Resistance type superconducting current limiter optimization configuration method in closed loop transfer scene

Abstract

The invention discloses an optimal configuration method for a resistance type superconducting current limiter in a closed-loop transfer scene. The method comprises the following steps: S1, simplifying and setting relay protection in a 10kv cable network; s2, calculating an impact current caused by loop closing transfer; s3, determining the access position of the resistance-type superconducting current limiter in the closed-loop transfer scene; s4, establishing a target function F1 by taking the lowest cost of the resistance type superconducting current limiter as a target; s5, establishing a target function F2 by taking the optimal matching degree of the resistance type superconducting current limiter and current protection as a target; s6, normalizing the objective functions of the F1 and the F2, and constructing a single objective function; s7, establishing constraint conditions of the optimization configuration model of the resistance type superconducting current limiter; and S8, solving the optimization configuration model of the resistance type superconducting current limiter to obtain an optimization configuration scheme of the resistance type superconducting current limiter. According to the method, the optimal configuration of the SFCL in the 10kV distribution network in the closed-loop transfer scene can be realized, and the current limiting ratio at the closed-loop point reaches a relatively high value, so that the reliable action of protection is ensured.

Description

Technical Field

[0001] The present invention relates to the field of resistive superconducting fault current limiters, and particularly to an optimized configuration method for resistive superconducting fault current limiters in the scenario of loop closing and power transfer. Background Art

[0002] Transient inrush currents will be generated during loop closing operations, and such currents may exceed the capacity of circuit breakers. Therefore, current limiters are required to limit the current to ensure the stability of the power grid. A resistive superconducting fault current limiter (RSFCL) has almost no loss during normal operation of the power grid due to the zero-resistance characteristic of superconducting materials. During a fault, it quickly quenches and introduces impedance to limit the short-circuit current. Its excellent performance has broad application prospects. The resistive superconducting fault current limiter can quickly quench and turn into a high-impedance state when a short circuit occurs, and can limit the short-circuit current to 10%-20% of the original value within 1 ms, significantly reducing the opening pressure of the circuit breaker. Moreover, its structure is simple. Compared with inductive or other types, the resistive structure is easier to implement and does not require an additional triggering device, making it suitable for the compactification requirements of the distribution network.

[0003] The resistive superconducting fault current limiter demonstrates the core advantage of fast current limiting in loop closing and power transfer, but key technical bottlenecks such as material costs and protection coordination need to be overcome. How to achieve the optimized configuration of the resistive superconducting fault current limiter is the main goal of technicians. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide an optimized configuration method for resistive superconducting fault current limiters in the scenario of loop closing and power transfer.

[0005] One technical solution to achieve the above purpose is: an optimized configuration method for resistive superconducting fault current limiters in the scenario of loop closing and power transfer, including the following steps: S1, simplify and set the relay protection in the 10 kV cable network;

[0006] S2, calculate the inrush current caused by loop closing and power transfer;

[0007] S3, determine the access position of the resistive superconducting fault current limiter in the scenario of loop closing and power transfer;

[0008] S4, establish an objective function F1 with the lowest cost of the resistive superconducting fault current limiter as the goal;

[0009] S5, establish an objective function F2 with the best coordination degree between the resistive superconducting fault current limiter and the current protection as the goal;

[0010] S6, normalize the objective functions of F1 and F2 to construct a single-objective function;

[0011] S7, establish the constraint conditions for the optimized configuration model of the resistive superconducting fault current limiter;

[0012] S8. Solve the optimal configuration model of the resistive superconducting fault current limiter to obtain the optimal configuration scheme of the resistive superconducting fault current limiter.

[0013] Further, the simplification of the relay protection in the 10 kV cable network in S1 includes:

[0014] 1) All faults in the cable network are considered as permanent faults, and no reclosing is added to the relay protection.

[0015] 2) For the three-stage current protection (instantaneous overcurrent protection, time-limited overcurrent protection, definite-time overcurrent protection), the 10 kV line protection adopts two-stage current protection, withdraw the time-limited overcurrent protection or definite-time overcurrent protection from operation, and adjust the operating time limits of the remaining two-stage protections to achieve coordination.

[0016] Further, the setting of the relay protection in the 10 kV cable network in S1 includes:

[0017] 1) Protections are installed only at the substation outlet in the 10 kV cable network.

