Method and apparatus for frequency domain diagnosis of power cable defect on basis of cross-interconnection box structure

Abstract

A method and apparatus for frequency domain diagnosis of a power cable defect on the basis of a cross-interconnection box structure. The method comprises: by means of a wiring terminal intersecting a three-phase shielding layer of a cross-interconnection box, injecting a broadband signal, and obtaining a time domain result (S101); according to the time domain result being mapped into a frequency domain, performing analysis, and obtaining impedance spectrum results of a left end and a right end of an injection cross-interconnection box (S102); and, according to the impedance spectrum results, diagnosing hidden danger defects of an outer sheath and a main insulation in a three-phase cable (S103). The present disclosure solves the problem in the related technology that traveling wave reflection method diagnosis strategies cannot avoid direct connection to a cable core wire when identifying a main insulation fault in a cable, which limits the application scenarios of a traveling wave injection method to only being applicable to inspection before a cable has been put into operation and cable defect assessment after a cable fault has occurred. Additionally, the present disclosure solves the problems of high device requirements and testing costs, leading to the inability to meet daily operation and maintenance inspection requirements of cables and various test scenarios.

Description

A method and device for frequency domain diagnosis of power cable defects based on cross-interconnection box structure

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese Patent Application No. 202410474143.X, filed by Tsinghua University on April 19, 2024, entitled "Method and Device for Frequency Domain Diagnosis of Power Cable Defects Based on Cross-Interconnection Box Structure". Technical Field

[0003] This application relates to the field of high voltage technology, and in particular to a method and apparatus for frequency domain diagnosis of power cable defects based on a cross-connection box structure. Background Technology

[0004] As a crucial component of urban power distribution networks, cable failures can threaten the safe and stable operation of the urban power grid, leading to economic losses. Providing early warnings of potential faults, assessing fault information, and pinpointing fault locations before they occur would greatly benefit cable system maintenance and safeguard the urban power grid. Since these potential defects do not pose a substantial threat to the urban cable network, traditional fault location strategies based on hard faults such as short circuits and open circuits are limited. New diagnostic strategies are needed for these soft faults.

[0005] In related technologies, the detection of potential hidden defects in power cables is mainly divided into traveling wave method and impedance method. The traveling wave method has higher identification and location accuracy than the impedance method. The traveling wave method can be further divided into traveling wave method based on power grid operating parameters and traveling wave method based on artificially injected signals. Since the traveling wave reflection method based on artificially injected signals can artificially control the frequency components of the injected system signal, it requires that the injection pole or return pole of the broadband signal be electrically directly connected to the cable core. That is, it requires that the intermediate joint of the in-service power cable be disconnected or the exposed core of the cable be manually cut open. It has a greater advantage in detecting even smaller hidden defects.

[0006] However, the traveling wave reflection method diagnostic strategy in related technologies cannot avoid direct electrical connection to the cable core when identifying main insulation faults in cables, which greatly limits the application scenarios of the traveling wave injection method. It can only be applied to the inspection before the cable is put into operation and the cable defect assessment after the cable has failed. Moreover, the equipment requirements and testing costs are high, which cannot meet the requirements of daily operation and maintenance inspection of cables and various testing scenarios, and urgently needs to be solved.

[0007] Summary of the Invention

[0008] This application provides a frequency domain diagnostic method and apparatus for power cable defects based on a cross-connection box structure. This addresses the limitations of the traveling wave reflection method in related technologies. When identifying main insulation faults in cables, the traveling wave reflection method cannot avoid direct electrical connection to the cable core, which greatly restricts its application. It can only be used for pre-construction testing and defect assessment after cable failure. Furthermore, the equipment requirements and testing costs are high, making it unsuitable for daily maintenance and inspection of cables and various testing scenarios.

[0009] The first aspect of this application provides a frequency domain diagnostic method for power cable defects based on a cross-connection box structure, comprising the following steps: injecting a broadband signal through the terminals of the three-phase shielding layers of the cross-connection box to obtain time domain results; mapping the time domain results to the frequency domain for analysis to obtain impedance spectrum results injected at the left and right ends of the cross-connection box; and diagnosing potential defects in the outer sheath and main insulation of the three-phase cable based on the impedance spectrum results.

