Method, system and equipment for detecting single-phase disconnection fault of power distribution network based on line voltage amplitude

Abstract

The invention is suitable for the technical field of line fault diagnosis, and provides a method, a system and equipment for detecting a single-phase broken line fault of a power distribution network based on a line voltage amplitude, and the method comprises the steps: collecting a zero-sequence voltage and a three-phase line voltage of each detection point in the power distribution network; whether the zero-sequence voltage effective value of any detection point is larger than a preset starting threshold value or not is judged, if yes, the ratio of the maximum value to the minimum value of the three-phase line voltage amplitude of the current detection point is calculated, and the standard deviation of the three-phase line voltage amplitude of the current detection point is calculated; and if the ratio is greater than a preset ratio threshold value and the standard deviation is greater than a preset standard deviation threshold value, determining that a single-phase disconnection fault occurs in a line section covered by the current detection point, and the fault section is located between the current detection point and an adjacent downstream detection point, thereby realizing rapid and accurate identification of the single-phase disconnection fault.

Description

Technical Field

[0001] This invention relates to the field of line fault diagnosis technology, and in particular to a method, system and equipment for detecting single-phase open-circuit faults in distribution networks based on line voltage amplitude. Background Technology

[0002] Single-phase open-circuit faults are common in power distribution networks. Their causes mainly include external damage, equipment aging, grid overload, lightning strikes, and severe weather. Power distribution networks have numerous branches and complex structures, with lines widely distributed and traversing various complex environments such as towns, mountains, and forests, further increasing the probability of open-circuit faults. The hazards of open-circuit faults are significant and far-reaching. First, for the power system, open-circuit faults can lead to power outages, voltage distortion, relay protection malfunctions, and increased system losses, affecting the safe and stable operation of the power grid. Second, open-circuit faults can cause equipment overvoltage, insulation damage, single-phase operation of motors, or even arc reignition, leading to equipment failure or damage. After a wire breaks, it may fall to the ground energized, increasing the risk of electric shock to people and animals, and may also cause fires, explosions, and traffic accidents, endangering public safety. Therefore, open-circuit faults have significant hazards and require serious attention.

[0003] In ungrounded neutral systems, the current after a wire break is extremely weak, making it difficult for traditional current-based relay protection to operate and identify the break location in a timely manner, thus posing a safety hazard. Current methods attempt to employ wavelet transform and current anomaly identification, but these often suffer from technical drawbacks such as computational complexity, poor real-time performance, or reliance on topology information. Summary of the Invention

[0004] This invention provides a method for detecting single-phase open-circuit faults in distribution networks based on line voltage amplitude, which addresses the problems of high computational complexity and poor real-time performance in existing methods.

[0005] The first aspect of this invention provides a method for detecting single-phase open-circuit faults in distribution networks based on line voltage amplitude, comprising: S1: Collect the zero-sequence voltage and three-phase line voltage at each detection point in the power distribution network; S2: Determine whether the effective value of the zero-sequence voltage at any detection point is greater than the preset start threshold. If yes, proceed to step S3; otherwise, return to step S1. S3: Calculate the ratio of the maximum to the minimum value of the three-phase line voltage amplitude at the current detection point, and calculate the standard deviation of the three-phase line voltage amplitude at the current detection point; S4: If the ratio is greater than a preset ratio threshold and the standard deviation is greater than a preset standard deviation threshold, then it is determined that a single-phase open circuit fault has occurred in the line section covered by the current detection point, and the fault section is located between the current detection point and the adjacent downstream detection point.

[0006] Furthermore, the preset startup threshold is: in: As the activation threshold, The ratio coefficient and , This is the system's rated phase voltage.

[0007] Furthermore, the calculation of the standard deviation of the three-phase line voltage amplitude at the current detection point includes: in: , , The instantaneous values ​​of the three-phase line voltages were collected. , , This refers to the amplitude of the three-phase line voltage. This is the arithmetic mean of the amplitudes of the three-phase line voltages. This represents the standard deviation of the three-phase voltage amplitude.