[0018] 2) The instantaneous overcurrent protection should avoid the maximum short-circuit current during the fault at the low-voltage side of the distribution transformer to prevent misoperation during the short-circuit at the low-voltage side.

[0019] 3) The time-limited overcurrent protection of the cable network needs to cooperate with the time-limited overcurrent protection of the lower-level line. At the same time, since the definite-time overcurrent protection is withdrawn, the time-limited overcurrent protection should avoid the maximum load current.

[0020] Further, in S2, the calculation model of the in-loop power transfer impact current I based on the Thevenin's theorem is used to calculate the impact current I imp , and there is I imp = U OC / Z eq

[0021] where, U OC is the open-circuit voltage seen from the in-loop point at the moment of in-loop closing, and Z eq is the equivalent impedance seen from the in-loop point.

[0022] Further, in S3, the connection position of the resistive superconducting fault current limiter in the in-loop power transfer scenario is at the in-loop point.

[0023] Further, in S4, the cost of the resistive superconducting fault current limiter includes the cost of the external device and the cost of the superconducting tape:

[0024] F1 = C out + C HTS

[0025] where: F1 is the total cost of the resistive superconducting fault current limiter; C outThe cost of the external device, including the costs of the inner and outer dewars and the casing, is a constant in a fixed application scenario; C HTS The cost of the superconducting tape is proportional to the length of the superconducting tape, and is taken as 100 yuan / meter.

[0026] Further, in S5, in the closed-loop transfer power supply scenario, the current at each protection point should be less than the setting value of Protection Section III after the resistive superconducting fault current limiter is connected, in order to ensure the correct operation of the protection. The objective function of protection coordination in the closed-loop transfer power supply scenario is defined as:

[0027]

[0028] Where:

[0029] I L : The rated maximum load current at the closed-loop point;

[0030] I M : The closed-loop inrush current after limitation;

[0031] F2: The ratio of the maximum rated load current at the closed-loop point to the closed-loop inrush current after limitation. The smaller the value, the better the effect of limiting the closed-loop inrush current.

[0032] Further, in S6, the normalization formulas for establishing the objective function with the lowest cost of the resistive superconducting fault current limiter as the goal and the objective function with the optimal coordination degree between the resistive superconducting fault current limiter and the current protection as the goal are:

[0033]

[0034] Where: l is the sum of the lengths of the superconducting tapes of all installed fault current limiters, l max is the sum of the maximum lengths of the superconducting tapes of all installed fault current limiters. F′1 is the cost objective function after normalization, and the smaller the better; the value of F2 is already in the range of [0,1], and it is also the smaller the better type, so no processing is required. There is

[0035] F′2 = F2

[0036] The single-objective function of the weighted summation method is defined as:

[0037] F′ = α·F′1 + β·F′2

[0038] Where: α and β are the weight coefficients specified by the user, satisfying α + β = 1, and are used to reflect the importance of the cost of the fault current limiter and the degree of protection coordination.

[0039] Further, in S7, the constraint conditions for the closed-loop transfer power supply scenario are:

[0040] S7.1. The inrush current at the loop closing and power transfer point after the access of RSFCL is lower than the setting values of the third-stage relay protection on both sides.

[0041]

[0042] Where: I RSFCL is the short-circuit current magnitude after the installation of RSFCL, is the smaller one of the setting values of the third-stage relay protection on both sides;

[0043] S7.2. The voltage per unit length of the superconducting strip of the superconducting fault current limiter is within the allowable range.

[0044]

[0045] Where: U RSFCL is the voltage across both ends of RSFCL, L is the length of the superconducting strip, and U safe is the allowable voltage per unit length of the superconducting strip.

[0046] Furthermore, S8 uses the peacock optimization algorithm to solve the optimization configuration model of the resistive superconducting fault current limiter and outputs the optimal limiter configuration scheme, where is the strip length.

