Built-in sound field measuring device of high-voltage electrical equipment and space optimization arrangement method

Abstract

The invention discloses a built-in sound field measuring device for high-voltage electrical equipment and a space optimization arrangement method, which comprise the design of an internal fiber bragg grating acoustic sensor and an external measuring loop of the high-voltage electrical equipment and the design of a space optimization arrangement scheme, and the device comprises the internal fiber bragg grating acoustic sensor and the external measuring loop. The detection frequency band of the fiber bragg grating acoustic sensor is designed according to the length of the grating region, and both ultrasound and audible sound are considered; polyimide is used as a coating material of the fiber bragg grating, so that high temperature resistance and insulation performance are better; the glass fiber reinforced plastic is used as a packaging material of the fiber bragg grating, so that the fiber bragg grating has higher mechanical strength and durability; a noise reduction device is designed according to the interference principle, and interference of optical noise in a measurement loop is suppressed; through the design of a transfer function and cut-off frequency, band-pass filtering is transplanted into a data collector, and the influence of high and low frequency interference during sound signal collection is inhibited. A space optimization arrangement scheme is designed in combination with various constraint factors, and the engineering application value of the measurement device is improved.

Description

Technical Field

[0001] The invention belongs to the field of electrical equipment and measurement technology, and in particular relates to a built-in sound field measurement device for high-voltage electrical equipment and a space optimization layout method. Background Art

[0002] As important basic equipment of the power system, high-voltage electrical equipment such as large power transformers and GIS undertakes the key tasks of power conversion and transmission. However, insulation defects will inevitably occur in high-voltage electrical equipment during the factory, transportation and operation. As the defects develop, there is a possibility of insulation degradation or even failure of high-voltage electrical equipment. In the process of insulation degradation, typical faults such as winding overheating, partial discharge and inter-turn short circuit will occur inside the high-voltage electrical equipment. Therefore, after the insulation problem occurs in the equipment, it is of great practical significance to effectively detect the typical faults inside it to ensure the safe operation of the equipment.

[0003] However, the current acoustic measurement technology for the operating status of high-voltage electrical equipment is mainly focused on external means, which cannot maintain higher performance while working internally, and has not yet solved the impact of noise interference on the sound field measurement process, making it difficult to meet the requirements for transparency of the working status of high-voltage electrical equipment (such as the article "Research on Internal and External Sensor Detection Methods in Ultrasonic Detection of Partial Discharge in Transformers", author: Li Zhili). At the same time, the existing fiber optic acoustic sensing technology only selects specific design structures and parameters to meet monitoring needs, and does not conduct in-depth theoretical analysis based on monitoring needs, thereby inferring the dynamic range of sensor design parameters, packaging materials and structural dimensions, which limits the installation requirements of fiber grating acoustic sensors in different application scenarios. In addition, the existing engineering applications of acoustic field measurement devices have not conducted theoretical analysis on spatial layout and installation measurement points, resulting in the measurement device failing to achieve the expected measurement effect, which has limited the large-scale field application of acoustic field monitoring devices to a certain extent (such as the article "Study on the Soundprint Characteristics of Arc Discharge in Transformers Based on Fiber Bragg Grating Sensing", author: Ji Tong), and the existing optimization configuration schemes for other sensors only consider the monitoring efficiency and range, and do not consider factors such as the allowed installation position, insulation margin, and fault location of the project, which lacks engineering practicality. (For example, "A Multi-parameter Sensor Optimization Configuration Method for Transformers", patent publication number: CN118746720A, first inventor: Qi Bo). Summary of the invention

[0004] In order to solve the defects existing in the prior art, the present invention discloses a design method of a sound field measurement device, and its technical solution is as follows:

[0005] A method for designing a sound field measurement device, including a method for designing a fiber grating acoustic sensor inside a high-voltage electrical device and a method for designing an external measurement circuit; the method is characterized by:

[0006] The design method of the fiber grating acoustic sensor inside the high-voltage electrical equipment includes the following contents:

[0007] (1) Determination of the grating length of the fiber Bragg grating: The grating length L of the fiber Bragg grating needs to satisfy:

[0008]

[0009] In the formula, R min is the minimum reflectivity set, f max is the upper limit of the detection frequency required by the sensor, v is the wave velocity of the sound wave in the medium inside the high-voltage electrical equipment, Ω is the coupling coefficient, Ω>0; tanh(x) is the hyperbolic tangent function, λmin is the minimum wavelength of the sound wave;

[0010] (2) Selection of coating material: A layer of coating material with a high elastic modulus is coated on the surface of the bare optical fiber to improve the mechanical strength of the fiber Bragg grating. Considering the electrical conductivity of metal, polyimide is used as the coating material of the fiber Bragg grating.

[0011] (3) Selection of packaging materials: The formula for the sound transmission coefficient T, which characterizes the quality of sound transmission performance, is as follows:

[0012] T=1-R (4)

[0013] Where R is the reflection coefficient;

[0014]

[0015] Where Z1 and Z2 are the acoustic impedances of the medium before the sound wave is incident and after the sound wave is transmitted; θ i ,θ t are the incident angle and the transmission angle respectively; glass fiber reinforced plastic is selected as the packaging material of the fiber grating;

[0016] (4) Determination of package size: The horizontal dimension of the internal fiber grating acoustic sensor is divided into two regions according to the location of the optical fiber and the grating. Region I is the region where the optical fiber is located, and region II is the region where the grating is located. Let the horizontal length of region I be X1 and the vertical length be Y1; let the horizontal length of region II be X2 and the vertical length be Y2.

