A method and device for cable end load analysis based on cable head-end impedance spectrum

Abstract

The application relates to a cable end load analysis method and device based on cable head end impedance spectrum, which comprises the following steps: connecting the output port of an impedance analyzer to the core and metal shielding layer of a test cable; connecting the cable end to a pure resistive load, a plurality of specific impedance angle loads and an actual load to be measured in sequence; under various load conditions, collecting a plurality of impedance spectrum data corresponding to the cable end connected to various loads by using the impedance analyzer to test the incident sweep frequency signal of the cable; drawing the impedance spectrum data by using a computer to obtain the impedance amplitude spectrum waveform and the impedance phase spectrum waveform under various load conditions; comparing the impedance spectrum waveform of the actual load to be measured with the impedance spectrum waveform under the pure resistive load; determining the shift of the impedance spectrum oscillation peak value of the actual load to be measured according to the comparison result; and determining whether the actual load to be measured is capacitive or inductive according to the shift. The application can quickly and effectively determine the nature of the cable end load.

Description

Technical Field

[0001] This invention relates to the field of cable end load characterization technology, specifically to a cable end load analysis method and apparatus based on the cable head impedance spectrum. Background Technology

[0002] Due to their small footprint and strong electrical and mechanical properties, distribution cables ensure the stability of power transmission and are of great significance in urban power transportation. With the development of urbanization, cable lines occupy an increasingly larger proportion of power transmission and distribution systems. To date, the State Grid Corporation of China operates over 550,000 kilometers of distribution network cables, with an urban cable coverage rate of 57.1%. The normal operation of cables is directly related to socio-economic development and the safety and reliability of power supply; therefore, defect and fault detection and end-load assessment of cables have become particularly important.

[0003] Traditional methods for determining whether a load is inductive, capacitive, or purely resistive typically require detecting the phase difference between the voltage and current flowing through the load, and this process takes at least a quarter of a signal cycle to determine. Current methods for load characterization also include analyzing load current waveform data based on fuzzy pattern recognition. This involves acquiring and studying the load current waveform, analyzing it using mathematical techniques such as Fourier transform, and finally identifying the load character using fuzzy pattern recognition. However, this method requires acquiring the current waveform at the load end and performing mathematical transformations such as FFT, making it complex and unable to determine the range of the load impedance angle. Other methods include wavelet analysis and neural network-based load identification, but these all have limitations. In wavelet analysis, the selection of different wavelets and decomposition levels significantly affects the identification results, but currently there is no theoretical guidance on the specific selection of wavelet functions and decomposition levels in practical problems; it can only be determined experimentally. Neural network-based load identification is not yet technically mature and requires further improvement to ensure its reliability. Summary of the Invention

[0004] The purpose of this invention is to propose a method and apparatus for analyzing cable end load based on the impedance spectrum of the cable head, which can quickly and effectively determine the load characteristics and impedance angle range of the cable end.

[0005] To achieve the above objectives, this invention proposes a cable end load analysis method based on the impedance spectrum of the cable head, comprising the following steps:

[0006] Connect the output port of the impedance analyzer to the conductor and metal shield of the test cable;

[0007] The test cable ends are connected in sequence to a purely resistive load, multiple loads with specific impedance angles, and the actual load to be tested. Under various load conditions, the impedance analyzer is used to sweep the incident frequency signal of the test cable to collect multiple impedance spectrum data corresponding to the various loads connected to the end of the test cable.

[0008] The computer plots the multiple impedance spectrum data to obtain impedance amplitude spectrum waveforms and impedance phase spectrum waveforms under various load conditions.

[0009] The impedance spectrum waveform of the actual load under test is compared with the impedance spectrum waveform of the purely resistive load. Based on the comparison result, the shift of the oscillation peak of the impedance spectrum of the actual load under test is determined, and based on the shift, it is determined whether the actual load under test is capacitive or inductive.

[0010] Preferably, the resistance value of the purely resistive load is different from the characteristic impedance value of the test cable.

[0011] Preferably, the specific impedance angles of the plurality of specific impedance angle loads are ±30°, ±45°, and ±60°, respectively.

[0012] Preferably, determining whether the actual load under test is capacitive or inductive based on the offset includes:

[0013] If the peak value of the impedance spectrum oscillation of the actual load under test leads that of the purely resistive load, then the actual load under test is capacitive; if the peak value of the impedance spectrum oscillation of the actual load under test lags that of the purely resistive load, then the actual load under test is inductive.