[0010] Optionally, in one embodiment of this application, the fused impedance spectrum of each phase of the impedance spectrum result is:

[0011] Among them, Z C,X Let X be the capacitance of phase X corresponding to the cross-connection box, where X = A, B, C, and Z. in,1 Z in,2 Z in,3 These represent the series fused impedance spectra of the corresponding signals, and α and β are the scaling factors of the test results, respectively:

[0012] Optionally, in one embodiment of this application, the step of diagnosing potential defects in the outer sheath and main insulation of a three-phase cable based on the impedance spectrum results includes: obtaining the potential defects in the outer sheath and main insulation using a preset analysis formula based on the combined impedance spectrum of each phase, wherein the preset analysis formula is:

[0013] Where X = A, B, C, A, B, C represent the A, B, and C phases corresponding to the MN cross-connection box, respectively, and Z... h (f) is the pre-updated health-state impedance spectrum in the system, γ h (f) is the propagation constant under healthy conditions, Z X Z represents the fused impedance spectrum of each phase. X (f) represents the fusion impedance spectrum resistance of phase X at frequency f, where f h f l Let f represent the upper frequency f used for integral transform analysis.h and lower limit frequency f l R X (·) represents the diagnostic result of phase X, e represents the natural constant, and L c This indicates the total length of the cable to be tested.

[0014] Optionally, in one embodiment of this application, after obtaining the time-domain result, the method further includes: using discrete wavelet transform and selecting a hard thresholding method to filter the time-domain waveform in the time-domain result, wherein the hard thresholding method is:

[0015] Where, ψ a,b Let K be the wavelet transform coefficient, ψ(·) be the wavelet basis function, and K be the wavelet transform coefficient. δ The values ​​represent the wavelet transform coefficients after hard thresholding, where a is the scale parameter in the wavelet transform, b is the time parameter in the wavelet transform, t represents time, and δ represents the set hard threshold.

[0016] A second aspect of this application provides a frequency domain diagnostic device for power cable defects based on a cross-connection box structure, comprising: a calculation module for injecting a broadband signal through the terminals of the three-phase shielding layers of the cross-connection box to obtain time domain results; an analysis module for mapping the time domain results to the frequency domain for analysis to obtain impedance spectrum results injected into the left and right ends of the cross-connection box; and a diagnostic module for diagnosing potential defects in the outer sheath and main insulation of the three-phase cable based on the impedance spectrum results.

[0017] Optionally, in one embodiment of this application, the fused impedance spectrum of each phase of the impedance spectrum result is:

[0018] Among them, Z C,X Let X be the capacitance of phase X corresponding to the cross-connection box, where X = A, B, C, and Z. in,1 Z in,2 Z in,3 These represent the series fused impedance spectra of the corresponding signals, and α and β are the scaling factors of the test results, respectively:

[0019] Optionally, in one embodiment of this application, the diagnostic module includes: a calculation unit, used to obtain potential defects in the outer sheath and main insulation based on the combined impedance spectrum of each phase using a preset analysis formula, wherein the preset analysis formula is:

[0020] Where X = A, B, C, A, B, C represent the A, B, and C phases corresponding to the MN cross-connection box, respectively, and Z...h (f) is the pre-updated health-state impedance spectrum in the system, β h (f) is the propagation constant under healthy conditions, Z X Z represents the fused impedance spectrum of each phase. X (f) represents the fusion impedance spectrum resistance of phase X at frequency f, where f h f l Let f represent the upper frequency f used for integral transform analysis. h and lower limit frequency f l R X (·) represents the diagnostic result of phase X, e represents the natural constant, and L c This indicates the total length of the cable to be tested.

[0021] Optionally, in one embodiment of this application, after obtaining the time-domain result, the method further includes: a filtering module, configured to use discrete wavelet transform and a hard thresholding method to filter the time-domain waveform in the time-domain result, wherein the hard thresholding method is:

[0022] Where, ψ a,b Let K be the wavelet transform coefficient, ψ(·) be the wavelet basis function, and K be the wavelet transform coefficient. δ The values ​​represent the wavelet transform coefficients after hard thresholding, where a is the scale parameter in the wavelet transform, b is the time parameter in the wavelet transform, t represents time, and δ represents the set hard threshold.

[0023] A third aspect of this application provides an electronic device, including: a memory, a processor, and a computer program stored in the memory and executable on the processor. The processor executes the program to implement the frequency domain diagnostic method for power cable defects based on a cross-connection box structure as described in the above embodiments.

[0024] A fourth aspect of this application provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described frequency domain diagnostic method for power cable defects based on a cross-connection box structure.

