CN114217175A - Power cable electric tree defect detection method and device and terminal - Google Patents
Power cable electric tree defect detection method and device and terminal Download PDFInfo
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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
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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
- G01R31/08—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
Abstract
The invention provides a power cable tree defect detection method, a device and a terminal. The method comprises the following steps: acquiring the conductance and capacitance characteristic parameters of cable sample sections with different electrical tree defect types based on an electrical tree aging experiment, 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 by 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 position of the electrical tree defect of the cable to be detected based on the positioning signal of the cable to be detected and the positioning signals of the cable sample sections with different electrical tree defect types. The method can detect the local defects of the cable and accurately determine the defect type and the fault position of the electric tree of the cable to be detected.
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 defects of electric branches of a power cable.
Background
The cable plays an extremely important role in the electric energy transmission of a modern urban power grid system, and the running state of the cable directly influences the safety and stability of a large-scale electric system. The design life of the cable is generally 20 to 30 years, while the cable in actual operation often induces permanent faults due to local latent defects such as local degradation or damage of insulation, and once the cable faults occur, the large-scale electrical system is shut down or even out of control, thereby causing serious economic loss and social influence. The power cable in the urban power supply system is laid in a cable trench or directly buried underground, under the action of temperature, electrical stress, mechanical force, moisture, oil, organic compounds, alkali, acid, microorganisms and the like, insulation is easy to corrode and permeate to form insulation local defects, and meanwhile, the underground power cable is often subjected to insulation damage due to mechanical external force to finally cause permanent faults of the cable. According to investigation, accidents caused by local insulation defects of the power cable account for about 40% of accidents of cable equipment. Therefore, improving the detection level of the local insulation defects of the power cable is the key for ensuring the stable operation of the power system.
At present, the conventional detection method for the cable running state comprises a non-electrical parameter method and an electrical parameter method. However, the existing method can only evaluate the overall state or general defects of the cable, but cannot detect the local defects of the cable and accurately determine the insulation defect type of the cable.
Disclosure of Invention
The embodiment of the invention provides a method, a device and a terminal for detecting defects of electric branches of a power cable, and aims to solve the problems that the existing method can only evaluate the overall state or universality 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.
In a first aspect, an embodiment of the present invention provides a method for detecting a power cable electrical branch defect, including:
acquiring the conductance and capacitance characteristic parameters of cable sample sections with different electrical tree defect types based on an electrical tree aging experiment, and simulating corresponding positioning signals according to the conductance 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 by 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 position of the electrical tree defect of the cable to be detected based on the positioning signal of the cable to be detected and the positioning signals of the cable sample sections with different electrical tree defect types.
In one possible implementation, obtaining a 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 detected to obtain a negative frequency signal of the cable to be detected, and obtaining a frequency domain signal of the cable to be detected according to the denoised positive frequency signal of the cable to be detected and the negative frequency signal of the cable to be detected.
In a possible implementation manner, obtaining a positioning signal of a cable to be tested based on a frequency domain signal of the cable to be tested includes:
the method comprises the steps of carrying out Fourier transform on a frequency domain signal of a cable to be detected to obtain a time domain signal of the cable to be detected, multiplying the time domain signal of the cable to be detected by the electromagnetic wave velocity to obtain a space domain signal of the cable to be detected, and comparing the space domain signal of the cable to be detected with the space domain signal of a non-fault cable to obtain a positioning signal of the cable to be detected.
In a possible implementation manner, based on an electrical tree aging experiment, conductance and capacitance characteristic parameters of cable sample sections with different electrical tree defect types are obtained, and corresponding positioning signals are simulated according to the conductance and capacitance characteristic parameters, including:
for each cable sample section, measuring the capacitance of the cable sample section by a network analyzer, and obtaining the conductance of the cable sample section by a three-electrode system; and according to the capacitance and conductance simulation of the cable sample section, obtaining a positive-frequency single-ended impedance spectrum function signal 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, the 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 protective 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 testing power supply, the testing electrode is connected with a testing interface of the digital pico-ampere meter, the grounding end of the digital pico-ampere meter is grounded, and the protective electrode is grounded.
In one possible implementation, the aging time duration is different for different cable sample sections.
