JP2015114185A - Partial discharge detection method, and partial discharge detection device - Google Patents

Abstract

A partial discharge detection method and a partial discharge detection device capable of detecting a partial discharge generated by applying an impulse voltage to a charging unit of an inspection object using an acoustic sensor attached to the inspection object. A partial discharge detection method includes a step of applying a first impulse voltage to a charging unit of an inspection object, and a step of acquiring a first measurement signal by an acoustic sensor mounted on an outer surface of the inspection object. Applying a low pass filter to the first measurement signal to obtain the second measurement signal; and removing a noise component caused by mechanical vibration of the inspection object from the second measurement signal Obtaining a measurement signal. The noise component is a fourth measurement signal acquired by the acoustic sensor when a second impulse voltage lower than the first impulse voltage, which does not cause partial discharge in the inspection object, is applied to the charging unit of the inspection object. To be determined. [Selection] Figure 6

Description

  The present invention relates to a technique for detecting a partial discharge generated inside an inspection object such as an electric device and an apparatus therefor.

  A typical example of internal abnormality during normal operation in electrical equipment represented by power substation equipment and power distribution equipment is partial discharge that occurs inside the equipment. Partial discharge is a precursor phenomenon of dielectric breakdown (all-path breakdown) of electrical equipment, and it is possible to prevent electrical breakdown of electrical equipment by establishing a technique for reliably detecting partial discharge.

  Generally, a high-voltage charging unit that can cause partial discharge in an electric device is not exposed and is housed in an insulating container or a metal casing (tank) having a ground potential. That is, the high-voltage charging part where partial discharge can occur is covered with another structure and cannot be directly observed. In addition, the signal accompanying partial discharge generated inside the equipment is very weak, and various external noises are superimposed on the signal accompanying partial discharge when operating in the field of electrical equipment. It is necessary to devise a method to extract the noise separately from the noise signal.

  As a method for detecting partial discharge during normal operation of an electric device, a method using an acoustic (AE) sensor is known.

  For example, Japanese Patent Laying-Open No. 2008-180681 (Patent Document 1) discloses an acoustic emission sensor that detects an elastic wave (ultrasound) signal generated by partial discharge in a transformer, and a discharge pulse signal that flows through a ground line when partial discharge occurs. A diagnostic system is disclosed that includes a current sensor for detecting a current sensor. Japanese Patent Laying-Open No. 2008-2322973 (Patent Document 2) discloses a partial discharge determination device including a current detector that detects a current pulse flowing to the ground due to partial discharge, and an ultrasonic sensor that detects an acoustic signal due to partial discharge. Is disclosed.

  The technologies disclosed in these prior art documents detect current flowing through a tank wall surface or a ground line generated by the occurrence of partial discharge using a current sensor, and accompany generation of partial discharge using an acoustic sensor. The generated acoustic signal is detected, and the presence / absence of the partial discharge is determined using the difference in the spatial propagation speed between the electrical signal and the acoustic signal generated in association with the generation of the partial discharge.

  That is, when a partial discharge occurs inside the device, first, a current pulse due to the partial discharge is detected by the current sensor. Next, after a predetermined time determined by the distance between the high-voltage charging unit and the acoustic sensor, an acoustic signal due to partial discharge is detected by the acoustic sensor. There is a predetermined case in which the current signal detected by the current sensor is synchronized with the cycle of the AC voltage applied to the electrical device, and the time difference between the detection signal by the current sensor and the detection signal by the acoustic sensor is substantially the same. If there is a predetermined number within the time, it is determined that the partial discharge. By adopting such a method, it becomes possible to separate a signal accompanying a partial discharge from a noise signal.

JP 2008-180681 A JP 2008-2322973 A

  The technology disclosed in the above-mentioned prior art documents is directed to preventive maintenance technology for preventing dielectric breakdown caused by deterioration over time after electrical equipment is installed in the field. It is applied during normal operation where is applied.

  On the other hand, a lightning impulse withstand voltage test is often imposed as an insulation test on electrical devices such as power transformers and power distribution devices before shipment. According to the standard (for example, the standard JEC0103 (2005) defined by the Electrical Standards Committee), when an impulse voltage having a prescribed voltage waveform is applied and the target electrical device does not break down, it is considered to be acceptable. ing. However, it is important to detect partial discharge, which is a precursor phenomenon of dielectric breakdown, in order to guarantee the insulation reliability of the product and to clarify the tolerance to the dielectric breakdown with respect to the applied voltage. is there. That is, there is a need to detect a partial discharge even during a lightning impulse withstand voltage test.

  For the need to detect such partial discharge, the method using the acoustic sensor disclosed in the prior art document as described above cannot be applied as it is. This is because, during the lightning impulse withstand voltage test, a larger noise is generated. Therefore, the method described in the prior art document that is assumed to be a test during normal operation appropriately generates partial discharge under the influence of this noise. This is because it cannot be detected.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide a partial discharge generated by applying an impulse voltage to a charging portion of an inspection object, and an acoustic sound attached to the inspection object. It is an object to provide a partial discharge detection method and a partial discharge detection device that can be detected using a sensor.

  A partial discharge detection method according to an aspect of the present invention includes a step of applying a first impulse voltage to a charging unit of an inspection object, a step of acquiring a timing at which application of the first impulse voltage is started, and an inspection Acquiring a first measurement signal by an acoustic sensor mounted on the outer surface of the object, acquiring a second measurement signal by applying a low-pass filter to the first measurement signal, and second measurement A step of acquiring a third measurement signal by removing a noise component caused by mechanical vibration of the inspection object from the signal, and a positional relationship between the charging unit and the acoustic sensor in the inspection object on the basis of the acquired timing Determining whether or not partial discharge has occurred in the inspection object based on the time waveform of the third measurement signal that appears within an effective measurement period determined according toThe noise component is a fourth measurement signal acquired by the acoustic sensor when a second impulse voltage lower than the first impulse voltage, which does not cause partial discharge in the inspection object, is applied to the charging unit of the inspection object. To be determined.

  Preferably, in the partial discharge detection method, a step of applying a second impulse voltage to a charging unit of the inspection object, a step of acquiring a fourth measurement signal by an acoustic sensor, and a low-pass filter for the fourth measurement signal Applying a reference signal for determining a noise component by applying.

  Preferably, in the partial discharge detection method, a plurality of acoustic sensors are attached to the outer surface of the inspection object, the first measurement signal is obtained, the second measurement signal is obtained, and the third measurement signal is obtained. And the step of determining whether or not partial discharge has occurred in the inspection object separately from the plurality of acoustic sensors, and determining that partial discharge has occurred in the inspection object. Then, the method further includes the step of locating the occurrence position of the partial discharge based on the difference in timing at which the time waveforms indicating the occurrence of the partial discharge appear in the plurality of third measurement signals respectively acquired from the plurality of acoustic sensors. .

  Preferably, the step of acquiring the timing includes a step of detecting, by an electromagnetic wave sensor, a change in the electromagnetic wave caused by the application of the first impulse voltage.

  Preferably, the step of acquiring the timing includes a step of detecting a change in current caused by application of the first impulse voltage by a current sensor.

