A power distribution network fault section locating method and system considering distributed power supply access

Abstract

The application discloses a kind of distribution network fault section locating method and system considering distributed power access, method includes the following steps: 1) measuring the negative sequence component at local distributed energy source, according to the mutation of negative sequence component, the judgment of fault starting is carried out;If it is true, then calibrate fault zero time, intercept a cycle of data;2) based on the transient voltage and current data measured at this end, the transient voltage of node n is calculated;Based on the transient voltage and current data measured at the other end, the transient voltage of node n+1 is calculated;3) traverse the transient voltage of all nodes in calculation interval, and the transient voltage difference of two adjacent nodes is calculated;4) according to the transient voltage difference, the fault section is judged, when the fault section is obtained, the adjacent switch of fault section is disconnected respectively, the accurate isolation of fault point is realized to ensure the normal operation of remaining system.The application has the advantages of simple operation, small amount of calculation, low cost and the like.

Description

TECHNICAL FIELD

[0001] The present application mainly relates to the technical field of power distribution network, and particularly relates to a power distribution network fault section positioning method and system considering distributed power supply access. BACKGROUND

[0002] The power distribution network involves a wide range and a large power supply range, and the line length thereof accounts for 90% of the total length of the network lines of the power system. Moreover, the power distribution network has a large number of branch nodes and a complex line structure and operation scenario, and is easily affected by factors such as adverse environment and human activities, resulting in frequent random line faults. Once a fault occurs in the power distribution network, it may cause power outage and cause a large amount of economic loss, and further affect the production and life of people. Therefore, quickly and accurately positioning the fault of the power distribution network is an important measure to ensure the safe and stable operation of the entire power system.

[0003] Under the scenario of the power distribution network with distributed power supply access, the topology structure and power flow distribution of the power distribution network are more complex. The access of the distributed power supply (DG) changes the structure of the power distribution network, and the distribution of the current and voltage in the power distribution network also changes with the different positions of the DG access. Moreover, the DG has characteristics such as output fluctuation and intermittence. Meanwhile, the access of the power electronic equipment also injects harmonics into the system, affecting the normal operation of the power distribution network. Under the scenario of the power distribution network with DG access, the single-phase grounding fault occurs, and the single-source radial power distribution network becomes a complex power distribution network with multiple sources. The influence of the DG on the fault characteristics cannot be ignored, and a new determination method and theoretical basis need to be proposed for the fault positioning of the power distribution network with distributed power supply access. Therefore, the fault positioning research of the new type of power distribution network has important significance. SUMMARY

[0004] In view of the technical problems in the prior art, the present application provides a power distribution network fault section positioning method and system considering distributed power supply access, which is simple to operate and low in cost.

[0005] To solve the above technical problems, the technical solution provided by the present application is as follows:

[0006] A power distribution network fault section positioning method considering distributed power supply access, comprising the following steps:

[0007] Step 1) measuring the negative sequence component at the local distributed energy source, and determining the fault start according to the mutation of the negative sequence component; if it is true, the fault zero time is calibrated, and one cycle of data is intercepted;

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

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

[0010] Step 4) determine the fault section according to the transient voltage difference, and disconnect the switches adjacent to the fault section when the fault section is obtained, so as to realize accurate isolation of the fault point and ensure normal operation of the remaining system.

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

[0012]

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

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

[0015] The negative sequence current component I DG - In the fault transient scenario, there is a clear mutation characteristic, and the occurrence of the distribution network line fault can be determined according to the mutation. The criterion is as follows:

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

[0017]

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

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

[0020] Assuming 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 end M is as follows:

[0021]

[0022] Among them, U M U is the measured voltage at terminal M. n For the calculated voltage at node n, I M Let M be the measured current, r1 and l1 be the equivalent positive sequence resistance and inductance parameters of the line, respectively, and L be the current measured at terminal M. M-n Let M be the distance from node 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 U represents the calculated voltage difference between corresponding adjacent nodes; n The calculated voltage of node n at the basic terminal M; U n 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 based on 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 criterion is as follows:

[0028] err n <err set (6)

[0029] Among them, err set Calculate the threshold value for the difference in transient voltage between adjacent nodes. When equation (6) holds, it is determined that the fault point falls between the two nodes.

