A distribution network fault section positioning method containing distributed photovoltaics

Abstract

This application discloses a method for locating fault sections in a distribution network containing distributed photovoltaic (PV) power systems, relating to the field of power system protection and fault location. The method includes dividing the feeder of the medium-voltage distribution network with distributed PV into multiple sections, setting a low-voltage measurement point on the low-voltage side of the distribution transformer corresponding to each section, and collecting the three-phase voltage signals of each low-voltage measurement point; obtaining the positive-sequence voltage component phase before and after the fault at each low-voltage measurement point; calculating the change between the positive-sequence voltage component phase before and after the fault at each low-voltage measurement point; comparing the magnitudes of the changes at each low-voltage measurement point, and determining the section corresponding to the low-voltage measurement point with the largest change as the fault section. This application eliminates the need for medium-voltage side measurements and complex communication, locating fault sections by comparing the positive-sequence phase changes on the low-voltage side, resulting in accurate location and low cost.

Description

Technical Field

[0001] This application relates to the field of power system protection and fault location, and in particular to a method for locating fault sections in distribution networks containing distributed photovoltaic power. Background Technology

[0002] The distribution network is a crucial link in the power system connecting the generation side and the user side. Common fault types include single-phase grounding, two-phase short circuits, two-phase-to-ground short circuits, and three-phase short circuits. After a fault occurs, rapid and accurate fault location and isolation are essential for ensuring the safe and stable operation of the distribution network and the reliability of power supply. Traditional medium-voltage distribution networks are mostly single-source radial structures, with fault current typically flowing unidirectionally from the substation side to the fault point. Therefore, fault location techniques based on impedance methods, traveling wave methods, and matrix methods have been widely applied and have achieved good results.

[0003] In recent years, with the widespread integration of distributed photovoltaic (PV) power sources into medium-voltage distribution networks, the distribution network has gradually evolved from a traditional single-source radial structure to a multi-source power supply structure, resulting in more complex variations in fault current distribution and fault characteristic quantities. After the integration of distributed PV, the direction, amplitude, and phase characteristics of the current in each branch may change during a fault, making traditional fault location methods applicable to single-source power supply distribution networks difficult to directly apply to medium-voltage distribution networks containing distributed PV. As the proportion of PV integration continues to increase, the power flow distribution and fault characteristics of the distribution network have changed significantly: First, the integration of PV power sources has led to the distribution network gradually exhibiting multi-source power supply and bidirectional power flow characteristics, challenging the traditional protection principles and fault location criteria based on the assumption of unidirectional power flow; second, the fault current of PV power sources is affected by inverter control strategies and current-limiting characteristics, resulting in a significant difference in fault response compared to traditional synchronous power sources, leading to a decrease in the adaptability of location methods based on fault current amplitude and impedance changes; third, the injected current from the PV inverter may also change the direction relationship of local branch currents, thereby causing confusion in fault direction discrimination and misjudgment of fault sections.

[0004] Existing fault location methods for distribution networks based on low-voltage side information mainly utilize the phasor ratio of positive and negative sequence voltages, characteristic voltage amplitudes, or their distribution patterns under fault conditions as criteria, but their utilization of phase change characteristics before and after the fault is insufficient. Especially under distributed photovoltaic grid-connected conditions, the distribution network operation mode, photovoltaic output level, and fault disturbance propagation patterns are more complex. Relying solely on absolute characteristic quantities under fault conditions is easily affected by amplitude fluctuations and changes in operating conditions. Furthermore, existing low-voltage side methods mostly focus on asymmetric fault scenarios, lacking sufficient uniform applicability to symmetric faults.

[0005] Specifically, the fault location method based on impedance characteristics in related technologies has the following shortcomings under distributed photovoltaic grid-connected conditions: After the distributed photovoltaic system is connected, the fault current is supplied by multiple power sources, which changes the fault circuit structure and equivalent impedance characteristics, weakening the effectiveness of traditional impedance criteria; the output current of the photovoltaic inverter is affected by the control strategy and current limiting circuit, and its amplitude and phase characteristics are significantly different from those of traditional synchronous power sources, which can easily cause impedance calculation errors; such methods usually rely on relatively complete voltage and current measurement conditions on the medium-voltage side, resulting in high engineering implementation costs.