In a second aspect, an embodiment of the present invention provides a power cable electrical tree defect detection apparatus, including:
the aging module is used for acquiring the conductance and capacitance characteristic parameters of cable sample sections with different electrical tree defect types based on an electrical tree aging experiment, and simulating corresponding positioning signals according to the conductance 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 detected based on the network analyzer, and multiplying the positive-frequency single-ended impedance spectrum function signal of the cable to be detected by a Hamming window function to obtain a denoised positive-frequency signal of the cable to be detected;
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 detected based on the frequency domain signal of the cable to be detected;
and the defect determining module is used for determining the type and the position of the electric branch defect of the cable to be detected based on the positioning signal of the cable to be detected and the positioning signals of the cable sample sections with different electric branch defect types.
In a possible implementation manner, the frequency domain signal obtaining module is specifically configured to:
and carrying out conjugate symmetry solving on the denoised positive frequency signal of the cable to be detected to obtain a negative frequency signal of the cable to be detected, and obtaining a frequency domain signal of the cable to be detected according to the denoised positive frequency signal of the cable to be detected and the negative frequency signal of the cable to be detected.
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, when executing the computer program, implements the steps of the power cable electrical tree defect detection method according to the first aspect or any one of the possible implementations of the first aspect.
In a fourth aspect, an embodiment of the present invention provides a computer storage medium, where a computer program is stored, and the computer program, when executed by a processor, implements the steps of the power cable electrical tree branch defect detection method according to 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 the electric branch defect of a power cable, which can detect the local defect of the cable and accurately determine the electric branch defect type and the fault position of the cable to be detected by comparing positioning signals of different electric branch defect types with the positioning signal of the cable to be detected; in addition, the influence of frequency spectrum leakage can be reduced by a method of multiplying the positive frequency single-ended impedance spectrum function signal of the cable to be tested by a Hamming window function.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive exercise.
Fig. 1 is a flowchart of an implementation of a method for detecting defects of electrical tree branches of a power cable according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a cable pattern section electrical branch aging circuit provided by an embodiment of the invention;
FIG. 3 is a schematic diagram of a capacitance measuring circuit according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a conductance measurement circuit provided by 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 diagram of a phase spectrum curve obtained by simulation according to an embodiment of the present invention;
FIG. 7 is a diagram illustrating a time domain function of a Hamming window provided by an embodiment of the present invention;
FIG. 8 is a diagram illustrating amplitude-frequency functions of a Hamming window provided by an embodiment of the present invention;
FIG. 9 is a schematic diagram of a positive frequency single-ended impedance spectrum function signal measurement of a cable under test according to an embodiment of the present invention;
FIG. 10 is a diagram illustrating a measurement result of a positive frequency single-ended impedance spectrum function signal of a cable under test 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 structural diagram of a power cable electrical tree defect detecting 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 particular system structures, techniques, etc. in order to provide a thorough understanding of the embodiments of the 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.
In order to make the objects, technical solutions and advantages of the present invention more apparent, the following description is made by way of specific embodiments with reference to the accompanying drawings.
Conventional methods for detecting the operating state of a cable include non-electrical parameter methods and electrical parameter methods. The non-electrical parameter method realizes the diagnosis of the operation state by detecting the physical and chemical properties of the cable, and is mainly used for the evaluation of the overall aging life of the cable, such as the detection of the Elongation At Break (EAB) and the compression modulus of the cable material. The cable electrical parameter detection method mainly comprises the steps of cable insulation resistance measurement, voltage withstanding test, leakage current test, dielectric loss detection and the like. However, the above electrical method can only evaluate the overall state or general defects of the cable, and cannot find the cable insulation local latent defects. The power cable insulation local defect positioning detection method based on the single-ended impedance method appearing in recent years proves great potential in power cable nondestructive fine detection, and a small amount of existing research shows that although the method can realize effective detection on the power cable local insulation defect, the classification of the type and the severity of the insulation defect is still required to be further researched.
In conclusion, the influence rule and action mechanism of different insulation defect types of the power cable on the single-ended impedance spectrum are analyzed in a refined mode, the relation between insulation defect parameters and single-ended impedance spectrum characteristics is mastered, equipment capable of identifying and positioning insulation defects is further developed, and theoretical and technical support can be provided for improving the overhaul refinement level of the power cable and improving the power supply reliability.
