CN114217175B - Power cable electrical tree defect detection method, device and terminal - Google Patents

Abstract

The present invention provides a method, device and terminal for detecting electrical tree defects in power cables. The method comprises: based on an electrical tree aging experiment, obtaining the conductivity and capacitance characteristic parameters of cable sample segments with different electrical tree defect types, and simulating the corresponding positioning signals; based on a network analyzer, obtaining the 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 the Hamming window function to obtain the denoised positive frequency signal of the cable to be tested; obtaining the frequency domain signal of the cable to be tested based on the denoised positive frequency signal of the cable to be tested; obtaining the positioning signal of the cable to be tested based on the frequency domain signal of the cable to be tested; determining the type and location of the electrical tree defect of the cable to be tested based on the positioning signal of the cable to be tested and the positioning signals of cable sample segments with different electrical tree defect types. The present invention can detect local defects of cables and accurately determine the type of electrical tree defects and fault locations of the cable to be tested.

Description

Power cable electrical tree defect detection method, device and terminal

Technical Field

The present invention relates to the technical field of safe cable operation, and in particular to a method, device and terminal for detecting electrical tree defects in power cables.

Background technique

Cables play an extremely important role in the transmission of electric energy in modern urban power grid systems, and their operating status directly affects the safety and stability of large electrical systems. The design life of cables is generally 20 to 30 years, but cables in actual operation often induce permanent faults due to local latent defects such as local insulation degradation or damage. Once a cable fault occurs, it will cause the shutdown or even loss of control of large electrical systems, causing serious economic losses and social impacts. Power cables in urban power supply systems are laid in cable trenches or directly buried underground. Under the action of temperature, electrical stress, mechanical force, moisture, oil, organic compounds, alkali, acid, microorganisms, etc., the insulation is susceptible to corrosion penetration and forms local insulation defects. At the same time, underground power cables often suffer insulation damage due to mechanical external forces, which eventually leads to permanent cable failures. According to surveys, 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 local defects in the insulation of power cables is the key to ensuring the stable operation of power systems.

At present, the conventional detection methods for cable operation status include non-electrical parameter method and electrical parameter method. However, the existing methods can only evaluate the overall status of the cable or universal defects, but cannot detect local defects of the cable and accurately determine the type of cable insulation defects.

Summary of the invention

The embodiments of the present invention provide a method, device and terminal for detecting electrical tree defects in power cables to solve the problem that the existing methods can only evaluate the overall state or universal defects of the cable but cannot detect local defects of the cable and accurately determine the type of cable insulation defects.

In a first aspect, an embodiment of the present invention provides a method for detecting electrical tree defects in a power cable, comprising:

Based on the electrical tree aging experiment, the conductivity and capacitance characteristic parameters of the cable sample sections with different types of electrical tree defects are obtained, and the corresponding positioning signals are simulated according to the conductivity and capacitance characteristic parameters;

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;

Obtaining a frequency domain signal of the cable under test based on the denoised positive frequency signal of the cable under test;

Obtaining a positioning signal of the cable to be tested based on the frequency domain signal of the cable to be tested;

The type and position of the electrical tree defect of the cable to be tested are determined based on the positioning signal of the cable to be tested and the positioning signals of cable sample sections with different types of electrical tree defects.

In a possible implementation, obtaining a frequency domain signal of the cable under test based on the denoised positive frequency signal of the cable under test includes:

The negative frequency signal of the cable under test is obtained by performing conjugate symmetry solution on the denoised positive frequency signal of the cable under test, and the frequency domain signal of the cable under test is obtained according to the denoised positive frequency signal of the cable under test and the negative frequency signal of the cable under test.

In a possible implementation, obtaining a positioning signal of the cable to be tested based on the frequency domain signal of the cable to be tested includes:

Perform Fourier transform on the frequency domain signal of the cable under test to obtain the time domain signal of the cable under test, multiply the time domain signal of the cable under test by the speed of the electromagnetic wave to obtain the space domain signal of the cable under test, and compare the space domain signal of the cable under test with the space domain signal of the non-fault cable to obtain the positioning signal of the cable under test.

