Distribution cable intermediate joint partial discharge signal detection and positioning method

Abstract

The invention discloses a power distribution cable intermediate joint partial discharge signal detection and positioning method, and relates to the technical field of power distribution equipment state monitoring, and the method comprises the steps: collecting the signal propagation characteristics of a partial discharge signal through a reference point array disposed at the periphery of a power distribution cable intermediate joint; constructing a discharge source space positioning equation set, and solving the discharge source space positioning equation set to obtain an initial solution; analyzing the time-frequency characteristics of the partial discharge signals, and identifying and classifying the partial discharge signals to obtain a discharge type judgment result; determining a corresponding position correction parameter based on the discharge type determination result; and fusing the position correction parameter with the initial solution, and continuously correcting the positioning result through a recursive iterative optimization algorithm until the positioning error is converged to a set threshold value. According to the invention, accurate mapping of the discharge type and the position feature is realized, and the positioning error is reduced; the adaptability and convergence of the algorithm are improved; and the anti-interference capability in a complex electromagnetic environment is enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of distribution equipment status monitoring, and specifically to a method for detecting and locating partial discharge signals at the intermediate joints of distribution cables. Background Art

[0002] The techniques of partial discharge detection and location are important means for evaluating the insulation status of intermediate joints of distribution cables. Traditional partial discharge detection mainly relies on the pulse current method and the ultrasonic method, which are relatively mature in laboratory environments. However, with the intelligent development of the distribution network, higher requirements are put forward for the accuracy, real-time performance, and self-adaptability of partial discharge detection and location. Especially in areas with complex structures and multi-layer distribution of insulating media such as cable intermediate joints, traditional detection methods have obvious limitations in terms of location accuracy and discharge type identification. The ultrasonic method is greatly affected by the reflection interference of the medium boundary, and its location accuracy is significantly reduced in multi-layer insulation structures; while the pulse current method, although highly sensitive, is difficult to accurately distinguish different types of discharge sources and is easily affected by external interference in complex electromagnetic environments.

[0003] Currently, the commonly used location methods in the industry mainly calculate based on time difference and energy attenuation characteristics. However, these methods often treat different types of discharge sources equally, ignoring the differences in spatial distribution and signal characteristics among various discharges. At the same time, there is a lack of an effective mapping mechanism between signal feature extraction and spatial location calculation in the existing technology, resulting in a deviation between the location result and the actual discharge physical characteristics. Especially when dealing with different types such as internal discharge, surface discharge, floating discharge, and corona discharge, due to the failure to fully consider their unique spatial distribution laws and signal propagation characteristics, the location accuracy and reliability are difficult to meet the engineering requirements. Summary of the Invention

[0004] In view of the above problems, the present invention is proposed.

[0005] Therefore, the present invention provides a method for detecting and locating partial discharge signals at the intermediate joints of distribution cables, which can solve the problems mentioned in the background art.

[0006] To solve the above technical problems, the present invention provides the following technical solutions: a method for detecting and locating partial discharge signals of a distribution cable intermediate joint, including: collecting the signal propagation characteristics of partial discharge signals through a reference point array arranged around the distribution cable intermediate joint; based on the signal propagation characteristics, constructing a spatial positioning equation set for the discharge source and solving the spatial positioning equation set for the discharge source to obtain an initial solution; analyzing the time-frequency characteristics of the partial discharge signals, identifying and classifying the partial discharge signals to obtain a discharge type determination result; determining corresponding position correction parameters based on the discharge type determination result; fusing the position correction parameters with the initial solution, and continuously correcting the positioning result through a recursive iterative optimization algorithm until the positioning error converges within a set threshold.

[0007] As a preferred solution of the method for detecting and locating partial discharge signals of the distribution cable intermediate joint according to the present invention, wherein: the reference point array includes a plurality of electrode sensors distributed in a ring shape, and each electrode sensor amplifies and filters the collected partial discharge signals through a signal conditioning circuit; the signal propagation characteristics include propagation time difference and energy attenuation characteristics.

[0008] As a preferred solution of the method for detecting and locating partial discharge signals of the distribution cable intermediate joint according to the present invention, wherein: based on the signal propagation characteristics, constructing a spatial positioning equation set for the discharge source and solving the spatial positioning equation set for the discharge source to obtain an initial solution includes the following steps: Establish a positioning equation set based on the propagation time difference. Specifically, assume that the coordinates of the discharge source are (x0, y0, z0), and the coordinates of the i-th sensor are (xᵢ, yᵢ, zᵢ), then the signal propagation time difference satisfies: ; where is the time difference between the signal arriving at the i-th sensor and the j-th sensor, v is the propagation speed of electromagnetic waves in the medium, , ∈[1,N] and i≠j, N is the total number of sensors; The spatial positioning equation set for the discharge source is expressed as: ; where , are the energy values when the signal arrives at the i-th and j-th sensors respectively, α is the attenuation coefficient of the medium, , are the distances from the discharge source to the i-th and j-th sensors respectively; Construct a composite error function: ; Among them, m represents the measured value, and c represents the calculated value. and are the weight coefficients, is the balance factor; The initial solution is solved by using the iterative least squares method; the initial solution represents the initial value of the spatial coordinates of the discharge source.

[0009] As a preferred solution of the partial discharge signal detection and location method for the middle joint of the distribution cable described in the present invention, wherein: the solution of the initial solution by using the iterative least squares method is represented by the following formula: ; Wherein, represents the number of iterations, is the Jacobian matrix, is the weight matrix, is the residual vector, is the step size factor; Let the weighted sum of squared residuals of the th iteration be : ; If the weighted sum of squared residuals of the current iteration is less than the average value of the previous two iterations, that is: ; Then let the step size factor be expressed as: ; Otherwise, let the step size factor be expressed as: .

