Fault current calculation method and system for high-voltage alternating-current submarine cable grounding system and storage medium

Abstract

The invention discloses a fault current calculation method and system for a high-voltage alternating-current submarine cable grounding system and a storage medium, and the method comprises the following steps: enabling a power supply device and an electric device to be equivalent to an impedance and series voltage source combination and a load impedance based on the Thevenin equivalence theorem; in combination with the double-end grounding characteristic, a submarine cable loop is equivalent according to a pi type, and a three-phase equivalent circuit is constructed; determining a fault phase, and dividing the submarine cable as a left side and a right side by a fault point; a voltage loop equation is listed based on the Kirchhoff theorem, and a matrix recursion rule is deduced in combination with a double-side elimination principle. And establishing an analytic relationship between the main sections of the submarine cables at the power side and the short-circuit side and the fault circulating current according to a recursion rule. And with a fault point current equation as a boundary condition, left sheath fault circulation distribution is solved simultaneously. And repeating the steps on the right side to obtain right side distribution so as to obtain fault phase whole-line distribution. According to the method, the circulation distribution can be accurately calculated, the fault analysis accuracy and efficiency are improved, and support is provided for submarine cable operation and maintenance and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power systems, in particular to a high-voltage alternating current submarine cable grounding system fault current calculation method, system and storage medium. BACKGROUND

[0002] With the promotion of economic globalization, offshore wind power technology gradually matures, and the mileage of submarine cable lines gradually increases. The operation performance of submarine cables has gradually become a research hotspot. Long-distance land cables usually use cross-connection to reduce the induced voltage and induced current of the metal sheath. However, due to the laying environment limitation, submarine cables cannot use cross-connection and other measures. When the submarine cable is mechanically damaged, etc., it will cause the grounding system of the submarine cable to fail. Due to the grounding of both ends of the metal sheath, a large current will be generated on the sheath, which will greatly reduce the transmission capacity, and in severe cases, it may affect national economic production. Therefore, it is necessary to study the calculation of the metal sheath current under the fault condition of the submarine cable grounding system. SUMMARY

[0003] The purpose of the present application is to provide a high-voltage alternating current submarine cable grounding system fault current calculation method, system and storage medium. The present application can realize the accurate distribution calculation of the fault phase full-line sheath fault current, help to improve the accuracy and efficiency of the submarine cable grounding system fault analysis, and provide reliable technical support for submarine cable operation and maintenance, fault diagnosis and system safety evaluation.

[0004] The technical scheme of the present application: the high-voltage alternating current submarine cable grounding system fault current calculation method is carried out according to the following steps: Step S1: based on the Thevenin equivalent theorem, the power supply equipment in the high-voltage alternating current submarine cable grounding system is equivalent to a combination of impedance and series voltage source, and the power consumption equipment is equivalent to a load impedance; combined with the characteristics of the double-end grounding 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 fault point phase, and divide the submarine cable into left and right sides with the fault point as the boundary; based on Kirchhoff's theorem, the voltage loop equation in the form of complex matrix is written for the power supply side and the short-circuit side of the left side of the fault point n Step S3: according to the matrix recursive law of the power supply side and the short-circuit side of the submarine cable k Step S4: based on Kirchhoff's current theorem, taking the fault point current equation as the boundary condition, the expressions of step S3 are solved to obtain the short-circuit point left sheath fault current distribution; Step S5: for the right side of the fault point k Step S6: according to the matrix recursive law of the power supply side and the short-circuit side of the submarine cable Step S7: based on Kirchhoff's current theorem, taking the fault point current equation as the boundary condition, the expressions of step S6 are solved to obtain the short-circuit point right sheath fault current distribution. Step S8: the fault current of the left and right sides of the fault point is obtained by combining the left and right sheath fault current distributions.n Repeat steps S2-S4 for the submarine cable line to obtain the sheath fault circulation current distribution on the right side, and then obtain the sheath fault circulation current distribution of the entire fault phase.

[0005] In the above-mentioned method for calculating the fault current of the high-voltage AC submarine cable grounding system, the fault type of the high-voltage AC submarine cable grounding system is a single-phase grounding short circuit fault, and the single phase is any one of the three phases ABC.

