Sheath steady-state voltage and circulating current calculation method based on multi-loop land cable distributed model

Abstract

The invention discloses a sheath steady-state voltage and circulating current calculation method based on a multi-loop land cable distributed model. The method comprises the following steps: 1, acquiring factors influencing the sheath steady-state induced voltage and circulating current of a multi-loop single-core land cable; 2, a distributed parameter model of the unit length of the multi-loop single-core land cable is established, and then a linear equation set matrix describing the whole multi-loop land cable system is obtained; 3, calculating series impedance of a multi-loop single-core land cable line in the system linear equation set matrix; 4, calculating parallel admittance between multi-loop single-core land cable lines in the system linear equation set matrix; 5, constructing an impedance matrix and an admittance matrix so as to complement the system linear equation set matrix; 6, determining boundary conditions of a system linear equation set matrix; 7, solving a system linear equation set matrix to obtain values of steady-state induced voltage and circulating current; and 8, calculating the steady-state induced voltage and circulating current of the multi-loop single-core land cable sheath with the same arrangement mode. According to the method, the repeated modeling and simulation calculation process is omitted, the adaptability of the model is improved, and the method has great engineering value.

Description

Technical Field

[0001] The present invention relates to a method for calculating induced voltage and circulating current of a sheath of a multi-loop single-core land cable, in particular to a method for quickly calculating steady-state induced voltage and circulating current of a sheath based on a distributed circuit model of a multi-loop single-core land cable. Background Art

[0002] The development of the electric power industry is related to the national economy and people's livelihood. With the sustained and rapid development of my country's economy and the continuous improvement of people's living standards, the demand for electricity is also growing rapidly. The huge social electricity consumption has triggered a huge demand for power transmission. Solving the problem of the channel for the transmission of electric energy and delivering large-capacity electric energy to users is one of the major problems to be solved in the development of electricity. At present, the mainstream transmission methods in China are mainly overhead line transmission and cable transmission. Compared with overhead line transmission, cable transmission has the advantages of not occupying surface corridors, being less affected by climate and environment, having high operating reliability, less maintenance workload, and flexible laying. It has been widely used in power transmission, distribution, and power consumption fields such as power station lead-out lines, cross-river and cross-sea transmission, internal power supply of industrial and mining enterprises, and urban power supply.

[0003] However, with the increasing power consumption in cities and the shrinking urban space, there are more and more cases of three- and four-circuit cable lines being laid close to each other, which leads to complex electromagnetic coupling relationships between different cable lines. Since the cable trench space is small, when the cable space is arranged asymmetrically, the three-phase imbalance of the line parameters will occur, making the calculation complicated. For high-voltage cables, their structure is usually designed as a single-core structure. When the high-voltage cable is in operation, an alternating magnetic field will definitely be generated. According to Faraday's law of electromagnetic induction, there will definitely be an induced voltage on the metal sheath of the high-voltage cable. If the metal sheath of the cable forms a loop, a circulating current will be generated on the metal sheath. The appearance of the cable metal sheath circulating current will bring many hazards to the high-voltage cable transmission line, such as greatly reducing the ability of the cable to transmit electric energy, and also causing the cable metal sheath to generate a lot of heat, resulting in a decrease in the main insulation capacity and shortening the service life of the cable. The grounding method of the high-voltage cable metal sheath is closely related to the sheath circulating current. In long-distance cable transmission lines, direct grounding at both ends of the cross-interconnection is the most commonly used grounding method. If the distance between the three cross-connected sections is close, the metal sheath circulation can be effectively reduced. However, in the actual system, the three cross-connected sections are uneven. In order to reduce the sheath circulation loss, according to the experience of power grid operation, the metal sheath circulation of the cable transmission line using the cross-connected grounding system generally does not exceed 10%. In actual power engineering, due to the bends and arrangement of underground tunnels, the lengths of the three cross-connected sections of cable cannot be guaranteed to be equal. When the unevenness of the three sections is relatively large, the voltage and current induced by the metal sheath are large. In severe cases, it will exceed the threshold, damage electrical equipment, and even bring safety hazards to operation and maintenance personnel. If the metal sheath is broken down, it will affect the safe operation of cable transmission.