[0006] Fault location methods based on transient traveling wave characteristics have the following shortcomings: they require high sampling frequency, wavefront identification accuracy, and measurement device performance, often necessitating the acquisition of high-frequency transient signals, resulting in high engineering implementation costs; under distributed photovoltaic grid-connected conditions, inverter access alters the fault transient process and high-frequency component propagation characteristics, increasing the difficulty of traveling wavefront extraction and identification; these methods generally rely heavily on multi-point synchronous measurement and communication coordination, limiting their widespread application in practical medium-voltage distribution networks.

[0007] The fault location method based on matrix analysis has the following shortcomings: it usually relies on relatively accurate network topology information, switch status information, and multi-point fault measurement information. Once the operation mode of the distribution network changes or the field information is incomplete, it can easily affect the accuracy of the location results; in the case of distributed photovoltaic grid connection, the fluctuation of photovoltaic output and the electrical quantity response during the fault period become more complicated, which increases the difficulty of matrix criterion design and model correction; the system configuration is complex, and the field implementation and maintenance costs are high.

[0008] While fault location methods based on low-voltage side voltage variation characteristics can reduce dependence on medium-voltage side measurement equipment to some extent, they still have the following shortcomings: Related schemes mostly focus on low-voltage side voltage amplitude changes, characteristic voltage magnitudes, or single response quantity analysis, and do not fully utilize phase information before and after the fault, especially the sequence component phase characteristics; under distributed photovoltaic grid-connected conditions, low-voltage side voltage amplitude characteristics are easily affected by operating modes, load levels, and photovoltaic output changes, resulting in insufficient characteristic differences between different fault sections, thus affecting the stability of the location results; existing low-voltage side methods are relatively insufficient in their synergistic utilization of fault type identification and fault section location, and have not fully explored the application value of low-voltage side phase information in fault analysis, leaving room for further improvement in adaptability to complex fault scenarios.

[0009] Therefore, it is necessary to study a fault location method for distributed photovoltaic grid-connected medium-voltage distribution networks based on low-voltage side phase information and oriented towards the changes in characteristics before and after a fault. Summary of the Invention

[0010] The purpose of this application is to provide a method for locating fault sections in distribution networks containing distributed photovoltaic (PV) systems, in order to solve the problems in related technologies where fault section location in distribution networks after PV integration relies on medium-voltage side measurement devices, is susceptible to PV output fluctuations, has poor adaptability to symmetrical faults, and does not fully utilize phase information.

[0011] To achieve the above objectives, this application provides the following solution: Firstly, this application provides a method for locating fault sections in a distribution network containing distributed photovoltaic power, including: The medium-voltage distribution network feeder of distributed photovoltaic grid connection is divided into multiple sections. A low-voltage measurement point is set on the low-voltage side of the distribution transformer in each section to collect the three-phase voltage signal of each low-voltage measurement point. Based on the three-phase voltage signals at each low-voltage measurement point, obtain the positive sequence voltage component phase before the fault and the positive sequence voltage component phase after the fault at each low-voltage measurement point. Calculate the change in the phase of the positive sequence voltage component before the fault and the phase of the positive sequence voltage component after the fault at each low-voltage measurement point; By comparing the magnitude of the changes at each low-pressure measurement point, the section corresponding to the low-pressure measurement point with the largest change is identified as the fault section.

[0012] Optionally, the formula for calculating the phase change of the positive sequence voltage component is: ; in, For low-pressure measurement points The phase change of the positive sequence voltage component. For low-pressure measurement points The positive sequence voltage component phase after the fault, For low-pressure measurement points The phase of the positive sequence voltage component before the fault.

[0013] Optionally, it also includes a fault type determination step: Obtain the phase of the negative sequence voltage component after a fault at each low-voltage measurement point; The fault type is determined based on the phase difference between the positive-sequence voltage component phase and the negative-sequence voltage component phase after a fault at at least one low-voltage measurement point. If the phase difference falls within the preset asymmetric fault characteristic range, it is determined to be an asymmetric fault; otherwise, it is determined to be a symmetric fault.

[0014] Optionally, the asymmetrical fault includes a single-phase ground fault, a two-phase short-circuit fault, or a two-phase ground short-circuit fault; If the phase difference falls within a preset asymmetric fault characteristic range, it is determined to be an asymmetric fault, specifically including: If the phase difference is within the range of 140 to 180 degrees, it is determined to be a single-phase ground fault; If the phase difference is within the range of 0 to 70 degrees, it is determined to be a two-phase short circuit fault or a two-phase ground short circuit fault.