[0006] The above-mentioned method for calculating the fault current of the high-voltage AC submarine cable grounding system and the process of constructing the three-phase equivalent circuit of the submarine cable grounding system are as follows: Equivalent power supply equipment to impedance Z spA , Z spB , Z spC and an ideal voltage source in series E A 、 E B 、 E C , the electrical equipment is equivalent to the 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 of 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 Segment, power segment n +1 paragraph.

[0007] In the aforementioned method for calculating the fault current of the high-voltage AC submarine cable grounding system, in step S2, the steps of writing the voltage loop equation and obtaining the recursive rule of the k-th segment matrix on the power supply side are as follows: First, the submarine cable is divided into the left side and the right side of the fault point at the fault point. The mesh on the left side of the fault point is analyzed. The loop equation of one phase written based on Kirchhoff's theorem is: ; Where, is the mutual impedance per unit length between phase A and phase j in the kth segment to the left of the short-circuit point, j =SA, AA, CB, SB, AB, CC, SC or AC; Z kLacc is the self-impedance per unit length of phase A of the kth section of the submarine cable on the left side of the short-circuit point; is the mutual impedance per unit length between the kth segment and the k-1th segment of phase A; is the mutual impedance per unit length between the kth segment and the k+1th segment of phase A; 、 On the left side of the short-circuit point k、 k -1 segment grounding voltage, l is the length of the submarine cable segment; Among them, since there is a capacitor C between the ABC three-phase core and the sheath and armor, the armor and capacitor are short-circuited to ground, and the grounding voltage of the k and k-1 sections to the left of the short-circuit point is and : ; ; in, 、 、 They are j 'Phase k, k-1, k+1 loop current; j '=CA, SA, AA, CB, SB, AB, CC, SC or AC; In the power supply section k = n +1, then: ; Where S k 、A k 、B k It is composed of the self-impedance and mutual impedance of the submarine cable, and k = n When +1, rewrite the above formula as: ; Where E is the amplitude of the three-phase voltages A, B, and C to the loop impedance; Secondly, based on the principle of double-side elimination, the above equation is transformed to obtain the recursive relationship of the current of the k+1 segment on the power supply side: ; Among them, the complex matrix and Calculated by the following formula: ; ; Finally, based on the above formula, the recursive formula for the power supply side sheath fault circulating current is obtained: ; Combine the above equations to get the power supply side k Segment recursion rule: .

[0008] In the aforementioned method for calculating the fault current of the high-voltage AC submarine cable grounding system, in step S2, the steps of writing the voltage loop equation and obtaining the recursive rule of the k-th segment matrix on the short-circuit side are as follows: First, in the short circuit section there isk =1, the complex matrix form of the three-phase submarine cable grounding system voltage loop equation is as follows: ; wherein, H is a matrix composed of fault resistances, I 0 is a fault current; Secondly, the above formula is transformed based on the principle of double-sided elimination, and the short-circuit section current recursive relationship is as follows: ; wherein, the complex matrix and are calculated by the following formula: ; ; Finally, the short-circuit side sheath fault loop current recursive formula is obtained based on the above formula: ; The above formula is solved to obtain the recursive law of the kth section on the short-circuit side: .

[0009] The aforementioned high-voltage alternating current submarine cable grounding system fault current calculation method, in step S3, the analytical relationship expression is obtained by solving the power source side sheath loop current recursive formula and the short-circuit side sheath fault loop current recursive formula: ; wherein, is the loop current of the kth section on the left side of the submarine cable short-circuit point, is the fault loop current at the fault point; and are complex matrices and , which are calculated by the following formula: ; wherein, I is a 9x9 unit matrix; is the impedance of the kth section on the left side, is the boundary matrix of the k+1th section on the left side; is the impedance of the kth section on the right side, is the power source side excitation source of the kth section, corresponding to the system operating parameters when there is no fault; is the short-circuit side excitation source of the kth section, corresponding to the additional electromagnetic characteristics introduced by the fault.

