Acoustic emission detection device and method for partial discharge of transformer

Abstract

The invention provides an acoustic emission detection device and method for partial discharge of a transformer. The device comprises a plurality of acoustic emission sensing assemblies located in the transformer. Each acoustic emission sensing assembly comprises a laser, an optical micro-ring acoustic emission sensor and a photoelectric detector; the laser is connected to a straight wave lead-in port of the optical micro-ring acoustic emission sensor through an optical fiber, and an emergent port of the optical micro-ring acoustic emission sensor is connected with the photoelectric detector through an optical fiber; after an acoustic emission signal in the transformer acts on the optical micro-ring acoustic emission sensor, the photoelectric detector detects the parameter change of a laser signal in a micro resonant cavity of the optical micro-ring acoustic emission sensor so as to realize the detection of the acoustic emission signal in the transformer. According to the invention, a direct wave signal can be obtained, a high-resolution acoustic emission signal can be obtained, and an acoustic emission curve with a high signal-to-noise ratio can be obtained by using the optical micro-ring acoustic emission sensor so as to realize accurate positioning of a partial discharge position.

Description

Technical Field

[0001] The invention belongs to the technical field of acoustic emission sensors, and in particular relates to an acoustic emission detection device and method for partial discharge of a transformer. Background Art

[0002] As an electric power equipment used to achieve high-low voltage conversion in the power system, the safety of the power transformer during operation is extremely important for the protection of power supply and people's lives. Once a power transformer fails during operation, it is very likely to cause a regional power outage. Due to the special structure of the power transformer, the insulation part cannot be guaranteed to be uniform everywhere, and it is inevitable that there will be gaps, adhesions and other production errors. These defects will form uneven spaces inside the transformer and then form uneven electric fields, which will then cause regional electric field distortion inside or on the surface of the insulator due to the continuous impact of the uneven electric field. When the power load increases or a lightning strike occurs, a sudden discharge will form and then a local discharge will form. The local discharge will continue to erode the electrical properties of the insulating medium and eventually make the insulating material completely lose its isolation effect. In practical applications, the local discharge characteristics are used as the main indicators for monitoring the insulation quality. During local discharge, the above-mentioned acoustic emission signal will be generated due to the continuous breakdown of the air.

[0003] At present, the commonly used transformer acoustic detection method is to install multiple piezoelectric ceramic sensors on the outside of the transformer oil tank to receive the ultrasonic waves generated by partial discharge. By comparing the intensity of the collected signals, the approximate location and intensity of the partial discharge can be determined, or a fiber optic sensor is placed inside the transformer oil tank to detect the acoustic emission signal. Piezoelectric ceramic acoustic emission sensors are easily affected by magnetic field interference. When used on strong magnetic field power equipment such as transformers, signal distortion and other phenomena will occur, affecting the detection sensitivity. Summary of the invention

[0004] The present invention aims at the problem of low sensitivity in the prior art and provides an acoustic emission detection device and method for transformer partial discharge.

[0005] In a first aspect, the present invention provides an acoustic emission detection device for partial discharge of a transformer, comprising a plurality of acoustic emission sensor components located inside the transformer;

[0006] Each of the acoustic emission sensing components comprises a laser, an optical microring acoustic emission sensor and a photodetector; the laser is connected to the direct wave guide input port of the optical microring acoustic emission sensor via an optical fiber, and the output port of the optical microring acoustic emission sensor is connected to the photodetector via an optical fiber;

[0007] The laser is used to emit a laser signal; the laser signal is transmitted to the optical microring acoustic emission sensor through an optical fiber and then transmitted to a photodetector through an optical fiber; the photodetector is used to detect the laser signal in the microresonant cavity of the optical microring acoustic emission sensor and convert the laser signal into an electrical signal;

[0008] After the acoustic emission signal inside the transformer acts on the optical microring acoustic emission sensor, the photoelectric detector detects the parameter change of the laser signal in the microresonant cavity of the optical microring acoustic emission sensor to realize the detection of the acoustic emission signal inside the transformer.

[0009] Optionally, the optical micro-ring acoustic emission sensor comprises a substrate layer and a straight waveguide and a racetrack-shaped waveguide located on the substrate layer; the straight waveguide is parallel to the straight waveguide of the racetrack-shaped waveguide;

[0010] The thickness of the substrate layer below the racetrack-shaped waveguide is smaller than the thickness of the substrate layer below the straight waveguide.

[0011] Optionally, the base layer is made of silicon dioxide.