[0014] Preferably, the method further includes:

[0015] The impedance spectrum curve of the actual load under test is compared with the impedance spectrum curves of multiple loads with specific impedance angles of the same nature. Based on the comparison results, it is determined which two impedance spectrum curves of the multiple loads with specific impedance angles the degree of shift of the impedance spectrum resonance peak of the actual load under test is between. Based on the two specific impedance angles corresponding to the two impedance spectrum curves, the impedance angle range of the actual load under test is determined.

[0016] The present invention also proposes a cable end load analysis device based on the impedance spectrum of the cable head end, which is used to implement the above-mentioned cable end load analysis method based on the impedance spectrum of the cable head end. The device includes an impedance analyzer, a computer, and a load characteristic determination module; the output port of the impedance analyzer is connected to the conductor and the metal shielding layer of the test cable.

[0017] The impedance analyzer is used to collect multiple impedance spectrum data corresponding to the various loads connected to the end of the test cable when the end of the test cable is connected to a purely resistive load, multiple specific impedance angle loads and the actual load to be tested in sequence.

[0018] The computer is used to plot the multiple impedance spectrum data to obtain impedance amplitude spectrum waveforms and impedance phase spectrum waveforms under various load conditions.

[0019] The load characteristic determination module is used to compare the impedance spectrum waveform of the actual load under test with the impedance spectrum waveform of the purely resistive load, determine the shift of the oscillation peak of the impedance spectrum of the actual load under test based on the comparison result, and determine whether the actual load under test is capacitive or inductive based on the shift.

[0020] Preferably, it further includes:

[0021] The impedance angle determination module is used to compare the impedance spectrum curve of the actual load under test with the impedance spectrum curves of multiple loads with specific impedance angles of the same nature. Based on the comparison results, it determines which two impedance spectrum curves of the multiple loads with specific impedance angles the degree of shift of the impedance spectrum resonance peak of the actual load under test is between. Based on the two specific impedance angles corresponding to the two impedance spectrum curves, it determines the impedance angle range of the actual load under test.

[0022] The present invention has at least the following beneficial effects:

[0023] This invention utilizes the impedance spectrum of the cable's beginning to determine the load characteristics and range of the load impedance angle at the cable's end. Compared to other load characteristic identification methods, this invention does not require acquiring voltage, current, or other related data at the cable's load end. It can determine the load characteristics and the range of the load impedance angle simply by measuring the impedance spectrum data at the cable's beginning. This invention extends the application of broadband impedance spectroscopy at the cable's beginning, allowing maintenance personnel to determine the load characteristics at the cable's end without adding any additional equipment, while simultaneously using impedance spectroscopy to locate and diagnose cable defects.

[0024] Other features and advantages of the present invention will be set forth in the following description. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a flowchart of a cable end load analysis method based on the impedance spectrum of the cable head in an embodiment of the present invention.

[0027] Figure 2 This is a flowchart illustrating a cable end load analysis method based on the impedance spectrum of the cable head in an embodiment of the present invention.

[0028] Figure 3 This is a schematic diagram comparing the impedance spectra of purely resistive loads with different resistance values ​​in an embodiment of the present invention.

[0029] Figure 4 This is a schematic diagram comparing the impedance spectra of loads with different properties in an embodiment of the present invention.

[0030] Figure 5 This is a schematic diagram comparing the impedance spectra of inductive loads with different impedance angles in an embodiment of the present invention.

[0031] Figure 6 This is a schematic diagram comparing the impedance spectra of capacitive loads with different impedance angles in an embodiment of the present invention.

[0032] Figure 7 This is a structural diagram of a cable end load analysis device based on the impedance spectrum of the cable head in an embodiment of the present invention.

[0033] Figure 8 This is a schematic diagram of the cable end load analysis device based on the impedance spectrum of the cable head end and the cable connection in an embodiment of the present invention.

[0034] Figure 9 This is a structural diagram of a cable end load analysis device based on the impedance spectrum of the cable head in an embodiment of the present invention. Detailed Implementation

[0035] The various exemplary embodiments, features, and aspects of this disclosure will now be described in detail with reference to the accompanying drawings. Furthermore, numerous specific details are set forth in the following detailed embodiments to better illustrate the invention. Those skilled in the art will understand that the invention can be practiced without certain specific details. In some instances, means well known to those skilled in the art have not been described in detail in order to highlight the spirit of the invention.

[0036] See Figure 1 One embodiment of the present invention proposes a method for cable end load analysis based on the impedance spectrum of the cable head, comprising the following steps:

[0037] Step S1: Connect the output port of the impedance analyzer to the conductor and metal shield of the test cable;

[0038] Specifically, the impedance analyzer is an instrument used to analyze the input impedance of a cable. It is an existing device, so its structure will not be described in detail in this embodiment. In this embodiment, the acquisition of cable impedance spectrum data can be achieved based on any type of impedance analyzer.