In a possible implementation, based on the electrical tree aging experiment, the conductivity and capacitance characteristic parameters of the cable sample segments with different electrical tree defect types are obtained, and the corresponding positioning signals are simulated according to the conductivity and capacitance characteristic parameters, including:

For each cable sample segment, the capacitance of the cable sample segment is measured by a network analyzer, and the conductance of the cable sample segment is obtained by a three-electrode system; the positive-frequency single-ended impedance spectrum function signal of the cable sample segment is simulated according to the capacitance and conductance of the cable sample segment, and the positioning signal of the cable sample segment is obtained based on the positive-frequency single-ended impedance spectrum function signal of the cable sample segment.

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 to the test electrode, the inner semi-conductive layer of the cable sample section is connected to the high-voltage electrode, and the protective electrode is placed flat on the surface of the insulation layer of the cable sample section;

The high voltage electrode is connected to a high voltage test power supply, the test electrode is connected to a test interface of a digital picoammeter, the ground terminal of the digital picoammeter is grounded, and the protection electrode is grounded.

In a possible implementation, different cable sample sections have different aging times.

In a second aspect, an embodiment of the present invention provides a power cable electrical tree defect detection device, comprising:

An aging module is used to obtain the conductivity and capacitance characteristic parameters of cable sample sections with different types of electrical tree defects based on an electrical tree aging experiment, and simulate corresponding positioning signals according to the conductivity and capacitance characteristic parameters;

A denoising module is used to obtain a positive frequency single-ended impedance spectrum function signal of the cable to be tested based on a network analyzer, and multiply 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;

A frequency domain signal acquisition module, used for obtaining a frequency domain signal of the cable under test based on the denoised positive frequency signal of the cable under test;

A positioning signal acquisition module, used 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 determination module is used to determine the type and location of the electrical tree defect of the cable to be tested based on the positioning signal of the cable to be tested and the positioning signals of cable sample sections with different types of electrical tree defects.

In a possible implementation, the frequency domain signal acquisition module is specifically used to:

The negative frequency signal of the cable under test is obtained by performing conjugate symmetry solution on the denoised positive frequency signal of the cable under test, and the frequency domain signal of the cable under test is obtained according to the denoised positive frequency signal of the cable under test and the negative frequency signal of the cable under test.

In a third aspect, an embodiment of the present invention provides a terminal comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the steps of the method for detecting electrical tree defects in power cables as described in the first aspect or any possible implementation method of the first aspect are implemented.

In a fourth aspect, an embodiment of the present invention provides a computer storage medium, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps of the power cable electrical tree defect detection method as described in the first aspect or any possible implementation method of the first aspect are implemented.

The embodiments of the present invention provide a method, device and terminal for detecting electrical tree defects in power cables. By comparing the positioning signals of different types of electrical tree defects with the positioning signals of the cable to be tested, local defects in the cable can be detected and the type of electrical tree defects and the fault location of the cable to be tested can be accurately determined. In addition, a method of multiplying the positive frequency single-ended impedance spectrum function signal of the cable to be tested with a Hamming window function can reduce the influence of spectrum leakage.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

FIG1 is a flow chart of a method for detecting electric tree defects in a power cable according to an embodiment of the present invention;

FIG2 is a schematic diagram of a cable sample section electrical tree aging circuit according to an embodiment of the present invention;

FIG3 is a schematic diagram of a capacitance measurement circuit provided by an embodiment of the present invention;

FIG4 is a schematic diagram of a conductivity measurement circuit provided in an embodiment of the present invention;

FIG5 is a schematic diagram of an amplitude spectrum curve obtained by simulation according to an embodiment of the present invention;

FIG6 is a schematic diagram of a phase spectrum curve obtained by simulation according to an embodiment of the present invention;

FIG7 is a schematic diagram of a time domain function of a Hamming window provided by an embodiment of the present invention;

