CN114217175B - Method, device and terminal for detecting electrical branch defects of power cable - Google Patents
Method, device and terminal for detecting electrical branch defects of power cable Download PDFInfo
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- G—PHYSICS
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/12—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing
- G01R31/1227—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials
- G01R31/1263—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation
- G01R31/1272—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation of cable, line or wire insulation, e.g. using partial discharge measurements
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
- G01R27/025—Measuring very high resistances, e.g. isolation resistances, i.e. megohm-meters
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
- G01R27/26—Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric constants ; Measuring impedance or related variables
- G01R27/2688—Measuring quality factor or dielectric loss, e.g. loss angle, or power factor
- G01R27/2694—Measuring dielectric loss, e.g. loss angle, loss factor or power factor
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
- G01R31/083—Locating faults in cables, transmission lines, or networks according to type of conductors in cables, e.g. underground
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
- G01R31/52—Testing for short-circuits, leakage current or ground faults
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
- Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
- Y04S10/00—Systems supporting electrical power generation, transmission or distribution
- Y04S10/50—Systems or methods supporting the power network operation or management, involving a certain degree of interaction with the load-side end user applications
- Y04S10/52—Outage or fault management, e.g. fault detection or location
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Abstract
The invention provides a method, a device and a terminal for detecting electrical branch defects of a power cable. The method comprises the following steps: based on an electrical branch aging experiment, acquiring conductivity and capacitance characteristic parameters of cable sample sections of different electrical branch defect types, and simulating corresponding positioning signals; based on a network analyzer, acquiring a positive frequency single-ended impedance spectrum function signal of the cable to be tested, and multiplying the positive frequency single-ended impedance spectrum function signal of the cable to be tested with a Hamming window function to obtain a denoised positive frequency signal of the cable to be tested; obtaining a frequency domain signal of the cable to be tested based on the denoised positive frequency signal of the cable to be tested; obtaining a positioning signal of the cable to be tested based on the frequency domain signal of the cable to be tested; and determining the type and the position of the electrical branch defect of the cable to be tested based on the positioning signals of the cable to be tested and the positioning signals of the cable sample sections of different electrical branch defect types. The invention can detect the local defect of the cable and accurately determine the type of the electrical branch defect and the fault position of the cable to be tested.
Description
Technical Field
The invention relates to the technical field of safe operation of cables, in particular to a method, a device and a terminal for detecting electrical branch defects of a power cable.
Background
The cable plays an extremely important role in the electric energy transmission of the modern urban power grid system, and the running state of the cable directly influences the safety and stability of the large-scale electric system. The design life of the cable is generally 20 to 30 years, but the cable in actual operation often induces permanent faults due to local latent defects such as local degradation or breakage of insulation, and once the cable faults occur, the cable faults can cause shutdown and even out of control of a large-scale electrical system, so that serious economic loss and social influence are caused. The power cable in the urban power supply system is laid in a cable trench or directly buried underground, and under the action of temperature, electric stress, mechanical force, moisture, oil quality, organic compounds, alkali, acid, microorganisms and the like, insulation is easy to corrode and permeate to form insulation local defects, meanwhile, the underground power cable is always subjected to insulation damage due to mechanical external force, and finally the cable is permanently failed. It has been investigated that accidents caused by local defects in the insulation of power cables account for about 40% of cable equipment accidents. Therefore, improving the detection level of the insulation local defect of the power cable is a key for guaranteeing the stable operation of the power system.
Currently, conventional methods for detecting the operation state of a cable include a non-electrical parameter method and an electrical parameter method. However, the existing method can only evaluate the overall state or the general defects of the cable, but cannot detect the local defects of the cable and accurately determine the type of the insulation defects of the cable.
Disclosure of Invention
The embodiment of the invention provides a method, a device and a terminal for detecting electrical branch defects of a power cable, which are used for solving the problem that the existing method can only evaluate the overall state or the universality defects of the cable, but can not detect the local defects of the cable and accurately determine the insulation defect types of the cable.
In a first aspect, an embodiment of the present invention provides a method for detecting an electrical branch defect of a power cable, including:
based on an electrical branch aging experiment, acquiring conductivity and capacitance characteristic parameters of cable sample sections of different electrical branch defect types, and simulating corresponding positioning signals according to the conductivity and capacitance characteristic parameters;
based on a network analyzer, acquiring a positive frequency single-ended impedance spectrum function signal of the cable to be tested, and multiplying the positive frequency single-ended impedance spectrum function signal of the cable to be tested with a Hamming window function to obtain a denoised positive frequency signal of the cable to be tested;
obtaining a frequency domain signal of the cable to be tested based on the denoised positive frequency signal of the cable to be tested;
Obtaining a positioning signal of the cable to be tested based on the frequency domain signal of the cable to be tested;
And determining the type and the position of the electrical branch defect of the cable to be tested based on the positioning signals of the cable to be tested and the positioning signals of the cable sample sections of different electrical branch defect types.
In one possible implementation manner, obtaining the frequency domain signal of the cable to be tested based on the denoised positive frequency signal of the cable to be tested includes:
And carrying out conjugate symmetry solving on the denoised positive frequency signal of the cable to be tested to obtain a negative frequency signal of the cable to be tested, and obtaining a frequency domain signal of the cable to be tested according to the denoised positive frequency signal of the cable to be tested and the negative frequency signal of the cable to be tested.