[0010] The aforementioned high-voltage alternating current submarine cable grounding system fault current calculation method, in step 3, the process of solving the sheath fault loop current distribution on the left side of the short-circuit point is as follows: Based on Kirchhoff's current law at the short-circuit point, we have: ; Computing fault loop current I 0The expression is as follows: .

[0011] The system for implementing the high-voltage alternating current submarine cable grounding system fault current calculation method comprises, in sequence, a submarine cable grounding system equivalent processing module, a pi-type equivalent circuit creation module, a loop equation column writing module, and a fault current calculation module. The submarine cable grounding system equivalent module is used for performing equivalent processing on the equal power supply equipment, the power utilization equipment, the equal power supply equipment equivalent grounding resistance, and the power utilization equipment equivalent grounding resistance in the submarine cable grounding system. The pi-type equivalent circuit creation module is used for collecting the equipment in the submarine cable grounding system after the equivalent processing, and forming a pi-type equivalent circuit of the submarine cable grounding system. The loop equation column writing module is used for writing loop equations for the fault phase. The fault current calculation module is used for solving the loop equations, and calculating the fault point full-line single-phase submarine cable grounding system fault loop current distribution.

[0012] A computer readable storage medium stores computer executable instructions, when the computer executable instructions are executed, the high-voltage alternating current submarine cable grounding system fault current calculation method is implemented.

[0013] Compared with the prior art, the present application has the following beneficial effects: 1. The present application establishes a multi-loop pi-type equivalent circuit, accurately restores complex electromagnetic characteristics, solves the fault current calculation deviation problem caused by coupling neglect, makes the submarine cable fault analysis more in line with the actual physical process, and uses the two-sided elimination principle to deduce the "power supply side / short circuit side segment-fault loop current" analytical relationship, deeply correlates the discrete segment local parameters and the full-line loop current global distribution, accurately propagates the segment current to the full-line loop current, and solves the long-distance submarine cable fault current distribution calculation continuity problem. The present application can completely output the fault phase full-line sheath fault loop current distribution, provide accurate quantitative basis for operation and maintenance personnel to locate the fault point and evaluate the fault influence range, greatly improve the fault diagnosis efficiency, and reduce the manual troubleshooting cost.

[0014] 2. The present application is aimed at the submarine cable double-end grounding and multi-segment coupling scene, simplifies the matrix operation complexity by customizing the two-sided elimination principle, makes the complex submarine cable fault model have engineering calculability, fills the gap of the high-voltage alternating current submarine cable grounding fault fine calculation method, and promotes the development of submarine cable fault analysis technology. The present application can support submarine cable sheath, armored thermal stability verification and grounding system design optimization, reduce the risk of fault expansion to system power failure, submarine cable burning and other accidents from the source, and ensure the safe operation of the submarine cable system. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the flow chart of the method for calculating the fault current of a submarine cable in a high-voltage AC submarine cable grounding system according to the present invention; Figure 2 Schematic diagram of the high-voltage AC submarine cable grounding system in Example 1 of the present invention; Figure 3 This is the π-type equivalent circuit of the high-voltage AC submarine cable grounding system in Example 1 of the present invention; Figure 4 1 is a circuit diagram of a high-voltage AC submarine cable grounding system in Example 1 of the present invention when a submarine cable grounding fault occurs; Figure 5 The distribution of submarine cable sheath fault circulation obtained by the present invention; Figure 6 is the relative error between the present invention and the simulation data. DETAILED DESCRIPTION

[0016] The present invention will be further described below with reference to the accompanying drawings and examples, but they are not intended to limit the present invention.

