A phase-to-phase fault locating method and system based on load side phase voltage

Abstract

The present application belongs to the technical field of power fault location, and discloses a phase-by-phase fault location method and system based on load side phase voltage. The present application establishes a mapping model between medium and low voltage sides, and completes accurate inversion of electrical quantities from the low voltage side to the high voltage side. In combination with the neutral point ungrounded distribution system topology and line equivalent parameters, the present application calculates the positive sequence current fault component by using the inversion obtained medium voltage side voltage phasor, and constructs effective fault line selection and section location criteria according to the distribution characteristics of the positive sequence current fault component. The inversion calculation result is verified by simulation based on the MATLAB simulation platform. The present application only needs to input the low voltage side phase voltage data, and can calculate the corresponding data of the medium voltage side, thereby breaking through the limitation of traditional methods which rely on medium voltage side measurement devices, and realizing the methodological innovation of solving the medium voltage side problem by using low voltage information.

Description

Technical Field

[0001] This invention belongs to the field of power fault location technology, and particularly relates to a method and system for locating successive faults based on load-side phase voltage. Background Technology

[0002] As the most direct and crucial link connecting electricity users, the power distribution network has received widespread attention and achieved significant development in recent years. As an important energy infrastructure, the distribution network plays a key role in ensuring a safe and stable power supply, supporting sustainable economic and social development, and improving people's livelihoods. Currently, the ungrounded neutral point system is widely used. Its advantage lies in its ability to effectively guarantee power supply reliability. In the event of a single-phase ground fault, the grounding current is relatively small, which is conducive to the self-extinguishing of the arc during transient faults; for permanent ground faults, it also allows the system to continue operating with the grounded point for a short period.

[0003] However, after a single-phase ground fault, sometimes a second ground fault occurs, meaning that before the first ground fault is isolated, another single-phase ground fault occurs at another location in the system. This type of fault often occurs because the voltage between the non-faulty phases and ground continues to rise after the first ground fault, thus breaking down existing weak points in the insulation and forming a second ground fault. With the increasing complexity of power distribution network structures and the rising proportion of cables, the probability of two-point ground faults also increases under severe weather conditions or external damage. If two-point ground faults are not handled promptly, they may cause fires in overhead lines.

[0004] Currently, the technology for locating single-phase grounding faults in ungrounded systems is relatively mature. However, for two-point grounding faults, research on fault characteristic analysis and location methods remains limited due to relatively insufficient attention paid to related studies. Current single-phase grounding fault handling devices on the market typically lack the ability to identify and clear successive grounding faults. After the device selects and clears the first fault point, the system's zero-sequence voltage remains above the set threshold due to the continued presence of the second grounding point, preventing the device from resetting or restarting. To promptly clear remaining fault points, field operators often need to manually test the lines or use line selection devices to sequentially disconnect the remaining lines. However, both manual testing and sequential disconnection operations can cause unnecessary short-term power outages on non-faulty lines, thus affecting power supply quality. Therefore, it is necessary to conduct in-depth research on successive grounding faults in ungrounded systems, clarify the fault characteristics of successive grounding faults, and propose detection methods suitable for successive grounding faults to enable timely handling measures and avoid short-term power outages on non-faulty lines caused by reliance on manual line testing.

[0005] In recent years, intelligent fusion terminals based on low-voltage distribution area data acquisition have been gradually deployed on a large scale. By constructing digital distribution areas, massive load-side data can be mined. Through in-depth research on the monitoring information of the distribution network load side, new solutions have been provided for medium-voltage side faults, and a lot of costs have been saved. Realizing the location of successive faults on the medium-voltage side through low-voltage side measurement data has important practical significance and theoretical research value.

[0006] Furthermore, with economic development, the requirements for power supply reliability are increasing, making accurate fault location crucial. The technology for locating single-phase grounding faults in distribution networks is relatively mature, mainly encompassing impedance methods and traveling wave methods. However, because two-point grounding faults are complex, research on their fault characteristics is insufficient, and theoretical calculations are challenging. When two faults occur simultaneously, their fault characteristics differ significantly from those of single-phase grounding faults. Using ordinary single-phase grounding fault location methods may lead to incorrect location results, and the accuracy of fault location cannot be guaranteed.

[0007] Currently used fault location methods typically require the configuration of high-voltage voltage transformers and other equipment, resulting in high construction and installation costs. In recent years, with the rapid development of low-voltage distribution IoT technology, data acquisition devices such as the Distribution Area Smart Convergence Terminal (TD-SFT) have been widely used, significantly improving the ability to collect data such as low-voltage side voltage amplitude. However, the current function of TD-SFT is mainly limited to monitoring loads and distributed power sources within the distribution area, and the utilization of its data in depth and breadth remains insufficient, especially in supporting medium-voltage side fault location, where the potential value of low-voltage side data has not been fully realized. Therefore, many scholars have conducted research to explore how to achieve accurate fault location on the medium-voltage side based on low-voltage side data.