[0015] Optionally, the positive-sequence voltage component phase and the negative-sequence voltage component phase are obtained in the following ways: The three-phase voltage signals at each low-voltage measurement point are subjected to Hilbert transform to construct analytical signals and obtain the complex phasors of the three-phase voltages. The positive-sequence voltage component complex phasor and the negative-sequence voltage component complex phasor are calculated from the complex phasors using the symmetrical component method; The phase of the complex phasor of the positive-sequence voltage component is extracted as the phase of the positive-sequence voltage component, and the phase of the complex phasor of the negative-sequence voltage component is extracted as the phase of the negative-sequence voltage component.

[0016] Optionally, the phase of the positive-sequence voltage component before and after the fault at each low-voltage measurement point is obtained, specifically including: Based on the three-phase voltage signals at each low-voltage measurement point, the fault initiation time is detected by voltage or current surges. Using the fault initiation time as the time boundary, the three-phase voltage signals of the period before the fault and the period after the fault are extracted respectively. Based on the three-phase voltage signals during the pre-fault and post-fault periods, the pre-fault positive sequence voltage phase and post-fault positive sequence voltage phase corresponding to each low-voltage measurement point are obtained.

[0017] According to the specific embodiments provided in this application, this application has the following technical effects: This application provides a method for locating fault sections in distribution networks containing distributed photovoltaic (PV) power. By setting measurement points on the low-voltage side of the distribution transformer, it eliminates the need for additional measurement devices or high-precision synchronous time communication networks on the medium-voltage side. Signal acquisition can be completed using only existing low-voltage monitoring equipment, significantly reducing system construction and maintenance costs. Simultaneously, by extracting the phase of the positive-sequence voltage components before and after the fault at each measurement point and calculating the change, the method uses the phase change at the same measurement point as the criterion, fundamentally eliminating the influence of distributed PV power output fluctuations, load switching, and changes in operating modes on fault characteristic quantities, thus solving the problems of traditional... The method addresses the issue of unstable location in photovoltaic scenarios. Furthermore, since the physical law that the closer the electrical distance to the fault point, the more drastic the positive-sequence phase change, holds true for all fault types, this application can achieve segment location without prior identification of the fault type, overcoming the shortcomings of existing low-voltage side methods in adapting to symmetrical faults. Finally, this application only needs to compare the relative magnitudes of the phase changes, without establishing an accurate distribution network impedance parameter model or solving the fault distance by simultaneously solving the first and last terminals. The calculation is simple, the response speed is fast, and it is suitable for rapid fault isolation and power restoration scenarios in medium-voltage distribution networks with a high proportion of distributed photovoltaics. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or related technologies, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the first process of a method for locating fault sections in a distribution network containing distributed photovoltaic power, as proposed in this application. Figure 2 This is a schematic diagram of the structure of distributed photovoltaic power grid integration; Figure 3 This is a schematic diagram of the positive-sequence equivalent network for distributed photovoltaic (PV) grid integration. Figure 4 This is a schematic diagram of the second process of a method for locating fault sections in a distribution network containing distributed photovoltaic power. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] To make the objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] In one exemplary embodiment, such as Figure 1 As shown, a method for locating fault sections in a distribution network containing distributed photovoltaic power is provided. This method includes steps 101 to 104. The following is in conjunction with… Figure 2 The schematic diagram of the power distribution network structure shown is as follows: Figure 3 The schematic diagram of the orthogonal order isomorphic network shown below provides a detailed explanation of this embodiment. Wherein: Step 101: Divide the medium-voltage distribution network feeder of the distributed photovoltaic grid into multiple sections, and set a low-voltage measurement point on the low-voltage side of the distribution transformer corresponding to each section to collect the three-phase voltage signal of each low-voltage measurement point.

[0023] Step 102: Based on the three-phase voltage signals of each low-voltage measurement point, obtain the positive sequence voltage component phase before the fault and the positive sequence voltage component phase after the fault at each low-voltage measurement point.

