A method and system for locating partial discharge defects in a transformer

Abstract

This invention belongs to the field of partial discharge detection technology and discloses a method and system for locating partial discharge defects in transformers. The method includes: inspecting the transformer; acquiring a detection electrical signal using an EFPI sensing unit and a detection acoustic signal using a piezoelectric ceramic ultrasonic sensor; transmitting both the detection electrical and acoustic signals to a data acquisition unit; and displaying, processing, and / or storing the acquired data using a host computer. Specifically, the existence of partial discharge is determined based on the detection electrical signal, and the location of the partial discharge defect is initially located. The precise location of the partial discharge defect is then achieved by combining the detection electrical and acoustic signals. The system includes an EFPI sensing unit, a piezoelectric ceramic ultrasonic sensor, a data acquisition unit, and a host computer. This invention can accurately locate partial discharge in transformers.

Description

Technical Field

[0001] This invention belongs to the field of partial discharge detection technology, and more specifically, relates to a method and system for locating partial discharge defects in transformers. Background Technology

[0002] Partial discharge is a common insulation fault in gas-insulated electrical equipment. It can be monitored from acoustic, optical, thermal, chemical, and mechanical perspectives to assess the operating status of the equipment. When partial discharge occurs in gas-insulated electrical equipment, the discharge space rapidly heats up, the gas expands rapidly due to heat, the pressure increases, and the gas in the discharge space vibrates, thereby generating ultrasonic waves.

[0003] Traditional ultrasonic methods use piezoelectric ceramic sensors attached to the outer casing of electrical equipment to detect ultrasonic signals transmitted from inside the equipment to the casing. However, this method is susceptible to environmental and electromagnetic interference. In addition, in field use, the signal attenuates rapidly due to factors such as reflection and interference of ultrasonic waves inside the transformer. When the detection point is far from the power source, the detection sensitivity, detection range, and detection efficiency are greatly reduced.

[0004] In recent years, optical detection technology has attracted attention in the power industry due to its advantages such as high sensitivity, strong anti-electromagnetic interference capability, and fast response speed. Optical ultrasonic detection technology uses fiber optic sensors to detect ultrasonic signals generated by partial discharge. Sensors can include fiber Michelson sensors, fiber optic Mach-Zehnder sensors, fiber Fabry-Perot sensors, fiber Bragg gratings, etc. Among them, the extrinsic fiber Fabry-Perot interferometer (EFPI) sensor, also known as an external cavity fiber Fabry-Perot interferometer, or simply EFPI sensor, has been applied to the detection and location of ultrasonic signals for partial discharges caused by insulation defects inside electrical equipment. However, solutions using EFPI sensors can typically only determine the presence of partial discharge or only roughly identify its location, without pinpointing the exact location.

[0005] Overcoming the shortcomings of traditional single detection technologies to achieve accurate localization of partial discharge in transformers is a technical problem that needs to be addressed in this field. Summary of the Invention

[0006] This invention provides a method and system for locating partial discharge defects in transformers, thereby solving the problem of poor accuracy in locating partial discharge defects in existing technologies.

[0007] This invention provides a method for locating partial discharge defects in a transformer, comprising the following steps:

[0008] The transformer is tested by using an EFPI sensing unit to acquire the electrical signal and a piezoelectric ceramic ultrasonic sensor to acquire the acoustic signal.

[0009] Both the detected electrical signal and the detected acoustic signal are transmitted to the data acquisition unit;

[0010] The host computer is used to display, process, and / or store the collected data;

[0011] Specifically, the presence of partial discharge is determined based on the detected electrical signal, and the location of the partial discharge defect is initially located. The location of the partial discharge defect is then precisely located by combining the detected electrical signal and the detected acoustic signal.

[0012] Preferably, in the detected electrical signals, the position of the EFPI sensor corresponding to the pulse with the largest signal amplitude or the most obvious characteristics is identified, and this position is regarded as the preliminary positioning position.