[0017] The axial force F in area I and area II is equal. According to the formula of axial force:

[0018] F=E1S1ε1=E2S2ε2 (6)

[0019] Where, E1 and E2 represent the elastic modulus of the packaging materials in regions Ⅰ and Ⅱ; S1 and S2 represent the axial force area of ​​the packaging materials in regions Ⅰ and Ⅱ; ε1 and ε2 represent the strains of the packaging materials in regions Ⅰ and Ⅱ;

[0020] The strain on the packaging material of the entire internal fiber Bragg grating acoustic sensor is:

[0021]

[0022] In the formula, ΔL represents the change in the transverse length after the axial force is applied, and L represents the original transverse length; 2ΔX1 and ΔX2 represent the change in the transverse length of regions I and II after the axial force is applied; 2X1 and X2 represent the original transverse length of regions I and II;

[0023] Combining equations (6) and (7), we can obtain:

[0024]

[0025] According to the definition of sensitivity enhancement factor in materials science:

[0026]

[0027] The sensitivity enhancement coefficient is the ratio of the grating strain to the packaging material strain. When the grating strain is greater than the packaging material strain, that is, K>1, the internal fiber Bragg grating acoustic sensor can maintain a high sensitivity. Since the packaging materials and thicknesses of regions I and II are the same, E2=E1, S2 / S1=Y2 / Y1, and equation (9) can be rewritten as:

[0028]

[0029] Only when Y1>Y2, K>1, the sensitivity is enhanced;

[0030] The external measurement circuit design method includes the following contents:

[0031] ① Design of optical interference noise reduction device: internal components include: beam splitter, interference analysis module, feedback control module;

[0032] ②Bandpass filter algorithm design: First, you need to select the sampling frequency f s , f s At least twice the high cutoff frequency;

[0033] Calculate the high and low normalized cutoff frequencies based on the sampling frequency:

[0034]

[0035] In the formula, ω H ,ω L are high and low normalized cutoff frequencies respectively; f H , f L are high and low cutoff frequencies respectively;

[0036] The Butterworth bandpass filter method is used for design, and its transfer function is:

[0037]

[0038] Where n is the order. In order to make the filter provide passband flatness and achieve a higher attenuation rate, s = jω is the complex frequency variable; K is the filter gain; B = ω H -ω L is the filter bandwidth; is the center frequency of the filter; Q k is the quality factor of the bandpass filter and is related to the pole position.

[0039] The present invention also discloses an acoustic field measuring device. The acoustic field measuring device is based on the above-mentioned design method, and includes an internal fiber grating acoustic sensor and an external measurement circuit. The characteristics are as follows: the internal fiber grating acoustic sensor includes an optical fiber, a grating, a coating material, and a packaging material; the grating is located in the middle part of an optical fiber and wraps the section of optical fiber to form a fiber grating; a layer of coating material is wrapped on the outside of the grating; and the optical fiber and the coating material are packaged on the outside by packaging material. The external measurement loop includes: a through-hole, an optical fiber jumper, a laser source, an optical circulator, an optical interference noise reduction device, a photoelectric detector, and a data collector with a built-in bandpass filtering function; the optical circulator is a three-port device, port 1 is connected to the laser source through an optical fiber jumper, port 2 is connected to the internal fiber grating acoustic sensor through an optical fiber jumper and a through-hole embedded on the surface of the high-voltage equipment, and port 3 is connected to the optical interference noise reduction device through an optical fiber jumper; the optical interference noise reduction device also has three ports, the input port is connected to the optical circulator, the feedback port is connected to the laser source, and the output port is connected to the photoelectric detector, all of which are connected through the optical fiber jumper; the photoelectric detector is connected to the data collector with a built-in bandpass filtering function through a power line.

[0040] The invention also discloses a method for optimizing the spatial arrangement of a sound field measurement device.

[0041] Beneficial Effects

[0042] The grating length within this range is selected to develop a fiber Bragg grating acoustic sensor to achieve simultaneous measurement of ultrasonic signals and audible sound signals.

[0043] Polyimide is used as the coating material of fiber Bragg grating, which can withstand temperatures up to 300°C and has better insulation performance. The strain response is basically the same as that of bare optical fiber.

[0044] Glass fiber reinforced plastics, which are a composite of glass fiber and polymer matrix (such as epoxy resin, etc.), are used as packaging materials for fiber gratings. They have higher mechanical strength and durability, and their acoustic impedance is more compatible with the internal medium of high-voltage electrical equipment.

