A fault identification and section positioning method for a distribution network containing distributed power sources

Abstract

The application discloses a kind of fault identification and section positioning method for distribution network with distributed power supply, comprising the following steps: obtaining the maximum value of positive sequence current amplitude variation and the maximum value of negative sequence current amplitude variation on the both sides of protected line;The maximum value of positive sequence current amplitude variation and the maximum value of negative sequence current amplitude variation are compared with the corresponding threshold respectively, to obtain the short-circuit fault type of line;Based on the short-circuit fault type of line, the rank correlation coefficient of positive sequence current amplitude or negative sequence current amplitude on both sides of line is calculated;The rank correlation coefficient is compared with the preset threshold value, to determine whether the fault is located in the protected line area or outside the area;According to the determination result of inside or outside the area, the corresponding protection instruction is issued.The application can overcome the defects of traditional method prone to misoperation and refusal, and does not need to add voltage transformer or hardware channel, to meet the engineering needs of high sensitivity, high reliability and low modification cost.

Description

Technical Field

[0001] This invention belongs to the field of power system relay protection technology, and in particular relates to a fault identification and section location method for distribution networks containing distributed power sources. Background Technology

[0002] The development of new energy power sources, primarily wind and solar power, is booming. These new energy power sources are widely connected to the distribution network in the form of distributed generation (DG), causing a decrease in the sensitivity and reliability of traditional relay protection methods in the distribution network. There is an urgent need to study relay protection methods adapted to DG access.

[0003] Currently, existing research on longitudinal protection methods for distribution networks containing distributed generation (DG) can be broadly categorized as follows: The first category utilizes the differences in fault characteristics between DG and generators to construct longitudinal protection methods based on similarity criteria. These methods determine whether the fault occurs within or outside the protection zone based on the similarity calculation results. While the principle is simple, the criteria are prone to falling into an undefined "0 / 0" pattern, leading to maloperation or failure to operate. The second category comprehensively utilizes voltage and current information from both sides of the line during a fault to extract impedance characteristics, enhancing the reliability of protection actions. However, this type of method requires simultaneous acquisition of voltage and current information, resulting in longer action demonstrations and sensitivity to transition resistance. The third category introduces the concept of signal energy, performing multiplication and integration operations on voltage and current information from both sides of the line during a fault. It utilizes transient energy information to design protection criteria, resulting in novel criteria with high reliability. However, this requires hardware with powerful real-time computing capabilities to handle complex calculations.

[0004] Therefore, there is an urgent need to propose a fault identification and section location method for distribution networks with distributed power sources to ensure reliable power supply to the power system. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a fault identification and section location method for distribution networks with distributed generation (DG) access, aiming to solve the insufficient sensitivity and reliability of traditional relay protection methods in distribution networks under DG integration conditions.

[0006] To achieve the above objectives, the present invention provides a method for fault identification and section location in distribution networks containing distributed power sources, comprising the following steps: Obtain the maximum value of the positive sequence current amplitude change and the maximum value of the negative sequence current amplitude change on both sides of the protected line; The maximum value of the positive sequence current amplitude change and the maximum value of the negative sequence current amplitude change are compared with the corresponding thresholds to obtain the short-circuit fault type of the line. Based on the short-circuit fault type of the line, the rank correlation coefficient is calculated for the positive-sequence current amplitude or negative-sequence current amplitude on both sides of the line. The rank correlation coefficient is compared with a preset threshold to determine whether the fault is located inside or outside the protected line area. Based on the determination results within or outside the zone, a corresponding protection command is issued.

[0007] Optionally, the process of obtaining the maximum value of the positive-sequence current amplitude change and the maximum value of the negative-sequence current amplitude change on both sides of the protected line includes: A sliding comparison is performed on the positive sequence current amplitude sequences synchronously collected on both sides of the line to extract the maximum change of each, thereby obtaining the maximum change of positive sequence current amplitude. The maximum change of positive sequence current amplitude includes the maximum change of positive sequence current amplitude on the system side and the maximum change of positive sequence current amplitude on the distributed power source side. A sliding comparison is performed on the negative sequence current amplitude sequences synchronously collected from both sides of the line to extract their respective maximum changes, thereby obtaining the maximum value of the negative sequence current amplitude change. The maximum value of the negative sequence current amplitude change includes the maximum value of the negative sequence current amplitude change on the system side and the maximum value of the negative sequence current amplitude change on the distributed power source side.