  According to another situation of this invention, the partial discharge detection apparatus which detects the partial discharge which generate | occur | produces by applying an impulse voltage to the charge part of a test subject is provided. The partial discharge detection device is detected by a timing acquisition means for acquiring a timing at which application of the first impulse voltage to the inspection object is started, an acoustic sensor mounted on the outer surface of the inspection object, and the acoustic sensor. A first signal processing unit that outputs a second measurement signal by applying a low-pass filter to the first measurement signal, and a noise component caused by mechanical vibration of the inspection object is removed from the second measurement signal. The second signal processing unit that outputs the third measurement signal at the second time, and the second signal processing unit that appears within an effective measurement period determined according to the positional relationship between the charging unit and the acoustic sensor in the inspection object, based on the acquired timing. And determining means for determining whether or not partial discharge has occurred in the inspection object based on the time waveform of the measurement signal of No. 3. The noise component is a fourth measurement signal acquired by the acoustic sensor when a second impulse voltage lower than the first impulse voltage, which does not cause partial discharge in the inspection object, is applied to the charging unit of the inspection object. To be determined.

  According to the present invention, there is provided a partial discharge detection method and a partial discharge detection device capable of detecting a partial discharge generated by applying an impulse voltage to a charging unit of an inspection object using an acoustic sensor attached to the inspection object. realizable.

It is a perspective sectional view showing the composition of the power transformer which is an example of the inspection object. It is a schematic diagram which shows the outline | summary of a lightning impulse withstand voltage test. It is a schematic diagram which shows the apparatus structural example of the partial discharge detection apparatus which concerns on this Embodiment. It is a figure for demonstrating the outline | summary of the noise removal process with respect to the acoustic sensor measurement signal performed in the partial discharge detection apparatus which concerns on this Embodiment. It is a figure which shows the relationship between the applied voltage (crest value) of the applied impulse voltage which concerns on this Embodiment, and the amplitude value of the noise component resulting from the mechanical vibration which arises by application of an impulse voltage. It is a flowchart which shows the process sequence of the partial discharge detection method which concerns on this Embodiment. It is an example of the time waveform acquired by the partial discharge detection method which concerns on this Embodiment. It is a flowchart which shows the process sequence of the partial discharge detection method which concerns on the 1st modification of this Embodiment. It is an example of the time waveform acquired by the partial discharge detection method which concerns on the 1st modification of this Embodiment. It is a flowchart which shows the process sequence of the partial discharge detection method which concerns on the 2nd modification of this Embodiment. It is an example of the time waveform acquired by the partial discharge detection method which concerns on the 2nd modification of this Embodiment. It is a flowchart which shows the process sequence of the partial discharge detection method which concerns on the 3rd modification of this Embodiment.

  Hereinafter, a partial discharge detection method and a partial discharge detection device according to embodiments of the present invention will be described with reference to the drawings. In the following description of the embodiments, the same or corresponding parts in the drawings will be denoted by the same reference numerals and description thereof will not be repeated.

  In the following description, a typical example of an electric device that is an inspection object will be described as a power transformer. However, the inspection object of the partial discharge detection method and the partial discharge detection device according to the present invention can be any electric device such as a power transformer or distribution device. For example, an outer iron type transformer, an inner iron type transformer, an insulated switchgear, and the like can be used as inspection objects.

[A. Related technologies and issues]
First, a related technique of the present invention and problems in the related technique will be described.

  A lightning impulse withstand voltage test is one of the insulation tests performed on electrical devices such as power transformers and power distribution devices before product shipment. This test is to ensure insulation performance even when an abnormal voltage waveform such as lightning surge or switching surge generated outside is applied during normal operation of electrical equipment such as power transformers. It is. Specifically, it is required that the dielectric breakdown does not occur even when a voltage waveform defined in the standard is applied to an electrical device. However, it is important to detect partial discharge, which is a precursor phenomenon of dielectric breakdown, in order to guarantee the insulation reliability of the product and to clarify the tolerance to dielectric breakdown for the applied voltage. is there.

  FIG. 1 is a perspective sectional view showing a configuration of a power transformer 1 which is an example of an inspection object. In FIG. 1, a part of each configuration is cut out. A power transformer 1 shown in FIG. 1 is an oil-cooled outer iron type power transformer, and mainly includes an iron core 2, a coil 3 formed of a winding wound around the iron core 2, an iron core 2, and a coil. And a tank 4 for storing 3. The tank 4 is filled with insulating oil (not shown), and the iron core 2 and the coil 3 are immersed in the insulating oil. As the cooling medium, a gas such as sulfur hexafluoride or air may be used instead of the insulating oil.

  FIG. 2 is a schematic diagram showing an outline of a lightning impulse withstand voltage test. Referring to FIG. 2, a charging unit (typically, a terminal unit) of power transformer 1 that is an object to be inspected is electrically connected to impulse voltage generator 10. The impulse voltage generator 10 applies the generated impulse voltage to the power transformer 1 that is an inspection object.

  Here, the operation principle of the impulse voltage generator 10 used during the lightning impulse withstand voltage test will be described. The impulse voltage generator 10 includes a plurality of capacitors 12 connected in parallel to the input terminal pair 16. When the input voltage V is applied via the input terminal pair 16, each of the plurality of capacitors 12 connected in parallel is charged to a voltage corresponding to the input voltage V. Thereafter, the plurality of spherical gaps 14 provided in association with the plurality of capacitors 12, respectively, are brought into contact with each other at the same time, whereby the plurality of capacitors 12 are simulated in series and discharge is started.

  When the discharge is started, the impulse having a waveform having a wavefront length (rise time) and a wave tail length (fall time), which is determined by a circuit constant including the impulse voltage generator 10 and the power transformer 1 to be inspected. Voltage is output. On the output side of the impulse voltage generator 10, a discharge resistor 17 and a wavefront length adjusting capacitor 18 are respectively connected between the ground line. The sizes of the discharge resistor 17 and the wavefront length adjusting capacitor 18 are adjusted so that the voltage waveform defined by the standard is applied to the inspection object.

  In the lightning impulse withstand voltage test using the impulse voltage generator 10, very strong electromagnetic noise due to spark discharge between the sphere gaps 14 is radiated simultaneously with the output of the impulse voltage due to its operation principle. Due to the presence of this electromagnetic noise, it is very difficult to detect a partial discharge generated inside the power transformer 1.

  Methods commonly used as a method for detecting partial discharge in high-voltage electrical equipment include (1) an electromagnetic wave method for detecting an electromagnetic wave generated with the occurrence of partial discharge using an electromagnetic wave sensor (antenna), (2 There are known a method of detecting a current pulse flowing with the occurrence of partial discharge, and a method of detecting an acoustic wave signal generated with the occurrence of partial discharge with an acoustic sensor.

  When the electromagnetic wave method (1) is used during a lightning impulse withstand voltage test, the electromagnetic waves resulting from the partial discharge are buried in the electromagnetic noise from the impulse voltage generator 10, and the partial discharge cannot be detected.

  Regarding the method of detecting the current pulse of (2), since electromagnetic noise from the impulse voltage generator 10 flows to the ground line through the capacitance of the inspection object, it is superimposed on the current pulse caused by the partial discharge. Therefore, partial discharge cannot be detected.

  The conventional method using the acoustic sensor (3) also has the following problems. For example, in the method disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 2008-180681 (Patent Document 1), it is necessary to detect a current pulse flowing through a tank wall surface or a ground line, which is generated when a partial discharge occurs, using a current sensor. However, under the influence of extremely strong electromagnetic noise radiated from the impulse voltage generator 10, current pulses due to partial discharge cannot be detected correctly. In addition, since electromagnetic noise flows to the ground line through the capacitance of the inspection object, there is also a problem that it is superimposed on a current pulse caused by partial discharge.

