Method and system for calculating fault current of high-voltage alternating current submarine cable grounding system and storage medium

Abstract

The application discloses a high-voltage alternating-current submarine cable grounding system fault current calculation method and system and a storage medium, and steps are as follows: based on Thevenin equivalent theorem, power supply and power consumption equipment are respectively equivalent to impedance and series voltage source combination and load impedance; combined with double-ended grounding characteristics, the submarine cable loop is equivalent to a π type, and a three-phase equivalent circuit is constructed; the fault phase is determined, and the submarine cable is divided into left and right sides at the fault point; based on Kirchhoff's theorem, voltage loop equations are written, and matrix recursive rules are derived combined with double-side elimination principle. The analytical relationship between the power supply side, the short-circuit side submarine cable main section and the fault circulating current is established according to the recursive rules. The fault point current equation is taken as a boundary condition, and the left side sheath fault circulating current distribution is solved. The right side distribution is obtained by repeating the above steps on the right side, and then the whole line distribution of the fault phase is obtained. The method can accurately calculate the circulating current distribution, improve the fault analysis accuracy and efficiency, and provide support for submarine cable operation and maintenance.

Description

Technical Field

[0001] This invention relates to the field of power systems, and in particular to a method, system, and storage medium for calculating fault current in a high-voltage AC submarine cable grounding system. Background Technology

[0002] With the advancement of economic globalization and the gradual maturation of offshore wind power technology, the mileage of submarine cable lines is increasing, and the operational performance of submarine cables is becoming a research hotspot. Long-distance terrestrial cables typically employ cross-interconnection to reduce the induced voltage and circulating current in the metallic sheath. However, submarine cables, limited by their laying environment, cannot utilize cross-interconnection or similar measures. When mechanical damage occurs to the submarine cable, it can lead to a failure in the cable grounding system. Because the metallic sheath is grounded at both ends, a significant circulating current will be generated within the sheath, resulting in a substantial decrease in its transmission capacity, which may, in severe cases, impact national economic production. Therefore, it is necessary to conduct research on the calculation of circulating current in the metallic sheath under fault conditions in submarine cable grounding systems. Summary of the Invention

[0003] The purpose of this invention is to provide a method, system, and storage medium for calculating fault current in a high-voltage AC submarine cable grounding system. This invention enables accurate calculation of the circulating fault current distribution across the entire sheath of the faulty phase, helping to improve the accuracy and efficiency of fault analysis in submarine cable grounding systems, and providing reliable technical support for submarine cable operation and maintenance, fault diagnosis, and system safety assessment.

[0004] The technical solution of this invention: a method for calculating the fault current of a high-voltage AC submarine cable grounding system, comprising the following steps:

[0005] Step S1: Based on Thevenin's equivalent theorem, the power supply equipment in the high-voltage AC submarine cable grounding system is equivalent to a combination of impedance and series voltage source, and the electrical equipment is equivalent to load impedance; combined with the double-end grounding characteristics of the submarine cable grounding system, the submarine cable loop part is equivalent to π type, and a three-phase equivalent circuit of the submarine cable grounding system is constructed.

[0006] Step S2: Determine the phase in which the fault occurred, and divide the submarine cable into left and right sides based on the fault point; based on Kirchhoff's theorem, analyze the left side of the fault point separately. n Write the voltage loop equations in complex matrix form for the power supply side and short-circuit side of the submarine cable mesh. Using the double-sided elimination principle, derive the first and second voltage loop equations for the power supply side and short-circuit side of the submarine cable. k Recurrence relation of segment matrices;

[0007] Step S3: Based on the power supply side and short-circuit side of the submarine cable... k Based on the recursive rules of the segment matrix, establish analytical relationship expressions between the main segments of the submarine cable on the power supply side and the short-circuit side and the fault circulation current;

[0008] Step S4: Based on Kirchhoff's current theorem, and using the fault point current equation as the boundary condition, solve the fault circulation current distribution on the left side of the sheath at the short-circuit point by simultaneously solving the expression in Step S3.