[0012] Optionally, the straight waveguide and the racetrack-shaped waveguide are both made of polystyrene.

[0013] Optionally, the spacing between the straight waveguide and the straight waveguide segments of the racetrack waveguide is 300 nanometers.

[0014] Optionally, a diameter of the microresonant cavity of the optical microring acoustic emission sensor is greater than or equal to 10 microns and less than or equal to 100 microns.

[0015] Optionally, the resonance condition of the microresonant cavity of the optical microring acoustic emission sensor satisfies:

[0016] (2πR+2L)n eff =mλ;

[0017] Wherein, R is the radius of the arc section waveguide of the racetrack-shaped waveguide; L is the length of the straight section waveguide of the racetrack-shaped waveguide; n eff is the effective refractive index; m is the resonance order; λ is the resonance wavelength.

[0018] Optionally, the electrical signal converted by the photodetector is processed by a bandpass filter, and then a wavelet transform is used to obtain a time-frequency diagram of the acoustic emission signal in the micro-resonant cavity of the optical micro-ring acoustic emission sensor.

[0019] Optionally, the plurality of acoustic emission sensor assemblies are arranged along the circumference of the inner wall of the transformer and are not in contact with the windings of the transformer.

[0020] In a second aspect, the present invention provides an acoustic emission detection method for transformer partial discharge, which is applied to the acoustic emission detection device for transformer partial discharge described in the first aspect, and the acoustic emission detection method comprises:

[0021] A laser signal is generated by a laser, and the laser signal is transmitted to an optical micro-ring acoustic emission sensor distributed inside the transformer through an optical fiber;

[0022] When local discharge occurs inside the transformer and an acoustic emission signal is generated, the acoustic emission signal acts on the optical microring acoustic emission sensor, causing the micro-resonance cavity structure in the optical microring acoustic emission sensor to change slightly under the action of the stress wave, and at the same time, the effective refractive index changes under the influence of the photoelastic effect, thereby changing the output spectrum of the laser signal and causing the resonance peak to shift;

[0023] The optical signal changes in the micro-resonant cavity are detected by a photodetector and converted into electrical signals, and the time-frequency diagram of the acoustic emission signal is obtained by using a wavelet transform algorithm.

[0024] According to the time-frequency diagram of the acoustic emission signal, a four-point positioning algorithm is used to locate the local discharge point that generates the acoustic emission signal.

[0025] The present invention provides an acoustic emission detection device and method for partial discharge of a transformer. An optical micro-ring acoustic emission sensor in the device is made of polystyrene and silicon dioxide as insulating materials and is not subject to electromagnetic interference. The sensor can be placed inside a transformer without being interfered by external noise and is less affected by the transformer when placed inside the transformer. A direct wave signal and a high-resolution acoustic emission signal can be obtained. The silicon dioxide with a membrane structure can be used to obtain an acoustic emission curve with a high signal-to-noise ratio to achieve accurate positioning of the partial discharge position. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solution of the present invention, the drawings required for use in the embodiments are briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 A diagram showing an application scenario of an acoustic emission detection device for partial discharge of a transformer provided by an embodiment of the present invention;

[0028] Figure 2 A schematic structural diagram of an acoustic emission detection device for partial discharge of a transformer provided by an embodiment of the present invention;

[0029] Figure 3 A schematic top view of an optical micro-ring acoustic emission sensor provided by an embodiment of the present invention;

[0030] Figure 4 A schematic side view of an optical microring acoustic emission sensor provided by an embodiment of the present invention;

[0031] Figure 5 An output spectrum diagram of the optical microring acoustic emission sensor provided by an embodiment of the present invention;

[0032] Figure 6 A schematic diagram of the principle of detecting acoustic emission signals of the optical micro-ring acoustic emission sensor provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] Example 1

[0035] like Figure 1 As shown, this embodiment provides an acoustic emission detection device for partial discharge of a transformer, comprising a plurality of acoustic emission sensor components 1 located inside the transformer. The plurality of acoustic emission sensor components 1 are arranged along the circumference of the inner wall of the transformer and do not contact the winding of the transformer.

[0036] Three optical micro-ring acoustic emission sensors 12 are arranged at equal intervals on each sensor support frame 2; each sensor support frame 2 is fixed to the inside of the transformer box 3 through a support frame connector 4, and each sensor support frame 2 is a distance away from the three-phase winding 6 of the transformer, and each sensor support frame 2 does not contact the iron yoke 5.

