High-voltage cable line parameter extraction method and system based on online monitoring

Abstract

The invention discloses a high-voltage cable line parameter extraction method and system based on online monitoring. The high-voltage cable line parameter extraction method comprises the steps of listing a multi-conductor transmission line equation containing a relation between voltage phasors and current phasors at the two ends of a cable based on a multi-conductor transmission line theory; multiple groups of cable operation data are collected at the two ends of the cable, and moments with different load amplitudes are selected for each group of cable operation data; reducing orders of a chain parameter matrix in the multi-conductor transmission line equation and the voltage phasor and the current phasor of the head end of the cable to obtain a multi-conductor transmission line equation after order reduction; substituting the acquired cable operation data into the multi-conductor transmission line equation after order reduction, and solving a chain parameter matrix after order reduction through matrix operation; and solving the length of the cable line by using the chain parameter matrix and the chain parameter matrix after order reduction. According to the method, the calculation precision of the theoretical value of the sheath circulating current is improved, and the misjudgment rate and the missed judgment rate based on online diagnosis of the sheath circulating current are reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of cable online monitoring, in particular to a method and system for extracting high-voltage cable line parameters based on online monitoring. Background Art

[0002] Compared to overhead lines, cable lines offer superior environmental resistance and high reliability. Cross-linked polyethylene single-core high-voltage cables are increasingly used in urban power grids, playing an increasingly important role in ensuring safe and reliable power supply. The health of these large-scale cable lines has a significant impact on the safe and stable operation of urban power grids. Furthermore, with rising customer electricity demand and increasing requirements for power supply reliability, improving the accuracy of power cable operating status monitoring has become a pressing issue. Single-core cables exhibit strong magnetic and electric field coupling between the core conductor and the metal sheath. The load current carried by the core of a three-phase cable generates an alternating magnetic field around the core, which interacts with the metal sheath to induce voltage. Electricity safety regulations stipulate that the metal sheath of single-core high-voltage cables must be grounded. The main grounding methods include single-end grounding, cross-connection grounding, and double-end grounding. Cross-connection grounding is generally used for cable lines with longer transmission distances, effectively reducing induced voltage and circulating current on the metal sheath. Defects in the grounding system usually cause changes in the metal sheath current. Therefore, the metal sheath circulating current is one of the important state quantities used for cable line status evaluation and fault diagnosis.

[0003] In 2013, Du Boxue, Li Zhonglei, Zhang Kai, and others published "Calculation and Application of Grounding Current in 220kV Cross-Linked Polyethylene Power Cables," which examined analytical formulas for calculating induced voltage in three-circuit cables without considering sheath-to-sheath mutual inductance. This formula can be extended to any arrangement of multi-circuit cables. IEEE Std 575-2014 provides the form of the metallic sheath grounding system for single-core AC cables and simplified calculation formulas for the metallic sheath induced voltage in single- and double-circuit cables. In 2019, Tu Jingyun published "Research on High-Voltage Cable Fault Diagnosis and Location Technology Based on Sheath Circulation Current Method," using an analytical method to calculate the sheath induced voltage, taking into account the induced electromotive force generated on the sheath by sheath current and earth current. In 2015, Yuan Yanling, Zhou Hao, Dong Jie and others calculated the current based on the equivalent circuit model in the "Online Monitoring and Fault Diagnosis Technology of High-voltage Power Cable Sheath Current" for three types of faults: water ingress into the cross-connection box, open circuit faults caused by loose connections at the joints, and cable joint breakdown. They developed fault diagnosis and positioning standards based on the ratio of the current in the fault situation to the current in the normal situation.

[0004] In summary, for a given operating cable line, the theoretical sheath circulating current values ​​under normal and faulty conditions can be calculated using the cable's structural and installation parameters. This can serve as the basis for the sheath circulating current online monitoring system. Improving the accuracy of online monitoring requires improving the calculation accuracy of the sheath circulating current under different conditions, thereby optimizing the fault diagnosis criteria. Existing research on improving the accuracy of cable sheath induced voltage and induced current calculations has focused solely on the accuracy of mutual inductance calculations, multi-circuit installations, and the accuracy of the induced voltage calculation formulas, ignoring the impact of actual field uncertainties. For actual operating cable lines, due to the age of engineering drawings, the lines may have undergone maintenance and repairs, resulting in changes to the original layout. This can lead to discrepancies between the actual lengths of the three cross-connected sections and those indicated on the drawings, resulting in imbalanced lengths among the three cross-connected sections. Substituting the theoretical cable lengths from the drawings into the sheath induced voltage and induced current formulas will result in significant discrepancies between the theoretical and actual sheath circulating current values, leading to misdiagnosis or omission of faults by the online monitoring system. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects of the above-mentioned prior art and provide a method and system for extracting high-voltage cable line parameters based on online monitoring. Starting from the theory of multi-conductor transmission lines, with the help of the relationship between the electrical parameters at both ends of the cable, the method writes equations to solve the reduced-order chain parameter matrix of the line; at the same time, according to the calculation method of the chain parameter matrix in the theory of multi-conductor transmission lines, the actual length of the cable is solved jointly.