In one possible implementation manner, obtaining the positioning signal of the cable to be measured based on the frequency domain signal of the cable to be measured includes:
performing Fourier transform on the frequency domain signal of the cable to be tested to obtain a time domain signal of the cable to be tested, multiplying the time domain signal of the cable to be tested by the wave speed of the electromagnetic wave to obtain a space domain signal of the cable to be tested, and comparing the space domain signal of the cable to be tested with the space domain signal of the non-fault cable to obtain a positioning signal of the cable to be tested.
In one possible implementation manner, based on an electrical branch aging experiment, obtaining electrical conductance and capacitance characteristic parameters of cable sample sections of different electrical branch defect types, and simulating corresponding positioning signals according to the electrical conductance and capacitance characteristic parameters, including:
For each cable sample section, measuring the capacitance of the cable sample section through a network analyzer, and obtaining the conductance of the cable sample section through a three-electrode system; and obtaining a positive frequency single-ended impedance spectrum function signal of the cable sample section according to the capacitance and the conductance simulation of the cable sample section, and obtaining a positioning signal of the cable sample section based on the positive frequency single-ended impedance spectrum function signal of the cable sample section.
In one possible implementation, a three-electrode system includes a high voltage electrode, a guard electrode, and a test electrode;
The outer semi-conductive layer of the cable sample section is connected with the test electrode, the inner semi-conductive layer of the cable sample section is connected with the high-voltage electrode, and the protection electrode is horizontally arranged on the surface of the insulating layer of the cable sample section;
the high-voltage electrode is connected with a high-voltage test power supply, the test electrode is connected with a test interface of the digital picoampere meter, the grounding ground of the digital picoampere meter is grounded, and the protection electrode is grounded.
In one possible implementation, the aging time period varies from cable segment to cable segment.
In a second aspect, an embodiment of the present invention provides a power cable electrical branch defect detection apparatus, including:
the aging module is used for acquiring the conductivity and capacitance characteristic parameters of the cable sample sections of different electrical branch defect types based on an electrical branch aging experiment, and simulating corresponding positioning signals according to the conductivity and capacitance characteristic parameters;
The denoising module is used for acquiring a positive frequency single-ended impedance spectrum function signal of the cable to be measured based on the network analyzer, multiplying the positive frequency single-ended impedance spectrum function signal of the cable to be measured by a Hamming window function, and obtaining a denoised positive frequency signal of the cable to be measured;
the frequency domain signal acquisition module is used for acquiring a frequency domain signal of the cable to be tested based on the denoised positive frequency signal of the cable to be tested;
The positioning signal acquisition module is used for acquiring a positioning signal of the cable to be tested based on the frequency domain signal of the cable to be tested;
The defect determining module is used for determining the type and the position of the electrical branch defect of the cable to be tested based on the positioning signals of the cable to be tested and the positioning signals of the cable sample sections of different electrical branch defect types.
In one possible implementation manner, the frequency domain signal acquisition module is specifically configured to:
And carrying out conjugate symmetry solving on the denoised positive frequency signal of the cable to be tested to obtain a negative frequency signal of the cable to be tested, and obtaining a frequency domain signal of the cable to be tested according to the denoised positive frequency signal of the cable to be tested and the negative frequency signal of the cable to be tested.
In a third aspect, an embodiment of the present invention provides a terminal, including a memory, a processor, and a computer program stored in the memory and executable on the processor, where the processor implements the steps of the power cable electrical branch defect detection method according to the first aspect or any one of the possible implementations of the first aspect when the processor executes the computer program.
In a fourth aspect, embodiments of the present invention provide a computer storage medium storing a computer program which, when executed by a processor, implements the steps of the power cable electrical branch defect detection method as described above in the first aspect or any one of the possible implementations of the first aspect.
The embodiment of the invention provides a method, a device and a terminal for detecting electric branch defects of a power cable, which can detect local defects of the cable and accurately determine the type of the electric branch defects and fault positions of the cable to be detected by comparing positioning signals of different types of the electric branch defects with positioning signals of the cable to be detected; in addition, the influence of spectrum leakage can be reduced by multiplying the signal of the positive frequency single-ended impedance spectrum function of the cable to be tested by the Hamming window function.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the embodiments or the description of the prior art will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flowchart of an implementation of a method for detecting a power cable electrical branch defect according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of an electrical branch aging circuit for a cable sample section according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a capacitance measurement circuit according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a conductance measurement circuit according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of a simulated amplitude spectrum provided by an embodiment of the present invention;
FIG. 6 is a schematic diagram of a simulated phase spectrum provided by an embodiment of the present invention;
FIG. 7 is a schematic diagram of a time domain function of a Hamming window provided by an embodiment of the present invention;
FIG. 8 is a schematic diagram of an amplitude-frequency function of a Hamming window provided by an embodiment of the present invention;
FIG. 9 is a schematic diagram of a signal measurement of a positive frequency single-ended impedance spectrum function of a cable under test according to an embodiment of the present invention;
FIG. 10 is a schematic diagram of a measurement result of a positive frequency single-ended impedance spectrum function signal of a cable to be tested according to an embodiment of the present invention;
FIG. 11 is a schematic diagram of a positioning signal of a cable under test according to an embodiment of the present invention;
FIG. 12 is a schematic diagram of a power cable electrical branch defect detection apparatus according to an embodiment of the present invention;
Fig. 13 is a schematic diagram of a terminal according to an embodiment of the present invention.