Referring to fig. 1, it shows a flowchart of an implementation of the method for detecting a power cable electrical tree defect according to an embodiment of the present invention, which is detailed as follows:
in S101, based on the electrical tree aging experiment, conductance and capacitance characteristic parameters of cable sample sections with different electrical tree defect types are obtained, and corresponding positioning signals are simulated according to the 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 by a network analyzer, and obtaining the conductance of the cable sample section by a three-electrode system; and according to the capacitance and conductance simulation of the cable sample section, obtaining a positive-frequency single-ended impedance spectrum function signal 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 protective 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 testing power supply, the testing electrode is connected with a testing interface of the digital pico-ampere meter, the grounding end of the digital pico-ampere meter is grounded, and the protective electrode is grounded.
In some embodiments of the invention, the aging time periods are different for different cable-like segments.
In the embodiment of the invention, a 10kV cable is segmented and cut into a cable sample section with the length of 20cm, copper shields and outer semi-conducting layers at the positions of 2.5cm at two ends are removed, and XLPE main insulation is reserved. The structure is shown in fig. 2. In order to build a needle-plate electrode structure required by the branch of the power generation, steel needles are inserted outside a cable sheath, the distance between the position of a needle point and a cable inner shielding layer 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 shown in FIG. 2.
And applying 10kV power frequency voltage to cable cores, wherein the pressurizing time is not more 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 switched off, and the grounding wire is removed for standby.
In this embodiment, the shield layer is a semiconductive layer. That is, the outer semiconductive layer is an outer shield layer, and the inner semiconductive layer is an inner shield layer.
And then carrying out electrical parameter measurement on the area containing the electrical tree defects. Firstly, a cable section is manufactured, wherein the cable section is of a circular ring structure and consists of an inner semi-conducting layer, an insulating layer and an outer semi-conducting layer. Wherein the external diameter of the sliced sample is 23mm, the internal diameter is 8mm, and the thickness of the sample is 5 mm.
When measuring the capacitance, the cable slice sample is connected with the testing end of the network analyzer through the outer semi-conductive layer thereof and is connected with the testing end of the network analyzer through the inner semi-conductive layer thereof for testing, and the capacitance value can be measured by using the S11 parameter because the insulation resistance is larger and the inductance is negligible, the frequency range is set to be 100kHz-300MHz during the measurement, and the capacitance value of each frequency band is read by the Smith chart. The capacitance measurement circuit diagram is shown in fig. 3, and is connected with a network analyzer through a measurement clamp.
Fig. 4 is a schematic structural diagram of a three-electrode system. The cable slice is a circular ring structure and consists of an inner semi-conducting layer, an insulating layer (crosslinked polyethylene) and an outer semi-conducting layer. Wherein the external diameter of the sliced sample is 23mm, the internal diameter is 8mm, and the thickness of the sample is 5 mm. The three electrodes are made of copper, the high-voltage electrode and the testing electrode are round pipes with adjustable radiuses, the protection electrode is circular, the diameter of the testing electrode is 22 mm-25 mm adjustable, the length of the testing electrode is 15mm, the diameter of the high-voltage electrode is 7 mm-10 mm adjustable, and the length of the high-voltage electrode is 15 mm. The outer diameter of the guard electrode was 20mm, the inner diameter was 10mm, and the thickness was 0.2 mm.
The test electrode is connected with a digital picoampere meter for measuring the conductance current. The digital piranha meter is model B2983A, the minimum 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 protective electrode is horizontally arranged on the surface of the insulation 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 protective electrode is grounded, the test electrode is connected with the test interface of the digital pico-meter, and the grounding end of the digital pico-meter is grounded.
For each cable sample section, the following steps are carried out to obtain a positioning signal of each cable sample section:
1) setting resistance, inductance, conductance and capacitance values of unit cable length before and after electrical branch aging, 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:
wherein Z0Is a characteristic impedance, ΓLIs 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 both functions of electrical parameters and frequency for a 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 converting a picoampere meter, the capacitance is measured by a network analyzer, and the inductance is unchanged and is the same as that of a fault-free cable.
The simulated amplitude spectrum and phase spectrum curves are shown in fig. 5 and 6.