FIG8 is a schematic diagram of an amplitude-frequency function of a Hamming window provided by an embodiment of the present invention;

9 is a schematic diagram of measuring a positive frequency single-ended impedance spectrum function signal of a cable to be tested provided by an embodiment of the present invention;

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 provided in an embodiment of the present invention;

11 is a schematic diagram of a positioning signal of a cable to be tested provided in an embodiment of the present invention;

12 is a schematic diagram of the structure of a power cable electrical tree defect detection device provided in an embodiment of the present invention;

FIG13 is a schematic diagram of a terminal provided in an embodiment of the present invention.

Detailed ways

In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present invention. However, it should be clear to those skilled in the art that the present invention may be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present invention.

In order to make the purpose, technical solutions and advantages of the present invention more clear, specific embodiments will be described below in conjunction with the accompanying drawings.

Conventional detection methods for cable operation status include non-electrical parameter method and electrical parameter method. The non-electrical parameter method realizes operation status diagnosis by detecting the physical and chemical properties of the cable, and is mainly used for the overall aging life assessment 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 includes the measurement of cable insulation resistance, withstand voltage test, leakage current test and dielectric loss detection. However, the above electrical methods can only evaluate the overall status or universal defects of the cable, but cannot detect local latent defects in cable insulation. The local defect location detection method of power cable insulation based on the single-ended impedance method that has emerged in recent years has proved its great potential in the non-destructive and refined detection of power cables. However, the existing small number of studies have shown that although this method can achieve effective detection of local insulation defects of power cables, the classification of insulation defect types and severity still needs further research.

In summary, a refined analysis of the influence of different types of insulation defects in power cables on the single-ended impedance spectrum and its mechanism of action, mastering the relationship between insulation defect parameters and single-ended impedance spectrum characteristics, and then developing equipment that can identify and locate insulation defects can provide theoretical and technical support for improving the level of refinement of power cable maintenance and enhancing power supply reliability.

Referring to FIG. 1 , it shows a flowchart of the implementation of the method for detecting electric tree defects in power cables provided by an embodiment of the present invention, which is described in detail as follows:

In S101, based on the electrical tree aging experiment, the conductivity and capacitance characteristic parameters of the cable sample sections with different electrical tree defect types are obtained, and the corresponding positioning signals are simulated according to the conductivity and capacitance characteristic parameters.

In some embodiments of the present invention, the above S101 may include:

For each cable sample segment, the capacitance of the cable sample segment is measured by a network analyzer, and the conductance of the cable sample segment is obtained by a three-electrode system; the positive-frequency single-ended impedance spectrum function signal of the cable sample segment is simulated according to the capacitance and conductance of the cable sample segment, and the positioning signal of the cable sample segment is obtained based on the positive-frequency single-ended impedance spectrum function signal of the cable sample segment.

In some embodiments of the present 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 to the test electrode, the inner semi-conductive layer of the cable sample section is connected to the high-voltage electrode, and the protective electrode is placed flat on the surface of the insulation layer of the cable sample section;

The high voltage electrode is connected to a high voltage test power supply, the test electrode is connected to a test interface of a digital picoammeter, the ground terminal of the digital picoammeter is grounded, and the protection electrode is grounded.

In some embodiments of the present invention, different cable sample sections have different aging times.

In the embodiment of the present invention, the 10kV cable is segmented and cut into cable sample sections of 20cm in length, the copper shielding and the outer semi-conductive layer at 2.5cm on both ends are removed, and the XLPE main insulation is retained. Its structure is shown in Figure 2. In order to build the needle-plate electrode structure required to induce electrical trees, steel needles are inserted into the outside of the cable sheath to ensure that the distance between the needle tip and the inner shielding layer of the cable is 2mm, the spacing between the steel needles is not less than 5mm, and the number of steel needles in a single group is not less than 10. For the convenience of drawing, only 3 steel needles are drawn in Figure 2.

