Fault distance measurement method and system for cable hybrid DC line based on single-terminal and double-terminal distance measurement

Abstract

The present invention belongs to the technical field of power system line protection, and provides a cable hybrid DC line fault distance measurement method and system based on single-end and double-end distance measurement. The method includes obtaining the fault current traveling wave signals at both ends of the cable hybrid fault section line; extracting the line mode component signal from the fault current traveling wave signal; performing multi-resolution morphological gradient analysis on the line mode component signal to determine the current mutation moment; determining the fault point location based on the current mutation moment and the selected distance measurement formula; the selection principle of the distance measurement formula is: based on the refraction and reflection of the fault current traveling wave, calculate its refraction and reflection coefficient, and select the distance measurement formula corresponding to the moment of the wave head with the largest wave head amplitude obtained by analysis; the two groups of single-end and double-end fault distance measurement formulas are obtained based on the distance between the fault point and one end of the fault section line and the combination of the single-end traveling wave distance measurement principle and the double-end traveling wave distance measurement principle, and each group of fault distance measurement formulas includes two fault distance measurement formulas.

Description

Technical Field

[0001] The present invention belongs to the technical field of power system line protection, and in particular relates to a cable hybrid DC line fault ranging method and system based on single-end and double-end ranging. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Compared with AC transmission systems, DC transmission systems have the advantages of low line loss, large transmission energy, simple and flexible structure, and easy interconnection of different power grids. DC transmission lines have a wide span, and the geographical environment along the line is complex and changeable. DC transmission lines may adopt a mixed connection method of overhead lines and cables. From the perspective of space, time and frequency, the fault distance measurement methods of DC transmission lines are mainly divided into: traveling wave method, fault analysis method and natural frequency method. Among them, the traveling wave method has higher accuracy and will not be affected by line structure and fault type. However, the distance measurement using the traveling wave method is highly dependent on the accurate calibration of the traveling wave head. The transition resistance directly affects the accurate calibration of the traveling wave head, and the selection of the traveling wave velocity will also affect the distance measurement accuracy.

[0004] For hybrid DC transmission lines with cables, the line wave impedance is not uniform, and it is necessary to consider the complex refraction and reflection caused by the different wave impedances of overhead lines and cables. The inventors found that the traditional single-line fault distance measurement method is no longer applicable, and the existing hybrid DC transmission line fault distance measurement algorithms have problems with reliability and low accuracy. Summary of the invention

[0005] In order to solve the technical problems existing in the above-mentioned background technology, the present invention provides a cable hybrid DC line fault ranging method and system based on single-end and double-end ranging, which adopts a combination of single-end traveling wave method and double-end traveling wave method for the fault section line, eliminates the error caused by the traveling wave velocity, derives two sets of fault ranging formulas, and then selects one set of ranging formulas with strong anti-transition resistance ability by analyzing the properties of the traveling wave head and the refraction and reflection conditions, so as to form a practical formula for cable hybrid DC transmission line fault ranging, which can improve the reliability and accuracy of hybrid DC transmission line fault ranging.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A first aspect of the present invention provides a cable hybrid DC line fault distance measurement method based on single-terminal and double-terminal distance measurement, comprising:

[0008] Acquire the fault current traveling wave signals at both ends of the cable mixed fault section line;

[0009] Extracting line mode component signal from fault current traveling wave signal;

[0010] Perform multi-resolution morphological gradient analysis on line mode component signals to determine the moment of current mutation;

[0011] Determine the fault location based on the current mutation time and the selected distance measurement formula;

[0012] The principle for selecting the distance measurement formula is as follows: based on the refraction and reflection of the fault current traveling wave, calculate its refraction and reflection coefficient, and select the distance measurement formula corresponding to the moment of the wave head with the largest wave head amplitude obtained by analysis;

[0013] The two groups of single-end and double-end fault distance measurement formulas are obtained based on the distance between the fault point and one end of the fault section line and the combination of the single-end traveling wave distance measurement principle and the double-end traveling wave distance measurement principle. Each group of fault distance measurement formulas includes two fault distance measurement formulas.

[0014] As an implementation method, two sets of single-end and double-end fault location formulas are derived by combining the single-end traveling wave method and the double-end traveling wave method for the fault section line to eliminate the error caused by the traveling wave velocity.