[0013] Preferably, during the precise positioning process, the detection acoustic signals corresponding to the high-voltage side measuring point and the low-voltage side measuring point of the transformer box are obtained respectively, and the side corresponding to the pulse with larger signal amplitude or more obvious characteristics is taken as the discharge side;

[0014] Acquire the detection acoustic signals corresponding to multiple measurement points at different locations on the discharge side, and find the measurement point location corresponding to the pulse with the largest signal amplitude or the most obvious feature as the candidate positioning location.

[0015] Determine whether the pulse of the candidate positioning position matches the pulse of the preliminary positioning position; if the pulses match, then the candidate positioning position is regarded as the precise positioning position.

[0016] Preferably, the method for locating partial discharge defects in the transformer further includes: determining whether the time difference between the pulse at the candidate location and the pulse at the preliminary location is less than a set time difference threshold; if the pulses match and the time difference between the two pulses is less than the time difference threshold, then the candidate location is regarded as the precise location.

[0017] Preferably, the detection acoustic signals corresponding to multiple measuring points at different positions in the vertical direction of the discharge side are obtained, and the measuring point position corresponding to the pulse with the largest signal amplitude or the most obvious characteristics in the vertical direction is identified as the first candidate positioning position.

[0018] Acquire the detection acoustic signals corresponding to multiple measurement points at different positions in the horizontal direction of the discharge side, and find the measurement point corresponding to the pulse with the largest signal amplitude or the most obvious characteristics in the horizontal direction as the second candidate positioning position.

[0019] The first candidate location and the second candidate location are used as the candidate location.

[0020] Preferably, after determining the first candidate positioning location, the detection sound signals corresponding to multiple measuring points at different locations within the horizontal region corresponding to the first candidate positioning location are obtained, and the measuring point corresponding to the pulse with the largest signal amplitude or the most obvious feature within the horizontal region is identified as the candidate positioning location.

[0021] Preferably, the EFPI sensing unit includes a light source, a circulator, an EFPI sensor, and a photodetector; continuous light emitted by the light source is transmitted to the EFPI sensor through the circulator, and after being reflected by the EFPI sensor, the light is transmitted to the photodetector through the circulator; the piezoelectric ceramic ultrasonic sensor and the photodetector are respectively connected to the data acquisition unit, and the data acquisition unit is connected to the host computer.

[0022] Preferably, the EFPI sensor includes an FP cavity composed of an optical fiber end face and the inner surface of an acoustically sensitive membrane; the target thickness of the acoustically sensitive membrane is 48 μm to 55 μm.

[0023] Preferably, the acoustic sensitive membrane with a first thickness is bonded to the end face of the quartz tube, the end face of the quartz tube is placed on a grinding machine, and the thickness of the acoustic sensitive membrane is ground to the target thickness using sandpaper. During the grinding process, the quartz tube is used as a handle to control the grinding force.

[0024] On the other hand, the present invention provides a system for locating partial discharge defects in a transformer, comprising: an EFPI sensing and detection unit, a piezoelectric ceramic ultrasonic sensor, a data acquisition unit, and a host computer;

[0025] The system for locating partial discharge defects in a transformer is used to perform the steps in the method for locating partial discharge defects in a transformer as described above.

[0026] One or more technical solutions provided in this invention have at least the following technical effects or advantages:

[0027] The method provided by this invention includes detecting a transformer, acquiring a detection electrical signal using an EFPI sensing unit, and acquiring a detection acoustic signal using a piezoelectric ceramic ultrasonic sensor; transmitting both the detection electrical and acoustic signals to a data acquisition unit; and displaying, processing, and / or storing the acquired data using a host computer. Specifically, the method involves determining the presence of partial discharge and initially locating the partial discharge defect based on the detection electrical signal, and then precisely locating the partial discharge defect by combining the detection electrical and acoustic signals. This invention effectively combines the advantages of electrical and acoustic signals, compensating for each other's shortcomings. It employs an integrated multi-parameter data acquisition design, enabling simultaneous acquisition of multiple parameters and multi-parameter comparative analysis. This provides more comprehensive information for equipment fault diagnosis, and through cross-validation and joint positioning, achieves more accurate positioning results. Attached Figure Description

[0028] Figure 1 This is a flowchart corresponding to a method for locating partial discharge defects in a transformer provided in Embodiment 1 of the present invention;

[0029] Figure 2 This is a schematic diagram showing the selection of measuring points and precise positioning for a method of locating partial discharge defects in a transformer, as provided in Embodiment 1 of the present invention. Detailed Implementation

[0030] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0031] Example 1:

[0032] Example 1 provides a method for locating partial discharge defects in a transformer, see [link to example]. Figure 1 This includes the following steps:

[0033] The transformer is tested by using an EFPI sensing unit to acquire the electrical signal and a piezoelectric ceramic ultrasonic sensor to acquire the acoustic signal.

