Fault diagnosis system and method for automatic power distribution network

Abstract

The invention discloses a fault diagnosis system and method for an automatic power distribution network, and relates to the technical field of power distribution network diagnosis, and the method comprises the steps: collecting electrical data, and calculating a bus zero-sequence voltage difference component and a feeder zero-sequence current; generating an event window based on the voltage difference component features; a residual zero-sequence current is obtained by fitting and stripping the capacitance component in the window; calculating a comprehensive score based on the ratio of the residual energy to the original energy so as to determine a fault feeder line; and further determining a fault section according to the score difference of adjacent measuring points along the fault feeder line. According to the invention, by stripping the capacitance response component, the problem of misjudgment caused by a first peak inversion phenomenon is effectively solved, and the accuracy of fault diagnosis is improved.

Description

Technical Field

[0001] This invention relates to the field of power distribution network diagnostic technology, and in particular to a fault diagnosis system and method for automated power distribution networks. Background Technology

[0002] Urban power distribution networks widely adopt underground cable ring network structures and mostly operate in low-current grounding mode. In such systems, single-phase grounding faults, especially intermittent arcing grounding faults, occur frequently. The arcing and extinguishing process during a fault causes a rapid change in the bus voltage to ground, which in turn drives the distributed capacitance of the cable line to ground to generate a charging and discharging displacement current. For power distribution systems with many outgoing lines and long cable lines, the capacitance effect to ground of non-faulty lines is significant. At the moment of voltage change, a large zero-sequence current spike may be generated, causing multiple lines to simultaneously exhibit a significant first spike component, or even the phenomenon that the first peak value of the zero-sequence current of non-faulty lines is greater than that of the faulty line, i.e., the first peak inversion phenomenon.

[0003] Existing fault diagnosis technologies for distribution networks typically rely on the magnitude of abrupt changes in the zero-sequence current amplitude or the polarity of the first half-wave as the basis for judgment. They generally use the logic of selecting and locating lines based on the maximum peak value or the largest abrupt change in the zero-sequence current. However, in the case of the inverted first peak, this judgment logic is easily affected by displacement current interference caused by the line-to-ground capacitance, which may misidentify non-faulty lines that generate the maximum zero-sequence current spike as faulty lines. This systematic misjudgment not only leads to a decrease in the accuracy of fault selection but also causes the fault location results to fluctuate between adjacent sections or result in location errors. This makes it difficult for maintenance personnel to quickly isolate the fault area and restore power supply, failing to meet the requirements of distribution automation systems for high reliability and accurate operation and maintenance. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing fault diagnosis systems in low-current grounding systems, where the inversion of the first peak of the zero-sequence current leads to misjudgments in traditional fault selection and location logic based on current amplitude or abrupt changes. This invention proposes a fault diagnosis system and method for automated power distribution networks.

[0005] To address the problems existing in the prior art, the present invention adopts the following technical solution: A fault diagnosis system for an automated power distribution network includes: The data construction module is used to collect the three-phase voltage of the distribution network bus and the three-phase current of each feeder, and to calculate the zero-sequence voltage differential component sequence of the bus and the zero-sequence current sequence of each feeder. The window generation module is used to generate a set of event windows based on the bus zero-sequence voltage difference component sequence; The residual calculation module is used to fit the zero-sequence current sequence of each feeder and the zero-sequence voltage difference component sequence of the bus in each event window in the event window set, so as to obtain the residual zero-sequence current sequence of each feeder in the corresponding event window. The fault selection module is used to calculate the comprehensive score of each feeder based on the residual zero-sequence current sequence and zero-sequence current sequence of each feeder in all event windows, and to identify the feeder with the highest comprehensive score as the faulty feeder. The section location module is used to acquire the automated measurement points on the faulty feeder line, calculate the comprehensive score of the automated measurement points, and determine the faulty section based on the difference in comprehensive scores between adjacent automated measurement points.

[0006] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention collects the zero-sequence voltage difference component of the bus and the zero-sequence current of the feeder, and uses the fitting relationship between the two to extract the capacitive current component driven by the rapid transition of the bus-to-ground voltage, thereby obtaining the residual zero-sequence current sequence that cannot be explained by the capacitive response; and constructs a comprehensive scoring mechanism based on the ratio of the residual total energy to the original total energy, which effectively suppresses the interference of the first peak inversion of the zero-sequence current caused by the significant ground capacitance effect of non-faulty feeders in underground cable ring networks, and ensures that when intermittent arc grounding faults occur, the faulty feeder can be accurately identified based on the residual energy ratio, avoiding the problem of misselection of feeders that may be caused by relying solely on the current amplitude or sudden change.