[0008] Furthermore, the preset ratio threshold satisfies: ;in: The ratio coefficient and .

[0009] Furthermore, the faulty section is located between the current detection point and the adjacent downstream detection point, including: When the first detection point in the distribution network that meets the criteria in step S4 is located, the fault section is located in the line section between the detection point and the adjacent downstream detection point. If the detection point is an end node, the fault section is located between the upstream connection point of the detection point and the end of the line.

[0010] The second aspect of this invention provides a single-phase open-circuit fault detection system for distribution networks based on line voltage amplitude, comprising: The voltage acquisition unit is used to acquire the zero-sequence voltage and three-phase line voltage at each detection point in the power distribution network. The zero-sequence voltage judgment unit is used to determine whether the effective value of the zero-sequence voltage at any detection point is greater than the preset start-up threshold. The ratio and standard deviation calculation unit is used to calculate the ratio of the maximum to the minimum value of the three-phase line voltage amplitude at the current detection point when the effective value of the zero-sequence voltage at any detection point is greater than the preset start threshold, and to calculate the standard deviation of the three-phase line voltage amplitude at the current detection point. The fault determination unit is used to determine that a single-phase open circuit fault has occurred in the line section covered by the current detection point if the ratio is greater than a preset ratio threshold and the standard deviation is greater than a preset standard deviation threshold, and the fault section is located between the current detection point and the adjacent downstream detection point.

[0011] A third aspect of the present invention provides a computer device, comprising: Memory, transceiver, processor, and bus system; The memory is used to store programs; The processor is configured to execute a program in the memory, including performing the method as described in any of the preceding statements; The bus system is used to connect the memory and the processor to enable communication between the memory and the processor.

[0012] As can be seen from the above technical solutions, the present invention has the following advantages: This invention first collects the zero-sequence voltage and three-phase line voltage at each detection point in the distribution network. When the conditions for protection activation are met, the ratio of the maximum to minimum amplitude is calculated, along with the standard deviation of the three-phase line voltage amplitude. The maximum / minimum ratio and the standard deviation are used as a composite criterion function to reflect line voltage variation and dispersion, respectively, and a simple threshold is set for discrimination. This invention's fault detection method does not rely on phase information and is suitable for low-current systems and no-current scenarios. The standard deviation provides an abstract statistical characteristic, exhibiting natural resistance to environmental interference. The calculation is simple and fast, making it suitable for real-time applications in open-type sensor terminals. Attached Figure Description

[0013] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0014] Figure 1 This is a schematic flowchart of an embodiment of a single-phase open-circuit fault detection method for distribution networks based on line voltage amplitude according to the present invention; Figure 2 This is a simulation model diagram of a single-phase open-circuit fault in an ungrounded system used in the simulation experiment of this invention. Detailed Implementation

[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] It should be understood that, when used in this specification, the terms “comprising” and “including” indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0017] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0018] It should also be further understood that the term "and / or" as used in this specification refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.

[0019] Example 1 Please see Figure 1 The present invention provides a method for detecting single-phase open-circuit faults in distribution networks based on line voltage amplitude, comprising the following steps: S1: Collect the zero-sequence voltage and three-phase line voltage at each detection point in the power distribution network; In this embodiment, the feeder terminal unit at each detection point synchronously acquires the local three-phase four-wire voltage signal through a built-in voltage transformer, wherein the zero-sequence voltage... It directly measures the three-phase voltage vector sum The equivalent value; or the zero-sequence component is obtained through an open delta winding, and the effective value is obtained through an AD conversion module. Three-phase line voltage is obtained by collecting line voltage data. , , The instantaneous waveform is processed by digital signal processing to extract the fundamental amplitude. , , All the above-mentioned detection points independently perform local data collection based on a unified time benchmark, with a sampling frequency of... .