[0034] Both the detected electrical signal and the detected acoustic signal are transmitted to the data acquisition unit;

[0035] The host computer is used to display, process, and / or store the collected data;

[0036] Specifically, the presence of partial discharge is determined based on the detected electrical signal, and the location of the partial discharge defect is initially located. The location of the partial discharge defect is then precisely located by combining the detected electrical signal and the detected acoustic signal.

[0037] Specifically, in the detected electrical signals, the position of the EFPI sensor corresponding to the pulse with the largest signal amplitude or the most obvious characteristics is identified, and this position is regarded as the preliminary positioning position.

[0038] During the precise positioning process, the detection acoustic signals corresponding to the high-voltage side and low-voltage side measuring points of the transformer tank are acquired, and the side corresponding to the pulse with larger signal amplitude or more obvious characteristics is designated as the discharge side. The detection acoustic signals corresponding to the measuring points at multiple different positions on the discharge side are acquired, and the measuring point position corresponding to the pulse with the largest signal amplitude or most obvious characteristics is identified as the candidate positioning position. It is then determined whether the pulse of the candidate positioning position matches the pulse of the preliminary positioning position. If the pulses match, the candidate positioning position is considered as the precise positioning position.

[0039] Based on the above scheme, it can further include: determining whether the time difference between the pulse of the candidate positioning position and the pulse of the preliminary positioning position is less than a set time difference threshold; if the pulses match and the time difference between the two pulses is less than the time difference threshold, then the candidate positioning position is regarded as the precise positioning position.

[0040] That is, after obtaining one or more candidate locations, the present invention determines the final precise location by combining the characteristics of the pulses at the preliminary location (whether the two pulses match, whether the time difference between the two pulses is small enough).

[0041] The candidate location can be obtained in the following two ways.

[0042] (1) Obtain the detection sound signals corresponding to multiple different measurement points located in the vertical direction of the discharge side, and find the measurement point position corresponding to the pulse with the largest signal amplitude or the most obvious feature in the vertical direction as the first candidate positioning position; obtain the detection sound signals corresponding to multiple different measurement points located in the horizontal direction of the discharge side, and find the measurement point corresponding to the pulse with the largest signal amplitude or the most obvious feature in the horizontal direction as the second candidate positioning position; use the first candidate positioning position and the second candidate positioning position as the candidate positioning position.

[0043] That is, method (1) obtains candidate positioning positions in the vertical and horizontal directions respectively, and then integrates the candidate positioning positions in these two directions into the final candidate positioning position.

[0044] (2) Obtain the detection sound signals corresponding to multiple different measurement points located in the vertical direction of the discharge side, and find the measurement point position corresponding to the pulse with the largest signal amplitude or the most obvious feature in the vertical direction as the first candidate positioning position; after determining the first candidate positioning position, obtain the detection sound signals corresponding to multiple different measurement points in the horizontal area corresponding to the first candidate positioning position, and find the measurement point corresponding to the pulse with the largest signal amplitude or the most obvious feature in the horizontal area as the candidate positioning position.

[0045] Method (2) first obtains the candidate positioning positions in the vertical direction (i.e., the first candidate positioning position), and then selects the final candidate positioning position within the horizontal area corresponding to the first candidate positioning position. Compared with method (1), method (2) reduces the detection range in the horizontal direction and has higher detection efficiency.

[0046] In addition, method (2) can also be replaced by first finding the candidate positioning positions in the horizontal direction, and then selecting the final candidate positioning position in the vertical area corresponding to the candidate positioning positions in the horizontal direction.