Apply 10kV power frequency voltage to the cable core for no more than 5 hours, and apply voltage to multiple groups of cable sample sections simultaneously to obtain cable sample sections with different electrical tree aging durations. After the aging is completed, disconnect the power supply and remove the ground wire for standby use.

In this embodiment, the shielding layer is a semiconductive layer, that is, the outer semiconductive layer is an outer shielding layer, and the inner semiconductive layer is an inner shielding layer.

Then the electrical parameters of the area containing the electrical tree defect were measured. First, the cable slice was made. The cable slice was a circular ring structure consisting of an inner semi-conductive layer, an insulating layer, and an outer semi-conductive layer. The outer diameter of the slice sample was 23mm, the inner diameter was 8mm, and the sample thickness was 5mm.

When measuring capacitance, the cable slice sample is connected to the test end of the network analyzer through its outer semi-conductive layer and connected to the ground through its inner semi-conductive layer for testing. Since its insulation resistance is large and its inductance is negligible, its capacitance value can be measured using the S11 parameter. The frequency range is set to 100kHz-300MHz during measurement, and the capacitance value of each frequency band is read from the Smith chart. The capacitance value measurement circuit diagram is shown in Figure 3, which is connected to the network analyzer through a measuring fixture.

See Figure 4, which is a schematic diagram of the structure of the three-electrode system. The cable slice is a circular ring structure, consisting of an inner semi-conductive layer, an insulating layer (cross-linked polyethylene), and an outer semi-conductive layer. The slice sample has an outer diameter of 23mm, an inner diameter of 8mm, and a sample thickness of 5mm. The three electrodes are all made of copper, where the high-voltage electrode and the test electrode are both circular tubes with adjustable radius, the protective electrode is in the shape of a ring, the test electrode has an adjustable diameter of 22mm to 25mm, and a length of 15mm, and the high-voltage electrode has an adjustable diameter of 7mm to 10mm, and a length of 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 to a digital picoammeter for measuring the conductance current. The model of the digital picoammeter is B2983A, with a minimum range of 2pA and a maximum reading rate of 20,000 readings per second.

When testing conductivity, connect the outer semi-conductive layer of the cable slice to the test electrode of the three-electrode system, place the protective electrode flat on the surface of the insulating slice, connect the inner semi-conductive layer of the cable slice to the high-voltage electrode, connect the high-voltage electrode to the high-voltage test power supply, connect the protective electrode to the ground, connect the test electrode to the test interface of the digital picoammeter, and ground the ground terminal of the digital picoammeter.

For each cable sample section, perform the following steps to obtain the positioning signal of each cable sample section:

1) Set the resistance, inductance, conductance, and capacitance values per unit cable length before and after electrical tree aging, and solve the single-ended impedance spectrum function signal at the positive frequency end according to the transmission line model (cable sample section). The broadband impedance spectrum formula is as follows:

Where _Z0 is the characteristic impedance, _ΓL is the reflection coefficient, α is the real part of the propagation coefficient of the impedance spectrum, and β is the imaginary part of the propagation coefficient. Both the characteristic impedance and the propagation coefficient are functions of the system's electrical parameters per unit length and frequency, as shown below:

Among them, 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. Among them, the resistance per unit length of the cable is calculated using the conductivity of copper (17.5μΩ·mm), the conductance is converted by a picoammeter, the capacitance is measured by a network analyzer, and the inductance is constant and is the same as the inductance of a fault-free cable.

The amplitude spectrum and phase spectrum curves obtained by simulation are shown in Figures 5 and 6.

2) Multiply the positive frequency domain impedance spectrum function with the Hamming window of the same length to reduce the influence of spectrum leakage, and then perform conjugate symmetry to solve the negative frequency signal. Use the fast Fourier algorithm to solve the time domain signal. 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, 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 sidelobe peak attenuation is 41 dB. The time domain function and amplitude-frequency function of the Hamming window are shown in Figures 7 and 8.

