Partial discharge measuring device

Abstract

To simplify a configuration and to reduce noise effect caused by external electromagnetic waves.SOLUTION: A partial discharge measuring device (10) includes: a partial discharge detection part (11) which detects a partial discharge current by measuring a current flowing from a measuring object (1), and an electromagnetic wave shield (12) which is provided at a position surrounding the partial discharge detection part and shields electromagnetic waves from outside. A route (R1) of the partial discharge current flowing from the measuring object to the partial discharge detection part and a route (R2) of noise current flowing to the electromagnetic wave shield (12) caused by the electromagnetic waves from outside are separated.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a partial discharge measurement device for measuring partial discharge of a measurement target.

Background Art

[0002] Patent Document 1 discloses a partial discharge measurement system including a partial discharge detection device that detects partial discharge generated in an electric motor and a measurement control device that controls measurement of partial discharge. Further, Patent Document 2 discloses a partial discharge determination device including an acoustic sensor used as partial discharge detection means installed on the outer surface of a transformer tank and a low-pass filter that removes noise components from the measurement signal of the acoustic sensor.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 1, mask processing is performed on a partial discharge signal with noise superimposed by a measurement control device, and in Patent Document 2, noise components are removed from an acoustic signal with electromagnetic noise components superimposed by a low-pass filter. Therefore, in Patent Documents 1-2, noise itself is included in the signal output from the partial discharge detection device, and as a result, a device or process for removing the noise is required. As a result, the detection sensitivity of partial discharge is reduced by the process of removing noise, and the configuration becomes more numerous or complicated for noise removal.

[0005] The present invention has been made in view of such circumstances, and an object thereof is to provide a partial discharge measuring device that can reduce the influence of noise caused by external electromagnetic waves while simplifying the configuration.

Means for Solving the Problems

[0006] The partial discharge measuring device according to the present invention is a partial discharge measuring device including a partial discharge detection unit that measures a current flowing from a measurement object and detects a partial discharge current, and an electromagnetic wave shield provided at a position surrounding the partial discharge detection unit to shield electromagnetic waves from the outside, wherein a path of the partial discharge current flowing from the measurement object to the partial discharge detection unit is separated from a path of a noise current flowing through the electromagnetic wave shield due to external electromagnetic waves.

Effects of the Invention

[0007] According to the present invention, the partial discharge detection unit can be shielded from external electromagnetic waves by the electromagnetic wave shield. Further, since the above-described current paths are separated, the noise current due to external electromagnetic waves can be made to flow through the electromagnetic wave shield without being superimposed on the partial discharge current. As a result, it is possible to avoid detection of noise caused by external electromagnetic waves in the detection by the partial discharge detection unit, and perform partial discharge measurement with reduced influence of noise due to electromagnetic waves. By reducing the influence of noise due to electromagnetic waves in this way, a device that performs mask processing or the like on the signal output from the partial discharge detection unit can be omitted, and the configuration can be simplified while enhancing the sensitivity of partial discharge detection.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0009] Hereinafter, an embodiment of the present invention (hereinafter abbreviated as "embodiment") will be described in detail. Note that the present invention is not limited to the following embodiments, and can be variously modified and implemented within the scope of the gist.

[0010] FIG. 1 is an overall configuration diagram of a partial discharge measurement circuit. In FIG. 1, the measurement object 1 of partial discharge in the present embodiment is not particularly limited, but is a high-voltage device such as a rotating machine, an inverter, or a power semiconductor.

[0011] Here, the prior art will be described. In high-voltage devices, a partial discharge test is performed to determine the insulation strength. In the partial discharge test, when an alternating voltage of a predetermined voltage is applied, it is measured that no partial discharge above a certain level occurs, and the partial discharge start voltage and the partial discharge extinction voltage are measured. Further, in an inverter or a rotating machine driven through an inverter, a pulsed rectangular wave voltage is applied during actual operation.