[0047] The EFPI sensing unit includes a light source, a circulator, an EFPI sensor, and a photodetector. Continuous light emitted by the light source is transmitted to the EFPI sensor through the circulator. After being reflected by the EFPI sensor, the light is transmitted to the photodetector through the circulator.

[0048] The piezoelectric ceramic ultrasonic sensor and the photodetector are respectively connected to the data acquisition unit, and the data acquisition unit is connected to the host computer.

[0049] This invention allows for quick installation without altering the original equipment structure, and does not affect the normal operation of the equipment after installation, making maintenance simple.

[0050] In addition, the present invention can transmit the detection data to the monitoring backend such as mobile terminal in real time, so that users can easily realize remote monitoring and management through the monitoring backend.

[0051] Specifically, the EFPI sensor includes an FP cavity composed of an optical fiber end face and the inner surface of an acoustically sensitive membrane; the target thickness of the acoustically sensitive membrane is 48 μm to 55 μm.

[0052] The present invention can bond an acoustically sensitive membrane with a first thickness to the end face of a quartz tube, place the end face of the quartz tube on a grinding machine, and use polishing sandpaper to grind the thickness of the acoustically sensitive membrane to the target thickness. During the grinding process, the quartz tube is used as a handle to control the grinding force.

[0053] The following explains the principle of using the EFPI sensing detection unit to determine the existence of partial discharge and to preliminarily locate the partial discharge defect.

[0054] When light enters the EFPI sensor, part of the light is reflected back into the fiber at the fiber end face, while the other part is refracted into the FP cavity and reflected again on the acoustic sensitive membrane, then coupled back into the fiber. The two reflected beams interfere. When an external ultrasonic signal causes the acoustic sensitive membrane of the EFPI sensor to vibrate, the cavity length of the FP cavity formed between the fiber end face and the acoustic sensitive membrane changes, resulting in a change in the optical path difference of the interference light.

[0055] When partial discharge occurs, the generated ultrasonic signal acts on the acoustic-sensitive diaphragm of the EFPI sensor, causing a change in the cavity length of the FP cavity. This alters the optical path difference between the two beams, ultimately leading to a change in the intensity of the reflected light. By demodulating the intensity of the interference light, the ultrasonic waves generated by partial discharge can be detected. In other words, by detecting changes in intensity, the ultrasonic vibration signal during partial discharge can be detected. This method has advantages such as fast frequency response and simple structure.

[0056] The deformation at the center point of the acoustic diaphragm affects the measurement range and accuracy of the EFPI sensor, and this deformation is only related to the thickness and radius of the diaphragm. When the sound wave frequency is close to the natural frequency of the EFPI sensor, the acoustic diaphragm will experience a large deformation due to resonance characteristics, making it impossible to maintain a linear relationship. To ensure a relatively flat frequency response for the EFPI sensor, the natural frequency of the acoustic diaphragm should be at least three times the maximum measurement frequency. For the EFPI sensor to achieve a relatively flat frequency response in the 20kHz to 80kHz range where partial discharge (PD) ultrasonic frequencies are concentrated, the natural frequency of the acoustic diaphragm is preferably around 240kHz.

[0057] For example, to balance the sensitivity and detection frequency range of the EFPI sensor, this invention selects an acoustic diaphragm thickness of 48 μm to 55 μm, a radius of 1500 μm, and a FP cavity length of 33.7 μm. The natural frequency of the EFPI sensor is calculated to be 234.85 kHz. Furthermore, by fitting the curve of the acoustic diaphragm's deformation as a function of pressure, the diaphragm deformation sensitivity of this EFPI sensor can reach 106.6 nm / kPa.

[0058] Considering that the acoustic sensitive membrane has a large radius and a thin thickness, it is very easy to break during preparation. Therefore, this invention first bonds the acoustic sensitive membrane with a radius of 1.75 mm and a thickness of 120 μm to the end face of a quartz tube. Then, the end face of the quartz tube is placed on a polishing machine, and the thickness of the membrane is polished to 50 μm using polishing sandpaper with an abrasive grit of 8000 grit. At this time, the quartz tube can be used as a handle to control the polishing force, which can greatly reduce the chance of the membrane breaking.

