Power distribution network fault section positioning method and system considering distributed power supply access

Abstract

The invention discloses a power distribution network fault section positioning method and system considering distributed power supply access, and the method comprises the steps: 1), measuring a negative-sequence component at a local distributed energy source, and carrying out the judgment of fault starting according to the break variable of the negative-sequence component; if yes, calibrating fault zero time, and intercepting data of a cycle; 2) calculating the transient voltage of a node n based on the transient voltage and current data measured by the home terminal; calculating the transient voltage of a node n + 1 based on the transient voltage and current data measured at the opposite end; 3) traversing transient voltages of all nodes in the calculation interval, and calculating a transient voltage difference value of two adjacent nodes; and 4) judging a fault section according to the transient voltage difference value, and when the fault section is obtained, respectively switching off adjacent switches of the fault section to realize accurate isolation of a fault point so as to ensure normal operation of a residual system. The method has the advantages of simplicity and convenience in operation, small calculation amount, low cost and the like.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of distribution network, and in particular to a method and system for locating a fault section of a distribution network taking into account access of distributed power sources. Background Art

[0002] The distribution network covers a wide range and has a large power supply range. Its line length reaches 90% of the total length of the power system network line. In addition, the distribution network line has many branch nodes, complex line structure and operation scenarios, and is easily affected by factors such as harsh environment and human activities, resulting in frequent random line failures. Once a distribution network fails, it may cause a power outage and cause a large amount of economic losses, which in turn affects people's production and life. Therefore, quickly and accurately locating distribution network faults is an important measure to ensure the safe and stable operation of the entire power system.

[0003] In the scenario of distributed generation access to the distribution network, the topological structure and power flow distribution of the distribution network are more complex. The access of distributed generation (DG) changes the structure of the distribution network. When DG is connected to different locations, the distribution of current and voltage in the distribution network also changes. DG also has the characteristics of output volatility and intermittency. At the same time, the access of power electronic equipment will also inject harmonics into the system, affecting the normal operation of the distribution network. When DG is connected to the distribution network, a single-phase grounding fault occurs, and the distribution network with fault characteristics mainly in the form of a single power source radial becomes a complex distribution network with multiple sources connected. The impact of DG on fault characteristics can no longer be ignored, and it is necessary to propose new judgment methods and theoretical basis for fault location of the distribution network under distributed generation access. Therefore, the research on fault location of the new distribution network is of great significance. Summary of the invention

[0004] In view of the technical problems existing in the prior art, the present invention provides a method and system for locating a fault section of a distribution network taking into account the access of distributed power sources, which is simple to operate and low in cost.

[0005] In order to solve the above technical problems, the technical solution proposed by the present invention is:

[0006] A method for locating a fault section of a distribution network considering the access of distributed power sources comprises the following steps:

[0007] Step 1) Measure the negative sequence component at the local distributed energy source, and determine whether the fault has started based on the mutation of the negative sequence component; if established, calibrate the zero time of the fault and capture one cycle of data;

[0008] Step 2) Calculate the transient voltage of node n based on the transient voltage and current data measured at the local end; Calculate the transient voltage of node n+1 based on the transient voltage and current data measured at the opposite end;

[0009] Step 3) traverse the transient voltages of all nodes in the calculation interval, and calculate the transient voltage difference between two adjacent nodes;

[0010] Step 4) The fault section is determined according to the transient voltage difference. When the fault section is obtained, switches adjacent to the fault section are disconnected respectively to achieve accurate isolation of the fault point to ensure normal operation of the remaining system.

[0011] Preferably, in step 1), the negative sequence current is calculated as follows:

[0012]

[0013] Among them, I DG - is the negative sequence current component of DG output; I a ,I b and I c They are the three-phase currents output by DG, is the rotation factor.