[0020] S2: Determine whether the effective value of the zero-sequence voltage at any detection point is greater than the preset start threshold. If yes, proceed to step S3; otherwise, return to step S1. The feeder terminal unit at each detection point collects the instantaneous zero-sequence voltage signal. Discrete processing is performed, and the effective value is calculated according to the power frequency period (20ms / 50Hz or 16.67ms / 60Hz): in: This represents the number of sampling points per cycle. The sampling time.

[0021] The calculated Compared with the preset startup threshold Real-time comparison is performed, with the preset start threshold being: ;in: As the activation threshold, The ratio coefficient and , This is the system's rated phase voltage. If... If the protection activation flag is triggered, proceed to step S3; If the condition is met, the timer is reset and the process returns to step S1. A delayed confirmation logic is added here, only confirming if... It is only considered a valid start-up if it lasts for more than 4 power frequency cycles; in addition, it is also designed to block instantaneous interference, such as lightning strikes and switching operations.

[0022] S3: Calculate the ratio of the maximum to the minimum value of the three-phase line voltage amplitude at the current detection point, and calculate the standard deviation of the three-phase line voltage amplitude at the current detection point; First, determine the instantaneous values ​​of the three-phase line voltages containing noise and harmonics. , , Perform a Discrete Fourier Transform on each phase line voltage to extract the amplitude of the fundamental frequency component: Similarly, calculate and ,in These are discrete sampled values.

[0023] Determine the maximum and minimum values ​​from the three-phase fundamental amplitude values: Calculate the ratio (Dimensionless quantity); When a single phase is disconnected, the voltage of the intact phase line is close to the rated value. ), the voltage of the line related to the broken line dropped sharply ( ),lead to Significantly increased.

[0024] Find the arithmetic mean and standard deviation of the three-phase line voltage amplitudes: in: , , The instantaneous values ​​of the three-phase line voltages were collected. This is the arithmetic mean of the amplitudes of the three-phase line voltages. This represents the standard deviation of the three-phase voltage amplitude. Under normal symmetrical operation... When a single phase is disconnected A sharp increase, i.e., an increase in amplitude dispersion, typical fault value .

[0025] Specifically, the preset ratio threshold satisfies: ;in: The ratio coefficient and The lower limit avoids the maximum normal imbalance (such as load asymmetry), and the lower limit ensures sensitivity to high-resistance faults. The optimal value is 1.25. The preset standard deviation threshold satisfies: ;in: It is a proportionality coefficient and , The system's rated line voltage; the lower limit is higher than normal fluctuations ( Upper limit: to prevent overload malfunction. In practical applications, the threshold can be further adjusted based on specific on-site working conditions and experimental results to improve the accuracy and applicability of fault detection.

[0026] S4: If the ratio is greater than a preset ratio threshold and the standard deviation is greater than a preset standard deviation threshold, then it is determined that a single-phase open circuit fault has occurred in the line section covered by the current detection point, and the fault section is located between the current detection point and the adjacent downstream detection point.

[0027] Specifically, if any detection point on the power distribution line... and If the above conditions are met simultaneously, it is determined that a single-phase open circuit fault has occurred on the line, and the fault section is located between the first detection point that meets the conditions and the previous detection point; if the following conditions are not met, it is determined that no single-phase open circuit fault has occurred on the line, and the process returns to step S1 to continue collecting data.

[0028] It should be noted that when the first detection point in the distribution network that satisfies the criterion in step S4 is located, the fault section is located in the line section between the detection point and the adjacent downstream detection point; if the detection point is an end node, the fault section is located between the upstream connection point of the detection point and the end of the line. The principle for the first action point is: the fault is located downstream of the earliest detection point that satisfies the criterion. A non-end point is where the fault is between this point and its adjacent downstream point; an end point is where the fault is between this point and its upstream connection point. The fault causes voltage asymmetry to propagate from the break point to the power source side, and the first detection point is closest to the fault location.