[0059] The light source in the EFPI sensing unit can specifically be a narrow-linewidth laser source emitting continuous light. After passing through the photodetector, the weak light signal is converted into an electrical signal and amplified on the photodetector.

[0060] This invention can determine whether a transformer has a partial discharge defect based on the detected electrical signal, and can also roughly determine the location of the defect. To further determine the precise location of the defect in the transformer, this invention combines the electrical signal obtained by the EFPI sensing detection unit and the acoustic signal obtained by the piezoelectric ceramic ultrasonic sensor for secondary precise localization.

[0061] Furthermore, the EFPI sensor acquires optical signals, and subsequent processing converts these weak signals into electrical signals. Since the signal propagation speed is the speed of light, the time required for detection is negligible. In contrast, the piezoelectric ceramic ultrasonic sensor is placed on the transformer housing. The discharge sound signal is transmitted to the sensor via the transformer oil medium, and the propagation speed of the ultrasonic signal in the transformer oil is approximately c² ≈ 1400 m / s. Therefore, the spatial linear distance Δs between the discharge defect and the piezoelectric ceramic ultrasonic sensor can be calculated using Δs = c² × Δt, where Δt is the time difference between the acoustic and optical signals.

[0062] The present invention will be further illustrated below with examples of the selection of measuring points.

[0063] See Figure 2 The electrical signal obtained by the EFPI sensing and detection unit and the piezoelectric ceramic ultrasonic sensor (i.e., Figure 2 The acoustic signal obtained by the ultrasonic probe is simultaneously input to two channels of the oscilloscope.

[0064] First, in the detected electrical signals, the position of the EFPI sensor corresponding to the pulse with the largest signal amplitude or the most obvious characteristics is identified, and this position is regarded as the preliminary positioning position.

[0065] Then, the detection acoustic signals corresponding to the high-voltage side and low-voltage side measuring points of the transformer box are obtained respectively, and the side corresponding to the pulse with larger signal amplitude or more obvious characteristics is taken as the discharge side.

[0066] For example, see Figure 2 Comparison of high-voltage side measuring points (measuring points) ) and low-pressure side measuring points (measuring points) The results showed that the pulse amplitude (relative value) at the high-voltage side measuring point was significantly larger, while the pulse amplitude at the low-voltage side measuring point was not significant, indicating that the discharge was located on the high-voltage side.

[0067] Then, the detection acoustic signals corresponding to multiple measurement points at different locations on the discharge side are acquired, and the measurement point location corresponding to the pulse with the largest signal amplitude or the most obvious characteristics is identified as the candidate positioning location; it is determined whether the pulse of the candidate positioning location matches the pulse of the preliminary positioning location; if the pulses match, the candidate positioning location is regarded as the precise positioning location.

[0068] For example, see Figure 2 Compare multiple measuring points in the vertical direction on the high-pressure side (including measuring points) It was found that the ultrasonic signals at all points in the vertical direction exhibited significant pulses, which matched the electrical signal pulses. Based on calculations, the measurement points... The ultrasonic amplitude is highest at point d, which is closest to the discharge source. Next, multiple measuring points in the horizontal direction on the high-voltage side (including measuring point d) are compared. ), and found that the same measuring point The ultrasonic amplitude at this location is still the highest, and it is closest to the discharge source. Therefore, it can be concluded that the partial discharge defect is located on the high-voltage side, based on the measuring point. Within a hemispherical space with center d and radius d.

[0069] Example 2:

[0070] Example 2 provides a system for locating partial discharge defects in a transformer, comprising: an EFPI sensing detection unit, a piezoelectric ceramic ultrasonic sensor, a data acquisition unit, and a host computer; the system for locating partial discharge defects in a transformer provided in Example 2 is used to perform the steps in the method for locating partial discharge defects in a transformer as provided in Example 1.

[0071] Since the functions of each device in the system provided in Embodiment 2 correspond to the steps in the method provided in Embodiment 1, Embodiment 2 can be understood by referring to the description of Embodiment 1, and will not be repeated here.