[0025] A fifth aspect of this application provides a computer program product, which, when executed, is used to implement the above-described frequency domain diagnostic method for power cable defects based on a cross-connection box structure.

[0026] This application embodiment can analyze the time-domain results obtained by injecting broadband signals into the terminals of the three-phase shielding layers of a cross-connection box, and then obtain the impedance spectrum results at both ends of the cross-connection box. This allows for the diagnosis of potential defects in the outer sheath and main insulation of the three-phase cable. Based on the time-domain testing method, the impedance spectrum of the cable system can be analyzed by testing only the voltage response, reducing the equipment requirements and testing costs for on-site testing. Furthermore, testing based on two cross-connection boxes can simultaneously analyze and diagnose potential defects in the outer sheath and main insulation of the three-phase cable. This enables the testing of the cable system's response characteristics by injecting broadband signals only from the metal connection points of the cross-connection box without disconnecting the electrical connections of any cable network. This allows the frequency domain reflection method to be applied to online testing or non-disconnection system testing scenarios. This solves the problem that the traveling wave reflection method diagnostic strategy in related technologies cannot avoid direct electrical connection to the cable core when identifying the main insulation fault of the cable. This greatly limits the application scenarios of the traveling wave injection method, which can only be used for cable inspection before commissioning and cable defect assessment after a fault has occurred. In addition, the equipment requirements and testing costs are high, which cannot meet the requirements of daily operation and maintenance inspection of cables and various testing scenarios.

[0027] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0028] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0029] Figure 1 is a flowchart of a frequency domain diagnostic method for power cable defects based on a cross-interconnection box structure according to an embodiment of this application;

[0030] Figure 2 is a schematic diagram of the test loop of an online diagnostic test method according to an embodiment of this application;

[0031] Figure 3 is a schematic diagram of the power cable defect frequency domain diagnostic device based on a cross-interconnection box structure according to an embodiment of this application;

[0032] Figure 4 is a schematic diagram of the structure of an electronic device according to an embodiment of this application.

[0033] Figure description: 10- Frequency domain diagnostic device for power cable defects based on cross-connection box structure: 100- Calculation module, 200- Analysis module and 300- Diagnostic module; 401- Memory, 402- Processor and 403- Communication interface. Detailed Implementation

[0034] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0035] The following describes a frequency domain diagnostic method and apparatus for power cable defects based on a cross-connection box structure, according to embodiments of this application, with reference to the accompanying drawings. Addressing the issue that the traveling wave reflection method, mentioned in the background art, cannot avoid direct electrical connection to the cable core when identifying main insulation faults, greatly limiting its application scenarios, it can only be used for pre-construction cable inspection and defect assessment after cable failure. Furthermore, it has high equipment requirements and testing costs, failing to meet the requirements of daily cable maintenance and inspection, and various diagnostic scenarios. This application provides a frequency domain diagnostic method for power cable defects based on a cross-connection box structure. In this method, by analyzing the time domain results obtained from injecting broadband signals into the terminals of the three-phase shielding layers of the cross-connection box, the impedance spectrum results at both ends of the cross-connection box can be obtained, thereby diagnosing potential defects in the outer sheath and main insulation of the three-phase cable. This solves the problem that the traveling wave reflection method diagnostic strategy in related technologies cannot avoid direct electrical connection to the cable core when identifying the main insulation fault of the cable. This greatly limits the application scenarios of the traveling wave injection method, which can only be used for cable inspection before commissioning and cable defect assessment after a cable has already failed. In addition, the equipment requirements and testing costs are high, which cannot meet the requirements of daily operation and maintenance inspection of cables and various diagnostic scenarios.

[0036] Specifically, Figure 1 is a flowchart illustrating a frequency domain diagnostic method for power cable defects based on a cross-connection box structure provided in an embodiment of this application.

[0037] As shown in Figure 1, the frequency domain diagnostic method for power cable defects based on the cross-connection box structure includes the following steps:

[0038] In step S101, a broadband signal is injected through the terminals of the three-phase shielding layer cross-connection box to obtain the time domain result.

[0039] In actual implementation, when performing frequency domain diagnosis of power cable defects, a broadband signal can be injected first through the terminals of the three-phase shielding layer cross-connection box to obtain time domain results.

[0040] For example, as shown in Figure 2, this is a test loop diagram of a non-intrusive online diagnostic test method for potential defects in power cables based on cross-connection box injection according to an embodiment of this application.

