Built-in sound field measurement device for high-voltage electrical equipment and spatial optimization arrangement method

Abstract

The application discloses a built-in sound field measuring device for high-voltage electrical equipment and a spatial optimization arrangement method, and relates to the design of an internal fiber grating sound sensor and an external measuring loop for high-voltage electrical equipment and the design of a spatial optimization arrangement scheme, wherein the device comprises the internal fiber grating sound sensor and the external measuring loop. The detection frequency band of the fiber grating sound sensor is designed by the length of the grating area, and both ultrasonic waves and audible sound are considered. Polyimide is used as the coating material of the fiber grating, and the fiber grating has better high-temperature resistance and insulation performance. Glass fiber reinforced plastic is used as the packaging material of the fiber grating, and the fiber grating has higher mechanical strength and durability. A noise reduction device is designed by the interference principle to suppress the interference of optical noise in the measuring loop. By the design of the transfer function and the cutoff frequency, the band-pass filtering is transplanted into the data collector to suppress the influence of high-frequency and low-frequency interference during the collection of sound signals. A spatial optimization arrangement scheme is designed in combination with various constraint factors, and the engineering application value of the measuring device is improved.

Description

Technical Field

[0001] The present 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] High-voltage electrical equipment, such as large power transformers and GIS, serves as essential infrastructure for power systems and plays a crucial role in the conversion and transmission of electrical energy. However, insulation defects inevitably develop during production, transportation, and operation. As these defects develop, the insulation of high-voltage electrical equipment can degrade and even fail. This process can lead to typical faults within high-voltage electrical equipment, such as winding overheating, partial discharge, and turn-to-turn short circuits. Therefore, effectively detecting these typical faults within equipment after insulation problems occur is crucial to ensure safe operation.

[0003] However, current acoustic measurement technologies for the operating status of high-voltage electrical equipment mainly focus on external means, which cannot maintain higher performance while working internally. In addition, the impact of noise interference on the sound field measurement process has not been resolved, making it difficult to meet the requirements for transparency of the operating 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, 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 to reversely infer the dynamic range of sensor design parameters, packaging materials and structural dimensions, limiting the installation requirements of fiber grating acoustic sensors in different application scenarios. Furthermore, existing engineering applications of acoustic field measurement devices lack theoretical analysis of spatial layout and installation measurement points, resulting in the measurement devices failing to achieve the desired measurement results. This, to a certain extent, limits the large-scale field application of acoustic field monitoring devices (e.g., the article "Study on the Acoustic Characteristics of Arc Discharge in Transformers Based on Fiber Bragg Grating Sensing," author: Ji Tong). Existing optimization configuration schemes for other sensors only consider monitoring efficiency and range, without considering factors such as the permitted installation location, insulation margin, and fault location, thus lacking engineering practicality. (e.g., "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 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 an acoustic field measurement device, including a method for designing an internal fiber Bragg grating acoustic sensor for high-voltage electrical equipment and a method for designing an external measurement circuit; the method is characterized by:

[0006] The design method of the fiber Bragg 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 meet the following requirements:

[0008]

[0009] Where R min is the set minimum reflectivity, f max is the upper limit of the detection frequency required by the sensor, v is the speed 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) Coating material selection: The surface of the bare optical fiber is coated with a coating material with a high elastic modulus 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 transmission angle respectively; glass fiber reinforced plastic is selected as the packaging material of fiber grating;

[0016] (4) Determination of package size: The horizontal dimension of the internal fiber Bragg 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 strain 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] Where ΔL represents the change in transverse length after the axial force is applied, and L represents the original transverse length. 2ΔX1 and ΔX2 represent the changes in transverse length of regions I and II after the axial force is applied. 2X1 and X2 represent the original transverse lengths of regions I and II.

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

[0024]

[0025] According to the definition of sensitivity enhancement coefficient 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 upper and lower normalized cutoff frequencies based on the sampling frequency:

[0034]

[0035] Where, 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 high 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, which is related to the pole position.