[0039] Step S2: Connect a purely resistive load, multiple loads with specific impedance angles, and the actual load to be tested to the end of the test cable in sequence. Under various load conditions, use the impedance analyzer to sweep the incident frequency signal of the test cable and collect multiple impedance spectrum data corresponding to the various loads connected to the end of the test cable.

[0040] Specifically, the resistance value of the purely resistive load is different from the characteristic impedance value of the test cable. It should be noted that the greater the difference between the resistance value of the selected purely resistive component and the characteristic impedance value of the test cable, the easier it is to judge and compare the subsequent waveforms, and the more obvious the judgment effect.

[0041] Step S3: The computer plots the multiple impedance spectrum data to obtain impedance amplitude spectrum waveforms and impedance phase spectrum waveforms under various load conditions;

[0042] Preferably, but not limited to, the specific impedance angles of the multiple specific impedance angle loads are ±30°, ±45°, and ±60°, respectively. That is, 8 impedance spectrum data can be obtained in step S2, and 8 impedance amplitude spectrum waveforms and 8 impedance phase spectrum waveforms can be obtained in step S3. It should be noted that if more specific impedance angles are selected for testing, more reference impedance spectrum curves will be obtained under the specific impedance angles, and the determination of the impedance angle range of the actual load under test will be more accurate. Furthermore, an impedance spectrum curve database under each specific impedance angle load can be established as a reference to improve accuracy and facilitate analysis and judgment.

[0043] Step S4: Compare the impedance spectrum waveform of the actual load under test with the impedance spectrum waveform of the purely resistive load, determine the shift of the oscillation peak of the impedance spectrum of the actual load under test based on the comparison result, and determine whether the actual load under test is capacitive or inductive based on the shift.

[0044] Further, determining whether the actual load under test is capacitive or inductive based on the offset includes:

[0045] If the peak value of the impedance spectrum oscillation of the actual load under test leads that of the purely resistive load, then the actual load under test is capacitive; if the peak value of the impedance spectrum oscillation of the actual load under test lags that of the purely resistive load, then the actual load under test is inductive.

[0046] Further, see Figure 2 The method further includes:

[0047] Step S5: Compare the impedance spectrum curve of the actual load under test with the impedance spectrum curves of multiple loads with specific impedance angles of the same nature. Based on the comparison results, determine which two impedance spectrum curves of the multiple loads with specific impedance angles the degree of shift of the impedance spectrum resonance peak of the actual load under test is between. Based on the two specific impedance angles corresponding to the two impedance spectrum curves, determine the impedance angle range of the actual load under test.

[0048] Specifically, based on the determination in step S4 that the nature of the actual load under test is capacitive or inductive, in step S5, the impedance spectrum curve of the actual load under test is further compared with the impedance spectrum curves of multiple loads with specific impedance angles of the same nature. The impedance angle range of the actual load under test is determined according to the comparison results. For example, if the degree of shift of the impedance spectrum resonance peak of the actual load under test is between the 45° and 60° impedance spectrum curves of the multiple loads with specific impedance angles, then the impedance angle range of the actual load under test is 45° to 60°. It can be understood that the more impedance spectrum curves at specific impedance angles used as comparison references, the more accurate the determination of the impedance angle range of the actual load under test will be.

[0049] To facilitate a further understanding of the embodiments of the present invention, the following supplementary description of the process of proposing the embodiments of the present invention is provided:

[0050] According to the formula for calculating the input impedance spectrum at the beginning of the cable:

[0051]

[0052] Among them, Γ L Let Γ be the reflection coefficient at the load end, l be the cable length, r be the propagation constant, V(l) be the voltage, I(l) be the current, and Γ be the propagation constant. L The expression is:

[0053]

[0054] Among them, Z L Let Z be the load impedance and Z0 be the characteristic impedance of the cable. As can be seen from formulas (1) and (2), the change in the load impedance at the end of the cable will cause a change in the reflection coefficient, which in turn will affect the measurement of the impedance spectrum at the beginning of the cable and produce different impedance spectrum waveforms.

[0055] Experimental verification has shown that loads of different properties (resistive, inductive, capacitive), or loads that are both inductive (capacitive) but have different impedance angles, will have obvious contrasting impedance spectra when connected to the same cable end.

[0056] The following example uses a 15m long cable. The relevant parameters of the cable are set as shown in Table 1. The characteristic impedance of the cable is calculated to be 34.6Ω. The frequency range for measuring the impedance spectrum is 1kHz-50MHz, and the sampling interval is 0.01MHz.