[0012] FIG. 2 is a graph showing an example of noise generated when a pulse voltage is applied. When measuring partial discharge during pulse voltage application by current, if electromagnetic waves are propagating in the measurement environment, as shown in FIG. 2, noise current may be generated by electromagnetic waves when the pulse voltage changes steeply. For this reason, in the prior art, the partial discharge signal is buried due to the influence of noise by electromagnetic waves, and it has been difficult to distinguish between the noise current and the partial discharge current. Therefore, the present invention enables partial discharge measurement with reduced influence of noise caused by external electromagnetic waves.

[0013] Returning to the description of the embodiments of the present invention, in the partial discharge measurement circuit shown in FIG. 1, a pulse voltage generator 2 is connected to the measurement object 1. A high-voltage pulse voltage is applied from the pulse voltage generator 2 to the measurement object 1. The pulse voltage applied from the pulse voltage generator 2 is measured by the voltage detector 3. The detection signal of the voltage detector 3 is output to the waveform display device 5.

[0014] A dummy sample 6 is provided in parallel with the measurement object 1, and a predetermined pulse voltage is also applied to the dummy sample 6 from the pulse voltage generator 2. The dummy sample 6 adopts an appropriate configuration in which partial discharge does not occur.

[0015] A partial discharge measurement device 10 is connected to the ground lines 1a and 6a of the measurement object 1 and the dummy sample 6. The detection signal of the partial discharge measurement device 10 is output to the waveform display device 5, and an HPF (high-pass filter) 8 is inserted between the output side of the partial discharge measurement device 10 and the input side of the waveform display device 5. The cut-off frequency of the HPF 8 is set to, for example, 10 MHz, and power supply noise and the like are removed.

[0016] FIG. 3 is a schematic configuration diagram of the partial discharge measurement device and its surroundings according to the embodiment. The partial discharge measurement device 10 includes a partial discharge detector 11, an electromagnetic shield 12, a first shield cable 13, a second shield cable 14, and a third shield cable 15.

[0017] The partial discharge detector 11 measures the current flowing from the measurement object 1 to detect the partial discharge current, and outputs the detection signal to the waveform display device 5 (see FIG. 1). In this embodiment, a high-frequency CT (Current Transformer) is used as the current sensor in the partial discharge detector 11. In the partial discharge detector 11, a first internal wiring 17 electrically connected to the measurement object 1 and a second internal wiring 18 electrically connected to the dummy sample 6 are alternately passed through the coil portion constituting the high-frequency CT. Thereby, signals such as power supply noise are removed from the detection signal output from the partial discharge detector 11 by a method called the differential method.

[0018] The electromagnetic shield 12 is provided at a position surrounding the partial discharge detection unit 11, and is provided, for example, in a box shape capable of accommodating the partial discharge detection unit 11 therein. The electromagnetic shield 12 is composed of a conductive material made of metal such as aluminum, iron, copper, etc., or an insulator coated with such a conductive material.

[0019] Also, the electromagnetic shield 12 is connected to the third shield cable 15 and set to the ground potential. Thereby, the electromagnetic shield 12 has a function of shielding electromagnetic waves from the surrounding environment outside the partial discharge measuring device 10, and it is prevented that the internal partial discharge detection unit 11 is affected by external electromagnetic waves.

[0020] The first shield cable 13 connects between the electromagnetic shield 12 and the measurement object 1. The second shield cable 14 connects between the electromagnetic shield 12 and the dummy sample 6. Each of the shield cables 13 and 14 is composed of a coaxial cable. One end of each of the shield cables 13 and 14 has an outer conductor constituting the coaxial cable electrically connected to the electromagnetic shield 12 to serve as a ground shield and shield external electromagnetic waves.

[0021] A first connector 21 is provided at the other end of the first shield cable 13, and the first connector 21 and the measurement object 1 are electrically connected via a first external wiring 22. A second connector 23 is provided at the other end of the second shield cable 14, and the second connector 23 and the dummy sample 6 are electrically connected via a second external wiring 24. The first external wiring 22 and the second external wiring 24 are composed of a bare wire or a coated wire including a conductor wire rod, and are used in a state where external electromagnetic waves are exposed without shielding. The lengths of the first external wiring 22 and the second external wiring 24 will be described later.