[0010] As a preferred solution of the partial discharge signal detection and location method for the middle joint of the distribution cable described in the present invention, wherein: the time-frequency characteristics of the partial discharge signal are analyzed, and the partial discharge signal is identified and classified to obtain the discharge type determination result, including the following steps: The wavelet transform is used to perform multi-scale decomposition on the partial discharge signal to extract the time-frequency characteristics; the partial discharge signal is decomposed into a high-frequency band, a medium-frequency band and a low-frequency band, the detail coefficients and approximation coefficients of each frequency band are obtained, and the energy distribution characteristics of the partial discharge signal are obtained based on the detail coefficients and approximation coefficients; Construct a time-frequency feature vector based on the energy distribution characteristics; the time-frequency feature vector includes the energy ratio of the high-frequency band to the low-frequency band, a pulse feature function, and waveform statistical features; wherein, the energy ratio of the high-frequency band to the low-frequency band is determined by wavelet coefficients and energy attenuation characteristics, the pulse feature function consists of an amplitude distribution and a time feature, and the waveform statistical features include waveform skewness and waveform kurtosis; Perform discharge type identification according to the time-frequency feature vector, and the criteria are as follows: If the energy ratio of the high-frequency band to the low-frequency band is greater than the unit value, and the pulse feature function achieves the global maximum value during the positive half-cycle of the power frequency, and at the same time the waveform skewness value is positive, then it is determined as internal discharge; If the energy ratio of the high-frequency band to the low-frequency band is less than the unit value, and the pulse feature function achieves the global maximum value during the negative half-cycle of the power frequency, and at the same time the waveform skewness value is negative, then it is determined as surface discharge; If the pulse feature function has multiple peaks within one power frequency cycle, and the degree of deviation of the amplitude ratio of adjacent peaks from the unit value is within the first preset range, and at the same time the phase difference between the peaks is greater than the basic segmentation unit of the power frequency cycle, then it is determined as floating discharge; If the pulse feature function shows multiple consecutive peaks within a local phase interval, and the peak sequence satisfies the exponential decay law, and at the same time the phase difference between adjacent peaks is less than the minimum segmentation unit of the power frequency cycle, then it is determined as corona discharge; Based on the above criteria, obtain the discharge type determination result.

[0011] As a preferred solution of the method for detecting and locating partial discharge signals at the middle joint of a distribution cable according to the present invention, wherein: based on the discharge type determination result, determine the corresponding position correction parameters, including the following steps: Construct a discharge position feature model; the discharge position feature model contains a position feature parameter matrix for different discharge types, and the position feature parameter matrix is established based on the energy ratio of the high and low frequency bands, the pulse feature function, and the waveform statistical features; Establish the coordinate conversion relationship between the rectangular coordinate system and the cylindrical coordinate system; Construct a basic position feature function : ; Wherein, is the position feature function, is the normalized value of the energy ratio of the high and low frequency bands, is the normalized pulse feature function, is the waveform skewness, is the waveform kurtosis, , , are the characteristic weight indices; If the discharge type determination result is internal discharge and surface discharge types, then construct a radial-dominant characteristic function : ; wherein, is the radial attenuation coefficient; is the radial correction factor; If the discharge type determination result is floating discharge type, then construct a balanced characteristic function : ; wherein, is the radial characteristic scale, is the angular characteristic scale, is the axial characteristic scale, is the balance factor; If the discharge type determination result is corona discharge type, then construct an axial-dominant characteristic function : ; wherein, is the angular modulation coefficient; is the height modulation coefficient; is the axial correction factor; Extract the calibration parameter matrix and transform the calibration parameter matrix from the cylindrical coordinate system to the rectangular coordinate system; According to the calibration parameter matrix in the rectangular coordinate system and the spatial coordinate values to be corrected, calculate the position calibration parameter by matrix multiplication.

[0012] As a preferred solution of the partial discharge signal detection and location method for the middle joint of the distribution cable described in the present invention, wherein: fuse the position calibration parameter with the initial solution, and continuously correct the location result through a recursive iterative optimization algorithm until the location error converges within a set threshold, including the following steps: Superpose and fuse the position calibration parameter and the initial solution in a weighted manner to obtain an iterative initial value; Construct an error evaluation function for iterative optimization; Update the iterative parameter based on the calculation result of the error evaluation function. When the relative change rate of the error evaluation function is less than a preset threshold, stop the iteration. Otherwise, by comparing the error magnitudes of two adjacent iterations, increase or decrease the value of the weight coefficient until the final location result is obtained.

[0013] To further solve the above technical problems, the present invention provides the following technical solution: a partial discharge signal detection and location system for a distribution cable intermediate joint, comprising: a signal acquisition module for acquiring the signal propagation characteristics of the partial discharge signal through a reference point array arranged around the distribution cable intermediate joint; a spatial location module for constructing a spatial location equation set of the discharge source based on the signal propagation characteristics and solving the spatial location equation set of the power source to obtain an initial solution; a pattern recognition module for analyzing the time-frequency characteristics of the partial discharge signal and identifying and classifying the partial discharge signal to obtain a discharge type determination result; a parameter extraction module for determining corresponding position correction parameters based on the discharge type determination result; and an optimization iteration module for fusing the position correction parameters with the initial solution and continuously correcting the location result through a recursive iteration optimization algorithm until the location error converges within a set threshold.

[0014] A computer device, comprising a memory and a processor, the memory storing a computer program, characterized in that when the processor executes the computer program, the steps of the above-mentioned partial discharge signal detection and location method for a distribution cable intermediate joint are implemented.

[0015] A computer-readable storage medium, having a computer program stored thereon, characterized in that when the computer program is executed by a processor, the steps of the above-mentioned partial discharge signal detection and location method for a distribution cable intermediate joint are implemented.