[0009] Step S5: On the right side of the fault point n Repeat steps S2-S4 for the submarine cable section to obtain the fault circulation current distribution of the right sheath, and then obtain the fault circulation current distribution of the entire sheath of the faulty phase.

[0010] The above-mentioned method for calculating the fault current of a high-voltage AC submarine cable grounding system refers to a single-phase ground fault, where the single phase is any one of the three phases A, B, and C.

[0011] The aforementioned method for calculating fault current in a high-voltage AC submarine cable grounding system involves the following process for constructing the three-phase equivalent circuit of the submarine cable grounding system:

[0012] The power supply equipment is equivalent to impedance Z. spA Z spB Z spC and ideal voltage sources in series E A , E B , E C The electrical equipment is equivalent to a load Z. aload Z bload Z cload The equivalent grounding resistance of power supply equipment and power consumption equipment is R LFP , R REF The total number of loops in the π-type equivalent circuit is determined to be 9. Taking the left side of the short-circuit point as an example, the tunnel cable system is divided into... n Section, power supply segment n +1 paragraph.

[0013] In the aforementioned method for calculating fault current in a high-voltage AC submarine cable grounding system, step S2, which involves writing the voltage loop equation and obtaining the recursive law of the k-th segment matrix on the power supply side, is as follows:

[0014] First, the submarine cable is divided into left and right sides based on the fault point. The mesh on the left side of the fault point is analyzed, and the loop equation for one phase, based on Kirchhoff's theorem, is as follows:

[0015] ;

[0016] In the formula, Let be the unit length mutual impedance between phase A and phase j in the k-th segment to the left of the short-circuit point. j =SA, AA, CB, SB, AB, CC, SC or AC; ZkLacc The self-impedance per unit length of phase A of the k-th segment of the submarine cable to the left of the short circuit point; Let be the unit length mutual impedance between the k-th segment and the (k-1)-th segment of phase A; Let be the unit length mutual impedance between the k-th segment and the (k+1)-th segment of phase A; , The left side of the short circuit point k , k -1 segment grounding electrode voltage, l This refers to the length of a micro-segment of the submarine cable.

[0017] Among them, since there is a capacitor C between the three-phase conductors of ABC and the sheath and armor, and the armor and capacitor are short-circuited and grounded, the grounding electrode voltage of the k and k-1 segments to the left of the short circuit point is obtained. and :

[0018] ;

[0019] ;

[0020] in, , , They are respectively j Current in the loop segments k, k-1, and k+1; j '=CA, SA, AA, CB, SB, AB, CC, SC or AC;

[0021] In the power supply section k = n +1, then:

[0022] ;

[0023] In the formula, S k A k B k It consists of the self-impedance and mutual impedance of the submarine cable, and in k = n When adding 1, the above expression is rewritten as:

[0024] ;

[0025] Where E is the magnitude of the three-phase voltages A, B, and C relative to the loop impedance;

[0026] Secondly, based on the principle of double-sided elimination, the above equation can be transformed to obtain the current recursive relationship for segment k+1 on the power supply side:

[0027] ;

[0028] Among them, complex matrix and Calculated by the following formula:

[0029] ;

[0030] ;

[0031] Finally, based on the above formula, the recursive formula for the circulating current of the power supply side sheath fault is obtained:

[0032] ;

[0033] Combining the above equations, we obtain the power supply side. k Segment recursion pattern:

[0034] .

[0035] In the aforementioned method for calculating fault current in a high-voltage AC submarine cable grounding system, step S2, which involves writing the voltage loop equation and obtaining the recursive law of the k-th segment matrix on the short-circuit side, is as follows:

[0036] First, in the short circuit section there is k =1, so the complex matrix form of the voltage loop equation for the three-phase submarine cable grounding system is as follows:

[0037] ;

[0038] in, H A matrix composed of faulty resistors. I 0 represents the fault current;

[0039] Secondly, based on the principle of two-sided elimination, the above equation is transformed to obtain the recursive relationship of the short-circuit current as follows:

[0040] ;

[0041] The complex matrix is ​​calculated by the following formula:

[0042] ;

[0043] ;

[0044] Finally, based on the above formula, the recursive formula for the short-circuit side sheath fault circulating current is obtained:

[0045] ;

[0046] Combining the above equations, we obtain the recursive rule for the k-th segment on the short-circuit side:

[0047] .

