 is a cross-sectional view showing an example of the configuration of a sensor according to the first embodiment. Sensor 17A shown in Figure 3 is an example of the sensor 17 described above. Sensor 17A is attached to the outer surface 1a of a grounded metal wall 1, and detects a partial discharge signal that occurs in the metal wall 1 due to a partial discharge that occurs inside the metal wall 1 (the side opposite to the outer surface 1a).

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

The electrode 3 is in close proximity to the outer surface 1a of the metal wall 1, forming a capacitance C between the electrode 3 and the outer surface 1a. The electrode 3 is, for example, a flat conductor.

The connector 5 is electrically connected to the electrode 3, and in this example, is electrically connected to the electrode 3 via a conductor 6. For example, one end of a coaxial cable is connected to the connector 5, and the other end of the coaxial cable is connected to the measuring instrument 18 (Figure 1) described above. The signal line of the coaxial cable is electrically connected to the electrode 3 via the conductor 6, and the shield wire of the coaxial cable is electrically connected to the case 2.

Case 2 is a conductive container that houses electrodes 3 and conductors 6 and supports connector 5. Case 2 functions as a shielding case that suppresses external noise.

The dielectric 7 is a plate-like member that forms the bottom wall of the sensor 17A. The dielectric 7 may be part of the housing of the sensor 17A, or may be a substrate attached to the case 2. The electrode 3 contacts the upper surface of the dielectric 7. This reduces the variation in capacitance C, improving the detection accuracy of the partial discharge signal. In addition, the case 2 and the electrode 3 are electrically insulated by the dielectric 7, so that the dielectric 7 can prevent the partial discharge signal that passes through the electrode 3 from leaking into the case 2.

The magnet 8 is an example of the mounting fixture 40 (Figure 1) described above. The magnet 8 detachably mounts the sensor 17A to the outer surface 1a so that the dielectric 7 is interposed between the electrode 3 and the outer surface 1a. This reduces the variation in capacitance C compared to a configuration in which the dielectric between the outer surface 1a and the electrode 3 is a gas such as air, improving the detection accuracy of the partial discharge signal.

The magnet 8 removably attaches the sensor 17A to the outer surface 1a of the metal wall 1 so that the dielectric 7 contacts the outer surface 1a of the metal wall 1. The contact between the dielectric 7 and the outer surface 1a reduces the variation in capacitance C, improving the detection accuracy of the partial discharge signal.

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 drilled in the dielectric 7 of the sensor 17A. The hole drilled in the dielectric 7 may pass through the dielectric 7, or may have a bottom so as not to pass through the dielectric 7. The position of the magnet 8 is fixed at the bottom of the hole, making it easy to attach the magnet 8.

In the example shown in FIG. 3, the sensor 17A is attached to the outer surface 1a of the metal wall 1 using the attractive force of the magnet 8, and the bottom surface of the dielectric 7 contacts the outer surface 1a. The top surface of the dielectric 7 contacts the electrode 3. In other words, a capacitor structure is obtained in which the dielectric 7 is interposed between the electrode 3 and the outer surface 1a. 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 conductor 6 and the connector 5.

The adjustment mechanism 19A is an example of the above-mentioned adjustment mechanism 19 (FIG. 1) that adjusts the capacitance C. The adjustment mechanism 19A changes the area S of the electrode 3 facing the outer surface 1a via the dielectric 7, thereby adjusting 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 a first electrode, and the movable electrode 10 is an example of a second electrode.

Figure 4 shows an example of the configuration of the adjustment mechanism 19A. Figure 4(a) is a schematic diagram showing the adjustment mechanism 19A in a plan view. Figure 4(b) is a schematic diagram showing the adjustment mechanism 19A in a side view. The adjustment mechanism 19A moves the movable electrode 10 to change the area S over which the fixed electrode 9 and the movable electrode 10 face the outer surface 1a of the metal wall 1 via the dielectric 7, thereby adjusting the capacitance C.

In this example, the adjustment mechanism 19A has a rotating shaft 4 that rotates the movable electrode 10. The adjustment mechanism 19A rotates the rotating shaft 4 manually or with a motor to rotate the movable electrode 10. By rotating the movable electrode 10, the adjustment mechanism 19A changes the area S where the fixed electrode 9 and the movable electrode 10 face the outer surface 1a of the metal wall 1 via the dielectric 7, thereby adjusting the capacitance C.

The adjustment mechanism 19A overlaps the fixed electrode 9 and the movable electrode 10 in a plan view of the fixed electrode 9 and the movable electrode 10 to change the area S over which the fixed electrode 9 and the movable electrode 10 face the outer surface 1a of the metal wall 1 via the dielectric 7, thereby adjusting the capacitance C. By overlapping the fixed electrode 9 and the movable electrode 10, the adjustment mechanism 19A can be made smaller.