[0029] The above method is verified and illustrated below with specific simulation experiments: like Figure 2 The simulation model of a single-phase open-circuit fault in a 10kV neutral-point ungrounded system is shown below, built using Matlab / Simulink simulation software. The system has a step-down transformer with a rated capacity of 20MVA, and rated voltages of 110kV and 10kV on the high and low voltage sides, respectively. It is assumed that the system has a total of 6 outgoing lines. For cable lines, This is a hybrid overhead-cable line system. The overhead line is located upstream for 3 km, and the cable line is located downstream for 6 km. The other four lines are also overhead. Line parameters are shown in Table 1. In the model, the three-phase balanced loads are connected in a delta configuration, set to 0.2 MVA, 0.5 MVA, 1 MVA, and 2 MVA respectively, with a power factor of 0.9. The faulty line has a phase A open circuit fault, with fault locations set at distances of 2km, 4km, and 7km from the busbar, and grounding resistances of 10Ω, 200Ω, 10Ω, 1000Ω, 10kΩ, and ∞, respectively. Six terminal detection points are set, with Q1, Q2, Q3, and Q4 located on the faulty line. Above, Q5 and Q6 are located 1km, 3km, 5km, and 8km from the busbar respectively, and are situated on the intact line. Above, they are 3km and 7km away from the busbar, respectively.

[0030] Table 1 Line Parameters (Ungrounded open circuit fault), load capacity 0.5MVA, fault location 4km from busbar, at each terminal detection point and The data and the line operation status determined based on the above-mentioned criteria are shown in Table 2.

[0031] Table 2 Detection points for open wire / ungrounded faults and Data and Judgment Results As can be seen from Table 2, the faulty section is located between Q2 and Q3. and The value is much greater than the set threshold. In this scenario, the transition resistance combination is changed, with other conditions remaining the same. The values ​​at each terminal detection point are... and The data and the determined line operation status are shown in Table 3: Table 3. Under different transition resistance conditions and Data and Judgment Results By changing the system structure, the location of the open circuit, the grounding resistance, and the load impedance, and conducting numerous simulations, combined with Tables 2 and 3 above, it can be seen that after a single-phase open circuit fault occurs in an ungrounded system... and The value is much greater than the set threshold, so the proposed single-phase open-circuit fault detection method based on line voltage amplitude can effectively detect single-phase open-circuit faults.

[0032] Example 2 An embodiment of a single-phase open-circuit fault detection system for distribution networks based on line voltage amplitude in this invention includes the following steps: The voltage acquisition unit is used to acquire the zero-sequence voltage and three-phase line voltage at each detection point in the power distribution network. The zero-sequence voltage judgment unit is used to determine whether the effective value of the zero-sequence voltage at any detection point is greater than the preset start-up threshold. The ratio and standard deviation calculation unit is used to calculate the ratio of the maximum to the minimum value of the three-phase line voltage amplitude at the current detection point when the effective value of the zero-sequence voltage at any detection point is greater than the preset start threshold, and to calculate the standard deviation of the three-phase line voltage amplitude at the current detection point. The fault determination unit is used to determine that a single-phase open circuit fault has occurred in the line section covered by the current detection point if the ratio is greater than a preset ratio threshold and the standard deviation is greater than a preset standard deviation threshold, and the fault section is located between the current detection point and the adjacent downstream detection point.

[0033] The functions of each unit in this embodiment are explained in the same way as those in Embodiment 1, and the technical effects are the same, so they will not be repeated here. The technical effects of this embodiment are the same as those of the method in Embodiment 1, so they will not be repeated here.

[0034] Example 3 A computer device, comprising: Memory, transceiver, processor, and bus system; The memory is used to store programs; The processor is used to execute a program in the memory, including the method of the above embodiments; The bus system is used to connect the memory and the processor to enable communication between the memory and the processor.

[0035] Those skilled in the art will recognize that the units of the various examples described in connection with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of the invention.