[0048] In the aforementioned method for calculating fault current in a high-voltage AC submarine cable grounding system, step S3 involves obtaining the analytical relationship expression by simultaneously applying the recursive formulas for the circulating current of the power supply side sheath and the fault circulating current of the short-circuit side sheath:

[0049] ;

[0050] In the formula, Let K be the loop current of the k-th segment to the left of the short-circuit point in the submarine cable. It is the fault circulation current at the fault point; and A complex matrix and Calculated by the following formula:

[0051] ;

[0052] in, I It is a 9×9 identity matrix; Let be the impedance of the left loop of the k-th segment. The boundary matrix of the left loop of the (k+1)th segment; The impedance of the right loop of segment k, It is the power supply-side excitation source of the k-th segment, corresponding to the system operating parameters when there is no fault; It is the short-circuit side excitation source of the k-th segment, corresponding to the additional electromagnetic characteristics introduced by the fault.

[0053] In the aforementioned method for calculating fault current in a high-voltage AC submarine cable grounding system, step 3, the process of solving the fault circulating current distribution on the left side of the short-circuit point is as follows:

[0054] Based on Kirchhoff's current law at the short-circuit point:

[0055] ;

[0056] Calculate fault circulation I The expression for 0 is as follows:

[0057] .

[0058] A system for implementing the aforementioned method for calculating fault current in a high-voltage AC submarine cable grounding system, the system comprising, in sequence, a submarine cable grounding system equivalent processing module, a π-type equivalent circuit creation module, a loop equation writing module, and a fault current calculation module;

[0059] The submarine cable grounding system equivalent module is used to perform equivalent processing on the power supply equipment, power consumption equipment, equivalent grounding resistance of the power supply equipment, and equivalent grounding resistance of the power consumption equipment in the submarine cable grounding system.

[0060] The π-type equivalent circuit creation module is used to integrate the equipment in the submarine cable grounding system after equivalent processing to form the π-type equivalent circuit of the submarine cable grounding system.

[0061] The loop equation writing module is used to write loop equations for the faulty phase;

[0062] The fault current calculation module is used to solve the loop equation and calculate the fault circulation current distribution of the single-phase submarine cable grounding system at the fault point.

[0063] A computer-readable storage medium storing computer-executable instructions that, when executed, implement the aforementioned method for calculating fault current in a high-voltage AC submarine cable grounding system.

[0064] Compared with the prior art, the present invention has the following beneficial effects:

[0065] 1. This invention establishes a multi-loop π-type equivalent circuit to accurately reproduce complex electromagnetic characteristics, solving the problem of fault current calculation deviation caused by neglecting coupling, and making submarine cable fault analysis more closely aligned with actual physical processes. This invention utilizes the double-sided elimination principle to derive the analytical relationship between "power supply side / short-circuit side segment-fault circulating current," deeply correlating the local parameters of discrete segments with the global distribution of circulating current along the entire line, achieving accurate recursion from segmented current to the entire circulating current, and solving the problem of continuity in calculating fault current distribution in long-distance submarine cables. This invention can completely output the fault circulating current distribution of the entire sheath of the fault phase, providing maintenance personnel with accurate quantitative basis for locating fault points and assessing the scope of fault impact, significantly improving fault diagnosis efficiency and reducing manual troubleshooting costs.

[0066] 2. This invention addresses the scenario of double-ended grounding and multi-segment coupling in submarine cables. By customizing the application of the double-sided elimination principle, it simplifies the complexity of matrix operations, making complex submarine cable fault models engineering-computable. This fills the gap in refined calculation methods for high-voltage AC submarine cable grounding faults and promotes the development of submarine cable fault analysis technology. This invention can support thermal stability verification of submarine cable sheaths and armor, as well as grounding system design optimization, reducing the risk of faults escalating into system outages, cable burnouts, and other accidents from the source, thus ensuring the safe operation of submarine cable systems. Attached Figure Description

[0067] Figure 1 This is a schematic diagram of the calculation method for submarine cable fault current in the high-voltage AC submarine cable grounding system of the present invention;

[0068] Figure 2 This is a schematic diagram of the high-voltage AC submarine cable grounding system in Embodiment 1 of the present invention;

[0069] Figure 3 This is the π-type equivalent circuit of the high-voltage AC submarine cable grounding system in Embodiment 1 of the present invention;

[0070] Figure 4 This is a circuit diagram of the submarine cable grounding system in Embodiment 1 of the present invention during a submarine cable grounding fault.

