Cable detection method and system based on mica tape and xlpe insulation structure

Abstract

The application relates to the technical field of cable detection of mica tape and XLPE insulation structure, and proposes a cable detection method and system based on mica tape and XLPE insulation structure. The method generates a composite electrical response by exciting a double-insulation structure through a multi-band composite wideband electrical detection signal, separates a synthetic mica tape wrapping insulation layer characteristic component and an XLPE extrusion insulation layer characteristic component from the composite impedance response by utilizing the essential difference between the wideband dielectric response characteristics of the synthetic mica tape and the XLPE, identifies double-characteristic transition peaks and respectively calculates an electrical insulation thermal aging index and a fire-resistant layer thermal stability index, realizes non-invasive layered independent detection of the double-insulation structure of the inner fire-resistant barrier and the outer electrical insulation of the cable, can respectively give accurate independent judgments when the fire-resistant layer has not deteriorated but the electrical insulation layer has been seriously aged or when the electrical insulation layer is in good condition but the fire-resistant layer has lost the porcelain ability, and avoids the problems of misjudgment and missed judgment.

Description

Technical Field

[0001] The present application relates to the technical field of cable detection for mica tape and XLPE insulation structures, and in particular to a cable detection method and system based on mica tape and XLPE insulation structures. Background Art

[0002] Cables based on synthetic mica tape and XLPE insulation structures adopt the "functional layering" design concept. The inner layer of synthetic mica tape is wrapped in multiple overlapping layers and cooperates with the magnesium oxide fire barrier to form the main fire-resistant barrier, the outer extruded XLPE insulation layer forms the main electrical insulation layer, and a full-profile stranded conductor is used to achieve seamless splicing to reduce line loss. This type of cable combines the excellent fire resistance of rigid mineral insulated cables and the construction convenience of flexible cables, and is widely used in occasions with extremely high fire safety requirements such as the mining industry.

[0003] However, existing detection methods for this type of cable mainly follow the detection means of conventional power cables, including DC withstand voltage tests, insulation resistance measurement, partial discharge detection, etc. The above detection methods have the following defects: First, it is impossible to perform layered independent evaluation on the dual insulation structure of "inner synthetic mica tape fire-resistant layer - outer XLPE electrical insulation layer", and only the overall insulation state of the two insulation layers working together can be obtained. When the fire-resistant layer has deteriorated while the electrical insulation layer still remains in good condition, the overall detection result may be misjudged as qualified; second, there is a lack of special detection means for the splicing interface quality of full-profile stranded conductors. Conventional DC resistance measurement can only reflect the overall resistance value of the conductor, and cannot detect defects such as poor local contact, tiny gaps or oxide layers at the profile splicing interface. The above defects will cause local overheating during long-term operation and further lead to insulation faults; third, the existing detection methods cannot evaluate cross-process systematic process deviations that may exist in the manufacturing process, such as abnormal wrapping tension that affects both the mica tape wrapping quality and the subsequent XLPE extrusion interface quality. Therefore, how to realize layered independent detection of the dual insulation structure of this type of cable, quantitative evaluation of the splicing interface of the full-profile stranded conductor, and comprehensive judgment of manufacturing quality consistency has become a problem to be solved. Summary of the Invention

[0004] The present application provides a cable detection method and system based on mica tape and XLPE insulation structures, the main purpose of which is to solve the problems that the dual insulation structure of this type of cable cannot be detected in a layered independent manner, the conductor splicing interface quality cannot be evaluated, and the accuracy of comprehensive manufacturing quality judgment is insufficient.

[0005] To achieve the above objectives, the cable detection method based on mica tape and XLPE insulation structure provided by the present application includes: S1. Obtain the structural parameters of the to-be-detected cable section based on the synthetic mica tape and XLPE insulation structure.

[0006] S2. Apply multi-modal composite detection signals to the cable section to be tested, and collect composite electrical response signals, magnetic field strength vector values, current amplitudes, and real-time temperature values.

[0007] S3. Based on the composite electrical response signal, construct a broadband impedance-frequency response characteristic spectrum, and construct the characteristic components of the synthetic mica tape wrapped insulation layer and the XLPE extruded insulation layer.

[0008] S4. Based on the current amplitude and real-time temperature value, extract the characteristic conductivity of the XLPE layer and the characteristic conductivity of the mica tape layer, and calculate the electrical insulation thermal aging index and the fire-resistant layer thermal stability index respectively.

[0009] S5. Based on the magnetic field strength vector value, construct a multi-directional magnetic field distribution topology map, and then construct a composite quality feature vector.

[0010] S6. Generation of comprehensive test results.

[0011] In a preferred embodiment, obtaining the structural parameters of the cable segment to be tested based on the synthetic mica tape and XLPE insulation structure includes: S201, obtaining the cable segment based on the synthetic mica tape and XLPE insulation structure, wherein the cable segment is a fully stranded conductor, a synthetic mica tape wrapped insulation layer around the fully stranded conductor, and an XLPE extruded insulation layer around the synthetic mica tape wrapped insulation layer.

[0012] S202, record the structural parameters of the cable section to be tested. The structural parameters include the nominal cross-sectional area and number of stranded conductors, the nominal thickness and number of synthetic mica tape wrapping insulation layers, and the nominal thickness of XLPE extruded insulation layers.

[0013] In a preferred embodiment, applying a multimodal composite detection signal to the cable segment to be tested includes: S301, wherein the multimodal composite detection signal includes a multi-band composite broadband electrical detection signal, a multi-directional electromagnetic excitation signal, and a temperature scanning detection signal.

[0014] S302, apply multi-band composite broadband electrical detection signals to the cable segment to be tested, and collect composite electrical response signals of the cable segment to be tested at each frequency point. The composite electrical response signals include voltage signal amplitude, voltage signal phase, current signal amplitude, and current signal phase at each frequency point.

[0015] S303 applies multi-directional electromagnetic excitation signals to the cable section to be tested and collects the magnetic field strength vector value of the space around the fully stranded conductor under each electromagnetic excitation direction.

[0016] S304 applies a temperature scanning detection signal to the cable section under test and collects the current amplitude and real-time temperature value at each sampling time.

[0017] In a preferred embodiment, the step of constructing a broadband impedance-frequency response feature spectrum based on the composite electrical response signal, and constructing the characteristic components of the synthetic mica tape wrapped insulation layer and the XLPE extruded insulation layer, includes: S401, calculating the impedance amplitude and impedance phase angle at each frequency point based on the voltage signal amplitude and current signal amplitude at each frequency point in the composite electrical response signal, and then constructing a broadband impedance-frequency response feature spectrum.

[0018] S402, construct a layered relaxation equivalent circuit model of a double-insulated structure, and construct the characteristic components of the synthetic mica tape-wrapped insulation layer by segmented frequency domain weighting and layered fitting. And construct the characteristic components of the XLPE extruded insulation layer. ;in and These represent the optimal first equivalent resistance and the optimal first equivalent capacitance of the synthetic mica tape wrapped insulation layer, respectively. This is expressed as the first relaxation time constant; and These represent the optimal second equivalent resistance and the optimal second equivalent capacitance of the XLPE extruded insulation layer, respectively. It is represented as the second relaxation time constant.

[0019] In a preferred embodiment, constructing the layered relaxation equivalent circuit model of the double-insulated structure includes: the total impedance of the layered relaxation equivalent circuit model of the double-insulated structure is:

[0020] in, The first equivalent resistance of the synthetic mica tape wrapping insulation layer, This is the first equivalent capacitance of the synthetic mica tape wrapped insulation layer. The second equivalent resistance of the XLPE extruded insulation layer. The second equivalent capacitance is the XLPE extruded insulation layer. For frequency, It is the imaginary unit.

[0021] In a preferred embodiment, the step of extracting the characteristic conductivity of the XLPE layer and the mica tape layer based on the current amplitude and real-time temperature value includes: S601, taking the ratio of the current amplitude to the DC detection voltage at each sampling time as the apparent insulation conductivity, multiplying the apparent insulation conductivity by the cable segment insulation geometric factor to obtain the normalized insulation conductivity; constructing a first measurement curve of conductivity changing with temperature based on the normalized insulation conductivity; constructing a second measurement curve of the natural logarithm of conductivity changing with temperature based on the first measurement curve, and calculating the first derivative of the second measurement curve with respect to temperature to obtain the first derivative curve.

[0022] S602, in the first derivative curve, within the melting point temperature range of XLPE, after taking the absolute value of the first derivative curve, search for the local maximum point as the first characteristic transition peak, and mark the peak temperature of the first characteristic transition peak as the XLPE thermally induced transition temperature; within the ceramic initiation temperature range of mica tape, search for the local maximum point as the second characteristic transition peak, and mark the peak temperature of the second characteristic transition peak as the mica tape thermally induced transition temperature; if neither the first characteristic transition peak nor the second characteristic transition peak is detected, it is determined that the insulation structure of the cable section to be tested has a serious defect, and an unqualified test result is directly generated.

[0023] S603, the insulation conductivity at the thermally induced transition temperature of XLPE is extracted from the first measurement curve as the characteristic conductivity of the XLPE layer, and the insulation conductivity at the thermally induced transition temperature of the mica tape is extracted from the first measurement curve as the characteristic conductivity of the mica tape layer.