Detailed Description
In the following description, for purposes of explanation and not limitation, specific details are set forth such as the particular system architecture, techniques, etc., in order to provide a thorough understanding of the embodiments of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail.
For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the following description will be made by way of specific embodiments with reference to the accompanying drawings.
Conventional methods for detecting the operation state of a cable include a non-electrical parameter method and an electrical parameter method. The non-electrical parameter method realizes the operation state diagnosis by detecting the physical and chemical properties of the cable, and is mainly used for evaluating the whole aging life of the cable, such as the Elongation At Break (EAB) and compression modulus detection of the cable material. The cable electrical parameter detection method mainly comprises measurement of cable insulation resistance, withstand voltage test, leakage current test, dielectric loss detection and the like. However, the above electrical method can only evaluate the overall state or the general defect of the cable, and cannot find the cable insulation local latency defect. The recent single-ended impedance method-based power cable insulation local defect positioning detection method proves great potential in nondestructive fine detection of the power cable, and a small amount of current researches show that although the method can realize effective detection of the power cable local insulation defect, the classification of the type and severity of the insulation defect is still to be further studied.
In summary, the influence rule and action mechanism of different insulation defect types of the power cable on the single-end impedance spectrum are analyzed in a refined manner, the relation between the insulation defect parameters and the single-end impedance spectrum characteristics is mastered, and further, equipment capable of realizing insulation defect identification and positioning is developed, so that theoretical and technical support can be provided for improving the maintenance refinement level of the power cable and improving the power supply reliability.
Referring to fig. 1, a flowchart of an implementation of the method for detecting an electrical branch defect of a power cable according to an embodiment of the present invention is shown, and details are as follows:
In S101, based on the electrical branch aging experiment, the electrical conductance and capacitance characteristic parameters of the cable sample sections with different electrical branch defect types are obtained, and the corresponding positioning signals are simulated according to the electrical conductance and capacitance characteristic parameters.
In some embodiments of the present invention, the S101 may include:
For each cable sample section, measuring the capacitance of the cable sample section through a network analyzer, and obtaining the conductance of the cable sample section through a three-electrode system; and obtaining a positive frequency single-ended impedance spectrum function signal of the cable sample section according to the capacitance and the conductance simulation of the cable sample section, and obtaining a positioning signal of the cable sample section based on the positive frequency single-ended impedance spectrum function signal of the cable sample section.
In some embodiments of the invention, a three electrode system includes a high voltage electrode, a guard electrode, and a test electrode;
The outer semi-conductive layer of the cable sample section is connected with the test electrode, the inner semi-conductive layer of the cable sample section is connected with the high-voltage electrode, and the protection electrode is horizontally arranged on the surface of the insulating layer of the cable sample section;
the high-voltage electrode is connected with a high-voltage test power supply, the test electrode is connected with a test interface of the digital picoampere meter, the grounding ground of the digital picoampere meter is grounded, and the protection electrode is grounded.
In some embodiments of the invention, the aging times are different for different cable sample segments.
In the embodiment of the invention, a 10kV cable is segmented, cut into a cable sample section with the length of 20cm, a copper shield and an outer semi-conductive layer at the positions of 2.5cm at two ends are removed, and XLPE main insulation is reserved. The structure of which is shown in figure 2. In order to build the needle-plate electrode structure required by leading the electric branch, steel needles are pricked into the outer side of the cable sheath, the distance between the needle point position and the inner shielding layer of the cable is ensured to be 2mm, the distance between the steel needles is not less than 5mm, and the number of the steel needles in a single group is not less than 10. For ease of drawing, only 3 steel needles are drawn in fig. 2.
And applying 10kV power frequency voltage at the cable core, wherein the pressurizing time is not longer than 5 hours, and synchronously applying voltage to a plurality of groups of cable sample sections to obtain cable sample sections with different electrical branch aging durations. And after the aging is finished, the power supply is disconnected, and the grounding wire is removed for standby.
In this embodiment, the shielding layer is a semiconductive layer. That is, the outer semiconductive layer is the outer shielding layer and the inner semiconductive layer is the inner shielding layer.
And then, carrying out electric parameter measurement on the area containing the electric branch defect. Firstly, a cable slice is manufactured, and the cable slice is of a circular ring structure and consists of an inner semi-conductive layer, an insulating layer and an outer semi-conductive layer. Wherein the outer diameter of the sliced sample is 23mm, the inner diameter is 8mm, and the thickness of the sample is 5mm.
When capacitance is measured, the cable slice sample is connected with the testing end of the network analyzer through the outer semi-conductive layer, and is tested through the connection of the inner semi-conductive layer, and the capacitance value of the cable slice sample can be measured by using the S11 parameter because the insulation resistance is large and the inductance is negligible, the frequency range is set to be 100kHz-300MHz during measurement, and the capacitance value of each frequency range is read by a Smith chart. The capacitance measuring circuit diagram is shown in fig. 3, and is connected with a network analyzer through a measuring clamp.