[0016] The beneficial effects of the present invention: The present invention adopts a ring-shaped distributed reference point array in cooperation with a dedicated signal conditioning circuit, overcoming the signal distortion problem of traditional acquisition methods under the complex structure of the cable intermediate joint. By combining the time difference of propagation and the energy attenuation characteristics to construct a composite error function, the reliability of the initial solution is improved. The present invention proposes a family of characteristic functions based on the discharge type, and effectively solves the specificity problem of different types of discharge sources in spatial location by constructing radial dominant type, balanced type and axial dominant type characteristic functions. Finally, the present invention realizes the deep fusion of characteristic quantities and spatial gradients by designing a multi-level correction parameter matrix, overcoming the technical bottleneck of the separation of characteristic information and spatial information in traditional methods. Description of the Drawings

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention, and those of ordinary skill in the art can also obtain other drawings based on these drawings without creative efforts.

[0018] Figure 1Schematic diagram of the overall process of the method for detecting and locating partial discharge signals in the middle joint of a distribution cable proposed by the present invention; Figure 2 Interaction schematic diagram in the system for detecting and locating partial discharge signals in the middle joint of a distribution cable proposed by the present invention; Figure 3 Computer equipment diagram in the method for detecting and locating partial discharge signals in the middle joint of a distribution cable proposed by the present invention. Specific implementation manners

[0019] To make the above objects, features, and advantages of the present invention more obvious and understandable, the specific implementation manners of the present invention will be described in detail below with reference to the accompanying drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0020] Many specific details are set forth in the following description in order to fully understand the present invention, but the present invention can also be implemented in other ways different from those described herein. Those skilled in the art can make similar generalizations without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0021] Example 1, referring to Figure 1 , which is an embodiment of the present invention, providing a method for detecting and locating partial discharge signals in the middle joint of a distribution cable.

[0022] Figure 1 The schematic diagram of the overall process of the method for detecting and locating partial discharge signals in the middle joint of a distribution cable is shown, including the following steps: S1: Collect the signal propagation characteristics of the partial discharge signal through a reference point array arranged around the middle joint of the distribution cable.

[0023] It should be noted that the reference point array includes a plurality of electrode sensors distributed in a ring shape, and each electrode sensor amplifies and filters the collected partial discharge signal through a signal conditioning circuit. The signal propagation characteristics include the propagation time difference and the energy attenuation characteristics.

[0024] Furthermore, it is first necessary to construct a complete signal acquisition system. For this purpose, a plurality of electrode sensors are arranged in the circumferential spatial position of the middle joint of the distribution cable to form a reference point array structure. The electrode sensor is of a ring shape, enabling it to uniformly cover the outer surface of the cable middle joint to ensure the omnidirectional acquisition of partial discharge signals. Through this spatially distributed arrangement in a ring shape, synchronous monitoring of partial discharge signals at different spatial positions can be achieved, providing basic data support for subsequent signal positioning calculations.

[0025] Each electrode sensor of the reference point array is configured with a dedicated signal conditioning circuit for processing the acquired original partial discharge signals. The signal conditioning circuit includes a preamplifier and a band-pass filter. The preamplifier is used to increase the amplitude level of weak discharge signals, and the band-pass filter is used to suppress power frequency interference and high-frequency noise and extract the effective frequency band components of partial discharge signals. After signal conditioning, the electrode sensor can accurately obtain the propagation time difference feature and energy attenuation feature of partial discharge signals. These two feature quantities contain the spatial position information of the discharge source. Among them, the propagation time difference feature reflects the timing relationship of the discharge signal reaching each sensor, and the energy attenuation feature reflects the intensity change law of the signal during spatial propagation.

[0026] S2: Based on the signal propagation characteristics, construct a spatial positioning equation set of the discharge source, and use the iterative least squares method to solve the initial solution of the constructed spatial positioning equation set of the discharge source.

[0027] Specifically, the initial solution represents the initial values of the spatial coordinates of the discharge source.

[0028] You are right. I will redesign the S2 scheme and only add clear interaction rules at key positions: S2.1: Establish a positioning equation set based on the propagation time difference.

[0029] Assume that the coordinates of the discharge source are (x0, y0, z0), and the coordinates of the i-th sensor are (xi, yi, zi). Then the propagation time difference of the signal satisfies: ; Among them, is the time difference between the signal reaching the i-th sensor and the j-th sensor, v is the propagation speed of electromagnetic waves in the medium, , ∈[1, N] and i≠j, N is the total number of sensors.

[0030] S2.2: Establish a spatial positioning equation set of the discharge source based on energy attenuation: ; Among them, , are the energy values of the signal when it reaches the i-th and j-th sensors respectively, α is the attenuation coefficient of the medium, , are the distances from the discharge source to the i-th and j-th sensors respectively.

[0031] S2.3: Construct a composite error function: ; Among them, m represents the measured value, and c represents the calculated value. and is the weight coefficient, is the balance factor.

[0032] S2.4: Solve the initial solution using the iterative least squares method: ; wherein, represents the number of iterations, is the Jacobian matrix, is the weight matrix, is the residual vector, is the step size factor.

[0033] Let the weighted sum of squared residuals for the th iteration be : ; If the weighted sum of squared residuals for the current iteration is less than the average of the previous two iterations, i.e.: ; Then let: ; Otherwise let: .

[0034] In a specific embodiment of the present invention, the process of calculating the discharge source location based on the obtained signal propagation characteristics is as follows: First, establish a positioning equation set based on the time difference. Since there is a time delay in the propagation process of the partial discharge signal, there is a difference in the time when different sensors receive the signal, and this time difference contains the location information of the discharge source. By analyzing the time difference of the signal arriving at adjacent sensors, a constraint equation reflecting the spatial location of the discharge source can be constructed. At the same time, considering the energy attenuation characteristics of the discharge signal in the propagation process, establish an energy attenuation positioning equation set. The signal energy decays as the propagation distance increases, and this attenuation law also reflects the spatial relationship between the discharge source and each sensor. By analyzing the ratio relationship of the signal energy at different sensors, supplementary constraint conditions required for the positioning calculation can be obtained. This method of combining dual characteristics has stronger anti-interference ability compared to the traditional single-characteristic positioning method.