[0057] Table 1 - Parameter Settings for Simulated Cables

[0058] Simulation parameters and their significance numerical values <![CDATA[Radius r of the core conductor c (mm)]]> 4 <![CDATA[Radius r of the shielding layer s (mm)]]> 9.5 <![CDATA[Cable core resistivity ρ c (Ω / m)]]> <![CDATA[1.75*10 -8 ]]> <![CDATA[Resistivity ρ of the shielding layer s (Ω / m)]]> <![CDATA[1.75*10 -8 ]]> XLPE dielectric constant ε (F / m) <![CDATA[2.04*10 -11 ]]> XLPE conductivity σ (S / m) <![CDATA[1*10 -16 ]]> <![CDATA[Magnetic permeability of vacuum μ0 (H / m)]]> <![CDATA[4π*10 -7 ]]>

[0059] The cable end load was set to purely resistive, with resistance values ​​set to impedance matching, 35Ω, and 50Ω respectively. The measured impedance spectrum waveforms were compared as follows: Figure 3 As shown; by Figure 3 It is evident that when the load at the end is a purely resistive resistor that is different from the characteristic impedance, both the amplitude and phase spectra at the cable head exhibit periodic fluctuations. Furthermore, the greater the difference between the load resistance and the characteristic impedance, the greater the oscillation amplitude, while the phase remains unchanged.

[0060] The impedance spectra of the cable ends with purely resistive (50Ω), inductive (50√2∠45°), and capacitive (50√2∠-45°) loads are compared below. Figure 4 As shown; by Figure 4 It can be seen that, compared with the impedance spectrum of a purely resistive load, the oscillation peak (resonance point) of the impedance spectrum waveform of a capacitive load is ahead, while the oscillation peak (resonance point) of the impedance spectrum waveform of an inductive load is lagging behind. Both the amplitude spectrum and the phase spectrum have this characteristic.

[0061] Impedance spectra of cables with the same load characteristics at the cable ends but different impedance angles, for example... Figure 5 , Figure 6 As shown, keeping the load impedance amplitude constant at 50Ω, the load impedance angle is changed to 30° and 60° respectively under inductive and capacitive conditions. Figure 5 It is evident that, using the impedance spectrum of a purely resistive load as a reference, as the impedance angle of an inductive load gradually increases, the hysteresis shift of its impedance spectrum resonance peak becomes more severe, and the oscillation amplitude becomes larger; from Figure 6 It is evident that, using the impedance spectrum of a purely resistive load as a reference, as the impedance angle of a capacitive load gradually increases, the leading shift of its impedance spectrum resonance peak becomes more severe, and the oscillation amplitude also increases. This characteristic is present in both the amplitude spectrum and the phase spectrum.

[0062] Based on the above three properties, the specific method for determining the load characteristics and impedance angle range at the end of the cable in the embodiments of the present invention can be derived.

[0063] Another embodiment of the present invention also proposes a cable end load analysis device based on the impedance spectrum of the cable head end, used to implement the cable end load analysis method based on the impedance spectrum of the cable head end described in the above embodiments, such as... Figure 7-8As shown, the device includes an impedance analyzer 1, a computer 2, and a load characteristic determination module 3; the output port of the impedance analyzer 1 is connected to the conductor and the metal shielding layer of the test cable.

[0064] The impedance analyzer 1 is used to collect multiple impedance spectrum data corresponding to the various loads connected to the end of the test cable when the end of the test cable is connected to a purely resistive load, multiple specific impedance angle loads and the actual load to be tested in sequence.

[0065] The computer 2 is used to plot the multiple impedance spectrum data to obtain impedance amplitude spectrum waveforms and impedance phase spectrum waveforms under various load conditions.

[0066] The load property determination module 3 is used to compare the impedance spectrum waveform of the actual load under test with the impedance spectrum waveform of the purely resistive load, determine the shift of the impedance spectrum oscillation peak of the actual load under test based on the comparison result, and determine whether the actual load under test is capacitive or inductive based on the shift.

[0067] See Figure 9 The apparatus in this embodiment further includes:

[0068] Impedance angle determination module 4 is used to compare the impedance spectrum curve of the actual load under test with the impedance spectrum curves of multiple loads with specific impedance angles of the same nature, and determine, based on the comparison result, which two impedance spectrum curves of the impedance spectrum resonant peak of the actual load under test are between, and determine the impedance angle range of the actual load under test based on the two specific impedance angles corresponding to the two impedance spectrum curves.