Referring to fig. 4, a schematic diagram of a three-electrode system is shown. The cable slice is of a circular structure and consists of an inner semiconductive layer, an insulating layer (crosslinked polyethylene) and an outer semiconductive layer. Wherein the outer diameter of the sliced sample is 23mm, the inner diameter is 8mm, and the thickness of the sample is 5mm. The three electrodes are made of copper, the shapes of the high-voltage electrode and the test electrode are round tubes with adjustable radiuses, the shape of the protection electrode is a round ring, the diameter of the test electrode is adjustable from 22mm to 25mm, the length of the test electrode is 15mm, the diameter of the high-voltage electrode is adjustable from 7mm to 10mm, and the length of the test electrode is 15mm. The outer diameter of the protective electrode is 20mm, the inner diameter is 10mm, and the thickness is 0.2mm.
The test electrode is connected with a digital picoammeter for measuring the conductance current. The digital picoampere meter is model B2983A, the minimum measuring range is 2pA, and the maximum reading rate is 20000 readings per second.
When the conductance is tested, the semi-conductive layer outside the cable slice is connected with the test electrode of the three-electrode system, the protection electrode is horizontally arranged on the surface of the insulating slice, the semi-conductive layer inside the cable slice is connected with the high-voltage electrode, the high-voltage electrode is connected with a high-voltage test power supply, the protection electrode is grounded, the test electrode is connected with the test interface of the digital picoampere meter, and the grounding of the digital picoampere meter is grounded.
For each cable sample section, the following steps are performed to obtain positioning signals of the respective cable sample section:
1) Setting resistance, inductance, conductance and capacitance values of a unit cable length before and after aging of the electric branch, and solving to obtain a single-ended impedance spectrum function signal of a positive frequency end according to a transmission line model (a cable sample section), wherein a broadband impedance spectrum formula is as follows:
Where Z 0 is the characteristic impedance, Γ L is the reflection coefficient, α is the real part of the impedance spectrum propagation coefficient, and β is the imaginary part of the propagation coefficient. The characteristic impedance and propagation coefficient are functions of electrical parameters and frequency per unit length of the system, as follows:
Where R is the resistance per unit length of the cable, L is the inductance per unit length of the cable, G is the conductance per unit length of the cable, and C is the capacitance per unit length of the cable. The resistance per unit cable length is calculated by using the conductivity (17.5 mu omega mm) of copper, the conductivity is obtained by conversion of a picometer, the capacitance is measured by a network analyzer, and the inductance is unchanged and the same as that of a fault-free cable.
The simulated amplitude spectrum and the spectrum curves are shown in fig. 5 and 6.
2) Multiplying the positive frequency domain impedance spectrum function with a hamming window with the same length to reduce the influence of spectrum leakage, then carrying out conjugate symmetry to solve a negative frequency signal, and utilizing a fast Fourier algorithm to solve a time domain signal, wherein the formula of the fast Fourier transform is as follows:
Where X is the time domain signal to be processed, N is the number of sampling points, and w n is the frequency corresponding to each sampling point.
The expression of the hamming window function is as follows:
the width of the main lobe of the Hamming window is The side lobe peak attenuation is 41dB, and the time domain function and the amplitude-frequency function of the Hamming window are shown in figures 7 and 8.
3) And discarding the imaginary part of the time domain signal, multiplying the time domain signal of the cable sample section with the electromagnetic wave velocity to obtain a space domain signal of the cable sample section, and comparing the space domain signal of the cable sample section with the space domain signal of the non-fault cable to obtain the positioning signal of the cable sample section.
A non-faulty cable is a good cable without electrical branch defects.
In S102, based on the network analyzer, a positive frequency single-ended impedance spectrum function signal of the cable to be tested is obtained, and the positive frequency single-ended impedance spectrum function signal of the cable to be tested is multiplied by a hamming window function to obtain a denoised positive frequency signal of the cable to be tested.
Before measurement, a measurement end is firstly manufactured to realize correct connection with a network analyzer. In the embodiment of the invention, in order to reduce errors caused by unmatched impedance of the measuring lead, the crimping N head is used for realizing effective connection of the cable conductor, the copper shield and the network analyzer. In the manufacturing process, the copper shield and the N-head metal shell are ensured to be completely pressed, and the conductor and the N-head needle electrode are well welded so as to reduce the impedance mismatch degree of the section.
During measurement, the cable to be measured is connected to a network analyzer through an N-type connector, and the waveform of the measured positive frequency single-ended impedance spectrum function signal is read through the network analyzer, wherein the connection mode is shown in fig. 9.
The model of the network analyzer is Agilent E5061B, the test frequency range is 100kHz to 2GHz, and the highest sampling point number is 1601.
Before measurement, the port 1 of the network analyzer is first calibrated, then the S11 parameter is measured, and the read waveform is shown in fig. 10. The upper curve is a measured S11 Smith chart, the chart adopts a two-dimensional circular coordinate system to realize the characterization of the impedance sampling parameters, and the chart can know that the measured cable S11 parameters show obvious periodic characteristics.
For a uniform transmission line (a perfect power cable may equally be a uniform transmission line), its amplitude spectrum exhibits the same periodic characteristics as the phase spectrum, and after inverse fourier transformation it will exhibit flat time domain curve characteristics. Along with the development of the electrical branch defect, the amplitude spectrum and the phase spectrum of the electrical branch defect are distorted, and the reason for the distortion is that the capacitance value and the conductivity value in unit length are changed caused by the electrical branch defect, and the changes cause larger distortion in a time domain curve and obvious local peak values when the frequency domain impedance spectrum and the phase spectrum are changed.