[0015] As an implementation method, when 0≤x R <L / 2, select As a distance measurement formula;

[0016] When L / 2≤x R When ≤L, select As a distance measurement formula;

[0017] Where, L is the total length of the fault section line; R is one end of the fault section line, which is the non-connected end of the overhead line and the cable; I is the other end of the fault section line; x R is the distance from the fault point to the R terminal; t1 and t3 are the first and second times when the initial traveling wave of the fault current reaches the R terminal; t2 and t4 are the first and second times when the initial traveling wave of the fault current reaches the I terminal.

[0018] As an implementation manner, the fault current traveling wave signal includes the fault current traveling wave signals on the positive and negative lines at both ends of the fault section line.

[0019] As an implementation method, a Karenbauer transformation matrix is ​​used to perform phase mode transformation decoupling on the fault current traveling wave signals on the positive and negative lines to obtain line mode components and zero mode signals.

[0020] As an implementation manner, during the process of performing multi-resolution morphological gradient analysis on the line-mode component signal, the number of analysis layers is set to 2, the polarities of the sudden changes in current at both ends of the faulty section are identified, and the current mutation time is determined, so as to obtain the times when the first and second initial traveling waves of the fault current reach both ends of the faulty section line.

[0021] The second aspect of the present invention provides a cable hybrid DC line fault location system based on single-ended and double-ended ranging, which includes:

[0022] A traveling wave signal acquisition module, which is used to acquire the fault current traveling wave signals at both ends of the faulty section line of the cable hybrid;

[0023] A line-mode component signal extraction module, which is used to extract the line-mode component signal from the fault current traveling wave signal;

[0024] A current mutation time determination module, which is used to perform multi-resolution morphological gradient analysis on the line-mode component signal to determine the current mutation time;

[0025] A fault point location determination module, which is used to determine the fault point location based on the current mutation time and the selected ranging formula;

[0026] Among them, the selection principle of the ranging formula is: based on the reflection and refraction conditions of the fault current traveling wave, calculate its reflection and refraction coefficients, and select the ranging formula corresponding to the time of the wave head with the largest wave head amplitude obtained by the analysis;

[0027] The two groups of single-ended and double-ended fault ranging formulas are obtained according to the distance between the fault point and one end of the faulty section line and by combining the single-ended traveling wave ranging principle and the double-ended traveling wave ranging principle. Each group of fault ranging formulas includes two fault ranging formulas.

[0028] As an implementation manner, in the fault point location determination module, the two groups of single-ended and double-ended fault ranging formulas are derived by combining the single-ended traveling wave method and the double-ended traveling wave method for the faulty section line to eliminate the error caused by the traveling wave velocity.

[0029] As an implementation manner, in the fault point location determination module:

[0030] When 0 ≤ x R < L / 2, select as the ranging formula;

[0031] When L / 2 ≤ x R ≤ L, select as the ranging formula;

[0032] Among them, L is the total length of the faulty section line; R is one end of the faulty section line and is the non-connected end of the overhead line and the cable; I is the other end of the faulty section line; xR is the distance from the fault point to the R terminal; t1 and t3 are the first and second times when the initial traveling wave of the fault current reaches the R terminal; t2 and t4 are the first and second times when the initial traveling wave of the fault current reaches the I terminal.

[0033] A third aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps in the cable hybrid DC line fault ranging method based on single-end and double-end ranging as described above.

[0034] A fourth aspect of the present invention provides an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, the steps in the cable hybrid DC line fault ranging method based on single-end and double-end ranging as described above are implemented.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The cable hybrid DC line fault distance measurement method based on single- and double-end distance measurement of the present invention obtains the fault current traveling waves at both ends of the overhead line and cable hybrid fault section, extracts the line mode components therein, determines the current mutation moment through multi-resolution morphological gradient analysis, adopts a combination of single-end traveling wave method and double-end traveling wave method, derives two groups of fault distance measurement formulas, analyzes the properties of the traveling wave head and the refraction and reflection conditions, selects one group of distance measurement formulas with strong resistance to transition resistance, and thus realizes the fault distance measurement of the cable hybrid DC transmission line. The method has a small amount of calculation, eliminates the influence of wave speed, has high distance measurement accuracy, and has strong resistance to transition resistance.