[0024] Specifically, based on the three-phase voltage signals at each low-voltage measurement point, the fault initiation time is detected by voltage or current surges. Using the fault initiation time as the time boundary, the three-phase voltage signals of the period before the fault and the period after the fault are extracted respectively. Based on the three-phase voltage signals during the pre-fault and post-fault periods, the pre-fault positive sequence voltage phase and post-fault positive sequence voltage phase corresponding to each low-voltage measurement point are obtained.

[0025] Step 103: Calculate the change in the phase of the positive-sequence voltage component before and after the fault at each low-voltage measurement point. The formula for calculating the change in the phase of the positive-sequence voltage component is: ; in, For low-pressure measurement points The phase change of the positive sequence voltage component. For low-pressure measurement points The positive sequence voltage component phase after the fault, For low-pressure measurement points The phase of the positive sequence voltage component before the fault.

[0026] Step 104: Compare the magnitude of the changes at each low-pressure measurement point, and determine the section corresponding to the low-pressure measurement point with the largest change as the fault section.

[0027] The basic principle of steps 101 to 104 above is as follows: When a short-circuit fault occurs in a medium-voltage distribution network, the fault disturbance is transmitted to the low-voltage side via the distribution transformer, causing the positive-sequence voltage phase at each measurement point to shift to varying degrees. The closer the electrical distance of a measurement point is to the fault point, the greater the phase change of its positive-sequence voltage component, and vice versa. Therefore, by calculating and sorting the phase change of each measurement point, the section corresponding to the measurement point with the largest change is identified as the fault section, thus achieving rapid and reliable section location. This method does not require the addition of voltage or current transformers on the medium-voltage side, nor does it require the deployment of a high-precision synchronous time communication network. It can complete signal acquisition and processing using only the existing low-voltage monitoring devices in the distribution area, significantly reducing system construction and maintenance costs. Meanwhile, since this application relies solely on the phase difference before and after a fault at the same measurement point, rather than the amplitude or direction of the fault current, it effectively overcomes the complex fault characteristics caused by multiple power sources, bidirectional power flow, and inverter current-limiting characteristics resulting from distributed photovoltaic (PV) integration. It exhibits strong robustness to PV output fluctuations, load changes, and operational mode alterations. Furthermore, the comparison law of this positive-sequence phase change holds true for all fault types, including single-phase grounding, two-phase short circuit, two-phase grounding short circuit, and three-phase short circuit. It allows for unified section location without prior fault type identification, overcoming the shortcomings of existing low-voltage side methods in adapting to symmetrical faults. In summary, the method provided in this application is computationally simple, has a fast response speed, and is suitable for rapid fault isolation and power restoration scenarios in medium-voltage distribution networks with a high proportion of distributed PV.

[0028] In medium-voltage distribution networks with distributed photovoltaic (PV) integration, low-voltage side electrical measurements can serve as an important basis for analyzing faults on the upstream medium-voltage side. Since low-voltage side smart meters, inverter controllers, and transformer monitoring devices are widely deployed, low-voltage side voltage signals offer advantages such as easy acquisition, flexible deployment, and low cost.

[0029] To further elucidate the relationship between medium-voltage faults and low-voltage responses, this application first analyzes the transmission pattern of fault disturbances from the medium-voltage side to the low-voltage side via the distribution transformer. Taking a common Dyn11 distribution transformer as an example, let the three-phase voltages on the medium-voltage side be... , , The three-phase voltages on the low-voltage side are respectively , , With a turns ratio of K, there is a fixed linear transformation relationship between the low-voltage side phase voltage and the medium-voltage side line voltage. The relationship between the low-voltage side phase voltage and the medium-voltage side phase voltage can be expressed as: ; Furthermore, the low-voltage side line voltage can be expressed as: ; in, , , These represent the low-voltage side line voltages. For the Dyn11 connection configuration, the zero-sequence component does not propagate outwards under ideal conditions and can be considered blocked or significantly suppressed; the positive-sequence and negative-sequence voltage components are scaled according to the turns ratio and accompanied by a fixed phase shift. Their phasor relationship can be written as: ; According to the above formula, the phase angles of the positive-sequence and negative-sequence voltages on the low-voltage side satisfy the following: ; in, The transformed positive-sequence voltage component. The transformed negative sequence voltage component. It is the positive sequence voltage component. It is a negative sequence voltage component. and These represent the phase angles of the positive sequence voltage on the low-voltage side and the negative sequence voltage on the low-voltage side, respectively.