In order to realize the positioning of the electrical branch defect, the amplitude spectrum and the phase spectrum data are derived after measurement, and the noise influence is reduced by utilizing a Hamming window, so that a denoised positive frequency signal is obtained.
In S103, a frequency domain signal of the cable to be tested is obtained based on the denoised positive frequency signal of the cable to be tested.
In some embodiments of the present invention, the step S103 may include:
And carrying out conjugate symmetry solving on the denoised positive frequency signal of the cable to be tested to obtain a negative frequency signal of the cable to be tested, and obtaining a frequency domain signal of the cable to be tested according to the denoised positive frequency signal of the cable to be tested and the negative frequency signal of the cable to be tested.
The denoised positive frequency signal of the cable to be tested and the denoised negative frequency signal of the cable to be tested together form a frequency domain signal of the cable to be tested.
In S104, a positioning signal of the cable to be measured is obtained based on the frequency domain signal of the cable to be measured.
In some embodiments of the present invention, the S104 may include:
performing Fourier transform on the frequency domain signal of the cable to be tested to obtain a time domain signal of the cable to be tested, multiplying the time domain signal of the cable to be tested by the wave speed of the electromagnetic wave to obtain a space domain signal of the cable to be tested, and comparing the space domain signal of the cable to be tested with the space domain signal of the non-fault cable to obtain a positioning signal of the cable to be tested.
And converting the frequency domain signal into a time domain, wherein the time domain signal is a function of the signal amplitude and time, and multiplying the transverse axis time data by the wave velocity in the cable, namely the wave velocity of the electromagnetic wave, so as to obtain the spatial domain signal of the signal amplitude and the position. Comparing the space domain signals of the cable to be tested with those of the non-fault cable to obtain the positioning signals of the cable to be tested, as shown in the electrical branch defect positioning chart in figure 11. Multiple electrical branch faults existing in the middle section of the cable can be clearly distinguished in the drawing.
In S105, the electrical branch defect type and position of the cable to be tested are determined based on the positioning signal of the cable to be tested and the positioning signals of the cable sample sections of different electrical branch defect types.
Comparing the positioning signals of the fault area of the cable to be tested with the positioning signals of the cable sample sections of different electrical branch defect types, and judging the same electrical branch defect type if the characteristics are the same. As shown in fig. 11, the defect location can be seen from this figure.
According to the embodiment of the invention, the local defects of the cable can be detected and the type of the electrical branch defect and the fault position of the cable to be detected can be accurately determined by comparing the positioning signals of different types of the electrical branch defect with the positioning signals of the cable to be detected; in addition, the method of multiplying the positive frequency single-ended impedance spectrum function signal of the cable to be tested by the Hamming window function can reduce the influence of spectrum leakage.
The embodiment of the invention is suitable for detecting and positioning the electrical branch aging defects in the insulation in the range of the 10kV distribution cable, prevents secondary damage problems possibly caused by traditional voltage withstanding test methods and the like, and meanwhile, the method is beneficial to finding early electrical branch aging phenomena in the insulation, can find the defect problems in the insulation in advance, and improves the accuracy and safety of cable overhaul.
By developing an electric branch accelerated aging experiment in a cable sample section in a laboratory, measuring data such as capacitance, conductance and the like of different electric branch types and different electric branch aging stages, corresponding infinitesimal parameter distribution characteristics are obtained, and effective support for reliability of measurement results is realized. Meanwhile, by utilizing the measurement result, single-ended impedance spectrum measurement can be directly carried out on the 10kV cable insulation in field operation, so that the distribution characteristics of each micro-element parameter are determined, the position of the electrical branch defect is determined by combining an IFFT algorithm, defect positioning is realized, and cable maintenance accuracy is improved.
The embodiment of the invention designs a three-electrode system structure for triggering and measuring a small-section cable sample, can realize accurate measurement of volume conductivity and surface conductivity, has adjustable radiuses of a measuring electrode and a high-voltage electrode, ensures full contact between the sample and the electrode, and controls experimental errors. The fast Fourier algorithm provided by the embodiment of the invention improves the algorithm calculation speed and the efficiency of locating and classifying faults. The advantage of narrow Hamming window side lobe width is fully utilized in the selection of the window function, and the influence of the window function on the original frequency spectrum is reduced as much as possible. During processing algorithm, labview software processed by a computer is utilized, the acquisition and display functions are powerful, the sampling data frequency can be selected, the stored data quantity can be changed, the window function type and length can be modified, and the fault positioning requirements of broadband impedance spectrums under different requirements can be met. The testing method of the network analyzer of the disposable N-head by direct compression joint, which is designed by the embodiment of the invention, is simple to realize, has good anti-interference capability of the system and provides a theoretical basis for realizing the field cable fault locating and overhauling technology.
Compared with the prior art, the device provided by the invention has the advantages that the structure is simple, the preparation of the test platform is easy, the real-time measurement of broadband impedance spectrum can be realized, and meanwhile, a research approach is provided for measuring the electrical parameters of the unit length of the cable, so that the device has an important significance for verifying and perfecting the theoretical model of the fault classification positioning technology.