2) Multiplying the impedance spectrum function of the positive frequency domain by a Hamming window with the same length to reduce the influence of frequency spectrum leakage, then carrying out conjugate symmetry to solve a negative frequency signal, and solving a time domain signal by using a fast Fourier algorithm, wherein the formula of fast Fourier transform is as follows:
where X is the time domain signal to be processed, N is the number of sampling points, wnIs the frequency corresponding to each sampling point.
The expression of the hamming window function is as follows:
hamming window has a main lobe width of
The attenuation of the sidelobe peak is 41dB, and the time domain function and the amplitude-frequency function of a Hamming window are shown in figures 7 and 8.
3) And (3) eliminating the imaginary part of the time domain signal, multiplying the time domain signal of the eliminated imaginary part of the cable sample section by the wave velocity of the electromagnetic wave 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 a positioning signal of the cable sample section.
A non-faulty cable is a perfect cable without electrical tree 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, so as 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 impedance mismatching of the measurement lead, the effective connection of the cable conductor, the copper shield and the network analyzer is realized by using the crimping type N head. In the manufacturing process, the copper shield and the N-head metal shell are completely pressed, and the conductor and the N-head pin electrode are welded well, so that the impedance mismatching degree of the section is reduced.
During measurement, the tested cable is connected to the network analyzer through the N-type connector, the waveform of the tested positive frequency single-ended impedance spectrum function signal is read through the network analyzer, and 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 maximum number of sampling points is 1601.
Before measurement, the port 1 of the network analyzer is firstly calibrated, and then the S11 parameter is measured, and the read waveform is shown in FIG. 10. The upper curve is a measured S11 Smith chart which adopts a two-dimensional circular coordinate system to realize the characterization of the impedance parameters, and the measured cable S11 parameters are known to present obvious periodic characteristics.
For a uniform transmission line (a perfect power cable can be equivalent to a uniform transmission line), the amplitude spectrum and the phase spectrum of the uniform transmission line have the same periodicity characteristic, and after being subjected to inverse Fourier transform, the uniform transmission line has a flat time domain curve characteristic. With the development of the electrical tree defect, the amplitude spectrum and the phase spectrum of the electrical tree defect are both distorted, and the distortion is caused by the changes of capacitance and conductance values in unit length caused by the electrical tree defect, and when the frequency domain impedance spectrum and the phase spectrum are changed, the changes cause larger distortion in a time domain curve and present an obvious local peak value.
In order to realize the positioning of the electric tree defects, the amplitude spectrum and the phase spectrum data are derived after the measurement, and the Hamming window is utilized to reduce the noise influence, so that the denoised positive frequency signal is obtained.
In S103, a frequency domain signal of the cable to be measured is obtained based on the denoised positive frequency signal of the cable to be measured.
In some embodiments of the present invention, the S103 may include:
and carrying out conjugate symmetry solving on the denoised positive frequency signal of the cable to be detected to obtain a negative frequency signal of the cable to be detected, and obtaining a frequency domain signal of the cable to be detected according to the denoised positive frequency signal of the cable to be detected and the negative frequency signal of the cable to be detected.
The denoised positive frequency signal of the cable to be tested and the negative frequency signal of the cable to be tested jointly form a frequency domain signal of the cable to be tested.
In S104, a positioning signal of the cable to be tested is obtained based on the frequency domain signal of the cable to be tested.
In some embodiments of the present invention, the S104 may include:
the method comprises the steps of carrying out Fourier transform on a frequency domain signal of a cable to be detected to obtain a time domain signal of the cable to be detected, multiplying the time domain signal of the cable to be detected by the electromagnetic wave velocity to obtain a space domain signal of the cable to be detected, and comparing the space domain signal of the cable to be detected with the space domain signal of a non-fault cable to obtain a positioning signal of the cable to be detected.
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 time data of the transverse axis by the wave speed in the cable, namely the wave speed of the electromagnetic wave to obtain the space domain signal of the signal amplitude and the position. Comparing the spatial domain signal of the cable to be tested with the spatial domain signal of the non-fault cable to obtain a positioning signal of the cable to be tested, such as the electrical tree defect positioning diagram shown in fig. 11. The figure can clearly distinguish the faults of a plurality of electric branches at the middle position of the cable.
In S105, the electrical tree 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 tree defect types.
And comparing the positioning signal of the fault area of the cable to be detected with the positioning signals of the cable sample sections with different electrical tree defect types, and judging the cable to be detected to have the same electrical tree defect type if the characteristics are the same. As shown in fig. 11, the defect position can be seen from the figure.