[0071] Figure 5 This is the distribution of fault circulation in the submarine cable sheath obtained by the present invention;

[0072] Figure 6 This is the relative error between the present invention and the simulation data. Detailed Implementation

[0073] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the present invention.

[0074] Example 1: Calculation method for submarine cable fault current in high-voltage AC submarine cable grounding system, as shown in the attached document. Figure 1 As shown, proceed with the following steps:

[0075] Step S1: Based on Thevenin's equivalent theorem, the power supply equipment in the high-voltage AC submarine cable grounding system is equivalent to a combination of impedance and series voltage source, and the electrical equipment is equivalent to load impedance; combined with the double-end grounding characteristics of the submarine cable grounding system, the submarine cable loop part is equivalent to π type, and a three-phase equivalent circuit of the submarine cable grounding system is constructed.

[0076] In this step, as shown in the attached document Figure 2 - Appendix Figure 4 As shown, the high-voltage AC submarine cable grounding system is a 500kV high-voltage AC submarine cable grounding system with double-ended grounding. The fault type is a single-phase grounding short-circuit fault, and the single phase is any one of the three phases A, B, and C.

[0077] The construction process of the three-phase equivalent circuit of the submarine cable grounding system is as follows:

[0078] Substations and other power supply equipment are equivalent to impedance Z. spA Z spB Z spC and ideal voltage sources in series E A , E B , E C Electrical equipment such as electric motors are equivalent to load Z. aload Z bload Z cload The equivalent grounding resistance of the substation and motor is R LFP , R REF The total number of loops in the π-type equivalent circuit is determined to be 9. Taking the left side of the short-circuit point as an example, the tunnel cable system is divided into... n Section, power supply section is n +1 segment;

[0079] Step S2: Determine the phase in which the fault occurred, and divide the submarine cable into left and right sides based on the fault point; based on Kirchhoff's theorem, analyze the left side of the fault point separately. n Write the voltage loop equations in complex matrix form for the power supply side and short-circuit side of the submarine cable mesh. Using the double-sided elimination principle, derive the first and second voltage loop equations for the power supply side and short-circuit side of the submarine cable. k Recurrence relation of segment matrices;

[0080] The fault-occurring phase can be any one of the three phases A, B, and C. In this embodiment, it is assumed that the fault-occurring phase is phase A during calculation. The steps of writing the voltage loop equation in complex matrix form on the power supply side and obtaining the recursive law of the k-th segment of the matrix on the power supply side are as follows:

[0081] First, the submarine cable is divided into left and right sides based on the fault point. The mesh on the left side of the fault point is analyzed, and the equation for the A-phase loop, based on Kirchhoff's theorem, is as follows:

[0082] ;

[0083] In the formula, Let be the unit length mutual impedance between phase A and phase j in the k-th segment to the left of the short-circuit point. j =SA, AA, CB, SB, AB, CC, SC or AC; Z kLacc The self-impedance per unit length of phase A of the k-th segment of the submarine cable to the left of the short circuit point; Let be the unit length mutual impedance between the k-th segment and the (k-1)-th segment of phase A; Let be the unit length mutual impedance between the k-th segment and the (k+1)-th segment of phase A; , The left side of the short circuit point k , k -1 segment grounding electrode voltage, l This refers to the length of a micro-segment of the submarine cable.