[0045] Through the transfer function and the calculated high and low normalized cutoff frequencies, a specific bandpass filter algorithm is designed and transplanted into the data collector to suppress the influence of low-frequency vibration and high-frequency electromagnetic waves on the acoustic signal acquisition;

[0046] An optical interference noise reduction device is introduced, including a beam splitter, an interference analysis module, and a feedback control module, so as to effectively reduce optical noise. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a structural schematic diagram of the sound field measurement device of the present invention;

[0048] Figure 2 This is a schematic diagram of the packaging dimensions of the internal fiber Bragg grating acoustic sensor of the present invention;

[0049] Figure 3 A flow chart of a method for optimizing the spatial arrangement of a sound field measurement device according to the present invention;

[0050] The invention comprises: a fiber grating acoustic sensor (1), an optical fiber (1-1), a grating (1-2), a coating material (1-3), a packaging material (1-4), an external measurement circuit (2), a through-hole (2-1), an optical fiber jumper (2-2), a laser source (2-3), an optical circulator (2-4), an optical interference noise reduction device (2-5), a photodetector (2-6), and a data acquisition device (2-7) with a built-in bandpass filtering function. DETAILED DESCRIPTION

[0051] Example 1

[0052] See also Figure 1-2 As shown in the figure, fiber grating acoustic sensor is developed

[0053] ① Determination of grating length: The grating length and reflectivity of the fiber Bragg grating play a vital role in the detection frequency band of the acoustic sensor. In order to obtain better monitoring results, the grating length is generally required to be less than 1 / 2 of the wavelength of the measured sound wave, so that the grating can feel the sound wave effect of uniform strain; and in order to ensure the signal-to-noise ratio of the output signal, the reflectivity of the fiber Bragg grating is generally required to be above a set minimum reflectivity. These two factors jointly determine the selection of the grating length of the fiber Bragg grating.

[0054] The wavelength of sound waves is expressed as:

[0055]

[0056] In the formula, v is the speed of sound waves in the medium inside the high-voltage electrical equipment; f is the frequency of the sound waves. For a specific high-voltage electrical equipment, v is a fixed value, which can be determined by determining the upper limit of the sound wave frequency f inside different high-voltage equipment. max To determine the lower limit of the sound wavelength λ min .

[0057] The reflectivity of the fiber Bragg grating has the following relationship with the grating length:

[0058] R = tanh 2 (ΩL) (2)

[0059] In the formula, R is the reflectivity of the fiber Bragg grating, Ω is the coupling coefficient (Ω>0); L is the length of the grating area; tanh(x) is the hyperbolic tangent function, which is a function positively correlated with x and gradually approaches 1 as x increases. Therefore, the length of the fiber Bragg grating area cannot be reduced indefinitely, which will reduce the reflectivity of the grating, thereby reducing the signal-to-noise ratio and affecting the monitoring effect.

[0060] Then the grating length L of the fiber Bragg grating needs to satisfy:

[0061]

[0062] In the formula, R min is the minimum reflectivity set, f max is the upper limit of the detection frequency required by the sensor. Taking the transformer as an example, R min Generally 0.9, f max Generally, it is 80kHz, and v is 1400-1500m / s, so the grating length L of the fiber Bragg grating used in the transformer is generally 6.3-9mm. Therefore, the present invention selects the grating length within this range to develop the fiber Bragg grating acoustic sensor, which can realize the simultaneous measurement of ultrasonic signals and audible sound signals.

[0063] ② Determination of coating materials: When high-voltage electrical equipment is working, the vibration of the body will cause mechanical impact to the sensor installed inside the equipment. At the same time, the oil flow rate inside the equipment is fast, which will also have a greater impact on the sensor. This requires the built-in fiber grating acoustic sensor to have high mechanical strength. However, the fiber grating itself is relatively fragile and is prone to breakage when subjected to a large impact, affecting the monitoring efficiency; even during installation, it may cause accidental breakage due to misoperation, which invisibly increases the monitoring cost; therefore, it is necessary to coat the surface of the bare optical fiber with a coating material with a relatively high elastic modulus to improve the mechanical strength of the fiber grating. Common coating materials are acrylate, polyimide and metal.

[0064] Considering that metal is conductive, it does not meet the insulation requirements of internal monitoring equipment of high-voltage electrical equipment and is therefore excluded first;

[0065] Acrylic acid has the advantages of faster curing and lower cost, but its elastic modulus and mechanical strength are not very high. When faced with strong impact, the internal fiber Bragg grating will still have the risk of breaking. In addition, the maximum operating temperature range of acrylic acid is about 90°C, which cannot withstand the high temperature environment inside high-voltage electrical equipment, so it is excluded.

[0066] Although polyimide is relatively expensive, its excellent mechanical strength makes it the first choice for fiber Bragg grating coating materials. In addition, the maximum temperature tolerance of polyimide material can reach 300°C and its insulation performance is better. Its strain response is basically the same as that of bare optical fiber. Therefore, the present invention uses polyimide as the coating material of fiber Bragg grating.

[0067] ③ Determination of packaging materials: When selecting packaging materials, first of all, materials that are resistant to high temperatures, corrosion, and electromagnetic interference should be selected; secondly, the material needs to have good sound transmission performance. The formula for the sound transmission coefficient T that characterizes the quality of sound transmission performance is as follows:

[0068] T=1-R (4)

[0069] Where R is the reflection coefficient.

[0070]

[0071] Where Z1 and Z2 are the acoustic impedances of the medium (oil) before the sound wave is incident and the medium after the sound wave is transmitted; θ i ,θ t are the incident angle and transmission angle respectively. If the acoustic impedance of the selected material is too large (Z2 is much larger than Z1), R is always close to 1, T is always close to 0, and the sound transmission performance is poor; if the acoustic impedance Z2 of the selected material is large, then only the component of the sound wave vertically incident on the dielectric material (θ i =0°) can be better absorbed by the dielectric material. With the increase of the incident angle, the reflection coefficient R will gradually increase, the sound transmission coefficient T will decrease, and the sound transmission performance will decrease. Only when Z1 and Z2 are not much different, the fiber grating acoustic sensor has a higher sound transmission performance and is less affected by the change of the incident angle.