[0030] The above relationship indicates that the positive and negative sequence voltage phase changes caused by medium-voltage side faults will be transmitted to the low-voltage side according to a deterministic law, thus providing a theoretical premise for medium-voltage fault location based on low-voltage side electrical quantities.

[0031] In another specific implementation scenario, with Figure 2 Taking the distributed photovoltaic (PV) grid connection structure shown as an example, the feeder is divided into sections A, B, and C, corresponding to low-voltage measurement points SM1, SM2, and SM3, respectively. Measurement points SM1, SM2, and SM3 correspond to three downstream branches connected to sections A, B, and C, respectively. Figure 2 In this diagram, T1 is the main transformer, connecting the 110kV high-voltage side and the 10kV medium-voltage side, reducing the voltage from 110kV to 10kV. F is the fault point, indicating a fault on the line, such as a short circuit. T2, T3, and T4 are distribution transformers, reducing the 10kV voltage to 0.4kV for user use. PV1 and PV2 are photovoltaic power sources, representing distributed photovoltaic power generation systems. T(PV1) and T(PV2) are photovoltaic grid-connected transformers, stepping up the voltage of the photovoltaic power and connecting it to the 10kV grid. LD1, LD2, and LD3 represent the electrical equipment or user loads connected to the 0.4kV low-voltage side of distribution transformers T2, T3, and T4, respectively. M1 is the measurement point of the main grid.

[0032] When a fault occurs in a section of the feeder, the fault disturbance propagates along the distribution network, causing varying degrees of change in the positive-sequence voltage component phase angle at different low-voltage measurement points. Because the low-voltage measurement points are located differently within the distribution network, their electrical distances and connections to the faulted section differ, resulting in different spatial distribution patterns for the positive-sequence phase changes before and after the fault at each measurement point. Therefore, this application does not rely on the absolute sequence component ratio under a single measurement point fault condition for judgment. Instead, it compares the relative distribution of the positive-sequence voltage component phase angle changes before and after the fault at multiple low-voltage measurement points, and combines this with the correspondence between each measurement point and the line section to achieve the identification and location of the faulted section.

[0033] The theoretical basis of the above segment location method can be further explained using an orthogonal equivalence network as follows: Figure 3 As shown, at any low-pressure measurement point SMi For the research object, the upstream medium-voltage distribution network can be equivalently represented as a Thevenin power source, and the distributed photovoltaic units can be regarded as controlled current sources in the positive-sequence network. Based on the positive-sequence equivalent network and the fault injection model, the complex phasor of the positive-sequence voltage component at the fault point can be expressed as: ; in, The positive sequence voltage at the fault point. This is the equivalent power supply voltage for medium-voltage distribution networks. This is the fault positive sequence current. This is the equivalent positive sequence impedance from the power source to the fault point.

[0034] Taking the representative low-voltage measurement points SM1, SM2, and SM3 shown in the diagram as examples, their positive sequence voltages after a fault can be expressed as follows: ; ; ; Before the fault, the system was in steady-state operation, and the equivalent power supply phase angle of the system can be taken as a reference. (This indicates its amplitude), that is: ; Therefore, the positive sequence voltage before the fault at each low-voltage measurement point can be expressed as follows: ; ; ; in, , , These represent the positive sequence voltages at measurement points SM1, SM2, and SM3 after the fault, respectively. , , These represent the positive sequence voltages at the corresponding measurement points before the fault; This represents the equivalent positive-sequence impedance on the system power supply side; This represents the equivalent impedance of the main transformer T1; , , , , These represent the positive sequence impedance of the line for each section of the feeder; This represents the total positive sequence impedance of section B; and These represent the equivalent impedances of the branches into which distributed photovoltaic units PV1 and PV2 are connected, respectively. , , These represent the positive sequence currents in the corresponding measured branches after a fault. , , This indicates the positive sequence current in the corresponding measured branch before the fault. and These represent the positive-sequence injection current of the distributed photovoltaic unit. Furthermore, in Figure 3 middle, The transformer impedance of the branch circuit connected to the distributed photovoltaic unit PV1. The transformer impedance of the branch circuit for the distributed photovoltaic unit PV2 is... The impedance of the low-voltage load LD1, The impedance of LD2 is the low-voltage load. The impedance of LD3 is for low-voltage load. This is the positive sequence voltage phasor at fault point F.