[0017] Example 1: Calculation method for submarine cable fault current in high voltage AC submarine cable grounding system, as shown in the attached Figure 1 As shown, follow the steps below: Step S1: Based on the Thevenin equivalence 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 power consumption equipment is equivalent to load impedance. In consideration of the double-terminal grounding characteristics of the submarine cable grounding system, the submarine cable loop is equivalent to a π-type circuit to construct a three-phase equivalent circuit of the submarine cable grounding system. In this step, as shown in the attached Figure 2 -Attached Figure 4 As shown in the figure, the high-voltage AC submarine cable grounding system is a double-end grounded 500kV high-voltage AC submarine cable grounding system. The fault type is a single-phase grounding short circuit fault, and the single phase is any one of the three phases ABC. The construction process of the three-phase equivalent circuit of the submarine cable grounding system is as follows: Equivalent power supply equipment such as substations to impedance Z spA , Z spB , Z spC and an ideal voltage source in series E A 、 E B 、 E C , the motor and other electrical equipment are equivalent to the load Z aload , Z bload , Z cload , the equivalent grounding resistance of the substation and the motor is RLFP 、 R REF , the total number of loops of 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 Segment, power segment is n +1 paragraph; Step S2: Determine the phase of the fault point, and divide the submarine cable into the left and right sides based on the fault point; Based on Kirchhoff's theorem, n Write the voltage loop equations in the form of complex matrices on the power supply side and the short-circuit side of the submarine cable mesh, and derive the voltage loop equations on the power supply side and the short-circuit side of the submarine cable by combining the double-side elimination principle. k Segment matrix recursion rule; The fault-occurring phase can be any one of the three phases ABC. 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 the form of a complex matrix on the power supply side and obtaining the recursive rule of the k-th segment matrix on the power supply side are as follows: First, the submarine cable is divided into the left side and the right side of the fault point at the fault point. The mesh on the left side of the fault point is analyzed. The A-phase loop equation based on Kirchhoff's theorem is: ; Where, is the mutual impedance per unit length between phase A and phase j in the kth segment to the left of the short-circuit point, j =SA, AA, CB, SB, AB, CC, SC or AC; Z kLacc is the self-impedance per unit length of phase A of the kth section of the submarine cable on the left side of the short-circuit point; is the mutual impedance per unit length between the kth segment and the k-1th segment of phase A; is the mutual impedance per unit length between the kth segment and the k+1th segment of phase A; 、 On the left side of the short-circuit point k 、 k -1 segment grounding voltage, l is the length of the submarine cable segment; Among them, since there is a capacitor C between the ABC three-phase core and the sheath and armor, the armor and capacitor are short-circuited and grounded, the grounding electrode voltage of the k and k-1 sections to the left of the short-circuit point can be obtained and : ; ; in, 、 、 They are j 'Phase k, k-1, k+1 loop current;j = CA, SA, AA, CB, SB, AB, CC, SC or AC; In the power supply section has k = 1, then: n ; In the formula, S k , A k , B k are composed of the self-impedance and mutual impedance of the submarine cable, and when k = 1, the above formula is rewritten as: n ; Wherein, E is the amplitude of the A, B, C three-phase voltage to the loop impedance; Secondly, based on the principle of double side elimination, the above formula is transformed, and the current recursive relationship of the power supply side, i.e. the k+1 section, is as follows: ; Wherein, the complex matrix and are calculated by the following formula: ; ; Finally, based on the above formula, the power supply side sheath fault circulating current recursive formula is obtained: ; The above formula is solved to obtain the recursive law of the power supply side k section: .

[0018] The step of writing the voltage loop equation in the form of the column write short circuit side complex matrix and obtaining the matrix recursive law of the kth section on the short circuit side is: Firstly, in the short circuit section has k = 1, the complex matrix form of the three-phase submarine cable grounding system voltage loop equation is obtained as follows: ; Wherein, H is a matrix composed of fault resistance, I 0 is the fault current; Secondly, based on the principle of double side elimination, the above formula is transformed, and the current recursive relationship of the short circuit section is as follows: ; Wherein, the complex matrix and are calculated by the following formula: ; ; ​​Finally, based on the above formula, the short-circuit side sheath fault circulating current recursive formula is obtained: ; The above formula is obtained by simultaneously solving the short-circuit side kth segment recursive rule: .

[0019] Step S3: According to the matrix recursive rule of the power supply side and the short-circuit side of the submarine cable, k the analytical relationship expression between the power supply side, the short-circuit side of the main segment of the submarine cable and the fault circulating current is established; In this step, the analytical relationship expression is obtained by simultaneously solving the power supply side sheath circulating current recursive formula and the short-circuit side sheath fault circulating current recursive formula: ; In the formula, is the loop current of the kth segment on the left side of the short-circuit point of the submarine cable, is the fault circulating current of the fault point; and are complex matrices and , which are calculated by the following formula: ; Wherein, I is a 9x9 unit matrix; is the impedance of the loop on the left side of the kth segment, is the boundary matrix of the loop on the left side of the k+1th segment; is the impedance of the loop on the right side of the kth segment, is the power supply side excitation source of the kth segment, corresponding to the system operating parameters when there is no fault; is the short-circuit side excitation source of the kth segment, corresponding to the additional electromagnetic characteristics introduced by the fault.