[0041] In this test, the object of the test can be an in-service three-phase cable that has not undergone any disconnection treatment, and the test location can be a cross-connection box between adjacent sections; the test circuit consists of a waveform generator, a signal acquisition device, a T-connector, and a signal connection cable.

[0042] In actual testing, impedance matching must be ensured between the internal resistance of the selected waveform generator and the connecting signal cable; the input resistance of the signal acquisition device should be as large as possible, approximating an open circuit state. The three-phase cable test based on the cross-connection box injection consists of two sets of tests, which are performed in two adjacent cross-connection boxes, as shown in Figure 2.

[0043] As shown in Figure 2, taking the identification of potential defects in cables with segments M, N, and O as an example, the specific operating steps are as follows:

[0044] Step 1: After assembling the test circuit according to the circuit in Figure 2, check whether the connection is electrically reliable, and record the lengths of the connecting signal cable 1 and the connecting signal cable 2, which are l1 and l2 respectively;

[0045] Step 2: Leave the injection and return poles at the end of cable segment 2 floating, output a wideband signal with a certain repetition frequency from the waveform generator, and collect the port signal U0 in steady state;

[0046] Step 3: Connect the injection terminals at the end of cable segment 2 to a / a / b of the cross-connection box MN, and connect the return terminals at the end of cable segment 2 to c / b / c of ​​the cross-connection box MN. Keep the previous waveform generator and signal acquisition device settings, and acquire the port signals U1, U2, and U3 in a single cycle under steady state in this case.

[0047] Step 4: Connect the injection terminals at the end of cable segment 2 to a / a / b of cross-connection box NO, and connect the return terminals at the end of cable segment 2 to c / b / c of ​​cross-connection box NO. Keep the previous waveform generator and signal acquisition device settings, and acquire the port signals U4, U5, and U6 in a single cycle under steady state in this case.

[0048] This application embodiment can obtain time-domain results by injecting broadband signals into the terminals of the three-phase shielding layer cross-connection box. This allows for the testing of the response characteristics of the cable system by injecting broadband signals only from the metal access point of the cross-connection box, even under unfavorable electrical connection conditions of any cable network. It also solves the limitation that the injection pole or return pole of the broadband signal must be electrically directly connected to the cable core, enabling the frequency domain reflection method to be applied to online testing or non-disconnection system testing scenarios. It is simple and easy to implement, and greatly expands the scope of application.

[0049] Optionally, in one embodiment of this application, after obtaining the time-domain result, the method further includes: using discrete wavelet transform and selecting a hard thresholding method to filter the time-domain waveform in the time-domain result, wherein the hard thresholding method can be expressed as:

[0050] Where, ψ a,b Let K be the wavelet transform coefficient, ψ(·) be the wavelet basis function, and K be the wavelet transform coefficient. δ The values ​​represent the wavelet transform coefficients after hard thresholding, where a is the scale parameter in the wavelet transform, b is the time parameter in the wavelet transform, t represents time, and δ represents the set hard threshold.

[0051] In some embodiments, after obtaining the time-domain result by injecting a broadband signal into the terminals of the three-phase shielded layer cross-connection box, the result needs to be analyzed. At this time, discrete wavelet transform can be used first, and a hard thresholding method can be selected to filter the acquired time-domain waveform. The formula can be expressed as follows:

[0052] Where, ψ a,b ψ(·) represents the wavelet transform coefficients, ψ(·) represents the wavelet basis functions, a represents the scale parameter in the wavelet transform, b represents the time parameter in the wavelet transform, and t represents time.

[0053] Here, a method with 5 levels of decomposition and hard thresholding can be used to filter out noise, that is:

[0054] Where, ψ a,b Let K be the wavelet transform coefficient, ψ(·) be the wavelet basis function, and K be the wavelet transform coefficient. δ The values ​​represent the wavelet transform coefficients after hard thresholding, where a is the scale parameter in the wavelet transform, b is the time parameter in the wavelet transform, t represents time, and δ represents the set hard threshold.

[0055] The filtered result can then be subjected to inverse wavelet transform to obtain the time-domain waveform after noise removal.

[0056] The embodiments of this application can use discrete wavelet transform and hard thresholding to filter the time-domain waveform after obtaining the time-domain results, effectively overcoming interference caused by accidental factors and providing a good filtering effect on errors caused by random interference or sampler instability.