[0035] In the process of solving the positioning equation set, the present invention adopts the iterative least squares method. First, construct a composite error function to organically integrate the time difference feature and the energy attenuation feature. By reasonably setting the weight coefficient and the balance factor, ensure that the two features play their respective advantages in the positioning calculation. This feature fusion strategy avoids the positioning deviation that may be brought by a single feature in the traditional method.

[0036] During the iterative solution process, the present invention introduces a step-size adaptive mechanism based on the change of residuals. By comparing the weighted sum of squared residuals of the current iteration with the previous two iterations, the iteration step-size is dynamically adjusted. When the residuals decline rapidly, a larger step-size is adopted to accelerate convergence; when the change of residuals slows down, a smaller step-size is adopted to improve accuracy. This adaptive mechanism effectively solves problems such as slow convergence or oscillation in traditional fixed-step algorithms.

[0037] Finally, through double-feature constraint and adaptive iterative optimization, an initial solution reflecting the spatial position of the discharge source is obtained. This positioning method makes full use of the complementarity of the two features of time difference and energy attenuation, and improves the accuracy of discharge source positioning in the electromagnetic environment of distribution cable joints through feature fusion and iterative optimization.

[0038] S3: Analyze the time-frequency characteristics of the partial discharge signal, identify and classify the partial discharge signal, and obtain the discharge type determination result.

[0039] S3.1: Use wavelet transform to perform multi-scale decomposition on the partial discharge signal and extract time-frequency characteristics. Select wavelet basis functions with good local characteristics and symmetry, decompose the signal into three frequency bands: high frequency, medium frequency, and low frequency, obtain the detail coefficients and approximation coefficients of each frequency band, and obtain the energy distribution characteristics of the signal.

[0040] Specifically, during the detection and positioning process of partial discharge signals in distribution cable joints, in order to effectively extract the time-frequency characteristics of the discharge signals, multi-scale wavelet transform is first used to decompose the collected partial discharge signals. Considering the characteristics of partial discharge signals such as non-stationarity, transience, and multi-scale, wavelet basis functions with good time-frequency localization characteristics, symmetry, and orthogonality are selected. This type of wavelet basis function can effectively separate different frequency band components while maintaining the integrity of signal characteristics.

[0041] During the wavelet decomposition process, the partial discharge signal is successively decomposed into three frequency bands: high frequency band (reflecting the fast-changing characteristics of discharge pulses), medium frequency band (reflecting the main energy distribution during the discharge process), and low frequency band (characterizing the slow-changing trend of discharge development). By calculating the wavelet coefficients of each frequency band, the detail coefficients and approximation coefficients of the signal at different scales are obtained. Among them, the detail coefficients reflect the local characteristics of the partial discharge signal in each frequency band, and the approximation coefficients characterize the overall trend of the signal. Based on these wavelet coefficients, the energy distribution law of the signal in different frequency bands is further analyzed to provide basic characteristics for subsequent discharge type identification. This multi-scale decomposition method fully considers the multi-dimensional characteristics of partial discharge signals in distribution cable joints and can effectively extract the characteristic information required for discharge type determination.

[0042] S3.2: Construct a time-frequency feature vector.

[0043] a. Energy ratio between high-frequency band and low-frequency band: ; Wherein, is the energy ratio between the high-frequency band and the low-frequency band, and are the wavelet coefficients of the high-frequency band and the low-frequency band respectively, is the number of sampling points, , are the energy values when the signal arrives at the i-th and j-th sensors respectively, , are the distances from the discharge source to the i-th and j-th sensors respectively.

[0044] b. Pulse characteristics: ; Wherein, is the pulse characteristic function at the phase , is the amplitude of the i-th pulse, is the corresponding phase, is the pulse width characteristic parameter, is the time difference between the signal arriving at the i-th sensor and the j-th sensor.

[0045] It should be noted that the pulse width characteristic parameter describes the time duration characteristic of the partial discharge pulse, reflects the time scale of charge accumulation and release during the discharge process, and its value is determined by the physical characteristics of the discharge development process, and has different distribution laws for different types of discharge mechanisms.

[0046] c. Waveform characteristics: ; Wherein, is the waveform skewness, is the waveform kurtosis, is the signal sampling value, is the mean value, is the standard deviation, and M is the number of sampling points.

[0047] The present invention combines the energy distribution characteristics obtained by wavelet decomposition with the energy attenuation characteristics in the signal propagation process. By introducing an energy attenuation compensation term, a mapping relationship between the high-low frequency band energy ratio and the discharge type is established. At the same time, the pulse characteristic function fully considers the time propagation characteristics, and the waveform statistical characteristics reflect the statistical laws of different discharge types. This multi-dimensional feature fusion strategy overcomes the limitations of traditional single-feature methods.

[0048] S3.3: Identify the discharge type according to the feature vector, and the criterion is as follows: If the energy ratio of the high-frequency band to the low-frequency band is greater than the unit value, and the pulse characteristic function achieves the global maximum within the positive half-cycle of the power frequency, and the waveform skewness value is positive, then it is determined as internal discharge; If the energy ratio of the high-frequency band to the low-frequency band is less than the unit value, and the pulse characteristic function achieves the global maximum within the negative half-cycle of the power frequency, and the waveform skewness value is negative, then it is determined as surface discharge; If the pulse characteristic function has multiple peaks within one power-frequency cycle, and the degree of deviation of the amplitude ratio of adjacent peaks from the unit value is within the first preset range, and the phase difference between the peaks is greater than the basic segmentation unit of the power-frequency cycle, then it is determined as floating discharge; wherein, the first preset range can be plus or minus ten percent; If the pulse characteristic function presents multiple continuous peaks within a local phase interval, and the peak sequence satisfies the exponential decay law, and the phase difference between adjacent peaks is less than the minimum segmentation unit of the power-frequency cycle, then it is determined as corona discharge; Based on the above criteria, the determination result of the discharge type is obtained.