  Furthermore, when an impulse voltage having an early rise time is applied to the inspection object, a charging current instantaneously flows, and mechanical vibration occurs in the inspection object itself. The inventors of the present application have found a new problem that appropriate detection of partial discharge is hindered by mechanical vibration caused by application of the impulse voltage. That is, when an impulse voltage is applied to the power transformer 1 that is an inspection object, a charging current instantaneously flows through the capacitance. When the charging current flows through the coil 3 of the power transformer 1, a physical force is generated between the windings, and mechanical vibration is generated in the coil 3. The elastic wave propagates to the insulating oil filling the tank 4 of the power transformer 1 due to the mechanical vibration of the coil 3. Here, when an attempt is made to detect a partial discharge generated inside the power transformer 1 using the acoustic sensor 30, regardless of whether or not a partial discharge occurs inside the power transformer 1, It became clear that noise components caused by mechanical vibrations were detected as acoustic signals. That is, the acoustic sensor 30 detects an acoustic signal after a lapse of a certain time from the application of the impulse voltage, regardless of whether or not partial discharge has occurred inside the inspection object.

  The method disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 2008-180681 (Patent Document 1) detects the presence or absence of partial discharge during normal operation. In the first place, a situation in which such mechanical vibration occurs is assumed. Not. That is, in the technique disclosed in Japanese Patent Application Laid-Open No. 2008-180681 (Patent Document 1), the influence of mechanical vibration generated on the inspection object itself is not taken into consideration at all, and the impulse voltage generator 10 as described above is used. Therefore, the partial discharge cannot be detected by the electromagnetic noise.

  In consideration of the problems in the prior art as described above, the partial discharge detection method and the partial discharge detection device according to the present embodiment avoid the influence of extremely strong electromagnetic noise generated from the impulse voltage generator 10 and By removing the influence of the mechanical vibration of the inspection object that occurs peculiarly during the impulse withstand voltage test, the partial discharge generated inside the device by applying the impulse voltage is appropriately detected.

[B. Device configuration]
First, an example of the device configuration of the partial discharge detection device according to the present embodiment will be described. FIG. 3 is a schematic diagram illustrating a device configuration example of the partial discharge detection device 100 according to the present embodiment. Referring to FIG. 3, partial discharge detection device 100 detects a partial discharge generated by applying an impulse voltage from impulse voltage generation device 10 to a charging portion of power transformer 1 (inspection object). Specifically, the partial discharge detection apparatus 100 includes an acoustic sensor 30 that is mounted on the outer surface of the inspection object, an input circuit 102, a low-pass filter 104, a waveform recording unit 106, and a signal processing unit 108.

  The acoustic sensor 30 is typically mounted on the outer surface of a metal casing (tank) that houses the high-voltage charging unit of the power transformer 1. The acoustic sensor 30 detects an elastic wave (stress wave) generated by a mechanical movement of a substance by an AE (Acoustic Emission) method, and outputs the detection result as an electric signal. In the present embodiment, the acoustic sensor 30 detects an acoustic signal resulting from the partial discharge generated inside the inspection object. In the following description, the raw electrical signal output from the acoustic sensor 30 is also referred to as “acoustic sensor measurement signal”.

  The input circuit 102 is electrically connected to an application cable 6 that electrically connects the impulse voltage generator 10 and the power transformer 1, and a time waveform of voltage applied to the power transformer 1 (hereinafter, “ And a voltage dividing circuit for stepping down to a voltage value that can be input to the waveform recording unit 106. That is, the input circuit 102 outputs a signal indicating an applied voltage waveform applied to the power transformer 1. The input circuit 102 has a function of acquiring a timing at which application of an impulse voltage to the power transformer 1 (inspection object) is started (hereinafter also referred to as “impulse voltage application start time”), as will be described later. Realize some.

  An acoustic sensor measurement signal from the acoustic sensor 30 is input to the low-pass filter 104, and an acoustic signal after passing through the low-pass filter 104 (hereinafter also referred to as “low-pass filter processing signal”) is output to the waveform recording unit 106. As will be described later, the low-pass filter 104 removes electromagnetic noise superimposed on the acoustic sensor measurement signal acquired by the acoustic sensor 30.

  The waveform recording unit 106 records the applied voltage waveform from the input circuit 102 and the time waveform of the low-pass filter processing signal from the low-pass filter 104. The waveform recording unit 106 is configured to record a time waveform for each of a plurality of impulse voltage applications. As the waveform recording unit 106, a general oscilloscope may be adopted.

  The signal processing unit 108 acquires the impulse voltage application start time and performs noise removal processing as described later, and then determines whether or not partial discharge has occurred inside the power transformer 1 (inspection target). to decide. The signal processing unit 108 outputs whether or not the partial discharge is detected as a diagnosis result. Note that an operator may perform part or all of the processing in the signal processing unit 108 as described later. In other words, the process for determining the presence or absence of the occurrence of partial discharge using the signal waveform recorded in the waveform recording unit 106 may be realized by any of fully automated, partially automated, and all manually.

[C. Overview of noise reduction processing]
Next, an outline of noise removal processing in the partial discharge detection method according to the present embodiment will be described. FIG. 4 is a diagram for explaining the outline of the noise removal process for the acoustic sensor measurement signal executed in the partial discharge detection apparatus 100 according to the present embodiment.

  Referring to FIG. 4, during the lightning impulse withstand voltage test of the electrical equipment, the acoustic sensor measurement signal 20 acquired by the acoustic sensor 30 includes a component 22 due to a partial discharge that is an original detection target, and an impulse voltage. A noise component 24 caused by the generator 10, a noise component 26 caused by mechanical vibration caused by application of the impulse voltage, and an external noise component 28 are included.

(1) Separation of noise component 24 caused by impulse voltage generator 10 In the partial discharge detection method according to the present embodiment, the influence of electromagnetic noise (noise component 24) radiated from impulse voltage generator 10 is expressed in terms of frequency. By separating, it avoids that component 22 resulting from partial discharge is buried in electromagnetic noise. More specifically, a low-pass filter processing signal is generated by applying the low-pass filter 104 (see FIG. 3) to the acoustic sensor measurement signal 20, and the noise component 24 is substantially removed from the low-pass filter processing signal. Will be.

(2) Removal of noise component 26 caused by mechanical vibration With respect to the noise component 26 caused by mechanical vibration, the noise component 26 is estimated and removed by an acoustic signal measured when partial discharge is not generated. More specifically, an impulse voltage having a high peak value at which a partial discharge can be generated using a mechanical vibration waveform (noise component 26) that appears when an impulse voltage having a low peak value that does not reliably generate a partial discharge is applied. By estimating and removing the mechanical vibration component that appears when the voltage is applied, only the component 22 resulting from the partial discharge is extracted.

  In general, when conducting a lightning impulse withstand voltage test on a large-capacity power device such as the power transformer 1, the test voltage defined in the standard is not applied suddenly. It is confirmed whether an impulse voltage having a wavefront length and a wavetail length is output. As confirmation work at this time, an impulse voltage having a low peak value that does not cause partial discharge reliably in the power transformer 1 is output several times. Even when an impulse voltage having a low peak value is applied, a charging current flows through the coil 3 of the power transformer 1, so that mechanical vibration is generated in the inspection object itself. A noise component 26 caused by the above is detected.