[0030] Considering that the fault current flowing through the line is very small in high-impedance fault scenarios, err is... n Since the amplitudes are all very small, we can select the smallest value by comparison.

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

[0032] where MIN i is the minimum value in err n+i , thus obtaining the corresponding fault section.

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

[0034] The application further discloses a computer program product comprising a computer program which, when executed by a processor, performs the steps of the method as described above.

[0035] The application further discloses a computer-readable storage medium having stored thereon a computer program which, when executed by a processor, performs the steps of the method as described above.

[0036] The application further discloses a power distribution network fault section positioning system considering distributed power supply access, comprising a memory and a processor connected to each other, wherein the memory has stored thereon a computer program which, when executed by the processor, performs the steps of the method as described above.

[0037] Compared with the prior art, the application has the following advantages:

[0038] The power distribution network fault section positioning method considering distributed power supply access can realize the section positioning of the power distribution network, thereby guiding the accurate removal of the fault point; only the voltage at the DG grid-connected point needs to be measured, no voltage measuring device needs to be installed at each feeder, and no additional engineering investment is needed, so that the cost is low; the above fault section positioning method only needs to solve a simple first-order differential equation, and has simple algorithm, small calculation amount and high degree of realization. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 It is a topological structure diagram of the distributed power supply access IEEE 33 node of the application.

[0040] Figure 2 It is a flowchart of the power distribution network fault section positioning method considering distributed power supply access of the application.

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

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

[0043] Figure 5 To calculate the transient voltage diagram of the node based on the transient voltage and current data in the application. DETAILED DESCRIPTION

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

[0045] As Figure 1 The distributed power supply is connected to the distribution network, and the standard IEEE 33 node has three DGs (photovoltaic PV1, PV2 and PV3).

[0046] As Figure 2 The method for locating the fault section of the distribution network considering the access of distributed power supply provided by the embodiment of the application includes the following steps:

[0047] Step 1) Measure the negative sequence component at the local DG, and determine the fault start according to the mutation of the negative sequence component. If it is true, the fault zero time is calibrated, and one cycle of data is intercepted.

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

[0049] Step 3) Traverse the transient voltage of all nodes in the calculation interval, and calculate the transient voltage difference of two adjacent nodes.

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

[0051] Specifically, in step 1), the determination of the fault start according to the mutation of the negative sequence component specifically includes:

[0052] The DG is mainly photovoltaic, direct-drive wind power and fuel cell and other inverter-type power supply. The output performance of the inverter-type DG mainly depends on the inverter control response. In the fault transient state, the control usually adopts the strategy to suppress the negative sequence current. The calculation method of the negative sequence current is as follows:

[0053]

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

[0055] As soon as an asymmetric fault occurs, causing voltage drop at the DG grid-connection point, I DG - will have a very high amplitude, which is reduced to zero after adjustment by the controller. It can be seen that I DG - has a sudden change in amplitude, and the amplitude of I DG - has a sudden change in amplitude. In the fault transient scenario, there is a clear characteristic of a sudden change, and the occurrence of distribution network line fault can be judged according to the sudden change. The criterion is as follows:

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

[0057]

[0058] wherein, formula (2) is a criterion based on the amplitude of I DG - , and if it is true, the point is recorded as t0; formula (3) is a criterion based on the integral of the amplitude of I DG - , and the starting point of the integral is t0, t w1 is an ultra-short time window; I set1 is a negative sequence component amplitude threshold, I set2 is a threshold value of the integral of the negative sequence component; if the above two criteria are true at the same time, the fault section positioning is started, otherwise it is not started.