[0072] Glass fiber and its related composites have similar acoustic impedance to the internal medium of high-voltage electrical equipment, but glass fiber itself is similar to the quartz glass material used to make fiber gratings, which is a brittle material with poor impact resistance; while the composite material of glass fiber and polymer matrix (such as epoxy resin, etc.) has higher mechanical strength and durability, and its acoustic impedance is more matched with the internal medium of high-voltage electrical equipment. Therefore, the present invention selects glass fiber reinforced plastic as the packaging material of fiber grating.

[0073] ④ Determination of package size: The horizontal dimension of the internal fiber grating acoustic sensor is divided into two areas according to the location of the optical fiber and the grating. Area 1 is the area where the optical fiber is located, and area 2 is the area where the grating is located. Let the horizontal length of area 1 be X1 and the vertical length be Y1; let the horizontal length of area 2 be X2 and the vertical length be Y2.

[0074] The axial force F in area 1 and area 2 is equal. According to the formula of axial force:

[0075] F=E1S1ε1=E2S2ε2 (6)

[0076] Wherein, E1 and E2 represent the elastic modulus of the packaging materials in regions 1 and 2; S1 and S2 represent the axial force area of ​​the packaging materials in regions 1 and 2; ε1 and ε2 represent the strains of the packaging materials in regions 1 and 2.

[0077] The strain on the packaging material of the entire internal fiber Bragg grating acoustic sensor is:

[0078]

[0079] In the formula, ΔL represents the change in the lateral length after being subjected to axial force, and L represents the original lateral length; 2ΔX1 and ΔX2 represent the change in the lateral length of regions 1 and 2 after being subjected to axial force; 2X1 and X2 represent the original lateral lengths of regions 1 and 2.

[0080] Combining equations (6) and (7), we can obtain:

[0081]

[0082] According to the definition of sensitivity enhancement factor in materials science:

[0083]

[0084] The sensitivity enhancement factor is the ratio of the grating strain to the packaging material strain. When the grating strain is greater than the packaging material strain, that is, K>1, the internal fiber Bragg grating acoustic sensor can maintain a high sensitivity. Since the packaging materials and thicknesses of regions 1 and 2 are the same, E2=E1, S2 / S1=Y2 / Y1, then equation (9) can be rewritten as:

[0085]

[0086] Only when Y1>Y2, K>1, the sensitivity is enhanced. The present invention designs K to be within the range of 1.6-2. The lateral size will not affect the sensitivity, X2 can be slightly longer than the gate length, and X1 can be selected and designed according to the actual installation environment.

[0087] 2. External measurement circuit construction

[0088] ① Design of optical interference noise reduction device: The light source selected for the measurement circuit of the present invention is a laser source, the purpose of which is to provide a stable light source for the internal fiber grating acoustic sensor. However, laser is coherent light, and when the optical signal propagates in the optical path, optical noise is inevitably generated, among which phase noise and frequency noise are dominant. Therefore, the present invention introduces an optical interference noise reduction device, the internal components of which include: a beam splitter, an interference analysis module, and a feedback control module.

[0089] The optical interference noise reduction device receives the optical signal transmitted by the circulator and separates the optical signal into two optical signals through a beam splitter, one is a reference beam with no frequency or phase shift, and the other is a measurement beam with a frequency or phase shift. The optical field formula of the reference beam is:

[0090]

[0091] The light field formula of the measurement beam is:

[0092]

[0093] Where E0 is the amplitude of the light field, v is the frequency of the light source under ideal conditions, and φ r (t) is the phase of the reference beam at time t, φ m (t) is the phase of the measurement beam at time t.

[0094] The reference beam and the measurement beam are recombined at the output end of the interference analysis module to form interference fringes. The intensity of the interference fringes is:

[0095] I(t)=|E r (t)+E m (t) 2 (13)

[0096] Substituting equations (11) and (12) into equation (13), we can simplify the equation to obtain:

[0097]

[0098] Where, Δφ(t)=φ m (t)-φ r (t) represents the phase difference between the two beams of light. The analysis module obtains the phase information of the optical noise by analyzing and monitoring the cos(Δφ(t)) term in the interference fringes. However, the noise phase is not fixed, and Δφ(t) will also change with time. Therefore, a feedback control module is required to feed back the phase difference information to the laser source in real time. The laser source then adjusts the frequency and phase of the light source through its internal phase modulation element, so that the frequency and phase of the optical signal received by the photodetector remain stable, thereby effectively reducing the optical noise.

[0099] ② Bandpass filter algorithm design: After the photoelectric detector receives a stable optical signal, it will convert the optical signal into an electrical signal and then transmit it to the data collector. Although the optical noise in the optical path has been suppressed, there will still be some interference inside the high-voltage electrical equipment that will have a certain impact on the monitoring effect of the internal fiber grating acoustic sensor. This is interference that the optical interference noise reduction device cannot suppress. At this time, it is necessary to transplant the filtering algorithm inside the data collector to filter out these interferences.