[0039] The present invention also discloses an acoustic field measuring device, which is based on the above-mentioned design method and includes an internal fiber grating acoustic sensor and an external measurement circuit. Its 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 optical fiber to form a fiber grating; a layer of coating material is wrapped around the outside of the grating; and the optical fiber and the coating material are encapsulated on the outside by 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 photodetector, 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 via an optical fiber jumper, port 2 is connected to the internal fiber grating acoustic sensor via an optical fiber jumper through a through-hole embedded in the surface of the high-voltage equipment, and port 3 is connected to the optical interference noise reduction device via an optical fiber jumper. The optical interference noise reduction device also has three ports: an input port connected to the optical circulator, a feedback port connected to the laser source, and an output port connected to the photodetector, all of which are connected via an optical fiber jumper. The photodetector is connected to the data collector with a built-in bandpass filtering function via 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 fiber Bragg grating acoustic sensors to achieve simultaneous measurement of ultrasonic signals and audible sound signals.

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

[0044] Glass fiber reinforced plastics (FRP), a composite of glass fiber and a polymer matrix (such as epoxy resin), are used as packaging materials for fiber Bragg 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] By using the transfer function and the calculated high and low normalized cutoff frequencies, a specific bandpass filtering algorithm is designed and transplanted into the data collector to suppress the influence of low-frequency vibrations 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, to effectively reduce optical noise. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 Schematic diagram of the structure of the sound field measurement device of the present invention;

[0048] Figure 2 Schematic diagram of the packaging dimensions of the internal fiber Bragg grating acoustic sensor of the present invention;

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

[0050] The invention comprises: a fiber Bragg 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 filter function. DETAILED DESCRIPTION

[0051] Example 1

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

[0053] ① Determining the grating length: The grating length and reflectivity of a fiber Bragg grating (FBG) are crucial to the detection band of the acoustic sensor. To achieve optimal monitoring results, the grating length is generally required to be less than 1 / 2 the wavelength of the measured sound wave. This allows the grating to sense the effects of the sound wave with uniform strain. To ensure the signal-to-noise ratio of the output signal, the FBG's reflectivity is generally required to be above a set minimum reflectivity. These two factors together determine the selection of the FBG grating length.

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

[0055]

[0056] Where v is the velocity of sound waves in the medium inside high-voltage electrical equipment; f is the frequency of 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 (FBG) has the following relationship with the grating length:

[0058] R = tanh 2 (ΩL) (2)

[0059] Where R is the fiber Bragg grating reflectivity, Ω is the coupling coefficient (Ω>0), L is the grating length, and tanh(x) is the hyperbolic tangent function, which is positively correlated with x and gradually approaches 1 as x increases. Therefore, the fiber Bragg grating length cannot be reduced indefinitely, as this will reduce the grating reflectivity, thereby lowering 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] Where R min is the set minimum reflectivity, 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 Typically, the frequency is 80kHz, and v is 1400-1500m / s. Therefore, the grating length L of the fiber Bragg grating used in transformers is generally 6.3-9mm. Therefore, the present invention selects a grating length within this range to develop a fiber Bragg grating acoustic sensor, which can achieve simultaneous measurement of ultrasonic and audible signals.

[0063] ② Determine the coating material: When high-voltage electrical equipment is operating, the vibration of the main body will cause mechanical shock to the sensors installed inside the equipment. At the same time, the rapid oil flow rate inside the equipment will also have a significant impact on the sensors. This requires the built-in fiber grating acoustic sensor to have high mechanical strength. However, the fiber grating itself is relatively fragile and prone to breakage when subjected to large impacts, affecting monitoring efficiency. Even accidental breakage due to misoperation during installation can invisibly increase monitoring costs. Therefore, it is necessary to coat 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 include 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] Acrylate 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 acrylate is about 90℃, which cannot withstand the high temperature environment inside high-voltage electrical equipment, so it is excluded.

[0066] Although polyimide is relatively expensive, its superior mechanical strength makes it the preferred coating material for fiber Bragg gratings (FBGs). Furthermore, polyimide can withstand temperatures up to 300°C, offers superior insulation properties, and exhibits strain response similar to that of bare optical fiber. Therefore, this invention uses polyimide as a coating material for fiber Bragg gratings.

[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, which 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 angle of incidence and the angle of transmission respectively. If the acoustic impedance of the selected material is too large (Z2 is much larger than Z1), then 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 perpendicular to the dielectric material (θ i =0°) can be better absorbed by the dielectric material. As the incident angle increases, the reflection coefficient R will gradually increase, the sound transmission coefficient T will decrease, and the sound transmission performance will deteriorate. Only when the difference between Z1 and Z2 is not large, the fiber Bragg grating acoustic sensor has high sound transmission performance and is less affected by the change of the incident angle.