[0008] Therefore, analyzing the fault characteristics of successive grounding faults in medium-voltage distribution networks and making full use of measurement data from the low-voltage side to study a method for fault location using phase voltage information from the low-voltage side has significant engineering value and practical significance. Summary of the Invention

[0009] To overcome the problems existing in related technologies, this invention discloses a method and system for locating successive faults based on load-side phase voltage, specifically involving a method for locating two-point successive grounding faults in an ungrounded system based on load-side phase voltage information. This invention achieves the following objectives while reducing equipment investment costs: It analyzes the fault characteristics of a two-point grounding fault occurring on the low-voltage side of an ungrounded neutral system, obtaining an expression for the fault voltage at any node. It establishes a mapping relationship and fault characteristics between the low-voltage and medium-voltage sides based on the transformer's wiring method, achieving accurate voltage information inversion; and it analyzes the phase voltage change characteristics on the low-voltage side based on the voltage mapping model to obtain corresponding phase selection criteria.

[0010] The positive sequence voltage fault component on the medium-voltage side and the positive sequence current fault component on the line impedance are calculated by inversion calculation. The distribution characteristics are used to propose fault line selection and section location criteria. The accuracy of the successive grounding fault location method under different transition resistances and different load sizes is verified by MATLAB simulation software.

[0011] The technical solution is as follows: The successive fault location method based on load-side phase voltage includes the following steps: S1. Establish a mapping model between the voltages on the low and medium voltage sides to complete the accurate inversion of electrical quantities from the low voltage side to the high voltage side. S2, combining the topology of the neutral point ungrounded distribution system and the equivalent parameters of the line, uses the voltage phasor of the medium voltage side obtained by inversion to calculate the positive sequence current fault component, and constructs an effective fault line selection and section location criterion based on the distribution characteristics of the positive sequence current fault component. S3, based on the MATLAB simulation platform, simulates and verifies the correctness of the inversion calculation results, the feasibility and accuracy under different transition resistances and different load sizes.

[0012] In step S1, establishing the mapping model between the medium and low voltage sides includes: The three phases on the medium-pressure side are designated as A, B, and C, and the corresponding three phases on the low-pressure side are designated as a, b, and c; on the medium-pressure side... Dot and Ground faults occurred in phases B and C respectively, with transition resistances of respectively. and ; Select phase A as the reference phase to obtain the positive and negative sequence networks after the fault; in, For the A-phase power supply of the system, and These are the positive-sequence and negative-sequence impedances of the system, respectively. They are respectively and Positive-sequence impedance and negative-sequence impedance between the busbar and the bus. They are respectively and The sum of the positive-sequence impedance and the sum of the negative-sequence impedance of the downstream line and load. These are the positive-sequence fault supplementary current sources and negative-sequence fault supplementary current sources at points 1 and 2, respectively. When non-faulty paths and capacitor shunts are ignored, by the superposition theorem, for the fault point... any previous node There are: ; In the formula, They are nodes The positive and negative sequence voltage components, for Phase A voltage during normal operation They are nodes Positive-sequence impedance and negative-sequence impedance to the busbar; Based on the definition of fault components, the node is obtained. Positive sequence voltage fault component at the location With negative sequence voltage fault component The expression is: ; For the fault point any previous node have: ; When load shunt is ignored and all transformers use the Dyn-11 connection method, the expression for the three-phase voltage on the low-voltage side of any node, including nodes on non-faulty lines, is as follows: ; In the formula, These are the nodes after the fault. Low-pressure side Phase voltage, Nodes during normal operation The low-voltage side voltage, For transformer turns ratio, Rotate the vector clockwise , It rotates counterclockwise. , It represents the imaginary part of a complex number.

[0013] Furthermore, any node on the medium-pressure side The correspondence between the positive-sequence voltage fault component and the low-voltage side phase voltage: ; A two-point ground fault with different phases is a series-to-series double fault, and the current sequence components at the two fault points satisfy the boundary conditions: ; In the formula, , indicates a clockwise rotation of 120 degrees.

[0014] Furthermore, the positive-sequence impedance and negative-sequence impedance of the line are equal, for the fault point any previous node Place, get: ; In the formula, It is a combination of current and impedance.