[0014] Preferably, in step 1), the specific process of determining the fault initiation according to the mutation amount of the negative sequence component is as follows:

[0015] Negative sequence current component I of distributed energy output DG - In the fault transient scenario, there are obvious mutation characteristics. The occurrence of distribution network line fault can be judged based on the mutation situation. The judgment criteria are as follows:

[0016] |I DG - |>I set1 (2)

[0017]

[0018] Wherein, formula (2) is based on I DG - The amplitude criterion is established, and the time point is recorded as t0; Formula (3) is based on I DG - The criterion for amplitude integration is that the starting point of integration is t0, t w1 is an ultra-short time window; I set1 is the negative sequence component amplitude threshold, I set2 is the threshold value of the negative sequence component integral; if the above two criteria are met at the same time, the fault section positioning is started, otherwise it will not be started.

[0019] Preferably, in step 2), the specific process of calculating the transient voltage of node n based on the transient voltage and current data measured at the local end is:

[0020] Assuming that the local measurement point is M and the opposite measurement point is N, the method for calculating the transient voltage of node n from the M end is as follows:

[0021]

[0022] Among them, U M is the measured voltage at the M terminal, U n is the calculated voltage at node n, I M is the measured current at terminal M, r1 and l1 are the equivalent positive sequence resistance and inductance parameters of the line respectively, L M-n is the distance from terminal M to node n.

[0023] Preferably, in step 3), the transient voltage values ​​of all nodes and adjacent nodes between the local end and the opposite end are traversed, and the absolute value of the difference between the transient voltage values ​​of two adjacent nodes is calculated as follows:

[0024] err n =|U n ' +1 -U n | (5)

[0025] Among them, err n Represents the calculated voltage difference between the corresponding adjacent nodes; U n is the calculated voltage of node n of the basic local terminal M; U n is the calculated voltage at node n; U n ' +1 The transient voltage of node n+1 is calculated based on the opposite end N.

[0026] Preferably, in step 4), the specific process of determining the fault section according to the transient voltage difference is as follows:

[0027] The fault section is determined based on the difference in transient voltage values ​​between two adjacent nodes. The design criteria are:

[0028] err n <err set (6)

[0029] Among them, err set The difference threshold value is calculated for the transient voltage of adjacent nodes. When formula (6) is established, it is judged that the fault point falls between the two nodes;

[0030] Considering the high-resistance fault scenario, the fault current flowing through the line is very small. At this time, err n The amplitudes are very small. At this time, the minimum value is selected by comparison:

[0031] MIN i =min{err n ,err n+1,...,err n+i} (7)

[0032] Among them, MIN i for err n+i The minimum value among them is used to obtain the corresponding fault section.

[0033] Preferably, in step 1), the window length T corresponding to one cycle is 20 ms.

[0034] The present invention also discloses a computer program product, comprising a computer program, wherein the computer program executes the steps of the method described above when executed by a processor.

[0035] The present invention further discloses a computer-readable storage medium on which a computer program is stored. When the computer program is executed by a processor, the steps of the method described above are executed.

[0036] The present invention also discloses a distribution network fault section positioning system considering the access of distributed power sources, comprising an interconnected memory and a processor, wherein a computer program is stored on the memory, and when the computer program is run by the processor, the steps of the method described above are executed.

[0037] Compared with the prior art, the advantages of the present invention are:

[0038] The method for locating a fault section of a distribution network considering the access of distributed power sources of the present invention can realize the section positioning of the distribution network, thereby guiding the accurate removal of the fault point; it only needs to measure the voltage at the DG grid connection point, does not need to install a voltage measuring device at each feeder, does not rely on additional engineering investment, and has low cost; the above-mentioned fault section locating method only needs to solve a simple first-order differential equation, has a simple algorithm, a small amount of calculation, and a high degree of feasibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a topological diagram of the distributed power supply of the present invention connected to the IEEE 33 node.

[0040] Figure 2 This is a flow chart of the method for locating a fault section of a distribution network taking into account the access of distributed power sources of the present invention.

[0041] Figure 3 It is a diagram showing the negative sequence current component output by DG1 when a fault occurs and the protection criterion result diagram based on the negative sequence component in the present invention; wherein (a) is a diagram showing the negative sequence current component; and (b) is a diagram showing the protection criterion result diagram based on the negative sequence component.