3) The imaginary part of the time domain signal is discarded, and the time domain signal of the cable sample section without the imaginary part is multiplied by the electromagnetic wave velocity to obtain the space domain signal of the cable sample section. The space domain signal of the cable sample section is compared 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 sound cable without any electrical tree defects.

In S102, based on the network analyzer, a positive frequency single-ended impedance spectrum function signal of the cable under test is obtained, and the positive frequency single-ended impedance spectrum function signal of the cable under test is multiplied by a Hamming window function to obtain a denoised positive frequency signal of the cable under test.

Before measurement, the measuring end should be made first to achieve correct connection with the network analyzer. In the embodiment of the present invention, in order to reduce the error caused by the impedance mismatch of the measuring lead, a crimped N head is used to achieve effective connection between the cable conductor, copper shield and network analyzer. During the production process, it should be ensured that the copper shield and the N head metal shell are completely pressed together, and the conductor and the N head needle electrode are welded intact to reduce the impedance mismatch of this section.

During measurement, the cable under test is connected to the 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. The connection method is shown in Figure 9.

The model of the network analyzer is Agilent E5061B, the test frequency range is 100kHz to 2GHz, and the maximum sampling point number is 1601.

Before the measurement, the No. 1 port of the network analyzer was calibrated first, and then its S11 parameter was measured. The read waveform is shown in Figure 10. The upper curve is the measured S11 Smith chart, which uses a two-dimensional circular coordinate system to represent the impedance parameters. It can be seen from the figure that the measured cable S11 parameter shows obvious periodic characteristics.

For a uniform transmission line (a good power cable can also be equivalent to a uniform transmission line), its amplitude spectrum and phase spectrum show the same periodic characteristics, and after the inverse Fourier transform, it will show a flat time domain curve characteristic. As the electrical tree defect develops, its amplitude spectrum and phase spectrum will be distorted. The reason for the above distortion is the change of capacitance and conductivity per unit length caused by the electrical tree defect. These changes will cause the frequency domain impedance spectrum and phase spectrum to change, and will cause greater distortion in the time domain curve, showing obvious local peaks.

In order to locate the electrical tree defects, the amplitude spectrum and phase spectrum data are exported after measurement, and the Hamming window is used to reduce the influence of noise to obtain the denoised positive frequency signal.

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 above S103 may include:

The negative frequency signal of the cable under test is obtained by performing conjugate symmetry solution on the denoised positive frequency signal of the cable under test, and the frequency domain signal of the cable under test is obtained according to the denoised positive frequency signal of the cable under test and the negative frequency signal of the cable under test.

The de-noised positive frequency signal of the cable under test and the negative frequency signal of the cable under test together constitute the frequency domain signal of the cable under test.

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 above S104 may include:

Perform Fourier transform on the frequency domain signal of the cable under test to obtain the time domain signal of the cable under test, multiply the time domain signal of the cable under test by the speed of the electromagnetic wave to obtain the space domain signal of the cable under test, and compare the space domain signal of the cable under test with the space domain signal of the non-fault cable to obtain the positioning signal of the cable under test.

The frequency domain signal is converted to the time domain. At this time, the time domain signal is a function of the signal amplitude and time. The spatial domain signal of the signal amplitude and position can be obtained by multiplying the horizontal axis time data with the wave velocity in the cable, that is, the electromagnetic wave velocity. The spatial domain signal of the cable to be tested is compared with the spatial domain signal of the non-faulty cable to obtain the positioning signal of the cable to be tested, as shown in the electrical tree defect positioning diagram in Figure 11. In the figure, multiple electrical tree faults in the middle section of the cable can be clearly identified.

In S105, the type and position of the electrical tree defect 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 with different types of electrical tree defects.

The positioning signal of the fault area of the cable to be tested is compared with the positioning signals of the cable sample sections with different electrical tree defect types. If the characteristics are the same, it can be determined that they are the same type of electrical tree defect. As shown in Figure 11, the defect location can be seen from this figure.