[0047] The optimization configuration method of the resistive superconducting fault current limiter in the loop closing and power transfer scenario of the present invention takes into account the simplified distribution network protection strategy, improves the response speed of relay protection, and can also avoid unnecessary tripping and system stability problems caused by overprotection; the present invention calculates the inrush current of loop closing and power transfer, considers the coordination with current protection, constructs a protection coordination index, further establishes a configuration model of RSFCL considering current protection coordination in the 10 kV distribution network, analyzes the characteristics of the optimization model, and uses the peacock optimization algorithm to solve and obtain the optimization configuration scheme of RSFCL in the loop closing and power transfer scenario. In a small-scale distribution network, the current limiting ratio at the loop closing point can reach a relatively high value, which can ensure the reliable operation of protection. Brief Description of the Drawings

[0048] Figure 1 is a schematic diagram of loop closing and power transfer of a single-loop network;

[0049] Figure 2 is a schematic diagram of a 10 kV single-source radial network;

[0050] Figure 3 is a schematic diagram of feeder load equivalence;

[0051] Figure 4 is a simplified equivalent diagram of a single-loop network;

[0052] Figure 5 is the Thevenin equivalent model for calculating the loop closing inrush current;

[0053] Figure 6 Schematic diagram of the access position of RSFCL in the closed-loop power transfer scenario;

[0054] Figure 7 Logic diagram for model solution using the peacock optimization algorithm;

[0055] Figure 8 Closed-loop current curve diagram before configuring RSFCL;

[0056] Figure 9 Closed-loop current curve diagram after configuring RSFCL; Specific implementation manners

[0057] For a better understanding of the technical solution of the present invention, the following will be described in detail through specific embodiments:

[0058] The optimization configuration method of the resistive superconducting fault current limiter in the closed-loop power transfer scenario of the present invention analyzes the impact of closed-loop power transfer on current protection, proposes a calculation model for the closed-loop impact current, and then analyzes the use of RSFCL to cope with the impact current in the closed-loop power transfer scenario.

[0059] Specifically, it includes the following steps:

[0060] S1, simplify and set the relay protection in the 10kV cable network.

[0061] The traditional three-stage current protection is a relay protection strategy widely used in the 10kV distribution network. It realizes the protection of power equipment in stages by setting different current thresholds and time delays. The advantage of this protection mechanism is that it can provide precise responses according to different fault types and fault locations, ensuring that the power grid can take prompt actions when a fault occurs to reduce equipment damage and maintain the overall stability of the system. For the object of the 10kV cable network, due to the characteristics of the cable network itself, such as the multi-use ring network wiring mode and the cancellation of reclosing input, its protection should also be simplified on the basis of the traditional three-stage current protection to adapt to the actual operation situation.

[0062] The simplification of the relay protection in the 10kV cable network in S1 includes:

[0063] 1) All faults in the cable network are considered as permanent faults, and no reclosing is added to the relay protection;

[0064] 2) For the instantaneous current quick-break protection, time-limited current quick-break protection, and definite-time overcurrent protection of the three-stage current protection, the 10kV line protection adopts two-stage current protection, withdraws the time-limited current quick-break protection or definite-time overcurrent protection from operation, and adjusts the action time limits of the remaining two-stage protections to achieve coordination.

[0065] The setting of relay protection in the 10 kV cable network in S1 includes:

[0066] 1) If switch protection is set for the sectional switches of the main line and tie line, and the branch line protection is coordinated with the upper-level protection, the upper limit of the action time will be further compressed, resulting in greater difficulty in coordinating the branch line protections and even inability to coordinate. At the same time, since the load current and short-circuit current directions in the sectional switches of the main line and tie line change with the line operation mode, the current relay protection devices cannot adapt to this change in current direction. Therefore, protection is only installed at the substation outlet in the 10 kV cable network.

[0067] 2) The instantaneous overcurrent protection avoids the maximum short-circuit current during the low-voltage side fault of the distribution transformer to prevent misoperation during the low-voltage side short circuit.

[0068] 3) The time-limited overcurrent protection of the cable network needs to be coordinated with the time-limited overcurrent protection of the lower-level lines. At the same time, since the definite-time overcurrent protection is withdrawn, the time-limited overcurrent protection should avoid the maximum load current. According to the investigation of the protection setting of the distribution network, it is found that in the operation of the 10 kV cable network, the time-limited overcurrent protection often simplifies the setting process by avoiding the maximum load current, and usually, the sensitivity can be satisfied.

[0069] The above simplified protection strategy can not only improve the response speed of relay protection but also avoid unnecessary tripping and system stability problems caused by overprotection.

[0070] S2, calculate the impact current caused by loop closing power transfer.

[0071] When planning and constructing the medium-voltage distribution network in China, in order to ensure the continuous and reliable power supply of the distribution network and avoid the generation of electromagnetic loop networks, the structure of "closed-loop design, open-loop operation" is often adopted to ensure continuous and reliable power supply to the user side. Therefore, the loop closing method of "first connect and then disconnect" is adopted during loop closing power transfer, that is, the loop closing operation is carried out when both sides of the loop closing point are in normal operation, and the electrical equipment to be powered off is withdrawn from the power grid after stable operation of the loop formation.