[0020] Step S4: Based on the Kirchhoff current theorem, taking the current equation of the fault point as the boundary condition, the short-circuit point left side sheath fault circulating current distribution is solved by simultaneously solving the expression of step S3; In this step, the process of solving the short-circuit point left side sheath fault circulating current distribution is as follows: Based on the Kirchhoff current law at the short-circuit point: ; The expression for calculating the fault circulating current I0 is as follows: .

[0021] Thus, the sheath fault circulating current distribution of the single-phase submarine cable grounding system on the left side of the fault point is calculated.

[0022] Step S5: For the right side of the short-circuit point, nAfter the above analysis (i.e., repeating the calculation process of steps S2-S4) of the segment submarine cable line, the sheath fault current distribution on the right side of the short-circuit point is obtained, and thus the sheath fault current distribution of the entire line of the fault phase is obtained; the above analysis of the segment submarine cable line refers to the analysis of the right side of the short-circuit point n After the above analysis of the segment submarine cable line, the sheath fault current distribution on the right side of the short-circuit point is obtained, and thus the sheath fault current distribution of the entire line of the fault phase is obtained; the above analysis of the segment submarine cable line refers to the analysis of the right side of the short-circuit point n The loop equation is written at the power supply side and the short-circuit point of the segment submarine cable line, the analytical relationship expression between the power supply side, the short-circuit side of the segment submarine cable and the fault current is obtained based on the bilateral elimination method, the current at the fault point is taken as the boundary condition, the sheath fault current distribution on the right side of the short-circuit point is obtained, and thus the sheath fault current distribution of the entire line of the fault phase is obtained.

[0023] The Figure 5 The Figure 6 For the sheath fault current distribution of the submarine cable obtained by using the present application, it can be seen from the figure that the present application can obtain the sheath fault current distribution curve of the submarine cable. It can be seen from Figure 5 that after the submarine cable fails, the metal sheath fault current increases first and then decreases, and the metal sheath current at the fault point reaches the maximum, and the metal sheath current near the power supply side is greater than that on the other side. With the fault point moving backward, the fault current decreases, and with the fault point being farther and farther away from the power supply side, the amplitude of the metal sheath current gradually decreases. Figure 6 The relative error of the present application and the simulation data is Figure 6 It can be seen that the maximum fault current of the metal sheath calculated by the present application and the simulation software is consistent, and when the fault point is set at 0km, the maximum relative error of the metal sheath current is less than 0.5%, which further verifies the accuracy and effectiveness of the method of the present application.

[0024] Embodiment 2: A system for realizing the high-voltage alternating-current submarine cable grounding system fault current calculation method of embodiment 1 is used for high-voltage alternating-current submarine cable grounding system submarine cable grounding fault current calculation, comprising 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 turn; The submarine cable grounding system equivalent module is used for equivalent processing of the equal power supply equipment, the power utilization equipment, the equivalent grounding resistance of the equal power supply equipment and the equivalent grounding resistance of the power utilization equipment in the submarine cable grounding system; The π-type equivalent circuit creation module is used for collecting the devices in the equivalent processed submarine cable grounding system to form a π-type equivalent circuit of the submarine cable grounding system; The loop equation writing module is used for writing loop equations for the fault phase; The fault current calculation module is used for solving the loop equations to calculate the fault current distribution of the entire single-phase submarine cable grounding system at the fault point.

[0025] The system is arranged in an electronic device, components of the electronic device can include, but are not limited to: at least one processing unit, at least one storage unit, a bus connecting different system components including the storage unit and the processing unit, a display unit.

[0026] The storage unit stores program codes, which can be executed by the processing unit, so that the processing unit executes the steps according to various exemplary embodiments of the present application described in the method part of embodiment 1 of the present specification.