[0059] Let t0 be the zero time of the fault, and the data of one cycle is intercepted backwardly as the calculation data for subsequent fault section positioning.

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

[0061] calculating the transient voltage of the node n based on the transient voltage and current data measured at the local end, and calculating the transient voltage of the node n+1 based on the transient voltage and current data measured at the opposite end, as shown in formula (4): Figure 5

[0062] The R-L model method is used to calculate the line impedance, and the power transmission line of the distribution network is a short line, so the influence of the distributed capacitance can be ignored, and the applicability of the R-L model method is very strong. Therefore, each line can be equivalent to R-L parameters. Assuming that the measurement point at the local end is M, and the measurement point at the opposite end is N, the method for calculating the transient voltage of the node n at the M end is as follows:

[0063]

[0064] wherein, U M is the measured voltage at the M end, and U n ​The calculated voltage of the node n is I M The measured current of the M end, and r1 and l1 are the equivalent positive sequence resistance and inductance parameters of the line, respectively M-n The distance from the M end to the node n.

[0065] The method for calculating the transient voltage of the node n+1 from the N end is similar, and the influence of the node load current is considered in the calculation process, and the calculated U 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 the adjacent two nodes as follows:

[0067] err n = |U n ′ +1 -U n | (5)

[0068] Wherein, err n represents the calculated voltage difference of the corresponding adjacent node.

[0069] According to the circuit principle, if the fault point is not in the interval of the M end—N end, then the difference of err n The voltage drop caused by a section of line can be calculated by formula (4), and the value of err n is small.

[0070] If the fault point is between the node n and the node n+1, U n is not affected by the fault point, and U n ′ +1 is also not affected by the fault point, and the value of err n is also small. However, when calculating the transient voltage U n+1 of the node n+1 from the M end, the circuit structure changes after passing through the fault point, formula (4) is no longer applicable, and the calculated value deviates from the actual value; U n ′ +2 is not affected by the fault point, and the value of err n+1 = |U n ′ +2 -U n+1 | is large.

[0071] Specifically, in step 4), fault locating and isolation includes:

[0072] According to the difference, it is judged that the fault section, according to the foregoing analysis, the transient voltage calculation value difference of the two nodes adjacent to the fault point is small, and the transient voltage calculation value difference of the two nodes not containing the fault point is large, and accordingly a criterion can be designed:

[0073] err n <err set (6)

[0074] err set is the transient voltage calculation difference threshold of adjacent nodes, and formula (6) is established to determine 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, and the amplitude of err n is very small at this time, and at this time, the minimum value can be selected by comparison method:

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

[0077] Wherein, MIN i is the minimum value of err n+i , and the corresponding fault section can be obtained.

[0078] After the fault section positioning is completed, the adjacent switches of the section need to be disconnected, and thus the fault point is isolated from the power distribution network, and the remaining system can operate normally.

[0079] The power distribution network fault section positioning method considering the access of distributed power supply of the application can realize the section positioning of the power distribution network, thereby guiding the accurate removal of the fault point; only the voltage at the DG grid connection point needs to be measured, without the need to install a voltage measuring device at each feeder, and without the need for additional engineering investment; the above fault section positioning method only needs to solve a simple first-order differential equation, and the algorithm is simple, the calculation amount is small, and the degree is high.

[0080] A standard IEEE 33-node power distribution network model as shown in Figure 1 is built in PSCAD / EMTDC, considering that three DGs are connected to node 5, node 14 and node 28, and the type is photovoltaic inverter power supply, and the capacity is 20kW. The sampling frequency of the measuring device is set to 10kHz, and the window length T of one cycle is 20ms.