[0004] At present, the induced voltage and circulating current of cable sheath are mainly studied by analytical method and numerical method at home and abroad. The analytical method is to analyze the relationship between various factors in the problem, and then use concise mathematical language, mathematical symbols and mathematical relationships to express the problem and solve it. The analytical method has advantages such as high accuracy and fast calculation speed for relatively simple problems, but when the actual problem has complex boundary conditions and its relationship cannot be accurately expressed by analytical method, the application of analytical method is subject to certain restrictions. Numerical method is a method for solving engineering electromagnetic field problems that has emerged with the rapid development of computer technology. It has no clear definition and mainly includes finite element method, moment method, boundary element method, finite difference method, etc. However, the numerical method requires modeling of the system, the steps are cumbersome, and the generalization performance is poor. Summary of the invention

[0005] In view of the problems existing in the prior art, the purpose of the present invention is to propose a method for calculating steady-state voltage and circulating current of the sheath based on a distributed model of a multi-circuit terrestrial cable. The method can achieve rapid calculation of steady-state induced voltage and circulating current of the sheath by obtaining distributed circuit parameters of the multi-circuit terrestrial cable, eliminating repeated modeling and simulation calculation processes and having better adaptability.

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

[0007] A method for calculating steady-state voltage and circulating current of a sheath based on a distributed model of a multi-loop terrestrial cable comprises the following steps:

[0008] Step 1: Obtain the factors that affect the steady-state induced voltage and circulating current of the sheath of a multi-circuit single-core land cable through theoretical analysis;

[0009] Step 2: Establish a distributed parameter model per unit length of a multi-loop single-core land cable. The longitudinal coupling between each single-core land cable is modeled by the impedance per unit length Z=R+jLω. The lateral coupling between the multi-loop single-core land cables and between the cable core and the sheath is modeled by the admittance per unit length Y=G+jCω. The linear equations of the steady-state induced voltage and circulating current of a single cable sheath are obtained from the distributed parameter model. The voltage between the cable core and the ground of the j-th single-core land cable is:

[0010]

[0011] In the formula, represents the voltage between the core of the j-th single-core land cable and the ground, and represent the core and sheath currents of the j-th single-core land cable, respectively. represents the self-impedance of the j-th single-core terrestrial cable core, represents the mutual impedance of the jth and ith single-core terrestrial cable cores, represents the mutual impedance between the core and sheath of the j-th single-core terrestrial cable, represents the mutual impedance between the j-th single-core terrestrial cable core and the i-th single-core terrestrial cable sheath;

[0012] The voltage between the sheath and ground of the jth single-core terrestrial cable is:

[0013]

[0014] In the formula, represents the voltage between the sheath and ground of the jth single-core land cable, represents the self-impedance of the j-th single-core land cable sheath, represents the mutual impedance of the jth and ith single-core terrestrial cable cores, represents the mutual impedance between the core and sheath of the j-th single-core terrestrial cable, represents the mutual impedance between the j-th single-core terrestrial cable core and the i-th single-core terrestrial cable sheath;

[0015] The current in the core of the jth single-core land cable is:

[0016]

[0017] In the formula, represents the self-admittance of the j-th single-core terrestrial cable core, represents the mutual admittance between the core and sheath of the j-th single-core terrestrial cable, represents the voltage between the jth cable core and sheath,

[0018]

[0019] The current of the sheath of the jth single-core terrestrial cable is:

[0020]

[0021] In the formula, represents the self-admittance of the j-th single-core terrestrial cable core;

[0022] Applying the above four equations to each single-core terrestrial cable in the multi-circuit terrestrial cable system will give a linear equation system describing the entire multi-circuit terrestrial cable system; the linear equation system of the multi-circuit terrestrial cable system can be written in matrix form as follows:

[0023]

[0024] Step 3, calculating the series impedance of the multi-loop single-core terrestrial cable line in the multi-loop terrestrial cable system linear equation matrix (5) according to the distributed parameter model, including the mutual impedance between the cable cores and sheaths of different single-core terrestrial cables, the mutual impedance between the cable cores, and the self-impedance between the cable cores of a single cable, and the mutual impedance between the cable cores and sheaths;