[0007] 2. This invention further applies a scoring mechanism based on residual energy proportion to automated measurement points along the faulty feeder. By calculating the comprehensive score difference between adjacent measurement points, the faulty section is determined. By utilizing the significant differentiation of residual characteristics of upstream and downstream measurement points after removing the capacitance component, quantitative evaluation of the faulty section is achieved. This overcomes the problem of fluctuating location results caused by the non-stationarity of the fault signal, thereby outputting stable and accurate section location results. This assists maintenance personnel in quickly isolating the faulty area and restoring power supply, meeting the high reliability maintenance requirements of the power distribution automation system. Attached Figure Description

[0008] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings: Figure 1 This is a functional block diagram of an automated power distribution network fault diagnosis system according to the present invention; Figure 2 This is a flowchart illustrating a fault diagnosis method for an automated power distribution network according to the present invention. Figure 3 This is a schematic diagram of fault location in the automated power distribution network of the present invention. Detailed Implementation

[0009] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0010] Example: This example provides a fault diagnosis system for an automated power distribution network. See [link to example]. Figure 1 Specifically, including: The data construction module is used to collect the three-phase voltage of the distribution network bus and the three-phase current of each feeder, and to calculate the zero-sequence voltage differential component sequence of the bus and the zero-sequence current sequence of each feeder. The window generation module is used to generate a set of event windows based on the bus zero-sequence voltage difference component sequence; The residual calculation module is used to fit the zero-sequence current sequence of each feeder and the zero-sequence voltage difference component sequence of the bus in each event window in the event window set, so as to obtain the residual zero-sequence current sequence of each feeder in the corresponding event window. The fault selection module is used to calculate the comprehensive score of each feeder based on the residual zero-sequence current sequence and zero-sequence current sequence of each feeder in all event windows, and to identify the feeder with the highest comprehensive score as the faulty feeder. The section location module is used to acquire the automated measurement points on the faulty feeder line, calculate the comprehensive score of the automated measurement points, and determine the faulty section based on the difference in comprehensive scores between adjacent automated measurement points.

[0011] In an embodiment of the present invention, the three-phase voltage of the distribution network bus and the three-phase current of each feeder are collected, and the zero-sequence voltage differential sequence of the bus and the zero-sequence current sequence of each feeder are calculated, including: In the low-current grounding distribution network of the urban underground cable ring network, the three-phase voltage of the distribution network bus and the three-phase current of each feeder are synchronously collected by the feeder terminal device in the distribution network. The collection frequency can be set to 10kHz to ensure that the instantaneous values ​​of the bus three-phase voltage and the instantaneous values ​​of the feeder three-phase current can be obtained synchronously at each sampling moment. During the collection process, the time scale of each sampling moment is kept consistent to avoid errors in subsequent calculations due to asynchronous sampling. The bus three-phase voltages are the bus A phase voltage, bus B phase voltage and bus C phase voltage. Each sampling moment is recorded in chronological order as the first sampling moment, the second sampling moment and so on up to the nth sampling moment.

[0012] For each sampling moment, the instantaneous values ​​of the bus phase A voltage, bus phase B voltage, and bus phase C voltage are collected. The three-phase voltages of the bus at that moment are summed and then divided by 3 to obtain the instantaneous value of the zero-sequence voltage at the corresponding sampling moment. The reason for using the method of summing the three-phase voltages and dividing by 3 is that in the distribution network, the zero-sequence voltage is essentially the unbalanced component of the three-phase voltage. When the three-phase voltages are symmetrical, the zero-sequence voltage is zero. Using the method of summing and averaging the three-phase voltages can accurately extract the instantaneous state of the bus zero-sequence voltage, which is consistent with the basic calculation principle of zero-sequence voltage in a low-current grounding system. At the same time, this calculation method is simple and reliable, and is convenient for real-time calculation in practical engineering applications. For the previous sampling moment adjacent to the t-th sampling moment, i.e., the (t-1)-th sampling moment, the same collection and calculation method as the t-th sampling moment is used to collect the instantaneous values ​​of the bus phase A voltage, bus phase B voltage, and bus phase C voltage at the (t-1)-th sampling moment, and calculate the instantaneous value of the previous zero-sequence voltage at the (t-1)-th sampling moment.