It should be understood that the sequence number of each step in the foregoing embodiment does not mean that the execution sequence of each process should be determined by the function and the internal logic, and should not limit the implementation process of the embodiment of the present invention.
The following are device embodiments of the invention, for details not described in detail therein, reference may be made to the corresponding method embodiments described above.
Fig. 12 is a schematic structural diagram of a power cable electrical branch defect detection device according to an embodiment of the present invention, and for convenience of explanation, only a portion related to the embodiment of the present invention is shown, which is described in detail below:
As shown in fig. 12, the power cable electrical branch defect detection apparatus 30 includes: the device comprises an aging module 31, a denoising module 32, a frequency domain signal acquisition module 33, a positioning signal acquisition module 34 and a defect determination module 35.
The aging module 31 is configured to obtain conductivity and capacitance characteristic parameters of cable sample sections of different types of electrical branch defects based on an electrical branch aging experiment, and simulate corresponding positioning signals according to the conductivity and capacitance characteristic parameters;
The denoising module 32 is configured to obtain a positive frequency single-ended impedance spectrum function signal of the cable to be measured based on the network analyzer, and multiply the positive frequency single-ended impedance spectrum function signal of the cable to be measured with a hamming window function to obtain a denoised positive frequency signal of the cable to be measured;
The frequency domain signal obtaining module 33 is configured to obtain a frequency domain signal of the cable to be tested based on the denoised positive frequency signal of the cable to be tested;
the positioning signal acquisition module 34 is configured to obtain a positioning signal of the cable to be tested based on the frequency domain signal of the cable to be tested;
The defect determining module 35 is configured to determine the type and the position of the electrical branch defect of the cable to be tested based on the positioning signal of the cable to be tested and the positioning signals of the cable sample sections of different electrical branch defect types.
In one possible implementation, the frequency domain signal acquisition module 33 is specifically configured to:
And carrying out conjugate symmetry solving on the denoised positive frequency signal of the cable to be tested to obtain a negative frequency signal of the cable to be tested, and obtaining a frequency domain signal of the cable to be tested according to the denoised positive frequency signal of the cable to be tested and the negative frequency signal of the cable to be tested.
In one possible implementation, the positioning signal acquisition module 34 is specifically configured to:
performing Fourier transform on the frequency domain signal of the cable to be tested to obtain a time domain signal of the cable to be tested, multiplying the time domain signal of the cable to be tested by the wave speed of the electromagnetic wave to obtain a space domain signal of the cable to be tested, and comparing the space domain signal of the cable to be tested with the space domain signal of the non-fault cable to obtain a positioning signal of the cable to be tested.
In one possible implementation, the aging module 31 is specifically configured to:
For each cable sample section, measuring the capacitance of the cable sample section through a network analyzer, and obtaining the conductance of the cable sample section through a three-electrode system; and obtaining a positive frequency single-ended impedance spectrum function signal of the cable sample section according to the capacitance and the conductance simulation of the cable sample section, and obtaining a positioning signal of the cable sample section based on the positive frequency single-ended impedance spectrum function signal of the cable sample section.
In one possible implementation, a three-electrode system includes a high voltage electrode, a guard electrode, and a test electrode;
The outer semi-conductive layer of the cable sample section is connected with the test electrode, the inner semi-conductive layer of the cable sample section is connected with the high-voltage electrode, and the protection electrode is horizontally arranged on the surface of the insulating layer of the cable sample section;
the high-voltage electrode is connected with a high-voltage test power supply, the test electrode is connected with a test interface of the digital picoampere meter, the grounding ground of the digital picoampere meter is grounded, and the protection electrode is grounded.
In one possible implementation, the aging time period varies from cable segment to cable segment.
Fig. 13 is a schematic diagram of a terminal according to an embodiment of the present invention. As shown in fig. 13, the terminal 4 of this embodiment includes: a processor 40, a memory 41 and a computer program 42 stored in the memory 41 and executable on the processor 40. The processor 40, when executing the computer program 42, implements the steps of the various power cable electrical branch defect detection method embodiments described above, such as S101 through S105 shown in fig. 1. Or the processor 40, when executing the computer program 42, performs the functions of the modules/units of the device embodiments described above, such as the functions of the modules/units 31-35 shown in fig. 12.
Illustratively, the computer program 42 may be partitioned into one or more modules/units that are stored in the memory 41 and executed by the processor 40 to complete the present invention. The one or more modules/units may be a series of computer program instruction segments capable of performing the specified functions, which instruction segments are used for describing the execution of the computer program 42 in the terminal 4. For example, the computer program 42 may be divided into modules/units 31 to 35 shown in fig. 12.
The terminal 4 may include, but is not limited to, a processor 40, a memory 41. It will be appreciated by those skilled in the art that fig. 13 is merely an example of the terminal 4 and does not constitute a limitation of the terminal 4, and may include more or less components than illustrated, or may combine certain components, or different components, e.g., the terminal may further include an input-output device, a network access device, a bus, etc.
The Processor 40 may be a central processing unit (Central Processing Unit, CPU), other general purpose Processor, digital signal Processor (DIGITAL SIGNAL Processor, DSP), application SPECIFIC INTEGRATED Circuit (ASIC), field-Programmable gate array (Field-Programmable GATE ARRAY, FPGA) or other Programmable logic device, discrete gate or transistor logic device, discrete hardware components, or the like. A general purpose processor may be a microprocessor or the processor may be any conventional processor or the like.