[0057] Step S102: Based on the time domain results, the frequency domain is mapped to the frequency domain for analysis to obtain the impedance spectrum results of the left and right ends of the injected cross-connection box.

[0058] As can be understood from the description of other embodiments, after obtaining the time-domain results, discrete wavelet transform can be used, and the hard thresholding method can be selected to filter the time-domain waveform in the time-domain results. In addition, this application can also map the time-domain results to the frequency domain for analysis, thereby obtaining the impedance spectrum results of the left and right ends of the injected cross-connection box.

[0059] Specifically, for the filtered signal, a Fast Fourier Transform can be performed to obtain U. i,f , where i = 0, 1, ..., 6;

[0060] The transformed results can be calculated using the following method to obtain the series fusion impedance spectrum corresponding to each test result, where i = 1, 2, ..., 6. The formula can be expressed as follows:

[0061] Wherein, variable Si is

[0062] Wherein, γ1 and γ2 are the propagation constants of cable segment 1 and cable segment 2, respectively, and Z1, Z2, Z... i These are the characteristic impedances of cable segment 1, cable segment 2, and the input impedance of the waveform generator, respectively. in,i For series fusion impedance spectrum, U 0,f U i,f S represents the frequency domain waveform of the steady-state signal measured under no-load conditions and the frequency domain waveform of the steady-state signal of the measured voltage numbered i (i = 1, 2, ..., 6), respectively. i For Z in,i The variable S in i l1 and l2 are the lengths of connecting cable 1 and connecting cable 2, respectively, and tanh(·) is the hyperbolic tangent function.

[0063] Step S103: Diagnose potential defects in the outer sheath and main insulation of the three-phase cable based on the impedance spectrum results.

[0064] Optionally, in one embodiment of this application, diagnosing potential defects in the outer sheath and main insulation of a three-phase cable based on impedance spectrum results includes: obtaining potential defects in the outer sheath and main insulation using a preset analysis formula based on the fused impedance spectrum of each phase, wherein the preset analysis formula may be:

[0065] Where X = A, B, C, A, B, C represent the A, B, and C phases corresponding to the MN cross-connection box, respectively, and Z... h (f) is the pre-updated health-state impedance spectrum in the system, γ h (f) is the propagation constant under healthy conditions, Z X Z represents the fused impedance spectrum of each phase. X(f) represents the fusion impedance spectrum resistance of phase X at frequency f, where f h f l Let f represent the upper frequency f used for integral transform analysis. h and lower limit frequency f l R X (·) represents the diagnostic result of phase X, e represents the natural constant, and L c This indicates the total length of the cable to be tested.

[0066] Optionally, in one embodiment of this application, the fused impedance spectrum of each phase of the impedance spectrum result can be:

[0067] Among them, Z C,X Let X be the capacitance of phase X corresponding to the cross-connection box, where X = A, B, C, and Z. in,1 Z in,2 Z in,3 These represent the series fused impedance spectra of the corresponding signals, and α and β are the scaling factors of the test results, respectively:

[0068] In some embodiments, the fused impedance spectrum of each phase can then be obtained sequentially using an integral transform based on the known structural parameters of the test system:

[0069] For the MN cross-connected box, the phase fusion impedance spectrum is as follows:

[0070] Among them, Z C,X Let X be the capacitance of phase X corresponding to the cross-connection box, where X = A, B, C, and Z. in,1 Z in,2 Z in,3 These represent the series fused impedance spectra of the corresponding signals, and α and β are the scaling factors of the test results, respectively:

[0071] After obtaining the combined impedance spectrum of each phase, the potential defects in the outer sheath and main insulation of the three-phase cable can be analyzed based on each combined impedance spectrum and a certain analytical formula. The analytical formula can be expressed as follows:

[0072] Where X = A, B, C, A, B, C represent the A, B, and C phases corresponding to the MN cross-connection box, respectively, and Z... h (f) is the pre-updated health-state impedance spectrum in the system, γ h(f) is the propagation constant under healthy conditions, Z X Z represents the fused impedance spectrum of each phase. X (f) represents the fusion impedance spectrum resistance of phase X at frequency f, where f h f i Let f represent the upper frequency f used for integral transform analysis. h and lower limit frequency f l R X (·) represents the diagnostic result of phase X, e represents the natural constant, and L c This represents the total length of the cable under test. Similarly, for the fusion impedance spectrum analysis of the NO cross-connection box, given an identification threshold of k, the location vectors Vmn and Vno are given by taking the left side of the extreme value after R(x)>k: V mn =[a0,a1,…,a s V no =[b0,b1,…,b p ]

[0073] Compare each phase positioning vector one by one; if |a i +b j -L c If |<ε, then the two location vectors are considered to correspond to the same defect, which is located in segment N; otherwise, it is located in segment M or segment O. Here, ε is the error tolerance limit, and a setting of 0.005Lc is recommended. Fm, Fn, and Fo are the fault location vectors identified in segments M, N, and O, respectively.