[0049] It should be noted that the unit value refers to the standard reference value when the energy ratio or amplitude ratio is equal to 1, and this value indicates that the two physical quantities being compared have equal magnitude, and it is an important reference benchmark for determining different discharge mechanisms in discharge type recognition.

[0050] Preferably, in the discharge type recognition step, the present invention establishes a systematic determination rule based on the discharge physical mechanism. By analyzing the typical characteristics of different types of discharges in the time-frequency domain, a complete determination criterion system is constructed. The present invention avoids the subjectivity of traditional empirical thresholds and provides reliable discharge type recognition results. In particular, the combination relationship of multiple characteristics is considered in the determination rule, enhancing the robustness of the recognition process.

[0051] S4: Based on the determination result of the discharge type, determine the corresponding position correction parameter.

[0052] S4.1: Construct a discharge position feature model, including the position feature parameter matrix of different discharge types.

[0053] Among them, the position feature parameter matrix is established based on the high-low frequency band energy ratio, the pulse characteristic function, and the waveform statistical characteristics, and reflects the spatial distribution law of different types of discharge sources.

[0054] It should be noted that the discharge position feature model is a complete feature representation system, which includes a position feature parameter matrix as its core component. The position feature parameter matrix is a specific data structure used for storage and calculation in the discharge position feature model.

[0055] S4.2: To ensure the unity of the coordinate system, first establish a coordinate transformation relationship: ; Among them, , , are the spatial position coordinates in the rectangular coordinate system; , , are the spatial position coordinates in the cylindrical coordinate system, is the radial distance, is the azimuth angle, is the axial height. Compared with directly calculating in the rectangular coordinate system, using the cylindrical coordinate system is more in line with the geometric structure characteristics of the cable joint and can more intuitively describe the spatial distribution law of the discharge source.

[0056] Establish the basic position feature function : ; Among them, is the position feature function, is the normalized value of the high-low frequency band energy ratio (between 0 and 1), is the normalized pulse feature function (between 0 and 1), is the waveform skewness, is the waveform kurtosis, , , are the feature weight exponents, which respectively adjust the contribution ratios of each feature quantity.

[0057] Preferably, the present invention proposes a basic position feature function of multi-feature fusion. Compared with the traditional method, this function not only considers the energy distribution characteristics, but also introduces an exponential weighting mechanism for pulse characteristics and waveform statistical characteristics. Through the dynamic adjustment of the three feature weight exponents, the adaptive fusion of different feature quantities in the positioning calculation is realized. In practical applications, this multi-feature fusion strategy can effectively suppress the positioning deviation that may be brought by a single feature, improve the stability of the positioning result, and the positioning accuracy after feature fusion is also improved compared with a single feature.

[0058] Specifically, for different discharge types, the specific form of the basic position feature function is also different. For internal discharge and surface discharge types, construct a radial-dominant feature function : ; Among them, is the radial attenuation coefficient, which is used to describe the influence degree of the axial height on the radial distribution, and characterizes the energy loss degree of the discharge signal during the radial propagation. The value range is 0.1 - 1.0. When is larger, it indicates that the radial propagation attenuation is slower; is the radial correction factor, which is used to correct the contribution weights at different radial positions and is a piecewise function related to the radial distance r, taking a larger value at the interface of the insulating layer.

[0059] Preferably, by introducing the exponential - type radial attenuation term and the radial correction factor, the present invention improves the positioning accuracy of the internal discharge source. Traditional methods often adopt a simple distance - attenuation model and fail to fully consider the coupling relationship between the internal discharge in the cable joint in the radial and axial directions, resulting in large positioning errors in the insulating medium stratified area. The radial - dominant characteristic function proposed by the present invention, through terms, establishes a quadratic coupling relationship between the axial height and the radial distance, which is more in line with the physical characteristics of the electric - field distribution. At the same time, by introducing the radial correction factor to dynamically weight the contributions at different radial positions, it effectively solves the positioning deviation caused by the non - uniformity of the insulating structure.

[0060] For the floating - discharge type, an equilibrium - type characteristic function is constructed : ; Among them, is the radial characteristic scale (usually 1 / 2 of the joint outer diameter), is the angular characteristic scale (taking the value of 2π), is the axial characteristic scale (usually 1 / 2 of the joint length), is the equilibrium factor, which is used to balance the component weights in three directions. The value range is 0.5 - 2.0. When = 1, it indicates that the weights in three directions are equal.

[0061] It should be noted that, aiming at the spatial movement characteristics of the floating discharge, the present invention designs an equilibrium characteristic function based on the normalized quadratic form. Compared with the prior art, this function realizes the precise quantification of spatial anisotropy by introducing the characteristic - scale parameters in three directions ( , , ). At the same time, overall modulation is carried out by using the equilibrium factor, overcoming the problem of unbalanced contributions in each direction in traditional methods. In addition, the selection of the quadratic - form structure also fully considers the random ionization characteristics of the floating discharge in the cavity, avoiding the direction deviation that may be caused by simple linear superposition.

[0062] For the corona discharge type, an axially dominant characteristic function is constructed. : ; wherein, is the angular modulation coefficient (the value range is 0.1 to 1), which adjusts the influence degree of the azimuth angle change, describes the modulation depth of the discharge intensity with the azimuth angle change, the value range is 0.1 - 1.0, and the smaller the value, the more uniform the angular distribution; is the height modulation coefficient (the value range is 1 to 10), which controls the dominant role of the axial component, the value range is 1.0 - 10.0, and the larger the value, the stronger the axial dominance; is the axial correction factor, which is used to correct the contribution weights at different height positions, compensates for the non-uniformity of the axial position, and is a piecewise continuous function about the height and takes a larger value at the joint end.