The embodiment of the present invention can detect local defects of the cable and accurately determine the type of electrical tree defect and the fault location of the cable to be tested by comparing the positioning signals of different electrical tree defect types with the positioning signal of the cable to be tested; in addition, the method of multiplying the positive frequency single-ended impedance spectrum function signal of the cable to be tested with the Hamming window function can reduce the influence of spectrum leakage.

The embodiment of the present invention is suitable for the detection and positioning of electrical tree aging defects in insulation within the range of 10kV distribution cables, preventing secondary damage problems that may be introduced by traditional methods such as voltage withstand testing. At the same time, the method helps to discover early electrical tree aging phenomena in insulation, and can discover such defects in insulation in advance, thereby improving the accuracy and safety of cable maintenance.

By conducting accelerated aging experiments of electrical tree branches in cable samples in the laboratory, measuring the capacitance, conductance and other data of different electrical tree types and different electrical tree aging stages, the corresponding micro-element parameter distribution characteristics can be obtained to effectively support the reliability of the measurement results. At the same time, using the above measurement results, the single-ended impedance spectrum measurement of the 10kV cable insulation in the field can be directly carried out to determine the distribution characteristics of each micro-element parameter, and the location of the electrical tree defect can be determined by combining the IFFT algorithm to achieve defect location and improve the accuracy of cable maintenance.

The embodiment of the present invention is designed to trigger a three-electrode system structure for measuring a small section of cable sample, which can achieve accurate measurement of bulk conductivity and surface conductivity, and the radius of the measuring electrode and the high-voltage electrode is adjustable, which ensures full contact between the sample and the electrode and controls the error of the experiment. The fast Fourier algorithm proposed in the embodiment of the present invention improves the algorithm calculation speed and the efficiency of locating and classifying faults. The selection of the window function fully utilizes the advantage of the narrow sidelobe width of the Hamming window to minimize the impact of the window function on the original spectrum. When processing the algorithm, the Labview software processed by the computer is used, and the acquisition and display functions are powerful, the sampling data frequency can be selected, the storage data volume can be changed, and the window function type and length can be modified, which can meet the fault location requirements of the broadband impedance spectrum under different requirements. The network analyzer test method designed by the embodiment of the present invention for directly crimping a disposable N head is simple to implement and has good system anti-interference ability, which provides a theoretical basis for realizing on-site cable fault location and maintenance technology.

Compared with the prior art, the device of the present invention has a simple structure and is relatively easy to prepare a test platform. It can realize real-time measurement of broadband impedance spectra and provide a research approach for measuring electrical parameters per unit length of cables, which is of great significance for verifying and improving the theoretical model of fault classification and location technology.

It should be understood that the order of execution of the steps in the above embodiment does not necessarily mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present invention.

The following is an embodiment of the device of the present invention. For details not described in detail, reference may be made to the corresponding method embodiment described above.

FIG12 shows a schematic diagram of the structure of a power cable electrical tree defect detection device provided by an embodiment of the present invention. For ease of explanation, only the parts related to the embodiment of the present invention are shown, which are described in detail as follows:

As shown in FIG. 12 , the power cable electrical tree defect detection device 30 includes: 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 .

An aging module 31 is used to obtain the conductivity and capacitance characteristic parameters of cable sample sections with different types of electrical tree defects based on an electrical tree aging experiment, and simulate corresponding positioning signals according to the conductivity and capacitance characteristic parameters;

A denoising module 32 is used to obtain a positive frequency single-ended impedance spectrum function signal of the cable to be tested based on a network analyzer, and multiply 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;

A frequency domain signal acquisition module 33, used to obtain a frequency domain signal of the cable under test based on the denoised positive frequency signal of the cable under test;

A positioning signal acquisition module 34, used 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 determination module 35 is used to determine the type and location of the electrical tree 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 with different electrical tree defect types.

In a possible implementation, the frequency domain signal acquisition module 33 is specifically used to:

The negative frequency signal of the cable under test is obtained by performing conjugate symmetry solution on the denoised positive frequency signal of the cable under test, and the frequency domain signal of the cable under test is obtained according to the denoised positive frequency signal of the cable under test and the negative frequency signal of the cable under test.