[0072] Figure 1 Taking a typical single-loop network as an example, assuming that when the equipment such as the 10 kV busbar of Substation A is under maintenance, the 10 kV busbar of Substation B needs to supply power to the feeder of Substation A, then the "10 kV feeder loop closing switch" is closed. After transferring the feeder load of Substation A to the busbar of Substation B, the 10 kV busbar of Substation A is withdrawn. In this way, uninterrupted power supply can be achieved, but due to the incomplete consistency of the amplitudes of the two power sources, the power source phase angles, and the system frequencies, an impact current will be generated at the moment of loop closing.

[0073] In actual 10kV distribution networks, there are often many branch loads on the feeder. To achieve the Thevenin equivalence, the branch loads need to be equivalent to impedances. Figure 2 One side of the 10kV ring network is selected for research. The voltage U1 at the head end and the power P2+Q2 at the end of the single power supply radiation network are known. The branch loads S1, S2, ..., S n-1 , S n The size is known, and the first-end power P1+Q1 and the terminal voltage U2 are calculated according to the forward-backward substitution method.

[0074] like Figure 3 As shown, the feeder branch load is equivalent to the equivalent impedance Z connected to point K. k , the line impedance Z on the left and right sides l1 , Z l2 According to the calculation, the line impedance and branch load between the power supply side and the closing point are simplified into a "T" type equivalent circuit. According to the voltage drop formula, the voltage U at the equivalent access point k , can be calculated at the head end according to formula (3) or at the end end according to formula (6).

[0075]

[0076] Since the total length of the feeder L is known, and

[0077] L=L1+L2 (7)

[0078] Combining equations (3), (6), and (7), we can solve for L1 and substitute it into equation (3) to obtain U k .

[0079] Further, according to equations (3) and (7), we can find I1 and I2, then Z k Calculated according to formula (10).

[0080]

[0081] According to the above method, the Thevenin equivalent is performed on both sides of the single ring network, which can be simplified to Figure 4 The circuit shown in the figure can be used to calculate the current magnitude at the protection installation. Further simplification can be obtained as follows Figure 5 The Thevenin equivalent circuit shown in the figure is used to calculate the closing-loop impulse current, which is used to quantitatively analyze the impact of closing-loop operation on relay protection. The closing-loop transfer current calculation model based on the Thevenin theorem is used to calculate the impulse current I caused by the closing-loop transfer. imp , there is I imp =U OC / Z eq

[0082] Among them, U OCis the open-circuit voltage seen from the loop closing point at the moment of loop closing, and Z eq is the equivalent impedance seen from the loop closing point.

[0083] S3. Determine the access position of the resistive superconducting fault current limiter in the loop closing and power transfer scenario.

[0084] To ensure the effectiveness of the RSFCL in the loop closing and power transfer scenario, it is crucial to select a suitable installation position. The main function of the RSFCL is to reduce the impact current caused by loop closing and power transfer and ensure the reliable operation of the relay protection device. For an operating distribution network, its active and reactive power balance can naturally be satisfied. If the impact current at the loop closing point can be limited within the III-section setting values of the two-side protection, then the currents in other branches and the node voltages are usually within the allowable range. Therefore, the core concern is the impact current at the loop closing point. The RSFCL is connected to the loop closing point in the case of loop closing and power transfer, as Figure 6 shown.

[0085] When configuring the RSFCL, the optimization objectives include two aspects: the economy of the limiter cost and the best coordination with the relay protection. The design of the objective function needs to fully reflect the requirements of the actual problem: on the one hand, reduce the cost by reducing the length of the superconducting tape of the limiter; on the other hand, ensure that the ratio of the limited current to the protection setting value is as large as possible within the allowable range to improve the protection sensitivity. The optimal parameters of the limiter should be optimized and determined by comprehensively considering the economic cost and the relay protection sensitivity. Therefore, the configuration steps are as follows:

[0086] S4. Establish the objective function F1 with the lowest cost of the resistive superconducting fault current limiter as the goal.