The memory 41 may be an internal storage unit of the terminal 4, such as a hard disk or a memory of the terminal 4. The memory 41 may also be an external storage device of the terminal 4, such as a plug-in hard disk, a smart memory card (SMART MEDIA CARD, SMC), a Secure Digital (SD) card, a flash memory card (FLASH CARD) or the like, which are provided on the terminal 4. Further, the memory 41 may also include both an internal storage unit and an external storage device of the terminal 4. The memory 41 is used for storing the computer program as well as other programs and data required by the terminal. The memory 41 may also be used for temporarily storing data that has been output or is to be output.
It will be apparent to those skilled in the art that, for convenience and brevity of description, only the above-described division of the functional units and modules is illustrated, and in practical application, the above-described functional distribution may be performed by different functional units and modules according to needs, i.e. the internal structure of the apparatus is divided into different functional units or modules to perform all or part of the above-described functions. The functional units and modules in the embodiment may be integrated in one processing unit, or each unit may exist alone physically, or two or more units may be integrated in one unit, where the integrated units may be implemented in a form of hardware or a form of a software functional unit. In addition, the specific names of the functional units and modules are only for distinguishing from each other, and are not used for limiting the protection scope of the present application. The specific working process of the units and modules in the above system may refer to the corresponding process in the foregoing method embodiment, which is not described herein again.
In the foregoing embodiments, the descriptions of the embodiments are emphasized, and in part, not described or illustrated in any particular embodiment, reference is made to the related descriptions of other embodiments.
Those of ordinary skill in the art will appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, or combinations of computer software and electronic hardware. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the solution. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
In the embodiments provided in the present invention, it should be understood that the disclosed apparatus/terminal and method may be implemented in other manners. For example, the apparatus/terminal embodiments described above are merely illustrative, e.g., the division of the modules or units is merely a logical function division, and there may be additional divisions when actually implemented, e.g., multiple units or components may be combined or integrated into another system, or some features may be omitted or not performed. Alternatively, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection via interfaces, devices or units, which may be in electrical, mechanical or other forms.
The units described as separate units may or may not be physically separate, and units shown as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.
In addition, each functional unit in the embodiments of the present invention may be integrated in one processing unit, or each unit may exist alone physically, or two or more units may be integrated in one unit. The integrated units may be implemented in hardware or in software functional units.
The integrated modules/units, if implemented in the form of software functional units and sold or used as stand-alone products, may be stored in a computer readable storage medium. Based on such understanding, the present invention may implement all or part of the procedures in the above-described embodiments of the method, or may be implemented by a computer program to instruct related hardware, where the computer program may be stored in a computer readable storage medium, and the computer program may implement the steps of the above-described embodiments of the method for detecting electrical branch defects of a power cable when executed by a processor. Wherein the computer program comprises computer program code which may be in source code form, object code form, executable file or some intermediate form etc. The computer readable medium may include: any entity or device capable of carrying the computer program code, a recording medium, a U disk, a removable hard disk, a magnetic disk, an optical disk, a computer Memory, a Read-Only Memory (ROM), a random access Memory (Random Access Memory, RAM), an electrical carrier signal, a telecommunications signal, a software distribution medium, and so forth. It should be noted that the computer readable medium may include content that is subject to appropriate increases and decreases as required by jurisdictions in which such content is subject to legislation and patent practice, such as in certain jurisdictions in which such content is not included as electrical carrier signals and telecommunication signals.
The above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention, and are intended to be included in the scope of the present invention.
Claims (9)
1. A method for detecting an electrical branch defect of a power cable, comprising:
Based on an electrical branch aging experiment, acquiring conductivity and capacitance characteristic parameters of cable sample sections of different electrical branch defect types, and simulating corresponding positioning signals according to the conductivity and capacitance characteristic parameters;
Based on a network analyzer, acquiring a positive frequency single-ended impedance spectrum function signal of a cable to be tested, and multiplying the positive frequency single-ended impedance spectrum function signal of the cable to be tested with a Hamming window function to obtain a denoised positive frequency signal of the cable to be tested;
Obtaining a frequency domain signal of the cable to be tested based on the denoised positive frequency signal of the cable to be tested;
Obtaining a positioning signal of the cable to be tested based on the frequency domain signal of the cable to be tested;
Determining the type and the position of the electrical branch defect of the cable to be tested based on the positioning signals of the cable to be tested and the positioning signals of the cable sample sections of different electrical branch defect types;
Based on the electrical branch aging experiment, the electrical conductance and capacitance characteristic parameters of the cable sample sections with different electrical branch defect types are obtained, and corresponding positioning signals are simulated according to the electrical conductance and capacitance characteristic parameters, comprising the following steps:
For each cable sample section, measuring the capacitance of the cable sample section through a network analyzer, and obtaining the conductance of the cable sample section through a three-electrode system; obtaining a positive frequency single-ended impedance spectrum function signal of the cable sample section according to the capacitance and the conductance simulation of the cable sample section, multiplying the positive frequency single-ended impedance spectrum function signal of the cable sample section by a Hamming window function, and then carrying out conjugate symmetry solving and fast Fourier transformation to obtain a time domain signal of the cable sample section; discarding the imaginary part of the time domain signal of the cable sample section, and multiplying the time domain signal of the cable sample section with the electromagnetic wave velocity to obtain a space domain signal of the cable sample section; and comparing the spatial domain signal of the cable sample section with the spatial domain signal of the non-fault cable to obtain a positioning signal of the cable sample section.