[0035] To characterize the impact of fault disturbances on different low-voltage measurement points, the phase change of the positive-sequence voltage component at any low-voltage measurement point SMi is defined as: ; in, and This represents the positive sequence voltage phase angle before and after the fault at measurement point SMi.

[0036] The aforementioned positive-sequence phase change primarily reflects the combined effect of the upstream positive-sequence network impedance and the current redistribution caused by the fault. Typically, low-voltage measurement points closer to the fault section experience more significant voltage disturbances, resulting in larger phase changes in their positive-sequence voltage components; while measurement points farther from the fault section exhibit relatively smaller phase changes. Therefore, the phase changes at each low-voltage measurement point along the feeder... The spatial distribution contains direct information about the location of the faulty section. For example, when a fault occurs in a section near SM3, it typically satisfies the following: ; The above formula indicates that the measurement point closest to the faulty section typically exhibits the largest positive-sequence phase change response. Based on this, this application compares the relative magnitudes of the positive-sequence phase changes before and after a fault at multiple low-voltage measurement points, and combines this with the topological positional relationship of each measurement point within the line to determine and locate the faulty section. Specifically, the relative distribution pattern of the positive-sequence phase changes before and after a fault at multiple low-voltage measurement points reflects the propagation and attenuation characteristics of fault disturbances in the feeder. Measurement points closer to the faulty section by electrical distance typically exhibit larger positive-sequence phase changes; measurement points farther from the faulty section exhibit relatively smaller positive-sequence phase changes. Therefore, by matching the magnitude pattern of the positive-sequence phase changes at multiple measurement points with the corresponding section location, faulty section identification can be achieved.

[0037] In another preferred embodiment of this application, to further improve the accuracy and adaptability of fault diagnosis, a fault type determination step may be included before or in parallel with step 102. The specific process is as follows: Step 201: Obtain the phase of the negative sequence voltage component after a fault at each low-voltage measurement point.

[0038] Specifically, the three-phase voltage signals at each low-voltage measurement point are subjected to Hilbert transform to construct analytical signals and obtain complex phasors of the three-phase voltages. The positive-sequence voltage component complex phasors and the negative-sequence voltage component complex phasors are calculated from the complex phasors using the symmetrical component method. The phase of the positive-sequence voltage component complex phasor is extracted as the positive-sequence voltage component phase, and the phase of the negative-sequence voltage component complex phasor is extracted as the negative-sequence voltage component phase.

[0039] Step 202: Determine the fault type based on the phase difference between the positive-sequence voltage component phase and the negative-sequence voltage component phase after a fault at at least one low-voltage measurement point.

[0040] The phase difference between the positive-sequence voltage component phase and the negative-sequence voltage component phase is defined as: ; Where wrap(.) means to constrain the phase difference to ( The interval is 180°. This represents the phase difference between the positive-sequence voltage component phase and the negative-sequence voltage component phase. The phase of the positive sequence voltage component. This represents the phase of the negative sequence voltage component.

[0041] If the phase difference falls within a preset asymmetrical fault characteristic range, it is determined to be an asymmetrical fault; otherwise, it is determined to be a symmetrical fault. The asymmetrical fault includes a single-phase ground fault, a two-phase short-circuit fault, or a two-phase-to-ground short-circuit fault.

[0042] Specifically, when a single-phase ground fault, a two-phase short-circuit fault, or a two-phase-to-ground short-circuit fault occurs, the medium-voltage distribution network exhibits a significant asymmetrical operating state, leading to a significant negative sequence component on the low-voltage side. Based on extensive simulation and experimental data, this embodiment summarizes the following criteria: If the phase difference is within the range of 140° to 180°, it is determined to be a single-phase ground fault; If the phase difference is within the range of 0° to 70°, it is determined to be a two-phase short circuit fault or a two-phase ground short circuit fault.

[0043] When the phase difference does not meet the aforementioned asymmetrical fault characteristic range, for example, when the phase difference is within the range of 70° to 140° or close to the boundary value and unstable, the current amplitude characteristics on the medium-voltage side or the current information at the main power grid measurement point are further combined to confirm whether it is a symmetrical fault, such as a three-phase short-circuit fault. This symmetrical fault branch confirmation step makes this method applicable not only to asymmetrical fault scenarios but also extendable to symmetrical fault scenarios, providing a reliable fault state premise for subsequent unified section location.