[0087] The cost of the resistive superconducting fault current limiter includes the cost of the external device and the cost of the superconducting tape:

[0088] F1 = C out + C HTS

[0089] where: F1 is the total cost of the resistive superconducting fault current limiter; C out is the cost of the external device, including the costs of the inner and outer dewars and the bushing. In a fixed application scenario, the cost of the external device takes a constant value; C HTS is the cost of the superconducting tape, which is proportional to the length of the superconducting tape and is taken as 100 yuan / meter. The cost of the parallel resistance of the RSFCL can be ignored compared with the costs of the external device and the superconducting tape. Therefore, the cost of the parallel resistance is not considered.

[0090] S5. Establish the objective function F2 with the best coordination between the resistive superconducting fault current limiter and the current protection as the goal.

[0091] In the scenario of loop closing power transfer, the purpose of connecting the RSFCL is to prevent the protection from malfunctioning. In the loop closing power transfer scenario, the current at each protection point should be less than the setting value of the third section of the protection after the resistive superconducting fault current limiter is connected, so as to ensure the correct operation of the protection.

[0092] Define the protection coordination objective function in the loop closing power transfer scenario as:

[0093]

[0094] Where:

[0095] I L : Rated maximum load current at the loop closing point;

[0096] I M : Loop closing inrush current after limitation;

[0097] F2: Ratio of the maximum rated load current at the loop closing point to the loop closing inrush current after limitation. The smaller the value, the better the effect of limiting the loop closing inrush current.

[0098] S6, normalize the objective functions of F1 and F2 to construct a single objective function.

[0099] Since the value ranges and dimensions of F1 and F2 are different, F1 and F2 need to be normalized to map the objective values to [0,1]. Since the installed RSFCL structure types are the same and the external device costs in the same scenario are the same, it can be considered that F1 is only related to the length of the superconducting tape. Therefore, use the length to normalize it. The normalization formula is:

[0100]

[0101] Where:

[0102] l is the sum of the lengths of the superconducting tapes of all installed current limiters, l max is the sum of the maximum lengths of the superconducting tapes of all installed current limiters. Currently, the maximum length of the superconducting tape of a single current limiter is taken as 204m. F′1 is the cost objective function after normalization, and the smaller the better.

[0103] In the case of loop closing power transfer, the value of F2 is already within the range of [0,1], and it is also of the type that the smaller the better, so no processing is required.

[0104] F′2 = F2

[0105] The single objective function defined by the weighted summation method is:

[0106] F′ = α·F′1 + β·F′2

[0107] Where: α, β: weight coefficients specified by the user, satisfying α + β = 1, used to reflect the importance of the limiter cost and the protection coordination degree. The weights are set according to the actual situation. If the actual distribution network has higher requirements for economy, then α is greater than β; conversely, if the actual distribution network has higher requirements for the reliability and sensitivity of relay protection, then β is greater than α. The weight coefficients can also be determined by means such as fuzzy membership functions. After the weight coefficients are determined, the optimal configuration problem is transformed into a single-objective optimization problem.

[0108] S7. Establish the constraint conditions of the optimal configuration model of the resistive superconducting fault current limiter.

[0109] 1) The inrush current at the loop transfer point after connecting the RSFCL is lower than the setting value of the third section of the relay protection on both sides.

[0110]

[0111] Where: I RSFCL is the short-circuit current magnitude after installing the RSFCL, and is the smaller one of the setting values of the third section of the relay protection on both sides.

[0112] 2) The voltage bearing capacity per unit length of the superconducting tape of the superconducting fault current limiter is within the allowable range.

[0113]

[0114] Where: U RSFCL is the voltage at both ends of the RSFCL, L is the length of the superconducting tape, and U safe is the allowable voltage per unit length of the superconducting tape.

[0115] S8. Solve the optimal configuration model of the resistive superconducting fault current limiter to obtain the optimal configuration scheme of the resistive superconducting fault current limiter.

[0116] Considering that the established RSFCL optimal configuration model belongs to a complex optimization problem with multiple constraints, including 0-1 variables and continuous real variables, traditional optimization algorithms may be difficult to achieve satisfactory results when dealing with such problems. Compared with other swarm intelligence optimization algorithms, the peacock optimization algorithm can not only effectively handle high-dimensional and multi-constraint optimization problems, but also has the advantages of simple principle, few parameters and strong optimization ability. Based on these advantages, the present invention selects the peacock optimization algorithm as the solution algorithm for the limiter optimal configuration model.