  It is considered that the noise component 26 caused by the mechanical vibration has the same period even if the peak value of the impulse voltage applied to the inspection object is changed, and only the amplitude value changes. The inventors of the present application experimentally clarified that the amplitude value of the noise component 26 caused by mechanical vibration is proportional to the square of the charging current flowing through the coil 3 of each winding, that is, proportional to the square of the applied voltage. .

  FIG. 5 is a diagram showing the relationship between the applied voltage (crest value) of the applied impulse voltage according to the present embodiment and the amplitude value of the noise component caused by the mechanical vibration caused by the application of the impulse voltage. As shown in FIG. 5, the inventors of the present application have found that the amplitude value of the noise component 26 caused by the mechanical vibration included in the acoustic sensor measurement signal is proportional to the square of the peak value of the impulse voltage. Using the relationship between the peak value of the applied impulse voltage and the amplitude value of the noise component caused by mechanical vibration, first, the acoustic sensor 30 obtains a low impulse voltage (peak value V2) at which partial discharge does not occur. The time waveform f2 (t) of the noise component resulting from the mechanical vibration appearing in the detected signal (acoustic sensor measurement signal 20) is acquired.

  Next, it is assumed that a high impulse voltage (crest value V1) conforming to the standard of the lightning impulse withstand voltage test is applied. With respect to the amplitude value of the time waveform of the noise component resulting from mechanical vibration obtained when a low impulse voltage (peak value V2) is applied, the peak value V1 when a high voltage is applied is divided by the peak value V2 when a low voltage is applied. By multiplying the square of the numerical value, the noise component 26 caused by mechanical vibration generated when a high impulse voltage is applied can be determined. That is, the time waveform f1 (t) of the noise component caused by the mechanical vibration appearing in the detection signal (acoustic sensor measurement signal 20) acquired by the acoustic sensor 30 when a high impulse voltage (peak value V1) is applied is as follows. It can be calculated by a simple formula.

Time waveform f1 (t) = time waveform f2 (t) × (V1 / V2) ²
By taking the difference between the low-pass filter processing signal acquired when a high voltage is applied and the time waveform f1 (t) of the noise component caused by the mechanical vibration when the high voltage is applied, the noise component 26 caused by the mechanical vibration is removed. can do. By adopting such a method, it is possible to remove the influence of mechanical vibration of the inspection object itself, which is caused by the charging current flowing through the inspection object by applying the impulse voltage. That is, the time waveform f2 (t) corresponds to a reference signal for determining the time waveform f1 (t) of the noise component 26.

(3) Removal of external noise component 28 As the external noise component 28, for example, an impact sound caused by a foreign object colliding with the tank 4 of the power transformer 1 during a lightning impulse withstand voltage test or generated outside the tank 4 is generated. It can be caused by elastic waves caused by sound. For such an external noise component 28, a minimum time and a maximum time required for the elastic wave signal accompanying the partial discharge to reach the acoustic sensor 30 are predicted in advance, and between this minimum time and the maximum time. By acquiring only the acoustic wave signal arriving at the acoustic sensor 30 as an effective acoustic signal, it is temporally separated.

[D. Specific processing procedure]
Next, a specific processing procedure of the partial discharge detection method according to the present embodiment will be described with reference to FIGS. FIG. 6 is a flowchart showing a processing procedure of the partial discharge detection method according to the present embodiment. FIG. 7 is an example of a time waveform acquired by the partial discharge detection method according to the present embodiment.

  FIG. 7A shows a time waveform measured when a low impulse voltage (crest value V2) at which partial discharge does not occur is applied to the charging part of the power transformer 1, and FIG. A time waveform measured when a partial discharge is actually generated by applying a high impulse voltage (peak value V1) to the charging part of the power transformer 1 is shown. In FIG. 7, (i) shows an example of a time waveform (applied voltage waveform) of the impulse voltage applied from the impulse voltage generator 10 to the charging part of the power transformer 1 that is the inspection object, (ii) ) Shows an example of a time waveform of the acoustic sensor measurement signal 20 acquired by the acoustic sensor 30, and (iii) shows an example of a time waveform of the acoustic signal (low-pass filter processing signal) after passing through the low-pass filter 104. (Iv) shows an example of a time waveform after the noise component 26 caused by the mechanical vibration of the power transformer 1 that is the inspection target is removed from the low-pass filter processing signal.

  Referring to FIG. 6, first, a time waveform f2 (t) for removing noise component 26 caused by mechanical vibration caused by application of impulse voltage is acquired in advance (steps S2 to S6). However, the process for acquiring the time waveform for removing the noise component 26 caused by the mechanical vibration may be performed independently of the processes in steps S8 to S22 described later. For example, when the object to be inspected is a plurality of electrical devices, and there is little variation in electrical characteristics and mechanical properties between them, the noise component 26 caused by mechanical vibration is removed for a certain electrical device. A time waveform may be acquired in advance and used in common for a plurality of electrical devices.

  More specifically, an impulse voltage (crest value V2: second impulse voltage) is applied to the charging part of the power transformer 1 that is the inspection object (step S2). That is, an impulse voltage having a low peak value that does not reliably generate a partial discharge inside the power transformer 1 is applied. In step S2, an impulse voltage as shown in FIG. 7A (i) is applied.

  Subsequently, the acoustic sensor measurement signal 20 (fourth measurement signal) generated with the application of the impulse voltage is acquired by the acoustic sensor 30 mounted on the outer surface of the inspection object (step S4). The acoustic sensor 30 is typically mounted on the outer surface of the tank 4. In step S4, an acoustic sensor measurement signal 20 as shown in (ii) of FIG.

  Furthermore, by applying the low-pass filter 104 to the acquired acoustic sensor measurement signal 20, a noise component 26 (noise component) caused by mechanical vibration caused by application of a high impulse voltage (crest value V1) that may cause partial discharge. A time waveform f2 (t) (reference signal) for determining is obtained (step S6). That is, the time waveform f2 (t) of the noise component caused by the mechanical vibration appearing in the detection signal (acoustic sensor measurement signal 20) acquired by the acoustic sensor 30 when a low impulse voltage (crest value V2) that does not cause partial discharge is applied. Is acquired. In step S6, a low-pass filter processing signal as shown in (iii) of FIG. 7A is acquired as a time waveform f2 (t). Details of the low-pass filter 104 will be described later.

  As shown in the time waveform of (iv) in FIG. 7A, if partial discharge does not occur inside the power transformer 1, the low-pass filter processing signal causes mechanical vibration of the power transformer 1 to occur. Removing the resulting noise component 26 leaves virtually no component.

  Through the above steps, a reference signal for removing the noise component 26 caused by the mechanical vibration from the acoustic sensor measurement signal 20 is prepared. Then, a normal lightning impulse withstand voltage test is performed.

  First, during the lightning impulse withstand voltage test, an impulse voltage (crest value V1: first impulse voltage) satisfying the standard is applied to the charging part of the power transformer 1 that is the inspection object (step S8). . That is, a process is performed in which the acoustic sensor 30 is mounted on the outer surface of a metal casing (tank) that houses the high-voltage charging unit of the power transformer 1 that is the inspection object, and an impulse voltage is applied to the inspection object. Is done. At this time, a high impulse voltage capable of generating a partial discharge inside the power transformer 1 is applied. During lightning impulse withstand voltage testing of general high-voltage equipment, the standard specifies the wave head length and wave tail length of the applied impulse voltage waveform, and the wave length depends on the rated voltage and capacity of the electrical equipment. High prices are also set. In step S8, an impulse voltage as shown in (i) of FIG. 7B is applied.