[0044] Through steps 201 to 202 described above, this embodiment achieves auxiliary identification of fault types, which helps maintenance personnel quickly understand the nature of the fault and provides reference information for subsequent segment location. It should be noted that even if this fault type judgment step is omitted, the segment location method in steps 101 to 104 can still run independently and accurately identify the faulty segment, because the comparison law of positive sequence phase change holds true for all fault types.

[0045] like Figure 4As shown, the overall implementation process of this application can be summarized as follows: First, measurement points are set on the low-voltage side of the distribution transformer corresponding to each section of the feeder to collect the three-phase voltage signals at each point. Second, the collected three-phase voltage signals are subjected to Hilbert transform to construct analytical signals to extract phase information, and the positive-sequence and negative-sequence voltage components and their phases at each measurement point are obtained using the symmetrical component method. Then, asymmetrical fault auxiliary identification is performed based on the positive and negative-sequence phase difference on the low-voltage side after the fault: if the phase difference falls within the range of 140° to 180°, it is determined to be a single-phase ground fault; if it falls within the range of 0° to 70°, it is determined to be a two-phase short circuit or a two-phase ground short circuit fault. If the phase difference is not within the above-mentioned asymmetrical characteristic range, the current amplitude characteristics of the main grid measurement points are further checked. If the symmetrical fault criteria are met, it is confirmed as a symmetrical fault, such as a three-phase short circuit. After completing the fault type judgment, the phase change of the positive-sequence voltage component before and after the fault at each low-voltage measurement point is calculated. Since the positive sequence phase change is greater for measurement points that are closer to the fault point, by comparing the relative magnitudes of the positive sequence phase changes at each measurement point, and combining the connection sequence of each measurement point in the distribution network and its correspondence with the line section, the section corresponding to the measurement point with the largest change is identified as the fault section.

[0046] The key points of this application are: first, asymmetric fault type identification based on the phase characteristics of the low-voltage side sequence components; and second, fault segment location based on the relative comparison of positive-sequence phase changes at multiple measurement points. The physical basis is that after a medium-voltage fault disturbance is transmitted to the low-voltage side via the distribution transformer, it leaves identifiable features in the voltage sequence components and their phase changes, thus enabling medium-voltage fault analysis and segment location using the low-voltage side phase information.

[0047] This application has the following beneficial effects: First, this application uses the phase change before and after the fault as the core criterion, rather than relying solely on the ratio of absolute order components or amplitude characteristics under fault conditions, thereby effectively reducing the impact of different operating modes, distributed photovoltaic power output fluctuations, and amplitude scale changes on the positioning results.

[0048] Second, this application achieves unified segment location for both asymmetrical and symmetrical faults. Specifically, it first utilizes the phase difference between the positive and negative sequence components after a fault on the low-voltage side to assist in the identification of asymmetrical faults. For cases where the asymmetrical fault criterion is not met, the symmetrical fault type is further confirmed by combining the current amplitude characteristics of the main grid measurement points. Based on this, the fault segment location is achieved by uniformly comparing the phase changes of the positive sequence voltage components before and after the fault at multiple low-voltage measurement points. Therefore, this application is applicable not only to asymmetrical fault scenarios such as single-phase ground faults, two-phase short-circuit faults, and two-phase-to-ground short-circuit faults, but also to symmetrical fault scenarios such as three-phase short-circuit faults, significantly expanding the applicability of the method.

[0049] Third, this application does not obtain the precise location of the fault by connecting the head end of the distribution network with the end of the fault section. Instead, it identifies the fault section by the relative distribution of phase changes and topological relationships of multiple low-voltage measurement points, which simplifies the fault location process and is more suitable for the rapid identification of fault sections.

[0050] Fourth, this application mainly utilizes the voltage phase information of the measurement points on the low-voltage side of the distribution transformer for fault analysis. It can achieve section location with less reliance on the addition of measurement devices on the medium-voltage side and complex communication conditions, which helps to reduce the system construction and implementation costs.

[0051] Fifth, in response to the problems of multiple power sources, bidirectional power flow, and complex fault characteristics in the distribution network after the integration of distributed photovoltaics, this application uses the phase characteristics of the low-voltage side sequence component and the relative distribution characteristics of the positive sequence phase changes of multiple measurement points for analysis. This can effectively reduce the adverse effects caused by photovoltaic reverse support, current distribution changes, and inverter control characteristics in traditional methods, and significantly improve the adaptability of fault section location in medium-voltage distribution networks containing distributed photovoltaics.