[0025] Step 4, calculating the parallel admittance between the multi-loop single-core terrestrial cable lines in the multi-loop terrestrial cable system linear equation matrix (5) according to the distributed parameter model, including the self-admittance between the cable cores of a single cable and the mutual admittance between the cable core and the sheath;

[0026] Step 5: Construct the impedance matrix and the admittance matrix to obtain the Z matrix of the linear equation system in step 2. l and Y l , thus completing the matrix of the system linear equations;

[0027] Step 6, determine the boundary conditions of the linear equation matrix (5) of the multi-circuit land cable system, including the input voltage of the multi-circuit single-core land cable and the location of the grounding box, which are determined by the specific network under study;

[0028] Step 7: Use the solution method of linear differential equations to solve the matrix of the system linear equations to obtain the values ​​of steady-state induced voltage and circulating current;

[0029] Step 8: For a new multi-circuit single-core land cable with the same arrangement, the steady-state induced voltage and circulating current of the sheath can be calculated by simply modifying the size information in the arrangement and the parameter information of the multi-circuit single-core land cable.

[0030] In step 1, the factors affecting the steady-state induced voltage and circulating current of the sheath of the multi-circuit single-core land cable are obtained through theoretical analysis, including: the arrangement of the multi-circuit single-core land cable, detailed arrangement cross-sectional dimension information, steady-state load current, sheath geometric radius, sheath unit resistance, grounding resistance at both ends, and soil resistivity; the arrangement methods include parallel arrangement, right-angle arrangement, and herringbone arrangement.

[0031] In step 2, a distributed parameter model of a multi-loop single-core terrestrial cable per unit length is established in the simulation software. The distributed parameter model of the n-loop single-core terrestrial cable consists of 2n+1 distributed transmission line models. In the first 2n transmission line models, the odd-numbered ones represent the cable cores (C n ), even-numbered ones represent the sheath of multi-circuit single-core terrestrial cables (S n), the 2n+1th transmission line represents the ground (g). The longitudinal coupling between each single-core land cable is modeled by the impedance per unit length Z=R+jLω. The lateral coupling between the multi-loop single-core land cables and between the cable core and the sheath is modeled by the admittance per unit length Y=G+jCω. The values ​​of the resistance R, inductance L, conductance G, and capacitance C parameters of the single-core land cable itself and between different land cables are determined by the internal structure of the single-core land cable and the laying method of the multi-loop single-core land cable.

[0032] In step 3, the series impedance of the multi-circuit single-core terrestrial cable line in the linear equation matrix of the multi-circuit terrestrial cable system is calculated according to the distributed parameter model, including the mutual impedance between the cable cores and sheaths of different cables, between the cable cores, and the self-impedance between the cable cores of a single cable, and the mutual impedance between the cable cores and the sheaths; the specific calculation formula is as follows:

[0033]

[0034] In the formula, represents the self-resistance of the jth single-core land cable core, R g Represents the resistance between the cable core and the ground. represents the self-inductance of the jth single-core land cable core, L g represents the inductance between the cable core and the ground, represents the mutual inductance of the jth and ith single-core terrestrial cable cores, represents the mutual inductance between the jth single-core terrestrial cable core and the ground, represents the mutual inductance between the core and sheath of the j-th single-core terrestrial cable, represents the mutual inductance between the j-th single-core land cable core and the i-th single-core land cable sheath, ω represents the frequency of the current in the cable, and j represents an imaginary unit. represents the self-resistance of the j-th single-core land cable sheath, represents the mutual inductance of the jth and ith single-core terrestrial cable cores, Represents the mutual inductance between the sheath of the j-th single-core terrestrial cable and the ground.

[0035] In step 4, the parallel admittance between the multi-loop single-core terrestrial cable lines in the matrix of the linear equations of the multi-loop terrestrial cable system is calculated according to the distributed parameter model, including the self-admittance between the cable cores of a single single-core terrestrial cable and the mutual admittance between the cable core and the sheath; the specific calculation formula is as follows:

[0036]

[0037]

[0038] In the formula, represents the self-conductance of the j-th single-core terrestrial cable core, represents the self-susceptance of the j-th single-core terrestrial cable core, represents the self-conductance of the sheath of the j-th single-core land cable, represents the self-susceptance of the j-th single-core terrestrial cable sheath, represents the mutual conductance between the j-th and i-th single-core terrestrial cable cores.