[0006] To this end, the present invention adopts the following technical solutions.

[0007] In a first aspect, the present invention provides a method for extracting parameters of a high-voltage cable line based on online monitoring, comprising: Step 1: Based on the multi-conductor transmission line theory, the three-phase cable line is regarded as a multi-port network, and the multi-conductor transmission line equation including the relationship between the voltage phasor and the current phasor at both ends of the cable is written; Step 2: Collect multiple sets of cable operation data at both ends of the cable, with each set of cable operation data collected at a time with a different load amplitude; Step 3, reducing the order of the chain parameter matrix and the voltage phasor and current phasor at the head end of the cable in the multi-conductor transmission line equation to obtain a reduced-order multi-conductor transmission line equation; Step 4: Substitute the collected cable operation data into the reduced-order multi-conductor transmission line equation, and solve the reduced-order chain parameter matrix through matrix operations; Step 5: Use the chain parameter matrix and the reduced-order chain parameter matrix to solve the length of the cable line.

[0008] Furthermore, in step 1, the three-phase cable line is considered as a 6-port network, and the multi-conductor transmission line equation containing the relationship between the voltage phasor and the current phasor at both ends of the cable is as follows: , Where, is the chain parameter matrix, L is the cable line length, V ( 0 ), I ( 0 ) are the voltage column vector and current column vector at the cable head end, V ( L ), I ( L ) are the voltage column vector and current column vector at the cable ends, respectively.

[0009] Furthermore, in step 2, the cable operation data includes three-phase core voltage, three-phase load current, three-phase sheath circulating current and three-phase sheath induced voltage.

[0010] Furthermore, in step 3, the multi-conductor transmission line equation containing the relationship between the voltage phasors and the current phasors at both ends of the cable is reduced to: , Where, represents the reduced chain parameter matrix, is the reduced-order cable head-end voltage matrix, is the reduced-order current matrix at the head end of the cable.

[0011] Furthermore, in step 3, the chain parameter matrix is ​​expressed as follows: , The voltage column vector and current column vector are expressed as follows: , , , , Where, V 0CA 、 V 0CB 、 V 0CC are the A, B, and C phase core voltages at the cable head end, V 0SA 、 V 0SB 、 V 0SC are the induced voltages of the A, B, and C phase sheaths at the cable head end, I 0CA 、 I0CB 、 I 0CC are the A, B, and C phase load currents at the cable head end, I 0SA 、 I 0SB 、 I 0SC They are the A, B, and C phase sheath circulating currents at the cable head end respectively; V LCA 、 V LCB 、 V LCC are the A, B, and C phase core voltages at the cable ends, V LSA 、 V LSB 、 V LSC are the induced voltages of the A, B, and C phase sheaths at the end of the cable, I LCA 、 I LCB 、 I LCC are the A, B, and C phase load currents at the cable ends, I LSA 、 I LSB 、 I LSC They are the A, B, and C phase sheath circulations at the cable ends respectively.

[0012] Furthermore, in step 3, the reduced-order cable head-end voltage matrix and current matrix The columns are written as follows: , .

[0013] Furthermore, in step 3, the reduced chain parameter matrix The columns are written as follows: , in, Multiply the corresponding position elements in the chain parameter matrix by the transformation matrix Income, Multiply the corresponding position elements in the chain parameter matrix by the transformation matrix ,by For example: .

[0014] Furthermore, in step 4, the reduced chain parameter matrix The calculation formula is as follows: , Where, 、 、……、 is the voltage column vector at the head end of the cable in the 6 sets of cable operation data collected, 、 、……、 is the current column vector at the head end of the cable in the 6 sets of cable operation data collected; 、 、……、 is the voltage column vector at the end of the cable in the 6 sets of cable operation data collected, 、 、……、 is the column vector of the current at the end of the cable in the 6 sets of cable operation data collected.

