Method and system for restraining three-phase current unbalance of power transmission line through series reactance

Abstract

The invention relates to the technical field of power system operation control, and discloses a method and a system for inhibiting three-phase current imbalance of a power transmission line through series reactance, which comprises the following steps: establishing a power transmission line mathematical model, and calculating the positive sequence impedance of each phase line in the power transmission line based on the power transmission line mathematical model, the power transmission line comprises a single-circuit line and / or a multi-circuit line; determining a phase line needing to be compensated in the same circuit and a final compensation reactance value of the phase line; and connecting the final compensation reactance value to the corresponding phase line in series to form a series reactance compensation balanced power transmission line. According to the method, the problem of three-phase current imbalance can be thoroughly solved from the source, the method is not influenced by the operation mode and the network topology change, and the method is more feasible than the whole-line complete rolling transposition.

Description

Technical Field

[0001] The present invention relates to the technical field of power system operation control, and in particular to a method and system for suppressing three-phase current imbalance of a transmission line with a series reactance. Background Art

[0002] The power grid generally adopts a three-phase transmission and transformation system, in which the parameters of generators, transformers and high-voltage loads generally have good three-phase symmetry. However, due to the spatial arrangement of overhead transmission lines, the electrical parameters of conductors of different phases may be different. For example, the positive sequence inductance of the middle phase of a three-phase overhead transmission line arranged in a line will be slightly smaller than that of the side phase. For double-circuit and multi-circuit transmission lines on the same tower, in addition to the phase-to-phase mutual inductance of the line, there is also mutual inductance between the conductors of each circuit, and the inductance symmetry between the three phases is affected by more complex factors. Therefore, for transmission lines with a length of more than 100km, the regulations require that the conductors be transposed to keep the electrical parameters of the three-phase conductors basically balanced. However, for transmission lines with a length of less than 100km, since the standard regulations do not require transposition, when such lines are double-circuit parallel, due to the unreasonable arrangement of the conductor phase sequence, the shunt coefficients of each phase between the two circuits are inconsistent, resulting in a more serious three-phase current imbalance. In this case, the symmetry of the three-phase current can generally be improved by changing the arrangement of the conductor phase sequence, but the conductor phase sequence arrangement may be inconvenient to adjust.

[0003] Existing methods for solving the problem of three-phase current imbalance in short-circuit ring networks have shortcomings and difficulties. Method 1: Symmetrical cyclic transposition of the entire line. This method is costly and difficult to implement. For very short lines, the conditions for achieving complete transposition may not be met. Method 2: Changing the phase sequence arrangement while keeping the line unchanged. This method does not fundamentally improve the three-phase symmetry of the line parameters, but only optimizes the shunt coefficient between the phases, so that the three-phase shunt ratios of the two parallel loops are basically the same, avoiding the phenomenon of three-phase current imbalance under the current operating mode. However, when the system operating mode changes and the network topology changes, three-phase current imbalance may still occur. Summary of the invention

[0004] The present invention proposes a method and system for suppressing three-phase current imbalance of a line by connecting a series reactor. The method is mainly aimed at short lines without symmetrical transposition. A compensating reactor is connected in series in an appropriate phase conductor to make the three-phase parameters of the line reach a basic balance, thereby fundamentally eliminating the three-phase current imbalance under the parallel working condition of the short line.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for suppressing three-phase current imbalance of a transmission line by using a series reactance, comprising:

[0007] Establishing a transmission line mathematical model, and calculating the positive sequence impedance of each phase conductor in the transmission line based on the transmission line mathematical model, wherein the transmission line includes a single-circuit line and / or a multi-circuit line;

[0008] Determine the phase line that needs to be compensated in the same circuit and the final compensation reactance value of the phase line;

[0009] The final compensation reactance value is connected in series to the corresponding phase line to form a transmission line with series inductance compensation balance.