According to the embodiment of the invention, the local defects of the cable can be detected and the electric tree defect types and fault positions of the cable to be detected can be accurately determined by comparing the positioning signals of different electric tree defect types with the positioning signal of the cable to be detected; in addition, the influence of frequency spectrum leakage can be reduced by a method of multiplying the positive frequency single-ended impedance spectrum function signal of the cable to be tested by a Hamming window function.
The embodiment of the invention is suitable for detecting and positioning the aging defect of the electrical tree in the insulation in the range of 10kV distribution cables, prevents the problem of secondary damage possibly introduced by the traditional voltage withstanding test and other methods, is beneficial to finding the aging phenomenon of the electrical tree in the early stage in the insulation, can find the defect problem in the insulation in advance, and improves the accuracy and the safety of cable maintenance.
The electric branch accelerated aging experiment in the cable sample section is carried out in a laboratory, and data such as capacitance, conductance and the like of different electric branch types and different electric branch aging stages are measured, so that corresponding infinitesimal parameter distribution characteristics are obtained, and effective support for reliability of measurement results is realized. Meanwhile, by using the measurement result, single-ended impedance spectrum measurement can be directly carried out on the insulation of the 10kV cable in field operation, so that the distribution characteristics of each infinitesimal parameter of the cable can be determined, the position of the electrical branch defect can be determined by combining an IFFT algorithm, the defect positioning can be realized, and the cable maintenance accuracy can be improved.
The embodiment of the invention designs a three-electrode system structure for initiating measurement of a small section of cable sample, can realize accurate measurement of bulk conductivity and surface conductivity, and the radius of the measuring electrode and the high-voltage electrode is adjustable, thereby ensuring sufficient contact between the sample and the electrode and controlling experimental errors. By the fast Fourier algorithm provided by the embodiment of the invention, the algorithm calculation speed is increased, and the efficiency of positioning and classifying faults is improved. The advantage of narrow side lobe width of a Hamming window 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. When the algorithm is processed, Labview software processed by a computer is utilized, the acquisition and display functions are strong, the sampling data frequency can be selected, the stored data quantity can be changed, the type and the length of the window function can be modified, and the fault positioning requirement of the broadband impedance spectrum under different requirements can be met. The method for testing the network analyzer by directly crimping the disposable N heads is simple to implement, has good system anti-interference capability, and provides a theoretical basis for realizing a field cable fault positioning and overhauling technology.
Compared with the prior art, the device has a simple structure, the test platform is easy to prepare, the real-time measurement of the broadband impedance spectrum can be realized, and a research approach is provided for measuring the electrical parameters of the cable in unit length, so that the device has important significance for verifying and perfecting the theoretical model of the fault classification positioning technology.
It should be understood that, the sequence numbers of the steps in the foregoing embodiments do not imply an execution sequence, and the execution sequence of each process should be determined by its function and inherent logic, and should not constitute any limitation to the implementation process of the embodiments of the present invention.
The following are embodiments of the apparatus of the invention, reference being made to the corresponding method embodiments described above for details which are not described in detail therein.
Fig. 12 is a schematic structural diagram of a power cable electrical tree defect detecting apparatus provided by an embodiment of the present invention, and for convenience of description, only the parts related to the embodiment of the present invention are shown, and detailed descriptions are as follows:
as shown in fig. 12, the power cable electrical tree defect detecting apparatus 30 includes: an aging module 31, a denoising module 32, a frequency domain signal acquisition module 33, a localization signal acquisition module 34, and a defect determination module 35.
The aging module 31 is used for acquiring the conductance and capacitance characteristic parameters of cable sample sections with different electrical tree defect types based on an electrical tree aging experiment, and simulating corresponding positioning signals according to the conductance 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 acquisition 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 acquiring 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;
and the defect determining module 35 is configured to determine the type and position of the electrical tree defect of the cable to be detected based on the positioning signal of the cable to be detected and the positioning signals of the cable sample sections with different electrical tree defect types.
In a possible implementation manner, the frequency domain signal obtaining module 33 is specifically configured to:
and carrying out conjugate symmetry solving on the denoised positive frequency signal of the cable to be detected to obtain a negative frequency signal of the cable to be detected, and obtaining a frequency domain signal of the cable to be detected according to the denoised positive frequency signal of the cable to be detected and the negative frequency signal of the cable to be detected.