[0015] Furthermore, in the chain parameter matrix of step 5, 、 、 、 They are all 6-order square matrices and are represented as follows:

[0016] in, Y is the unit admittance matrix of the cable line, γ 2 is a matrix YZ The eigenvalues ​​of Z is the unit impedance matrix of the cable line; T I The column vector of the matrix YZ The eigenvector, unit impedance and admittance matrix are calculated by electromagnetic field method according to the geometric structure and medium parameters of the three-phase cable; Will 、 and Written as a block matrix consisting of 4 3-order square matrices, the matrix is ​​written by block matrix operation 、 The expression of simultaneous equations to solve the matrix , calculate the cable line length L .

[0017] In a second aspect, the present invention provides a high-voltage cable line parameter extraction system based on online monitoring, which is used to implement the above-mentioned high-voltage cable line parameter extraction method, and includes: Equation Writing Unit: Based on multi-conductor transmission line theory, the three-phase cable line is considered as a multi-port network, and the multi-conductor transmission line equation including the relationship between the voltage phasor and the current phasor at both ends of the cable is written; Cable operation data acquisition unit: collects multiple sets of cable operation data at both ends of the cable, and each set of cable operation data is selected at a time with different load amplitudes; Reduced-order equation acquisition unit: reduces the order of the chain parameter matrix and the voltage phasor and current phasor at the head end of the cable in the multi-conductor transmission line equation to obtain the reduced-order multi-conductor transmission line equation; Reduced-order chain parameter moment solving unit: Substitute the collected cable operation data into the reduced-order multi-conductor transmission line equation and solve the reduced-order chain parameter matrix through matrix operations; Cable line length solving unit: uses the chain parameter matrix and the reduced-order chain parameter matrix to solve the length of the cable line.

[0018] The beneficial effects of the present invention are as follows: the present invention can use the voltage and current data at both ends of the cable to reversely infer the actual parameters of the high-voltage cable line, can effectively calculate the actual length of the three cross-connected sections of the cable, eliminate the influence of on-site uncertain factors, improve the accuracy of the sheath circulation calculation, optimize the fault judgment criteria, and thus improve the accuracy of fault diagnosis. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 This is a flow chart of a method for extracting high-voltage cable line parameters based on online monitoring according to the present invention; Figure 2 A schematic diagram of a cross-connection model of a three-phase cable for simulation of the present invention; Figure 3 This is a composition diagram of a high-voltage cable line parameter extraction system based on online monitoring of the present invention. DETAILED DESCRIPTION

[0021] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0022] Example 1 This embodiment provides a method for extracting high-voltage cable line parameters based on online monitoring. Figure 1 As shown, the steps are as follows: Step 1: Based on the multi-conductor transmission line theory, the three-phase cable line is regarded as a multi-port network, and the multi-conductor transmission line equation including the relationship between the voltage phasor and the current phasor at both ends of the cable is written; Step 2: Collect multiple sets of cable operation data at both ends of the cable, with each set of cable operation data collected at a time with a different load amplitude; Step 3, reducing the order of the chain parameter matrix and the voltage phasor and current phasor at the head end of the cable in the multi-conductor transmission line equation to obtain a reduced-order multi-conductor transmission line equation; Step 4: Substitute the collected cable operation data into the reduced-order multi-conductor transmission line equation, and solve the reduced-order chain parameter matrix through matrix operations; Step 5: Use the chain parameter matrix and the reduced-order chain parameter matrix to solve the length of the cable line.

[0023] The above-mentioned high-voltage cable line parameter extraction method is described in detail below, and the three-phase cable line is regarded as a 6-port network.

[0024] For a three-phase cable line, based on the multi-conductor transmission line theory, the core and metal sheath of a three-phase single-core high-voltage cable can each form a loop with the earth. Therefore, a single-loop three-phase cable can be regarded as six transmission lines with the earth as the loop. The voltage and current of the parallel three-phase cables satisfy the following equations:

[0025] Where, V 、 I are the voltage and current column vectors of the multi-conductor transmission line composed of three-phase cables at point z, Z、Y are the unit-length impedance matrix and admittance matrix of the transmission line, respectively. Accurate calculation of the cable's impedance and admittance parameters is the basis for calculating voltage and current using the multi-conductor transmission line model. These parameters can be calculated using electromagnetic field methods based on the three-phase cable's geometry and medium parameters, and will not be further elaborated here.