[0037] like Figure 2 and Figure 3 As shown, each acoustic emission sensing component 1 includes a laser 11, an optical microring acoustic emission sensor 12 and a photodetector 13; the laser 11 is connected to the direct wave guide incident port of the optical microring acoustic emission sensor 12 through an optical fiber, and the output port of the optical microring acoustic emission sensor 12 is connected to the photodetector 13 through an optical fiber.

[0038] The laser 11 is used to emit a laser signal; the laser signal is transmitted to the optical microring acoustic emission sensor 12 through an optical fiber and then transmitted to the photodetector 13 through an optical fiber; the photodetector 13 is used to detect the laser signal in the microresonant cavity of the optical microring acoustic emission sensor 12 and convert the laser signal into an electrical signal.

[0039] After the acoustic emission signal inside the transformer acts on the optical micro-ring acoustic emission sensor 12, the photodetector 13 detects the parameter change of the laser signal in the micro-resonance cavity of the optical micro-ring acoustic emission sensor 12 to realize the detection of the acoustic emission signal inside the transformer.

[0040] like Figure 3 and Figure 4 As shown, the optical micro-ring acoustic emission sensor 12 includes a substrate layer 121 and a straight waveguide 122 and a racetrack-shaped waveguide 123 located on the substrate layer 121; the straight waveguide 122 is parallel to the straight waveguide of the racetrack-shaped waveguide 123; the thickness of the substrate layer 121 below the racetrack-shaped waveguide 123 is less than the thickness of the substrate layer 121 below the straight waveguide 122 (i.e., the substrate layer 121 in the center of the racetrack-shaped waveguide 123 is etched into a film structure). Exemplarily, the substrate layer 121 is made of silicon dioxide. The straight waveguide 122 and the racetrack-shaped waveguide 123 are both made of polystyrene.

[0041] The optical racetrack-shaped micro-resonant cavity is of micron size, and in this embodiment, the size is between 10 microns and 100 microns. A smaller racetrack-shaped micro-resonant cavity structure can be prepared by electron beam etching and nanoimprinting. The distance between the racetrack-shaped waveguide 123 and the straight waveguide 122 used in this embodiment is 300 nanometers. By etching a silicon dioxide film structure under the optical racetrack-shaped micro-resonant cavity, the selection of sound signals in a specific band and the increase of sound sensitivity can be achieved.

[0042] like Figure 5 The output spectrum of the polystyrene optical racetrack-shaped microresonator is shown. The working principle of the optical racetrack-shaped microresonator is that light of a specific wavelength meets the resonance condition in the microresonator:

[0043] (2πR+2L)n eff =mλ.

[0044] Wherein, R is the radius of the arc segment waveguide of the racetrack-shaped waveguide (123); L is the length of the straight segment waveguide of the racetrack-shaped waveguide (123); n eff is the effective refractive index; m is the resonance order; λ is the resonance wavelength.

[0045] When the resonance condition is met, coherent enhancement will occur in the optical racetrack-shaped microresonator, resulting in a lack of corresponding wavelength light energy in the output spectrum, reducing the transmittance of the structure. Since the resonance wavelength condition appears periodically, the resonance peak will also appear periodically in the spectrum.

[0046] like Figure 6As shown, it is a schematic diagram of an optical racetrack-shaped micro-resonant cavity acoustic emission sensor (i.e., an optical micro-ring acoustic emission sensor) detecting an acoustic signal. When the acoustic emission signal acts on the runway structure, the optical racetrack-shaped micro-resonant cavity structure will be slightly changed under the action of stress waves. At the same time, under the influence of the photoelastic effect, the stress change of the material will cause the change of its refractive index, that is, the effective refractive index of the optical racetrack-shaped micro-resonant cavity will change, which will change the output spectrum of the optical racetrack-shaped micro-resonant cavity to a certain extent, causing the resonance peak to shift, and positioning the wavelength of the optical signal emitted by the laser 11 at the half-peak of the resonance peak. Here, the optical racetrack-shaped micro-resonant cavity sensor has the best detection sensitivity. Through the photodetector 13, the output energy of a specific light wavelength can be detected to demodulate the amplitude information of the acoustic signal. The sensitivity can be further increased by etching the silicon dioxide film structure. The sensitivity of the optical racetrack-shaped micro-resonant cavity is represented by the Q value. The steeper the resonance spectrum, the higher the Q value of the sensor. The Q value of the optical racetrack-shaped micro-resonant cavity of this embodiment is as high as 7*106, so that it can respond to weak acoustic emission signals.