[0010] As an optimization, the transmission line mathematical model is characterized by an impedance matrix Z:

[0011]

[0012] Where n is the number of wires, and the diagonal element Z is ii is the self-impedance of the i-phase conductor (i∈[1,n]), and the off-diagonal element Z ij is the mutual impedance between different i-phase conductors and j-phase conductors, i, j∈[1,n] and i≠j.

[0013] As an optimization, the specific process of calculating the positive sequence impedance of each phase line in the transmission line is:

[0014] A1. Determine the relationship between the voltage difference at both ends of the transmission line and the current of the transmission line:

[0015]

[0016] in, represents the voltage difference across the transmission line, represents the current of the transmission line;

[0017] A2. Perform equivalent transformation on the formula in A1 to obtain the following formula:

[0018]

[0019] in, They represent the voltage difference and current at both ends of the i-th phase line, respectively, i∈[1,n], n is the total number of conductors in the transmission line;

[0020] A3. Therefore, the positive sequence impedance of each phase line is obtained, and the specific expression is:

[0021]

[0022] Among them, Z s represents the positive sequence impedance matrix of the transmission line, Z i Represents the positive sequence impedance of the phase conductor in the i-th phase line.

[0023] As an optimization, the principle for determining the phase lines that need to be compensated in the same circuit is:

[0024] In the three-phase line of the same transmission line, the phase with the smallest impedance modulus is selected as the phase conductor that needs to be compensated.

[0025] As an optimization, the specific process of determining the final compensation reactance value is:

[0026] B1. Determine the impedance matrix of the transmission line, and calculate the positive sequence impedance of each phase conductor in the transmission line from this (impedance matrix); the voltage difference can be given arbitrarily and does not need to be specifically determined. Different voltages will calculate different currents, and the ratio of voltage to current remains unchanged.

[0027] B2. According to the calculated line positive sequence impedance, determine the conductor phase that needs to be compensated (the phase with the smallest positive sequence impedance);

[0028] B3. Given an initial compensation reactance value, connect the inductance of the initial compensation reactance value in series to the transmission line, calculate the three-phase current phasors of the loop line, and evaluate the three-phase current balance;

[0029] B4. Determine whether the three-phase current balance meets expectations. If so, regard the initial compensation reactance value at this time as the final compensation reactance value. Otherwise, adjust the initial compensation reactance value and return to B3.

[0030] As an optimization, in step B1, the specific method of setting the initial compensation reactance value includes:

[0031] The initial compensation reactance value is assigned to be 0, and the value is gradually increased and iterated according to a certain step size to obtain the minimum inductance that satisfies the compensation effect, which has better technical and economic performance.

[0032] As an optimization, in B3, the three-phase current amplitudes in the same transmission line are basically equal, and the phase-to-phase amplitude difference is less than the requirement (when the difference between the three-phase current amplitudes in the same transmission line is less than the set threshold), which means that the three-phase current balance meets expectations.

[0033] The present invention also discloses a system for suppressing three-phase current imbalance of a transmission line by using a series reactance, which is used to implement the above-mentioned method for suppressing three-phase current imbalance of a transmission line by using a series reactance, and is characterized by comprising:

[0034] Establishing a transmission line mathematical model, and calculating the positive sequence impedance of each phase line in the transmission line based on the transmission line mathematical model, wherein the transmission line includes a single-circuit line and a multi-circuit line;

[0035] Determine the phase line that needs to be compensated in the same circuit and the final compensation reactance value of the phase line;

[0036] The final compensation reactance value is connected in series to the corresponding phase line to form a transmission line with series inductance compensation balance.

[0037] The present invention also discloses an electronic device, characterized in that it includes at least one processor and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute a method for suppressing three-phase current imbalance in a transmission line using a series reactance as described above.

[0038] The present invention also discloses a storage medium storing a computer program, characterized in that when the computer program is executed by a processor, the method for suppressing three-phase current imbalance of a transmission line by using a series reactance is implemented.