[0027] The storage unit can include a readable medium in the form of a volatile storage unit, such as a random access memory (RAM) and / or a cache memory, and can further include a read-only memory (ROM).

[0028] The storage unit can also include programs / utilities with a set of (at least one) program modules, such programs / modules include, but are not limited to: an operating system, one or more application programs, other program modules, and program data, each of which or some combination of which can include implementation of a network environment.

[0029] The bus can be one or more of several types of bus structures, including a storage unit bus or storage unit controller, a peripheral bus, a graphics acceleration port, a processing unit bus, or a local bus using any of a variety of bus architectures.

[0030] The electronic device can also communicate with one or more external devices (such as a keyboard or a pointing device, a Bluetooth device, etc.), and can also communicate with one or more devices that enable a user to interact with the electronic device (such as a router, a modem, etc.), and / or with any devices (such as a router, a modem, etc.) that enable the electronic device to communicate with one or more other computing devices. Such communication can be carried out through an input / output (I / O) interface. In addition, the electronic device can also communicate with one or more networks (such as a local area network (LAN), a wide area network (WAN), and / or a public network, such as the Internet) through a network adapter. The network adapter communicates with other modules of the electronic device through the 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, etc.

[0031] Those skilled in the art can clearly understand, through the above description of the embodiments, that the embodiments described herein can be implemented by software, or by software in combination with necessary hardware. Therefore, the technical solutions according to the embodiments of the present disclosure can be embodied in the form of a software product. The software product can be stored in a non-volatile storage medium (which can be a CD-ROM, a U disk, a mobile hard disk, etc.) or on a network, and includes a plurality of instructions to enable a computing device (which can be a personal computer, a server, a terminal device, or a network device, etc.) to perform the methods according to the embodiments of the present disclosure.

[0032] In the exemplary embodiments of the present disclosure, a computer readable storage medium is also provided, which stores a program product capable of implementing the above-mentioned method of the present disclosure. In some possible embodiments, various aspects of the present disclosure can also be implemented in the form of a program product, which includes program codes for causing a terminal device to perform the steps according to various exemplary embodiments of the present disclosure described in the above-mentioned "Exemplary Methods" section of the present disclosure when the program product is run on the terminal device.

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 the Thevenin equivalence 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 power consumption equipment is equivalent to load impedance. In consideration of the double-terminal grounding characteristics of the submarine cable grounding system, the submarine cable loop is equivalent to a π-type circuit to construct a three-phase equivalent circuit of the submarine cable grounding system. Step S2: Determine the fault point phase, and divide the submarine cable into the left and right sides based on the fault point; based on Kirchhoff's theorem, n Write the voltage loop equations in the form of complex matrices on the power supply side and the short-circuit side of the submarine cable mesh, and derive the voltage loop equations on the power supply side and the short-circuit side of the submarine cable by combining the double-side elimination principle. k Segment matrix recursion rule; Step S3: According to the power supply side and the short circuit side of the submarine cable k Based on the recursive rule of the segment matrix, the analytical relationship expression between the main segment of the submarine cable and the fault circulation current on the power supply side and the short-circuit side of the submarine cable is established; Step S4: Based on Kirchhoff's current theorem and taking the fault point current equation as the boundary condition, the expression of step S3 is combined to solve the sheath fault circulating current distribution on the left side of the short-circuit point; Step S5: Check the right side of the fault point n Repeat steps S2-S4 for the submarine cable line to obtain the sheath fault circulation current distribution on the right side, and then obtain the sheath fault circulation current distribution of the entire fault phase.

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 ABC.

3. The method for calculating fault current in a high-voltage AC submarine cable grounding system according to claim 1, wherein: The construction process of the three-phase equivalent circuit of the submarine cable grounding system is as follows: Equivalent power supply equipment to impedance Z spA 、Z spB 、Z spC and an ideal voltage source in series E A 、 E B 、 E C , the electrical equipment is equivalent to the 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 of 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 Segment, power segment n +1 paragraph.