[0084] Among them, since there is a capacitor C between the three-phase conductors of ABC and the sheath and armor, and the armor and capacitor are short-circuited and grounded, the grounding electrode voltage of the k and k-1 segments to the left of the short circuit point can be obtained. and :

[0085] ;

[0086] ;

[0087] in, , , They are respectively j Current in the loop segments k, k-1, and k+1; j'=CA, SA, AA, CB, SB, AB, CC, SC or AC;

[0088] In the power supply section k = n +1, then:

[0089] ;

[0090] In the formula, S k A k B k It consists of the self-impedance and mutual impedance of the submarine cable, and in k = n When adding 1, the above expression is rewritten as:

[0091] ;

[0092] Where E is the magnitude of the three-phase voltages A, B, and C relative to the loop impedance;

[0093] Secondly, based on the principle of two-sided elimination, the above equation can be transformed to obtain the current recursive relationship on the power supply side, i.e., segment k+1, as follows:

[0094] ;

[0095] Among them, complex matrix and Calculated by the following formula:

[0096] ;

[0097] ;

[0098] Finally, based on the above formula, the recursive formula for the circulating current of the power supply side sheath fault is obtained:

[0099] ;

[0100] Combining the above equations, we obtain the power supply side. k Segment recursion pattern:

[0101] .

[0102] The steps for writing the voltage loop equation in complex matrix form on the short-circuit side and obtaining the recursive law of the k-th segment matrix on the short-circuit side are as follows:

[0103] First, in the short circuit section there is k =1, so the complex matrix form of the voltage loop equation for the three-phase submarine cable grounding system is as follows:

[0104] ;

[0105] in,H A matrix composed of faulty resistors. I 0 represents the fault current;

[0106] Secondly, based on the principle of two-sided elimination, the above equation is transformed to obtain the recursive relationship of the short-circuit current as follows:

[0107] ;

[0108] The complex matrix is ​​calculated by the following formula:

[0109] ;

[0110] ;

[0111] Finally, based on the above formula, the recursive formula for the short-circuit side sheath fault circulating current is obtained:

[0112] ;

[0113] Combining the above equations, we obtain the recursive rule for the k-th segment on the short-circuit side:

[0114] .

[0115] Step S3: Based on the power supply side and short-circuit side of the submarine cable... k Based on the recursive rules of the segment matrix, establish analytical relationship expressions between the main segments of the submarine cable on the power supply side and the short-circuit side and the fault circulation current;

[0116] In this step, the analytical relational expression is obtained by simultaneously applying the recursive formulas for the circulating current of the power supply side sheath and the fault circulating current of the short-circuit side sheath:

[0117] ;

[0118] In the formula, Let K be the loop current of the k-th segment to the left of the short-circuit point in the submarine cable. It is the fault circulation current at the fault point; and A complex matrix and Calculated by the following formula:

[0119] ;

[0120] in, I It is a 9×9 identity matrix; Let be the impedance of the left loop of the k-th segment. The boundary matrix of the left loop of the (k+1)th segment; The impedance of the right loop of segment k, It is the power supply-side excitation source of the k-th segment, corresponding to the system operating parameters when there is no fault; It is the short-circuit side excitation source of the k-th segment, corresponding to the additional electromagnetic characteristics introduced by the fault.

[0121] Step S4: Based on Kirchhoff's current theorem, and using the fault point current equation as the boundary condition, solve the fault circulation current distribution on the left side of the sheath at the short-circuit point by simultaneously solving the expression in Step S3.

[0122] In this step, the process of solving the circulating current distribution of the fault in the sheath to the left of the short-circuit point is as follows:

[0123] Based on Kirchhoff's current law at the short-circuit point:

[0124] ;

[0125] The expression for calculating the fault circulating current I0 is as follows:

[0126] .

[0127] This allows for the calculation of the fault circulation current distribution in the sheath of the single-phase submarine cable grounding system to the left of the fault point.

[0128] Step S5: For the right side of the short circuit point n After performing the above analysis on the section of submarine cable (i.e., repeating the calculation process of steps S2-S4), the fault circulation current distribution of the sheath on the right side of the short-circuit point is obtained, thereby obtaining the fault circulation current distribution of the sheath of the faulty phase along the entire line; the aforementioned analysis of the fault circulation current distribution on the right side of the short-circuit point... n The above analysis of the submarine cable line refers to the analysis of the section to the right of the fault point. n The loop equations are written at the power supply side and short circuit point of the submarine cable line. Based on the double-sided elimination method, the analytical relationship expression between the main section of the submarine cable on the power supply side and the short circuit side and the fault circulating current is obtained. The current at the fault point is used as the boundary condition to obtain the fault circulating current distribution of the sheath on the right side of the short circuit point. Thus, the fault circulating current distribution of the sheath of the fault phase is obtained.