[0015] Furthermore, regarding the fault point any previous node Place, get: ; In the formula: ; In step S2, the effective fault selection and section location criteria are constructed as follows: When considering a robust line shunt, a positive sequence fault additional network is required in the event of a two-point ground fault. For the system's positive-sequence admittance, They are respectively Positive-sequence admittance with the bus and total positive-sequence admittance downstream of the fault point. To improve the route Total positive sequence admittance of the line and load; any sound line Positive sequence current fault component at the outlet The expression is: ; In the formula, For any sound line and its total positive-sequence admittance for the load, There are two fault points respectively. The positive sequence current fault component at the location. The positive sequence admittance for Line 3 and the total load; Since the total admittance of any healthy line and its load is much smaller than the system admittance, therefore: ; In the formula, Each is an arbitrary line The amplitude of the positive sequence current fault component of fault line 1 and fault line 2. After completing fault line and phase selection, the positive sequence current fault component of each section is calculated. The positive sequence voltage fault component of the corresponding node is obtained using the low-voltage side phase voltage. This allows for the determination of any two nodes... and The difference between the positive sequence voltage fault components is used to determine the value of any segment given the length of each segment and the impedance per unit length. Positive sequence current fault component: ; In the formula, For any segment The positive sequence current fault component, For nodes and The difference between the positive sequence voltage fault components, For nodes and The positive sequence impedance between; An auxiliary section with a positive sequence current fault component of 0 is added after the end section of the main line and each branch line. First, the main line is judged to find the section where the positive sequence current fault component is significantly greater than that downstream. If there is no branch line downstream of the section, the section is the fault section. If there is a branch line leading out downstream of the positioning section, the above judgment process is repeated for the branch line with the power supply point as the starting point and the end node of the branch line as the ending point, until there is no branch line leading out after the output positioning section, which is determined as the final fault section.

[0016] Another object of the present invention is to provide a successive fault location system based on load-side phase voltage, which is implemented by the successive fault location method based on load-side phase voltage, and the system includes: The mapping model establishment module is used to establish a mapping model between the voltages on the low and medium voltage sides, and to complete the accurate inversion of electrical quantities from the low voltage side to the high voltage side. The fault line selection and section location module is used to combine the topology of the neutral point ungrounded power distribution system and the equivalent parameters of the line, use the voltage phasor of the medium voltage side obtained by inversion to calculate the positive sequence current fault component, and construct an effective fault line selection and section location criterion based on the distribution characteristics of the positive sequence current fault component. The MATLAB simulation platform is used to simulate and verify the correctness of the inversion calculation results, the feasibility and accuracy under different transition resistances and different load sizes.

[0017] Furthermore, the load-side phase voltage-based successive fault location system is mounted on a computer device, which includes at least one processor, a memory, and a computer program stored in the memory and executable on the at least one processor. When the processor executes the computer program, it implements the functions of the load-side phase voltage-based successive fault location system.

[0018] Furthermore, the load-side phase voltage-based successive fault location system is mounted on a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, it can realize the functions of the load-side phase voltage-based successive fault location system.

[0019] Furthermore, the successive fault location system based on load-side phase voltage is applied to the successive fault location of load-side phase voltage in a 10kV medium-voltage distribution network.

[0020] Combining all the above technical solutions, the beneficial effects of this invention are as follows: First, this invention achieves accurate voltage information inversion by establishing a mapping relationship between medium and low voltage sides. The positive-sequence voltage fault component on the medium-voltage side, obtained from the inversion calculation, is combined with line parameters to calculate the current fault component in each section. Based on its distribution characteristics, fault selection and section location criteria are proposed. Verification using a MATLAB simulation platform shows that this method can achieve accurate location under different transition resistances, and it does not require additional medium-voltage side measurement equipment, only low-voltage side TD-SFT measurement data, thus fully utilizing low-voltage data. This patented technology has significant engineering application value and broad industry application prospects. It not only provides a new technical means for distribution network fault location but also helps promote the efficient utilization of low-voltage monitoring data and improve the intelligent operation and maintenance level of the power grid. This achievement has positive significance for building a safe, reliable, and efficient new power system and provides practical technical support for achieving the "dual-carbon" goal.

[0021] Secondly, this invention proposes the core idea of ​​using low-voltage side data to solve medium-voltage side faults and establishes a medium- and low-voltage side voltage mapping model based on transformer turns ratio. This model only needs to input low-voltage side phase voltage data to calculate the corresponding medium-voltage side data, breaking through the limitation of traditional methods that rely on medium-voltage side measurement devices and realizing a methodological innovation of using low-voltage information to solve medium-voltage side problems.