  Then, the timing when the application of the impulse voltage is started is acquired (step S16). That is, the process of acquiring the impulse voltage waveform in the waveform recording unit 106 and acquiring the impulse voltage application start time is executed. As an acquisition method of this timing, an impulse voltage waveform as shown in (i) of FIG. 7B is taken into the waveform recording unit 106, and the timing when the amplitude value exceeds a predetermined threshold value is determined as the impulse voltage. It can be determined as the application start time. Since the impulse voltage at the time of the lightning impulse withstand voltage test is a high voltage, it is taken into the waveform recording unit 106 via the input circuit 102 including a voltage dividing circuit.

  In parallel with step S16, the acoustic sensor measurement signal 20 (first measurement signal) is acquired by the acoustic sensor 30 mounted on the outer surface of the power transformer 1 that is the inspection object (step S10). That is, in parallel with the process of taking the impulse voltage waveform into the waveform recording unit 106, the acoustic sensor measurement signal 20 accompanying the application of the impulse voltage is acquired by the acoustic sensor 30 mounted on the outer surface of the tank 4 of the power transformer 1. Is executed. In step S10, an acoustic sensor measurement signal 20 as shown in (ii) of FIG. 7B is acquired.

  Subsequently, the low-pass filter processing signal (second measurement signal) is obtained by applying the low-pass filter 104 to the acoustic sensor measurement signal 20 (first measurement signal) (step S12). That is, the process of removing the electromagnetic noise superimposed on the acoustic sensor measurement signal 20 detected by the acoustic sensor 30 through the low-pass filter 104 is executed. In step S12, a low-pass filter processing signal as shown in (iii) of FIG. 7B is acquired.

  As described above, the impulse voltage generator 10 outputs the required impulse voltage by generating a spark discharge between the spherical gaps 14 installed in the apparatus. The extremely strong electromagnetic noise generated by the spark discharge between the sphere gaps 14 is a major factor that makes it difficult to detect the partial discharge. On the other hand, the time for which electromagnetic noise continues intensively is about several tens of microseconds (time range 52 shown in (ii) of FIG. 7B). The propagation speed of the acoustic signal in the insulating oil in the tank 4 of the power transformer 1 is generally 1500 meters per second. Although depending on the size of the tank 4, it takes about several hundred microseconds to several milliseconds for an acoustic signal emitted from the coil 3 accommodated in the tank 4 to reach the acoustic sensor 30. That is, the time range (time range 54 shown in (ii) of FIG. 7B) in which the acoustic signal generated with the application of the impulse voltage is acquired by the acoustic sensor 30 is radiated from the impulse voltage generator 10. It is after the decay of most of the very strong electromagnetic noise. This is a great advantage of using the acoustic sensor 30 as a means for detecting partial discharge.

  However, even after most of the electromagnetic noise is attenuated, the acoustic sensor measurement signal 20 still has a waveform in which the electromagnetic noise component is superimposed. Therefore, by passing the acquired acoustic sensor measurement signal 20 through the low-pass filter 104, an electromagnetic noise component (noise component 24 caused by the impulse voltage generator 10) is removed from the acoustic sensor measurement signal 20. The low-pass filter 104 of the partial discharge detection device 100 shown in FIG. 3 applies a low-pass filter to the acoustic sensor measurement signal 20 (first measurement signal) detected by the acoustic sensor 30 to provide a low-pass filter processing signal (second signal). This corresponds to a signal processing unit that outputs a measurement signal. Note that the function of the low-pass filter 104 may be realized by digital signal processing in the waveform recording unit 106 and / or the signal processing unit 108.

  As the low-pass filter 104, a filter having a cutoff frequency characteristic capable of separating the original acoustic signal and electromagnetic noise in terms of frequency is selected. The electromagnetic noise radiated by the spark discharge between the spherical gaps 14 of the impulse voltage generator 10 has a strong component on the order of several hundred MHz, while the acoustic signal is several tens to several hundred kHz. For example, by adopting the low-pass filter 104 having a cutoff frequency of about 1 MHz, it is possible to remove the component of the electromagnetic noise superimposed on the acoustic sensor measurement signal 20 and pass only the component of the acoustic signal to be detected.

  Through the above steps, the main component of the acoustic signal generated by applying the impulse voltage can be acquired by removing electromagnetic noise. However, at this point, the noise component 26 caused by the mechanical vibration of the coil 3 of the power transformer 1 caused by the instantaneous flow of the charging current regardless of whether or not the partial discharge is generated inside the power transformer 1. Is included in the low-pass filtered signal. Therefore, in the next step, processing for removing the noise component 26 caused by mechanical vibration included in the low-pass filter processing signal is executed.

  That is, the mechanical vibration removal signal (third measurement signal) is obtained by removing the noise component 26 caused by the mechanical vibration of the power transformer 1 that is the inspection target from the low-pass filter processing signal (second measurement signal). Obtained (step S14). In step S14, a mechanical vibration removal signal as shown in (iv) of FIG. 7B is acquired. That is, the mechanical vibration component is removed from the acoustic signal when the high voltage is applied based on the mechanical vibration component of the inspection object that appears in the acoustic sensor 30 when the low voltage is applied so that partial discharge does not occur. .

More specifically, the time as a noise component is obtained by multiplying the amplitude of the time waveform f2 (t) (reference signal) acquired in advance by the execution of the above-described step S6 by (wave height value V1 / wave height value V2) ^2. A mechanical vibration removal signal is obtained by calculating a waveform and subtracting this from the low-pass filter processing signal. As described above, the noise component 26 caused by the mechanical vibration caused by the application of the impulse voltage does not cause partial discharge in the power transformer 1 that is the object to be inspected, and the impulse voltage of the peak value V1 that satisfies the standard (first). The acoustic sensor measurement signal acquired by the acoustic sensor 30 when the impulse voltage (second impulse voltage) having a lower peak value V2 is applied to the charging part of the power transformer 1 (inspection object). 20 (fourth measurement signal).

  From the acoustic sensor measurement signal acquired by the acoustic sensor 30 through the above steps, the influence (noise component 24) due to electromagnetic noise radiated from the impulse voltage generator 10 and the mechanical vibration of the coil 3 of the power transformer 1 are obtained. It is possible to remove the influence (noise component 26) caused by the above. However, there is a possibility that the external noise other than the partial discharge signal mentioned here is superimposed on the acoustic sensor measurement signal acquired using the acoustic sensor 30. For example, the acoustic sensor 30 is mounted on the outer surface of the tank 4 due to an impact sound caused by a foreign object colliding with the tank 4 of the power transformer 1 during a lightning impulse withstand voltage test or an elastic wave caused by a sound generated outside the tank 4. It is conceivable that it is detected as external noise. Therefore, as the last step of the partial discharge detection method according to the present embodiment, processing for removing the influence of external noise is executed.

  The propagation speed of the acoustic signal in the insulating oil in the tank 4 of the power transformer 1 is generally 1500 meters per second. Based on the propagation speed and the distance between the high-voltage charging unit and the acoustic sensor 30 in the structure of the power transformer 1 that is known in advance, the acoustic wave signal accompanying the partial discharge is generated from the acoustic voltage sensor from the impulse voltage application start time. The time difference until reaching 30 can be predicted within a certain time range. That is, the minimum time and the maximum time required for the elastic wave signal accompanying the partial discharge to reach the acoustic sensor 30 are predicted in advance, and the elastic wave that arrives at the acoustic sensor 30 between the minimum time and the maximum time is predicted. Only the signal is acquired as a valid acoustic signal.