[0037] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0039] Figure 1 is a flow chart of fault location measurement according to an embodiment of the present invention;

[0040] Figure 2 A schematic diagram of a cable hybrid DC transmission line according to an embodiment of the present invention;

[0041] Figure 3(a) shows the current at the R terminal;

[0042] Figure 3(b) shows the fault current at the fault section M;

[0043] FIG4( a ) shows the propagation of traveling waves when the fault point is located in the first half of the fault section according to an embodiment of the present invention;

[0044] FIG4( b ) shows the propagation of traveling waves when the fault point is located in the second half of the fault section according to an embodiment of the present invention;

[0045] FIG5( a ) is a Perterson equivalent circuit diagram of the R terminal of an embodiment of the present invention;

[0046] FIG5( b ) is a Perterson equivalent circuit diagram of the M terminal of an embodiment of the present invention;

[0047] FIG5( c ) is a Perterson equivalent circuit diagram at a fault point according to an embodiment of the present invention. DETAILED DESCRIPTION

[0048] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0049] It should be noted that the following detailed descriptions are all illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0050] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0051] Embodiment 1

[0052] Reference Figure 1 This embodiment provides a cable hybrid DC line fault distance measurement method based on single-terminal and double-terminal distance measurement, which specifically includes the following steps:

[0053] S101: Acquire fault current traveling wave signals at both ends of a cable mixed fault section line.

[0054] like Figure 2 As shown, the fault location model of this embodiment includes a rectifier side, an inverter side and a DC hybrid line. The DC hybrid line is connected between the rectifier side and the inverter side and consists of two sections of transmission lines, one section close to the rectifier side is an overhead line, and the other section close to the inverter side is a cable line. Electrical quantity collection devices are installed near the rectifier side, near the inverter side and at the connection between the overhead line and the cable.

[0055] The fault current traveling wave signal of this embodiment includes the fault current traveling wave signals on the positive and negative lines at both ends of the fault section line. An electrical quantity collection point is set at the connection between the overhead line and the cable, and when a fault occurs in a section of the cable hybrid DC transmission line, the fault current signals on the positive and negative lines of the section close to both ends of the line are collected.

[0056] When a fault occurs in the overhead line section of the hybrid DC line, the fault current traveling wave signal is obtained from the rectifier side of the section and the measurement point at the connection between the overhead line and the cable line, with a sampling frequency of 1 MHz.

[0057] S102: extracting a line mode component signal from the fault current traveling wave signal.

[0058] In this embodiment, the Karenbauer transformation matrix is ​​used to perform phase mode transformation and decoupling on the fault current traveling wave signals on the positive and negative lines to obtain line mode components and zero mode signals.

[0059] There is coupling between the positive and negative poles of the high-voltage DC transmission line. In order to improve the ranging accuracy, the phase mode transformation matrix must be used to decouple the current. The phase mode transformation matrix is ​​shown in formula (1).

[0060]

[0061] After decoupling by the phase mode transformation matrix, the fault current can be decomposed into the current line mode component and the zero mode component. The line mode component is less affected by factors such as frequency, transition resistance and external environment and is relatively stable. Therefore, the current line mode component is selected for subsequent processing. The decoupled current line mode component can be calculated by formula (2).

[0062]

[0063] Where i1 is the current line mode component, i0 is the current zero mode component, i p is the positive current on the DC side, i n is the negative current on the DC side.

[0064] S103: Perform multi-resolution morphological gradient analysis on the line mode component signal to determine the moment of current mutation.

[0065] like Figure 3(a)-Figure 3(b) As shown, in the process of multi-resolution morphological gradient analysis of the line mode component signal, the number of analysis layers is set to 2, the polarity of the current mutation at both ends of the fault section is identified, and the current mutation moment is determined, so as to obtain the time when the initial traveling wave of the fault current reaches both ends of the fault section line for the first and second time.

[0066] As a signal waveform processing method, mathematical morphology has its unique advantages in analyzing transient waveform characteristics. The multi-resolution morphological gradient can accurately identify the rising and falling edges in the waveform. In order to highlight the edge information in the signal, the morphological gradient (MG) is defined as formula (3):

[0067]

[0068] Where f is the original signal and g is the structural element.

[0069] On the basis of morphological gradient, in order to highlight the rising edge and falling edge in the current signal respectively, a multi-resolution morphological gradient (MMG) algorithm is introduced, in which flat structure elements g with the same length but opposite origin positions are used. + and g - , as shown in formula (4):

[0070]

[0071] Where g + The origin of the signal is at the head end, which is used to identify the rising edge of the signal; g - The origin is at the end, which is used to identify the falling edge of the signal; a is the number of layers of MMG analysis. When the number of layers of MMG analysis is 1, G 0 is the original signal, After a times g + Processed signal, After a times g - Processed signal.