[0022] Third, this invention does not require large-scale modification of primary equipment or the installation of numerous monitoring terminals. It utilizes widely distributed and easily monitored low-voltage side voltage information, significantly reducing data acquisition costs and system complexity. This reduces equipment investment and offers high economic and practical value. This invention analyzes the fault characteristics of successive grounding faults and proposes a corresponding fault location method, solving the problem that single-phase grounding fault protection devices cannot isolate two fault points. Through theoretical derivation and simulation verification, this invention can achieve accurate location under different transition resistances and load sizes, demonstrating the method's strong robustness and wide applicability. Attached Figure Description

[0023] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the disclosure of the invention and, together with the description, serve to explain the principles of this disclosure; Figure 1 This is a typical neutral-point ungrounded power distribution system topology diagram provided by the present invention; Figure 2 This is a flowchart of the successive fault location method based on load-side phase voltage provided by the present invention; Figure 3 The present invention provides a positive sequence equivalent network diagram of successive grounding faults; Figure 4 The present invention provides a negative sequence equivalent network diagram for successive grounding faults; Figure 5 The present invention provides a positive sequence network diagram considering the proper routing of circuits; Figure 6 The simulation model topology diagram provided by this invention; Figure 7 A diagram showing the magnitude of voltage changes at each node of a branch line provided by the present invention. Figure 8 The voltage variation amplitude diagram of each node of the main line of Line 2 provided by this invention Figure 9 A comparison chart of the inversion calculation results and simulation results of each node of a branch line provided by the present invention; Figure 10 A comparison chart of the inversion calculation results and simulation results of each node of the second main line provided by the present invention; Figure 11 The present invention provides a diagram showing the amplitude of the positive sequence current fault component in each section of the main line under different transition resistance conditions. Figure 12 The present invention provides a diagram showing the amplitude of the positive sequence current fault component in each section of the main line of Line 2 under different transition resistance conditions. Figure 13 The present invention provides a diagram showing the amplitude of the positive sequence current fault component in each section of the main line under different load conditions. Figure 14 The present invention provides a diagram showing the amplitude of the positive sequence current fault component in each section of the main line of Line 2 under different load conditions. Detailed Implementation

[0024] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0025] The innovation of this invention lies in the fact that it only utilizes existing low-voltage side equipment, without the need for additional medium-voltage side measuring devices, and the relatively dense distribution of intelligent fusion terminals on the low-voltage side can further narrow the fault range and achieve precise positioning.

[0026] Example 1.

[0027] The typical neutral-point ungrounded distribution system topology diagram (distribution network structure with ungrounded neutral point) involved in the successive fault location method based on load-side phase voltage provided in this embodiment of the invention is shown in the figure below. Figure 1As shown, all transformers in the distribution area are equipped with TD-SFT on their low-voltage side to monitor the load and distributed renewable energy sources within the distribution area in real time and upload relevant information to the main station of the information system. The transformers typically use the standard Dyn-11 connection method. The zero-sequence components of the transformer's medium-voltage and low-voltage sides are electrically isolated. The electrical quantities on the low-voltage side cannot reflect the information of the zero-sequence components on the medium-voltage side; therefore, it is only necessary to analyze the distribution characteristics of the positive-sequence and negative-sequence components.

[0028] For example, such as Figure 2 The successive fault location method based on load-side phase voltage provided in this embodiment of the invention converts low-voltage side measurement data into medium-voltage side electrical quantity information through inversion calculation, thereby achieving accurate judgment of fault sections.

[0029] S1. Establish a mapping model between the voltages on the low and medium voltage sides to complete the accurate inversion of electrical quantities from the low voltage side to the high voltage side. S2, combining the topology of the neutral point ungrounded distribution system and the equivalent parameters of the line, uses the voltage phasor of the medium voltage side obtained by inversion to calculate the positive sequence current fault component, and constructs an effective fault line selection and section location criterion based on the distribution characteristics of the positive sequence current fault component. S3, based on the MATLAB simulation platform, simulates and verifies the correctness of the inversion calculation results, the feasibility and accuracy under different transition resistances and different load sizes.

[0030] For example, in step S1, establishing a mapping model between the medium and low voltage sides (medium and low voltage side voltage mapping model) includes: The three phases on the medium-pressure side are designated A, B, and C, and the corresponding three phases on the low-pressure side are designated a, b, and c. Assuming that... Figure 1 The medium pressure side shown Dot and Ground faults occurred in phases B and C respectively, with transition resistances of respectively. and Taking phase A as the reference phase, the positive and negative sequence networks after the fault can be obtained as follows: Figure 3 Successive ground fault positive sequence equivalent network diagram and Figure 4 The equivalent network diagram of the negative sequence of successive grounding faults is shown below.