[0039] Compared with the prior art, the present invention has the following advantages:

[0040] 1. The actual parameter information of multi-circuit single-core land cables is combined, so the electrical characteristics of the cable sheath can be simulated more accurately. Since the distributed parameter model of multi-circuit single-core land cables is established, the lack of accuracy of the concentrated parameter model in calculating long-distance power transmission is improved, and it is more suitable for refined steady-state induced voltage and circulating current analysis.

[0041] 2. Since the distributed parameter model takes into account the loop structure, the coupling within a single cable, and the coupling between cables when it is established, it is able to handle the electromagnetic coupling relationship between complex multi-loop cable systems.

[0042] 3. Since the differential equations of the system are established in advance and the model only needs to deal with one-dimensional spatial changes along the length of the cable, it is possible to quickly calculate the steady-state induced voltage and circulating current of the sheath, eliminating repeated modeling and simulation calculation processes.

[0043] In conclusion, the method of the present invention solves the problems of heavy modeling and simulation work and large amount of repetition in the prior art, and has great engineering value. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 The present invention shows a flow chart of a method for rapidly calculating steady-state induced voltage and circulating current of a sheath based on a distributed circuit model of a multi-loop single-core terrestrial cable.

[0045] Figure 2 A schematic diagram of the distributed parameter model per unit length of a multi-loop single-core terrestrial cable is shown. DETAILED DESCRIPTION

[0046] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0047] The purpose of the present invention is to propose a method for calculating steady-state induced voltage and circulating current of the sheath based on a distributed model of a multi-loop terrestrial cable. The method can achieve rapid calculation of steady-state induced voltage and circulating current of the sheath by obtaining distributed circuit parameters of the multi-loop terrestrial cable, thereby eliminating repeated modeling and simulation calculation processes and having better adaptability.

[0048] To achieve the above object, the present invention provides a method for calculating steady-state induced voltage and circulating current of a sheath based on a distributed model of a multi-loop terrestrial cable, comprising the following steps:

[0049] Step 1: Obtain the factors that affect the steady-state induced voltage and circulating current of the sheath of a multi-circuit single-core land cable through theoretical analysis, mainly including: the arrangement of the multi-circuit single-core land cable, detailed arrangement cross-sectional dimension information, steady-state load current, sheath geometric radius, sheath unit resistance, grounding resistance at both ends, and soil resistivity. The arrangement methods include parallel arrangement, right-angle arrangement, and herringbone arrangement.

[0050] Step 2: Establish a distributed parameter model per unit length of a multi-loop single-core terrestrial cable. Figure 2 As shown in FIG. 1 , the distributed parameter model of the n-loop single-core terrestrial cable consists of 2n+1 distributed transmission line models. Among the first 2n transmission line models, the odd-numbered ones represent the cores of the multi-loop single-core terrestrial cable (C n ), even-numbered ones represent the sheath of multi-circuit single-core terrestrial cables (S n ), the 2n+1th transmission line represents the ground (g). The longitudinal coupling between each single-core land cable is modeled by the impedance per unit length Z=R+jLω, the lateral coupling between the multi-loop single-core land cables and between the cable core and the sheath is modeled by the admittance per unit length Y=G+jCω, and the values ​​of the resistance R, inductance L, conductance G, and capacitance C between the single-core land cable itself and different land cables are determined by the internal structure of the single-core land cable and the laying method of the multi-loop single-core land cable. The voltage v(x, t) and the current i(x, t) are functions of time t and distance x. The linear equations for the sheath induced voltage and circulating current are obtained from the distributed parameter model. Under steady-state conditions, the effective values ​​of voltage and current are only functions of distance. The voltage between the cable core and the ground of the jth single-core land cable is:

[0051]

[0052] In the formula, represents the voltage between the core of the j-th single-core land cable and the ground, and represent the core and sheath currents of the j-th single-core land cable, respectively. represents the self-impedance of the j-th single-core terrestrial cable core, represents the mutual impedance of the jth and ith single-core terrestrial cable cores, represents the mutual impedance between the core and sheath of the j-th single-core terrestrial cable, represents the mutual impedance between the j-th single-core terrestrial cable core and the i-th single-core terrestrial cable sheath.