[0074] This application embodiment can diagnose potential defects in the outer sheath and main insulation of three-phase cables based on the impedance spectrum of each phase. Furthermore, based on the testing of two cross-connection boxes, it can simultaneously analyze potential defects in the outer sheath and main insulation of three-phase cables and provide diagnostic location. This allows for testing the response characteristics of the cable system by injecting a broadband signal from the metal access point of the cross-connection box without disconnecting the electrical connection of any cable network. This reduces equipment requirements and testing costs while meeting the daily operation and maintenance inspection requirements and various diagnostic needs of cables.

[0075] The frequency domain diagnostic method for power cable defects proposed in this application can diagnose hidden defects in the outer sheath and main insulation of three-phase cables by analyzing the time domain results obtained from injecting broadband signals into the terminals of the three-phase shielding layers of the cross-connection box. This allows for the determination of the impedance spectrum results at both ends of the cross-connection box, thereby identifying these defects. This solves the problem that the traveling wave reflection method in related technologies, when identifying main insulation faults, cannot avoid direct electrical connection to the cable core, greatly limiting its application to pre-construction testing and defect assessment after cable failure. Furthermore, it has high equipment requirements and testing costs, failing to meet the requirements of daily maintenance and inspection, and various diagnostic scenarios.

[0076] Next, referring to the accompanying drawings, a frequency domain diagnostic device for power cable defects based on a cross-connection box structure, according to an embodiment of this application, is described.

[0077] Figure 3 is a schematic diagram of the power cable defect frequency domain diagnostic device based on the cross-connection box structure according to an embodiment of this application.

[0078] As shown in Figure 3, the power cable defect frequency domain diagnostic device 10 based on the cross-interconnection box structure includes: a calculation module 100, an analysis module 200, and a diagnostic module 300.

[0079] The calculation module 100 is used to inject a broadband signal through the terminals of the three-phase shielding layer cross-connection box to obtain time-domain results.

[0080] Analysis module 200 is used to map the time domain results to the frequency domain for analysis, and obtain the impedance spectrum results of the left and right ends of the injected cross-connect box.

[0081] The diagnostic module 300 is used to diagnose potential defects in the outer sheath and main insulation of three-phase cables based on impedance spectrum results.

[0082] Optionally, in one embodiment of this application, the fused impedance spectrum of each phase of the impedance spectrum result can be:

[0083] Among them, Z C,X Let X be the capacitance of phase X corresponding to the cross-connection box, where X = A, B, C, and Z. in,1 Z in,2 Z in,3 These represent the series fused impedance spectra of the corresponding signals, and α and β are the scaling factors of the test results, respectively:

[0084] Optionally, in one embodiment of this application, the diagnostic module 300 includes a calculation unit.

[0085] The calculation unit is used to determine potential defects in the outer sheath and main insulation based on the combined impedance spectrum of each phase using a preset analysis formula. The preset analysis formula can be:

[0086] Where X = A, B, C, A, B, C represent the A, B, and C phases corresponding to the MN cross-connection box, respectively, and Z... h (f) is the pre-updated health-state impedance spectrum in the system, β h (f) is the propagation constant under healthy conditions, Z X Z represents the fused impedance spectrum of each phase. X (f) represents the fusion impedance spectrum resistance of phase X at frequency f, where f h f l Let f represent the upper frequency f used for integral transform analysis. h and lower limit frequency f l R X (·) represents the diagnostic result of phase X, e represents the natural constant, and L c This indicates the total length of the cable to be tested.

[0087] Optionally, in one embodiment of this application, after obtaining the time-domain result, a filtering module is further included.

[0088] The filtering module is used to filter the time-domain waveform in the time-domain result using discrete wavelet transform and a hard thresholding method. The hard thresholding method can be expressed as:

[0089] Where, ψ a,b Let K be the wavelet transform coefficient, ψ(·) be the wavelet basis function, and K be the wavelet transform coefficient. δ The values ​​represent the wavelet transform coefficients after hard thresholding, where a is the scale parameter in the wavelet transform, b is the time parameter in the wavelet transform, t represents time, and δ represents the set hard threshold.