[0100] During the operation of high-voltage electrical equipment, the vibration of its body will generate a large number of low-frequency signals below 5kHz; the strong electromagnetic environment inside the electrical equipment will also generate a large number of high-frequency electromagnetic wave signals. After analysis, these high-frequency electromagnetic wave signals are mostly above 500kHz. By analyzing the frequency band differences of acoustic signals, low-frequency vibration signals and high-frequency electromagnetic wave signals, a bandpass filtering algorithm is designed to allow signals in specific frequency bands to enter the data collector, thereby filtering out high and low frequency interference signals.

[0101] First, we need to select the sampling frequency f s , f s At least twice the high cutoff frequency, the present invention selects f s =1.25MHz.

[0102] Calculate the high and low normalized cutoff frequencies based on the sampling frequency:

[0103]

[0104] In the formula, ω H ,ω L are high and low normalized cutoff frequencies respectively; f H , f L are the high and low cutoff frequencies respectively.

[0105] The Butterworth bandpass filter method is used for design, and its transfer function is:

[0106]

[0107] Where n is the order. In order to make the filter provide passband flatness and achieve a higher attenuation rate, we use fourth-order filtering, that is, n = 4; s = jω is the complex frequency variable; K is the filter gain, generally K = 1; B = ω H -ω L is the filter bandwidth; is the center frequency of the filter; Q k is the quality factor of the bandpass filter and is related to the pole position.

[0108] Through the transfer function and the calculated high and low normalized cutoff frequencies, a specific bandpass filtering algorithm can be designed. Transplanting it into the data collector can suppress the influence of low-frequency vibrations and high-frequency electromagnetic waves on the acquisition of acoustic signals.

[0109] Example 2

[0110] A sound field measurement device, based on the sound field measurement device design method of embodiment 1, comprises an internal fiber Bragg grating sound sensor (1) and an external measurement circuit (2), and is characterized in that: the internal fiber Bragg grating sound sensor (1) comprises an optical fiber (1-1), a grating (1-2), a coating material (1-3), and a packaging material (1-4); the grating is located in the middle part of an optical fiber and wraps the optical fiber to form a fiber Bragg grating; a layer of coating material is wrapped on the outside of the grating; and the optical fiber and the coating material are packaged on the outside by packaging material.

[0111] The external measurement circuit comprises:

[0112] A through-hole (2-1), an optical fiber jumper (2-2), a laser source (2-3), an optical circulator (2-4), an optical interference noise reduction device (2-5), a photodetector (2-6), and a data collector with a built-in bandpass filtering function (2-7); the optical circulator is a three-port device, port 1 is connected to the laser source through an optical fiber jumper, port 2 is connected to the internal fiber grating acoustic sensor through an optical fiber jumper via a through-hole embedded in the surface of the high-voltage equipment, and port 3 is connected to the optical interference noise reduction device through an optical fiber jumper; the optical interference noise reduction device also has three ports, the input port is connected to the optical circulator, the feedback port is connected to the laser source, and the output port is connected to the photodetector, all of which are connected through an optical fiber jumper; the photodetector is connected to the data collector with a built-in bandpass filtering function through a power line.

[0113] Example 3

[0114] See also Figure 3 The present invention discloses a method for optimizing the spatial arrangement of a sound field measurement device, comprising the following steps:

[0115] Step 1: Through simulation calculation, it is found that there are a number of measuring points that can effectively monitor the internal acoustic signals of high-voltage electrical equipment;

[0116] Design and build an equivalent scaled model of high-voltage electrical equipment, and set the sound source function at the location where faults may occur inside the high-voltage electrical equipment:

[0117]

[0118] Where A is the energy flow, which is a constant; f0 is the pulse width; t p The time it takes for the pulse to reach its peak.

[0119] The interior of the high-voltage electrical equipment is evenly divided into l×m×n small areas in three dimensions, and a probe is set at the center point of each area to monitor the sound pressure received at that point. The velocity v received by the probe at each monitoring point can be obtained from the sound pressure:

[0120] p=ρcv (18)

[0121] In the formula, p is the sound pressure at the monitoring point; ρ is the medium density, c is the sound speed in the medium, and v is the speed received at the monitoring point. The minimum sensitivity A required for different monitoring points to detect sound signals can be obtained through the relationship between v and sensor sensitivity. min :

[0122]

[0123] In the formula, v0 is the reference speed, which is generally 1m / s. That is, when the sensitivity is 0dB, the conversion relationship between the sensor voltage and the sound speed is 1V / (m / s). Assume that the sensitivity of the fiber Bragg grating acoustic sensor is A. When A min <A, keep the point; when A min > A, discard this point. Finally, there are a theoretical installation positions that meet the requirements.

[0124] Step 2: According to the requirements of the design institute and the actual project, as well as the internal structure of the high-voltage electrical equipment, there are b installation locations allowed on site. For example, in order not to damage the internal electromagnetic shielding design of the high-voltage electrical equipment or affect the normal operation of the high-voltage electrical equipment, the design institute will restrict the monitoring device measurement points. The fiber grating acoustic sensor can only be fixedly installed on the internal support structure. After these constraints, there are b installation locations allowed on site that meet the requirements.

[0125] Step 3: The sets of a and b are not in a containment relationship, but have a partial intersection. Let c = a∩b, that is, take the intersection of the theoretically installable positions and the on-site allowable installation positions, and get c installation points after the first step of optimization.