[0026] The voltage and current at the end and beginning of a three-phase cable line can be expressed using the link parameter matrix:

[0027] Where, L is the cable line length, V ( 0 ), I ( 0 ) are the voltage column vector and current column vector at the cable head end, V ( L ), I ( L ) are the voltage column vector and current column vector at the cable end respectively. The block matrix in the chain parameter matrix is 、 、 、 They are all six-order square matrices and can be expressed as:

[0028] Where, T I is the current mode transformation matrix, and its column vector is YZ Eigenvectors of a matrix; yes YZ The eigenvalues ​​of the matrix, where 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 They are all third-order square matrices.

[0029] At the beginning and end of the cable line, the three-phase core voltage, three-phase sheath induced voltage, three-phase load current and three-phase sheath induced current are measured respectively.

[0030] First, the chain parameter matrix is ​​reduced to the block matrix of the first column of the chain parameter matrix 、 、 、 and the block matrix of the third column 、 、 、 Multiply by the column vector , the block matrix of the second column 、 、 、 Multiply by the column vector , the block matrix of the fourth column 、 、 、 Substitute the measured data at both ends of the cable into the chain parameter matrix equation, where only the data measured at the first end are selected. A Phase core voltage, three-phase sheath induced voltage, A The load current of each phase and the three-phase sheath induction current are calculated, and the equation is as follows:

[0031] The reduced chain parameter matrix is ​​a 12×6 matrix, where 、 、 、 、 、 、 、 、 、 、 、 The six sets of data collected at different load amplitudes are substituted into the above equation to solve the reduced chain parameter matrix. The equation is written as follows:

[0032]

[0033] Where, V 0CA 、 V 0CB 、 V 0CC are the A, B, and C phase core voltages at the cable head end, V 0SA 、 V 0SB 、 V 0SC are the induced voltages of the A, B, and C phase sheaths at the cable head end, I 0CA 、 I 0CB 、 I 0CC are the A, B, and C phase load currents at the cable head end, I 0SA 、 I 0SB 、 I 0SC They are the A, B, and C phase sheath circulating currents at the cable head end respectively; V LCA 、 V LCB 、 V LCC are the A, B, and C phase core voltages at the cable ends, V LSA 、 V LSB 、 V LSC are the induced voltages of the A, B, and C phase sheaths at the end of the cable, I LCA 、 I LCB 、I LCC are the A, B, and C phase load currents at the cable ends, I LSA 、 I LSB 、 I LSC They are the A, B, and C phase sheath circulations at the cable ends respectively.

[0034] Next, starting from the reduced-order link parameter matrix, the cable length of the first cross-connection segment is calculated by combining the calculation formula of the link parameter matrix. L . The impedance matrix of the cable Z and the admittance matrix Y It can be found that:

[0035]

[0036]

[0037]

[0038] in, γ 2 is a matrix YZ The eigenvalues ​​of The column vector of the matrix YZ The eigenvector of 、 and are all 6-order square matrices, and For a diagonal matrix, 、 and They are written as block matrices consisting of four third-order square matrices.

[0039] , , , Substitute the above three block matrices into the matrix :

[0040] in 、 It can be obtained by calculating the reduced-order chain parameter matrix, 、 The expression:

[0041]

[0042] Subtract the two equations and make the following changes to make the matrix K Using the matrix A 、 B 、 C 、 D 、 and express:

[0043] From this formula we can get the matrix K， Simultaneous Matrix K It can also be written as the following diagonal matrix.

[0044]

[0045] For functions , and its inverse function is ,Will K Substituting any element in the matrix into the inverse function, we can find the corresponding , substitute the corresponding eigenvalues The length of the cable can be obtained L .

[0046] The following simulation is performed using the above high-voltage cable line parameter extraction method: This simulation uses PSCAD to build a cross-connection model of three-phase cables, such as Figure 2 As shown, the cross-connection section is 1500m long, each cross-connection section is 500m long, and the cable is 64 / 110YJLW02-630mm 2 The structural parameters of the power supply are simulated; three 110kV single-phase AC voltage source models are used, and the three-phase phase angles differ by 120°.

[0047] Adjust the load and measure the load current, sheath circulating current, core voltage and sheath voltage to obtain 6 sets of data. and The form is written as follows: , , , , , , , , , , , , , , The above two matrices can be used to solve ,in

[0048]

[0049] The impedance matrix Z and admittance matrix Y of the cable per unit length can be obtained:

[0050]

[0051]

[0052]

[0053]

[0054]

[0055] Substituting the above matrix into the formula, we can calculate the matrix K ,

[0056]

[0057]

[0058] in, , we can calculate:

[0059] The calculated length is the same as the cable length set in the simulation, which verifies the calculation accuracy of the high-voltage cable line parameter extraction method of the present invention.