The fixed electrode 9 is fixed to the top surface of the dielectric 7 with adhesive or the like. The fixed electrode 9 and the movable electrode 10 have the same semicircular shape, and the rotating shaft 4 is fixed to the diametric center of the movable electrode 10 with adhesive or the like. The conducting wire 6 is fixed to the fixed electrode 9 with solder or the like, for example, to the outer edge of the fixed electrode 9 as shown in FIG. 5.

Figure 5 is a diagram illustrating the capacitance adjustment operation in the adjustment mechanism. By rotating the rotating shaft 4 protruding outside the sensor 17A clockwise in a plan view, the effective area of the electrode 3 can be changed, and the capacitance C of the above-mentioned capacitor structure can be adjusted.

If the shape of the fixed electrode 9 and the movable electrode 10 in a plan view is a semicircle and the area of the semicircle is _S1 , then when the rotation shaft 4 rotates by approximately 180°, the effective area of the electrode 3 becomes approximately 2× _S1 . This doubles the capacitance C of the capacitor structure, making it possible to adjust the signal detection band of the sensor 17. Note that the shapes of the fixed electrode 9 and the movable electrode 10 are not limited to semicircles.

Figure 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, thereby increasing the effective area of the electrode 3 and thus the capacitance C.

The adjustment mechanism 19A adjusts the capacitance C by moving one of the pair of electrodes (in this example, the movable electrode 10), but it may also adjust the capacitance C by moving both electrodes.

Figure 7 is a cross-sectional view showing an example of the configuration of a sensor according to the second embodiment. Sensor 17B shown in Figure 7 is an example of the sensor 17 described above. Sensor 17B is attached to the outer surface 1a of a grounded metal wall 1, and detects a partial discharge signal that occurs in the metal wall 1 due to a partial discharge that occurs inside the metal wall 1 (the side opposite to the outer surface 1a). In the second embodiment, the description of the same configuration as in the above embodiment will be omitted by invoking the above description.

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

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

The multiple partial electrodes 31-36 are fixed to the upper surface of the dielectric 7 with adhesive or the like, with a gap between them and without contact. In the example shown in FIG. 7, the electrode 3 includes six partial electrodes 31-36 of the same shape. The number of partial electrodes may be any number and is not limited to six.

The adjustment mechanism 19B has at least one switch element (in this example, five switch elements 21-25, one less than the number of partial electrodes 31-36) that switches between conduction and non-conduction between the partial electrodes 31-36. The adjustment mechanism 19B changes the effective area S of the partial electrodes 31-36 facing the outer surface 1a via the dielectric 7 by turning on or off each of the multiple switch elements 21-25, thereby adjusting the capacitance C.

In this example, adjacent partial electrodes among the multiple partial electrodes 31 to 36 are connected in parallel via the conductor 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 manually or by a drive circuit (not shown).

8 is a diagram illustrating an example of combinations of on/off states of the multiple switch elements 21 to 25 in the switch element states S1 to S6. FIG. 9 is a diagram illustrating the relationship between the switch element states S1 to S6 and the capacitance C. When the switch elements 21 to 25 are all in the off state, the effective area S of the sensor 17B is the area _s1 of one partial electrode 31. When the switch elements 21 to 25 that are all in the off state are turned on in ascending order, the effective area S increases by _s1 and the capacitance C increases. When the switch elements 21 to 25 that are all in the on state are turned off in descending order, the effective area S decreases by _s1 and the capacitance C decreases.

Figure 10 is a cross-sectional view showing an example of the configuration of a sensor according to the third embodiment. Sensor 17C shown in Figure 10 is an example of the sensor 17 described above. Sensor 17C is attached to the outer surface 1a of a grounded metal wall 1, and detects a partial discharge signal that occurs in the metal wall 1 due to a partial discharge that occurs inside the metal wall 1 (the side opposite to the outer surface 1a). In the third embodiment, the description of the same configuration as in the above-mentioned embodiments will be omitted by invoking the above description.

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

The adjustment mechanism 19C is an example of the above-mentioned 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.

In the example shown in FIG. 10, the adjustment mechanism 19C has a movement mechanism 43 that moves the electrode 3 in a direction in which the distance d changes. The movement mechanism 43 has a rod 42 that moves in a direction in which the distance d changes, a support part 44 that supports the rod 42, and a screw 41 that fixes the rod 42 to the support part 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 adhesive or the like. The support part 44 is a cylindrical part fixed to the outside of the case 2. The middle part of the rod 42 that penetrates the case 2 penetrates the hollow part of the cylindrical support part 44 and is fixed to the inner wall of the support part 44 by the screw 41 that penetrates from the side of the support part 44 toward the hollow part. By loosening the screw 41, the rod 42 can be moved in a direction in which the distance d changes. The distance d changes as the rod 42 moves up and down.

With the screw 41 loosened, the adjustment mechanism 19C moves the rod 42 vertically, either manually or by a motor, to move the electrode 3 vertically (see FIG. 11). By moving the electrode 3 vertically, 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 at the distance d (distance d1) at which the target capacitance C is obtained, and fixes the rod 42 to the support part 44 by tightening the screw 41.