[0072] S104: Determine the fault point location based on the current mutation time and the selected distance measurement formula.

[0073] Based on the refraction and reflection of the fault current traveling wave, the refraction and reflection coefficient is calculated. Considering the accuracy of wave head identification, the distance measurement formula corresponding to the wave head with the largest wave head amplitude obtained by analysis is selected.

[0074] The two groups of single-end and double-end fault distance measurement formulas are obtained based on the distance between the fault point and one end of the fault section line and the combination of the single-end traveling wave distance measurement principle and the double-end traveling wave distance measurement principle. Each group of fault distance measurement formulas includes two fault distance measurement formulas.

[0075] In this embodiment, two sets of single-end and double-end fault location formulas are derived by combining the single-end traveling wave method and the double-end traveling wave method for the fault section line to eliminate the error caused by the traveling wave velocity.

[0076] Assume that t0 is the time when the fault occurs, v is the line wave speed, L is the total length of the fault section line; R is one end of the fault section line; I is the other end of the fault section line; x R is the distance from the fault point to the R terminal; t1 and t3 are the first and second times when the initial traveling wave of the fault current reaches the R terminal; t2 and t4 are the first and second times when the initial traveling wave of the fault current reaches the I terminal. The traveling wave propagation is shown in Figure 4(a)-Figure 4(b) shown.

[0077] When 0≤x R When <L / 2, the following formula can be obtained according to the principle of double-end traveling wave ranging and the principle of single-end traveling wave ranging:

[0078]

[0079] After eliminating the wave speed, two ranging formulas can be obtained:

[0080]

[0081]

[0082] When L / 2≤x R When ≤L, the following can be obtained by the same logic:

[0083]

[0084] After eliminating the wave speed, we can get two ranging formulas

[0085]

[0086]

[0087] Analyze the properties of the traveling wave head and the refraction and reflection conditions, assuming that the forward traveling wave is u f , the reflected wave is u q , the wave impedance of the overhead line is Z L , the wave impedance of the cable is Z C , and Z L >Z C , the transition resistance at the fault point is R f , the boundary element of VSC can be equivalent to capacitor C, Figure 2 Take the example to analyze the traveling wave refraction and reflection at the R and M ends when a fault occurs in the overhead line.

[0088] When an overhead line fails, the traveling wave reflection coefficients reaching the R and M terminals and the fault point are analyzed respectively. The Perterson equivalent circuit diagram is shown in the figure below. Figure 5(a)-Figure 5(c) shown.

[0089] According to Perterson's law, we can get

[0090]

[0091] From the equivalent circuit in Fig. 5(a), according to the three-element method of the first-order circuit, we can obtain

[0092]

[0093] According to Eqs. (11) and (12), the reflected wave at the R end can be obtained as

[0094]

[0095] Let \(t = 0\) in the above formula, then

[0096] \(u\) f \(= -u\) q (14)

[0097] That is, the voltage reflection coefficient is -1. According to Eq. (11), the current reflection coefficient is 1.

[0098] Similarly, according to Fig. 5(b), the reflected wave at the M end can be obtained as

[0099]

[0100] That is, the voltage reflection coefficient is negative. According to Eq. (11), the current reflection coefficient is positive.

[0101] According to Fig. 5(c), the reflected wave at the fault point can be obtained as

[0102]

[0103]

[0104] That is, the voltage reflection coefficient is negative. According to Eq. (11), the current reflection coefficient is positive.

[0105] In summary, when \(0\leq x\) R \(< L / 2\), from Fig. 4(a), we know that

[0106] Select as the ranging formula;

[0107] When \(L / 2\leq x\) R \(\leq L\), from Fig. 4(b), we know that

[0108] Select as the ranging formula.

[0109] Therefore,

[0110] When \(0\leq x\) R \(< L / 2\), select As a distance measurement formula;

[0111] When L / 2≤x R ≤L, select As a distance measurement formula.

[0112] It should be noted here that, considering the accuracy of wave head recognition at high transition resistance, according to the wave head properties, refraction and reflection conditions and anti-transition resistance capability of the fault current traveling wave signal, the technicians in this field select the wave head amplitude with the largest value in the above two sets of ranging formulas as the final ranging formula, namely, formula (7) and formula (10). For specific analysis, please refer to the above analysis and will not be repeated here.