[0024] In a preferred embodiment, the calculation of the electrical insulation thermal aging index and the fire-resistant layer thermal stability index includes: S701, obtaining the standard normalized characteristic conductivity of the XLPE layer at the XLPE thermal transition temperature under the same geometric factor conditions in the standard unaged state of the cable segment to be tested, calculating the first deviation ratio between the normalized characteristic conductivity of the XLPE layer and the standard normalized characteristic conductivity, and obtaining the electrical insulation thermal aging index.

[0025] S702, obtain the standard normalized characteristic conductivity of the mica tape layer under the standard unaged state of the cable segment to be tested at the thermally induced transition temperature of the mica tape under the same geometric factor conditions, calculate the second deviation ratio between the normalized characteristic conductivity of the mica tape layer and the standard normalized characteristic conductivity, and obtain the thermal stability index of the fire-resistant layer.

[0026] In a preferred embodiment, the step of constructing a multi-directional magnetic field distribution topology map based on the magnetic field strength vector value, and then constructing a composite quality feature vector, includes: S801, constructing a multi-directional magnetic field distribution topology map based on the magnetic field strength vector value of each spatial location under each electromagnetic excitation direction.

[0027] S802, based on the grayscale map of magnetic field intensity distribution in each direction, calculate the spatial average value of magnetic field intensity under each electromagnetic excitation direction, and calculate the magnetic field anisotropy index based on the spatial average value of magnetic field intensity in each direction; pair each electromagnetic excitation direction according to the angular symmetry relationship, and calculate the directional symmetry difference index between each pairing direction.

[0028] S803 calculates the magnetic field gradient topological distortion index based on the magnetic field gradient distribution vector diagram in each direction.

[0029] S804 calculates the global dispersion of the magnetic field direction angle under each electromagnetic excitation direction based on the magnetic field direction angle distribution diagram in each direction.

[0030] S805, Construct a comprehensive feature vector of the splicing quality of the full-type stranded conductor. ,in For magnetic field anisotropy index, For the directional symmetry difference index, For the topological distortion index of the magnetic field gradient and This represents the global dispersion of the magnetic field direction angle under each electromagnetic excitation direction.

[0031] In a preferred embodiment, the generation of the comprehensive test results includes: evaluating the quality status of the synthetic mica tape wrapped insulation layer based on the characteristic components of the synthetic mica tape wrapped insulation layer; evaluating the quality status of the XLPE extruded insulation layer based on the characteristic components of the synthetic mica tape wrapped insulation layer and the XLPE extruded insulation layer; evaluating the interface bonding quality status between the synthetic mica tape wrapped insulation layer and the XLPE extruded insulation layer based on the characteristic components of the synthetic mica tape wrapped insulation layer and the XLPE extruded insulation layer; evaluating the insulation thermal aging and fire-resistant layer thermal stability status based on the electrical insulation thermal aging index and the fire-resistant layer thermal stability index; and evaluating the splicing quality status of the full-type stranded conductor based on the comprehensive feature vector of splicing quality.

[0032] If all five judgment results are qualified, a comprehensive inspection result indicating that the overall manufacturing quality of the cable segment under inspection is qualified will be generated; if any one of the judgments is unqualified, an unqualified inspection result will be generated. At the same time, all unqualified items and their corresponding defect types will be summarized to generate a defect report as the comprehensive inspection result.

[0033] To address the aforementioned issues, this application also provides a system for cable testing based on mica tape and XLPE insulation structure. The system includes a structural parameter acquisition module for acquiring structural parameters of the cable segment to be tested based on synthetic mica tape and XLPE insulation structure.

[0034] The multimodal composite detection signal application module applies multimodal composite detection signals to the cable segment to be tested and collects composite electrical response signals, magnetic field strength vector values, current amplitudes, and real-time temperature values.

[0035] The broadband impedance spectrum characteristic decomposition module constructs a broadband impedance-frequency response characteristic spectrum based on the composite electrical response signal, and constructs characteristic components of the synthetic mica tape wrapped insulation layer and XLPE extruded insulation layer.

[0036] The insulation thermal aging and fire resistance stability assessment module extracts the characteristic conductivity of the XLPE layer and the mica tape layer based on the current amplitude and real-time temperature value, and calculates the electrical insulation thermal aging index and the fire resistance layer thermal stability index, respectively.

[0037] The magnetic field topology reconstruction and assembly quality analysis module constructs a multi-directional magnetic field distribution topology map based on the magnetic field intensity vector value, and then constructs a comprehensive feature vector of the assembly quality.

[0038] The comprehensive diagnostic results generation and output module is used to generate comprehensive test results.

[0039] Compared with the prior art, this application has the following beneficial effects: 1. This application further excites the full-shaped stranded conductor to generate a multi-directional magnetic field distribution by multi-directional electromagnetic excitation signal. Based on multi-dimensional characteristic parameters such as magnetic field anisotropy index, directional symmetry difference index, magnetic field gradient topological distortion index, and magnetic field direction angle dispersion, a comprehensive feature vector of conductor splicing quality is constructed. This enables quantitative detection of the contact state and splicing tightness of the full-shaped stranded conductor splicing interface and automatic identification of defect types. It can detect local defects at the splicing interface that cannot be detected by conventional DC resistance detection, ensuring that the design advantages of the stranded conductor splicing (reducing line loss by 10% to 15%) are fully realized in actual manufacturing.

[0040] 2. This application also comprehensively evaluates five dimensions: the quality status of the synthetic mica tape wrapped insulation layer, the quality status of the XLPE extruded insulation layer, the quality status of the interface bonding of the double insulation layer, the thermal aging of the insulation and the thermal stability of the fire-resistant layer, and the quality status of the splicing of the full-type stranded conductor. It also introduces coupling analysis of cross-structural characteristic parameters to identify systematic process deviations. This can identify cross-process manufacturing deviations that cannot be detected by single-structure inspection, thus comprehensively improving the accuracy, comprehensiveness and reliability of the manufacturing quality inspection of this type of cable. Attached Figure Description

[0041] Figure 1 A schematic flowchart illustrating a cable testing method based on mica tape and XLPE insulation structure provided in an embodiment of this application; Figure 2 A functional block diagram of a cable testing method based on mica tape and XLPE insulation structure provided in an embodiment of this application; Figure 3 This is a schematic diagram of the cable structure based on mica tape and XLPE insulation in this application; Figure 4 This is a schematic diagram of the temperature-scanning conductivity measurement curve and the identification of the dual-characteristic transition peaks in this application. The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0042] It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit this application.

[0043] This application provides a cable testing method based on mica tape and XLPE insulation structure. The executing entity of the cable testing method based on mica tape and XLPE insulation structure includes, but is not limited to, at least one of the following electronic devices that can be configured to execute the method provided in this application: a server, a terminal, etc. In other words, the cable testing method based on mica tape and XLPE insulation structure can be executed by software or hardware installed on a terminal device or a server device. The server includes, but is not limited to, a single server, a server cluster, a cloud server, or a cloud server cluster. The server can be an independent server or a cloud server that provides basic cloud computing services such as cloud services, cloud databases, cloud computing, cloud functions, cloud storage, network services, cloud communication, middleware services, domain name services, security services, content delivery networks (CDNs), and big data and artificial intelligence platforms.

[0044] Reference Figure 1 The diagram shown is a flowchart illustrating a cable testing method based on mica tape and XLPE insulation structure according to an embodiment of this application. In this embodiment, the cable testing method based on mica tape and XLPE insulation structure includes: S1, obtaining the structural parameters of the cable segment to be tested based on synthetic mica tape and XLPE insulation structure.

[0045] In this embodiment of the application, obtaining the structural parameters of the cable segment to be tested based on the synthetic mica tape and XLPE insulation structure includes: S201, obtaining the cable segment based on the synthetic mica tape and XLPE insulation structure, wherein the cable segment is a fully stranded conductor, a synthetic mica tape wrapped insulation layer around the fully stranded conductor, and an XLPE extruded insulation layer around the synthetic mica tape wrapped insulation layer.

[0046] S202, record the structural parameters of the cable section to be tested. The structural parameters include the nominal cross-sectional area and number of stranded conductors, the nominal thickness and number of synthetic mica tape wrapping insulation layers, and the nominal thickness of XLPE extruded insulation layers.

[0047] It should be noted that the specific implementation method for obtaining cable segments based on synthetic mica tape and XLPE insulation structure is as follows: a cable sample segment of a predetermined length is cut from the cable manufacturing production line, ensuring that the cable sample segment contains a complete three-layer structure: a fully stranded conductor, a synthetic mica tape wrapped insulation layer composed of multiple overlapping layers of synthetic mica tape and a magnesium oxide fireproof layer, and an XLPE extruded insulation layer; the fully stranded conductor is seamlessly spliced ​​using a pre-formed regular shape; the synthetic mica tape wrapped insulation layer uses a synergistic fireproofing technology of multiple overlapping layers of synthetic mica tape and a magnesium oxide fireproof layer; and the XLPE extruded insulation layer and the synthetic mica tape wrapped insulation layer constitute a double insulation structure.