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

[0082] Figure 3The fault time in (a) is 20 ms, and it can be seen that the negative sequence component of the current output by PV1 before the fault is zero, and the negative sequence component suddenly changes at the initial stage 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 shown in (b). Figure 3 As shown in (b), I set1 = 7, I set2 = 35; the criterion based on the amplitude of the negative sequence component exceeds the threshold value at 0.5 ms, and the zero time is recorded as 0.5 ms. The data of t w1 = 5 ms is intercepted, and the integral of the absolute value of the negative sequence component also exceeds the threshold value. When the two criteria are met at the same time, the fault can be responded to, and the influence of abnormal points at the sampling time can be eliminated through integration. The above results show that the starting criterion based on the negative sequence mutation variable can effectively respond to the fault.

[0083] Still taking the above fault scenario as an example, after the fault starting criterion is met, the transient voltage of the adjacent node can be calculated according to the voltage and current measured at the PVs on both sides. The data window is the voltage and current data of PV1 and PV3 intercepted from the zero time point to the rear for T = 20 ms.

[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. Then, err8 = U9' - U8 can be calculated, and the difference values of other adjacent nodes can be calculated in the same way, which will not be described again. As shown in (c), the results of err8 and err9 are as follows: Figure 4 err set = 0.06. Within one cycle after the fault, the amplitude of err8 gradually decreases to a stable value, and the waveform of err9 is similar. The amplitude of err9 is much larger than that of err8 within the time window, and there is a significant difference between the amplitudes of the two. By setting a threshold value, err8 and err9 can be effectively distinguished. When the difference value err n is less than the threshold value err set within an entire cycle, 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 that when the voltage of node 9 is calculated 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 as the same current flowing through the fault point on both sides. This makes the calculated current smaller than the current without the fault, as shown below:

[0086]

[0087] The calculated transient voltage U n will be offset upward from the actual value, and U n '+1 The calculation is unaffected, then err n It will increase.

[0088] To verify the applicability of the proposed fault location method, a one-step test was conducted to assess the effectiveness of fault segment location, taking into account interference factors. Since this method uses the full fault quantity, noise interference is negligible; therefore, only the effect of high transition resistance needs to be considered.

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

[0090] Table 1. Differences with Transition Resistance

[0091]

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

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

[0094] The present invention further discloses a computer-readable storage medium having a computer program stored thereon, the computer program executing the steps of the method described above when run by a processor.

[0095] The present invention also discloses a fault location system for a distribution network considering distributed power source access, comprising a memory and a processor connected to each other, wherein the memory stores a computer program, and the computer program executes the steps of the method described above when run by the processor.

[0096] The products, media, and systems of the present invention, corresponding to the methods described above, also possess the advantages described above.

[0097] The present application can realize all or part of the processes in the above-mentioned embodiment methods, and can also be completed by computer program instruction related hardware. The computer program can be stored in a computer readable storage medium. When the computer program is executed by a processor, the steps of the above-mentioned method embodiment can be realized. The computer program includes computer program code, which can be in the form of source code, object code, executable files or some intermediate forms, etc. The computer readable storage medium includes any entity or device capable of carrying computer program code, recording medium, U disk, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signal, telecommunication signal and software distribution medium, etc. The memory is used to store computer programs and / or modules. The processor realizes various functions by running or executing the computer programs and / or modules stored in the memory, and calling the data stored in the memory. The memory can include high-speed random access memory, and can also include non-volatile memory, such as hard disk, memory, plug-in hard disk, smart media card (SMC), secure digital (SD) card, flash card, at least one magnetic disk storage device, flash memory device, or other volatile solid-state storage device, etc.

[0098] The above is only the preferred embodiment of the present application, and the protection scope of the present application is not limited to the above-mentioned embodiment. Any technical solution falling within the concept of the present application shall fall within the protection scope of the present application. It should be noted that, for ordinary skilled persons in the art, some improvements and refinements without departing from the principle of the present application shall be considered as the protection scope of the present application.