[0031] in, For the A-phase power supply of the system, and These are the positive-sequence and negative-sequence impedances of the system, respectively. They are respectively and Positive-sequence impedance and negative-sequence impedance between the busbar and the bus. They are respectively and The sum of the positive-sequence impedance and the sum of the negative-sequence impedance of the downstream line and load. These are the positive-sequence fault supplementary current sources and negative-sequence fault supplementary current sources at points 1 and 2, respectively. Since the fault current mainly flows along the fault path, when non-fault paths and current shunting to capacitors are ignored, the superposition theorem states that for the fault point... any previous node There are: ; In the formula, They are nodes The positive and negative sequence voltage components, for Phase A voltage during normal operation They are nodes Positive-sequence impedance and negative-sequence impedance to the busbar; Based on the definition of fault components, the node can be obtained. Positive sequence voltage fault component at the location With negative sequence voltage fault component The expression is: ; Similarly, for the fault point any previous node have: ; This invention innovatively proposes that, when load shunt is ignored and all transformers adopt the Dyn-11 connection method, the expression for the three-phase voltage on the low-voltage side of any node, including nodes on non-faulty lines, can be expressed as: ; In the formula, These are the nodes after the fault. Low-pressure side Phase voltage, Nodes during normal operation The low-voltage side voltage, For transformer turns ratio, Rotate the vector clockwise , It rotates counterclockwise. , It represents the imaginary part of a complex number.

[0032] This invention innovatively proposes a method to obtain arbitrary nodes on the medium-pressure side. The correspondence between the positive sequence voltage fault component and the low-voltage side phase voltage: ; A two-point ground fault with different phases is a series-to-series double fault, and the current sequence components at the two fault points satisfy the boundary conditions: ; In the formula, , indicates a clockwise rotation of 120 degrees.

[0033] Since the positive-sequence impedance and negative-sequence impedance of a line are generally considered to be equal, this invention innovatively proposes that, for fault points... any previous node At this point, according to the above formula, we can obtain: ; In the formula, It is a combination of current and impedance.

[0034] It is a combination of positive-sequence current fault component and line positive-sequence impedance, which varies with the node position; it is a combination of positive-sequence current fault component and system positive-sequence impedance, which does not vary with the node position; and it is a combination of negative-sequence current fault component and system negative-sequence impedance, which does not vary with the node position.

[0035] This invention innovatively proposes a method for addressing fault points. any previous node From the above formula, we can obtain: ; The innovative aspects of this invention are as follows: ; The above formula derives the fault component expressions for each node, establishes the mapping model for the medium and low voltage sides, performs complete feature analysis, and solves for the feature quantities.

[0036] For example, when a two-point ground fault of different phases occurs in the system, from equations (7) and (8), it can be seen that for a line with a B-phase ground fault on the medium-voltage side, the voltage change of phase c on the low-voltage side of each node before the fault point is only related to the system impedance and is not related to the impedance between the node and the bus. The voltage change amplitude of phase c at each node is the same. The voltage changes of phase a and phase b are related to the impedance between the node and the bus. The voltage changes of phase a and phase b at each node are different. For a line with a C-phase ground fault on the medium-voltage side, the voltage change of phase a on the low-voltage side of each node before the fault point is only related to the system impedance and is not related to the impedance between the node and the bus. The voltage change amplitude of phase a at each node is the same. The voltage changes of phase b and phase c are related to the impedance between the node and the bus. The voltage changes of phase b and phase c at each node are different. Similarly, if a faulty phase is phase A, the voltage changes of phase b on the low-voltage side of each node before the fault point are only related to the system impedance and not to the impedance between the node and the busbar; the magnitudes of the phase b voltage changes are the same at each node. The voltage changes of phases a and c are related to the impedance between the node and the busbar; the magnitudes of the phase a and phase c voltage changes are different at each node. For each healthy branch line and the line after the fault point, since the fault current is very small, the three-phase voltage changes at each node are approximately the same as those at the branch line connection point and the fault point, respectively. Based on these characteristics, the faulty phases at two fault points can be determined, enabling phase selection for successive faults.

[0037] For example, in step S2, combining the topology of the neutral-point ungrounded distribution system and the equivalent parameters of the lines, the positive-sequence current fault component is calculated using the inverted medium-voltage side voltage phasor. Based on the distribution characteristics of the positive-sequence current fault component, effective fault line selection and section location criteria are constructed, including: When considering the proper shunt routing of the line, the positive sequence fault supplementary network in the event of a two-point ground fault is as follows: Figure 5 The positive sequence network diagram is shown below when considering the proper routing of traffic.