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

[0040] The series compensation method proposed in the present invention completely balances the three-phase line parameters by connecting phase-by-phase inductive elements with smaller inductance in the line. This is a method to fundamentally balance the three-phase parameters of the line, which can completely solve the problem of three-phase current imbalance from the root, and is not affected by changes in operating mode and network topology. At the same time, it is more feasible than complete rolling transposition of the entire line. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0042] Figure 1 It is a flow chart of a method for suppressing three-phase current imbalance of a transmission line with a series reactance according to the present invention;

[0043] Figure 2 It is a schematic diagram of the compensation balance of the series inductance of the transmission line;

[0044] Figure 3 Flow chart for calculating the final compensation reactance value;

[0045] Figure 4 is a system wiring diagram of an embodiment;

[0046] Figure 5 The wiring diagram of the local power grid in the embodiment, wherein (a) is a schematic diagram of the wire arrangement of the plant A line; (b) is a schematic diagram of the wire arrangement of the plant B line; (c) is a schematic diagram of the wire arrangement of the plant A and B lines;

[0047] Figure 6 The system grid and power flow and current distribution diagram before the A and B lines are put into operation in the embodiment;

[0048] Figure 7 The system grid and power flow and current distribution diagram after the A and B lines are put into operation in the embodiment;

[0049] Figure 8 The reactance parameters and current distribution diagram of each line of the system in the embodiment;

[0050] Fig. 9 This is a comparison diagram of the effects before and after compensation in the embodiment. DETAILED DESCRIPTION

[0051] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0052] This embodiment 1 provides a method for suppressing three-phase current imbalance of a transmission line by series reactance, such as Figure 1 As shown, including:

[0053] S1. Establishing a mathematical model of a power transmission line, and calculating the positive sequence impedance of each phase line in the power transmission line based on the mathematical model of the power transmission line, wherein the power transmission line includes a single-circuit line and / or a double-circuit line;

[0054] This step consists of two sub-steps.

[0055] 1. Step 1: Establish a mathematical model of the transmission line

[0056] The mathematical model of a transmission line is represented by the impedance matrix Z:

[0057]

[0058] Where Z is the impedance matrix, Z ij represents the mutual impedance between the i-th phase line and the j-th phase line, i, j∈[1,n], n represents the number of conductors (single-loop line n=3, double-loop line n=6), and the diagonal elements in the impedance matrix are the conductor self-impedance, the non-diagonal elements are the mutual impedance between the conductors, and the non-diagonal elements Z ij is the mutual impedance between different i-phase conductors and j-phase conductors, i, j∈[1,n] and i≠j.

[0059] 2. Step 2: Calculate the positive sequence impedance of the transmission line

[0060] The voltage difference at both ends of the transmission line and the line current satisfy:

[0061]

[0062] therefore,

[0063] in: are the voltage difference and current on both sides of the line, respectively. They are all phasors, representing the voltage difference and current at both ends of the i-th phase line, respectively, i∈[1,n], and n is the total number of conductors in the transmission line.

[0064] The line positive sequence impedance is:

[0065]

[0066] Among them, Z s represents the positive sequence impedance matrix of the transmission line, Z i represents the positive sequence impedance of the phase conductor in the i-th phase line, i.e., Z1, Z2, ... Z n are the positive sequence impedances of the phase conductors respectively (the positive sequence impedances of the 1st to nth phase conductors respectively).

[0067] S2. determining the phase line that needs to be compensated in the same circuit and the final compensation reactance value of the phase line;

[0068] Step 3: Determine the compensation phase and compensation reactance value

[0069] (1) The specific principles for determining the phase lines that need to be compensated in the same circuit are:

[0070] Among the three-phase lines of the same transmission line, the phase with the smallest impedance modulus is selected as the phase line that needs to be compensated.

[0071] That is, the phase with the smallest impedance modulus is selected as the series inductance compensation phase in the three-phase conductor of the same transmission line. For example, when the single-circuit line is n=3, the phase with the smallest amplitude among Z1, Z2, and Z3 is selected for compensation. When the double-circuit line is n=6, the phase with the smallest amplitude among Z1, Z2, and Z3 and the phase with the smallest amplitude among Z4, Z5, and Z6 are selected for compensation. For multi-circuit lines, the same is true.