[0113] Taking a single-pole fault on the line as an example, the transition resistance is 300Ω. The ranging method combining the single-end ranging and double-end ranging principles adopted in this embodiment is compared with the currently commonly used ranging formulas (18) and (19). The results are shown in Table 1.

[0114] When it is determined to be an overhead line fault, the commonly used distance measurement formula is:

[0115]

[0116] When it is determined to be a cable fault, the commonly used distance measurement formula is:

[0117]

[0118] Table 1 Comparison of fault location results

[0119]

[0120]

[0121] It can be seen from Table 1 that the ranging formula based on the single-end and double-end hybrid principle proposed in the present disclosure has greatly improved ranging accuracy compared with the traditional hybrid line double-end line ranging formula because it eliminates the influence of wave speed.

[0122] Embodiment 2

[0123] This embodiment provides a cable hybrid DC line fault distance measurement system based on single-terminal and double-terminal distance measurement, which specifically includes the following modules:

[0124] A traveling wave signal acquisition module, which is used to acquire the fault current traveling wave signals at both ends of the cable mixed fault section line;

[0125] A line mode component signal extraction module, which is used to extract a line mode component signal from a fault current traveling wave signal;

[0126] A current mutation moment determination module is used to perform multi-resolution morphological gradient analysis on the line mode component signal to determine the current mutation moment;

[0127] A fault point location determination module, which is used to determine the fault point location based on the current mutation moment and the selected distance measurement formula;

[0128] Based on the refraction and reflection of the fault current traveling wave, calculate its refraction and reflection coefficient, and select the distance measurement formula corresponding to the moment of the wave head with the largest wave head amplitude obtained by analysis;

[0129] The two groups of single-end and double-end fault distance measurement formulas are obtained based on the distance between the fault point and one end of the fault section line and the combination of the single-end traveling wave distance measurement principle and the double-end traveling wave distance measurement principle. Each group of fault distance measurement formulas includes two fault distance measurement formulas.

[0130] Specifically, in the fault point location determination module, two sets of single-end and double-end fault distance measurement formulas are derived by combining the single-end traveling wave method and the double-end traveling wave method for the fault section line to eliminate the error caused by the traveling wave velocity.

[0131] In the fault point location determination module,

[0132] When 0≤x R When ≤L / 2, select As a distance measurement formula;

[0133] When L / 2≤x R When ≤L, select As a distance measurement formula;

[0134] Where, L is the total length of the fault section line; R is one end of the fault section line, which is the non-connected end of the overhead line and the cable; I is the other end of the fault section line; x R is the distance from the fault point to the R terminal; t1 and t3 are the first and second times when the initial traveling wave of the fault current reaches the R terminal; t2 and t4 are the first and second times when the initial traveling wave of the fault current reaches the I terminal.

[0135] It should be noted here that each module in this embodiment corresponds to each step in Example 1 one by one, and the specific implementation process is the same, which will not be repeated here.

[0136] Embodiment 3

[0137] This embodiment provides a computer-readable storage medium on which a computer program is stored. When the program is executed by a processor, the steps in the cable hybrid DC line fault ranging method based on single-terminal and double-terminal ranging as described above are implemented.

[0138] Embodiment 4

[0139] This embodiment provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, the steps in the cable hybrid DC line fault ranging method based on single-end and double-end ranging as described above are implemented.

[0140] The present invention is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems) and computer program products of the embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram and the combination of the processes and / or blocks in the flowchart and / or block diagram can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0141] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A cable hybrid DC line fault distance measurement method based on single-terminal and double-terminal distance measurement, characterized in that: include: Acquire the fault current traveling wave signals at both ends of the cable mixed fault section line; Extracting line mode component signal from fault current traveling wave signal; Perform multi-resolution morphological gradient analysis on line mode component signals to determine the moment of current mutation; Determine the fault location based on the current mutation time and the selected distance measurement formula; Among them, the selection principle of the ranging formula is as follows: Based on the reflection and refraction conditions of the traveling wave of the fault current, calculate its reflection and refraction coefficients, and select the ranging formula corresponding to the moment of the wave head with the largest wave head amplitude obtained through analysis. Specifically, when 0 ≤ x R < L / 2, Select As the ranging formula; When L / 2≤x R ≤L, I t3 >I t4 ,choose As a distance measurement formula; Where, L is the total length of the fault section line; R is one end of the fault section line, which is the non-connected end of the overhead line and the cable; I is the other end of the fault section line; x R is the distance from the fault point to the R end; Z L is the wave impedance of the overhead line, Z C is the wave impedance of the cable, and Z L >Z C ; R F is the transition resistance of the fault point; t1 and t3 are the time when the initial traveling wave of the fault current reaches the R terminal for the first and second time respectively; t2 and t4 are the time when the initial traveling wave of the fault current reaches the I terminal for the first and second time respectively; The two groups of single-end and double-end fault distance measurement formulas are obtained based on the distance between the fault point and one end of the fault section line and the combination of the single-end traveling wave distance measurement principle and the double-end traveling wave distance measurement principle. Each group of fault distance measurement formulas includes two fault distance measurement formulas.