[0048] Furthermore, the number of stranded conductors is determined based on the nominal cross-sectional area of ​​the cable. Each strand has a pre-formed, regularly shaped splicing interface, achieving seamless splicing through precise geometric fit during the stranding process. The overlap rate of the mica tape in the synthetic mica tape wrapped insulation layer is greater than or equal to 25%, and the filling density of the magnesium oxide fireproof layer meets the fire resistance requirements. The XLPE extruded insulation layer is wrapped around the outer periphery of the synthetic mica tape wrapped insulation layer through a three-layer co-extrusion process, forming a tight interface bond.

[0049] It should be noted that the specific implementation method for recording structural parameters is as follows: the nominal cross-sectional area and number of strands of the fully stranded conductor, the nominal thickness and number of wrapping layers of the synthetic mica tape insulation layer, and the nominal thickness of the XLPE extruded insulation layer are obtained through measuring instruments or production line parameter recording systems, and the above parameters are stored in the parameter register of the detection system according to a preset data format; the nominal cross-sectional area is used to determine the rated current carrying capacity and resistivity reference value of the conductor, the number of strands is used to evaluate the total number of conductor splicing interfaces, the nominal thickness and number of wrapping layers of the synthetic mica tape insulation layer are used to calculate the standard capacitance and resistance values ​​of the mica tape layer, and the nominal thickness of the XLPE extruded insulation layer is used to calculate the standard capacitance and resistance values ​​of the XLPE layer.

[0050] Furthermore, when recording structural parameters, the volume resistivity and dielectric constant of the mica tape material in the synthetic mica tape wrapped insulation layer and the volume resistivity and dielectric constant of the XLPE material in the XLPE extruded insulation layer are recorded simultaneously as material property parameters for subsequent evaluation standard value calculation.

[0051] It should be noted that the specific implementation method for establishing structural parameters as a structural feature parameter file is as follows: all recorded structural parameters and material property parameters are stored in the non-volatile memory of the detection system in a structured data format to form a structural feature parameter file uniquely associated with the cable segment to be tested; the structural feature parameter file is used to dynamically calculate the standard resistance value and standard capacitance value of each insulation layer.

[0052] Furthermore, the structural characteristic parameter file also includes traceability information such as the cable model, batch number, and production date, which is used to trace the parameter records of the manufacturing process when the test results are unqualified, and to help locate the process links with quality defects.

[0053] S2. Apply multi-modal composite detection signals to the cable section to be tested, and collect composite electrical response signals, magnetic field strength vector values, current amplitudes, and real-time temperature values.

[0054] In this embodiment of the application, applying a multi-mode composite detection signal to the cable segment to be tested includes: S301, where the multi-mode composite detection signal includes a multi-band composite broadband electrical detection signal, a multi-directional electromagnetic excitation signal, and a temperature scanning detection signal.

[0055] S302, apply multi-band composite broadband electrical detection signals to the cable segment to be tested, and collect composite electrical response signals of the cable segment to be tested at each frequency point. The composite electrical response signals include voltage signal amplitude, voltage signal phase, current signal amplitude, and current signal phase at each frequency point.

[0056] S303 applies multi-directional electromagnetic excitation signals to the cable section to be tested and collects the magnetic field strength vector value of the space around the fully stranded conductor under each electromagnetic excitation direction.

[0057] S304 applies a temperature scanning detection signal to the cable section under test and collects the current amplitude and real-time temperature value at each sampling time.

[0058] It should be noted that the multi-band composite broadband electrical detection signal includes a subset of low-frequency detection signals, a subset of mid-frequency transition detection signals, and a subset of high-frequency detection signals; the multi-directional electromagnetic excitation signal is formed by arranging multiple electromagnetic excitation coils evenly distributed along the circumference in the axial direction of the cable segment under test, and sequentially passing AC excitation current to each electromagnetic excitation coil to form electromagnetic excitation on the fully stranded conductor in different directions; the temperature scanning detection signal is a continuous heating signal that heats from the initial temperature to the highest test temperature at a constant heating rate, and a DC detection voltage is applied during the heating process.

[0059] It should be noted that the multi-band composite broadband electrical detection signal is used to excite the double insulation structure of the cable segment under test to generate a composite electrical response signal. The low-frequency detection signal subset has a frequency range of 50Hz to 1kHz, a frequency scan step of 50Hz, and contains 20 discrete frequency points. In this frequency band, the dipole relaxation peaks of crosslinking byproducts (cumyl alcohol, acetophenone, etc.) in the XLPE extruded insulation layer are typically located between 10Hz and 500Hz at room temperature (Neimanise et al., 2001), and their contribution to the total impedance is dominant. The high-frequency detection signal subset has a frequency range of 10kHz to 1MHz, and the frequency scan adopts a logarithmically equal interval method, containing 30 discrete frequency points. It is used to excite the synthetic mica tape wrapped insulation layer to generate a dielectric response. The synthetic mica tape, as an inorganic mineral material, exhibits a significantly increased dielectric loss factor at high frequencies, demonstrating a clear dielectric relaxation phenomenon. The frequency range of the detection signal subset in the mid-frequency transition section is 1 kHz to 10 kHz, with a frequency scan step size of 500 Hz, encompassing 19 discrete frequency points. In the mid-to-high frequency range, the Maxwell-Wagner-Sillars interface polarization relaxation (1 kHz to 100 kHz, Tuncere et al., 2007) at the multiple heterogeneous interfaces of mica flakes, adhesive, and magnesium oxide particles in the synthetic mica tape-wrapped insulating layer dominates the contribution to the total impedance. The two relaxation mechanisms are fundamentally different, with the relaxation time constant ratio τ_x / τ_m ranging from 40 to 40,000, far exceeding the minimum separation ratio of 5 to 10 required for the resolvability of the two arcs in the Nyquist plot (Barsoukov & Macdonald, 2018).

[0060] Furthermore, the voltage amplitude of the low-frequency detection signal is set to 0.5V to 5V to avoid polarization accumulation effect on the XLPE material; the voltage amplitude of the high-frequency detection signal is set to 0.2V to 2V to avoid dielectric breakdown risk to the magnesium oxide fireproof layer in the synthetic mica tape.

[0061] It should be noted that the multi-directional electromagnetic excitation signal is used to excite the fully stranded conductor to generate a magnetic field distribution. At least four electromagnetic excitation coils are arranged circumferentially and uniformly in the axial direction of the cable segment to be tested. The axial direction of each electromagnetic excitation coil is perpendicular to the axial direction of the cable segment to be tested, and the axial directions of each electromagnetic excitation coil form a 45-degree angle with each other. An AC excitation current with a constant amplitude of 1A to 10A and a frequency of 50Hz is sequentially passed through each electromagnetic excitation coil. Only one electromagnetic excitation coil is energized at a time, while the other electromagnetic excitation coils are in an open-circuit state, forming electromagnetic excitation of the fully stranded conductor in different directions.

[0062] Furthermore, the multi-directional electromagnetic excitation signal generates M electromagnetic excitations in different directions, where M≥4; under each electromagnetic excitation direction, the excitation duration is set to 2 to 5 seconds to ensure that the electromagnetic field distribution of the fully stranded conductor reaches a steady state. Through multi-directional electromagnetic excitation, the magnetic field distribution characteristics of the fully stranded conductor in different directions can be obtained, which can be used for subsequent detection of the contact state and bonding tightness of the splicing interface.

[0063] It should be noted that the temperature scanning detection signal is used to excite the double insulation layer of the cable segment under test to produce a thermally induced phase change response. The constant heating rate is set to 2°C / min to 10°C / min, the initial temperature is room temperature (25°C), and the maximum test temperature is 950°C to 1000°C. This ensures that the XLPE extruded insulation layer undergoes the melting point temperature (approximately 100°C to 110°C) to complete the melting phase change, while simultaneously allowing the synthetic mica tape wrapped insulation layer to undergo the ceramic initiation temperature (approximately 600°C to 900°C) to begin the ceramic formation process. During the heating process, microcurrent signals passing through the insulation structure of the cable segment under test are continuously acquired at preset time intervals, and the amplitude of the DC detection voltage is set to 100V to 1000V.

[0064] Furthermore, during the application of the temperature scanning detection signal, the insulation conductivity at each temperature point is calculated based on the ratio of the current amplitude to the DC detection voltage at each sampling moment, forming a first measurement curve of conductivity versus temperature and a second measurement curve of the natural logarithm of conductivity versus temperature. Specifically, the XLPE extruded insulation layer exhibits an exponential increase in conductivity near its melting point, corresponding to a positive abrupt change in the slope of the first measurement curve; the synthetic mica tape wrapped insulation layer exhibits a sharp decrease in conductivity near its ceramicization temperature, corresponding to a negative abrupt change in the slope of the first measurement curve. By analyzing these two characteristic abrupt change temperatures, the degree of thermal aging of the XLPE layer and the ceramicization performance of the mica tape layer can be evaluated, respectively.

[0065] S3. Based on the composite electrical response signal, construct a broadband impedance-frequency response characteristic spectrum, and construct the characteristic components of the synthetic mica tape wrapped insulation layer and the XLPE extruded insulation layer.