[0060] The present invention starts from the actual needs on site, uses online monitoring data to eliminate the influence of uncertain factors on site, and calculates the accurate parameters of the cable line, which can provide a good basis for the subsequent calculation of the theoretical value of the sheath circulating current. The high-precision calculated value of the sheath circulating current can provide an accurate judgment basis for the online monitoring of cable faults based on the sheath circulating current.

[0061] The present invention can rely on the existing sheath circulation online monitoring system to complete the calculation, and no additional monitoring equipment is required, which greatly reduces hardware expenses.

[0062] Example 2 This embodiment provides a high-voltage cable line parameter extraction system based on online monitoring, which is used to implement the high-voltage cable line parameter extraction method described in Example 1. Figure 3 As shown, it consists of an equation writing unit, a cable operation data acquisition unit, a reduced-order equation acquisition unit, a reduced-order chain parameter moment solving unit and a cable line length solving unit.

[0063] Equation Writing Unit: Based on multi-conductor transmission line theory, the three-phase cable line is considered as a multi-port network, and the multi-conductor transmission line equation including the relationship between the voltage phasor and the current phasor at both ends of the cable is written; Cable operation data acquisition unit: collects multiple sets of cable operation data at both ends of the cable, and each set of cable operation data is selected at a time with different load amplitudes; Reduced-order equation acquisition unit: reduces the order of the chain parameter matrix and the voltage phasor and current phasor at the head end of the cable in the multi-conductor transmission line equation to obtain the reduced-order multi-conductor transmission line equation; Reduced-order chain parameter moment solving unit: Substitute the collected cable operation data into the reduced-order multi-conductor transmission line equation and solve the reduced-order chain parameter matrix through matrix operations; Cable line length solving unit: uses the chain parameter matrix and the reduced-order chain parameter matrix to solve the length of the cable line.

[0064] It should be noted that each unit in the above-mentioned high-voltage cable line parameter extraction system based on online monitoring can be implemented in whole or in part through software, hardware, and a combination thereof. The above-mentioned units can be embedded in or independent of the processor in the computer device in the form of hardware, or can be stored in the memory of the computer device in the form of software, so that the processor can call and execute the corresponding operations of the above-mentioned units. For the specific definition of a high-voltage cable line parameter extraction system based on online monitoring, please refer to the definition of a high-voltage cable line parameter extraction method based on online monitoring (i.e., Example 1) above. The two have the same functions and effects and will not be repeated here.

[0065] The above description of the embodiments is intended to facilitate understanding and application of the present invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for extracting high-voltage cable line parameters based on online monitoring, characterized in that: include: Step 1: Based on the multi-conductor transmission line theory, the three-phase cable line is regarded as a multi-port network, and the multi-conductor transmission line equation including the relationship between the voltage phasor and the current phasor at both ends of the cable is written; Step 2: Collect multiple sets of cable operation data at both ends of the cable, with each set of cable operation data collected at a time with a different load amplitude; Step 3, reducing the order of the chain parameter matrix and the voltage phasor and current phasor at the head end of the cable in the multi-conductor transmission line equation to obtain a reduced-order multi-conductor transmission line equation; Step 4: Substitute the collected cable operation data into the reduced-order multi-conductor transmission line equation, and solve the reduced-order chain parameter matrix through matrix operations; Step 5: Use the chain parameter matrix and the reduced-order chain parameter matrix to solve the length of the cable line.

2. A method for extracting high-voltage cable line parameters based on online monitoring according to claim 1, characterized in that: In step 1, the three-phase cable line is considered as a 6-port network. The multi-conductor transmission line equation containing the relationship between the voltage phasor and the current phasor at both ends of the cable is as follows: ， Where, is the chain parameter matrix, L is the cable line length, V ( 0 ), I ( 0 ) are the voltage column vector and current column vector at the cable head end, V ( L ), I ( L ) are the voltage column vector and current column vector at the cable ends, respectively.

3. A method for extracting high-voltage cable line parameters based on online monitoring according to claim 1, characterized in that: In step 2, the cable operation data includes three-phase core voltage, three-phase load current, three-phase sheath circulating current and three-phase sheath induced voltage.