2. The cable hybrid DC line fault distance measurement method based on single-terminal and double-terminal distance measurement according to claim 1, characterized in that: The two sets of single-end and double-end fault location formulas are derived by combining the single-end traveling wave method and the double-end traveling wave method on the fault section line to eliminate the error caused by the traveling wave velocity.

3. The cable hybrid DC line fault distance measurement method based on single-terminal and double-terminal distance measurement according to claim 1, characterized in that: The fault current traveling wave signal includes the fault current traveling wave signals on the positive and negative lines at both ends of the fault section line.

4. The cable hybrid DC line fault distance measurement method based on single-terminal and double-terminal distance measurement according to claim 3, characterized in that: The Karenbauer transformation matrix is ​​used to perform phase mode transformation and decoupling on the fault current traveling wave signals on the positive and negative lines to obtain line mode components and zero mode signals.

5. The cable hybrid DC line fault distance measurement method based on single-terminal and double-terminal distance measurement according to claim 1, characterized in that: In the process of multi-resolution morphological gradient analysis of line mode component signals, the number of analysis layers is set to 2, the polarity of the current mutation at both ends of the fault section is identified, and the moment of the current mutation is determined, so as to obtain the moment when the initial traveling wave of the fault current reaches both ends of the fault section line for the first and second time.

6. A cable hybrid DC line fault distance measurement system based on single-terminal and double-terminal distance measurement, characterized in that: include: A traveling wave signal acquisition module, which is used to acquire the fault current traveling wave signals at both ends of the cable mixed fault section line; A line mode component signal extraction module, which is used to extract a line mode component signal from a fault current traveling wave signal; A current mutation moment determination module is used to perform multi-resolution morphological gradient analysis on the line mode component signal to determine the current mutation moment; A fault point location determination module, which is used to determine the fault point location based on the current mutation moment and the selected distance measurement formula; Among them, the selection principle of the ranging formula is: based on the reflection and refraction conditions of the traveling wave of the fault current, calculate its reflection and refraction coefficients, and select the ranging formula corresponding to the moment of the wave head with the largest wave head amplitude obtained from the analysis. Specifically, when 0 ≤ x R < L / 2, Select as the ranging formula; When L / 2≤x R ≤L, choose As a distance measurement formula; Where, L is the total length of the fault section line; R is one end of the fault section line, which is the non-connected end of the overhead line and the cable; I is the other end of the fault section line; x R is the distance from the fault point to the R end; Z L is the wave impedance of the overhead line, Z C is the wave impedance of the cable, and Z L >Z C ; R F is the transition resistance of the fault point; t1 and t3 are the time when the initial traveling wave of the fault current reaches the R terminal for the first and second time respectively; t2 and t4 are the time when the initial traveling wave of the fault current reaches the I terminal for the first and second time respectively; The two groups of single-end and double-end fault distance measurement formulas are obtained based on the distance between the fault point and one end of the fault section line and the combination of the single-end traveling wave distance measurement principle and the double-end traveling wave distance measurement principle. Each group of fault distance measurement formulas includes two fault distance measurement formulas.

7. The cable hybrid DC line fault distance measurement system based on single-end and double-end distance measurement according to claim 6, characterized in that: In the fault point location determination module, two sets of single-end and double-end fault distance measurement formulas are derived by combining the single-end traveling wave method and the double-end traveling wave method for the fault section line to eliminate the error caused by the traveling wave velocity.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps in the cable hybrid DC line fault distance measurement method based on single-end and double-end distance measurement as described in any one of claims 1 to 5 are implemented.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the program, the steps in the cable hybrid DC line fault ranging method based on single-end and double-end ranging are implemented as described in any one of claims 1 to 5.

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