[0066] In this embodiment of the application, the step of constructing a broadband impedance-frequency response feature spectrum based on the composite electrical response signal and constructing the feature components of the synthetic mica tape wrapped insulation layer and the XLPE extruded insulation layer includes: S401, calculating the impedance amplitude and impedance phase angle at each frequency point based on the voltage signal amplitude and current signal amplitude at each frequency point in the composite electrical response signal, and then constructing a broadband impedance-frequency response feature spectrum.

[0067] S402, construct a layered relaxation equivalent circuit model of a double-insulated structure, and construct the characteristic components of the synthetic mica tape-wrapped insulation layer by segmented frequency domain weighting and layered fitting. And construct the characteristic components of the XLPE extruded insulation layer. ;in and These represent the optimal first equivalent resistance and the optimal first equivalent capacitance of the synthetic mica tape wrapped insulation layer, respectively. This is expressed as the first relaxation time constant; and These represent the optimal second equivalent resistance and the optimal second equivalent capacitance of the XLPE extruded insulation layer, respectively. It is represented as the second relaxation time constant.

[0068] It should be noted that the specific implementation method for constructing a broadband impedance-frequency response characteristic spectrum is as follows: the impedance amplitude is the ratio of the voltage signal amplitude to the current signal amplitude; the impedance phase angle is the difference between the voltage signal phase and the current signal phase. With frequency as the horizontal axis and impedance amplitude as the vertical axis, the impedance amplitude data at each frequency point are smoothly connected to obtain the impedance amplitude-frequency curve; with frequency as the horizontal axis and impedance phase angle as the vertical axis, the impedance phase data at each frequency point are smoothly connected to obtain the impedance phase-frequency curve; based on the impedance phase angle, the dielectric loss factor at each frequency point is calculated, and with frequency as the horizontal axis and dielectric loss factor as the vertical axis, the dielectric loss factor-frequency curve is obtained; with the real part of the impedance as the horizontal axis and the negative value of the imaginary part of the impedance as the vertical axis, the complex impedance data at each frequency point is plotted on the complex plane to obtain the complex impedance Nyquist plot.

[0069] Furthermore, after constructing the broadband impedance-frequency response characteristic spectrum, the spectrum is subjected to quality pre-check, including impedance data continuity detection and data consistency detection, to identify and mark abnormal data points. The overall fitting weight of the marked suspicious data points is reduced by 50% during the fitting process.

[0070] It should be noted that the specific implementation method of segmented frequency domain weighting and hierarchical fitting is as follows: each frequency point is divided into three frequency band regions: low frequency band, mid frequency transition band, and high frequency band. A comprehensive fitting weight is assigned to each frequency point in each frequency band region, as shown in the table below:

[0071] Furthermore, the objective function is to minimize the weighted sum of the squared relative deviations between the model-predicted and measured values ​​of the impedance amplitude at each frequency point and the squared relative deviations between the model-predicted and measured values ​​of the impedance phase angle.

[0072] in, and Frequency points The following is based on the total impedance The calculated impedance magnitude and impedance phase angle, and Frequency points The measured impedance amplitude and impedance phase angle are as follows. The total number of frequency points. Frequency point The overall fitting weights; Using the impedance amplitude and impedance phase angle at various frequency points in the low-frequency band, fix and The initial estimates are calculated based on the nominal thickness and material properties using a parallel plate capacitance model and a volume resistance model. The impedance amplitude and impedance phase angle at various frequency points in the low-frequency region are used to... and The equivalent parameters of the first round XLPE layer are obtained by prioritizing fitting. and Using the impedance amplitude and impedance phase angle at various frequency points in the high-frequency band to... and The first round of equivalent parameters of the mica band layer were obtained by prioritizing fitting. and ,Will , , and As the initial values ​​for iteration, the impedance amplitude and impedance phase angle at all frequency points are used to perform joint nonlinear least squares fitting across the entire frequency band with the comprehensive fitting weight of each frequency point. The optimal parameters are obtained by iteratively solving the objective function value to converge to below the preset convergence threshold, thus obtaining the optimal first equivalent resistance, the optimal first equivalent capacitance, the optimal second equivalent resistance, and the optimal second equivalent capacitance.

[0073] Furthermore, an initial estimate is made, calculated as follows: Initial estimate of the first equivalent resistance. ,in This refers to the nominal thickness of the insulating layer wrapped around the synthetic mica tape. The bulk conductivity of mica tape material, The effective cross-sectional area of ​​the synthetic mica tape wrapping insulation layer; the initial estimate of the first equivalent capacitance. ,in The vacuum permittivity, is the relative permittivity of the mica tape material.

[0074] It should be noted that in the objective function In frequency The following is based on the total impedance The impedance magnitude is calculated using the expression. The method for calculating the impedance magnitude is as follows: ; In frequency The following is based on the total impedance The impedance phase angle is calculated using the expression. The method for calculating the impedance phase angle is as follows: ,in Let be the real part of the total impedance. This represents the imaginary part of the total impedance. Frequency point The overall fitting weights.

[0075] It should be noted that the first relaxation time constant of the synthetic mica tape wrapped around the insulating layer... The second relaxation time constant of the XLPE extruded insulation layer After constructing the feature components, the cable segment to be tested was measured three times under the same conditions, and three sets of feature components were obtained respectively. , , and , , The coefficient of variation of each element in each feature component is calculated. If the coefficient of variation of any element exceeds the preset stability threshold of 5%, the detection result is determined to be unstable and needs to be re-detected. The median of the three measurement results is used as the final feature component value.

[0076] In this embodiment of the application, the construction of the layered relaxation equivalent circuit model of the double-insulated structure includes: the total impedance of the layered relaxation equivalent circuit model of the double-insulated structure is:

[0077] in, The first equivalent resistance of the synthetic mica tape wrapping insulation layer, This is the first equivalent capacitance of the synthetic mica tape wrapped insulation layer. The second equivalent resistance of the XLPE extruded insulation layer. The second equivalent capacitance is the XLPE extruded insulation layer. For frequency, It is the imaginary unit.

[0078] It should be noted that the specific implementation method for constructing the layered relaxation equivalent circuit model of the double-insulated structure is as follows: the synthetic mica tape wrapped insulation layer is equivalent to the first relaxation unit, and the first relaxation unit consists of a first equivalent resistor. and the first equivalent capacitance The complex impedance expression is formed by parallel connection. The XLPE extruded insulation layer is equivalent to a second relaxation unit, which is composed of a second equivalent resistance. Second equivalent capacitance The complex impedance expression is formed by parallel connection. The two relaxation units are connected in series, and the total impedance is the sum of the two. The first equivalent resistance comprehensively reflects the insulation resistance of the synthetic mica tape wrapped insulation layer, including the mica tape bulk resistance and the ionic conductivity effect of the magnesium oxide fireproof layer; the first equivalent capacitance comprehensively reflects the dielectric properties of the synthetic mica tape wrapped insulation layer, including the interlayer polarization capacitance of the mica tape and the dielectric properties of the magnesium oxide fireproof layer; the second equivalent resistance comprehensively reflects the insulation resistance of the XLPE extruded insulation layer; the second equivalent capacitance comprehensively reflects the dielectric properties of the XLPE extruded insulation layer, including the XLPE geometric capacitance and the relaxation capacitance of the polar groups.

[0079] S4. Based on the current amplitude and real-time temperature value, extract the characteristic conductivity of the XLPE layer and the characteristic conductivity of the mica tape layer, and calculate the electrical insulation thermal aging index and the fire-resistant layer thermal stability index respectively.

[0080] In this embodiment of the application, the extraction of characteristic conductivity of the XLPE layer and the mica band layer based on current amplitude and real-time temperature value includes: S601, the ratio of the current amplitude to the DC detection voltage at each sampling time is taken as the apparent insulation conductance. The apparent insulation conductance is multiplied by the cable segment insulation geometric factor to obtain the normalized insulation conductance. Based on the normalized insulation conductance, a first measurement curve of conductivity changing with temperature is constructed. Based on the first measurement curve, a second measurement curve of the natural logarithm of conductivity changing with temperature is constructed. The first derivative of the second measurement curve with respect to temperature is obtained to obtain the first derivative curve.

[0081] S602, in the first derivative curve, within the melting point temperature range of XLPE, after taking the absolute value of the first derivative curve, search for a local maximum point as the first characteristic transition peak, and mark the peak temperature of the first characteristic transition peak as the XLPE thermally induced transition temperature. Within the ceramic initiation temperature range of the mica tape, search for a local maximum point as the second characteristic transition peak, and mark the peak temperature of the second characteristic transition peak as the mica tape thermally induced transition temperature; if neither the first characteristic transition peak nor the second characteristic transition peak is detected, it is determined that the insulation structure of the cable section to be tested has a serious defect, and an unqualified test result is directly generated.

[0082] S603, the insulation conductivity at the thermally induced transition temperature of XLPE is extracted from the first measurement curve as the characteristic conductivity of the XLPE layer, and the insulation conductivity at the thermally induced transition temperature of the mica tape is extracted from the first measurement curve as the characteristic conductivity of the mica tape layer.