[0042] Figure 4 This is a simulation result diagram of the transient voltage calculation difference of two groups of adjacent nodes when a fault occurs in the present invention.

[0043] Figure 5 Schematic diagram of calculating the transient voltage of a node based on transient voltage and current data in the present invention. DETAILED DESCRIPTION

[0044] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0045] like Figure 1 The figure shows the distributed generation connected to the distribution network, with standard IEEE 33 nodes and three DGs (photovoltaic PV1, PV2 and PV3) connected.

[0046] like Figure 2 As shown, the method for locating a fault section of a distribution network considering the access of distributed power sources provided in an embodiment of the present invention includes the following steps:

[0047] Step 1) Measure the negative sequence component at the local DG, and determine whether the fault has started based on the mutation of the negative sequence component. If it is established, calibrate the zero time of the fault and capture the data of one cycle;

[0048] Step 2) Calculate the transient voltage of node n based on the transient voltage and current data measured at the local end; Calculate the transient voltage of node n+1 based on the transient voltage and current data measured at the opposite end;

[0049] Step 3) traverse the transient voltages of all nodes in the calculation interval, and calculate the transient voltage difference between two adjacent nodes;

[0050] Step 4) The fault section is determined according to the transient voltage difference. When the fault section is obtained, switches adjacent to the fault section are disconnected respectively to achieve accurate isolation of the fault point to ensure normal operation of the remaining system.

[0051] Specifically, in step 1), the fault initiation is determined according to the mutation amount of the negative sequence component, which specifically includes:

[0052] DG is mainly an inverter power source such as photovoltaic, direct-drive wind power and fuel cell. The output performance of inverter DG mainly depends on the inverter control response. In the case of transient faults, the control usually adopts a strategy to suppress the negative sequence current. The calculation method of negative sequence current is as follows:

[0053]

[0054] Among them, I DG - is the negative sequence current component of DG output; I a ,I b and I c They are the three-phase currents output by DG, is the rotation factor,

[0055] As long as an asymmetric fault occurs and causes a voltage drop at the DG grid connection point, I DG - It will produce a very high amplitude. After being adjusted by the controller, I DG - The amplitude of drops to zero. It can be seen that I DG - In the fault transient scenario, there are obvious mutation characteristics. The occurrence of distribution network line fault can be judged based on the mutation situation. The judgment criteria are as follows:

[0056] |I DG - |>I set1 (2)

[0057]

[0058] Wherein, formula (2) is based on I DG - The criterion of amplitude is established. If it is established, the point is recorded as t0; Formula (3) is based on I DG - The criterion for amplitude integration is that the starting point of integration is t0, t w1 is an ultra-short time window; I set1 is the negative sequence component amplitude threshold, I set2 is the threshold value of the negative sequence component integral; if the above two criteria are met at the same time, the fault section positioning is started, otherwise it will not be started.

[0059] Let t0 be the fault zero time, and intercept the data of one cycle backward as the calculation data for the subsequent fault section location.

[0060] Specifically, in step 2), the transient voltage calculation of node n and node n+1 includes:

[0061] The transient voltage of node n is calculated based on the transient voltage and current data measured at the local end, and the transient voltage of node n+1 is calculated based on the transient voltage and current data measured at the opposite end. Figure 5 As shown:

[0062] The RL model method is used to calculate line impedance. The transmission lines of the distribution network are all short lines, and the influence of distributed capacitance can be ignored. The RL model method is very applicable. Therefore, each line segment can be equivalent to an RL parameter. Assuming that the measurement point at this end is M and the measurement point at the other end is N, the method for calculating the transient voltage of node n from the M end is as follows:

[0063]

[0064] Among them, U M is the measured voltage at the M terminal, U nis the calculated voltage at node n, I M is the measured current at terminal M, r1 and l1 are the equivalent positive sequence resistance and inductance parameters of the line respectively, L M-n is the distance from terminal M to node n.

[0065] The method of calculating the transient voltage of node n+1 from the N terminal is similar. In the calculation process, the influence of the node load current must be considered, and U can be calculated. n ' +1 .