  More specifically, the time obtained by dividing the shortest distance from the high voltage charging part in the structure of the power transformer 1 to the mounting position of the acoustic sensor 30 by the propagation speed of the acoustic signal in the insulating oil is t1, When the time obtained by dividing the longest distance between the high voltage charging part and the acoustic sensor 30 in the structure of the transformer 1 by the propagation speed of the acoustic signal in the insulating oil is t2, the impulse voltage application start time is used as a reference, Generation of partial discharge using only acoustic signal components appearing within a predetermined time range t1 to t2 determined by the distance between the high voltage charging part and the mounting position of the acoustic sensor 30 in the structure of the power transformer 1 By determining whether or not there is, the possibility of misdiagnosing external noise as occurrence of partial discharge can be substantially eliminated. That is, it is determined whether or not an acoustic signal component appears in a predetermined time range t1 to t2 determined by the positional relationship between the high voltage charging unit and the acoustic sensor 30 (step S18). When an acoustic signal component appears in the predetermined time range t1 to t2 (in the case of YES in step S18), a partial discharge is generated inside the power transformer 1 that is the inspection object. (Step S20). On the other hand, when the acoustic signal component does not appear during the predetermined time range t1 to t2 (in the case of NO in step S18), partial discharge occurs in the power transformer 1 that is the inspection target. It is determined that it has not occurred (step S22).

  Thus, within the effective measurement period that is determined according to the positional relationship between the charging unit and the acoustic sensor 30 in the power transformer 1 that is the inspection object, with reference to the timing at which the application of the acquired impulse voltage is started. Based on the time waveform of the mechanical vibration removal signal (third measurement signal) that appears, it is determined whether or not partial discharge has occurred in the inspection object. That is, of the acoustic signal waveform from which the mechanical vibration component is removed, the acoustic signal that appears within a predetermined time range determined by the high voltage charging portion of the inspection object and the mounting position of the acoustic sensor 30 with reference to the impulse voltage application start time. Is determined to be partial discharge.

  Through the above steps, even during the lightning impulse withstand voltage test of the power transformer 1, noise caused by the impulse voltage generator 10, noise caused by mechanical vibration of the coil 3 of the power transformer 1, and other external The influence of noise can be avoided, and the partial discharge generated inside the power transformer 1 can be detected appropriately.

  The signal processing unit 108 of the partial discharge detection device 100 illustrated in FIG. 3 includes a function of acquiring the timing at which application of the impulse voltage is started, which is shown in step S16 described above. Further, the signal processing unit 108 removes the noise component 26 caused by the mechanical vibration of the power transformer 1 as the inspection target from the low-pass filter processing signal (second measurement signal) shown in step S14 described above. Thus, based on the function of acquiring the mechanical vibration removal signal (third measurement signal) and the acquired timing shown in step S20, the charging unit and the acoustic sensor 30 in the power transformer 1 that is the inspection target A function of determining whether or not partial discharge has occurred in the inspection object based on a time waveform of a mechanical vibration removal signal (third measurement signal) that appears within an effective measurement period determined according to the positional relationship with Have.

  By using the partial discharge detection device 100 having such a signal processing unit 108, the above-described processing procedure can be executed. As a result, when an impulse voltage is applied to the power transformer 1 that is an object to be inspected using the impulse voltage generator 10, a partial discharge generated inside the power transformer 1 can be detected.

  In addition, according to the partial discharge detection method according to the present embodiment, it is caused by the influence of electromagnetic noise radiated from the impulse voltage generator 10 and the charging current flowing through the inspection object by applying the impulse voltage. The influence of mechanical vibration of the inspection object itself can be removed. Thereby, it is possible to appropriately detect the partial discharge generated inside the device during the lightning impulse withstand voltage test.

[E. First modified example of timing acquisition at which application of impulse voltage is started]
In the above-described embodiment, it is applied to the power transformer 1 as means for obtaining the timing (impulse voltage application start time) at which application of the impulse voltage to the power transformer 1 (inspection object) is started. The method of taking the time waveform (applied voltage waveform) of the voltage to be acquired and acquiring the impulse voltage application start time based on this temporal change was illustrated. Instead of such a method, the voltage application start time may be acquired using an electromagnetic wave sensor. Hereinafter, the modification which acquires voltage application start time using an electromagnetic wave sensor is illustrated.

  FIG. 8 is a flowchart showing a processing procedure of the partial discharge detection method according to the first modification of the present embodiment. FIG. 9 is an example of a time waveform acquired by the partial discharge detection method according to the first modification of the present embodiment. FIG. 9A shows a time waveform measured when a low impulse voltage (crest value V2) at which partial discharge does not occur is applied to the charging part of the power transformer 1, and FIG. A time waveform measured when a partial discharge is actually generated by applying a high impulse voltage (peak value V1) to the charging part of the power transformer 1 is shown. In FIG. 9, (i) shows an example of a time waveform in which electromagnetic noise radiated from the impulse voltage generator 10 is acquired by an electromagnetic wave sensor. Other (ii) to (iv) are the same as (ii) to (iv) in FIG.

  In this modification, an electromagnetic wave sensor is provided in place of the input circuit 102 in the partial discharge detection device 100 shown in FIG. As the electromagnetic wave sensor, an electromagnetic wave antenna is typically used. However, any electromagnetic wave sensor may be employed as long as it can detect electromagnetic noise emitted by the impulse voltage generator 10.

  As described above, the impulse voltage generator 10 uses spark discharge between the spherical gaps 14 as an operation principle, and very strong electromagnetic noise is emitted simultaneously with the output of the impulse voltage. This electromagnetic noise is an obstacle to detecting partial discharge, but in principle, it is emitted at the same timing as impulse voltage application, so it is used to obtain the impulse voltage application start time. it can. In particular, there are many frequency band components of about several hundred MHz as frequency components included in electromagnetic noise, and when an electromagnetic noise waveform is acquired using an electromagnetic wave sensor, the rise in the detection signal is very fast (FIG. 9). (A) And the detection result of the electromagnetic wave sensor shown to (i) of (b)).

  Therefore, by adopting a method of acquiring the impulse voltage application start time using an electromagnetic wave sensor, the impulse voltage application start time can be acquired more accurately. In addition, when a time waveform (applied voltage waveform) of a voltage applied to the power transformer 1 is taken in, a relatively high voltage signal is input, so the insulation resistance of the input circuit 102 must be considered. However, in the case of an electromagnetic wave sensor, there is an advantage that such points need not be taken into consideration.

  The processing procedure according to this modification shown in FIG. 8 employs step S16A instead of step S16, as compared to the processing procedure according to the present embodiment shown in FIG. In step S <b> 16 </ b> A, a process of acquiring a time waveform of electromagnetic noise radiated from the impulse voltage generator 10 in the waveform recording unit 106 using an electromagnetic wave sensor and acquiring an impulse voltage application start time is executed. As a method for acquiring this timing, the timing at which the amplitude value exceeds a predetermined threshold value can be determined as the impulse voltage application start time. That is, the step of acquiring the timing when the application of the impulse voltage is started includes the step of detecting the change of the electromagnetic wave caused by the application of the impulse voltage by the electromagnetic wave sensor.