[0083] It should be noted that the cable segment insulation geometry factor is predetermined based on the structural parameters and effective test length of the cable segment under test, and remains constant during the temperature scan.

[0084] It should be noted that a first measurement curve of conductivity versus temperature is constructed with temperature as the horizontal axis and normalized insulation conductivity as the vertical axis. A second measurement curve of conductivity versus temperature is constructed with temperature as the horizontal axis and the natural logarithm of normalized insulation conductivity as the vertical axis. The first derivative curve is obtained by taking the first derivative of the second measurement curve with respect to temperature.

[0085] The specific implementation method for constructing the first and second measurement curves is as follows: For each sampling time, record the real-time temperature value at that time. and current amplitude The amplitude of the DC detection voltage is Calculate the apparent insulation conductance at this sampling time. (Unit: Siemens S).

[0086] Furthermore, based on the structural parameters and effective test length of the cable segment under test... Calculate the insulation geometric factor of cable segment For coaxial cylindrical insulating structures, the geometric factor... ,in It is the outer radius of the insulation structure (the distance from the outer surface of the XLPE extruded insulation layer to the conductor axis). The inner radius of the insulation structure is the distance from the inner surface of the synthetic mica tape wrapped around the insulation layer to the conductor axis. and It is calculated from the outer radius of the fully stranded conductor, the nominal thickness of the synthetic mica tape wrapped insulation layer, and the nominal thickness of the XLPE extruded insulation layer.

[0087] Calculate the normalized insulation conductivity at this sampling time. (Unit: S / m). During the temperature scan, the insulation geometry of the cable segment remains constant; therefore, the change in normalized insulation conductivity with temperature only reflects the change in the intrinsic conductivity of the material.

[0088] Plotting temperature on the horizontal axis and normalized insulation conductivity on the vertical axis, the normalized insulation conductivity data at each sampling time are smoothly connected to obtain a first measurement curve of conductivity versus temperature. Plotting temperature on the horizontal axis and the natural logarithm of the normalized insulation conductivity on the vertical axis, the natural logarithm of the normalized insulation conductivity at each sampling time is smoothly connected to obtain a second measurement curve of conductivity's natural logarithm versus temperature. The first derivative of the second measurement curve with respect to temperature is calculated using the following method: Thus, the first derivative curve is obtained.

[0089] Furthermore, XLPE, as a polymer material, undergoes a melting phase transition near its melting point (approximately 100°C to 110°C) during heating. This intensifies molecular chain segment movement and significantly increases ion mobility, leading to an exponential increase in electrical conductivity with rising temperature, manifested as a positive local maximum peak on the first derivative curve. Synthetic mica tape, as an inorganic mineral material, sintersulates near its ceramic initiation temperature (approximately 600°C to 900°C) during heating, forming a continuous and dense ceramic shell. This blocks ion migration pathways within the material, causing a sharp decrease in electrical conductivity with increasing temperature, manifested as a negative extreme peak on the first derivative curve. Taking the absolute value of the first derivative curve transforms this negative extreme peak into a positive maximum peak. Based on the fundamental difference in these two thermal behaviors, characteristic transition peaks of the two insulating layers can be separated and identified in the first derivative curve.

[0090] It should be noted that the specific implementation method for identifying the first and second characteristic transition peaks is as follows: In the first derivative curve, local maxima are searched within the melting point temperature range of XLPE (80℃ to 130℃). If a local maximum exists with an amplitude exceeding a preset noise threshold (the preset noise threshold is 3 times the standard deviation of the first derivative curve), then this local maximum is marked as the first characteristic transition peak, and its corresponding peak temperature is marked as the XLPE thermally induced transition temperature. Local maxima are searched within the ceramic initiation temperature range of the mica belt (500℃ to 950℃). If a local maximum exists with an amplitude exceeding a preset noise threshold, it is marked as the second characteristic transition peak, and its corresponding peak temperature is marked as the thermally induced transition temperature of the mica belt. If no local maximum amplitude exceeding the noise threshold is detected within the XLPE melting point temperature range, it is determined that the XLPE extruded insulation layer may have been severely thermally degraded and lost its melting properties; if no local maximum amplitude exceeding the noise threshold is detected within the mica tape ceramicization initiation temperature range, it is determined that the synthetic mica tape wrapped insulation layer may have lost its ceramicization ability; both of these situations directly generate unqualified test results.

[0091] Furthermore, the preset noise threshold is set by calculating the mean of the entire first derivative curve. and standard deviation Set the noise threshold to Only local maxima with amplitudes exceeding the threshold are retained as valid feature transition peaks.

[0092] It should be noted that the specific implementation method for extracting the normalized characteristic conductivity is as follows: In the first measurement curve of conductivity changing with temperature, locate the temperature point corresponding to the thermally induced transition temperature of XLPE, read the insulation conductivity value at this temperature point, and use it as the normalized characteristic conductivity of the XLPE layer; locate the temperature point corresponding to the thermally induced transition temperature of the mica tape, read the insulation conductivity value at this temperature point, and use it as the normalized characteristic conductivity of the mica tape layer.

[0093] In this embodiment of the application, the calculation of the electrical insulation thermal aging index and the fire-resistant layer thermal stability index includes: S701, obtaining the standard normalized characteristic conductivity of the XLPE layer in the standard unaged state of the cable segment to be tested at the XLPE thermally induced transition temperature under the same geometric factor conditions, calculating the first deviation ratio between the normalized characteristic conductivity of the XLPE layer and the standard normalized characteristic conductivity, and obtaining the electrical insulation thermal aging index.

[0094] S702, obtain the standard normalized characteristic conductivity of the mica tape layer under the standard unaged state of the cable segment to be tested at the thermally induced transition temperature of the mica tape under the same geometric factor conditions, calculate the second deviation ratio between the normalized characteristic conductivity of the mica tape layer and the standard normalized characteristic conductivity, and obtain the thermal stability index of the fire-resistant layer.

[0095] It should be noted that the standard normalized characteristic conductivity Samples of qualified cables from the same batch, in an unaged state, were tested with the same effective length. and the same geometric factor The statistical median obtained from the measurements was determined. Since the geometric factors of the cable segment to be tested are consistent with those of the standard sample, the first deviation ratio was calculated. When geometric factors cancel each other out, the deviation ratio only reflects the change in the intrinsic conductivity of the material; by mapping the first deviation ratio to a dimensionless value between 0 and 1 through an S-shaped function, the electrical insulation thermal aging index is obtained. The expression for the sigmoid function is: ,in The steepness coefficient of the S-curve of the XLPE layer. The offset coefficient, steepness coefficient, and deviation coefficient of the S-curve for the XLPE layer were determined through calibration experiments. Electrical insulation thermal aging index. The closer to 1, the lower the degree of thermal aging of the XLPE electrical insulation layer; the closer to 0, the more severe the degree of thermal aging.

[0096] It should be noted that the standard normalized characteristic conductivity Samples of qualified cables from the same batch, in an unaged state, were tested with the same effective length. and the same geometric factor The statistical median obtained from the measurements is determined. The second deviation ratio is calculated. Since the geometric factors are consistent, the deviation ratio only reflects the degree of change in the intrinsic electrical conductivity of the mica strip material near the ceramic forming temperature. Mapping the second deviation ratio to a dimensionless value between 0 and 1 using an S-shaped function yields the thermal stability index of the refractory layer. The expression for the sigmoid function is: ,in This represents the steepness coefficient of the S-shaped curve of the mica zone layer. The offset coefficient, steepness coefficient, and offset coefficient of the S-shaped curve of the mica zone layer are determined through calibration experiments. The thermal stability index of the refractory layer is also considered. The closer to 1, the better the porcelain-forming performance of the mica tape refractory layer is maintained; the closer to 0, the more severely the porcelain-forming performance of the refractory layer has deteriorated.

[0097] Furthermore, the characteristic conductivity of the XLPE layer reflects the ion migration ability of the XLPE material near its melting point. When XLPE undergoes thermal aging, the molecular chains break, generating more polar groups and free volume, increasing ion migration and leading to an increase in characteristic conductivity, a larger first deviation ratio, and a decrease in the thermal aging index of electrical insulation. The characteristic conductivity of the mica tape layer reflects the degree of densification of the mica tape material near its ceramicization temperature. When the mica tape has good ceramicization performance, the sintered ceramic shell is dense and continuous, effectively blocking ion migration, reducing the characteristic conductivity, resulting in a negative second deviation ratio with a large absolute value, and the thermal stability index of the refractory layer is close to 1. When the mica tape's ceramicization performance deteriorates, insufficient sintering or cracks appear in the ceramic shell, the decrease in characteristic conductivity is reduced or even not reduced, and the thermal stability index of the refractory layer decreases.

[0098] S5. Based on the magnetic field strength vector value, construct a multi-directional magnetic field distribution topology map, and then construct a composite quality feature vector.

[0099] In this embodiment of the application, the step of constructing a multi-directional magnetic field distribution topology map based on the magnetic field strength vector value, and then constructing a composite quality feature vector, includes: S801, constructing a multi-directional magnetic field distribution topology map based on the magnetic field strength vector value of each spatial position under each electromagnetic excitation direction.