[0126] Step 4: To ensure that the sensor will not threaten the internal insulation of high-voltage electrical equipment after installation, the insulation margin of the installation point must be greater than the insulation margin required by the high-voltage electrical equipment. Taking the transformer as an example, first obtain the electric field distribution in the oil gap inside the transformer through simulation calculation and other means, select the power lines at each installation point, and integrate the power plant to obtain the average field strength E1:

[0127]

[0128] Where d is the length of the power line, in mm; then the permissible field strength E2 is calculated:

[0129] E2=A×d -0.37 (twenty one)

[0130] In the formula, A is a constant, which is related to the location of the power line and whether there is gas in the oil. The ratio of the two is the insulation margin q at the oil gap where the installation point is located:

[0131]

[0132] If the insulation margin q is greater than the insulation margin q' required by the high-voltage electrical equipment, the point is retained; otherwise, the point is discarded. Finally, there are d installation points that meet the internal insulation margin requirements of the high-voltage electrical equipment.

[0133] Step 5: In order to locate the internal fault of high-voltage electrical equipment, it is necessary to select some points that meet the positioning requirements from the d points. In a three-dimensional space, assuming that the coordinates of the fault source are (x, y, z), s installation points are selected with coordinates (x1, y1, z1), (x2, y2, z2), ..., (x s ,y s ,z s ), the following relationship can be satisfied:

[0134]

[0135] Where t1, t2, …, t s is the time when the acoustic signal pulse is received at different installation points. c is the speed of sound in the medium inside the high-voltage electrical equipment. However, the location of the fault source obtained by solving these s points may be a location inside the equipment where the fault cannot occur, and there may even be a situation where the fault source after positioning is outside the equipment. Therefore, it is necessary to introduce t points so that the analytical solution (x, y, z) obtained satisfies the following relationship:

[0136] (x,y,z)∈D(20)

[0137] Where D is the coordinate set of possible fault locations inside the equipment. Let e ​​= s + t. Therefore, after the third step of optimization, there are e points that can accurately locate the internal faults of the equipment.

[0138] Step 6: Unlike the above variables, e is a variable parameter, that is, the point that meets the fault location requirement is within a range. Considering the economic requirements, under the premise of meeting all the above space optimization factors, the fewer sensors used, the better. On the one hand, it reduces the production cost of the sensor, and on the other hand, it reduces the risk cost of the negative impact of the sensor on the high-voltage electrical equipment after installation. Let f = e min After four steps of space optimization, the number of installation points of the internal fiber grating sensors is finally determined to be f, and the locations of the points are determined.

[0139] like Figure 3As shown in the figure, through simulation calculation, it is concluded that there are a monitoring points inside the high-voltage electrical equipment that can effectively measure the acoustic signal of the internal fault. From the perspective of the actual internal structure of the high-voltage electrical equipment and the actual requirements of the project, there are b installation points allowed on site. Taking the two primary factors into consideration, the intersection of the two installation point sets is taken to obtain the theoretical installation points of the acoustic sensor, which are c; after the sensor is installed inside the high-voltage electrical equipment, it will affect the electric field distribution around it. At this time, it is necessary to consider whether the insulation margin of the high-voltage electrical equipment meets the requirements. Further screening in c obtains that there are d installation points that meet the insulation margin requirements; in order to accurately obtain the location of the fault point, e installation points are selected in d. By analyzing the time delay and amplitude of the acoustic signal received by the sensor at different monitoring positions, the theoretical fault source position inside the high-voltage electrical equipment can be accurately located; and combined with cost factors and economic needs, the least number of sensors are selected to achieve the purpose under the premise of meeting the monitoring needs. After analyzing multiple factors, there are f optimal installation points in space, and the location of the points has been determined.

[0140] The present invention proposes for the first time a built-in sound field measurement device for high-voltage electrical equipment and a method for optimizing the spatial layout, which solves the technical problem that the traditional sound field measurement method cannot be effectively applied inside high-voltage electrical equipment. By analyzing different grating area lengths and reflectivities, a high-sensitivity fiber grating acoustic sensor that takes into account both audible sound and ultrasound is designed and developed; and suitable coating materials and packaging materials and dimensions are selected to ensure its applicability to the measurement of fault acoustic signals inside high-voltage electrical equipment; according to the potential noise interference in the monitoring process of the acoustic measurement device, the existing measurement circuit is optimized to improve the signal-to-noise ratio of the measurement device; combining multiple factors, a four-step optimization is used to propose an optimal layout method for the sound field measurement device inside high-voltage electrical equipment, which provides new technical support for the on-site engineering application of built-in sound field measurement devices.