[0066] The specific steps of step 3) include: traversing the transient voltage values ​​of all nodes and adjacent nodes between the local end and the opposite end, and calculating the absolute value of the difference between two adjacent nodes as follows:

[0067] err n =|U n ' +1 -U n | (5)

[0068] Among them, err n Represents the calculated voltage difference between corresponding adjacent nodes.

[0069] According to the circuit principle, if the fault point is not within the range of M-N, then err n The difference is only the voltage drop caused by a section of the line, which can be calculated by formula (4). At this time, err n The value of is smaller.

[0070] If the fault point is between node n and node n+1, calculate U from the M end. n Not affected by the fault point, similarly U n ' +1 It is also not affected by the fault point. At this time, err n The value of is also relatively small. However, the transient voltage U of node n+1 is calculated from the M terminal. n+1 When passing through the fault point, the circuit structure changes, formula (4) is no longer applicable, and its calculated value will deviate from the actual value; U n ' +2 The calculation of is not affected by the fault point. At this time, err n+1 =|U n ' +2 -U n+1 | has a larger value.

[0071] Specifically, in step 4), fault location and isolation include:

[0072] The fault section is judged according to the difference. From the above analysis, it can be seen that the difference of transient voltage calculation values ​​of nodes on both sides of the fault point is small, while the difference of transient voltage calculation values ​​of other two nodes not containing the fault point is large. Based on this, the judgment criterion can be designed:

[0073] err n <err set (6)

[0074] Among them, err set The difference threshold value is calculated for the transient voltage of adjacent nodes. When equation (6) is established, it is judged that the fault point falls between two nodes.

[0075] Considering the high-resistance fault scenario, the fault current flowing through the line is very small. At this time, err n The amplitudes are very small. At this time, the minimum value can be selected by comparison:

[0076] MIN i =min{err n ,err n+1 ,...,err n+i} (7)

[0077] Among them, MIN i for err n+i The minimum value in , from which the corresponding fault section can be obtained;

[0078] After the fault section is located, the switches adjacent to the section need to be disconnected separately. At this point, the fault point is isolated from the distribution network and the remaining systems can operate normally.

[0079] The method for locating the fault section of the distribution network considering the access of distributed power sources of the present invention can realize the section positioning of the distribution network, thereby guiding the accurate removal of the fault point; it only needs to measure the voltage at the DG grid connection point, does not need to install a voltage measuring device at each feeder, and does not rely on additional engineering investment; the above-mentioned fault section locating method only needs to solve a simple first-order differential equation, the algorithm is simple, the calculation amount is small, and the feasibility is high.

[0080] In PSCAD / EMTDC, Figure 1 The standard IEEE 33-node distribution network model shown in the figure considers three DGs connected to nodes 5, 14 and 28, which are photovoltaic inverters with a capacity of 20 kW. The sampling frequency of the measurement device is set to 10 kHz, and the window length of one cycle is T = 20 ms.

[0081] Assuming that a single-phase metallic ground fault occurs at point f between nodes 8 and 9, the negative sequence current output by PV1 before and after the fault can be calculated by equation (1): Figure 3 As shown in (a).

[0082] Figure 3In (a), the fault time is 20ms. It can be seen that the negative sequence component of the current output by PV1 is zero before the fault. The negative sequence component suddenly changes at the beginning of the fault. The negative sequence component does not continue to increase, but is suppressed to a smaller amplitude. The action of the starting criterion is as follows: Figure 3 As shown in (b), I set1 =7,I set2 =35; Based on the criterion of the amplitude of the negative sequence component, the threshold value is exceeded at 0.5ms, and 0.5ms is recorded as the zero moment, and t w1 =5ms data, the absolute value of the negative sequence component is integrated, and the integral value also exceeds the threshold value; when the two criteria are established at the same time, it is possible to respond to the fault and eliminate the influence of the abnormal point during sampling by integration. The above results show that the startup criterion based on the negative sequence mutation quantity can effectively respond to the fault.