[0117] The Peacock Optimization Algorithm (POA) is a heuristic optimization algorithm that mimics the courtship behavior of peacocks. This behavior reflects the combination of natural selection and sexual selection, that is, by showing superior genetic characteristics to improve the adaptability of individuals, so as to better transmit genes in the population. The basic process is as follows:

[0118] 1) Initialize the peacock population: Randomly initialize a certain number of peacock individuals in the solution space. Among them, the top 5 with the highest fitness are adult male peacocks, 30% are female peacocks, and the rest are juvenile peacocks. After each iteration, the identity of each individual needs to be re-assigned according to the fitness. Each individual represents a solution, and the decision variables of the individual are used as the solution to the optimization problem, expressed as:

[0119] X i =(x i1 ,x i2 ,…,x id )

[0120] Among them, X i is the decision vector of the i-th peacock, and x ij is the decision variable of the i-th peacock in the j-th dimension.

[0121] 2) Fitness evaluation: Evaluate the solution of each peacock according to the objective function and calculate the fitness value. The fitness value represents the quality of the solution. The higher the fitness f(X i ), the more opportunities the individual will have to guide the search of other individuals:

[0122] f(X i )=f(x i1 ,x i2 ,...,x id )

[0123] 3) Male peacocks display courtship: Male peacocks with higher fitness will show their superiority and attract other female peacock individuals through the behavior of "displaying their tails". During the display process, the optimal solution X best will attract other individuals to move towards it, thereby improving the overall solution quality.

[0124] 4) Female peacocks adaptively approach male peacocks: According to the display behavior of peacocks with higher fitness, individuals will imitate the optimal solution to update their positions. The specific update formula is:

[0125] x h =x h (t)+3θ(x c，N -x h (t))

[0126] Among them: x h is the position of the female peacock, xc，N is the position of the Nth male peacock, and θ is the operator that balances the local exploration and global search of the female peacock.

[0127] 5) Adaptive food search of juvenile peacocks: Juvenile peacocks randomly select a male peacock to move, and at the same time, randomly optimize in the search space by means of the Levy flight mechanism.

[0128] 6) Convergence condition: When the change of the solution tends to be stable or reaches the maximum number of iterations, the algorithm stops. Finally, the optimal solution in the peacock population is output.

[0129] The application in the solution of the optimized configuration model of the superconducting fault current limiter considering protection coordination is as follows.

[0130] After reading the basic data such as the initial distribution network topology structure and current protection settings, it enters the solution layer of the optimized configuration model. This layer takes the superconducting strip length of the fault current limiter, the installation position of the fault current limiter, and the installation quantity as decision variables, and the dimension of the decision variables is determined by the number of alternative installation positions, the number of fault current limiters, and the parameter setting range. When using the peacock optimization algorithm for solution, each iteration of each peacock individual needs to go through steps such as fitness calculation and constraint condition judgment. Subsequently, the optimized fault current limiter configuration parameters are input into the system simulation model to calculate the corresponding optimized objective function value. Finally, according to the fitness value of the individual, the population evolves until the given maximum number of iterations or convergence condition is met.

[0131] When using the peacock optimization algorithm for solution in the case of DG access, since some decision variables (such as strip length) are continuous, while the installation position and the switch quantity used to judge whether the RSFCL is accessed are discrete, therefore, continuous variables and discrete variables need to be processed separately during the optimization process. Specifically, continuous variables are directly represented by real numbers, discrete variables represent the installation position through integer values, and the switch quantity is encoded by 0-1 variables. To avoid excessive increase in the amount of calculation, after each iteration, the decision vector of the peacock individual is discretized and then input into the simulation model for optimization calculation to ensure the calculation efficiency. For the DG access scenario, the fitness calculation during the optimization process includes two main objectives: on the one hand, it is the cost of the RSFCL (determined by the external device cost and the strip length of the fault current limiter), and on the other hand, it is to improve the protection sensitivity. When evaluating the fitness, for individuals that do not meet the constraint conditions, they will be corrected through penalty functions to ensure that the constraint conditions during the optimization process are effectively maintained.

[0132] In each round of iteration, the fitness of the peacock individual is weighted and calculated according to the weight of the optimized objective function, and the position update is completed through imitation and display behaviors. The optimization process will continue until the maximum number of iterations or the convergence condition is met. Finally, the peacock optimization algorithm will output the optimal fault current limiter configuration scheme, including the strip length, the installation quantity, and the installation position.