[0129] Appendix Figure 5 - Appendix Figure 6 The figure shows the distribution of fault circulation in the submarine cable sheath obtained using this invention. As can be seen from the figure, this invention can obtain the fault circulation distribution curve of the submarine cable sheath. Figure 5 It can be seen that when a fault occurs in the submarine cable, the circulating current in the metallic sheath first increases and then decreases, reaching its maximum at the fault point. The circulating current in the metallic sheath closer to the power source is greater than that on the other side. As the fault point moves further away, the circulating current shows a decreasing trend, and the amplitude of the circulating current in the metallic sheath gradually decreases as the fault point moves further away from the power source. Figure 6 The relative error between the present invention and the simulation data is denoted by [the following]. Figure 6It can be seen that the maximum fault circulation result of the metal sheath calculated by the present invention and the simulation software is in good agreement. When the fault point is set at 0km, the maximum relative error of the metal sheath circulation is less than 0.5%, which further verifies the accuracy and effectiveness of the method of the present invention.

[0130] Example 2: A system for calculating the fault current of a high-voltage AC submarine cable grounding system as described in Example 1, used for calculating the fault current of a submarine cable grounding system, including a submarine cable grounding system equivalent processing module, a π-type equivalent circuit creation module, a loop equation writing module, and a fault current calculation module connected in sequence;

[0131] The submarine cable grounding system equivalent module is used to perform equivalent processing on the power supply equipment, power consumption equipment, equivalent grounding resistance of the power supply equipment, and equivalent grounding resistance of the power consumption equipment in the submarine cable grounding system.

[0132] The π-type equivalent circuit creation module is used to integrate the equipment in the submarine cable grounding system after equivalent processing to form the π-type equivalent circuit of the submarine cable grounding system.

[0133] The loop equation writing module is used to write loop equations for the faulty phase;

[0134] The fault current calculation module is used to solve the loop equation and calculate the fault circulation current distribution of the single-phase submarine cable grounding system at the fault point.

[0135] The system is arranged in an electronic device, and the components of the electronic device may include, but are not limited to: at least one processing unit, at least one storage unit, a bus connecting different system components (including storage units and processing units), and a display unit.

[0136] The storage unit stores program code, which can be executed by the processing unit to perform the steps described in the method section of Embodiment 1 above, according to various exemplary embodiments of the present invention.

[0137] The storage unit may include readable media in the form of volatile storage units, such as random access memory (RAM) and / or cache storage units, and may further include read-only memory (ROM).

[0138] The storage unit may also include a program / utility having a set (at least one) of program modules, including but not limited to: an operating system, one or more application programs, other program modules, and program data, each or some combination of these examples may include an implementation of a network environment.

[0139] A bus can represent one or more of several types of bus structures, including a memory cell bus or memory cell controller, a peripheral bus, a graphics acceleration port, a processing unit, or a local bus that uses any of the various bus structures.

[0140] The electronic device can also communicate with one or more external devices (e.g., keyboards, pointing devices, Bluetooth devices, etc.), one or more devices that enable a user to interact with the electronic device, and / or any device that enables the electronic device to communicate with one or more other computing devices (e.g., routers, modems, etc.). This communication can be performed via input / output (I / O) interfaces. Furthermore, the electronic device can communicate with one or more networks (e.g., local area networks (LANs), wide area networks (WANs), and / or public networks, such as the Internet) via a network adapter. The network adapter communicates with other modules of the electronic device via a bus. Further, other hardware and / or software modules can be used in conjunction with the electronic device, including but not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, and data backup storage systems.