[0063] It should be noted that based on the physical mechanism of corona discharge, the present invention proposes a characteristic function with axially dominant characteristics. Traditional methods mostly adopt a uniform attenuation model, which fails to reflect the progressive development characteristics of corona discharge in the axial direction. The present invention designs a composite exponential term structure to unify the radial and angular components under the modulation of the axial scale, which not only maintains the spatial directionality of corona discharge but also considers the influence of radial diffusion. In addition, through the cooperation of the angular modulation coefficient and the height modulation coefficient, the present invention realizes the non-uniform distribution characteristics of the discharge intensity in space; meanwhile, an axial correction factor is introduced to correct the axial position, improving the positioning accuracy of the boundary region.

[0064] S4.3: Extract the calibration parameter matrix based on the position characteristic function: ; wherein, is a 3×3 calibration parameter matrix, , , are the partial derivatives corresponding to the characteristic function respectively, is a 3×3 orthogonal transformation matrix from the characteristic space to the physical space, and each element represents the correction amount of the discharge characteristics to the spatial position.

[0065] Preferably, compared with the traditional method that only considers gradient information, the multi-level calibration parameter matrix structure provided by the present invention establishes a deep fusion relationship between the characteristic quantity and the spatial gradient by introducing the row weighting mechanism of the energy ratio and the pulse characteristics. Thereby, the calibration parameter not only contains the change trend of the position characteristics but also incorporates the physical characteristic information of the discharge signal, improving the calibration accuracy. At the same time, through the introduction of the orthogonal transformation matrix, the unified mapping from the characteristic space to the physical space is realized, ensuring the physical meaning of the calibration parameter.

[0066] S4.4: Convert the calibration parameter matrix from the cylindrical coordinate system to the rectangular coordinate system: ; where is the calibration parameter matrix in the rectangular coordinate system, the first row corresponds to the correction amount in the direction, the second row corresponds to the correction amount in the direction, and the third row corresponds to the correction amount in the direction.

[0067] It should be noted that the present invention adopts a rotation matrix structure in the coordinate transformation. Different from the traditional simple coordinate transformation, this matrix introduces dynamic compensation of the radial distance on the basis of the angle transformation. This design takes into account the non-linear characteristics of the discharge source at different radial positions. At the same time, by maintaining the independence of the direction component, the cumulative error in the coordinate transformation process is avoided.

[0068] S4.5: Based on the above calculation results, obtain the position calibration parameters in the space rectangular coordinate system: ; where , , are the finally obtained position calibration parameters, representing the correction amounts in the x, y, and z directions respectively; , , are the spatial coordinate values to be corrected.

[0069] It should be noted that the present invention realizes the unified calculation of the position calibration parameters in the form of matrix multiplication. This method is not only simple and intuitive in form, but more importantly, it realizes the coupled calculation of the correction amounts in each direction through matrix operations, overcoming the cumulative error that may be caused by independent calibration in each direction in the traditional method.

[0070] Preferably, step S4 effectively solves the technical problems of single feature and poor adaptability in the traditional positioning method. The exponential weighted fusion mechanism introduced in the basic position feature function realizes the adaptive combination of different feature quantities, significantly improving the reliability of the positioning result; the design of the feature function for different discharge types fully considers the physical mechanism, making the positioning result have a clear physical meaning; the calibration parameter matrix innovatively realizes the deep fusion of feature quantities and spatial gradients, solving the problem of the disconnection between feature information and spatial information; at the same time, the improved coordinate transformation method ensures the spatial consistency of the positioning result.

[0071] S5: Integrate the position correction parameters with the initial solution, and continuously correct the positioning result through a recursive iterative optimization algorithm until the positioning error converges within the set threshold.

[0072] S5.1: Superpose and integrate the position correction parameters and the initial solution in a weighted manner to obtain the initial value of the iteration.

[0073] Among them, two weight coefficients are used to adjust the contribution ratios of the position correction parameters and the historical iteration amount respectively, and the initial values of the weight coefficients can be preset according to experience.

[0074] S5.2: Construct an error evaluation function for iterative optimization.

[0075] Among them, the error evaluation function includes a mean square error term and a norm constraint term. The mean square error term is used to evaluate the positioning accuracy, and the norm constraint term is used to prevent iterative divergence. The coefficient of the constraint term can be preset according to experience.

[0076] S5.3: Update the iterative parameters based on the calculation result of the error evaluation function. Stop the iteration when the relative change rate of the error evaluation function is less than the preset threshold. Otherwise, compare the error magnitudes of two adjacent iterations, increase or decrease the value of the weight coefficient until the final positioning result is obtained.

[0077] It should be noted that during the partial discharge positioning process of the distribution cable intermediate joint, the preset threshold is a key parameter for evaluating the convergence degree of the iterative calculation. This threshold reflects the error tolerance between the results of two adjacent iterations, and its value needs to be balanced between positioning accuracy and calculation efficiency. Based on the structural characteristics of the cable intermediate joint and the actual engineering requirements, the preset threshold is usually set in the form of a relative error. Specifically, when the relative change rate of the error evaluation function is less than this threshold, it is considered that the iterative calculation has reached the convergence state. Considering the typical size of the distribution cable intermediate joint (diameter 50 - 150 mm, length 300 - 500 mm) and the requirement for partial discharge positioning accuracy (usually requiring the positioning error not to exceed 5% of the joint size), combined with experimental verification, this threshold is preferably set in the range of 0.5% - 2%. An excessively large threshold will reduce the positioning accuracy, while an excessively small threshold will lead to a significant increase in the calculation amount and may fall into numerical oscillation.