[0100] S802, based on the grayscale map of magnetic field intensity distribution in each direction, calculate the spatial average value of magnetic field intensity under each electromagnetic excitation direction, and calculate the magnetic field anisotropy index based on the spatial average value of magnetic field intensity in each direction; pair each electromagnetic excitation direction according to the angular symmetry relationship, and calculate the directional symmetry difference index between each pairing direction.

[0101] S803 calculates the magnetic field gradient topological distortion index based on the magnetic field gradient distribution vector diagram in each direction.

[0102] S804 calculates the global dispersion of the magnetic field direction angle under each electromagnetic excitation direction based on the magnetic field direction angle distribution diagram in each direction.

[0103] S805, Construct a comprehensive feature vector of the splicing quality of the full-type stranded conductor. ,in For magnetic field anisotropy index, For the directional symmetry difference index, For the topological distortion index of the magnetic field gradient and This represents the global dispersion of the magnetic field direction angle under each electromagnetic excitation direction.

[0104] It should be noted that the specific implementation method for constructing the multi-directional magnetic field distribution topology map is as follows: for the d-th electromagnetic excitation direction, from the magnetic field intensity vector value Extract the magnetic field strength amplitude at each spatial location. A two-dimensional grayscale matrix is ​​constructed with radial positions as rows and angular positions as columns. The grayscale value reflects the magnitude of the magnetic field strength, resulting in a grayscale map of the magnetic field strength distribution in each direction; the spatial gradient of the magnetic field strength amplitude is calculated, including the radial gradient component. The angular gradient component reflects the rate of change of magnetic field strength along the radial direction. To reflect the rate of change of magnetic field intensity along the angular direction, a vector diagram of the magnetic field gradient distribution in each direction is constructed; the magnetic field direction angle is extracted. ,in For radial magnetic field components, For the angular magnetic field components, a magnetic field direction angle distribution map is constructed for each direction. The above three sets of maps together constitute the multi-directional magnetic field distribution topology map.

[0105] Furthermore, the magnetic field sensor array is arranged in a polar coordinate grid, with a radial step size of 0.5 mm and an angular step size of 15 degrees, covering a ring-shaped area extending from the conductor surface outward to the outer surface of the insulation layer. The excitation duration in each electromagnetic excitation direction is set to 2 to 5 seconds to ensure that the electromagnetic field distribution reaches a steady state.

[0106] It should be noted that the physical basis for calculating the magnetic field anisotropy index is as follows: The strands of a fully-formed stranded conductor are joined together in a pre-fabricated, regularly shaped manner to form a circular cross-section. When the interfaces between the strands are in good contact, the conductivity distribution across the conductor cross-section is uniform, and the current is uniformly distributed across the conductor cross-section. According to Ampere's circuital law, the spatial average value of the magnetic field strength under different electromagnetic excitation directions is essentially the same. The value is small; when there is poor contact or gaps at the splicing interface, the contact resistance at the interface increases, the current distribution on the conductor cross-section is no longer uniform, and the magnetic field distribution under different electromagnetic excitation directions varies. The value increases. The number of electromagnetic excitation directions, M, is 4, and the axial directions of each electromagnetic excitation coil form a 45-degree angle with each other.

[0107] Furthermore, the magnetic field anisotropy index is calculated based on the spatial average value of the magnetic field intensity in each direction:

[0108] Where M represents the number of electromagnetic excitation directions. Let be the spatial average value of the magnetic field strength under the d-th electromagnetic excitation direction. This is the overall mean of the spatial average of the magnetic field strength under all electromagnetic excitation directions.

[0109] It should be noted that the electromagnetic excitation directions are paired according to angular symmetry, and the directional symmetry difference index between each pair of directions is calculated:

[0110] Where p and q are the indices of two electromagnetic excitation directions with an angle difference of 180 degrees, and the maximum value of the direction symmetry difference index among all paired directions is taken. As a characteristic of magnetic field symmetry.

[0111] Furthermore, the directional symmetry difference index is used to evaluate the symmetry of the magnetic field distribution in the symmetrical direction of a fully stranded conductor. For conductors with good bonding quality, the magnetic field distribution in the symmetrical direction should be consistent, and the directional symmetry difference index should approach 0. If there are local asymmetric defects at the bonding interface, the magnetic field distribution in the symmetrical direction will differ, and the directional symmetry difference index will increase. The maximum value of the directional symmetry difference index among all pairing directions is taken as the magnetic field symmetry characteristic.

[0112] It should be noted that, after extracting the radial and angular gradient components in each direction, radial gradient outliers are marked within a normal range of twice the standard deviation of the mean radial gradient, and angular gradient outliers are marked within a normal range of twice the standard deviation of the mean angular gradient. The proportions of radial and angular gradient outliers in each direction are statistically analyzed, and the magnetic field gradient topological distortion index is calculated.

[0113] in, The proportion of radial gradient anomalies under the d-th electromagnetic excitation direction. The proportion of angular gradient anomalies under the d-th electromagnetic excitation direction. and These are the weighting coefficients for the radial gradient and the angular gradient, respectively. ; It should be noted that the number of radial gradient outliers is counted. and its proportion of all spatial locations Based on angular gradient components Constructing the angle gradient distribution matrix Detect outliers in the angle gradient using the same method, and count the number of outliers. and their proportions Radial gradient weight coefficients Set to 0.6, for the angle gradient weighting coefficient. A value of 0.4 is used because the radial gradient is more sensitive to defects at the splicing interface, hence it is given a higher weight. The larger the topological distortion exponent of the magnetic field gradient, the more severe the current density distortion at the splicing interface, and the worse the splicing quality.

[0114] Furthermore, in a normal, uniform conductor, the magnetic field strength decreases radially but remains essentially constant along the angular direction. When local defects exist at the splicing interface, the current density near the defect is distorted, causing the magnetic field gradient in that region to deviate from the normal range. By detecting the proportion of abnormal magnetic field gradient points, the severity and extent of the defects at the splicing interface can be quantitatively assessed.

[0115] It should be noted that the physical basis for calculating the dispersion of the magnetic field direction angle is as follows: When the fully stranded conductors are well-joined, the current direction is uniformly distributed along the conductor axis, and the resulting magnetic field direction varies regularly in the circumferential direction, with the magnetic field direction angle at each spatial location deviating little from the theoretical value. However, when there are defects at the joining interface, the current density direction at the defect deflects, causing the local magnetic field direction to deviate from the overall trend. Increase. Number of radial positions. and number of angle positions The number of radial positions is determined by the grid density of the polar coordinates. The ratio of the conductor's outer radius to its radial step size, and the number of angular positions. It is the ratio of 360 degrees to the angle step size.

[0116] Furthermore, the global dispersion of the magnetic field direction angle under each electromagnetic excitation direction is calculated:

[0117] in, Let be the magnetic field direction angle at radial position i and angular position j under the d-th electromagnetic excitation direction. Let I be the average of the magnetic field direction angles at all spatial positions under the d-th electromagnetic excitation direction, where I is the number of radial positions and J is the number of angular positions. The average of the dispersion of the magnetic field direction angles in each direction is taken. As a characteristic of the dispersion of magnetic field direction angle.

[0118] S6. Generation of comprehensive test results.

[0119] In this embodiment of the application, the generation of the comprehensive test results includes: evaluating the quality status of the synthetic mica tape wrapped insulation layer based on the characteristic components of the synthetic mica tape wrapped insulation layer; evaluating the quality status of the XLPE extruded insulation layer based on the characteristic components of the XLPE extruded insulation layer; evaluating the interface bonding quality status between the synthetic mica tape wrapped insulation layer and the XLPE extruded insulation layer based on the characteristic components of the synthetic mica tape wrapped insulation layer and the XLPE extruded insulation layer; evaluating the insulation thermal aging and fire-resistant layer thermal stability status based on the electrical insulation thermal aging index and the fire-resistant layer thermal stability index; and evaluating the splicing quality status of the full-type stranded conductor based on the comprehensive feature vector of splicing quality.

[0120] If all five judgment results are qualified, a comprehensive inspection result indicating that the overall manufacturing quality of the cable segment under inspection is qualified will be generated; if any one of the judgments is unqualified, an unqualified inspection result will be generated. At the same time, all unqualified items and their corresponding defect types will be summarized to generate a defect report as the comprehensive inspection result.

[0121] It should be noted that the characteristic components of the synthetic mica tape wrapped insulation layer are based on... The optimal first equivalent resistance Standard value of resistance of mica tape wrapped insulation layer Compare and select the optimal first equivalent capacitance. Standard value of capacitance with mica tape wrapped insulation layer Compare the first relaxation time constants. Standard value of relaxation time constant of mica tape wrapped insulation layer Compare; when and and exist to If the quality is within the specified range, the quality of the synthetic mica tape wrapping insulation layer is determined to be qualified; otherwise, it is determined to be unqualified and the corresponding defect type is output.