[0069] It should be noted that the apparatus of the above embodiments corresponds to the method of the above embodiments. Therefore, the parts of the apparatus of the above embodiments that are not described in detail can be obtained by referring to the content of the method of the above embodiments. That is, the specific steps of the method of the above embodiments can be understood as the functions that the apparatus of the above embodiments can achieve, and will not be described again here.

[0070] As can be seen from the above description of the embodiments, the embodiments of the present invention have the following advantages:

[0071] This invention utilizes the impedance spectrum of the cable's beginning to determine the load characteristics and range of the load impedance angle at the cable's end. Compared to other load characteristic identification methods, this invention does not require acquiring voltage, current, or other related data at the cable's load end. It can determine the load characteristics and the range of the load impedance angle simply by measuring the impedance spectrum data at the cable's beginning. This invention extends the application of broadband impedance spectroscopy at the cable's beginning, allowing maintenance personnel to determine the load characteristics at the cable's end without adding any additional equipment, while simultaneously using impedance spectroscopy to locate and diagnose cable defects.

[0072] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for analyzing cable end load based on the impedance spectrum of the cable head, characterized in that, Includes the following steps: Connect the output port of the impedance analyzer to the conductor and metal shield of the test cable; The test cable ends are connected in sequence to a purely resistive load, multiple loads with specific impedance angles, and the actual load to be tested. Under various load conditions, the impedance analyzer is used to sweep the incident frequency signal of the test cable to collect multiple impedance spectrum data corresponding to the various loads connected to the end of the test cable. The computer plots the multiple impedance spectrum data to obtain impedance amplitude spectrum waveforms and impedance phase spectrum waveforms under various load conditions; The impedance spectrum waveform of the actual load under test is compared with that of the purely resistive load. Based on the comparison result, the shift of the peak value of the impedance spectrum oscillation of the actual load under test is determined, and the actual load under test is determined to be capacitive or inductive based on the shift. If the peak value of the impedance spectrum oscillation of the actual load under test leads that of the purely resistive load, the actual load under test is capacitive; if the peak value of the impedance spectrum oscillation of the actual load under test lags that of the purely resistive load, the actual load under test is inductive. The impedance spectrum curve of the actual load under test is compared with the impedance spectrum curves of multiple loads with specific impedance angles of the same nature. Based on the comparison results, it is determined which two impedance spectrum curves of the multiple loads with specific impedance angles the degree of shift of the impedance spectrum resonance peak of the actual load under test is between. Based on the two specific impedance angles corresponding to the two impedance spectrum curves, the impedance angle range of the actual load under test is determined.

2. The cable end load analysis method based on the impedance spectrum of the cable head end according to claim 1, characterized in that, The resistance value of the purely resistive load is different from the characteristic impedance value of the test cable.

3. The cable end load analysis method based on the impedance spectrum of the cable head as described in claim 1, characterized in that, The specific impedance angles of the multiple specific impedance angle loads are ±30°, ±45°, and ±60°, respectively.

4. A cable end load analysis device based on the impedance spectrum of the cable head, characterized in that, The apparatus for implementing the cable end load analysis method based on the cable head impedance spectrum as described in any one of claims 1-3 includes an impedance analyzer, a computer, and a load characteristic determination module; the output port of the impedance analyzer is connected to the conductor and the metal shielding layer of the test cable. The impedance analyzer is used to collect multiple impedance spectrum data corresponding to the various loads connected to the end of the test cable when the end of the test cable is connected to a purely resistive load, multiple specific impedance angle loads and the actual load to be tested in sequence. The computer is used to plot the multiple impedance spectrum data to obtain impedance amplitude spectrum waveforms and impedance phase spectrum waveforms under various load conditions. The load characteristic determination module is used to compare the impedance spectrum waveform of the actual load under test with the impedance spectrum waveform of the purely resistive load, determine the shift of the impedance spectrum oscillation peak of the actual load under test based on the comparison result, and determine whether the actual load under test is capacitive or inductive based on the shift. If the impedance spectrum oscillation peak of the actual load under test leads that of the purely resistive load, the actual load under test is capacitive; if the impedance spectrum oscillation peak of the actual load under test lags that of the purely resistive load, the actual load under test is inductive. The impedance angle determination module is used to compare the impedance spectrum curve of the actual load under test with the impedance spectrum curves of multiple loads with specific impedance angles of the same nature. Based on the comparison results, it determines which two impedance spectrum curves of the multiple loads with specific impedance angles the degree of shift of the impedance spectrum resonance peak of the actual load under test is between. Based on the two specific impedance angles corresponding to the two impedance spectrum curves, it determines the impedance angle range of the actual load under test.

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