[0141] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions only describe the principles of the present invention. The present invention may be subject to various changes and improvements without departing from the spirit and scope of the present invention. These changes and improvements fall within the scope of the present invention. The scope of protection claimed by the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for designing an acoustic field measurement device, including a method for designing an internal fiber Bragg grating acoustic sensor of a high-voltage electrical device and a method for designing an external measurement circuit; the characteristics of the method are as follows: The design method of the fiber grating acoustic sensor inside the high-voltage electrical equipment includes the following contents: (1) Determination of the grating length of the fiber Bragg grating: The grating length L of the fiber Bragg grating needs to satisfy: In the formula, R min is the minimum reflectivity set, f max is the upper limit of the detection frequency required by the sensor, v is the wave velocity of the sound wave in the medium inside the high-voltage electrical equipment, Ω is the coupling coefficient, Ω>0; tanh(x) is the hyperbolic tangent function, λmin is the minimum wavelength of the sound wave; (2) Selection of coating material: A layer of coating material with a high elastic modulus is coated on the surface of the bare optical fiber to improve the mechanical strength of the fiber Bragg grating. Considering the electrical conductivity of metal, polyimide is used as the coating material of the fiber Bragg grating. (3) Selection of packaging materials: The formula for the sound transmission coefficient T, which characterizes the quality of sound transmission performance, is as follows: T=1-R (4) Where R is the reflection coefficient; Where Z1 and Z2 are the acoustic impedances of the medium before the sound wave is incident and after the sound wave is transmitted; θ i ,θ t are the incident angle and the transmission angle respectively; glass fiber reinforced plastic is selected as the packaging material of the fiber grating; (4) Determination of package size: The horizontal dimension of the internal fiber grating acoustic sensor is divided into two regions according to the location of the optical fiber and the grating. Region I is the region where the optical fiber is located, and region II is the region where the grating is located. Let the horizontal length of region I be X1 and the vertical length be Y1; let the horizontal length of region II be X2 and the vertical length be Y2. The axial force F in area I and area II is equal. According to the formula of axial force: F=E1S1ε1=E2S2ε2 (6) Where, E1 and E2 represent the elastic modulus of the packaging materials in regions Ⅰ and Ⅱ; S1 and S2 represent the axial force area of ​​the packaging materials in regions Ⅰ and Ⅱ; ε1 and ε2 represent the strains of the packaging materials in regions Ⅰ and Ⅱ; The strain on the packaging material of the entire internal fiber Bragg grating acoustic sensor is: In the formula, ΔL represents the change in the transverse length after the axial force is applied, and L represents the original transverse length; 2ΔX1 and ΔX2 represent the change in the transverse length of regions I and II after the axial force is applied; 2X1 and X2 represent the original transverse length of regions I and II; Combining equations (6) and (7), we can obtain: According to the definition of sensitivity enhancement factor in materials science: The sensitivity enhancement coefficient is the ratio of the grating strain to the packaging material strain. When the grating strain is greater than the packaging material strain, that is, K>1, the internal fiber Bragg grating acoustic sensor can maintain a high sensitivity. Since the packaging materials and thicknesses of regions I and II are the same, E2=E1, S2 / S1=Y2 / Y1, and equation (9) can be rewritten as: Only when Y1>Y2, K>1, the sensitivity is enhanced; The external measurement circuit design method includes the following contents: ① Design of optical interference noise reduction device: internal components include: beam splitter, interference analysis module, feedback control module; ②Bandpass filter algorithm design: First, you need to select the sampling frequency f s , f s At least twice the high cutoff frequency; Calculate the high and low normalized cutoff frequencies based on the sampling frequency: In the formula, ω H ,ω L are high and low normalized cutoff frequencies respectively; f H , f L are high and low cutoff frequencies respectively; The Butterworth bandpass filter method is used for design, and its transfer function is: Where n is the order. In order to make the filter provide passband flatness and achieve a higher attenuation rate, s = jω is the complex frequency variable; K is the filter gain; B = ω H -ω L is the filter bandwidth; is the center frequency of the filter; Q k is the quality factor of the bandpass filter and is related to the pole position.

2. The design method of the sound field measurement device according to claim 1 is characterized in that: the working process of the optical interference noise reduction device is as follows: receiving the optical signal transmitted by the circulator, separating the optical signal into two optical signals through a beam splitter, one is a reference beam with no frequency and phase shift, and the other is a measurement beam with frequency and phase shift; the optical field formula of the reference beam is: The light field formula of the measurement beam is: Where E0 is the amplitude of the light field, v is the frequency of the light source under ideal conditions, and φ r (t) is the phase of the reference beam at time t, φ m (t) is the phase of the measurement beam at time t; The reference beam and the measurement beam are recombined at the output end of the interference analysis module to form interference fringes; the intensity of the interference fringes is: I(t)=|E r (t)+E m (t) 2 (13) Substituting equations (11) and (12) into equation (13), we can simplify the equation to obtain: Where, Δφ(t)=φ m (t)-φ r (t) represents the phase difference between the two beams of light. The interference analysis module obtains the phase information of the optical noise by analyzing and monitoring the cos(Δφ(t)) term in the interference fringes. However, the noise phase is not fixed and Δφ(t) will also change with time. Therefore, a feedback control module is required to feed back the phase difference information to the laser source in real time. The laser source then adjusts the frequency and phase of the light source through its internal phase modulation element to keep the frequency and phase of the optical signal received by the photodetector stable, thereby reducing the optical noise.