In a possible implementation, the positioning signal acquisition module 34 is specifically used to:

Perform Fourier transform on the frequency domain signal of the cable under test to obtain the time domain signal of the cable under test, multiply the time domain signal of the cable under test by the speed of the electromagnetic wave to obtain the space domain signal of the cable under test, and compare the space domain signal of the cable under test with the space domain signal of the non-fault cable to obtain the positioning signal of the cable under test.

In a possible implementation, the aging module 31 is specifically configured to:

For each cable sample segment, the capacitance of the cable sample segment is measured by a network analyzer, and the conductance of the cable sample segment is obtained by a three-electrode system; the positive-frequency single-ended impedance spectrum function signal of the cable sample segment is simulated according to the capacitance and conductance of the cable sample segment, and the positioning signal of the cable sample segment is obtained based on the positive-frequency single-ended impedance spectrum function signal of the cable sample segment.

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 to the test electrode, the inner semi-conductive layer of the cable sample section is connected to the high-voltage electrode, and the protective electrode is placed flat on the surface of the insulation layer of the cable sample section;

The high voltage electrode is connected to a high voltage test power supply, the test electrode is connected to a test interface of a digital picoammeter, the ground terminal of the digital picoammeter is grounded, and the protection electrode is grounded.

In a possible implementation, different cable sample sections have different aging times.

FIG13 is a schematic diagram of a terminal provided by an embodiment of the present invention. As shown in FIG13 , 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. When the processor 40 executes the computer program 42, the steps in the above-mentioned embodiments of the power cable electrical tree defect detection method are implemented, such as S101 to S105 shown in FIG1 . Alternatively, when the processor 40 executes the computer program 42, the functions of the modules/units in the above-mentioned device embodiments are implemented, such as the functions of the modules/units 31 to 35 shown in FIG12 .

Exemplarily, the computer program 42 may be divided into one or more modules/units, which 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 implementing specific functions, which are used to describe the execution process of the computer program 42 in the terminal 4. For example, the computer program 42 may be divided into modules/units 31 to 35 as shown in FIG. 12 .

The terminal 4 may include, but is not limited to, a processor 40 and a memory 41. Those skilled in the art will appreciate that FIG13 is merely an example of the terminal 4 and does not constitute a limitation on the terminal 4, and may include more or fewer components than shown in the figure, or a combination of certain components, or different components, for example, the terminal may also include input and output devices, network access devices, buses, etc.

The processor 40 may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor, etc.

The memory 41 may be an internal storage unit of the terminal 4, such as a hard disk or 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 card, etc. equipped 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 to store 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.

The technicians in the relevant field can clearly understand that for the convenience and simplicity of description, only the division of the above-mentioned functional units and modules is used as an example for illustration. In practical applications, the above-mentioned function allocation can be completed by different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiment can be integrated in a processing unit, or each unit can exist physically separately, or two or more units can be integrated in one unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of software functional units. In addition, the specific names of the functional units and modules are only for the convenience of distinguishing each other, and are not used to limit the scope of protection of this application. The specific working process of the units and modules in the above-mentioned system can refer to the corresponding process in the aforementioned method embodiment, which will not be repeated here.

In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

Those of ordinary skill in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

In the embodiments provided by the present invention, it should be understood that the disclosed devices/terminals and methods can be implemented in other ways. For example, the device/terminal embodiments described above are only schematic. For example, the division of the modules or units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple 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 each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

If the integrated module/unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by the processor, the steps of the above-mentioned power cable electrical tree defect detection method embodiments can be implemented. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium may include: any entity or device capable of carrying the computer program code, recording medium, U disk, mobile hard disk, disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electric carrier signal, telecommunication signal and software distribution medium. It should be noted that the content contained in the computer-readable medium can be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electric carrier signals and telecommunication signals.

The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection 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.