[0141] From the above description of the embodiments, those skilled in the art will readily understand that the embodiments described herein can be implemented by software or by combining software with necessary hardware. Therefore, the technical solutions according to the embodiments of this disclosure can be embodied in the form of a software product, which can be stored in a non-volatile storage medium (such as a CD-ROM, USB flash drive, external hard drive, etc.) or on a network, including several instructions to cause a computing device (such as a personal computer, server, terminal device, or network device, etc.) to execute the methods according to the embodiments of this disclosure.

[0142] In exemplary embodiments of this disclosure, a computer-readable storage medium is also provided, on which a program product capable of implementing the methods described above is stored. In some possible embodiments, various aspects of the invention may also be implemented as a program product comprising program code that, when the program product is run on a terminal device, causes the terminal device to perform the steps of the various exemplary embodiments of the invention described in the "Exemplary Methods" section above.

Claims

1. A method for calculating fault current in a high-voltage AC submarine cable grounding system, characterized by: Follow these steps: Step S1: Based on Thevenin's equivalent theorem, the power supply equipment in the high-voltage AC submarine cable grounding system is equivalent to a combination of impedance and series voltage source, and the electrical equipment is equivalent to load impedance; combined with the double-end grounding characteristics of the submarine cable grounding system, the submarine cable loop part is equivalent to π type, and a three-phase equivalent circuit of the submarine cable grounding system is constructed. Step S2: Determine the phase in which the fault occurs, and divide the submarine cable into left and right sides with the fault point as the boundary; based on Kirchhoff's theorem, write the voltage loop equations in complex matrix form for the power supply side and the short circuit side of the n segments of the submarine cable mesh on the left side of the fault point, respectively; and derive the recursive law of the k-th segment matrix on the power supply side and the short circuit side of the submarine cable by combining the double-sided elimination principle. Step S3: Based on the recursive rules of the k-th segment matrix on the power supply side and short-circuit side of the submarine cable, establish the analytical relationship expression between the main segment of the submarine cable on the power supply side and short-circuit side and the fault circulation current; Step S4: Based on Kirchhoff's current theorem, and using the fault point current equation as the boundary condition, solve the fault circulation current distribution on the left side of the sheath at the short-circuit point by simultaneously solving the expression in Step S3. Step S5: Repeat steps S2-S4 for the n segments of submarine cable to the right of the fault point to obtain the fault circulation current distribution of the sheath on the right side, and then obtain the fault circulation current distribution of the sheath of the entire fault phase. The construction process of the three-phase equivalent circuit of the submarine cable grounding system is as follows: The power supply equipment is equivalent to impedance Z. spA Z spB Z spC and the ideal voltage source E in series A E B E C The electrical equipment is equivalent to a load Z. aload Z bload Z cload The equivalent grounding resistance of the power supply equipment and the electrical equipment is R. LFP R REF The total number of loops in the π-type equivalent circuit is determined to be 9. Taking the left side of the short circuit point as an example, the tunnel cable system is divided into n segments, with the power supply segment being n+1 segments.

2. The method for calculating fault current in a high-voltage AC submarine cable grounding system according to claim 1, characterized in that: The fault type of the high-voltage AC submarine cable grounding system is a single-phase grounding short-circuit fault, where the single phase is any one of the three phases A, B, and C.