[0072] (2) Determine the compensating reactance value.

[0073] Figure 2 Shown is a schematic diagram of parameter compensation for a single transmission line series inductor.

[0074] Compensation is performed in the middle phase. Before compensation, the voltage difference between the two ends of the line and the line current meet Where Z is the impedance matrix of the line, we have:

[0075]

[0076] After the compensating reactance ΔZ is connected in series, the same voltage difference is applied to the system in which the compensating reactance is connected in series with the transmission line, and the result is:

[0077]

[0078] Due to the mutual inductance coupling between phases, the line impedance is related to the input. Z1, Z2, ... Z before compensation n and the compensated Z1', Z2'...Z n ', in addition to the change in the impedance of the compensation phase, the impedance of the non-compensation phase is also not equal, so the inductance required for compensation is not Z1, Z2...Z n The difference between the large and small elements in the matrix needs to be calculated iteratively.

[0079] For example, after the intermediate phase is compensated, the new impedance needs to be brought into the matrix equation and recalculated, that is, Z′2 is not equal to ΔZ+Z2.

[0080] Therefore, in some embodiments, the specific process of determining the final compensation reactance value is:

[0081] B1. Determine the impedance matrix of the transmission line, and calculate the positive sequence impedance of each phase conductor in the transmission line;

[0082] B2. According to the calculated line positive sequence impedance, determine the conductor phase that needs to be compensated (the phase with the smallest positive sequence impedance);

[0083] B3. Given an initial compensation reactance value, connect the inductance of the initial compensation reactance value in series to the transmission line, calculate the three-phase current phasors of the line, and evaluate the three-phase current balance; assign the initial compensation reactance value to 0, and gradually increase iteratively according to a certain step size to obtain the minimum inductance that satisfies the compensation effect, so as to obtain better technical and economic performance. When the difference between the three-phase current amplitudes in the same transmission line is less than the set threshold, it means that the three-phase current balance is in line with expectations.

[0084] After the initial compensation reactance value increases, the impedance of each inductance of the transmission line will change before and after the increase, and the new impedance matrix after the series inductance is recalculated. It is iterated step by step from zero to obtain the minimum inductance that satisfies the step effect, which minimizes the calculation cost.

[0085] Calculate the three-phase current phasors of the circuit according to Calculated. B4. Determine whether the three-phase current balance meets expectations. If so, the initial compensation reactance value at this time is regarded as the final compensation reactance value. Otherwise, adjust the initial compensation reactance value and return to B3. In some embodiments, the three-phase current amplitudes in the same power transmission line are basically equal, and the phase amplitude difference is less than the requirement, which means that the three-phase current balance meets expectations.

[0086] Calculate the three-phase current balance, and correct ΔZ according to the three-phase current balance. After repeated iterations, the compensation impedance ΔZ is finally obtained. For example, for the three-phase lines marked 1, 2, and 3, the process is as follows Figure 3 shown.

[0087] S3. Connecting the final compensation reactance value in series to the corresponding phase line to form a transmission line with series reactance compensation balance.

[0088] That is, the fourth step: connect the compensating reactance in series to the required phases of the corresponding lines to form a transmission line with series reactance compensation balance.

[0089] Next, the method of the present invention is described through some specific embodiments.

[0090] like Figure 4 Shown is a sample system wiring diagram.

[0091] Figure 4 The following is a partial wiring diagram of a 500kV power grid, which has three power plants. The transmission lines include: single-circuit line of power plant A, double-circuit line of power plant B, and double-circuit line of power plant A and B, a total of 5 lines. The line details are shown in Table 1 below.

[0092] Table 1 Line details

[0093]

[0094] In the above example system, the plant A line and the plant B line were built and put into operation first, and the plant A and B lines were built and put into operation later. Before the plant A and B lines were built and put into operation, the three-phase currents of each line were basically balanced. However, after the plant A and B lines were built and put into operation, the three-phase current imbalance of each line appeared to varying degrees. The grid structure and power flow / three-phase current distribution before and after the plant A line was put into operation are shown in the figure. Figure 6 , Figure 7 shown.