[0038] For the system's positive-sequence admittance, They are respectively Positive-sequence admittance with the bus and total positive-sequence admittance downstream of the fault point. To improve the route Total positive sequence admittance of the line and load; any sound line Positive sequence current fault component at the outlet The expression is: ; In the formula, For any sound line and its total positive-sequence admittance for the load, There are two fault points respectively. The positive sequence current fault component at the location. The positive sequence admittance for Line 3 and the total load; Since the total admittance of any healthy line and its load is much smaller than the system admittance, therefore: ; In the formula, Each is an arbitrary line The amplitude of the positive sequence current fault component of fault line 1 and fault line 2. It can be seen that formulas (10) and (11) give the specific expressions for the positive sequence current fault component of the first segment of the line, and the criteria for fault line selection are analyzed. Therefore, by comparing the amplitude of the positive sequence current fault component at the outlet of each line, the two lines with the largest amplitude can be selected as the fault lines. After the fault line selection is completed, the changes in the three-phase voltage on the low-voltage side of each node before and after the fault are calculated. The phases with the same changes at each node are taken as characteristic phases. The correspondence between characteristic phases and fault phases is shown in Table 1. The fault phase can be determined based on the correspondence.

[0039] Table 1. Correspondence between characteristic phases and fault phases

[0040] After completing fault line and phase selection, the positive sequence current fault component of each section is calculated. The positive sequence voltage fault component of the corresponding node can be obtained using the low-voltage side phase voltage. It is easy to obtain the positive sequence voltage fault component of any two nodes. and The difference between the positive sequence voltage fault components can be calculated for any segment given the length of each segment and the impedance per unit length. Positive sequence current fault component: Get any two nodes and The difference between the positive sequence voltage fault components is used to determine the value of any segment given the length of each segment and the impedance per unit length. Positive sequence current fault component: ; In the formula, For any segment The positive sequence current fault component, For nodes and The difference between the positive sequence voltage fault components, For nodes and The positive sequence impedance between; Formula (12) is used to calculate the average value of the positive sequence current fault component of the entire section. The magnitudes of the positive sequence current fault components of each section before the fault point are approximately equal and much larger than those after the fault point. The magnitudes of the positive sequence current fault components of each section after the fault point are close to zero. The calculated value of the positive sequence current fault component of the fault section is between the two. This characteristic can be used to determine the fault section. That is, the equivalent average current of the section is calculated by combining the positive sequence voltage fault component calculated above with the line impedance, and the fault section is identified by its distribution characteristics.

[0041] An auxiliary section with a positive-sequence current fault component of 0 is added after the end sections of the main line and each branch line. First, the main line is judged to find the section where the positive-sequence current fault component is significantly greater than that downstream. If there is no branch line downstream of the section, this section is the fault section. If there is a branch line leading out downstream of the identified section, the above judgment process is repeated for the branch line, starting from the power source point and ending at the end node of the branch line, until there is no branch line leading out after the output identified section. This is then determined as the final fault section.

[0042] Example 2.

[0043] The successive fault location system based on load-side phase voltage provided in this embodiment of the invention includes: The mapping model establishment module is used to establish a mapping model between the voltages on the low and medium voltage sides, and to complete the accurate inversion of electrical quantities from the low voltage side to the high voltage side. The fault line selection and section location module is used to combine the topology of the neutral point ungrounded power distribution system and the equivalent parameters of the line, use the voltage phasor of the medium voltage side obtained by inversion to calculate the positive sequence current fault component, and construct an effective fault line selection and section location criterion based on the distribution characteristics of the positive sequence current fault component. The MATLAB simulation platform is used to simulate and verify the correctness of the inversion calculation results and the feasibility and accuracy under different transition resistances and different load sizes.

[0044] To verify the validity and reliability of this invention patent, a power distribution network simulation model was built using the MATLAB platform, as follows: Figure 6 The simulation model topology diagram is shown and is used to verify the accuracy of the mapping model and the correctness of the positioning method.