[0053] The voltage between the sheath and ground of the jth single-core terrestrial cable is:

[0054]

[0055] In the formula, represents the voltage between the sheath and ground of the jth single-core land cable, represents the self-impedance of the j-th single-core land cable sheath, represents the mutual impedance of the jth and ith single-core terrestrial cable cores, represents the mutual impedance between the core and sheath of the j-th single-core terrestrial cable, represents the mutual impedance between the j-th single-core terrestrial cable core and the i-th single-core terrestrial cable sheath.

[0056] The current in the core of the jth single-core land cable is:

[0057]

[0058] In the formula, represents the self-admittance of the j-th single-core terrestrial cable core, represents the mutual admittance between the core and sheath of the j-th single-core terrestrial cable, represents the voltage between the jth cable core and sheath,

[0059]

[0060] The current of the sheath of the jth single-core terrestrial cable is:

[0061]

[0062] In the formula, represents the self-admittance of the j-th single-core terrestrial cable core.

[0063] Formulas (1)(2)(3)(4) form a linear equation group describing the induced voltage and circulating current of the sheath of a single-core land cable. Applying the above four formulas to each single-core land cable in a multi-circuit land cable system can obtain a linear equation group describing the entire multi-circuit land cable system. The linear equation group of the multi-circuit land cable system is written in matrix form as follows:

[0064]

[0065] Where V represents the voltage and current of the cable core, V = [V c V s ] T , I represents the voltage and current of the sheath, I=[I c I s ] T . Z l and Y l are the impedance matrix and the admittance matrix, Where Z c Represents the self-impedance and mutual impedance between the cable cores, Z s Represents the self-impedance and mutual impedance between the sheaths, Z cs Represents the mutual impedance between the cable core and the sheath, Y c represents the self-admittance and mutual admittance between the cable cores, Ys represents the self-admittance and mutual admittance between the sheaths, Y cs It represents the mutual admittance between the cable core and the sheath.

[0066] Step 3: Calculate the series impedance of the multi-circuit single-core terrestrial cable line in the multi-circuit terrestrial cable system linear equation matrix (5) according to the distributed parameter model, including the mutual impedance between different cable cores and sheaths, between cable cores, and the self-impedance between single cable cores, and the mutual impedance between the cable core and sheath.

[0067]

[0068]

[0069] In the formula, represents the self-resistance of the jth single-core land cable core, R g Represents the resistance between the cable core and the ground. represents the self-inductance of the jth single-core land cable core, L g represents the inductance between the cable core and the ground, represents the mutual inductance of the jth and ith single-core terrestrial cable cores, represents the mutual inductance between the jth single-core terrestrial cable core and the ground, represents the mutual inductance between the core and sheath of the j-th single-core terrestrial cable, represents the mutual inductance between the j-th single-core land cable core and the i-th single-core land cable sheath, ω represents the frequency of the current in the cable, and j represents an imaginary unit. represents the self-resistance of the j-th single-core land cable sheath, represents the mutual inductance of the jth and ith single-core terrestrial cable cores, Represents the mutual inductance between the sheath and the ground of the j-th single-core land cable. The sheath self-resistance and self-inductance can be determined by the manufacturing parameters of the cable and the arrangement of the cable. The cable core self-resistance and self-inductance, the mutual resistance and mutual inductance between the cable cores, the mutual resistance and mutual inductance between the cable core and the sheath, and the mutual resistance and mutual inductance between the cable core, the sheath and the ground can be determined by the manufacturing parameters of the cable and the arrangement of the cable.

[0070] Step 4: Calculate the parallel admittance between the multi-loop single-core terrestrial cable lines in the multi-loop terrestrial cable system linear equation matrix (5) according to the distributed parameter model, including the self-admittance between the cores of a single cable and the mutual admittance between the core and the sheath.

[0071]

[0072] In the formula, represents the self-conductance of the j-th single-core terrestrial cable core, represents the self-susceptance of the j-th single-core terrestrial cable core, represents the self-conductance of the sheath of the j-th single-core land cable, represents the self-susceptance of the j-th single-core terrestrial cable sheath, represents the mutual conductance between the j-th and i-th single-core terrestrial cable cores.