[0095] Depend on Figure 6 , Figure 7 It can be seen that before the A and B lines were put into operation, the system did not form a ring network, and the line current was balanced in three phases. After the A and B lines were put into operation, the system formed a ring network, and the currents of the two paths were divided. Combined with the influence of the tower type and the order of hanging lines, the currents of each phase in different paths were divided in different proportions, forming a Figure 7The three-phase current unbalance phenomenon is shown.

[0096] Next, the series reactance compensation line parameter balancing method proposed in the present invention is used to fundamentally solve the problem of three-phase current imbalance in the ring network caused by the imbalance of three-phase line parameters.

[0097] Next, the following process is performed on the line.

[0098] 1. Establishing the Transmission Line Impedance Model

[0099] In the impedance of high-voltage transmission lines, the reactance component is much larger than the resistance, so the resistance can be ignored in modeling calculations. The impedance matrix can be obtained through electromagnetic transient simulation software. The following impedance unit is ohm.

[0100] (1) Factory A Line:

[0101]

[0102] (2) Plant B Line

[0103]

[0104] (3) Line A and B

[0105]

[0106] 2. Calculate the positive sequence impedance of the line

[0107] (1) Calculation of the impedance of plant A line

[0108] Given a three-phase positive sequence symmetrical unit voltage difference vector, that is, a three-phase positive sequence voltage with an amplitude of 1 (the same below):

[0109] Impedance matrix (unit: Ω):

[0110]

[0111] Current matrix (unit: A):

[0112]

[0113] Three-phase positive sequence impedance (unit: Ω):

[0114]

[0115] (2) Calculation of the impedance of Plant B line

[0116] Given a three-phase positive sequence symmetrical voltage difference vector:

[0117] Impedance Matrix:

[0118]

[0119] Current Matrix:

[0120]

[0121] Three-phase positive sequence impedance:

[0122]

[0123] (3) Calculation of impedance of line A and line B

[0124] Given a three-phase positive sequence symmetrical voltage difference vector:

[0125]

[0126] Impedance Matrix:

[0127]

[0128] Current Matrix:

[0129]

[0130] Three-phase positive sequence impedance:

[0131]

[0132] The parameters of the above three channel transmission lines are shown in Table 2 below.

[0133] Table 2 Transmission line parameters

[0134]

[0135]

[0136] Now that the positive sequence impedance of the three-circuit transmission line has been obtained, the mechanism of the three-phase current imbalance is briefly analyzed here. The reactance parameters and current distribution of the line are sorted out and marked in the system wiring diagram, such as Figure 8 shown.

[0137] After Line A and Line B were put into operation, the power transmission path from the power plant to the system was changed from the original only channel of Line A and Line B (marked as "Path 1" in the figure) to a new channel for transmission from Line A and Line A and Line B (marked as Path 2 in the figure).

[0138] The total reactance of path 1 is:

[0139]

[0140] The total reactance of path 2 is:

[0141]

[0142] The flow splitting coefficient from the power plant to substation B via two different paths: path 1 and path 2:

[0143]

[0144] According to the above relationship, we can get:

[0145] I 1a =1.9629I 2a

[0146] I 1b =1.6900I 2b (twenty three)

[0147] I 1c =1.4976I 2c

[0148] Considering that the sum of the phase currents of the two paths should be three-phase balanced, that is:

[0149] I 1a +I 2a =I 1b +I 2b =I 1c +I 2c (twenty four)

[0150] Therefore, we have:

[0151] 2.9629I 2a =2.6900I 2b =2.4976I 2c (25)

[0152] According to the above two equations, we can infer that:

[0153]

[0154] The relationship between the three-phase current magnitudes shown in the above formula is Figure 4 The actual situation is consistent with that of the previous data, indicating that the three-phase current imbalance in the system after the completion and operation of Line A and Line B is caused by the inconsistent shunt ratios of the phases A, B, and C in the two paths after the ring network is formed, and the reason for the inconsistent shunt ratios is the inconsistent three-phase impedance. By compensating the series reactance of the line with a smaller reactance phase, the three-phase impedance can be basically balanced, thereby eliminating the three-phase current imbalance.