Figure 12 is a diagram illustrating the relationship between distance d1 and capacitance C. As distance d1 increases, the distance d between electrode 3 and outer surface 1a increases, and therefore capacitance C decreases.

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

REFERENCE SIGNS LIST 1 metal wall 1a outer surface 2 case 3 electrode 4 rotating shaft 5 connector 6 conducting wire 7 dielectric 8 magnet 9 fixed electrode 10 movable electrode 11 high voltage equipment 12 source 13 bushing 14 high voltage power supply 15 lead wire 16 ground wire 17, 17B, 17C sensor 18 measuring instrument 19, 19A, 19B, 19C adjustment mechanism 21, 22, 23, 24, 25 switch element 31, 32, 33, 34, 35 partial electrode 40 attachment 41 screw 42 rod 43 moving mechanism 44 support 100 partial discharge measuring device

Claims (20)

A sensor for detecting a current flowing through a metal wall due to a partial discharge occurring inside the metal wall,
an electrode that is in close proximity to an outer surface of the metal wall to form a capacitance between the electrode and the outer surface;
a connector electrically connected to the electrode;
a mounting tool for removably mounting the sensor to the outer surface of the metal wall so that the electrode is proximate to the outer surface of the metal wall;
an adjustment mechanism for adjusting the capacitance;
A dielectric material;
a conductive case that houses the electrodes ;
the case and the electrodes are electrically insulated by the dielectric;
The mounting fixture removably mounts 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. The sensor of claim 1, wherein the dielectric forms a bottom wall of the sensor. The sensor according to claim 2, wherein the dielectric is a plate-like member that forms the bottom wall. The sensor of claim 1, wherein the dielectric is part of the housing of the sensor. A sensor for detecting a current flowing through a metal wall due to a partial discharge occurring inside the metal wall,
an electrode that is in close proximity to an outer surface of the metal wall to form a capacitance between the electrode and the outer surface;
a connector electrically connected to the electrode;
a mounting tool for removably mounting the sensor to the outer surface of the metal wall so that the electrode is proximate to the outer surface of the metal wall;
an adjustment mechanism for adjusting the capacitance;
A substrate that is a dielectric material;
The mounting fixture removably mounts 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. The sensor according to any one of claims 1 to 5, wherein the mounting fixture removably mounts the sensor to the outer surface of the metal wall such that the dielectric contacts the outer surface of the metal wall. The sensor according to any one of claims 1 to 6, wherein the electrode is in contact with the dielectric. The sensor of claim 7, wherein the electrode contacts the upper surface of the dielectric. The sensor according to claim 1 , wherein the case functions as a shield case . The sensor of claim 1 , wherein the case supports the connector. 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. The electrodes include a first electrode and a second electrode,
The sensor according to claim 11 , wherein the adjustment mechanism adjusts the capacitance by moving at least one movable electrode of the first electrode and the second electrode to change an area of the first electrode and the second electrode facing the outer surface. A sensor for detecting a current flowing through a metal wall due to a partial discharge occurring inside the metal wall,
an electrode that is in close proximity to an outer surface of the metal wall to form a capacitance between the electrode and the outer surface;
a connector electrically connected to the electrode;
a mounting tool for removably mounting the sensor to the outer surface of the metal wall so that the electrode is proximate to the outer surface of the metal wall;
an adjustment mechanism for adjusting the capacitance,
The electrodes include a first electrode and a second electrode,
The adjustment mechanism has a rotation shaft that rotates at least one of the first electrode and the second electrode, and by rotating the rotation shaft, the area over which the first electrode and the second electrode face the outer surface is changed, thereby adjusting the capacitance. A sensor for detecting a current flowing through a metal wall due to a partial discharge occurring inside the metal wall,
an electrode that is in close proximity to an outer surface of the metal wall to form a capacitance between the electrode and the outer surface;
a connector electrically connected to the electrode;
a mounting tool for removably mounting the sensor to the outer surface of the metal wall so that the electrode is proximate to the outer surface of the metal wall;
an adjustment mechanism for adjusting the capacitance,
The electrodes include 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 adjusts the capacitance by overlapping the first electrode and the second electrode to change the area where the first electrode and the second electrode face the outer surface. the first electrode is a fixed electrode,
The sensor of claim 12 , wherein the second electrode is a movable electrode. The electrode includes a plurality of partial electrodes,
The sensor of claim 11, wherein the adjustment mechanism has at least one switch element that switches between conduction and non-conduction between the multiple partial electrodes, and by turning the switch element on or off, the effective area of the multiple partial electrodes facing the outer surface is changed and the capacitance is adjusted. The sensor according to any one of claims 1 to 10, wherein the adjustment mechanism adjusts the capacitance by changing the distance at which the electrode faces the outer surface. The sensor of claim 17, wherein the adjustment mechanism changes the distance by moving the electrodes. 20. The sensor of claim 18, wherein the adjustment mechanism includes a rod fixed to the electrode and a movement mechanism for moving the rod to move the electrode. A sensor according to any one of claims 1 to 19;
and a measuring instrument that measures the partial discharge based on a sensor signal output from the connector.

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