[0083] Still taking the above fault scenario as an example, after the fault start criterion is established, the transient voltage of the adjacent node will be calculated based on the voltage and current measured at the PVs on both sides. The data window starts at time zero and intercepts the PV1 and PV3 voltage and current data for T = 20ms.

[0084] The voltage U8 of node 8 is calculated from the voltage and current data of PV1, and the voltage U9′ of node 9 is calculated from the voltage and current data of PV3, and then err8=U9′-U8 can be calculated; the difference calculation of other adjacent nodes is similar, so it will not be repeated here. Among them, the results of err8 and err9 are as follows Figure 4 As shown, err set =0.06. Within one cycle after the fault, the amplitude of err8 gradually decreases and converges to a stable value, and the waveform of err9 is similar. However, within the time window, the amplitude of err9 is much larger than that of err8, and there is a significant difference between the two amplitudes. By setting the threshold value, err8 and err9 can be effectively distinguished. n Both are less than the threshold value err set When , it can be considered that the fault point is between node n and node n+1, and the switch corresponding to the node needs to be disconnected.

[0085] The reason is: when calculating the voltage of node 9 from PV1, the fault point is within the range of PV1-node 9, and the current directions on both sides of the fault point are opposite, but in the calculation, it is still considered that the same current flows through both sides of the fault point. This makes the calculated current smaller than the current without fault, as shown below:

[0086]

[0087] U n The calculated transient voltage will shift upwards from the actual value, while U n '+1 The calculation of err is not affected. n Will increase.

[0088] In order to verify the adaptability of the proposed fault location method, the effect of fault section location is tested in one step considering interference factors. Since the method uses the full fault quantity, the interference of noise can be ignored, so only the influence of high transition resistance needs to be considered.

[0089] Still taking the single-phase grounding fault at point f between node 8 and node 9 as an example, considering different transition resistances, the difference between two groups of adjacent nodes is calculated, and the average value of the first 5ms is taken, as shown in Table 1.

[0090] Table 1 Difference with transition resistance

[0091]

[0092] As can be seen from Table 1, the criterion err n <err set It has a certain ability to resist transition resistance and can effectively respond to 50Ω and 100Ω fault scenarios; when the transition resistance is very high, the err n <err set will fail, and the criterion MIN needs to be relied upon at this time i =min{err n ,err n+1 ,...,err n+i}Compare each set of differences and select the smallest one, which is the fault section.

[0093] The present invention also discloses a computer program product, comprising a computer program, wherein the computer program executes the steps of the method described above when executed by a processor.

[0094] The present invention further discloses a computer-readable storage medium on which a computer program is stored. When the computer program is executed by a processor, the steps of the method described above are executed.

[0095] The present invention also discloses a distribution network fault section positioning system considering the access of distributed power sources, comprising an interconnected memory and a processor, wherein a computer program is stored on the memory, and when the computer program is run by the processor, the steps of the method described above are executed.

[0096] The product, medium and system of the present invention correspond to the above method and also have the advantages described in the above method.

[0097] The present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by hardware related to computer program instructions. The computer program can be stored in a computer-readable storage medium, and the computer program can implement the steps of the above-mentioned method embodiment when executed by the processor. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. Computer-readable storage media include: any entity or device that can carry computer program code, recording medium, U disk, mobile hard disk, disk, optical disk, computer memory, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), electric carrier signal, telecommunication signal and software distribution medium. The memory is used to store computer programs and / or modules, and the processor implements various functions by running or executing computer programs and / or modules stored in the memory, and calling data stored in the memory. The memory may include high-speed random access memory and may also include non-volatile memory, such as a hard disk, an internal memory, a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, a flash card (Flash Card), at least one disk storage device, a flash memory device, or other volatile solid-state storage devices.

[0098] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A method for locating a fault section of a distribution network considering the access of distributed power sources, characterized in that: Includes steps: Step 1) Measure the negative sequence component at the local distributed energy source, and determine whether the fault has started based on the mutation of the negative sequence component; if established, calibrate the zero time of the fault and capture one cycle of data; Step 2) Calculate the transient voltage of node n based on the transient voltage and current data measured at the local end; Calculate the transient voltage of node n+1 based on the transient voltage and current data measured at the opposite end; Step 3) traverse the transient voltages of all nodes in the calculation interval, and calculate the transient voltage difference between two adjacent nodes; Step 4) The fault section is determined according to the transient voltage difference. When the fault section is obtained, switches adjacent to the fault section are disconnected respectively to achieve accurate isolation of the fault point to ensure normal operation of the remaining system.