[0047] By positioning the wavelength of the optical signal emitted by the laser 11 at the half-peak of the resonance peak (where the sensor has the best detection sensitivity), the photodetector 13 can be used to detect the output energy change of a specific optical wavelength, thereby demodulating the amplitude information of the acoustic signal. The photoelastic effect enables the optical racetrack-shaped micro-resonance cavity to convert the acoustic emission signal into a measurable optical signal change, achieving high-sensitivity detection of the acoustic emission signal, which helps to accurately identify and locate the partial discharge phenomenon in the transformer.

[0048] The photoelastic effect and the structural design of the optical racetrack-shaped microresonant cavity determine the resonance conditions and the initial output spectrum shape, and the photoelastic effect dynamically adjusts the output spectrum according to the stress changes caused by the acoustic emission signal.

[0049] At the same time, the choice of materials will also affect the strength of the photoelastic effect. For example, the photoelastic properties of the structure composed of polystyrene and silicon dioxide when subjected to stress enable the microresonator to effectively convert the acoustic emission signal into an optical signal change, and by optimizing the structure and materials, the detection system's response sensitivity and accuracy to the acoustic emission signal are improved.

[0050] The acoustic emission signal consists of a sinusoidal part and a natural exponential. The amplitude of the acoustic emission signal will decay rapidly over time. The frequency of the acoustic emission signal generated by partial discharge in the transformer is generally between 20 and 400 kHz.

[0051] After the electrical signal converted by the photodetector 13 is processed by a bandpass filter, the wavelet transform is used to obtain the time-frequency diagram of the acoustic emission signal in the micro-resonant cavity of the optical micro-ring acoustic emission sensor 12. The specific time node of the occurrence of the high-frequency signal of the acoustic emission can be clearly analyzed by the wavelet transform. The wavelet transform is obtained by convolving the wavelet function with the detection signal with the wavelet characteristics. The wavelet characteristics are: 1) The integral value of the wavelet function in the time domain is zero; 2) The wavelet contains finite energy. The selection of different wavelet functions will affect the accuracy of the time-frequency diagram to a certain extent, and affect the positioning accuracy. The wavelet function used in this embodiment is the Morlet wavelet function.

[0052] The acoustic emission signal time-frequency diagram contains the information of the signal in the time and frequency domain. The local discharge process will generate acoustic emission signals, which will carry relevant information about the location of the discharge point when propagating to the sensor.

[0053] When partial discharge occurs, the acoustic emission signal generated will propagate in the medium at a certain speed. The time and frequency characteristics of the signal generated by the discharge point at different locations reaching the sensor will be different. By analyzing the signal characteristics in the time-frequency diagram, the partial discharge point can be located.

[0054] In summary, the acoustic emission detection device for partial discharge of a transformer provided in this embodiment, wherein the optical micro-ring acoustic emission sensor is composed of polystyrene and silicon dioxide as insulating materials and is not affected by electromagnetic interference, can be placed inside the transformer without being disturbed by external noise, and is less affected by the transformer when placed inside the transformer, can obtain direct wave signals, can obtain high-resolution acoustic emission signals, and can obtain an acoustic emission curve with a high signal-to-noise ratio by using membrane-structured silicon dioxide to achieve precise positioning of the partial discharge position.

[0055] Example 2

[0056] This embodiment provides an acoustic emission detection method for transformer partial discharge, which is applied to the acoustic emission detection device for transformer partial discharge described in the embodiment. The acoustic emission detection method includes:

[0057] A laser signal is generated by a laser and transmitted to an optical micro-ring acoustic emission sensor distributed inside the transformer through an optical fiber.

[0058] When local discharge occurs inside the transformer and an acoustic emission signal is generated, the acoustic emission signal acts on the optical microring acoustic emission sensor, causing the micro-resonant cavity structure in the optical microring acoustic emission sensor to change slightly under the action of the stress wave. At the same time, the effective refractive index changes under the influence of the elastic-photoelectric effect, thereby changing the output spectrum of the laser signal and causing the resonance peak to shift.

[0059] The optical signal changes in the micro-resonant cavity are detected by a photodetector and converted into electrical signals, and the time-frequency diagram of the acoustic emission signal is obtained using a wavelet transform algorithm.

[0060] According to the time-frequency diagram of the acoustic emission signal, a four-point positioning algorithm is used to locate the local discharge point that generates the acoustic emission signal.

[0061] The present invention has been described in detail above in conjunction with specific implementations and exemplary examples, but these descriptions cannot be understood as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, a variety of equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its implementation methods, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be subject to the attached claims.