[0013] Subsequently, the difference between the instantaneous value of the zero-sequence voltage at sampling time t and the instantaneous value of the zero-sequence voltage at sampling time t-1 is calculated to obtain the bus zero-sequence voltage difference component at sampling time t. The difference is calculated by subtracting the instantaneous value of the zero-sequence voltage at the current time from that at the previous time because the bus zero-sequence voltage will change sharply when an intermittent arc grounding fault occurs in a low-current grounding system. This sharp change characteristic cannot be reflected by the instantaneous value of the zero-sequence voltage at a single moment. However, the difference between the instantaneous values ​​of the zero-sequence voltage at two adjacent sampling times can effectively capture this sharp change phenomenon, highlight the voltage change characteristics when the fault occurs, and provide a reliable data source for the generation of subsequent event window sets.

[0014] Following the same acquisition and calculation method described above, the bus zero-sequence voltage difference component corresponding to each sampling time from the 2nd sampling time to the nth sampling time is calculated sequentially. Since there is no instantaneous value of zero-sequence voltage from the previous sampling time at the 1st sampling time, the bus zero-sequence voltage difference component at that time is not calculated. Then, all the calculated bus zero-sequence voltage difference components are arranged sequentially according to the order of sampling time, that is, starting from the bus zero-sequence voltage difference component at the 2nd sampling time, and arranged sequentially up to the bus zero-sequence voltage difference component at the nth sampling time, thus forming a complete bus zero-sequence voltage difference component sequence. This sequence can continuously and completely reflect the change law of bus zero-sequence voltage difference component with sampling time, and completely preserve the time characteristics of the sudden change of zero-sequence voltage when the fault occurs. This provides continuous and reliable basic data support for the subsequent window generation module to identify local extreme points and sign-stable segments based on the bus zero-sequence voltage difference component sequence.

[0015] The zero-sequence current of any feeder in the distribution network can be obtained by summing the three-phase currents collected at each sampling time. The reason for using the summation of three-phase currents to calculate the zero-sequence current is that, according to the core definition of the zero-sequence component in the power system, in a three-phase AC distribution network, the zero-sequence current is essentially the algebraic sum of the three-phase currents. When the distribution network is operating normally, the three-phase currents are in a balanced state, and the sum of the three-phase currents is approximately zero, resulting in a very small zero-sequence current. However, when a single-phase ground fault occurs in the distribution network, the balance of the three-phase currents of the faulty feeder is broken, the sum of the three-phase currents is no longer zero, and it will exhibit a change pattern strongly correlated with the fault characteristics. Through this direct summation calculation method, the zero-sequence current component reflecting the feeder ground fault can be accurately extracted, effectively separating the positive and negative sequence components in the three-phase current, highlighting the abnormal current characteristics caused by the fault. At the same time, this calculation method is simple and efficient, without the need to introduce complex correction coefficients, and can meet the real-time calculation needs of distribution automation terminals, ensuring the timeliness of fault diagnosis.

[0016] For each feeder in the power distribution network, the zero-sequence current is calculated at each sampling time according to the same calculation formula and logic. After the zero-sequence current of the feeder is calculated at all sampling times, the zero-sequence currents of the feeder at each sampling time are arranged in order according to the sampling time to form the zero-sequence current sequence of the feeder. Each feeder corresponds to an independent zero-sequence current sequence. These zero-sequence current sequences can completely record the dynamic changes of the zero-sequence current of each feeder at different sampling times, clearly showing the response characteristics of the zero-sequence current of each feeder when a fault occurs. In particular, they can accurately capture the peak difference of the zero-sequence current of each feeder under the phenomenon of first peak inversion. The phenomenon of inverted first peak refers to the situation in underground cable ring network distribution networks with low current grounding where, during a single-phase grounding or intermittent arcing grounding event, the zero-sequence current of multiple feeders simultaneously exhibits a significant first peak component at the beginning of the same event. The feeder with the largest amplitude of this first peak is not necessarily the faulty feeder, but rather a healthy feeder with a larger equivalent capacitance to ground. The physical cause is that arcing or extinguishing during an arcing grounding event causes a rapid transition in the common component of the bus-to-ground voltage, thereby driving the distributed capacitance to ground of each feeder to generate a displacement current component. This displacement current component follows the natural law that the capacitance current is proportional to the rate of change of the voltage to ground. That is, for the same bus zero-sequence voltage change rate, the larger the equivalent capacitance to ground of the feeder, the larger the zero-sequence current peak generated by the charging and discharging of the capacitor. Therefore, a larger first peak of zero-sequence current is more likely to appear on healthy feeders with longer cables or more branches, leading to a systematic misjudgment of the traditional diagnostic logic of selecting and locating faults based on the largest first peak or the largest abrupt change in zero-sequence current.