3. The method for calculating fault current in a high-voltage AC submarine cable grounding system according to claim 1, characterized in that: In step S2, the steps for writing the voltage loop equation and obtaining the recursive law of the k-th segment matrix on the power supply side are as follows: First, the submarine cable is divided into left and right sides based on the fault point. The mesh on the left side of the fault point is analyzed, and the loop equation for one phase, based on Kirchhoff's theorem, is as follows: ； In the formula, Z represents the unit-length mutual impedance between phase A and phase j in the k-th segment to the left of the short-circuit point, where j = SA, AA, CB, SB, AB, CC, SC, or AC; kLacc The self-impedance per unit length of phase A of the k-th segment of the submarine cable to the left of the short circuit point; Let be the unit length mutual impedance between the k-th segment and the (k-1)-th segment of phase A; Let be the unit length mutual impedance between the k-th segment and the (k+1)-th segment of phase A; , These are the grounding electrode voltages of segments k and k-1 to the left of the short circuit point, respectively, and l is the length of the submarine cable micro-segment; Among them, since there is a capacitor C between the three-phase conductors of ABC and the sheath and armor, and the armor and capacitor are short-circuited and grounded, the grounding electrode voltage of the k and k-1 segments to the left of the short circuit point is obtained. and : ； ； in, , , These are the loop currents in segments k, k-1, and k+1 of phase j', respectively; j' = CA, SA, AA, CB, SB, AB, CC, SC, or AC; In the power supply segment, k = n + 1, then: ； In the formula, S k A k B k Composed of the self-impedance and mutual impedance of the submarine cable, and when k=n+1, the above equation can be rewritten as: ； Where E is the magnitude of the three-phase voltages A, B, and C relative to the loop impedance; Secondly, based on the principle of double-sided elimination, the above equation can be transformed to obtain the current recursive relationship for segment k+1 on the power supply side: ； Among them, complex matrix and Calculated by the following formula: ； ； Finally, based on the above formula, the recursive formula for the circulating current of the power supply side sheath fault is obtained: ； Combining the above equations, we obtain the recursive law for the k-segment on the power supply side: 。 4. The method for calculating fault current in a high-voltage AC submarine cable grounding system according to claim 3, characterized in that: In step S2, the steps for writing the voltage loop equation and obtaining the recursive law of the k-th segment matrix on the short-circuit side are as follows: First, with k=1 in the short-circuit section, the complex matrix form of the voltage loop equation for the three-phase submarine cable grounding system is obtained as follows: ； Where H is the matrix formed by the fault resistors, and I0 is the fault current; Secondly, based on the principle of two-sided elimination, the above equation is transformed to obtain the recursive relationship of the short-circuit current as follows: ； Among them, complex matrix and Calculated by the following formula: ； ； Finally, based on the above formula, the recursive formula for the short-circuit side sheath fault circulating current is obtained: ； Combining the above equations, we obtain the recursive rule for the k-th segment on the short-circuit side: 。 5. The method for calculating fault current in a high-voltage AC submarine cable grounding system according to claim 4, characterized in that: In step S3, the analytical relational expression is obtained by simultaneously applying the recursive formulas for the circulating current of the power supply side sheath and the fault circulating current of the short-circuit side sheath: ； In the formula, Let K be the loop current of the k-th segment to the left of the short-circuit point in the submarine cable. It is the fault circulation current at the fault point; and A complex matrix and Calculated by the following formula: ； Where I is a 9×9 identity matrix; Let be the impedance of the left loop of the k-th segment. The boundary matrix of the left loop of the (k+1)th segment; The impedance of the right loop of segment k, It is the power supply-side excitation source of the k-th segment, corresponding to the system operating parameters when there is no fault; It is the short-circuit side excitation source of the k-th segment, corresponding to the additional electromagnetic characteristics introduced by the fault.

6. The method for calculating fault current in a high-voltage AC submarine cable grounding system according to claim 5, characterized in that: In step 3, the process of solving the circulating current distribution of the fault in the sheath to the left of the short-circuit point is as follows: Based on Kirchhoff's current law at the short-circuit point: ； The expression for calculating the fault circulating current I0 is as follows: 。 7. A system for implementing the fault current calculation method for a high-voltage AC submarine cable grounding system according to any one of claims 1-6, characterized in that: The system includes a submarine cable grounding system equivalent processing module, a π-type equivalent circuit creation module, a loop equation writing module, and a fault current calculation module connected in sequence. The submarine cable grounding system equivalent module is used to perform equivalent processing on the power supply equipment, power consumption equipment, equivalent grounding resistance of the power supply equipment, and equivalent grounding resistance of the power consumption equipment in the submarine cable grounding system. The π-type equivalent circuit creation module is used to integrate the equipment in the submarine cable grounding system after equivalent processing to form the π-type equivalent circuit of the submarine cable grounding system. The loop equation writing module is used to write loop equations for the faulty phase; The fault current calculation module is used to solve the loop equation and calculate the fault circulation current distribution of the single-phase submarine cable grounding system at the fault point.

8. A computer-readable storage medium storing computer-executable instructions that, when executed, implement the fault current calculation method for a high-voltage AC submarine cable grounding system according to any one of claims 1-6.

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