[0133] The specific process of using the Peacock Optimization Algorithm for model solution is as Figure 7 shown.

[0134] Next, taking the actual 10 kV distribution network as an example, the effectiveness of the method of the present invention considering the current protection coordination for the RSFCL in the optimal configuration under the scenario of closed-loop power transfer in the 10 kV distribution network is verified, as Figure 6 shown. The setting results of the current protection are shown in Table 1. The access point of the RSFCL has been determined as the closed-loop point, and the maximum current at the closed-loop point is limited by the setting values of the third section of Protection A and Protection B. The value of this example is 232 A.

[0135] Table 1 Setting values of each protection

[0136]

[0137] In this example, the number of peacock individuals is set to 30, the number of iterations is 50, and α = β = 0.5. The optimization results of the iteration curve are shown in Table 2.

[0138] Table 2 Optimal configuration results of the RSFCL under the scenario of closed-loop power transfer in the 10 kV power grid

[0139]

[0140] The current simulation waveforms at the closed-loop point before and after the optimal configuration are as Figure 8 and Figure 9 shown.

[0141] From Figure 8 it can be seen that before the RSFCL is configured, the current at the closed-loop point increases sharply at the moment of closing the loop, and then drops to nearly 0. It can be seen that both protections on both sides of the single-loop network are affected by the closing impact current and misoperate. From Figure 9 it can be calculated that after the RSFCL is configured, the current limiting ratio of the RSFCL at the closed-loop point reaches 73.7%, and it can be seen from the figure that the current magnitude at the closed-loop point remains at the normal level after closing the loop, and the protection does not misoperate. This waveform shows that the configuration of the RSFCL effectively solves the problem of non-reliability of the current protection and verifies the effectiveness of the optimal configuration model.

[0142] Further adjust the values of α and β in the objective function, compare the optimization results under different weights, and display the results in Table 3.

[0143] Table 3 Optimization results under different weights

[0144]

[0145] It can be analyzed from the above table that since the scale of this network is not large, the current-limiting effect of the RSFCL is very good, and it can reach more than 75%. Under ideal circumstances, if there is no upper limit requirement for the cost, the current-limiting ratio can be further improved, and the weight can be further adjusted according to the actual situation in the future.

[0146] In summary, the present invention can achieve the optimal configuration of the RSFCL in the scenario of closed-loop transfer power supply. In a small-scale distribution network, the current-limiting ratio at the closed-loop point can reach a relatively high value, thus ensuring the reliable operation of the protection.

[0147] Those of ordinary skill in the art in this technical field should recognize that the above embodiments are only used to illustrate the present invention, rather than to limit the present invention. As long as it is within the scope of the spirit of the present invention, the changes and modifications to the above embodiments will fall within the scope of the claims of the present invention.

Claims

1. Optimization configuration method of resistive superconducting fault current limiter in the scenario of closed-loop power transfer, characterized in that, It includes the following steps: S1, simplify and set the relay protection in the 10 kV cable network; S2, calculate the impact current caused by loop closing power transfer; S3, determine the access position of the resistive superconducting fault current limiter (RSFCL) in the loop closing power transfer scenario; S4, establish the objective function F1 with the lowest cost of the resistive superconducting fault current limiter as the goal; S5, establish the objective function F2 with the best cooperation degree between the resistive superconducting fault current limiter and the current protection as the goal; S6, normalize the objective functions of F1 and F2 to construct a single-objective function; S7, establish the constraint conditions for the optimization configuration model of the resistive superconducting fault current limiter; S8, solve the optimization configuration model of the resistive superconducting fault current limiter to obtain the optimized configuration scheme of the resistive superconducting fault current limiter.

2. The optimized configuration method of the resistive superconducting fault current limiter in the distributed power source access scenario according to claim 1, wherein The simplification of the relay protection in the 10 kV cable network in S1 includes: 1) All faults in the cable network are considered as permanent faults, and no reclosing is added to the relay protection. 2) For the instantaneous overcurrent protection, time-limited overcurrent protection, and definite-time overcurrent protection of the three-stage current protection, the 10 kV line protection adopts two-stage current protection, withdraws the time-limited overcurrent protection or definite-time overcurrent protection from operation, and adjusts the operating time limits of the remaining two-stage protections to achieve coordination.