4. A method for extracting high-voltage cable line parameters based on online monitoring according to claim 2, characterized in that: In step 3, the multi-conductor transmission line equation containing the relationship between the voltage phasors and the current phasors at both ends of the cable is reduced to: ， Where, represents the reduced chain parameter matrix, is the reduced-order cable head-end voltage matrix, is the reduced-order current matrix at the head end of the cable.

5. A method for extracting high-voltage cable line parameters based on online monitoring according to claim 4, characterized in that: In step 3, the chain parameter matrix is ​​expressed as follows: ， The voltage column vector and current column vector are expressed as follows: ， ， ， ， Where, V 0CA 、 V 0CB 、 V 0CC are the A, B, and C phase core voltages at the cable head end, V 0SA 、 V 0SB 、 V 0SC are the induced voltages of the A, B, and C phase sheaths at the cable head end, I 0CA 、 I 0CB 、 I 0CC are the A, B, and C phase load currents at the cable head end, I 0SA 、 I 0SB 、 I 0SC They are the A, B, and C phase sheath circulating currents at the cable head end respectively; V LCA 、 V LCB 、 V LCC are the A, B, and C phase core voltages at the cable ends, V LSA 、 V LSB 、 V LSC are the induced voltages of the A, B, and C phase sheaths at the end of the cable, I LCA 、 I LCB 、 I LCC are the A, B, and C phase load currents at the cable ends, I LSA 、 I LSB 、 I LSC They are the A, B, and C phase sheath circulations at the cable ends respectively.

6. A method for extracting high-voltage cable line parameters based on online monitoring according to claim 5, characterized in that: In step 3, the reduced-order cable head end voltage matrix is and current matrix The columns are written as follows: ， 。 7. A method for extracting high-voltage cable line parameters based on online monitoring according to claim 5, characterized in that: In step 3, the reduced chain parameter matrix The columns are written as follows: ， in, Multiply the corresponding position elements in the chain parameter matrix by the transformation matrix Income, Multiply the corresponding position elements in the chain parameter matrix by the transformation matrix .

8. A method for extracting high-voltage cable line parameters based on online monitoring according to claim 6, characterized in that: In step 4, the reduced chain parameter matrix The calculation formula is as follows: ， Where, 、 、……、 is the voltage column vector at the head end of the cable in the 6 sets of cable operation data collected, 、 、……、 is the current column vector at the head end of the cable in the 6 sets of cable operation data collected; 、 、……、 is the voltage column vector at the end of the cable in the 6 sets of cable operation data collected, 、 、……、 is the column vector of the current at the end of the cable in the 6 sets of cable operation data collected.

9. The method for extracting high-voltage cable line parameters based on online monitoring according to claim 6, characterized in that: In the chain parameter matrix of step 5, 、 、 、 They are all 6-order square matrices and are represented as follows: in, Y is the unit admittance matrix of the cable line, γ 2 is a matrix YZ The eigenvalues ​​of Z is the unit impedance matrix of the cable line; T I The column vector of the matrix YZ The eigenvector, unit impedance and admittance matrix are calculated by electromagnetic field method according to the geometric structure and medium parameters of the three-phase cable; Will 、 and Written as a block matrix consisting of 4 3-order square matrices, the matrix is ​​written by block matrix operation 、 The expression of simultaneous equations to solve the matrix , calculate the cable line length L .

10. A high-voltage cable line parameter extraction system based on online monitoring, used to implement the high-voltage cable line parameter extraction method according to any one of claims 1 to 9, characterized in that: include: Equation Writing Unit: Based on multi-conductor transmission line theory, the three-phase cable line is considered as a multi-port network, and the multi-conductor transmission line equation including the relationship between the voltage phasor and the current phasor at both ends of the cable is written; Cable operation data acquisition unit: collects multiple sets of cable operation data at both ends of the cable, and each set of cable operation data is selected at a time with different load amplitudes; Reduced-order equation acquisition unit: reduces the order of the chain parameter matrix and the voltage phasor and current phasor at the head end of the cable in the multi-conductor transmission line equation to obtain the reduced-order multi-conductor transmission line equation; Reduced-order chain parameter moment solving unit: Substitutes the collected cable operation data into the reduced-order multi-conductor transmission line equation and solves the reduced-order chain parameter matrix through matrix operations; Cable line length solving unit: uses the chain parameter matrix and the reduced-order chain parameter matrix to solve the length of the cable line.

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