[0078] In summary, the present invention uses a reference point array with a circular distribution in combination with a dedicated signal conditioning circuit to overcome the signal distortion problem of traditional acquisition methods under the complex structure of cable joints. By combining the time difference of propagation and the energy attenuation characteristics to construct a composite error function, the reliability of the initial solution is improved. The present invention proposes a family of characteristic functions based on the discharge type. By constructing radial-dominant, balanced, and axial-dominant characteristic functions, the specificity problem of different types of discharge sources in spatial positioning is effectively solved. Finally, the present invention realizes the deep fusion of characteristic quantities and spatial gradients by designing a multi-level correction parameter matrix, overcoming the technical bottleneck of the separation of characteristic information and spatial information in traditional methods.

[0079] Embodiment 2 is an embodiment of the present invention, which provides a partial discharge signal detection and positioning system for a distribution cable joint, as Figure 2 shown, which is an interaction schematic diagram of the system, including: A signal acquisition module for collecting the signal propagation characteristics of partial discharge signals through a reference point array arranged around the distribution cable joint; A spatial positioning module for constructing a spatial positioning equation set of the discharge source based on the signal propagation characteristics, and solving the spatial positioning equation set of the discharge source to obtain an initial solution; A pattern recognition module for analyzing the time-frequency characteristics of partial discharge signals, and identifying and classifying partial discharge signals to obtain a discharge type determination result; A parameter extraction module for determining corresponding position correction parameters based on the discharge type determination result; An optimization iteration module for fusing the position correction parameters with the initial solution, and continuously correcting the positioning result through a recursive iteration optimization algorithm until the positioning error converges within a set threshold.

[0080] Embodiment 3, referring to Figure 3 , is an embodiment of the present invention. The difference from the previous embodiment is that if the function is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The foregoing storage medium includes: various media such as USB flash drives, mobile hard disks, read-only memories (ROMs), random access memories (RAMs), magnetic disks, or optical discs that can store program codes.

[0081] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a definite sequence list of executable instructions for implementing logical functions, and can be specifically implemented in any computer-readable medium for use by an instruction execution system, apparatus, or device (such as a computer-based system, a system including a processor, or other systems that can fetch and execute instructions from the instruction execution system, apparatus, or device), or in conjunction with these instruction execution systems, apparatuses, or devices. For the purposes of this specification, a "computer-readable medium" can be any device that can contain, store, communicate, propagate, or transport a program for use by or in conjunction with an instruction execution system, apparatus, or device.

[0082] More specific examples (a non-exhaustive list) of computer-readable media include the following: an electrical connection part with one or more wirings (electronic device), a portable computer disk cartridge (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disc read-only memory (CDROM). Additionally, a computer-readable medium can even be paper or other suitable media on which the program can be printed, because the program can be obtained electronically, for example, by optically scanning the paper or other media, then editing, interpreting, or otherwise processing it as appropriate, and then storing it in a computer memory.

[0083] It should be understood that various parts of the present invention can be implemented by hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, any one or a combination of the following techniques well known in the art can be used: discrete logic circuits having logic gate circuits for implementing logical functions on data signals, application-specific integrated circuits having appropriate combinational logic gate circuits, programmable gate arrays (PGAs), field programmable gate arrays (FPGAs), etc.

[0084] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A method for detecting and locating partial discharge signals at intermediate joints of distribution cables, characterized in that: include: The signal propagation characteristics of the partial discharge signal are collected by means of an array of reference points arranged around the middle joint of the distribution cable; Based on the signal propagation characteristics, construct a discharge source spatial positioning equation group, and solve the power source spatial positioning equation group to obtain an initial solution; Analyzing the time-frequency characteristics of the partial discharge signal, identifying and classifying the partial discharge signal, and obtaining a discharge type determination result; Based on the discharge type determination result, determining corresponding position correction parameters; The position correction parameters are integrated with the initial solution, and the positioning result is continuously corrected through a recursive iterative optimization algorithm until the positioning error converges to a set threshold.

2. The method for detecting and locating partial discharge signals of intermediate joints of distribution cables according to claim 1, characterized in that: The reference point array includes a plurality of electrode sensors distributed in a ring shape, and each electrode sensor amplifies and filters the collected local discharge signal through a signal conditioning circuit; the signal propagation characteristics include propagation time difference and energy attenuation characteristics.

3. The method for detecting and locating partial discharge signals of intermediate joints of distribution cables according to claim 2, characterized in that: Based on the signal propagation characteristics, a discharge source spatial positioning equation group is constructed, and the discharge source spatial positioning equation group is solved to obtain an initial solution, including the following steps: Establish a positioning equation group based on the propagation time difference. Specifically, assume that the coordinates of the discharge source are (x0, y0, z0) and the coordinates of the i-th sensor are (xᵢ, yᵢ, zᵢ). Then the signal propagation time difference satisfies: ； in, is the time difference between the signal reaching the i-th sensor and the j-th sensor, v is the propagation speed of electromagnetic waves in the medium, , ∈[1,N] and i≠j, N is the total number of sensors; The discharge source spatial positioning equation group is expressed as: ； in, , are the energy values ​​of the signal when it reaches the i-th and j-th sensors, α is the attenuation coefficient of the medium, , are the distances from the discharge source to the i-th and j-th sensors respectively; Construct the composite error function: ； Among them, m represents the measured value, c represents the calculated value, and is the weight coefficient, is the balance factor; An iterative least square method is used to solve an initial solution; the initial solution represents the initial value of the spatial coordinate of the discharge source.