[0072] Glass fiber and its related composites have similar acoustic impedances to the dielectric media within high-voltage electrical equipment. However, glass fiber itself, similar to the quartz glass used to make fiber Bragg gratings (FBGs), is a brittle material with poor impact resistance. Composites of glass fiber and a polymer matrix (such as epoxy resin) offer greater mechanical strength and durability, and their acoustic impedance more closely matches that of the dielectric media within high-voltage electrical equipment. Therefore, this invention uses fiberglass reinforced plastic (FRP) as the encapsulation material for FBGs.

[0073] ④ Package Dimensions: The horizontal dimensions of the internal fiber Bragg grating acoustic sensor are divided into two regions based on the location of the optical fiber and grating. Region 1 is the region where the optical fiber is located, and Region 2 is the region where the grating is located. Let Region 1 have a horizontal length of X1 and a vertical length of Y1; let Region 2 have a horizontal length of X2 and a vertical length of 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] Where E1 and E2 represent the elastic modulus of the packaging materials in regions 1 and 2; S1 and S2 represent the axial force-bearing areas 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] Where ΔL represents the change in lateral length after being subjected to axial force, L represents the original lateral length; 2ΔX1 and ΔX2 represent the changes in 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 coefficient 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, and Equation (9) can be rewritten as:

[0085]

[0086] Sensitivity is enhanced only when Y1>Y2 and K>1. The present invention sets K to a value between 1.6 and 2. The lateral dimensions do not affect sensitivity; X2 can be slightly longer than the gate length, and X1 can be selected and designed based on the actual installation environment.

[0087] 2. External measurement circuit construction

[0088] ① Optical Interference Noise Reduction Device Design: The measurement circuit of this invention uses a laser as the light source to provide a stable light source for the internal fiber Bragg grating acoustic sensor. However, laser light is coherent, and when the optical signal propagates along the optical path, it inevitably generates optical noise, primarily phase noise and frequency noise. Therefore, this invention incorporates an optical interferometer noise reduction device, whose internal components 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 it into two optical beams 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 and 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 is 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 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:

[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 optical noise by analyzing and monitoring the cos(Δφ(t)) term in the interference fringes. However, the noise phase is not fixed; Δφ(t) also changes over time. Therefore, a feedback control module is required to feed this phase difference information back 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, maintaining a stable frequency and phase of the optical signal received by the photodetector, thereby effectively reducing optical noise.

[0099] ② Bandpass filtering algorithm design: After receiving a stable optical signal, the photodetector converts it into an electrical signal and transmits it to the data collector. Although optical noise in the optical path has been suppressed, some interference within the high-voltage electrical equipment itself can affect the monitoring performance of the internal fiber Bragg grating acoustic sensor. This interference cannot be suppressed by the optical interferometer noise reduction device. In this case, a filtering algorithm must be implanted within the data collector to filter out this interference.

[0100] During operation, high-voltage electrical equipment generates numerous low-frequency signals below 5kHz due to its vibration. The strong electromagnetic environment within the equipment also generates numerous high-frequency electromagnetic wave signals. Analysis shows that these high-frequency electromagnetic wave signals are mostly above 500kHz. By analyzing the frequency band differences between acoustic signals, low-frequency vibration signals, and high-frequency electromagnetic wave signals, a bandpass filtering algorithm was designed to allow signals in specific frequency bands to enter the data logger, thereby filtering out both 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 upper and lower normalized cutoff frequencies based on the sampling frequency:

[0103]

[0104] Where, 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, which is related to the pole position.