[0155] 3. Determine the compensation difference

[0156] According to the positive sequence impedance of the three-circuit line shown in Table 2, the conductor with the smallest impedance phase in each circuit is compensated. The compensation phase of each line is determined as follows:

[0157] Table 3 Compensation phase

[0158] Compensation Phase Remark Factory A Line Phase A Intermediate phase Factory B Line Phase A Interphase Plant B Line 2 Phase A Interphase A and B line Phase C Interphase Line A and B Phase C Interphase

[0159] Observing the three-phase conductor data in Table 2, no matter double-circuit or single-circuit lines, the impedance of the phase in the three-phase conductor is lower, while the impedance of the two side phase conductors is roughly the same and slightly larger than the middle phase. This is the result of the mutual coupling of the magnetic field generated by the three-phase positive sequence current in the three-phase conductor.

[0160] 4. Determine the value of compensation reactance

[0161] The initial value ΔZ of the compensation reactance of each phase is set according to the maximum and minimum phase difference, and the maximum and minimum phase difference between the three-phase currents is set to no more than 2% as the target. After iterative calculation, the inductance that needs to be compensated is shown in the following table:

[0162] Table 4 Compensation reactance values

[0163]

[0164]

[0165] From the data in Table 4, it can be seen that the compensation reactance value finally obtained through iterative calculation is not the same as the difference between the large and small phases in the original positive-sequence impedance, but needs to be obtained through iterative calculation.

[0166] 5. Compensation by inserting compensating reactance in series

[0167] Compensate the line according to the series compensation reactance values ​​provided in Table 4:

[0168] 1. Insert a 0.933mH inductor in series into phase A of plant A line;

[0169] 2. Connect 5.99mH inductor in series to phase A of line 1 and line 2 of plant B respectively;

[0170] 3. Connect a 7.452mH inductor in series in the first and second phases of wire A and B respectively.

[0171] VI. Effect Verification

[0172] The line current distribution before and after compensation is as follows: Fig. 9 shown.

[0173] Before compensation, the five circuits in the system all had significant three-phase current imbalance, with the maximum phase-to-phase current difference exceeding 18%. After compensation, the maximum phase-to-phase current did not exceed 2%, significantly improving the three-phase current imbalance in the system.

[0174] Embodiment 2 further discloses a system for suppressing three-phase current imbalance of a transmission line by using a series reactance, which is used to implement the aforementioned method for suppressing three-phase current imbalance of a transmission line by using a series reactance, and is characterized by comprising:

[0175] Establishing a transmission line mathematical model, and calculating the positive sequence impedance of each phase line in the transmission line based on the transmission line mathematical model, wherein the transmission line includes a single-circuit line and a multi-circuit line;

[0176] Determine the phase line that needs to be compensated in the same circuit and the final compensation reactance value of the phase line;

[0177] The final compensation reactance value is connected in series to the corresponding phase line to form a transmission line with series reactance compensation balance.

[0178] Embodiment 3 also discloses an electronic device, characterized in that it comprises at least one processor and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute a method for suppressing three-phase current imbalance in a transmission line using a series reactance as described above.

[0179] Embodiment 4 further discloses a storage medium storing a computer program, characterized in that when the computer program is executed by a processor, the method of using a series reactance to suppress three-phase current imbalance in a transmission line is implemented.

[0180] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for suppressing three-phase current imbalance in a transmission line by using a series reactance, characterized in that: include: Establishing a transmission line mathematical model, and calculating the positive sequence impedance of each phase line in the transmission line based on the transmission line mathematical model, wherein the transmission line includes a single-circuit line and / or a multi-circuit line; Determine the phase line that needs to be compensated in the same circuit and the final compensation reactance value of the phase line; The final compensation reactance value is connected in series to the corresponding phase line to form a transmission line with series inductance compensation balance.