[0122] Furthermore, when When the insulation resistance of the synthetic mica tape wrapping insulation layer is deemed unqualified, it indicates defects such as excessive interlayer gaps, mica tape damage, or discontinuous distribution of the magnesium oxide fire-resistant layer in the multi-layer overlapping wrapping of the synthetic mica tape; when When the dielectric properties of the synthetic mica tape wrapping insulation layer are deemed unqualified, it indicates that the dielectric constant of the synthetic mica tape wrapping insulation layer deviates from the design value, possibly due to uneven mica tape wrapping tension leading to changes in interlayer dielectric properties; when Not here to When the range is within the specified range, the relaxation characteristics of the synthetic mica tape wrapping insulation layer are found to be abnormal, indicating that the interfacial polarization characteristics of the synthetic mica tape wrapping insulation layer have changed, which may be due to interlayer contamination of the mica tape or abnormal distribution of magnesium oxide fireproof layer material.

[0123] It should be noted that the characteristic components of the XLPE extruded insulation layer are... The optimal second equivalent resistance Standard value of resistance of XLPE extruded insulation layer Comparison, and select the optimal second equivalent capacitance. XLPE extruded insulation layer capacitor standard value Compare the second relaxation time constant. Compared with the standard value of dielectric loss factor of XLPE extruded insulation layer, when and If the condition is met, the quality status of the XLPE extruded insulation layer is determined to be qualified; otherwise, it is determined to be unqualified and the corresponding defect type is output.

[0124] Furthermore, when When the insulation resistance of the XLPE extruded insulation layer is deemed unqualified, it indicates that the XLPE extruded insulation layer may have defects such as insufficient cross-linking, excessive material impurities, or insufficient thickness; when If the dielectric properties of the XLPE extruded insulation layer are deemed unqualified, it indicates that the dielectric constant of the XLPE extruded insulation layer deviates from the design value, and there may be defects such as uneven extrusion thickness or uneven crosslinking.

[0125] It should be noted that the characteristic components of the synthetic mica tape wrapped insulation layer are based on... Characteristic components of XLPE extruded insulation layer With the optimal first equivalent resistance and the optimal first equivalent capacitance Constructing the first feature vector With the optimal second equivalent resistance and the optimal second equivalent capacitance Constructing the second feature vector Calculate the coherence coefficient between the first eigenvector and the second eigenvector. ,in for and covariance, for standard deviation for Standard deviation; Calculate the characteristic components of the synthetic mica tape wrapping insulation layer. Characteristic components of XLPE extruded insulation layer Mutual information entropy A comprehensive quality evaluation index combining interface components is constructed based on coherence coefficient and mutual information entropy. ,in and These are the weighting coefficients. , The maximum possible value of mutual information entropy; Combined with preset interface quality threshold If a comparison is made, If the interface bonding quality between the synthetic mica tape wrapped insulation layer and the XLPE extruded insulation layer is satisfactory, it is considered unsatisfactory.

[0126] It should be noted that the electrical insulation thermal aging index is... With the first preset threshold If a comparison is made, If the thermal aging degree of the XLPE insulation layer is within the allowable range, it is determined that the thermal aging exceeds the standard; otherwise, the thermal stability index of the refractory layer is... With the second preset threshold If a comparison is made, If the refractory layer of the mica tape is found to have qualified ceramic-forming properties, it is determined that the thermal stability of the refractory layer is unqualified.

[0127] It should be noted that this is based on the composite quality feature vector. The magnetic field anisotropy index Compared with the preset anisotropy threshold By comparison, the maximum value of the directional symmetry difference index is determined. The difference threshold between the preset symmetry and the threshold Comparison of the magnetic field gradient topological distortion index With the preset gradient distortion threshold Compare and calculate the overall score of the assembled quality. ,in , , and These are the preset thresholds corresponding to the magnetic field anisotropy index, the orientation symmetry difference index, the magnetic field gradient topological distortion index, and the global dispersion of the magnetic field orientation angle, respectively. , , and These are the weighting coefficients corresponding to the magnetic field anisotropy index, the orientation symmetry difference index, the magnetic field gradient topological distortion index, and the global dispersion of the magnetic field orientation angle, respectively. ; , , and The default values ​​are 0.30, 0.25, 0.25, and 0.20 respectively. Each weight can be optimized and adjusted based on the detection sensitivity of known defect samples through calibration experiments. If the splicing quality of the fully stranded conductor is deemed acceptable, it is deemed unacceptable and the dominant defect type is output.

[0128] Furthermore, the global dispersion of the magnetic field direction angle is used to detect the degree of local current direction deflection caused by defects at the splicing interface. When there is poor contact or gaps at the splicing interface, the current density direction at the defect deviates from the conductor axis, causing the local magnetic field direction angle to deviate from the theoretical value of the circumferential tangential, thus increasing the global dispersion of the magnetic field direction angle. This index has high sensitivity to the spatial location of defects at the splicing interface and complements the magnetic field anisotropy index and the magnetic field gradient topological distortion index. The four-dimensional feature vector comprehensively characterizes the splicing quality from four dimensions: overall uniformity, symmetry, local distortion, and directional consistency.

[0129] Furthermore, the defect report includes the name of the nonconformity, a description of the defect type, the measured and standard values ​​of the corresponding characteristic parameters, and recommended maintenance or remedial measures.

[0130] like Figure 2 The diagram shown is a functional block diagram of a cable testing method based on mica tape and XLPE insulation structure provided in an embodiment of this application.

[0131] The system 100 of the cable testing method based on mica tape and XLPE insulation structure described in this application can be installed in an electronic device. Depending on the functions implemented, the system 100 may include a structural parameter acquisition module 101, a multimodal composite detection signal application module 102, a broadband impedance spectrum characteristic decomposition module 103, an insulation thermal aging and fire resistance stability assessment module 104, a magnetic field topology reconstruction and splicing quality analysis module 105, and a comprehensive diagnostic result generation and output module 106. The module described in this application can also be called a unit, referring to a series of computer program segments that can be executed by the processor of an electronic device and perform a fixed function, stored in the memory of the electronic device.

[0132] In this embodiment, the functions of each module / unit are as follows: The structural parameter acquisition module acquires the structural parameters of the cable segment under test based on synthetic mica tape and XLPE insulation structure.

[0133] The multimodal composite detection signal application module applies multimodal composite detection signals to the cable segment to be tested and collects composite electrical response signals, magnetic field strength vector values, current amplitudes, and real-time temperature values.

[0134] The broadband impedance spectrum characteristic decomposition module constructs a broadband impedance-frequency response characteristic spectrum based on the composite electrical response signal, and constructs characteristic components of the synthetic mica tape wrapped insulation layer and XLPE extruded insulation layer.

[0135] The insulation thermal aging and fire resistance stability assessment module extracts the characteristic conductivity of the XLPE layer and the mica tape layer based on the current amplitude and real-time temperature value, and calculates the electrical insulation thermal aging index and the fire resistance layer thermal stability index, respectively.

[0136] The magnetic field topology reconstruction and assembly quality analysis module constructs a multi-directional magnetic field distribution topology map based on the magnetic field intensity vector value, and then constructs a comprehensive feature vector of the assembly quality.

[0137] The comprehensive diagnostic results generation and output module is used to generate comprehensive test results.

[0138] In the embodiments provided in this application, it should be understood that the disclosed methods and systems can be implemented in other ways. For example, the system embodiments described above are merely illustrative; for instance, the division of modules is only a logical functional division, and other division methods may be used in actual implementation.

[0139] The modules described as separate components may or may not be physically separate. The components shown as modules may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs.

[0140] Furthermore, the functional modules in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or in the form of hardware plus software functional modules.

[0141] It will be apparent to those skilled in the art that this application is not limited to the details of the exemplary embodiments described above, and that this application can be implemented in other specific forms without departing from the spirit or essential characteristics of this application.

[0142] The embodiments of this application can acquire and process relevant data based on artificial intelligence technology. Artificial intelligence is the theory, method, technology, and application system that uses digital computers or machines controlled by digital computers to simulate, extend, and expand human intelligence, perceive the environment, acquire knowledge, and use that knowledge to obtain optimal results.

[0143] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the spirit and scope of the technical solutions of this application.

Claims

1. A cable testing method based on mica tape and XLPE insulation structure, characterized in that, The method includes: S1. Obtain the structural parameters of the cable segment to be tested based on synthetic mica tape and XLPE insulation structure; S2. Apply multi-modal composite detection signals to the cable section to be tested, and collect composite electrical response signals, magnetic field strength vector values, current amplitudes, and real-time temperature values. S3. Based on the composite electrical response signal, construct a wideband impedance-frequency response characteristic spectrum, and construct the characteristic components of the synthetic mica tape wrapped insulation layer and the XLPE extruded insulation layer. S4. Based on the current amplitude and real-time temperature value, extract the characteristic conductivity of the XLPE layer and the characteristic conductivity of the mica tape layer, and calculate the electrical insulation thermal aging index and the fire-resistant layer thermal stability index respectively. S5. Based on the magnetic field intensity vector value, construct a multi-directional magnetic field distribution topology map, and then construct a composite quality feature vector; S6. Generation of comprehensive test results.