[0108] By using 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 measuring device, based on the sound field measuring device design method of embodiment 1, comprises an internal fiber Bragg grating (FBG) acoustic sensor (1) and an external measuring circuit (2), and is characterized in that: the internal fiber Bragg grating (FBG) acoustic 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 of an optical fiber and wraps around the optical fiber to form a fiber Bragg grating; a layer of coating material is wrapped around the outside of the grating; and the optical fiber and the coating material are packaged outside with a 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 via an optical fiber jumper, port 2 is connected to the internal fiber grating acoustic sensor via an optical fiber jumper through a through-hole embedded in the surface of the high-voltage equipment, and port 3 is connected to the optical interference noise reduction device via 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 via an optical fiber jumper; the photodetector is connected to the data collector with a built-in bandpass filtering function via 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 measurement points that can effectively monitor the internal acoustic signals of high-voltage electrical equipment;

[0116] Design and build an equivalent scale 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. 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 calculated from the sound pressure:

[0120] p=ρcv (18)

[0121] Where 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 velocity received at the monitoring point. The relationship between v and sensor sensitivity can be used to obtain the minimum sensitivity A required for different monitoring points to detect sound signals. 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: Based on the design institute's and project's requirements, as well as the internal structure of the high-voltage electrical equipment, there are b permitted installation locations on site. For example, to avoid damaging the internal electromagnetic shielding design of the high-voltage electrical equipment or affecting its normal operation, the design institute may restrict the monitoring device's measurement points. Fiber Bragg grating acoustic sensors can only be fixedly installed on internal support structures. With these constraints in place, there are b permitted installation locations on site that meet these requirements.

[0125] Step 3: The sets a and b belong to are not in a containment relationship, but rather have a partial intersection. Let c = a ∩ b, that is, taking the intersection of the theoretically possible installation locations and the permitted installation locations on site, we obtain c installation points after the first step of optimization.

[0126] Step 4: To ensure that the sensor installation does not threaten the internal insulation of high-voltage electrical equipment, the insulation margin of the installation location 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 calculations and other means, select the power lines at each installation location, 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] Where A is a constant that 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 required insulation margin q' for the high-voltage electrical equipment, the point is retained; otherwise, it is discarded. Ultimately, 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 d points. In a three-dimensional space, assuming that the coordinates of the fault source are (x, y, z), s points are selected with the coordinates of (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 it takes for the acoustic signal pulse to be received at different installation locations. c is the speed of sound in the medium inside the high-voltage electrical equipment. However, the fault source location obtained by solving with these s points may be a location inside the equipment where the fault cannot possibly occur, or even located outside the equipment. Therefore, it is necessary to introduce t points so that the analytical solution (x, y, z) satisfies the following relationship:

[0136] (x,y,z)∈D(20)

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

[0138] Step 6: Unlike the variables above, e is a variable parameter, meaning that the points that meet the fault location requirements are within a range. Considering economic requirements, while meeting all the above space optimization factors, the fewer sensors used, the better. This reduces both the cost of sensor production and the risk of negative impacts on high-voltage electrical equipment after sensor installation. Let f = e. min After four steps of spatial optimization, the number of internal fiber Bragg grating sensor installation points is finally determined to be f, and the locations of the points are all determined.

[0139] like Figure 3As shown in the figure, simulation calculations show that there are a monitoring points within the high-voltage electrical equipment that can effectively measure the acoustic signals of internal faults. However, considering the actual internal structure of the high-voltage electrical equipment and actual engineering requirements, there are b installation points allowed on-site. Taking the two primary factors into consideration, the intersection of the two installation point sets yields c theoretical installation points for acoustic sensors. Once installed within the high-voltage electrical equipment, the sensors will affect the surrounding electric field distribution. Therefore, it is necessary to consider whether the insulation margin of the high-voltage electrical equipment meets the requirements. Further screening within c yields d installation points that meet the insulation margin requirements. To accurately locate the fault point, e installation points were selected from d. By analyzing the time delay and amplitude of the acoustic signals received by sensors at different monitoring locations, the theoretical fault source within the high-voltage electrical equipment can be accurately located. Considering cost factors and economic needs, the minimum number of sensors was selected to achieve the desired goal while meeting the monitoring requirements. After analyzing multiple factors, the optimal spatial installation points are f, and their locations have been determined.