[0008] Optionally, the process of comparing the maximum value of the positive-sequence current amplitude change and the maximum value of the negative-sequence current amplitude change with their corresponding thresholds to obtain the short-circuit fault type of the line includes: When the maximum change in the positive sequence current amplitude on both sides of the protected line is greater than or equal to the preset positive sequence threshold, a three-phase short circuit fault is determined to exist. When the maximum value of the negative sequence current amplitude change on both sides of the protected line is greater than or equal to the preset negative sequence threshold, a two-phase short circuit fault is determined to exist.

[0009] Optionally, the process of calculating the rank correlation coefficient of the positive-sequence current amplitude or the negative-sequence current amplitude on both sides of the line based on the short-circuit fault type includes: If the fault is determined to be a three-phase short circuit, the positive sequence current amplitude sequence on both sides of the line is selected; if the fault is determined to be a two-phase short circuit, the negative sequence current amplitude sequence on both sides of the line is selected. The selected positive sequence current amplitude sequence or negative sequence current amplitude sequence is paired in time order, and the Kendall rank correlation coefficient is calculated to obtain the corresponding rank correlation coefficient.

[0010] Optionally, the process of comparing the rank correlation coefficient with a preset threshold to determine whether the fault is located within or outside the protected line area includes: Take the absolute value of the calculated rank correlation coefficient; if the absolute value is equal to 1, the fault is determined to be located outside the protected line area; if the absolute value is not equal to 1, the fault is determined to be located inside the protected line area.

[0011] Optionally, the process of issuing a protection command based on the determination result within or outside the zone includes: If the fault is determined to be within the zone, a trip command is sent to the protection devices on both sides of the line; if the fault is determined to be outside the zone, a blocking command is sent to the protection devices on both sides of the line.

[0012] Optionally, the formula for calculating the rank correlation coefficient is as follows: ; In the formula, C represents the uniform logarithm, and D represents the inconsistent logarithm. This represents the number of data pairs where there are duplicate values ​​only in variable X. This represents the number of data pairs that have duplicate values ​​only in the variable Y.

[0013] The present invention also provides a computer device, including a memory, a processor, and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the method.

[0014] The present invention also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method.

[0015] The present invention also provides a computer program product, including a computer program that, when executed by a processor, implements the steps of the method.

[0016] Compared with the prior art, the present invention has the following advantages and technical effects: This invention is based on a simple technical approach: "initially judging the fault type by only taking the maximum value of the positive / negative sequence current amplitude change on both sides of the line, then calculating the rank correlation coefficient of the corresponding sequence component amplitude sequence, and using whether the coefficient is equal to 1 as the sole criterion for in-zone / out-zone operation." This approach achieves accurate fault type identification and reliable output of trip / blocking commands even under harsh conditions such as low voltage ride-through, power fluctuation, and high transition resistance of distributed power sources. It directly overcomes the shortcomings of traditional methods, such as easy false tripping and failure to trip, and does not require the addition of voltage transformers or hardware channels, thus meeting the engineering requirements of high sensitivity, high reliability, and low modification cost. Attached Figure Description

[0017] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a schematic diagram of a power distribution network structure containing DG according to an embodiment of the present invention; Figure 2 This is a schematic diagram illustrating the maximum value of the positive / negative sequence amplitude variation in an embodiment of the present invention; Figure 3 This is a flowchart of a method according to an embodiment of the present invention; Figure 4This is a schematic diagram showing the calculation results of Kendall's tau-b correlation coefficient for two-phase short circuits in an embodiment of the present invention; Figure 5 This is a schematic diagram illustrating the calculation results of Kendall's tau-b correlation coefficient for three-phase short circuits according to an embodiment of the present invention. Figure 6 This is a schematic diagram showing the calculation results of the Pearson correlation coefficient for different outputs of the 150Ω transition resistor two-phase short-circuit DG in an embodiment of the present invention. Detailed Implementation

[0018] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0019] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0020] Example 1 This embodiment provides a method for fault identification and section location in distribution networks containing distributed power sources, including the following steps: Obtain the maximum value of the positive sequence current amplitude change and the maximum value of the negative sequence current amplitude change on both sides of the protected line; The maximum value of the positive sequence current amplitude change and the maximum value of the negative sequence current amplitude change are compared with the corresponding thresholds to obtain the short-circuit fault type of the line. Based on the short-circuit fault type of the line, the rank correlation coefficient is calculated for the positive-sequence current amplitude or negative-sequence current amplitude on both sides of the line. The rank correlation coefficient is compared with a preset threshold to determine whether the fault is located inside or outside the protected line area. Based on the determination results within or outside the zone, a corresponding protection command is issued.