2. The cable testing method based on mica tape and XLPE insulation structure as described in claim 1, characterized in that, The acquisition of structural parameters of the cable segment under test based on synthetic mica tape and XLPE insulation structure includes: S201, Obtain a cable segment based on synthetic mica tape and XLPE insulation structure, wherein the cable segment consists of a fully stranded conductor, a synthetic mica tape wrapping insulation layer around the fully stranded conductor, and an XLPE extruded insulation layer around the synthetic mica tape wrapping insulation layer. S202, record the structural parameters of the cable section to be tested. The structural parameters include the nominal cross-sectional area and number of stranded conductors, the nominal thickness and number of synthetic mica tape wrapping insulation layers, and the nominal thickness of XLPE extruded insulation layers.

3. The cable testing method based on mica tape and XLPE insulation structure as described in claim 1, characterized in that, The application of a multimodal composite detection signal to the cable segment under test includes: S301, the multimodal composite detection signal includes multi-band composite broadband electrical detection signal, multi-directional electromagnetic excitation signal and temperature scanning detection signal; S302, apply a multi-band composite broadband electrical detection signal to the cable segment to be tested, and collect the composite electrical response signal of the cable segment to be tested at each frequency point. The composite electrical response signal includes the voltage signal amplitude, voltage signal phase, current signal amplitude, and current signal phase at each frequency point. S303, apply multi-directional electromagnetic excitation signals to the cable section to be tested, and collect the magnetic field strength vector value of the space around the full-type stranded conductor under each electromagnetic excitation direction; S304 applies a temperature scanning detection signal to the cable section under test and collects the current amplitude and real-time temperature value at each sampling time.

4. The cable testing method based on mica tape and XLPE insulation structure as described in claim 1, characterized in that, The process of constructing a broadband impedance-frequency response characteristic spectrum based on the composite electrical response signal, and constructing characteristic components of the synthetic mica tape wrapped insulation layer and XLPE extruded insulation layer, includes: S401, based on the voltage signal amplitude and current signal amplitude at each frequency point in the composite electrical response signal, calculates the impedance amplitude and impedance phase angle at each frequency point, and then constructs a broadband impedance-frequency response characteristic spectrum; S402, construct a layered relaxation equivalent circuit model of a double-insulated structure, and construct the characteristic components of the synthetic mica tape-wrapped insulation layer by segmented frequency domain weighting and layered fitting. And construct the characteristic components of the XLPE extruded insulation layer. ;in and These represent the optimal first equivalent resistance and the optimal first equivalent capacitance of the synthetic mica tape wrapped insulation layer, respectively. This is expressed as the first relaxation time constant; and These represent the optimal second equivalent resistance and the optimal second equivalent capacitance of the XLPE extruded insulation layer, respectively. It is represented as the second relaxation time constant.

5. The cable testing method based on mica tape and XLPE insulation structure as described in claim 4, characterized in that, The construction of the hierarchical relaxation equivalent circuit model of the double-insulation structure includes: The total impedance of the layered relaxation equivalent circuit model of the double-insulated structure is: in, The first equivalent resistance of the synthetic mica tape wrapping insulation layer, This is the first equivalent capacitance of the composite mica tape wrapped insulation layer. The second equivalent resistance of the XLPE extruded insulation layer. The second equivalent capacitance is the XLPE extruded insulation layer. For frequency, It is the imaginary unit.

6. The cable testing method based on mica tape and XLPE insulation structure as described in claim 1, characterized in that, The extraction of characteristic conductivity of the XLPE layer and the mica band layer based on current amplitude and real-time temperature includes: S601, the ratio of the current amplitude to the DC detection voltage at each sampling moment is taken as the apparent insulation conductance. The apparent insulation conductance is multiplied by the cable segment insulation geometric factor to obtain the normalized insulation conductance. Based on the normalized insulation conductance, a first measurement curve of conductivity as a function of temperature is constructed. Based on the first measurement curve, a second measurement curve of the natural logarithm of conductivity as a function of temperature is constructed. The first derivative of the second measurement curve with respect to temperature is obtained to obtain the first derivative curve. S602, in the first derivative curve, within the melting point temperature range of XLPE, after taking the absolute value of the first derivative curve, search for local maxima as the first characteristic transition peak, and mark the peak temperature of the first characteristic transition peak as the XLPE thermally induced transition temperature; within the ceramic initiation temperature range of mica tape, search for local maxima as the second characteristic transition peak, and mark the peak temperature of the second characteristic transition peak as the mica tape thermally induced transition temperature; if neither the first characteristic transition peak nor the second characteristic transition peak is detected, it is determined that the insulation structure of the cable section to be tested has serious defects, and an unqualified test result is directly generated; S603, the insulation conductivity at the thermally induced transition temperature of XLPE is extracted from the first measurement curve as the characteristic conductivity of the XLPE layer, and the insulation conductivity at the thermally induced transition temperature of the mica tape is extracted from the first measurement curve as the characteristic conductivity of the mica tape layer.

7. The cable testing method based on mica tape and XLPE insulation structure as described in claim 1, characterized in that, The calculation of the electrical insulation thermal aging index and the fire-resistant layer thermal stability index includes: S701, obtain the standard normalized characteristic conductivity of the XLPE layer under the standard unaged state of the cable segment to be tested at the XLPE thermal transition temperature and under the same geometric factor conditions, calculate the first deviation ratio between the normalized characteristic conductivity of the XLPE layer and the standard normalized characteristic conductivity, and obtain the electrical insulation thermal aging index. S702, obtain the standard normalized characteristic conductivity of the mica tape layer under the standard unaged state of the cable segment to be tested at the thermally induced transition temperature of the mica tape under the same geometric factor conditions, calculate the second deviation ratio between the normalized characteristic conductivity of the mica tape layer and the standard normalized characteristic conductivity, and obtain the thermal stability index of the fire-resistant layer.

8. The cable testing method based on mica tape and XLPE insulation structure as described in claim 1, characterized in that, The process of constructing a multi-directional magnetic field distribution topology map based on magnetic field strength vector values, and then constructing a composite quality feature vector, includes: S801, based on the magnetic field intensity vector values ​​at each spatial location under each electromagnetic excitation direction, constructs a multi-directional magnetic field distribution topology map; S802, based on the grayscale distribution of magnetic field intensity in each direction, calculate the spatial average value of magnetic field intensity under each electromagnetic excitation direction, and calculate the magnetic field anisotropy index based on the spatial average value of magnetic field intensity in each direction; pair each electromagnetic excitation direction according to the angular symmetry relationship and calculate the directional symmetry difference index between each pairing direction. S803, based on the magnetic field gradient distribution vector diagram in each direction, calculate the magnetic field gradient topological distortion index; S804, based on the magnetic field direction angle distribution diagram in each direction, calculates the global dispersion of the magnetic field direction angle under each electromagnetic excitation direction; S805, Construct a comprehensive feature vector of the splicing quality of the full-type stranded conductor. ,in For magnetic field anisotropy index, For the directional symmetry difference index, For the topological distortion index of the magnetic field gradient and This represents the global dispersion of the magnetic field direction angle under each electromagnetic excitation direction.

9. The cable testing method based on mica tape and XLPE insulation structure as described in claim 1, characterized in that, The generation of the comprehensive detection results includes: The quality status of synthetic mica tape wrapped insulation layer is evaluated based on the characteristic components of synthetic mica tape wrapped insulation layer; the quality status of XLPE extruded insulation layer is evaluated based on the characteristic components of XLPE extruded insulation layer; the interface bonding quality status between synthetic mica tape wrapped insulation layer and XLPE extruded insulation layer is evaluated based on the characteristic components of synthetic mica tape wrapped insulation layer and XLPE extruded insulation layer; the thermal aging of insulation and the thermal stability of fire-resistant layer are evaluated based on the thermal aging index of electrical insulation and the thermal stability index of fire-resistant layer; and the splicing quality status of full-type stranded conductor is evaluated based on the comprehensive feature vector of splicing quality. If all five judgment results are qualified, a comprehensive inspection result indicating that the overall manufacturing quality of the cable segment under inspection is qualified will be generated; if any one of the judgments is unqualified, an unqualified inspection result will be generated. At the same time, all unqualified items and their corresponding defect types will be summarized to generate a defect report as the comprehensive inspection result.

10. A system for implementing the cable testing method based on mica tape and XLPE insulation structure according to any one of claims 1-9, characterized in that, include: The structural parameter acquisition module acquires the structural parameters of the cable segment under test based on synthetic mica tape and XLPE insulation structure. The multimodal composite detection signal application module applies a multimodal composite detection signal to the cable segment to be tested and acquires composite electrical response signals, magnetic field strength vector values, current amplitudes, and real-time temperature values. The broadband impedance spectrum characteristic decomposition module constructs a broadband impedance-frequency response characteristic spectrum based on the composite electrical response signal, and constructs characteristic components of the synthetic mica tape wrapped insulation layer and XLPE extruded insulation layer. The insulation thermal aging and fire resistance stability assessment module extracts the characteristic conductivity of the XLPE layer and the mica tape layer based on the current amplitude and real-time temperature value, and calculates the electrical insulation thermal aging index and the fire resistance layer thermal stability index respectively. The magnetic field topology reconstruction and assembly quality analysis module constructs a multi-directional magnetic field distribution topology map based on the magnetic field intensity vector value, and then constructs a comprehensive feature vector of the assembly quality. The comprehensive diagnostic results generation and output module is used to generate comprehensive test results.

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