Cable local defect positioning method based on amplitude impedance spectrum and phase impedance spectrum

Abstract

The invention relates to the technical field of cable local defect positioning, in particular to a cable local defect positioning method based on an amplitude impedance spectrum and a phase impedance spectrum, and the method comprises the steps: calculating the input impedance spectrum of a cable through measuring the electrical parameters of the cable and calculating the distribution parameters of the cable by means of a transmission line theory; using integral transformation to convert an impedance spectrum on a frequency domain into a transformation function on a space, and realizing extraction of local defect position information of the cable; and accurately positioning the defect position of the cable by designing a diagnosis function.

Description

Technical Field

[0001] This invention relates to the field of cable local defect location technology, and in particular to a method for locating cable local defects based on amplitude impedance spectrum and phase impedance spectrum. Background Technology

[0002] With the further development of urban construction, overhead transmission lines are gradually being replaced by power cables, which are increasingly accounting for a larger proportion of the power grid and have become an important component of the power system. In the distribution network, cables are the primary medium for transferring electrical energy, and their failure directly determines the safety and economy of the entire power system. With the widespread use of power cables, power cable failures are gradually increasing. Because most cables are buried underground, locating faults is difficult, necessitating large-scale power outages for maintenance, which can cause inconvenience to people's lives and production, and even lead to significant economic losses.

[0003] The steps for determining the fault location are as follows: First, measure the insulation impedance to determine the nature of the fault; second, perform preliminary distance measurement to calculate the fault distance; then, probe the cable path to find the burial depth; finally, perform precise location determination to pinpoint the exact location of the fault. The most important steps are distance measurement and location determination. Distance measurement roughly calculates the distance between the fault point and the test end, delineating the approximate area where the fault is located; location determination further narrows down the measurement range of the fault point, combining this with the cable laying path to pinpoint the exact location of the fault.

[0004] There are currently two main methods for cable fault location: impedance ranging and traveling wave ranging. Impedance ranging is simple and intuitive in principle, but it is easily affected by cable characteristic parameters and fault resistance. Traveling wave ranging is convenient to operate, requiring only a detection device to be set up at one end of the faulty cable to measure the fault distance. However, both methods generally suffer from problems such as difficulty in identifying reflected waveforms, large pulse delay measurement errors, and poor positioning accuracy. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes a method for locating local defects in cables based on amplitude impedance spectrum and phase impedance spectrum, thereby achieving precise location of local defects in cables.

[0006] To achieve the above objectives, this invention provides a method for locating local defects in cables based on amplitude impedance spectrum and phase impedance spectrum, the specific steps of which are as follows: S1: Measure the electrical parameters of the healthy state and the electrical parameters of the cable with local defects, calculate the distributed parameters of both, and calculate the input impedance spectrum based on the distributed parameters; S2: Perform an integral transformation on the calculated impedance spectrum function; S3: Based on the obtained integral transform function, obtain the amplitude quotient diagnostic function, amplitude difference diagnostic function, phase quotient diagnostic function, and phase difference diagnostic function; S4: Observe the images of the amplitude quotient diagnostic function, amplitude difference diagnostic function, phase quotient diagnostic function and phase difference diagnostic function, and determine the location of local defects according to the judgment criteria; The amplitude quotient judgment function is: The amplitude difference judgment function is The phase quotient judgment function is: The phase difference determination function is In the formula, and For the amplitude integral transform function and phase integral transform function of the healthy cable, and These are the amplitude integral transform function and the phase integral transform function for cables with local defects.

[0007] Compared with the prior art, the present invention has the following beneficial effects: This invention only requires measuring the basic electrical parameters of the cable, making it simple to operate. At the same time, it uses four diagnostic functions—amplitude quotient diagnostic function, amplitude difference diagnostic function, phase quotient diagnostic function, and phase difference diagnostic function—to determine the location of local defects in the cable with high accuracy. Attached Figure Description

[0008] Figure 1 This is a flowchart of the method of the present invention. Figure 2 This is a diagram of the cable distributed parameter model. Figure 3 This is a logic diagram of the judgment criteria. Figure 4 This is a cross-sectional view of a coaxial single-core XLPE cable. Figure 5 This is the graph of the amplitude quotient judgment function. Figure 6 This is a graph of the amplitude difference judgment function. Figure 7 This is a graph of the phase quotient judgment function. Figure 8 This is a graph of the phase difference determination function. Detailed Implementation