[0052] In summary, this application enables the effective identification of faulty sections in the distribution network, providing a basis for rapid fault isolation and power restoration, thereby helping to reduce the scope of fault impact and improve the safety and reliability of distribution network operation. This application effectively overcomes the problems of existing methods, such as strong dependence on medium-voltage side measurement conditions, susceptibility to the complexities of fault characteristics after distributed photovoltaic integration, and insufficient utilization of low-voltage side phase characteristics. It has high engineering practical value and broad application prospects.

[0053] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0054] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for locating fault sections in a distribution network containing distributed photovoltaic power, characterized in that, The method includes: The medium-voltage distribution network feeder of distributed photovoltaic grid connection is divided into multiple sections. A low-voltage measurement point is set on the low-voltage side of the distribution transformer in each section to collect the three-phase voltage signal of each low-voltage measurement point. Based on the three-phase voltage signals at each low-voltage measurement point, obtain the positive sequence voltage component phase before the fault and the positive sequence voltage component phase after the fault at each low-voltage measurement point. Calculate the change in the phase of the positive sequence voltage component before the fault and the phase of the positive sequence voltage component after the fault at each low-voltage measurement point; By comparing the magnitude of the changes at each low-pressure measurement point, the section corresponding to the low-pressure measurement point with the largest change is identified as the fault section.

2. The method for locating fault sections in a distribution network containing distributed photovoltaic power according to claim 1, characterized in that, The formula for calculating the phase change of the positive sequence voltage component is: ； in, For low-pressure measurement points The phase change of the positive sequence voltage component. For low-pressure measurement points The positive sequence voltage component phase after the fault, For low-pressure measurement points The phase of the positive sequence voltage component before the fault.

3. The method for locating fault sections in a distribution network containing distributed photovoltaic power according to claim 1, characterized in that, It also includes a fault type determination step: Obtain the phase of the negative sequence voltage component after a fault at each low-voltage measurement point; The fault type is determined based on the phase difference between the positive-sequence voltage component phase and the negative-sequence voltage component phase after a fault at at least one low-voltage measurement point. If the phase difference falls within the preset asymmetric fault characteristic range, it is determined to be an asymmetric fault; otherwise, it is determined to be a symmetric fault.

4. The method for locating fault sections in a distribution network containing distributed photovoltaic power according to claim 3, characterized in that, The asymmetrical faults include single-phase ground faults, two-phase short-circuit faults, or two-phase ground short-circuit faults. If the phase difference falls within a preset asymmetric fault characteristic range, it is determined to be an asymmetric fault, specifically including: If the phase difference is within the range of 140 to 180 degrees, it is determined to be a single-phase ground fault; If the phase difference is within the range of 0 to 70 degrees, it is determined to be a two-phase short circuit fault or a two-phase ground short circuit fault.

5. The method for locating fault sections in a distribution network containing distributed photovoltaic power according to claim 3, characterized in that, The positive-sequence voltage component phase and the negative-sequence voltage component phase are obtained respectively through the following methods: The three-phase voltage signals at each low-voltage measurement point are subjected to Hilbert transform to construct analytical signals and obtain the complex phasors of the three-phase voltages. The positive-sequence voltage component complex phasor and the negative-sequence voltage component complex phasor are calculated from the complex phasors using the symmetrical component method; The phase of the complex phasor of the positive-sequence voltage component is extracted as the phase of the positive-sequence voltage component, and the phase of the complex phasor of the negative-sequence voltage component is extracted as the phase of the negative-sequence voltage component.

6. The method for locating fault sections in a distribution network containing distributed photovoltaic power according to claim 1, characterized in that, Obtain the positive sequence voltage component phase before and after the fault at each low-voltage measurement point, specifically including: Based on the three-phase voltage signals at each low-voltage measurement point, the fault initiation time is detected by voltage or current surges. Using the fault initiation time as the time boundary, the three-phase voltage signals of the period before the fault and the period after the fault are extracted respectively. Based on the three-phase voltage signals during the pre-fault and post-fault periods, the pre-fault positive sequence voltage phase and post-fault positive sequence voltage phase corresponding to each low-voltage measurement point are obtained.

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