Claims

1. An acoustic emission detection device for partial discharge of a transformer, characterized in that: It comprises a plurality of acoustic emission sensor components (1) located inside a transformer; Each of the acoustic emission sensing components (1) comprises a laser (11), an optical microring acoustic emission sensor (12) and a photodetector (13); the laser (11) is connected to a direct waveguide input port of the optical microring acoustic emission sensor (12) via an optical fiber, and an output port of the optical microring acoustic emission sensor (12) is connected to the photodetector (13) via an optical fiber; The laser (11) is used to emit a laser signal; the laser signal is transmitted to the optical microring acoustic emission sensor (12) through an optical fiber and then transmitted to a photodetector (13) through an optical fiber; the photodetector (13) is used to detect the laser signal in the microresonant cavity of the optical microring acoustic emission sensor (12) and convert the laser signal into an electrical signal; After the acoustic emission signal inside the transformer acts on the optical micro-ring acoustic emission sensor (12), the photoelectric detector (13) detects parameter changes of the laser signal in the micro-resonance cavity of the optical micro-ring acoustic emission sensor (12), thereby realizing detection of the acoustic emission signal inside the transformer.

2. The acoustic emission detection device for transformer partial discharge according to claim 1, characterized in that: The optical micro-ring acoustic emission sensor (12) comprises a substrate layer (121) and a straight waveguide (122) and a racetrack-shaped waveguide (123) located on the substrate layer (121); the straight waveguide (122) is parallel to the straight waveguide segment of the racetrack-shaped waveguide (123); The thickness of the base layer (121) below the racetrack-shaped waveguide (123) is smaller than the thickness of the base layer (121) below the straight waveguide (122).

3. The acoustic emission detection device for transformer partial discharge according to claim 2, characterized in that: The material of the base layer (121) is silicon dioxide.

4. The acoustic emission detection device for transformer partial discharge according to claim 2, characterized in that: The straight waveguide (122) and the racetrack-shaped waveguide (123) are both made of polystyrene.

5. The acoustic emission detection device for transformer partial discharge according to claim 2, characterized in that: The spacing between the straight waveguide (122) and the straight waveguide (123) is 300 nanometers.

6. The acoustic emission detection device for transformer partial discharge according to claim 1, characterized in that: The diameter of the micro-resonance cavity of the optical micro-ring acoustic emission sensor (12) is greater than or equal to 10 microns and less than or equal to 100 microns.

7. The acoustic emission detection device for transformer partial discharge according to claim 2, characterized in that: The resonance condition of the micro-resonance cavity of the optical micro-ring acoustic emission sensor (12) satisfies: (2πR+2L)n eff =mλ; Wherein, R is the radius of the arc segment waveguide of the racetrack-shaped waveguide (123); L is the length of the straight segment waveguide of the racetrack-shaped waveguide (123); n eff is the effective refractive index; m is the resonance order; λ is the resonance wavelength.

8. The acoustic emission detection device for transformer partial discharge according to claim 1, characterized in that: The electrical signal converted by the photoelectric detector (13) is processed by a bandpass filter, and then a wavelet transform is used to obtain a time-frequency diagram of the acoustic emission signal in the micro-resonant cavity of the optical micro-ring acoustic emission sensor (12).

9. The acoustic emission detection device for transformer partial discharge according to claim 1, characterized in that: The plurality of acoustic emission sensor components (1) are arranged along the circumference of the inner wall of the transformer and are not in contact with the winding of the transformer.

10. A method for detecting partial discharge of a transformer by acoustic emission, characterized in that: The acoustic emission detection device for transformer partial discharge according to any one of claims 1 to 9, wherein the acoustic emission detection method comprises: A laser signal is generated by a laser, and the laser signal is transmitted to an optical micro-ring acoustic emission sensor distributed inside the transformer through an optical fiber; When local discharge occurs inside the transformer and an acoustic emission signal is generated, the acoustic emission signal acts on the optical microring acoustic emission sensor, causing the micro-resonance cavity structure in the optical microring acoustic emission sensor to change slightly under the action of the stress wave, and at the same time, the effective refractive index changes under the influence of the photoelastic effect, thereby changing the output spectrum of the laser signal and causing the resonance peak to shift; The optical signal changes in the micro-resonant cavity are detected by a photodetector and converted into electrical signals, and the time-frequency diagram of the acoustic emission signal is obtained by using a wavelet transform algorithm. According to the time-frequency diagram of the acoustic emission signal, a four-point positioning algorithm is used to locate the local discharge point that generates the acoustic emission signal.

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