[0036] In the embodiments provided by the present invention, it should be understood that the division of units is only a logical functional division. In actual implementation, there may be other division methods, such as multiple units can be combined into one unit, one unit can be split into multiple units, or some features can be ignored.

[0037] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0038] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, read-only memory (ROM), random access memory (RAM), portable hard drives, magnetic disks, or optical disks.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the specification of the present invention.

Claims

1. A method for detecting single-phase open-circuit faults in distribution networks based on line voltage amplitude, characterized in that, include: S1: Collect the zero-sequence voltage and three-phase line voltage at each detection point in the power distribution network; S2: Determine whether the effective value of the zero-sequence voltage at any detection point is greater than the preset start threshold. If yes, proceed to step S3; otherwise, return to step S1. S3: Calculate the ratio of the maximum to the minimum value of the three-phase line voltage amplitude at the current detection point, and calculate the standard deviation of the three-phase line voltage amplitude at the current detection point; S4: If the ratio is greater than a preset ratio threshold and the standard deviation is greater than a preset standard deviation threshold, then it is determined that a single-phase open circuit fault has occurred in the line section covered by the current detection point, and the fault section is located between the current detection point and the adjacent downstream detection point.

2. The method for detecting single-phase open-circuit faults in distribution networks based on line voltage amplitude according to claim 1, characterized in that, The preset startup threshold is: in: As the activation threshold, The ratio coefficient and , This is the system's rated phase voltage.

3. The method for detecting single-phase open-circuit faults in distribution networks based on line voltage amplitude according to claim 1, characterized in that, The calculation of the standard deviation of the three-phase line voltage amplitude at the current detection point includes: in: , , The instantaneous values ​​of the three-phase line voltages were collected. , , This refers to the amplitude of the three-phase line voltage. This is the arithmetic mean of the amplitudes of the three-phase line voltages. This represents the standard deviation of the three-phase voltage amplitude.

4. The method for detecting single-phase open-circuit faults in distribution networks based on line voltage amplitude according to claim 3, characterized in that, The preset ratio threshold satisfies: ;in: The ratio coefficient and .

5. The method for detecting single-phase open-circuit faults in distribution networks based on line voltage amplitude according to claim 3, characterized in that, The preset standard deviation threshold satisfies: ;in: It is a proportionality coefficient and , This is the system's rated line voltage.

6. The method for detecting single-phase open-circuit faults in distribution networks based on line voltage amplitude according to claim 1, characterized in that, The faulty section is located between the current detection point and the adjacent downstream detection point, including: When the first detection point in the distribution network that meets the criteria in step S4 is located, the fault section is located in the line section between the detection point and the adjacent downstream detection point. If the detection point is an end node, the fault section is located between the upstream connection point of the detection point and the end of the line.

7. A single-phase open-circuit fault detection system for distribution networks based on line voltage amplitude, characterized in that, The method described in any one of claims 1 to 6 includes: The voltage acquisition unit is used to acquire the zero-sequence voltage and three-phase line voltage at each detection point in the power distribution network. The zero-sequence voltage judgment unit is used to determine whether the effective value of the zero-sequence voltage at any detection point is greater than the preset start-up threshold. The ratio and standard deviation calculation unit is used to calculate the ratio of the maximum to the minimum value of the three-phase line voltage amplitude at the current detection point when the effective value of the zero-sequence voltage at any detection point is greater than the preset start threshold, and to calculate the standard deviation of the three-phase line voltage amplitude at the current detection point. The fault determination unit is used to determine that a single-phase open circuit fault has occurred in the line section covered by the current detection point if the ratio is greater than a preset ratio threshold and the standard deviation is greater than a preset standard deviation threshold, and the fault section is located between the current detection point and the adjacent downstream detection point.

8. A computer device, characterized in that, include: Memory, transceiver, processor, and bus system; The memory is used to store programs; The processor is configured to execute a program in the memory, including performing the method as described in any one of claims 1 to 6; The bus system is used to connect the memory and the processor to enable communication between the memory and the processor.

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