In one possible implementation, the positioning signal obtaining module 34 is specifically configured to:
the method comprises the steps of carrying out Fourier transform on a frequency domain signal of a cable to be detected to obtain a time domain signal of the cable to be detected, multiplying the time domain signal of the cable to be detected by the electromagnetic wave velocity to obtain a space domain signal of the cable to be detected, and comparing the space domain signal of the cable to be detected with the space domain signal of a non-fault cable to obtain a positioning signal of the cable to be detected.
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 by a network analyzer, and obtaining the conductance of the cable sample section by a three-electrode system; and according to the capacitance and conductance simulation of the cable sample section, obtaining a positive-frequency single-ended impedance spectrum function signal 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, the 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 protective 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 testing power supply, the testing electrode is connected with a testing interface of the digital pico-ampere meter, the grounding end of the digital pico-ampere meter is grounded, and the protective electrode is grounded.
In one possible implementation, the aging time duration is different for different cable sample sections.
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 said memory 41 and executable on said processor 40. The processor 40, when executing the computer program 42, implements the steps in the various power cable electrical tree defect detection method embodiments described above, such as S101 to S105 shown in fig. 1. Alternatively, the processor 40, when executing the computer program 42, implements the functions of the modules/units in the above-described device embodiments, such as the modules/units 31 to 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 implement the present invention. The one or more modules/units may be a series of computer program instruction segments capable of performing specific functions, which are used to describe the execution of the computer program 42 in the terminal 4. For example, the computer program 42 may be divided into the 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. Those skilled in the art will appreciate that fig. 13 is merely an example of a terminal 4 and is not intended to be limiting of terminal 4, and may include more or fewer components than those shown, or some components in combination, or different components, e.g., the terminal may also include input-output devices, network access devices, buses, etc.
The Processor 40 may be a Central Processing Unit (CPU), other general purpose Processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other Programmable logic device, discrete Gate or transistor logic, discrete hardware components, etc. 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 Media Card (SMC), a Secure Digital (SD) Card, a Flash memory Card (Flash Card) and the like 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 and other programs and data required by the terminal. The memory 41 may also be used to temporarily store 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-mentioned division of the functional units and modules is illustrated, and in practical applications, the above-mentioned function distribution may be performed by different functional units and modules according to needs, that is, the internal structure of the apparatus is divided into different functional units or modules to perform all or part of the above-mentioned functions. Each functional unit and module in the embodiments may be integrated in one processing unit, or each unit may exist alone physically, or two or more units are integrated in one unit, and the integrated unit may be implemented in a form of hardware, or in a form of software functional unit. In addition, specific names of the functional units and modules are only for convenience of distinguishing from each other, and are not used for limiting the protection scope of the present application. The specific working processes of the units and modules in the system may refer to the corresponding processes in the foregoing method embodiments, and are not described herein again.
In the above embodiments, the descriptions of the respective embodiments have respective emphasis, and reference may be made to the related descriptions of other embodiments for parts that are not described or illustrated in a certain embodiment.
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 implementation. 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 ways. For example, the above-described apparatus/terminal embodiments are merely illustrative, and for example, the division of the modules or units is only one logical division, and there may be other divisions when actually implemented, for example, a plurality of units or components may be combined or may be integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, devices or units, and may be in an electrical, mechanical or other form.
The units described as separate parts may or may not be physically separate, and parts displayed 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 can be selected according to actual needs to achieve the purpose of the solution of the embodiment.
In addition, functional units in the embodiments of the present invention may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit. The integrated unit can be realized in a form of hardware, and can also be realized in a form of a software functional unit.
The integrated modules/units, if implemented in the form of software functional units and sold or used as separate products, may be stored in a computer readable storage medium. Based on such understanding, all or part of the flow of the method according to the embodiments of the present invention may be implemented by a computer program, which may be stored in a computer-readable storage medium, and when the computer program is executed by a processor, the steps of the embodiments of the power cable electrical tree defect detection method may be implemented. Wherein the computer program comprises computer program code, which may be in the form of source code, object code, an executable file or some intermediate form, etc. The computer-readable medium may include: any entity or device capable of carrying the computer program code, recording medium, usb disk, removable hard disk, magnetic disk, optical disk, computer Memory, Read-Only Memory (ROM), Random Access Memory (RAM), electrical carrier wave signals, telecommunications signals, software distribution medium, and the like. It should be noted that the computer readable medium may contain other components which may be suitably increased or decreased as required by legislation and patent practice in jurisdictions, for example, in some jurisdictions, computer readable media which may not include electrical carrier signals and telecommunications signals in accordance with legislation and patent practice.