[0021] As a specific implementation method, such as Figure 1 The diagram shows a typical structure of a distribution network with DG (Distribution and Generation). Line AB is the protected line, f1~f5 are faults within the protected area, and f6~f7 are faults outside the protected area. For faults within the protected area, the method in this embodiment can confirm that the fault occurs within the protected line section based on the fault type, thereby causing the protection devices on both sides to trip. For faults outside the protected area, the method in this embodiment can confirm that the fault occurs outside the protected line section based on the fault type, thereby causing the protection devices on both sides to lock out. Thus, the purpose of fault type identification and section location in active distribution networks is achieved.

[0022] The specific steps are as follows: 1) Adjust the positive and negative sequence current amplitudes on both sides of the line every 50 seconds. A single sampling is performed, and the data is grouped according to a 50ms time scale. Each data group contains 1000 pairs of positive-sequence current amplitude information and 1000 pairs of negative-sequence current amplitude information. To more accurately determine the occurrence of a fault, the data used in this embodiment to calculate the correlation coefficient comes from a fusion data group formed by combining the data group that satisfies the fault type identification criterion of equation (1) or (2) with the previous data group of that data group (i.e., the fusion data group contains 2000 pairs of positive-sequence current amplitude information and 2000 pairs of negative-sequence current amplitude information). (1) (2) In equations (1) and (2) , These represent the maximum values ​​of the positive-sequence and negative-sequence current amplitude changes on the system side, respectively. , These represent the maximum values ​​of the positive-sequence and negative-sequence current amplitude changes on the DG side, respectively.

[0023] A visual description of the maximum variation of the positive / negative sequence current amplitude on both sides is as follows: Figure 2 As shown.

[0024] 2) When the positive sequence current on both sides of the line satisfies equation (1), it is determined that a three-phase short circuit fault has occurred in the system; when the negative sequence current on both sides of the line satisfies equation (2), it is determined that a two-phase short circuit fault has occurred in the system. At this point, the fault type has been determined, but the specific location still needs to be further determined. 3) Based on step 2), calculate the Kendall's tau-b correlation coefficients of the positive and negative sequence current amplitudes on both sides of the fused data group line. Determine whether the fault occurs within or outside the zone based on the correlation coefficient calculation results. If the fault occurs within the zone, trip the protection on both sides; if the fault occurs outside the zone, block the protection on both sides. The Kendall's tau-b correlation coefficient calculation formula is as shown in equation (3): (3) In the formula, C represents the consistent logarithm (data changes in the same direction), and D represents the inconsistent logarithm (data changes in opposite directions). This represents the number of data pairs where there are duplicate values ​​only in variable X. This represents the number of data pairs that have duplicate values ​​only in the variable Y.

[0025] To more intuitively illustrate the application of this correlation coefficient calculation formula in the method of this embodiment, the following is used: Figure 2 The simulation data is used for demonstration. The data contains the amplitudes of the current sequence components at both ends of the line. Figure 2Simultaneous traversal of the mid-order component amplitudes can form a total of =10 data pairs, namely (0.071,0.082), (0.06,0.073); (0.071,0.11), (0.06,0.067); (0.071,0.161), (0.06,0.061); (0.071,0.189), (0.06,0.055); (0.082,0.11), (0.073,0.06) 7); (0.082,0.161), (0.073,0.061); (0.082,0.189), (0.073,0.055); (0.11,0.161), (0.067,0.061); (0.11,0.189), (0.067,0.055); (0.161,0.189), (0.061,0.055). For example, the data pairs (0.071, 0.082) and (0.06, 0.073) represent data pairs formed by the magnitudes of the current sequence components on the DG side of the system at sampling times of 0.47s and 0.49s. In Kendall's tau-b correlation coefficient calculation algorithm, the observation for this data pair is that it changes from 0.071 to 0.082 and from 0.06 to 0.073. Both variables increase simultaneously, so they are considered to be data pairs with the same direction of change (i.e., C attribute data pairs in the definition). The definition of D attribute data pairs is similar. Therefore, for these 10 data pairs, it is not difficult to derive C=7 and D=3 in equation (3). Because the magnitudes of the sequence components on both sides do not show equal data, , The values ​​are all 0. Substituting the parameter values ​​into equation (3), the Kendall's tau-b correlation coefficient for these 10 pairs of data is calculated to be 0.4, indicating that the current sequence components at both ends show a relatively general correlation.