  In this modification, an electromagnetic wave sensor is used to acquire the impulse voltage application start time. By adopting such a configuration, it is possible to use an electromagnetic wave that includes a high-frequency component and has a fast rise, and can more clearly grasp the impulse voltage application start time.

[F. Second Modified Example Regarding Timing Acquisition at which Impulse Voltage Application is Started]
In the above-described embodiment, it is applied to the power transformer 1 as means for obtaining the timing (impulse voltage application start time) at which application of the impulse voltage to the power transformer 1 (inspection object) is started. The method of taking the time waveform (applied voltage waveform) of the voltage to be acquired and acquiring the impulse voltage application start time based on this temporal change was illustrated. Instead of such a method, the voltage application start time may be acquired using a current sensor. That is, when an impulse voltage is applied from the impulse voltage generator 10 to the power transformer 1 that is an inspection object, a charging current flows through the capacitance of the power transformer 1. This charging current is detected using a current sensor. Hereinafter, a modification example in which the voltage application start time is acquired using a current sensor will be exemplified.

  FIG. 10 is a flowchart showing a processing procedure of the partial discharge detection method according to the second modification of the present embodiment. FIG. 11 is an example of a time waveform acquired by the partial discharge detection method according to the second modification of the present embodiment. FIG. 11A shows a time waveform measured when a low impulse voltage (crest value V2) at which partial discharge does not occur is applied to the charging portion of the power transformer 1, and FIG. A time waveform measured when a partial discharge is actually generated by applying a high impulse voltage (peak value V1) to the charging part of the power transformer 1 is shown. In FIG. 11, (i) shows an example of a time waveform in which the charging current flowing through the capacitance of the power transformer 1 is acquired by the current sensor when the impulse voltage is applied from the impulse voltage generator 10. Indicates. Other (ii) to (iv) are the same as (ii) to (iv) in FIGS. 7 and 9.

  In this modification, a current sensor is provided in place of the input circuit 102 in the partial discharge detection device 100 shown in FIG.

  As described above, when the impulse voltage is applied from the impulse voltage generator 10 to the power transformer 1, a charging current flows through the capacitance of the power transformer 1. Since the rise time of the impulse voltage is as short as about 1 microsecond and the frequency component of the charging current is also high, the voltage application start time is clearly acquired by the process of acquiring the impulse voltage application start time using a current sensor. (The detection result of the electromagnetic wave sensor shown in (i) of FIGS. 11A and 11B).

  Therefore, by adopting a method of acquiring the impulse voltage application start time by measuring the charging current flowing through the capacitance of the power transformer 1 using a current sensor, the impulse voltage application start time is obtained. Can be obtained more accurately.

  The processing procedure according to this modification shown in FIG. 10 employs step S16B instead of step S16 as compared to the processing procedure according to the present embodiment shown in FIG. In step S16B, the time waveform of the charging current flowing through the capacitance of the power transformer 1 when the impulse voltage is applied from the impulse voltage generator 10 is taken into the waveform recording unit 106 using a current sensor. Then, a process of acquiring the impulse voltage application start time is executed. As a method for acquiring this timing, the timing at which the amplitude value exceeds a predetermined threshold value can be determined as the impulse voltage application start time. That is, the step of acquiring the timing at which the application of the impulse voltage is started includes the step of detecting a change in current caused by the application of the impulse voltage by the current sensor.

  In this modification, a current sensor is used to acquire the impulse voltage application start time. By adopting such a configuration, it is possible to use a current signal that includes a high-frequency component and has a fast rise, and can more clearly grasp the impulse voltage application start time.

[G. Positioning function of position where partial discharge is occurring (third modification)]
In the description of the above-described embodiment and its modified examples, the embodiment has been described in which the partial discharge generated inside the inspection object is detected using one acoustic sensor 30 as a basic configuration. The acoustic sensor 30 may be mounted on the outer surface of the inspection object, and the position where the partial discharge is generated may be located (specified).

  In order to uniquely determine the position of the partial discharge generated inside the tank 4 having a three-dimensional structure, in principle, four acoustic sensors 30 are necessary. However, by performing simultaneous measurement with five or more acoustic sensors 30, it is possible to improve the accuracy of position determination of partial discharge. Hereinafter, description will be made assuming that four or more acoustic sensors 30 are mounted on the outer surface of the tank 4 that houses the high-voltage charging unit of the power transformer 1. Further, in the partial discharge detection device 100 shown in FIG. 3, the same number of low-pass filters 104 as the number of mounted acoustic sensors 30 are provided, and the waveform recording units 106 are output from the respective low-pass filters 104. It is assumed that the low-pass filter processing signal can be recorded. Since other parts are the same as those described above, detailed description will not be repeated.

  Even when a plurality of acoustic sensors 30 are mounted on the outer surface of the tank 4, noise due to mechanical vibration of the coil 3 of the power transformer 1 in each of the acoustic sensors 30 that applies an impulse voltage to the power transformer 1. Components are detected. However, in general, the distance between the high voltage charging unit and each acoustic sensor 30 in the structure of the power transformer 1 is different from each other, or the angle from each acoustic sensor 30 to the high voltage charging unit is different. Therefore, each of the acoustic sensors 30 detects different unique mechanical vibration waveforms.

  Even in such a case, the noise component 26 caused by the mechanical vibration appearing in each of the acoustic sensors 30 has the same period and amplitude even if the peak value of the impulse voltage applied to the inspection object is changed. Only the value changes. Further, the amplitude value of the noise component 26 caused by mechanical vibration is proportional to the square of the charging current flowing through the coil 3 of each winding, that is, proportional to the square of the applied voltage. About such a characteristic, it is not different from the case where the acoustic sensor 30 is one. However, the proportionality constant related to the change of the amplitude value is different for each acoustic sensor 30.

  Considering such characteristics, the mechanical vibration waveform (noise component 26) that appears when an impulse voltage having a low peak value that does not reliably generate partial discharge is applied is measured for each acoustic sensor 30, and actually, If the mechanical vibration waveform is removed by using the above-described method from the mechanical vibration waveform that appears in each of the acoustic sensors 30 when an impulse waveform having a peak value defined in the standard is applied, in each of the acoustic sensors 30, Only components resulting from the partial discharge that is the original detection target can be extracted.

  In addition, based on the time waveform of the mechanical vibration removal signal (third measurement signal) that appears within an effective measurement period determined according to the positional relationship between the charging unit and each of the acoustic sensors 30, partial discharge at the inspection object is performed. In this effective measurement period (time range t1 to t2), a unique value is used for each acoustic sensor 30.

  In addition, with the impulse voltage application start time as a common reference, a portion inside the power transformer 1 for each of the acoustic sensors 30 based on the time delay from the impulse voltage application start time until each acoustic signal appears. The position where the discharge occurs can be determined. That is, by acquiring the arrival time difference between the partial discharge signals appearing in each of the acoustic sensors 30 from the waveform recording unit 106, the position where the partial discharge is generated can be determined based on the propagation speed of the acoustic signal in the insulating oil. Since the well-known method can be employ | adopted about the determination method of the generation | occurrence | production position of this partial discharge, detailed description is not performed.

  FIG. 12 is a flowchart showing the processing procedure of the partial discharge detection method according to the third modification of the present embodiment. Of the steps shown in FIG. 12, those that perform substantially the same processing as the steps shown in the flowchart of FIG. 6 are given the same step numbers. Specifically, assuming that N (N ≧ 4) acoustic sensors 30 are mounted, for example, for step S4_1, the first acoustic sensor 30 is substantially the same as step S4 in FIG. Indicates that is executed.