[0009] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0010] like Figures 1 to 8 As shown, this invention provides a method for locating local defects in cables based on amplitude impedance spectrum and phase impedance spectrum, including the following steps: S1: Measure the electrical parameters of the healthy state and the electrical parameters of the cable with local defects, calculate the distributed parameters of both, and calculate the input impedance spectrum based on the distributed parameters; S2: Perform an integral transformation on the calculated impedance spectrum function; S3: Based on the obtained integral transform function, obtain the amplitude quotient diagnostic function, amplitude difference diagnostic function, phase quotient diagnostic function, and phase difference diagnostic function; S4 Observe the images of the amplitude quotient diagnostic function, amplitude difference diagnostic function, phase quotient diagnostic function and phase difference diagnostic function, and determine the location of local defects according to the judgment criteria.

[0011] Specifically, in step S1, the electrical parameters of a healthy cable and the electrical parameters of a cable with local defects are measured, and the electrical parameters include at least the core conductor radius. Shielding layer radius Conductivity of cable core conductor Shielding layer conductivity .

[0012] Specifically, in step S1, the distributed parameters include capacitance, inductance, and conductance, and the specific formula for calculating the distributed parameters is as follows: resistance inductance electrical conductivity capacitance in, Represents the permeability of free space. Indicates the angular frequency of an electrical signal. Represents the dielectric constant of the dielectric. It represents the permeability of the dielectric.

[0013] Specifically, in step S1, the propagation coefficient and characteristic impedance of the cable are calculated based on the distributed parameters: Propagation coefficient Characteristic impedance in, These represent the distributed resistance, distributed inductance, distributed conductance, and distributed capacitance of the cable, respectively. The real part of the propagation coefficient is represented by the number of digits. Represents the imaginary part of the propagation coefficient. It represents the imaginary unit.

[0014] Based on transmission line theory and the distributed parameter model of cables, such as Figure 2 As shown, combining Kirchhoff's voltage law and Kirchhoff's current law, we obtain the following equation: in, This indicates the distance of the current cable position from the end load.

[0015] The above formula can be simplified to obtain When When the expression approaches 0, the above equation becomes Rewrite the above equation using the phasor method. Solving the differential equations yields phasors and phasor The display expression in, Indicates the incident voltage wave. This represents a reflected voltage wave.

[0016] Note that when When this occurs, it means that the distance between this position of the cable and the end load is 0, then the end load... .

[0017] Define the reflection coefficient at the load end of the cable. , This indicates a short circuit in the end load. The incident signal remains the same in magnitude but has a reversed phase and is reflected. This indicates that the end load is open-circuited. The incident signal remains unchanged in magnitude and phase during reflection.

[0018] Total length is Cable start-up impedance spectrum The input impedance spectrum at the cable's head end is a complex phasor, possessing both phase and amplitude characteristics. The amplitude of the impedance spectrum is denoted as... phase , The function is used to calculate the phase angle.

[0019] Using integral transform, the impedance spectrum in the frequency domain is obtained. Transform into an integral transform function in space This allows for the extraction of local defect features in cables.

[0020] Selected , which serves as the kernel function for the integral transform.

[0021] Amplitude integral transform function of healthy cable Phase integral transform function .

[0022] in, This represents the amplitude of the input impedance spectral function at the beginning of the healthy cable. This represents the phase of the input impedance spectrum function at the beginning of the healthy cable.

[0023] Amplitude integral transform function of a cable with local defects Phase integral transform function ,in, This indicates the amplitude of the input impedance spectrum at the beginning of a cable with localized defects. This indicates the phase of the input impedance spectrum at the beginning of a cable with local defects.

[0024] Define the amplitude quotient judgment function Define the amplitude difference judgment function Define the phase quotient judgment function Define phase difference judgment function .

[0025] Judgment criteria: If the amplitude quotient judgment function and the phase quotient judgment function are both greater than 10, and the amplitude difference judgment function and the phase difference judgment function are both greater than 0, then the cable is considered to be at this position. There are local defects, such as Figure 3 As shown.