4. The method for calculating fault current in a high-voltage AC submarine cable grounding system according to claim 1, wherein: In step S2, the steps of writing the voltage loop equation and obtaining the recursive rule of the k-th segment matrix on the power supply side are as follows: First, the submarine cable is divided into the left side and the right side of the fault point at the fault point. The mesh on the left side of the fault point is analyzed. The loop equation of one phase written based on Kirchhoff's theorem is: ； Where, is the mutual impedance per unit length between phase A and phase j in the kth segment to the left of the short-circuit point, j =SA, AA, CB, SB, AB, CC, SC or AC; Z kLacc is the self-impedance per unit length of phase A of the kth section of the submarine cable on the left side of the short-circuit point; is the mutual impedance per unit length between the kth segment and the k-1th segment of phase A; is the mutual impedance per unit length between the kth segment and the k+1th segment of phase A; 、 On the left side of the short-circuit point k 、 k -1 segment grounding voltage, l is the length of the submarine cable segment; Among them, since there is a capacitor C between the ABC three-phase core and the sheath and armor, the armor and capacitor are short-circuited to ground, and the grounding voltage of the k and k-1 sections to the left of the short-circuit point is and : ； ； in, 、 、 They are j 'Phase k, k-1, k+1 loop current; j '=CA, SA, AA, CB, SB, AB, CC, SC or AC; In the power supply section k = n +1, then: ； Where S k 、A k 、B k It is composed of the self-impedance and mutual impedance of the submarine cable, and k = n When +1, rewrite the above formula as: ； Where E is the amplitude of the three-phase voltages A, B, and C to the loop impedance; Secondly, based on the principle of double-side elimination, the above equation is transformed to obtain the recursive relationship of the current of the k+1 segment on the power supply side: ； Among them, the complex matrix and Calculated by the following formula: ； ； Finally, based on the above formula, the recursive formula for the power supply side sheath fault circulating current is obtained: ； Combine the above equations to get the power supply side k Segment recursion rule: 。 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 S2, the steps of writing the voltage loop equation and obtaining the recursive rule of the k-th segment matrix of the short-circuit side are as follows: First, in the short circuit section there is k =1, the complex matrix form of the voltage loop equation of the three-phase submarine cable grounding system is as follows: ； in, H is the matrix of fault resistance, I 0 is the fault current; Secondly, based on the principle of double-sided elimination, the above formula is transformed to obtain the recursive relationship of the short-circuit current as follows: ； where the complex matrix sum is calculated as follows: ； ； 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 can obtain the recursive rule for the kth section on the short-circuit side: 。 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 S3, the analytical relationship expression is obtained by combining the recursive formula of the power supply side sheath circulating current and the recursive formula of the short-circuit side sheath fault circulating current: ； Where, is the loop current of the kth section on the left side of the short-circuit point of the submarine cable, is the fault circulation current at the fault point; and is a complex matrix and , calculated by the following formula: ； in, I is a 9×9 unit matrix; is the impedance of the left loop of segment k, The boundary matrix of the left loop of the k+1th segment; The impedance of the right loop of segment k is, is the power supply side excitation source of the kth segment, corresponding to the system operating parameters when there is no fault; It is the short-circuit side excitation source of the kth section, corresponding to the additional electromagnetic characteristics introduced by the fault.

7. The method for calculating fault current in a high-voltage AC submarine cable grounding system according to claim 6, characterized in that: In step 3, the process of solving the sheath fault circulating current distribution on the left side of the short-circuit point is as follows: Based on Kirchhoff's current law at the short-circuit point: ； Calculation of fault circulation current I The expression for 0 is as follows: 。 8. A system for implementing the method for calculating fault current in a high-voltage AC submarine cable grounding system according to any one of claims 1 to 7, 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, which are connected in sequence; The submarine cable grounding system equivalent module is used to perform equivalent processing on the equivalent 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 gather the devices in the submarine cable grounding system after equivalent processing to form a π-type equivalent circuit of the submarine cable grounding system; The loop equation writing module is used to write the loop equation for the fault 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 along the entire fault point.

9. A computer-readable storage medium storing computer-executable instructions, wherein when the computer-executable instructions are executed, the method for calculating the fault current of the high-voltage AC submarine cable grounding system according to any one of claims 1 to 8 is implemented.

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