4. The method for detecting and locating partial discharge signals of intermediate joints of distribution cables according to claim 3, characterized in that: The iterative least square method is used to solve the initial solution by the following formula: ； in, represents the number of iterations, is the Jacobian matrix, is the weight matrix, is the residual vector, is the step size factor; Order The weighted residual sum of squares for the iterations is : ； If the weighted residual sum of squares of the current iteration is smaller than the average of the previous two iterations, that is: ； Then let the step size factor It is expressed as: ； Otherwise, let the step size factor It is expressed as: 。 5. The method for detecting and locating partial discharge signals of intermediate joints of distribution cables according to claim 4, characterized in that: Analyzing the time-frequency characteristics of the partial discharge signal, identifying and classifying the partial discharge signal, and obtaining a discharge type determination result includes the following steps: The partial discharge signal is decomposed into a multi-scale manner using wavelet transform to extract time-frequency features; the partial discharge signal is decomposed into a high frequency band, a medium frequency band and a low frequency band, detail coefficients and approximate coefficients of each frequency band are obtained, and energy distribution features of the partial discharge signal are obtained based on the detail coefficients and approximate coefficients; A time-frequency feature vector is constructed based on the energy distribution characteristics; the time-frequency feature vector includes an energy ratio between a high-frequency band and a low-frequency band, a pulse characteristic function and a waveform statistical feature; wherein the energy ratio between the high-frequency band and the low-frequency band is determined by wavelet coefficients and energy attenuation characteristics, the pulse characteristic function is composed of amplitude distribution and time characteristics, and the waveform statistical features include waveform skewness and waveform kurtosis; The discharge type is identified according to the time-frequency feature vector, and the criteria are as follows: If the energy ratio of the high-frequency band to the low-frequency band is greater than unity, and the pulse characteristic function If the global maximum value is obtained in the positive half cycle of the power frequency and the waveform skewness value is positive, it is judged as internal discharge; If the energy ratio of the high-frequency band to the low-frequency band is less than unity, and the pulse characteristic function If the global maximum value is obtained in the negative half cycle of the power frequency and the waveform skewness value is negative, it is judged as surface discharge; If the pulse characteristic function If multiple peaks appear in one power frequency cycle, and the amplitude ratio of adjacent peaks deviates from the unit value to a degree within a first preset range, and the phase difference of the peaks is greater than the basic segment unit of the power frequency cycle, it is determined to be a suspended discharge; If the pulse characteristic function If there are multiple continuous peaks in the local phase interval, and the peak sequence satisfies the exponential decay law, and the phase difference between adjacent peaks is less than the minimum segment unit of the power frequency cycle, it is determined to be corona discharge; Based on the above criteria, the discharge type determination result is obtained.

6. The method for detecting and locating partial discharge signals of intermediate joints of distribution cables according to claim 5, characterized in that: Based on the discharge type determination result, determining the corresponding position correction parameter comprises the following steps: Constructing a discharge position characteristic model; the discharge position characteristic model includes a position characteristic parameter matrix of different discharge types, and the position characteristic parameter matrix is ​​established based on the high- and low-frequency band energy ratio, the pulse characteristic function and the waveform statistical characteristics; Establish the coordinate transformation relationship between the rectangular coordinate system and the cylindrical coordinate system; Constructing basic position feature function : ； in, is the position characteristic function, is the normalized value of the energy ratio of high and low frequency bands, is the normalized pulse characteristic function, is the waveform skewness, is the waveform kurtosis, , , is the feature weight index; If the discharge type is determined to be internal discharge or surface discharge, a radial dominant characteristic function is constructed. : ； in, is the radial attenuation coefficient; is the radial correction factor; If the discharge type is determined to be a suspended discharge type, a balanced characteristic function is constructed. : ； in, is the radial characteristic scale, is the angular characteristic scale, is the axial characteristic scale, is the equilibrium factor; If the discharge type is determined to be a corona discharge type, an axial dominant characteristic function is constructed. : ； in, is the angular modulation coefficient; is the height modulation coefficient; is the axial correction factor; Extracting a correction parameter matrix, and transforming the correction parameter matrix from a cylindrical coordinate system to a rectangular coordinate system; According to the correction parameter matrix in the rectangular coordinate system and the space coordinate value to be corrected, the position correction parameters are calculated by matrix multiplication.

7. The method for detecting and locating partial discharge signals of intermediate joints of distribution cables according to claim 6, characterized in that: The position correction parameters are integrated with the initial solution, and the positioning result is continuously corrected by a recursive iterative optimization algorithm until the positioning error converges to a set threshold, including the following steps: The position correction parameter is superimposed and fused with the initial solution in a weighted manner to obtain an iterative initial value; Construct an iterative optimization error evaluation function; The iteration parameters are updated based on the calculation result of the error evaluation function. When the relative change rate of the error evaluation function is less than a preset threshold, the iteration is stopped. Otherwise, by comparing the error sizes of two adjacent iterations, the value of the weight coefficient is increased or decreased until the final positioning result is obtained.

8. A partial discharge signal detection and positioning system for an intermediate joint of a distribution cable, based on a partial discharge signal detection and positioning method for an intermediate joint of a distribution cable according to any one of claims 1 to 7, characterized in that: include, A signal acquisition module, used to acquire signal propagation characteristics of partial discharge signals through an array of reference points arranged around the middle joint of the distribution cable; A spatial positioning module, used for constructing a set of discharge source spatial positioning equations based on the signal propagation characteristics, and solving the set of discharge source spatial positioning equations to obtain an initial solution; A pattern recognition module, used to analyze the time-frequency characteristics of the partial discharge signal, identify and classify the partial discharge signal, and obtain a discharge type determination result; A parameter extraction module, which determines corresponding position correction parameters based on the discharge type determination result; The optimization iteration module is used to merge the position correction parameters with the initial solution and continuously correct the positioning result through a recursive iterative optimization algorithm until the positioning error converges to a set threshold.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method for detecting and locating partial discharge signals at intermediate joints of distribution cables according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method for detecting and locating partial discharge signals at intermediate joints of distribution cables according to any one of claims 1 to 7 are implemented.

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