[0026] 4) Provide protection tripping decisions. Based on the first three steps, when a two-phase / three-phase short circuit is detected in the system, if the absolute value of the Kendall's tau-b correlation coefficient of the current sequence component amplitudes on both sides is not 1, then the fault is determined to occur within the protected line section, thus causing the protection devices on both sides to trip; if the absolute value of the correlation coefficient calculation result is 1, then the fault is determined to occur outside the protected line section, thus causing the protection devices on both sides to lock out. The overall process is as follows: Figure 3 As shown.

[0027] As a specific implementation method, a system such as PSCAD was built. Figure 1 A 10kV distribution network model with DG, where the voltage on the infinite power source system side... =10.5kV, all lines are 50km long, line parameters =0.27Ω / km, =0.35Ω / km, load per phase 2+j0.5MVA, fault points within the zone are set as f1~f5, respectively 0.5, 10, 25, 40, and 49.5km away from bus A, and fault points outside the zone are set as f6 and f7, respectively 0.5 and 5km away from bus B. The longitudinal protection method proposed in this embodiment is verified, and the Pearson correlation coefficient is selected as a comparison to verify the superiority of the method in this embodiment.

[0028] 1) The method's adaptability to changes in DG output: Table 1

[0029] Table 1 shows the fault type identification results for DG outputs of 0.4 / 0.8 / 1.6MW. As can be seen from Table 1, for faults both inside and outside the zone, the maximum values ​​of the positive / negative sequence current amplitude changes on both sides of the line satisfy equation (1) or (2). Based on this, the Kendall's tau-b correlation coefficients for each fused data group are calculated, and the results are as follows: Figures 4-5 As shown. Calculations show that the absolute values ​​of Kendall's tau-b correlation coefficients for faults within the zone are all non-1, while the absolute values ​​for faults outside the zone are all 1, which meets the requirements. Figure 3 The method and principle are explained, and the correct tripping decision is given.

[0030] 2) Method for testing fault transition resistance withstand capability: A 150Ω transition resistor was set for the seven fault points mentioned above, and the simulation results are shown in Tables 2 and 3.

[0031] Table 2

[0032] Table 3

[0033] Table 2 shows the adaptability analysis of different output methods for a two-phase short-circuit DG with a 150Ω transition resistance, and Table 3 shows the adaptability analysis of different output methods for a three-phase short-circuit DG with a 150Ω transition resistance. As can be seen from Tables 2 and 3, with the increase of the transition resistance, the changes in the positive and negative sequence current amplitudes on both sides of the line decrease significantly for faults inside and outside the protection zone. This is unfavorable for traditional longitudinal differential protection and can easily lead to protection failure. However, in the method proposed in this embodiment, based on satisfying the fault type identification criteria, Kendall's tau-b correlation coefficient still provides correct tripping decisions for faults inside and outside the protection zone, further verifying the effectiveness of the method proposed in this embodiment.

[0034] 3) Comparison with Pearson correlation coefficient: Depend on Figure 6 It can be seen that the absolute value of the Pearson correlation coefficient is 1 when there is a fault within the zone, resulting in the protection being blocked. Comparison with Table 2 shows that Kendall's tau-b correlation coefficient strictly distinguishes between faults inside and outside the zone, providing the correct tripping decision.

[0035] Example 2 Taking fault f1 within the zone as an example, the research method of this embodiment is explained in detail: First, the three-phase current on both sides of the line is measured every 50 seconds. Continuous sampling and positive / negative sequence decomposition were performed. Then, a two-phase / three-phase short circuit was set at f1 at a certain moment in the simulation. It was found that the maximum value of the change in the negative / positive sequence current amplitude at this time satisfied equation (2) / (1), and the fault type was accurately identified. Then, the Kendall's tau-b correlation coefficient of the current negative / positive sequence component amplitude on both sides of the fused data group was calculated. It was found that for the f1 fault, the absolute value of the Kendall's tau-b correlation coefficient was not 1, and it was determined to be a two-phase / three-phase short circuit fault in the zone, so a trip command was given to the protection devices on both sides. Finally, the output of DG and the fault transition resistance were changed, and the above simulation steps were repeated. It was found that the method proposed in this embodiment can give an accurate trip / blocking command based on the fault type identification criteria (i.e., equations (1) and (2)) and the Kendall's tau-b correlation coefficient. That is, this method can adapt to the fluctuation of DG output and has a certain ability to withstand the transition resistance. The specific simulation results have been given by the above simulation data.