[0045] (1) Verification of the correctness and accuracy of the mapping model: Set up a metallic ground fault in phase B and phase C of the branch line section A(03-02)-A(03-03) of line 1 and the main line section B(04)-B(05) of line 2, respectively. The changes in the three-phase voltage on the low-voltage side of each node of the faulty branch line 1 and the faulty main line 2 are as follows: Figure 7 The voltage variation amplitude diagram of each node of a branch line provided by this invention and Figure 8The voltage variation amplitude diagram of each node of the main line of Line 2 provided by this invention is shown. The positive sequence voltage fault components of each node on the medium-voltage side of Line 1 and Line 2 are calculated based on the low-voltage side phase voltage. The calculation results are compared with the actual simulation results. Figure 9 A comparison diagram of the inversion calculation results and simulation results of each node of a branch line provided by this invention. Figure 10 A comparison chart of the inversion calculation results and simulation results of each node of the second main line provided by the present invention; (2) Validity Verification: To verify the effectiveness of the fault location method and analyze the influence of the transition resistance on the proposed fault location method, the fault sections were set as A(06)-A(07) and B(05)-B(06), with both fault points located in the middle of the sections. The transition resistance was set to 250Ω for both fault sections, 500Ω for both fault sections, and 0Ω and 1000Ω for both fault sections. The location results are as follows: Figure 11 The present invention provides a diagram showing the amplitude of the positive sequence current fault component in each section of the main line under different transition resistance conditions. Figure 12 The present invention provides a diagram showing the amplitude of the positive sequence current fault component in each section of the main line of Line 2 under different transition resistance conditions. Depend on Figures 11-12 It can be seen that the section positioning results are A(06)-A(07) and B(05)-B(06) under different transition resistances and different load sizes, and the positioning results are correct.

[0046] The section A(06)-A(07) and B(05)-B(06) are still set to have metallic grounding faults at 50% of their respective locations. The load values ​​are set to 100%, 50%, and 20% of the reference load, respectively. The characteristic current distribution at the 50% preset location is used as the section location result for display. The location result is as follows: Figure 13 The present invention provides amplitude diagrams of positive sequence current fault components in various sections of the main line under different load conditions. Figure 14 The present invention provides a diagram showing the amplitude of the positive sequence current fault component in each section of the main line of Line 2 under different load conditions.

[0047] Depend on Figures 13-14 It can be seen that the section location results under different load conditions are A(06)-A(07) and B(05)-B(06), which can also correctly identify the fault section.

[0048] The above experiments demonstrate that, taking the successive faults in different lines of an ungrounded system as an example, this invention uses the MATLAB platform to build a simulation model. Through simulation experiments, the accuracy of the mapping model and the correctness of the section location are verified, effectively solving the problem of locating successive grounding faults.

[0049] This invention proposes a method for locating successive grounding faults in a neutral-point ungrounded system, which solves the problem that traditional single-phase grounding fault protection methods cannot identify two fault points; This invention does not require additional medium-voltage side measurement equipment; it only needs to utilize existing transformer measurement data, thus reducing reliance on electrical quantity measurement units and lowering the operation and maintenance costs of the distribution network. This invention improves the reliability and economy of system operation, and provides a guarantee for the safe and efficient operation of the power distribution network.

[0050] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention and within the spirit and principles of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for locating successive faults based on load-side phase voltage, characterized in that, The method includes the following steps: S1. Establish a mapping model between the voltages on the low and medium voltage sides to complete the accurate inversion of electrical quantities from the low voltage side to the high voltage side. S2, combining the topology of the neutral point ungrounded distribution system and the equivalent parameters of the line, uses the voltage phasor of the medium voltage side obtained by inversion to calculate the positive sequence current fault component, and constructs an effective fault line selection and section location criterion based on the distribution characteristics of the positive sequence current fault component. S3, based on the MATLAB simulation platform, simulates and verifies the correctness of the inversion calculation results, the feasibility and accuracy under different transition resistances and different load sizes.

2. The successive fault location method based on load-side phase voltage according to claim 1, characterized in that, In step S1, establishing the mapping model between the medium and low voltage sides includes: The three phases on the medium-pressure side are designated as A, B, and C, and the corresponding three phases on the low-pressure side are designated as a, b, and c; on the medium-pressure side... Point and Ground faults occurred in phases B and C respectively, with transition resistances of respectively. and ; Select phase A as the reference phase to obtain the positive and negative sequence networks after the fault; in, For the A-phase power supply of the system, and These are the positive-sequence and negative-sequence impedances of the system, respectively. They are respectively and Positive-sequence impedance and negative-sequence impedance between the busbar and the bus. They are respectively and The sum of the positive-sequence impedance and the sum of the negative-sequence impedance of the downstream line and load. These are the positive-sequence fault supplementary current sources and negative-sequence fault supplementary current sources at points 1 and 2, respectively. When non-faulty paths and capacitor shunts are ignored, by the superposition theorem, for the fault point... any previous node There are: ； In the formula, They are nodes The positive and negative sequence voltage components. for Phase A voltage during normal operation They are nodes Positive-sequence impedance and negative-sequence impedance to the busbar; Based on the definition of fault components, the node is obtained. Positive sequence voltage fault component at the location With negative sequence voltage fault component The expression is: ； For the fault point any previous node have: ； When load shunt is ignored and all transformers use the Dyn-11 connection method, the expression for the three-phase voltage on the low-voltage side of any node, including nodes on non-faulty lines, is as follows: ； In the formula, These are the nodes after the fault. Low-pressure side Phase voltage, Nodes during normal operation The low-voltage side voltage, For transformer turns ratio, Rotate the vector clockwise , It rotates counterclockwise. , It represents the imaginary part of a complex number.