Claims

1. A method for fault section location of distribution network considering distributed generation (DG) integration, characterized in that, The method comprises the steps of: Step 1) measuring the negative sequence component at the local distributed power supply, judging the fault start according to the mutation of the negative sequence component, if true, marking the fault zero time, and intercepting one cycle of data; Step 2) calculating the transient voltage of the node based on the transient voltage and current data measured at the local end; calculating the transient voltage of the node based on the transient voltage and current data measured at the opposite end n Step 2) calculating the transient voltage of the node based on the transient voltage and current data measured at the local end; calculating the transient voltage of the node based on the transient voltage and current data measured at the opposite end n Step 2) calculating the transient voltage of the node based on the transient voltage and current data measured at the local end; calculating Step 3) calculating the transient voltage of all nodes in the calculation interval, and calculating the transient voltage difference between two adjacent nodes; Step 4) judging the fault section according to the transient voltage difference, and disconnecting the adjacent switches of the fault section to realize the accurate isolation of the fault point and ensure the normal operation of the remaining system.

2. The method of claim 1, wherein, In step 1), the calculation method of the negative sequence current is as follows: (1) wherein, is the negative sequence current component output by the DG; , and are the three-phase currents output by the DG, respectively, is the rotation factor.

3. The method of claim 2, wherein, In step 1), the specific process of judging the fault start according to the mutation of the negative sequence component is as follows: Negative sequence current component output by distributed power supply There is obvious mutation variable characteristic in the fault transient state scene, and the distribution network line fault occurrence can be judged according to the mutation variable condition, and the criterion is as follows: (2) (3) Wherein, formula (2) is based on the amplitude criterion, if the time point is recorded as ; formula (3) is based on the amplitude integral criterion, the starting point of the integral is , is the ultra-short time window; is the negative sequence component amplitude threshold, is the negative sequence component integral threshold value; if the above two criteria are met simultaneously, the fault section positioning is started, otherwise it is not started.

4. The method for fault section location of distribution network considering distributed generation access according to claim 1 or 2 or 3, characterized in that, In step 2), the transient voltage of the node is calculated based on the transient voltage and current data measured at the local end n The specific process of calculating the transient voltage of the node is as follows: Assuming the measurement point at this end is M, and the measurement point at the other end is N, the calculation node at M end n The method of transient voltage is as follows: (4) wherein, is the measured voltage at the M end, is the transient voltage at the M end based on the M end node n is the measured current at the M end, and and are the equivalent positive sequence resistance and inductance parameters of the line, respectively, is the distance from the M end to the node n .

5. The method for fault section location of distribution network considering distributed generation access according to claim 1 or 2 or 3, characterized in that, In step 3), the transient voltage values of all nodes between the local end and the opposite end and adjacent nodes are traversed, and the absolute value of the difference between the transient voltage values of two adjacent nodes is calculated as follows: (5) wherein, represents an absolute value of a transient voltage difference value corresponding to the adjacent node; is a transient voltage based on the local M computing node n +1. is a transient voltage based on the remote N computing node n +1.

6. The method for fault section location of distribution network considering distributed generation access according to claim 5, characterized in that, In step 4), the specific process of judging the fault section according to the transient voltage difference is as follows: According to the difference between the transient voltage values of two adjacent nodes, the fault section is judged, and the criterion is designed: (6) wherein The difference threshold value is calculated for the transient voltage of the adjacent nodes, and formula (6) is established to determine whether the fault point falls between the two nodes. Considering the high resistance fault scenario, the fault current flowing through the line is small, at this time The amplitude of the value is very small, at this time, by comparing the method, select the minimum value: (7) wherein is the minimum value in the set {a, b, c, d, e, f, g, h, i, j, k, 1, m, n, o, p, q, r, s, t 7. The method for fault section location of distribution network considering distributed generation according to claim 6, characterized in that, In step 1), the window length of one cycle corresponds to ms.

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

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

10. A power distribution network fault section location system considering distributed generation access, comprising a memory and a processor connected to each other, wherein the memory has stored a computer program, and the computer program comprises the following steps of: The computer program is executed by the processor to perform the steps of the method according to any one of claims 1-7.

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