[0036] Example 3 This embodiment also discloses a computer device, including a memory, a processor, and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the method described in Embodiment 1.

[0037] Example 4 This embodiment also discloses a computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the steps of the method described in Embodiment 1.

[0038] Example 5 This embodiment also discloses a computer program product, including a computer program that, when executed by a processor, implements the steps of the method described in Embodiment 1.

[0039] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for fault identification and section location in distribution networks containing distributed power sources, characterized in that, Includes the following steps: Obtain the maximum value of the positive sequence current amplitude change and the maximum value of the negative sequence current amplitude change on both sides of the protected line; The maximum value of the positive sequence current amplitude change and the maximum value of the negative sequence current amplitude change are compared with the corresponding thresholds to obtain the short-circuit fault type of the line. Based on the short-circuit fault type of the line, the rank correlation coefficient is calculated for the positive-sequence current amplitude or negative-sequence current amplitude on both sides of the line. The rank correlation coefficient is compared with a preset threshold to determine whether the fault is located inside or outside the protected line area. Based on the determination results within or outside the zone, a corresponding protection command is issued; The process of obtaining the maximum values ​​of the positive-sequence current amplitude change and the maximum values ​​of the negative-sequence current amplitude change on both sides of the protected line includes: A sliding comparison is performed on the positive sequence current amplitude sequences synchronously collected on both sides of the line to extract the maximum change of each, thereby obtaining the maximum change of positive sequence current amplitude. The maximum change of positive sequence current amplitude includes the maximum change of positive sequence current amplitude on the system side and the maximum change of positive sequence current amplitude on the distributed power source side. The negative sequence current amplitude sequences synchronously collected from both sides of the line are compared by sliding comparison, and the maximum change of each is extracted to obtain the maximum value of negative sequence current amplitude change. The maximum value of negative sequence current amplitude change includes the maximum value of negative sequence current amplitude change on the system side and the maximum value of negative sequence current amplitude change on the distributed power source side. The process of comparing the rank correlation coefficient with a preset threshold to determine whether the fault is located within or outside the protected line area includes: Take the absolute value of the calculated rank correlation coefficient; if the absolute value is equal to 1, the fault is determined to be located outside the protected line area; if the absolute value is not equal to 1, the fault is determined to be located inside the protected line area. The process of calculating the rank correlation coefficient of the positive-sequence current amplitude or the negative-sequence current amplitude on both sides of the line based on the short-circuit fault type includes: If the fault is determined to be a three-phase short circuit, the positive sequence current amplitude sequence on both sides of the line is selected; if the fault is determined to be a two-phase short circuit, the negative sequence current amplitude sequence on both sides of the line is selected. The selected positive sequence current amplitude sequence or negative sequence current amplitude sequence is paired in time order, and the Kendall rank correlation coefficient is calculated to obtain the corresponding rank correlation coefficient.

2. The method according to claim 1, characterized in that, The process of comparing the maximum value of the positive-sequence current amplitude change and the maximum value of the negative-sequence current amplitude change with their corresponding thresholds to obtain the short-circuit fault type of the line includes: When the maximum change in the positive sequence current amplitude on both sides of the protected line is greater than or equal to the preset positive sequence threshold, a three-phase short circuit fault is determined to exist. When the maximum value of the negative sequence current amplitude change on both sides of the protected line is greater than or equal to the preset negative sequence threshold, a two-phase short circuit fault is determined to exist.

3. The method according to claim 1, characterized in that, The process of issuing a protection command based on the determination result within or outside the zone includes: If the fault is determined to be within the zone, a trip command is sent to the protection devices on both sides of the line; if the fault is determined to be outside the zone, a blocking command is sent to the protection devices on both sides of the line.

4. The method according to claim 1, characterized in that, The formula for calculating the rank correlation coefficient is shown below: ； In the formula, C represents the uniform logarithm, and D represents the inconsistent logarithm. This represents the number of data pairs where there are duplicate values ​​only in variable X. This represents the number of data pairs that have duplicate values ​​only in the variable Y.

5. A computer device comprising a memory, a processor, and a computer program stored in the memory, characterized in that, The processor executes the computer program to implement the steps of the method according to any one of claims 1-4.

6. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the computer program implements the steps of the method according to any one of claims 1-4.

7. A computer program product, comprising a computer program, characterized in that, When executed by a processor, the computer program implements the steps of the method according to any one of claims 1-4.

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