3. The successive fault location method based on load-side phase voltage according to claim 2, characterized in that, Any node on the medium-pressure side The correspondence between the positive-sequence voltage fault component and the low-voltage side phase voltage: ； A two-point ground fault with different phases is a series-to-series double fault, and the current sequence components at the two fault points satisfy the boundary conditions: ； In the formula, , indicates a clockwise rotation of 120 degrees.

4. The successive fault location method based on load-side phase voltage according to claim 3, characterized in that, The positive-sequence impedance and negative-sequence impedance of the line are equal, for the fault point any previous node Place, get: ； In the formula, It is a combination of current and impedance.

5. The successive fault location method based on load-side phase voltage according to claim 4, characterized in that, For the fault point any previous node Place, get: ； In the formula: 。 6. The successive fault location method based on load-side phase voltage according to claim 1, characterized in that, In step S2, the effective fault selection and section location criteria are constructed as follows: When considering a robust line shunt, a positive sequence fault additional network is required in the event of a two-point ground fault. For the system's positive-sequence admittance, They are respectively Positive-sequence admittance with the bus and total positive-sequence admittance downstream of the fault point. To improve the line Total positive sequence admittance of the line and load; any sound line Positive sequence current fault component at the outlet The expression is: ； In the formula, For any sound line and its total positive-sequence admittance for the load, There are two fault points respectively. The positive sequence current fault component at the location. The positive sequence admittance for Line 3 and the total load; Since the total admittance of any healthy line and its load is much smaller than the system admittance, therefore: ； In the formula, Each is an arbitrary line The amplitude of the positive sequence current fault component of fault line 1 and fault line 2. After completing fault line and phase selection, the positive sequence current fault component of each section is calculated. The positive sequence voltage fault component of the corresponding node is obtained using the low-voltage side phase voltage. This allows for the determination of any two nodes... and The difference between the positive sequence voltage fault components is used to determine the value of any segment given the length of each segment and the impedance per unit length. Positive sequence current fault component: ； In the formula, For any segment The positive sequence current fault component, For nodes and The difference between the positive sequence voltage fault components, For nodes and The positive sequence impedance between; An auxiliary section with a positive sequence current fault component of 0 is added after the end section of the main line and each branch line. First, the main line is judged to find the section where the positive sequence current fault component is significantly greater than that downstream. If there is no branch line downstream of the section, the section is the fault section. If there is a branch line leading out downstream of the positioning section, the above judgment process is repeated for the branch line with the power supply point as the starting point and the end node of the branch line as the ending point, until there is no branch line leading out after the output positioning section, which is determined as the final fault section.

7. A successive fault location system based on load-side phase voltage, characterized in that, The system is implemented using the successive fault location method based on load-side phase voltage as described in any one of claims 1-6. The system comprises: The mapping model establishment module is used to establish a mapping model between the voltages on the low and medium voltage sides, and to complete the accurate inversion of electrical quantities from the low voltage side to the high voltage side. The fault line selection and section location module is used to combine the topology of the neutral point ungrounded power distribution system and the equivalent parameters of the line, use the voltage phasor of the medium voltage side obtained by inversion to calculate the positive sequence current fault component, and construct an effective fault line selection and section location criterion based on the distribution characteristics of the positive sequence current fault component. The MATLAB simulation platform is used to simulate and verify the correctness of the inversion calculation results, the feasibility and accuracy under different transition resistances and different load sizes.

8. The successive fault location system based on load-side phase voltage according to claim 7, characterized in that, The load-side phase voltage-based successive fault location system is mounted on a computer device, which includes at least one processor, a memory, and a computer program stored in the memory and executable on the at least one processor. When the processor executes the computer program, it implements the functions of the load-side phase voltage-based successive fault location system.

9. The successive fault location system based on load-side phase voltage according to claim 7, characterized in that, The load-side phase voltage-based successive fault location system is mounted on a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, it can realize the functions of the load-side phase voltage-based successive fault location system.

10. The successive fault location system based on load-side phase voltage according to claim 7, characterized in that, The application of the load-side phase voltage-based successive fault location system in the successive fault location of load-side phase voltage in a 10kV medium-voltage distribution network.

Images