The above-mentioned embodiments are only used for illustrating the technical solutions of the present invention, and not for limiting the same; although the present 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 solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; such modifications and substitutions do not substantially depart from the spirit and scope of the embodiments of the present invention, and are intended to be included within the scope of the present invention.
Claims (10)
1. A power cable electric tree defect detection method is characterized by comprising the following steps:
acquiring the conductance and capacitance characteristic parameters of cable sample sections with different electrical tree defect types based on an electrical tree aging experiment, and simulating corresponding positioning signals according to the conductance 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 by 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 electric branch defect of the cable to be detected based on the positioning signal of the cable to be detected and the positioning signals of the cable sample sections with different electric branch defect types.
2. The method for detecting the electrical branch defect of the power cable according to claim 1, wherein the obtaining the frequency domain signal of the cable to be detected based on the denoised positive frequency signal of the cable to be detected comprises:
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 the electrical branch defect of the 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:
carrying out Fourier transform on the frequency domain signal of the cable to be detected to obtain a time domain signal of the cable to be detected, multiplying the time domain signal of the cable to be detected by the electromagnetic wave velocity to obtain a space domain signal of the cable to be detected, and comparing the space domain signal of the cable to be detected with the space domain signal of the non-fault cable to obtain a positioning signal of the cable to be detected.
4. The method for detecting the electrical branch defect of the power cable according to claim 1, wherein the step of obtaining the conductance and capacitance characteristic parameters of the cable sample sections of different electrical branch defect types based on the electrical branch aging experiment and simulating the corresponding positioning signals according to the conductance and capacitance characteristic parameters comprises the steps of:
for each cable sample section, measuring the capacitance of the cable sample section by a network analyzer, and obtaining the conductance of the cable sample section by a three-electrode system; and according to the capacitance and conductance simulation of the cable sample section, obtaining a positive-frequency single-ended impedance spectrum function signal 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.
5. The power cable electrical tree defect detection method of claim 4, wherein the three-electrode system comprises a high voltage electrode, a guard electrode and a test electrode;
the outer semi-conducting layer of the cable sample section is connected with the test electrode, the inner semi-conducting layer of the cable sample section is connected with the high-voltage electrode, and the protective 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 pico-meter, the grounding end of the digital pico-meter is grounded, and the protection electrode is grounded.
6. A power cable electrical tree defect detection method according to any one of claims 1 to 5 wherein different cable-like sections age differently.
7. The utility model provides a power cable electricity branch defect detecting device which characterized in that includes:
the aging module is used for acquiring the conductance and capacitance characteristic parameters of cable sample sections with different electrical tree defect types based on an electrical tree aging experiment, and simulating corresponding positioning signals according to the conductance 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 detected based on the network analyzer, and multiplying the positive-frequency single-ended impedance spectrum function signal of the cable to be detected by a Hamming window function to obtain a denoised positive-frequency signal of the cable to be detected;
the frequency domain signal acquisition module is used for acquiring a frequency domain signal of the cable to be detected based on the denoised positive frequency signal of the cable to be detected;
the positioning signal acquisition module is used for acquiring a positioning signal of the cable to be detected based on the frequency domain signal of the cable to be detected;
and the defect determining module is used for determining the type and the position of the electric branch defect of the cable to be detected based on the positioning signal of the cable to be detected and the positioning signals of the cable sample sections with different electric branch defect types.
8. The power cable electrical branch defect detection apparatus of claim 7, 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.
9. 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, when executing the computer program, carries out the steps of the power cable electrical tree defect detection method according to any one of the preceding claims 1 to 6.
10. A computer storage medium, in which a computer program is stored, which computer program, when being executed by a processor, is adapted to carry out the steps of the power cable electrical branch defect detection method as set forth in any one of the preceding claims 1 to 6.
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