[0017] It should be noted that the three-phase voltage of the distribution network bus refers to the three instantaneous voltage signals obtained by measuring the A-phase voltage, B-phase voltage, and C-phase voltage at the bus of the substation or switching station, respectively. These signals characterize the three-phase potential state and ground voltage state of the bus supplying power. The three-phase bus voltage is typically acquired by a voltage transformer and output as a voltage sequence that varies with the sampling time. Changes in the three-phase bus voltage can reflect ground voltage offsets and imbalances caused by faults such as single-phase grounding or arcing grounding. The three-phase current of each feeder refers to the current at its outgoing line of each feeder in the distribution network. At the switch or the beginning of the line, three instantaneous current signals are obtained by measuring the A-phase current, B-phase current, and C-phase current respectively. These signals are used to characterize the three-phase current flow state when the feeder supplies power to downstream loads and branches. The three-phase current of each feeder is usually collected by a current transformer and output as a current sequence that varies with the sampling time. Different feeders correspond to different feeder numbers. The changes in the three-phase current of each feeder can reflect the zero-sequence current component and capacitive displacement current component generated by the feeder in a fault event, providing a basic input for subsequent construction of feeder zero-sequence current sequence, residual zero-sequence current sequence, and comprehensive scoring.

[0018] It should be noted that the bus zero-sequence voltage difference component refers to the incremental value calculated based on the instantaneous values ​​of the bus zero-sequence voltage at adjacent sampling times. It is used to characterize the change amplitude of the common component of the bus-to-ground voltage at adjacent sampling times. The instantaneous value of the bus zero-sequence voltage is obtained by the arithmetic mean of the three-phase voltage of the bus. The bus zero-sequence voltage difference component is obtained by subtracting the instantaneous value of the bus zero-sequence voltage at the previous sampling time from the instantaneous value of the bus zero-sequence voltage at the current sampling time. The bus zero-sequence voltage difference component can highlight the rapid transition of the voltage to ground caused by arcing and extinguishing during arc grounding and suppress the slow drift background. Therefore, it serves as a key input for event window generation and capacitance component fitting and stripping. The zero-sequence current of each feeder refers to the zero-sequence component current formed by the three-phase currents of each feeder at a certain sampling time in the distribution network. It is used to characterize the magnitude of the common current component of the feeder in the three-phase-to-ground loop. The reason for using the summation of the three-phase currents to obtain the zero-sequence current of each feeder is that in the three-phase system, the zero-sequence component has the same amplitude in the three phases. Its synthesis in the phasor sense can be reflected by the superposition of the three phase-in-phase components. Moreover, when faults such as single-phase grounding or arc grounding occur, the displacement current generated by the charging and discharging of the cable to ground capacitance and the ground current introduced by the fault channel will be reflected in the feeder current in the form of zero sequence. Therefore, the zero-sequence current of each feeder is an important input quantity for characterizing the first peak inversion phenomenon and subsequent residual stripping and fault diagnosis.

[0019] In an embodiment of the present invention, an event window set is generated based on the bus zero-sequence voltage differential component sequence, including: After obtaining the bus zero-sequence voltage difference component sequence through synchronous acquisition and calculation, the local extreme points in the sequence are identified. During this identification process, the bus zero-sequence voltage difference component corresponding to each sampling time (excluding the first and last sampling times) is judged one by one. Specifically, the absolute value of the bus zero-sequence voltage difference component at the current sampling time must be greater than or equal to the absolute value of the bus zero-sequence voltage difference component at the previous sampling time, and simultaneously, the absolute value of the bus zero-sequence voltage difference component at the current sampling time must be greater than the absolute value of the bus zero-sequence voltage difference component at the next sampling time. The absolute value is used as the criterion because the local extreme point corresponds to the peak position of the sudden change in the zero-sequence voltage of the bus, which can accurately capture the instantaneous change characteristics of the zero-sequence voltage when an intermittent arc grounding fault occurs. In the actual identification process, for each intermediate sampling time in the sequence, the bus zero-sequence voltage difference component before and after the current time is extracted in sequence, the absolute values ​​of the three are calculated respectively, and then compared according to the above standard. The sampling time that meets the standard is the local extreme point. All sampling times that meet the standard together constitute the set of local extreme points of the bus zero-sequence voltage difference component sequence.