2. A method for suppressing three-phase current imbalance in a transmission line by using a series reactance according to claim 1, characterized in that: The transmission line mathematical model is characterized by the impedance matrix Z: Where n is the number of wires, and the diagonal element Z is ii is the self-impedance of the i-phase conductor, i∈[1,n], and the off-diagonal element Z ij is the mutual impedance between different i-phase conductors and j-phase conductors, i, j∈[1,n] and i≠j.

3. A method for suppressing three-phase current imbalance in a transmission line by using a series reactance according to claim 2, characterized in that: The specific process of calculating the positive sequence impedance of each phase line in the transmission line is: A1. Determine the relationship between the voltage difference at both ends of the transmission line and the current of the transmission line: in, represents the voltage difference across the transmission line, represents the current of the transmission line; A2. Perform equivalent transformation on the formula in A1 to obtain the following formula: in, They represent the voltage difference across the i-th phase and the current of that phase, respectively. The voltage difference is given as a symmetrical positive sequence phasor, i∈[1,n], and n is the total number of conductors in the transmission line; A3. Therefore, the positive sequence impedance of each phase line is obtained, and the specific expression is: Among them, Z s represents the positive sequence impedance matrix of the transmission line, Z i Represents the positive sequence impedance of the phase conductor in the i-th phase line.

4. A method for suppressing three-phase current imbalance in a transmission line by using a series reactance according to claim 1, characterized in that: The principle for determining the phase conductors that need to be compensated in the same circuit is: Among the three-phase conductors of the same transmission line, the phase with the smallest impedance modulus is selected as the phase conductor that needs to be compensated.

5. The method for suppressing three-phase current imbalance of a transmission line by using a series reactance according to claim 3, characterized in that: The specific process of determining the final compensation reactance value is: B1. Determine the impedance matrix of the transmission line, and calculate the positive sequence impedance of each phase conductor in the transmission line; B2. Determine the conductor phase that needs to be compensated based on the calculated line positive sequence impedance, wherein the conductor phase that needs to be compensated is the phase with the smallest positive sequence impedance; B3. Given an initial compensation reactance value, connect the inductance of the initial compensation reactance value in series to the transmission line, calculate the three-phase current phasors of the loop line, and evaluate the three-phase current balance; B4. Determine whether the three-phase current balance meets expectations. If so, regard the initial compensation reactance value at this time as the final compensation reactance value. Otherwise, adjust the initial compensation reactance value and return to B3.

6. A method for suppressing three-phase current imbalance in a transmission line by using a series reactance according to claim 5, characterized in that: In step B3, the specific method of setting the initial compensation reactance value includes: The initial compensation reactance value is assigned to be 0, and the value is gradually increased and iterated according to a certain step size to obtain the minimum inductance that satisfies the compensation effect, which has better technical and economic performance.

7. A method for suppressing three-phase current imbalance in a power transmission line by using a series reactance according to claim 5, characterized in that: In B3, when the differences between the amplitudes of the three-phase currents in the same transmission line are all smaller than the set threshold, it means that the three-phase current balance is in line with expectations.

8. A system for suppressing three-phase current imbalance of a transmission line with a series reactance, used to implement a method for suppressing three-phase current imbalance of a transmission line with a series reactance as claimed in any one of claims 1 to 7, characterized in that: include: Establishing a transmission line mathematical model, and calculating the positive sequence impedance of each phase line in the transmission line based on the transmission line mathematical model, wherein the transmission line includes a single-circuit line and a multi-circuit line; Determine the phase line that needs to be compensated in the same circuit and the final compensation reactance value of the phase line; The final compensation reactance value is connected in series to the corresponding phase line to form a transmission line with series inductance compensation balance.

9. An electronic device, characterized in that: It includes at least one processor and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute a method for suppressing three-phase current imbalance in a transmission line using a series reactance as described in any one of claims 1 to 7.

10. A storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, a method for suppressing three-phase current imbalance of a transmission line with a series reactance as described in any one of claims 1 to 7 is implemented.

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