  Referring to FIG. 12, first, an impulse voltage (crest value V2: second impulse voltage) is applied to the charging portion of power transformer 1 that is an inspection object (step S2). Then, steps S4 and S6 are executed for each of the acoustic sensors 30, and a time waveform f2 (t) (reference signal) unique to each acoustic sensor 30 for determining the noise component 26 (noise component) is acquired. The

  Subsequently, an impulse voltage (crest value V1: first impulse voltage) satisfying the standard is applied to the charging part of the power transformer 1 that is the inspection object (step S8). Then, the timing when the application of the impulse voltage is started is acquired (step S16).

  In parallel with step S <b> 16, steps S <b> 10 to S <b> 14 are executed for each of the acoustic sensors 30 to acquire a mechanical vibration removal signal (third measurement signal). Furthermore, for each of the acoustic sensors 30, in the corresponding mechanical vibration removal signal, an acoustic signal component is present between the time ranges t1 to t2 unique to each acoustic sensor 30 determined by the positional relationship between the high voltage charging unit and the acoustic sensor 30. It is determined whether or not it appears (step S18). When the acoustic signal component does not appear in the predetermined time range t1 to t2 (in the case of NO in step S18), if the partial discharge does not occur in the power transformer 1 that is the inspection object. Determination is made (step S22).

  On the other hand, when an acoustic signal component appears in the predetermined time range t1 to t2 (in the case of YES in step S18), partial discharge occurs in the power transformer 1 that is the inspection object. It is determined that it has occurred (step S20). Then, the location process of the position where the partial discharge is generated in step S30 is executed. When partial discharge is generated inside the power transformer 1, it is normally determined YES in step S18 for all acoustic sensors 30.

  As described above, the step S10 for obtaining the acoustic sensor measurement signal 20 (first measurement signal) by attaching the plurality of acoustic sensors 30 to the outer surface of the inspection object and the low-pass filter processing signal (second measurement signal) are obtained. Step S12 to be acquired, Step S14 to acquire a mechanical vibration removal signal (third measurement signal), and Step S18 to determine whether or not partial discharge has occurred in the inspection target are separately provided for the plurality of acoustic sensors 30. Each is executed.

  And if it is judged that the partial discharge has generate | occur | produced inside the power transformer 1 which is a test object (in the case of YES in step S18), a plurality of mechanical vibrations respectively acquired from the plurality of acoustic sensors 30 will be described. The occurrence position of the partial discharge is determined based on the difference in timing at which the time waveform indicating the occurrence of the partial discharge appears in the removal signal (step S30). That is, the position where the partial discharge is generated is determined based on the time difference between the acoustic signals caused by the partial discharges appearing in each acoustic sensor 30.

  According to this modification, during a lightning impulse withstand voltage test of an electrical device, a plurality of acoustic sensors 30 are used to detect acoustic signals caused by partial discharges by each acoustic sensor 30 and show partial discharges that appear in each acoustic sensor 30. Based on the time difference of the time waveform, it is possible to determine the location where the partial discharge occurs in the power transformer 1. Therefore, it is possible to feed back to the design of the electric device and obtain useful information at the time of repair.

[H. advantage]
According to the partial discharge detection method according to the present embodiment, the influence of electromagnetic noise radiated from the impulse voltage generator 10 and the impulse voltage are applied to the inspection object during the lightning impulse withstand voltage test of the electrical equipment. After removing the influence of mechanical vibration of the inspection object itself caused by the flow of the charging current and the influence of external noise, the partial discharge generated inside the device is determined. Therefore, even in a state where there is a lot of external noise such as during a lightning impulse withstand voltage test, it is possible to appropriately detect a partial discharge generated inside the device.

  The configuration illustrated as the above-described embodiment is an example of the embodiment of the present invention, and can be combined with another known technique, and a part thereof is omitted without departing from the gist of the present invention. It is also possible to change and configure it.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1 power transformer, 2 iron core, 3 coil, 4 tank, 6 applied cable, 10 impulse voltage generator, 12 capacitor, 14 ball gap, 16 input terminal pair, 17 discharge resistance, 18 wave head length adjusting capacitor, 20 acoustic Sensor measurement signal, 30 acoustic sensor, 100 partial discharge detection device, 102 input circuit, 104 low-pass filter, 106 waveform recording unit, 108 signal processing unit.

Claims (6)

Applying a first impulse voltage to the charging part of the inspection object;
Obtaining a timing at which application of the first impulse voltage is started;
Obtaining a first measurement signal by an acoustic sensor mounted on the outer surface of the inspection object;
Obtaining a second measurement signal by applying a low pass filter to the first measurement signal;
Obtaining a third measurement signal by removing a noise component caused by mechanical vibration of the inspection object from the second measurement signal;
Based on the time waveform of the third measurement signal, which appears within an effective measurement period determined according to the positional relationship between the charging unit and the acoustic sensor in the inspection object, based on the acquired timing, And determining whether or not partial discharge has occurred in the inspection object,
The noise component is acquired by the acoustic sensor when a second impulse voltage lower than the first impulse voltage that does not cause partial discharge in the inspection object is applied to the charging unit of the inspection object. A partial discharge detection method that is determined based on the fourth measurement signal. Applying the second impulse voltage to the charging unit of the inspection object;
Obtaining the fourth measurement signal by the acoustic sensor;
The partial discharge detection method according to claim 1, further comprising: obtaining a reference signal for determining the noise component by applying the low-pass filter to the fourth measurement signal. Attaching a plurality of acoustic sensors to the outer surface of the inspection object, obtaining the first measurement signal, obtaining the second measurement signal, and obtaining the third measurement signal; Determining whether or not partial discharge has occurred in the inspection object, and performing each separately for the plurality of acoustic sensors;
When it is determined that a partial discharge has occurred in the inspection object, based on a difference in timing at which time waveforms indicating the occurrence of partial discharge appear in a plurality of third measurement signals respectively acquired from a plurality of acoustic sensors. The partial discharge detection method according to claim 1, further comprising a step of locating a partial discharge occurrence position.   The partial discharge detection method according to any one of claims 1 to 3, wherein the step of acquiring the timing includes a step of detecting, by an electromagnetic wave sensor, a change in an electromagnetic wave generated by applying the first impulse voltage.   The partial discharge detection method according to claim 1, wherein the step of acquiring the timing includes a step of detecting a change in current caused by application of the first impulse voltage by a current sensor. A partial discharge detection device for detecting a partial discharge generated by applying an impulse voltage to a charged part of an inspection object,
Timing acquisition means for acquiring timing at which application of the first impulse voltage to the inspection object is started;
An acoustic sensor mounted on the outer surface of the inspection object;
A first signal processing unit that outputs a second measurement signal by applying a low-pass filter to the first measurement signal detected by the acoustic sensor;
A second signal processing unit that outputs a third measurement signal by removing a noise component caused by mechanical vibration of the inspection object from the second measurement signal;
Based on the time waveform of the third measurement signal, which appears within an effective measurement period determined according to the positional relationship between the charging unit and the acoustic sensor in the inspection object, based on the acquired timing, And a judging means for judging whether or not partial discharge occurs in the inspection object,
The noise component is acquired by the acoustic sensor when a second impulse voltage lower than the first impulse voltage that does not cause partial discharge in the inspection object is applied to the charging unit of the inspection object. A partial discharge detection device determined based on the fourth measurement signal.

Images