2. The method for detecting electrical branch defects of a power cable according to claim 1, wherein the obtaining the frequency domain signal of the cable to be tested based on the denoised positive frequency signal of the cable to be tested includes:
And carrying out conjugate symmetry solving on the denoised positive frequency signal of the cable to be tested to obtain a negative frequency signal of the cable to be tested, and obtaining a frequency domain signal of the cable to be tested according to the denoised positive frequency signal of the cable to be tested and the negative frequency signal of the cable to be tested.
3. The method for detecting electrical branch defects of a power cable according to claim 1, wherein the obtaining the positioning signal of the cable to be detected based on the frequency domain signal of the cable to be detected comprises:
performing Fourier transform on the frequency domain signal of the cable to be tested to obtain a time domain signal of the cable to be tested, multiplying the time domain signal of the cable to be tested by the wave speed of electromagnetic waves to obtain a space domain signal of the cable to be tested, and comparing the space domain signal of the cable to be tested with the space domain signal of a non-fault cable to obtain a positioning signal of the cable to be tested.
4. The method of claim 1, wherein the three-electrode system comprises a high voltage electrode, a guard electrode, and a test electrode;
the outer semi-conductive layer of the cable-like segment is connected with the test electrode, the inner semi-conductive layer of the cable-like segment is connected with the high-voltage electrode, and the protection electrode is horizontally arranged on the surface of the insulating layer of the cable-like segment;
The high-voltage electrode is connected with a high-voltage test power supply, the test electrode is connected with a test interface of the digital picoampere meter, the grounding ground of the digital picoampere meter is grounded, and the protection electrode is grounded.
5. The method for detecting electrical branch defects of a power cable according to any one of claims 1 to 4, wherein the aging time period varies from one cable segment to another.
6. A power cable electrical branch defect detection device, comprising:
The aging module is used for acquiring the conductivity and capacitance characteristic parameters of the cable sample sections with different electrical branch defect types based on an electrical branch aging experiment, and simulating corresponding positioning signals according to the conductivity and capacitance characteristic parameters;
The denoising module is used for acquiring a positive frequency single-ended impedance spectrum function signal of the cable to be measured based on the network analyzer, multiplying the positive frequency single-ended impedance spectrum function signal of the cable to be measured by a Hamming window function, and obtaining a denoised positive frequency signal of the cable to be measured;
The frequency domain signal acquisition module is used for acquiring a frequency domain signal of the cable to be tested based on the denoised positive frequency signal of the cable to be tested;
the positioning signal acquisition module is used for acquiring a positioning signal of the cable to be tested based on the frequency domain signal of the cable to be tested;
The defect determining module is used for determining the type and the position of the electrical branch defect of the cable to be tested based on the positioning signals of the cable to be tested and the positioning signals of the cable sample sections of different electrical branch defect types;
the aging module is specifically used for:
For each cable sample section, measuring the capacitance of the cable sample section through a network analyzer, and obtaining the conductance of the cable sample section through a three-electrode system; obtaining a positive frequency single-ended impedance spectrum function signal of the cable sample section according to the capacitance and the conductance simulation of the cable sample section, multiplying the positive frequency single-ended impedance spectrum function signal of the cable sample section by a Hamming window function, and then carrying out conjugate symmetry solving and fast Fourier transformation to obtain a time domain signal of the cable sample section; discarding the imaginary part of the time domain signal of the cable sample section, and multiplying the time domain signal of the cable sample section with the electromagnetic wave velocity to obtain a space domain signal of the cable sample section; and comparing the spatial domain signal of the cable sample section with the spatial domain signal of the non-fault cable to obtain a positioning signal of the cable sample section.
7. The power cable electrical branch defect detection apparatus according to claim 6, wherein the frequency domain signal acquisition module is specifically configured to:
And carrying out conjugate symmetry solving on the denoised positive frequency signal of the cable to be tested to obtain a negative frequency signal of the cable to be tested, and obtaining a frequency domain signal of the cable to be tested according to the denoised positive frequency signal of the cable to be tested and the negative frequency signal of the cable to be tested.
8. A terminal comprising a memory, a processor and a computer program stored in the memory and executable on the processor, characterized in that the processor implements the steps of the power cable electrical branch defect detection method according to any one of the preceding claims 1 to 5 when the computer program is executed.
9. A computer storage medium storing a computer program, characterized in that the computer program when executed by a processor implements the steps of the power cable electrical branch defect detection method according to any one of the preceding claims 1 to 5.
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| CN116125214B (en) * | 2022-09-30 | 2023-09-29 | 国网浙江省电力有限公司电力科学研究院 | Partial discharge and electric branch variable frequency measurement method and system |
| CN115508416A (en) * | 2022-11-24 | 2022-12-23 | 石家庄铁道大学 | Cable degradation evaluation method based on characteristic impedance analysis |
| CN116256563B (en) * | 2023-05-15 | 2023-10-24 | 成都理工大学 | Tree impedance test platform for 10kV tree line fault and measurement method |
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