[0022] The third shield cable 15 is composed of a coaxial cable and is grounded to shield external electromagnetic waves. Connected to the third shield cable 15 are the first internal wiring 17 and the second internal wiring 18 that have passed through the partial discharge detector 11, in addition to the electromagnetic shield 12.

[0023] FIG. 4 is an explanatory diagram of the current path of the partial discharge measuring device according to the embodiment. By applying a predetermined pulse voltage from the pulse voltage generator 2 (see FIG. 1) to the measurement object 1, partial discharge occurs in the measurement object 1. The partial discharge current caused by such partial discharge flows from the measurement object 1 through the path R1 indicated by the thick solid line in FIG. 4 to the partial discharge detector 11. This path R1 is composed of the first external wiring 22 that constitutes the ground wire 1a (see FIG. 1), the first shield cable 13, the first internal wiring 17, and the third shield cable 15.

[0024] On the other hand, when electromagnetic waves are propagating in the surrounding environment outside the partial discharge measuring device 10, a noise current flows through the electromagnetic shield 12 due to the electromagnetic waves. Such a noise current flows through the path R2 indicated by the thick broken line in FIG. 4. This path R2 is composed of the electromagnetic shield 12 and the third shield cable 15. Therefore, in the partial discharge measuring device 10, the path R1 of the partial discharge current flowing from the measurement object 1 and the path R2 of the noise current flowing through the electromagnetic shield 12 are separated. When the paths R1 and R2 merge in the third shield cable 15, the merging point is set to the ground potential, so that the separated state of the paths R1 and R2 is maintained.

[0025] A pulse voltage is also applied to the dummy sample 6 connected in parallel with the measurement object 1, but no partial discharge occurs, so no partial discharge current flows. The current path flowing from the dummy sample 6 is composed of the second external wiring 24, the second shield cable 14, the second internal wiring 18, and the third shield cable 15. In the partial discharge detector 11, since the first internal wiring 17 and the second internal wiring 18 are staggered, a signal based only on the partial discharge current from which signals such as power supply noise have been removed from the current flowing from the measurement object 1 is output to the waveform display device 5.

[0026] According to the above embodiment, the electromagnetic shield 12 can shield the partial discharge detection unit 11 from the electromagnetic waves propagating outside the partial discharge measurement device 10. Moreover, since the respective paths R1 and R2 shown in FIG. 4 are separated, the noise current caused by external electromagnetic waves can be made to flow into the electromagnetic shield 12 without being superimposed on the current flowing through the first internal wiring 17 or the like.

[0027] Thereby, it is possible to avoid the detection of noise caused by external electromagnetic waves by the detection by the partial discharge detection unit 11, and it is possible to perform partial discharge measurement with reduced influence of noise due to electromagnetic waves. By reducing the influence of noise due to electromagnetic waves in this way, it is possible to omit a device that performs various processes such as mask processing on the signal output from the partial discharge detection unit 11. Therefore, in the present embodiment, since the above-described various processes can be omitted, for example, when the frequency range of noise is wide, it is possible to prevent the detection sensitivity from decreasing due to attenuation of the detection signal other than noise, and the sensitivity of partial discharge detection can be increased. Furthermore, it is possible to minimize the adoption of a device that performs various processes and simplify the configuration.

[0028] In addition, since the configuration is such that the first and second shield cables 13 and 14 are used for connection, it is also possible to shield electromagnetic waves between the measurement object 1 or the dummy sample 6 and the electromagnetic shield 12. Therefore, not only the electromagnetic shield 12 but also the first and second shield cables 13 and 14 can suppress the superposition of the noise current caused by external electromagnetic waves on the partial discharge current, and the influence of noise due to electromagnetic waves in partial discharge measurement can be further reduced.

[0029] Here, an experiment was conducted to compare the influence of noise when the lengths of the respective external wirings 22 and 24 were changed in the partial discharge detection device of the above embodiment. The results of such an experiment are shown in the graph of FIG. 5.