[0140] This invention proposes for the first time a built-in sound field measurement device for high-voltage electrical equipment and a spatial optimization layout method, solving the technical problem that traditional sound field measurement methods cannot be effectively applied inside high-voltage electrical equipment. By analyzing different grating lengths and reflectivities, a high-sensitivity fiber Bragg grating acoustic sensor that takes into account both audible sound and ultrasonic sound was designed and developed. Appropriate coating materials, packaging materials, and dimensions were selected to ensure its applicability for measuring fault acoustic signals inside high-voltage electrical equipment. Based on the potential noise interference present in the monitoring process of the acoustic measurement device, the existing measurement circuit was optimized to improve the signal-to-noise ratio of the measurement device. Combining multiple factors, a four-step optimization method for the optimal layout of the sound field measurement device inside high-voltage electrical equipment was proposed, providing 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 merely illustrate the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for designing an acoustic field measurement device, including a method for designing a fiber Bragg grating acoustic sensor inside a high-voltage electrical device and a method for designing an external measurement circuit; the method is characterized by: The design method of the fiber Bragg 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 meet the following requirements: ； Where R min is the set minimum reflectivity, f max is the upper limit of the detection frequency required by the sensor, v is the speed 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) Coating material selection: The surface of the bare optical fiber is coated with a coating material with a high elastic modulus 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 transmission angle respectively; glass fiber reinforced plastic is selected as the packaging material of fiber grating; (4) Determination of package size: The horizontal dimension of the internal fiber Bragg 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: ； 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 strain 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: ； Where ΔL represents the change in transverse length after the axial force is applied, and L represents the original transverse length. 2ΔX1 and ΔX2 represent the changes in transverse length of regions I and II after the axial force is applied. 2X1 and X2 represent the original transverse lengths of regions I and II. Combining equations (6) and (7), we can obtain: ； According to the definition of sensitivity enhancement coefficient 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 upper and lower normalized cutoff frequencies based on the sampling frequency: ； Where, 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 high 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, which 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 optical interference noise reduction device operates as follows: receiving an optical signal transmitted by a circulator, separating the optical signal into two optical beams through a beam splitter, one being a reference beam with no frequency or phase shift, and the other being 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 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: ； 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 light signal received by the photodetector stable, thereby reducing optical noise.

3. A sound field measurement device, comprising an internal fiber Bragg grating acoustic sensor and an external measurement circuit, based on the design method of a sound field measurement device according to any one of claims 1 to 2, and characterized by: The internal fiber Bragg grating acoustic sensor includes 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 Bragg grating; a layer of coating material is wrapped around the outside of the grating; and the outside of the optical fiber and the coating material are encapsulated by the 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 photodetector, 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 via an optical fiber jumper, port II is connected to the internal fiber grating acoustic sensor via an optical fiber jumper through a through-hole embedded in the surface of the high-voltage equipment, and port III is connected to the optical interference noise reduction device via 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 via an optical fiber jumper; the photodetector is connected to the data collector with a built-in bandpass filtering function via 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 determined that there are a number of measurement points that can effectively monitor the internal acoustic signals of high-voltage electrical equipment; Step 2: Based on 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 the number of allowable installation locations on site: b; 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 possible installation positions and the on-site allowed installation positions, and we get c installation points after the first step of optimization. Step 4: To ensure that the installed sensors do not threaten the internal insulation of the high-voltage electrical equipment, the insulation margin at 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: To locate the internal fault of the high-voltage electrical equipment, select e points that meet the positioning requirements from d points. d points are the installation points that ultimately meet the internal insulation margin requirements of the high-voltage electrical equipment. 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 spatial optimization, the number of internal fiber Bragg grating sensor installation points is finally determined to be f, and the locations of the points are all determined.

5. The method for optimizing the spatial arrangement of a sound field measurement device according to claim 4, wherein: The step 1 further includes the following: Design and build an equivalent scale 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 it takes 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 from the sound pressure: p = ρcv (18); Where 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 velocity 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 sensor sensitivity. min : ； Where 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 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, wherein: Step 4 further includes the following: selecting power lines at the locations of the installation points, integrating the electric field to obtain an average field strength E1: ； Where d is the length of the power line in mm; then the permissible field strength E2 is calculated: E2=A×d -0.37 (21); Where A is a constant, which is related to the position of the power line and whether there is gas in the oil; the ratio of the two is the insulation margin at the oil gap where the installation point is located. : ； If the insulation margin If the insulation margin q' is greater than that 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.

7. The method for optimizing the spatial arrangement of a sound field measurement device according to claim 4, wherein: 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 it takes for different installation points to receive the acoustic signal pulse; c is the speed of sound in the medium inside the high-voltage electrical equipment. However, the fault source location obtained by solving these s points may be a location inside the equipment where the fault cannot occur, or even the fault source may be located outside the equipment. Therefore, it is necessary to introduce t points so that the analytical solution (x, y, z) 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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