[0090] It should be noted that the foregoing explanation of the embodiment of the frequency domain diagnostic method for power cable defects based on the cross-interconnection box structure also applies to the frequency domain diagnostic device for power cable defects based on the cross-interconnection box structure in this embodiment, and will not be repeated here.

[0091] The frequency domain diagnostic device for power cable defects based on a cross-connection box structure proposed in this application can analyze the time domain results obtained by injecting broadband signals into the terminals of the three-phase shielding layers of the cross-connection box, and then obtain the impedance spectrum results of the injected signals at both ends of the cross-connection box. This allows for the diagnosis of potential defects in the outer sheath and main insulation of the three-phase cable. This solves the problem that the traveling wave reflection method in related technologies, when identifying main insulation faults, cannot avoid direct electrical connection to the cable core, greatly limiting the application scenarios of the traveling wave injection method. It can only be used for pre-construction testing and defect assessment after cable failure, and the equipment requirements and testing costs are high, failing to meet the requirements of daily operation and maintenance inspections and various diagnostic scenarios.

[0092] Figure 4 is a schematic diagram of the structure of an electronic device provided in an embodiment of this application. The electronic device may include:

[0093] The memory 401, the processor 402, and the computer program stored on the memory 401 and capable of running on the processor 402.

[0094] When the processor 402 executes the program, it implements the frequency domain diagnosis method for power cable defects based on the cross-connection box structure provided in the above embodiments.

[0095] Furthermore, electronic devices also include:

[0096] Communication interface 403 is used for communication between memory 401 and processor 402.

[0097] The memory 401 is used to store computer programs that can run on the processor 402.

[0098] The memory 401 may include high-speed RAM memory, and may also include non-volatile memory, such as at least one disk storage device.

[0099] If the memory 401, processor 402, and communication interface 403 are implemented independently, they can be interconnected via a bus to communicate with each other. The bus can be an Industry Standard Architecture (ISA) bus, a Peripheral Component Interconnect (PCI) bus, or an Extended Industry Standard Architecture (EISA) bus, etc. Buses can be categorized as address buses, data buses, control buses, etc. For ease of representation, only one thick line is used in Figure 4, but this does not imply that there is only one bus or one type of bus.

[0100] Optionally, in a specific implementation, if the memory 401, processor 402, and communication interface 403 are integrated on a single chip, then the memory 401, processor 402, and communication interface 403 can communicate with each other through an internal interface.

[0101] Processor 402 may be a central processing unit (CPU), an application specific integrated circuit (ASIC), or one or more integrated circuits configured to implement the embodiments of this application.

[0102] This application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described frequency domain diagnostic method for power cable defects based on a cross-connection box structure.

[0103] This application also provides a computer program product that can run computer instructions. When these computer instructions are executed by a processor, they implement the frequency domain diagnostic method for power cable defects based on a cross-connection box structure provided in this application.

[0104] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0105] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "N" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0106] Any process or method described in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or N executable instructions for implementing custom logic functions or processes, and the scope of the preferred embodiments of this application includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as should be understood by those skilled in the art to which embodiments of this application pertain.

[0107] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of computer-readable media include: an electrical connection having one or more wires (electronic device), a portable computer disk drive (magnetic device), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Alternatively, the computer-readable medium may be paper or other suitable media on which the program can be printed, since the program can be obtained electronically by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in a computer memory.

[0108] It should be understood that the various parts of this application can be implemented using hardware, software, firmware, or a combination thereof. In the above embodiments, the N steps or methods can be implemented using software or firmware stored in memory and executed by a suitable instruction execution system. If implemented in hardware, as in another embodiment, it can be implemented using any one or more of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0109] Those skilled in the art will understand that all or part of the steps of the methods in the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, the program includes one or a combination of the steps of the method embodiments.

[0110] Furthermore, the functional units in the various embodiments of this application can be integrated into a processing module, or each unit can exist physically separately, or two or more units can be integrated into a module. The integrated module can be implemented in hardware or as a software functional module. If the integrated module is implemented as a software functional module and sold or used as an independent product, it can also be stored in a computer-readable storage medium.

[0111] The storage medium mentioned above can be a read-only memory, a disk, or an optical disk, etc. Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of this application.