3. A sound field measurement device, which is based on the design method of the sound field measurement device according to any one of claims 1-2, comprises an internal fiber Bragg grating acoustic sensor and an external measurement circuit, and is characterized by: The internal fiber grating acoustic sensor comprises an optical fiber, a grating, a coating material, and a packaging material; the grating is located in the middle of an optical fiber and wraps the optical fiber to form a fiber grating; a coating material is wrapped around the outer side of the grating; and the outer side of the optical fiber and the coating material is packaged by a packaging material; The external measurement circuit includes: a through-hole, an optical fiber jumper, a laser source, an optical circulator, an optical interference noise reduction device, a photoelectric detector, and a data collector with a built-in bandpass filtering function; the optical circulator is a three-port device, port I is connected to the laser source through an optical fiber jumper, port II is connected to the internal fiber grating acoustic sensor through an optical fiber jumper and a through-hole embedded on the surface of the high-voltage equipment, and port III is connected to the optical interference noise reduction device through an optical fiber jumper; the optical interference noise reduction device also has three ports, the input port is connected to the optical circulator, the feedback port is connected to the laser source, and the output port is connected to the photoelectric detector, all of which are connected through the optical fiber jumper; the photoelectric detector is connected to the data collector with a built-in bandpass filtering function through a power line.

4. A method for optimizing the spatial arrangement of a sound field measurement device, the method being based on the sound field measurement device of claim 3, characterized in that: Step 1: Through simulation calculation, it is found that there are a number of measuring points that can effectively monitor the internal acoustic signals of high-voltage electrical equipment; Step 2: According to the actual requirements of the project, the internal structure of the high-voltage electrical equipment, and the constraints on the monitoring device measurement points, determine that there are b installation locations allowed on site; Step 3: The sets of a and b are not in a containment relationship, but have a partial intersection. Let c = a∩b, that is, take the intersection of the theoretically installable positions and the on-site allowable installation positions, and get c installation points after the first step of optimization; Step 4: To ensure that the sensor will not threaten the internal insulation of the high-voltage electrical equipment after installation, the insulation margin of the installation location must be greater than the insulation margin required by the high-voltage electrical equipment. The electric field distribution in the oil gap inside the high-voltage electrical equipment is obtained through simulation calculation; Step 5: In order to locate the internal fault of the high-voltage electrical equipment, it is necessary to select e points that meet the positioning requirements from d points; Step 6: Unlike the above variables, e is a variable parameter, that is, the points that meet the fault location requirements are within a range; let f = e min After four steps of space optimization, the number of installation points of the internal fiber grating sensors is finally determined to be f, and the locations of the points are determined.

5. The method for optimizing the spatial arrangement of a sound field measurement device according to claim 4, characterized in that: The step 1 further includes the following contents: Design and build an equivalent scaled model of high-voltage electrical equipment, and set the sound source function at the location where faults may occur inside the high-voltage electrical equipment: Where A is the energy flow, which is a constant; f0 is the pulse width; t p The time taken for the pulse to reach its peak; The interior of the high-voltage electrical equipment is evenly divided into l×m×n small areas in three dimensions. A probe is set at the center point of each area to monitor the sound pressure received at the center point. The velocity v received by the probe at each monitoring point is obtained by the sound pressure: p=ρcv (18) In the formula, p is the sound pressure at the monitoring point; ρ is the medium density, c is the sound velocity in the medium, and v is the speed received at the monitoring point. The minimum sensitivity A required for different monitoring points to detect the sound signal is obtained through the relationship between v and the sensor sensitivity. min : In the formula, v0 is the reference speed, which is 1m / s, that is, when the sensitivity is 0dB, the conversion relationship between the sensor voltage and the sound speed is 1V / (m / s); let the sensitivity of the fiber Bragg grating acoustic sensor be A, when A min <A, keep the point; when A min >A, discard this point, and finally there are a theoretical installation positions that meet the requirements.

6. The method for optimizing the spatial arrangement of a sound field measurement device according to claim 4, characterized in that: The step 4 further includes the following contents: selecting the power lines at the locations of the installation points, integrating the electric field to obtain the average field strength E1: Where d is the length of the power line, in mm; then the permissible field strength E2 is calculated: <h2 style=";text-align:left;direction:ltr">E2 = A×d<h2 style=";text-align:left;direction:ltr"> -0.37 <h2 style=";text-align:left;direction:ltr"> (21) In the formula, A is a constant, which is related to the location of the power line and whether there is gas in the oil; the ratio of the two is the insulation margin q at the oil gap where the installation point is located: If the insulation margin q is greater than the insulation margin q' required by the high-voltage electrical equipment, the point is retained; otherwise, the point is discarded; ultimately, there are d installation points that meet the internal insulation margin requirements of the high-voltage electrical equipment.

7. The method for optimizing the spatial arrangement of a sound field measurement device according to claim 4, characterized in that: The step 5 further includes the following contents: in a three-dimensional space, assuming that the coordinates of the fault source are (x, y, z), s installation points are selected with coordinates (x1, y1, z1), (x2, y2, z2), ..., (x s ,y s ,z s ), satisfying the following relationship: Where t1, t2, …, t s is the time when the acoustic signal pulse is received at different installation points; c is the speed of sound in the medium inside the high-voltage electrical equipment; however, the location of the fault source obtained by solving these s points may be a location inside the equipment where the fault cannot occur, and even the fault source after positioning may be outside the equipment; therefore, it is necessary to introduce t points so that the analytical solution (x, y, z) obtained satisfies the following relationship: (x,y,z)∈D(20) Where D is the coordinate set of possible fault locations inside the equipment; let e = s + t. Therefore, after the third step of optimization, there are e points that can accurately locate the internal faults of the equipment.

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