[0072] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for locating partial discharge defects in a transformer, characterized in that, Includes the following steps: The transformer is tested by using an EFPI sensing unit to acquire the electrical signal and a piezoelectric ceramic ultrasonic sensor to acquire the acoustic signal. Both the detected electrical signal and the detected acoustic signal are transmitted to the data acquisition unit; The collected data can be displayed, processed, and / or stored using a host computer. Specifically, the presence of partial discharge is determined and the location of partial discharge defects is initially located based on the detected electrical signal, and the location of partial discharge defects is precisely located by combining the detected electrical signal and the detected acoustic signal. The EFPI sensing and detection unit includes a light source, a circulator, an EFPI sensor, and a photodetector. Continuous light emitted by the light source is transmitted to the EFPI sensor through the circulator. After being reflected by the EFPI sensor, the light is transmitted to the photodetector through the circulator. The piezoelectric ceramic ultrasonic sensor and the photodetector are respectively connected to the data acquisition unit, and the data acquisition unit is connected to the host computer. In the detected electrical signals, the position of the EFPI sensor corresponding to the pulse with the largest signal amplitude or the most obvious characteristics is identified, and this position is regarded as the preliminary positioning position. During the precise positioning process, the detection acoustic signals corresponding to the high-voltage side and low-voltage side measuring points of the transformer tank are acquired, and the side corresponding to the pulse with larger signal amplitude or more obvious characteristics is designated as the discharge side. The detection acoustic signals corresponding to multiple measuring points at different locations on the discharge side are acquired, and the measuring point location corresponding to the pulse with the largest signal amplitude or most obvious characteristics is identified as a candidate positioning location. It is determined whether the pulse at the candidate positioning location matches the pulse at the preliminary positioning location. It is also determined whether the time difference between the pulse at the candidate positioning location and the pulse at the preliminary positioning location is less than a set time difference threshold. If the pulses match and the time difference between the two pulses is less than the time difference threshold, then the candidate positioning location is considered the precise positioning location. The spatial straight-line distance Δs between the discharge defect and the piezoelectric ceramic ultrasonic sensor is calculated by Δs=c2×Δt, where Δt is the time difference between the acoustic and optical signals and c2 is the propagation speed of the ultrasonic signal in the transformer oil.

2. The method for locating partial discharge defects in a transformer according to claim 1, characterized in that, Acquire the detection acoustic signals corresponding to multiple measurement points at different positions in the vertical direction of the discharge side, and find the measurement point position corresponding to the pulse with the largest signal amplitude or the most obvious characteristics in the vertical direction as the first candidate positioning position; Acquire the detection acoustic signals corresponding to multiple measurement points at different positions in the horizontal direction of the discharge side, and find the measurement point corresponding to the pulse with the largest signal amplitude or the most obvious characteristics in the horizontal direction as the second candidate positioning position. The first candidate location and the second candidate location are used as the candidate location.

3. The method for locating partial discharge defects in a transformer according to claim 2, characterized in that, After determining the first candidate positioning location, the detection sound signals corresponding to multiple different measurement points in the horizontal area corresponding to the first candidate positioning location are obtained respectively, and the measurement point corresponding to the pulse with the largest signal amplitude or the most obvious feature in the horizontal area is identified as the candidate positioning location.

4. The method for locating partial discharge defects in a transformer according to claim 1, characterized in that, The EFPI sensor includes an FP cavity consisting of an optical fiber end face and the inner surface of an acoustically sensitive membrane; the target thickness of the acoustically sensitive membrane is 48 μm to 55 μm.

5. The method for locating partial discharge defects in a transformer according to claim 4, characterized in that, A sound-sensitive membrane with a first thickness is bonded to the end face of a quartz tube. The end face of the quartz tube is placed on a polishing machine, and sandpaper is used to polish the thickness of the sound-sensitive membrane to the target thickness. During the polishing process, the quartz tube is used as a handle to control the polishing force.

6. A system for locating partial discharge defects in a transformer, characterized in that, include: EFPI sensing and detection unit, piezoelectric ceramic ultrasonic sensor, data acquisition unit and host computer; The system for locating partial discharge defects in a transformer is used to perform the steps in the method for locating partial discharge defects in a transformer as described in any one of claims 1-5.

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