2. The method for locating a fault section of a distribution network considering the access of distributed power sources according to claim 1, characterized in that: In step 1), the negative sequence current is calculated as follows: Among them, I DG - is the negative sequence current component of DG output; I a ,I b and I c They are the three-phase currents output by DG, is the rotation factor.

3. The method for locating a fault section of a distribution network considering the access of distributed power sources according to claim 2, characterized in that: In step 1), the specific process of determining the fault initiation according to the mutation amount of the negative sequence component is as follows: Negative sequence current component I of distributed energy output DG - In the fault transient scenario, there are obvious mutation characteristics. The occurrence of distribution network line fault can be judged based on the mutation situation. The judgment criteria are as follows: |I DG - |>I set1 (2) Wherein, formula (2) is based on I DG - The amplitude criterion is established, and the time point is recorded as t0; Formula (3) is based on I DG - The criterion for amplitude integration is that the starting point of integration is t0, t w1 is an ultra-short time window; I set1 is the negative sequence component amplitude threshold, I set2 is the threshold value of the negative sequence component integral; if the above two criteria are met at the same time, the fault section positioning is started, otherwise it will not be started.

4. The method for locating a fault section of a distribution network considering the access of distributed power sources according to claim 1, 2 or 3, characterized in that: In step 2), the specific process of calculating the transient voltage of node n based on the transient voltage and current data measured at the local end is: Assuming that the local measurement point is M and the opposite measurement point is N, the method for calculating the transient voltage of node n from the M end is as follows: Among them, U M is the measured voltage at the M terminal, U n is the calculated voltage at node n, I M is the measured current at terminal M, r1 and l1 are the equivalent positive sequence resistance and inductance parameters of the line respectively, L M-n is the distance from terminal M to node n.

5. The method for locating a fault section of a distribution network considering the access of distributed power sources according to claim 1, 2 or 3, characterized in that: In step 3), the transient voltage values ​​of all nodes and adjacent nodes between the local end and the opposite end are traversed, and the absolute value of the difference between the transient voltage values ​​of two adjacent nodes is calculated as follows: err n =|U n ′ +1 -THE n | (5) Among them, err n Represents the calculated voltage difference between the corresponding adjacent nodes; U n is the calculated voltage of node n of the basic local terminal M; U n is the calculated voltage at node n; U n ' +1 The transient voltage of node n+1 is calculated based on the opposite end N.

6. The method for locating a fault section of a distribution network considering the access of distributed power sources according to claim 5, characterized in that: In step 4), the specific process of determining the fault section according to the transient voltage difference is as follows: The fault section is determined based on the difference in transient voltage values ​​between two adjacent nodes. The design criteria are: err n <err set (6) Among them, err set The difference threshold value is calculated for the transient voltage of adjacent nodes. When formula (6) is established, it is judged that the fault point falls between the two nodes; Considering the high-resistance fault scenario, the fault current flowing through the line is very small. At this time, err n The amplitudes are very small. At this time, the minimum value is selected by comparison: MY i =min{err n ,err n+1 ,...,err n+i } (7) Among them, MIN i for err n+i The minimum value among them is used to obtain the corresponding fault section.

7. The method for locating a fault section of a distribution network considering the access of distributed power sources according to claim 6, characterized in that: In step 1), the window length of a corresponding cycle is T=20ms.

8. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are performed.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the computer program performs the steps of the method according to any one of claims 1 to 7.

10. A distribution network fault section location system considering the access of distributed power sources, comprising a memory and a processor connected to each other, wherein a computer program is stored in the memory, characterized in that: When the computer program is executed by a processor, the computer program performs the steps of the method according to any one of claims 1 to 7.

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