[0030] FIG. 5 is a graph showing the relationship between the length of each external wiring and the noise intensity by experiment. In the graph of FIG. 5, the horizontal axis represents the length (wiring length) of each external wiring 22, 24, and the vertical axis represents the noise intensity. The noise intensity is a relative value when the noise intensity measured under the condition that the length of each external wiring 22, 24 is 100 cm is set to 1.0.

[0031] The length (wiring length) of each external wiring 22, 24 is the length of the range that is non-shielded and exposed from external electromagnetic waves. Specifically, for each external wiring 22, 24, the end on the side of each shield cable 13, 14 serving as the length reference is the tip of each connector 21, 23, and the end on the side of the measurement object 1 or the dummy sample 6 is the tip of a connection terminal (not shown) such as a crimp terminal provided on each external wiring 22, 24.

[0032] In this experiment, except for changing the length of each external wiring 22, 24, the partial discharge current was measured under the same conditions, and the noise intensity in the measurement was measured. In the graph of FIG. 5, when the length of each external wiring 22, 24 is 1 cm, 2 cm, or 5 cm, the noise intensity becomes an approximate value of 0.4 or less, and the influence of noise can be reduced well. The noise intensity increased rapidly between the cases where the length of each external wiring 22, 24 was 5 cm and 10 cm. And in the range where the length of each external wiring 22, 24 is 10 cm or more and 100 cm or less, the noise intensity becomes 0.6 or more, and as the length of each external wiring 22, 24 increases, the noise intensity gradually increases. Therefore, from the viewpoint of reducing the influence of noise well in the partial discharge measuring device 10, it can be understood that it is preferable to set the length of each external wiring 22, 24 to 1 cm or more and 5 cm or less.

[0033] Note that the present invention is not limited to the above-described embodiments, and can be implemented with various modifications. In each of the above embodiments, the size, shape, etc. shown in the accompanying drawings are not limited thereto, and can be appropriately changed within the range in which the effects of the present invention are exhibited. In addition, it can be implemented with appropriate changes as long as it does not deviate from the scope of the object of the present invention.

[0034] The partial discharge detection unit 11 is not limited to the high-frequency CT, and various modifications are possible as long as partial discharge can be detected in the same manner as in the above-described embodiment. For example, it may be a current measurement device using a shunt resistor.

[0035] Also, when the influence of power supply noise or the like superimposed on the current flowing through the partial discharge measurement device 10 is small, the HPF 8 and the dummy sample 6 may be omitted.

[0036] Also, the voltage applied to the measurement object 1 does not prevent the voltage from being measured as a triangular wave or a sine wave other than the pulse voltage as shown in FIG. 2. Even when a voltage other than the pulse voltage is applied, partial discharge can be detected by the partial discharge detection unit 11 in the same manner as described above.

Explanation of Signs

[0037] 1: Measurement object 10: Partial discharge measurement device 11: Partial discharge detection unit 12: Electromagnetic shield 13: First shield cable (shield cable) 14: Second shield cable (shield cable) 22: First external wiring (wiring) 24: Second external wiring (wiring) R1: Path of partial discharge current R2: Path of noise current

Claims

1. A partial discharge measuring device comprising a partial discharge detection unit that measures the current flowing from the measurement object to detect a partial discharge current, and an electromagnetic wave shield provided at a position surrounding the partial discharge detection unit to shield electromagnetic waves from the outside, wherein a path of the partial discharge current flowing from the measurement object to the partial discharge detection unit is separated from a path of noise current flowing through the electromagnetic wave shield due to electromagnetic waves from the outside.

2. The partial discharge measuring device according to claim 1, further comprising a shield cable that connects between the measurement object and the electromagnetic wave shield to shield electromagnetic waves from the outside.

3. The partial discharge measuring device according to claim 2, further comprising unshielded wiring for electromagnetic waves from the outside between the shield cable and the measurement object, wherein the length of the wiring is set to be 1 cm or more and 5 cm or less.

Images