[0073] Step 5: Construct the impedance matrix and the admittance matrix to obtain the Z in the linear equation matrix (5) of the multi-loop terrestrial cable system in step 2. l and Y l , thus completing the linear equation matrix (5) of the multi-loop terrestrial cable system:

[0074]

[0075] Step 6: Determine the boundary conditions of the linear equation matrix (5) of the multi-circuit terrestrial cable system, such as the input voltage of the multi-circuit single-core terrestrial cable, the location of the grounding box, etc., which are determined by the specific network under study.

[0076] Step 7: Use the method of solving linear differential equations to solve the linear equation matrix (5) of the multi-loop terrestrial cable system to obtain the values ​​of the steady-state induced voltage and circulating current.

[0077] Step 8: For a new multi-circuit single-core land cable with the same arrangement, the steady-state induced voltage and circulating current of the sheath can be calculated by simply modifying the size information in the arrangement and the parameter information of the multi-circuit single-core land cable, eliminating the process of re-modeling and simulation.

Claims

1. A method for calculating steady-state voltage and circulating current of sheath based on a distributed model of a multi-loop terrestrial cable, characterized in that: The following steps are involved: Step 1: Obtain the factors that affect the steady-state induced voltage and circulating current of the sheath of a multi-circuit single-core land cable through theoretical analysis; Step 2: Establish a distributed parameter model per unit length of a multi-loop single-core land cable. The longitudinal coupling between each single-core land cable is modeled by the impedance per unit length Z=R+jLω. The lateral coupling between the multi-loop single-core land cables and between the cable core and the sheath is modeled by the admittance per unit length Y=G+jCω. The linear equations of the steady-state induced voltage and circulating current of a single cable sheath are obtained from the distributed parameter model. The voltage between the cable core and the ground of the j-th single-core land cable is: In the formula, represents the voltage between the core of the j-th single-core land cable and the ground, and They represent the core and sheath currents of the j-th single-core land cable, represents the self-impedance of the j-th single-core terrestrial cable core, represents the mutual impedance of the jth and ith single-core terrestrial cable cores, represents the mutual impedance between the core and sheath of the j-th single-core terrestrial cable, represents the mutual impedance between the j-th single-core terrestrial cable core and the i-th single-core terrestrial cable sheath; The voltage between the sheath and ground of the jth single-core terrestrial cable is: In the formula, represents the voltage between the sheath and ground of the jth single-core land cable, represents the self-impedance of the j-th single-core land cable sheath, represents the mutual impedance of the jth and ith single-core terrestrial cable cores, represents the mutual impedance between the core and sheath of the j-th single-core terrestrial cable, represents the mutual impedance between the j-th single-core terrestrial cable core and the i-th single-core terrestrial cable sheath; The current in the core of the jth single-core land cable is: In the formula, represents the self-admittance of the j-th single-core terrestrial cable core, represents the mutual admittance between the core and sheath of the j-th single-core terrestrial cable, represents the voltage between the jth cable core and sheath, The current of the sheath of the jth single-core terrestrial cable is: In the formula, represents the self-admittance of the j-th single-core terrestrial cable core; Applying the above four equations to each single-core terrestrial cable in the multi-circuit terrestrial cable system will give a linear equation system describing the entire multi-circuit terrestrial cable system; the linear equation system of the multi-circuit terrestrial cable system can be written in matrix form as follows: Step 3, calculating the series impedance of the multi-loop single-core terrestrial cable line in the multi-loop terrestrial cable system linear equation matrix (5) according to the distributed parameter model, including the mutual impedance between the cable cores and sheaths of different single-core terrestrial cables, the mutual impedance between the cable cores, and the self-impedance between the cable cores of a single cable, and the mutual impedance between the cable cores and sheaths; Step 4, calculating the parallel admittance between the multi-loop single-core terrestrial cable lines in the multi-loop terrestrial cable system linear equation matrix (5) according to the distributed parameter model, including the self-admittance between the cable cores of a single cable and the mutual admittance between the cable core and the sheath; Step 5: Construct the impedance matrix and the admittance matrix to obtain the Z matrix of the linear equation system in step 2. l and Y l , thus completing the matrix of the system linear equations; Step 6, determine the boundary conditions of the linear equation matrix (5) of the multi-circuit land cable system, including the input voltage of the multi-circuit single-core land cable and the location of the grounding box, which are determined by the specific network under study; Step 7: Use the solution method of linear differential equations to solve the matrix of the system linear equations to obtain the values ​​of steady-state induced voltage and circulating current; Step 8: For a new multi-circuit single-core land cable with the same arrangement, the steady-state induced voltage and circulating current of the sheath can be calculated by simply modifying the size information in the arrangement and the parameter information of the multi-circuit single-core land cable.