[0026] Use such as Figure 3 The coaxial single-core XLPE cable shown has the following simulated cable parameters: copper core radius 3.5mm, inner semiconductor layer 0.5mm, insulation layer 4.6mm, outer semiconductor layer 0.5mm, sheath 1.4mm, and permeability. H / m, conductivity S / m.

[0027] The total cable length is set at 50m, with localized damage locations ranging from 30m to 30.3m, and the signal frequency range is 1kHz-120MHz.

[0028] Using the integral kernel function The simulation yields the amplitude quotient judgment function, amplitude difference judgment function, phase quotient judgment function, and phase difference judgment function, such as... Figure 5 , 6 As shown in Figures 7 and 8.

[0029] observe Figure 5 , 6 Note that only at 30.1m are the amplitude quotient diagnostic function and the phase difference diagnostic function greater than 0, and both are greater than 10. Therefore, according to the judgment criteria, it is determined that there is a local defect in the cable at 30.1m.

Claims

1. A method for locating local defects in cables based on amplitude impedance spectrum and phase impedance spectrum, characterized in that, Includes the following steps: S1: Measure the electrical parameters of the healthy state and the electrical parameters of the cable with local defects, calculate the distributed parameters of both, and calculate the input impedance spectrum based on the distributed parameters; S2: Perform an integral transformation on the calculated impedance spectrum function; S3: Based on the obtained integral transform function, obtain the amplitude quotient diagnostic function, amplitude difference diagnostic function, phase quotient diagnostic function, and phase difference diagnostic function; S4: Observe the images of the amplitude quotient diagnostic function, amplitude difference diagnostic function, phase quotient diagnostic function and phase difference diagnostic function, and determine the location of local defects according to the judgment criteria; The amplitude quotient judgment function is: The amplitude difference judgment function is The phase quotient judgment function is: The phase difference determination function is In the formula, and For the amplitude integral transform function and phase integral transform function of the healthy cable, and These are the amplitude integral transform function and the phase integral transform function for cables with local defects.

2. The cable local defect location method based on amplitude impedance spectrum and phase impedance spectrum according to claim 1, characterized in that: In step S1, the electrical parameters include at least the cable core conductor radius. Shielding layer radius Conductivity of cable core conductor Shielding layer conductivity .

3. The cable local defect location method based on amplitude impedance spectrum and phase impedance spectrum according to claim 2, characterized in that: In step S1, the distributed parameters include capacitance, inductance, and conductance. The specific formula for calculating the distributed parameters is as follows: resistance inductance electrical conductivity capacitance in, Represents the permeability of free space. Indicates the angular frequency of an electrical signal. Represents the dielectric constant of the dielectric. It represents the permeability of the dielectric.

4. The cable local defect location method based on amplitude impedance spectrum and phase impedance spectrum according to claim 3, characterized in that: In step S1, the input impedance spectrum at the beginning of the cable is: in, Indicates the angular frequency of an electrical signal. Indicates the characteristic impedance of the cable. The reflection coefficient at the load end of the cable. Indicates the propagation coefficient of the cable. Indicates the total length of the cable; The input impedance spectrum at the cable's head end is a complex phasor, possessing both phase and amplitude characteristics. The amplitude of the impedance spectrum is denoted as... phase .

5. The cable local defect location method based on amplitude impedance spectrum and phase impedance spectrum according to claim 4, characterized in that: In step S2, the specific method for performing an integral transformation on the calculated impedance spectrum function is as follows: Selected , as the kernel function of the integral transform; The amplitude integral transform function and phase integral transform function of the healthy cable are as follows: in, This represents the amplitude of the input impedance spectral function at the beginning of the healthy cable. This represents the phase of the input impedance spectrum function at the beginning of the healthy cable; The amplitude integral transform function and phase integral transform function for a cable with local defects are as follows: in, This indicates the amplitude of the input impedance spectrum at the beginning of a cable with localized defects. This indicates the phase of the input impedance spectrum at the beginning of a cable with local defects.

6. The cable local defect location method based on amplitude impedance spectrum and phase impedance spectrum according to claim 1, characterized in that, It also includes the following steps: In step S4, the judgment criterion is: If the amplitude quotient judgment function and the phase quotient judgment function are both greater than 10, and the amplitude difference judgment function and the phase difference judgment function are both greater than 0, then the cable is considered to have a local defect at that location.

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