3. The optimized configuration method of the resistive superconducting fault current limiter in the distributed power source access scenario according to claim 2, wherein The setting of the relay protection in the 10 kV cable network in S1 includes: 1) Install protection only at the substation outlet of the 10 kV cable network. 2) The instantaneous overcurrent protection should avoid the maximum short-circuit current during the fault on the low-voltage side of the distribution transformer to prevent misoperation during the short circuit on the low-voltage side. 3) The time-limited overcurrent protection of the cable network needs to cooperate with the time-limited overcurrent protection of the lower-level line. At the same time, since the definite-time overcurrent protection is withdrawn, the time-limited overcurrent protection should avoid the maximum load current.

4. The optimized configuration method of the resistive superconducting fault current limiter in the distributed power source access scenario according to claim 1, wherein In S2, a loop closing transfer current calculation model based on Thevenin's theorem is used to calculate the impact current I caused by loop closing transfer imp , there is I imp = U OC / Z eq Among them, U OC is the open-circuit voltage seen from the loop closing point at the moment of loop closing, and Z eq is the equivalent impedance seen from the loop closing point.

5. The optimized configuration method of the resistive superconducting fault current limiter in the distributed power source access scenario according to claim 1, characterized in that In S3, the access position of the resistive superconducting fault current limiter in the loop closing power transfer scenario is at the loop closing point.

6. The optimized configuration method of the resistive superconducting fault current limiter in the distributed power source access scenario according to claim 1, characterized in that, In S4, the cost of the resistive superconducting fault current limiter includes the cost of external devices and the cost of superconducting tapes: F1 = C out + C HTS Among them: F1 is the total cost of the resistive superconducting fault current limiter; C out is the cost of the external device, including the costs of the inner and outer dewars and the casing. In a fixed application scenario, the cost of the external device is a constant; C HTS is the cost of the superconducting tape, which is proportional to the length of the superconducting tape and is 100 yuan per meter.

7. The optimized configuration method of the resistive superconducting fault current limiter in the distributed power source access scenario according to claim 1, wherein In S5, in the loop closing power transfer scenario, the current at each protection point after the access of the resistive superconducting fault current limiter should be less than the setting value of the third section of the protection to ensure the correct operation of the protection. Define the protection cooperation objective function in the loop closing power transfer scenario as: Where: I L : Rated maximum load current at the closing loop point; I M : The restricted closing loop impact current; F2: The ratio of the maximum rated load current at the loop closing point to the limited loop closing impact current. The smaller the value, the better the effect of limiting the loop closing impact current.

8. The optimized configuration method of the resistive superconducting fault current limiter in the distributed power source access scenario according to claim 1, wherein In S6, the normalization formula for establishing the objective function with the lowest cost of the resistive superconducting fault current limiter as the goal and the objective function with the best cooperation degree between the resistive superconducting fault current limiter and the current protection as the goal is: where: l is the sum of the lengths of all superconducting tapes of the installed current limiters, l max is the sum of the maximum lengths of the superconducting tapes of all installed current limiters, F′1 is the cost objective function after normalization, and the smaller the better; the value of F2 is already in the range of [0, 1], and it is also the smaller the better, so no processing is required. There is F′2 = F2 The single-objective function defined by the weighted summation method is: F′ = α·F′1 + β·F′2 Where: α and β are the weight coefficients specified by the user, satisfying α + β = 1, and are used to reflect the importance of the cost of the current limiter and the protection cooperation degree.

9. The optimized configuration method of the resistive superconducting fault current limiter in the distributed power source access scenario according to claim 1, wherein In S7, the constraint conditions for the loop closing power transfer scenario are: S7.1, the impact current at the loop closing power transfer point after the access of the RSFCL is lower than the setting values of the third sections of the relay protections on both sides. Where: I RSFCL is the magnitude of the short-circuit current after the installation of the RSFCL, is the smaller one of the setting values of the third section of the relay protection on both sides; S7.2, the pressure borne by the superconducting tape per unit length of the superconducting fault current limiter is within the allowable range. Where: U RSFCL is the voltage across the RSFCL, L is the length of the superconducting tape, and U safe is the voltage that the superconducting tape per unit length can withstand.

10. The optimized configuration method of the resistive superconducting fault current limiter in the distributed power source access scenario according to claim 1, wherein The S8 uses the peacock optimization algorithm to solve the optimal configuration model of the resistive superconducting fault current limiter, and outputs the optimal limiter configuration scheme, where the strip length is the output.

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