2. The method for calculating steady-state voltage and circulating current of sheath based on a multi-loop terrestrial cable distributed model according to claim 1, characterized in that: In step 1, the factors affecting the steady-state induced voltage and circulating current of the sheath of the multi-circuit single-core land cable are obtained through theoretical analysis, including: the arrangement of the multi-circuit single-core land cable, detailed arrangement cross-sectional dimension information, steady-state load current, sheath geometric radius, sheath unit resistance, grounding resistance at both ends, and soil resistivity; the arrangement methods include parallel arrangement, right-angle arrangement, and herringbone arrangement.

3. The method for calculating steady-state induced voltage and circulating current of sheath based on a multi-loop terrestrial cable distributed model according to claim 1, characterized in that: In step 2, a distributed parameter model of a multi-loop single-core terrestrial cable per unit length is established in the simulation software. The distributed parameter model of the n-loop single-core terrestrial cable consists of 2n+1 distributed transmission line models. In the first 2n transmission line models, the odd-numbered ones represent the cable cores (C n ), even-numbered ones represent the sheath of multi-circuit single-core terrestrial cables (S n ), the 2n+1th transmission line represents the ground (g). The longitudinal coupling between each single-core land cable is modeled by the impedance per unit length Z=R+jLω. The lateral coupling between the multi-loop single-core land cables and between the cable core and the sheath is modeled by the admittance per unit length Y=G+jCω. The values ​​of the resistance R, inductance L, conductance G, and capacitance C parameters of the single-core land cable itself and between different land cables are determined by the internal structure of the single-core land cable and the laying method of the multi-loop single-core land cable.

4. The method for calculating steady-state voltage and circulating current of sheath based on a multi-circuit terrestrial cable distributed model according to claim 1, characterized in that: In step 3, the series impedance of the multi-circuit single-core terrestrial cable line in the linear equation matrix of the multi-circuit terrestrial cable system is calculated according to the distributed parameter model, including the mutual impedance between the cable cores and sheaths of different cables, between the cable cores, and the self-impedance between the cable cores of a single cable, and the mutual impedance between the cable cores and the sheaths; the specific calculation formula is as follows: In the formula, represents the self-resistance of the jth single-core land cable core, R g Represents the resistance between the cable core and the ground. represents the self-inductance of the jth single-core land cable core, L g represents the inductance between the cable core and the ground, represents the mutual inductance of the jth and ith single-core terrestrial cable cores, represents the mutual inductance between the jth single-core terrestrial cable core and the ground, represents the mutual inductance between the core and sheath of the j-th single-core terrestrial cable, represents the mutual inductance between the j-th single-core land cable core and the i-th single-core land cable sheath, ω represents the frequency of the current in the cable, and j represents an imaginary unit. represents the self-resistance of the j-th single-core land cable sheath, represents the mutual inductance of the jth and ith single-core terrestrial cable cores, Represents the mutual inductance between the sheath of the j-th single-core terrestrial cable and the ground.

5. The method for calculating steady-state voltage and circulating current of sheath based on a multi-circuit terrestrial cable distributed model according to claim 1, characterized in that: In step 4, the parallel admittance between the multi-loop single-core terrestrial cable lines in the matrix of the linear equations of the multi-loop terrestrial cable system is calculated according to the distributed parameter model, including the self-admittance between the cable cores of a single single-core terrestrial cable and the mutual admittance between the cable core and the sheath; the specific calculation formula is as follows: In the formula, represents the self-conductance of the j-th single-core terrestrial cable core, represents the self-susceptance of the j-th single-core terrestrial cable core, represents the self-conductance of the sheath of the j-th single-core land cable, represents the self-susceptance of the j-th single-core terrestrial cable sheath, represents the mutual conductance between the j-th and i-th single-core terrestrial cable cores.

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