Claims

1. A frequency domain diagnostic method for power cable defects based on a cross-connection box structure, characterized in that, Includes the following steps: A broadband signal was injected into the terminals of the three-phase shielded cross-connection box to obtain the time-domain results; Based on the time-domain results, the impedance spectrum results of the left and right ends of the injected cross-connect box are obtained by mapping the time-domain results to the frequency domain. Based on the impedance spectrum results, potential defects in the outer sheath and main insulation of the three-phase cable can be diagnosed.

2. The method according to claim 1, characterized in that, The impedance spectrum for each phase is as follows: Among them, Z C,X For the X phase of the cross-connection box, X = A, B, C, Z in,1 Z in,2 Z in,3 These represent the series fused impedance spectra of the corresponding signals, and α and β are the scaling factors of the test results, respectively:

3. The method according to claim 2, characterized in that, The method of diagnosing potential defects in the outer sheath and main insulation of three-phase cables based on the impedance spectrum results includes: Based on the combined impedance spectrum of each phase, the potential defects of the outer sheath and main insulation are obtained using a preset analysis formula, wherein the preset analysis formula is: Where X = A, B, C, A, B, C represent phases A, B, and C corresponding to the MN cross-connect box, respectively, and Z h (f) is the pre-updated health-state impedance spectrum in the system, γ h (f) is the propagation constant under healthy conditions, Z X Z represents the fused impedance spectrum of each phase. X (f) represents the fusion impedance spectrum resistance of phase X at frequency f, where f h f l Let f represent the upper frequency f used for integral transform analysis. h and lower limit frequency f l R X (·) represents the diagnostic result of phase X, e represents the natural constant, and L c This indicates the total length of the cable to be tested.

4. The method according to claim 1, characterized in that, After obtaining the time-domain result, the following is also included: Discrete wavelet transform is used, and a hard thresholding method is selected to filter the time-domain waveform in the time-domain result. The hard thresholding method is as follows: Where, ψ a,b Let K be the wavelet transform coefficient, ψ(·) be the wavelet basis function, and K be the wavelet transform coefficient. δ The values ​​represent the wavelet transform coefficients after hard thresholding, where a is the scale parameter in the wavelet transform, b is the time parameter in the wavelet transform, t represents time, and δ represents the set hard threshold.

5. A frequency domain diagnostic device for power cable defects based on a cross-connection box structure, characterized in that, include: The calculation module is used to inject broadband signals through the terminals of the three-phase shielded cross-connection box to obtain time-domain results; The analysis module is used to map the time-domain results to the frequency domain for analysis, and obtain the impedance spectrum results of the left and right ends of the injected cross-connect box; The diagnostic module is used to diagnose potential defects in the outer sheath and main insulation of three-phase cables based on the impedance spectrum results.

6. The apparatus according to claim 5, characterized in that, The impedance spectrum for each phase is as follows: Among them, Z C,X For the X phase of the cross-connection box, X = A, B, C, Z in,1 Z in,2 Z in,3 These represent the series fused impedance spectra of the corresponding signals, and α and β are the scaling factors of the test results, respectively:

7. The apparatus according to claim 6, characterized in that, The diagnostic module includes: The calculation unit is used to determine the potential defects of the outer sheath and main insulation based on the combined impedance spectrum of each phase using a preset analysis formula, wherein the preset analysis formula is: Where X = A, B, C, A, B, C represent phases A, B, and C corresponding to the MN cross-connect box, respectively, and Z h (f) is the pre-updated health-state impedance spectrum in the system, γ h (f) is the propagation constant under healthy conditions, Z X Z represents the fused impedance spectrum of each phase. X (f) represents the fusion impedance spectrum resistance of phase X at frequency f, where f h f l Let f represent the upper frequency f used for integral transform analysis. h and lower limit frequency f l R X (·) represents the diagnostic result of phase X, e represents the natural constant, and L c This indicates the total length of the cable to be tested.

8. An electronic device, characterized in that, include: The method includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the frequency domain diagnostic method for power cable defects based on a cross-connection box structure as described in any one of claims 1-4.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, The program is executed by the processor to implement the frequency domain diagnostic method for power cable defects based on a cross-connection box structure as described in any one of claims 1-4.

10. A computer program product, characterized in that, When the computer program is executed, it is used to implement the frequency domain diagnostic method for power cable defects based on a cross-connection box structure as described in any one of claims 1-4.

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