[0020] After identifying local extrema, the sign-stable segment of each local extrema is further determined. A sign-stable segment refers to a continuous sampling period in which the zero-sequence voltage difference component of the bus remains unchanged in sign. Its boundary is strictly defined as two adjacent zero-crossing points. A zero-crossing point is the sampling moment when the zero-sequence voltage difference component of the bus changes from positive to negative or from negative to positive; that is, the sampling moment when the product of the current sampling moment's zero-sequence voltage difference component and the previous sampling moment's zero-sequence voltage difference component is less than or equal to zero. When determining the sign-stable segment of each local extrema, it is necessary to use that local extrema as a reference point and then... The left boundary of the symbol-stable segment is determined by finding the nearest zero-crossing point to the extreme point on the left, and the right boundary is determined by finding the nearest zero-crossing point to the extreme point on the right. The continuous time period consisting of all sampling times between the left and right boundaries is the symbol-stable segment where the local extreme point is located. Zero-crossing points are used as the boundaries of the symbol-stable segment because they indicate a change in the sign of the zero-sequence voltage difference component of the bus. Each symbol-stable segment corresponds to a complete zero-sequence voltage steep change process, which can fully contain the instantaneous characteristic information of the fault and avoid mutual interference between the characteristics of different steep change events.

[0021] After determining the symbol stability segment where each local extremum point is located, each symbol stability segment is directly defined as a candidate event window. Since different local extremum points may be located within the same symbol stability segment, multiple candidate event windows may overlap, meaning that the sampling time ranges of two or more candidate event windows may intersect. In this case, it is necessary to perform overlap judgment and merging processing on all candidate event windows. The merging principle is to integrate all candidate event windows with overlapping parts into a unified event window. The left boundary of the merged event window is the leftmost boundary of all overlapping candidate event windows, and the right boundary is the rightmost boundary of all overlapping candidate event windows. For candidate event windows without overlapping parts, their original range remains unchanged, and no merging processing is performed. The reason for merging overlapping candidate event windows is that overlapping candidate event windows essentially correspond to the same zero-sequence voltage abrupt change event. Merging can avoid repeated analysis of the same fault event, reduce redundant calculations in subsequent residual calculations and feeder scoring, and ensure that each event window can completely cover all the characteristic information of a fault abrupt change.

[0022] After completing the overlap judgment and merging of all candidate event windows, the final event window set can be formed. Each event window in this event window set corresponds to an independent bus zero-sequence voltage abrupt change event, which can accurately capture the instantaneous characteristics when the fault occurs. This provides a reasonable and accurate time range for subsequent fitting calculations and residual calculations of the feeder zero-sequence current and bus zero-sequence voltage difference components in each event window, ensuring the accuracy and reliability of subsequent fault line selection and section location. Furthermore, it is completely based on the characteristics of the bus zero-sequence voltage difference component sequence itself for adaptive partitioning, adapting to the suddenness and non-stationarity characteristics of intermittent arc grounding faults, thus improving the system's adaptability.

[0023] In an embodiment of the present invention, within each event window of the event window set, the zero-sequence current sequence of each feeder and the bus zero-sequence voltage difference component sequence are fitted to obtain the residual zero-sequence current sequence of each feeder within the corresponding event window, including: After the window generation module outputs the event window set, the residual calculation module iterates through each event window in the event window set, and represents the event window with the set of sampling time indices contained in the event window, where any sampling time index within the event window is denoted as t. For the k-th feeder, the residual calculation module reads the zero-sequence current sequence of the feeder from the data construction module and extracts the zero-sequence current subsequence within the event window, denoted as t. Simultaneously, the bus zero-sequence voltage difference component sequence is read and the bus zero-sequence voltage difference component sub-sequence within the event window is extracted and denoted as... ,in This represents the instantaneous value of the zero-sequence current of the k-th feeder at sampling time t within the event window. This represents the bus zero-sequence voltage difference component at sampling time t within the event window; subsequently, for and Linear fitting is performed within the event window to obtain the fitted capacitive current component sequence. The linear fitting employs a single-coefficient proportional fit in the least squares sense, aiming to ensure that the capacitive current component sequence explains as much as possible the displacement current component driven by the rapid transition of the bus-to-ground voltage. Specifically, the fitting coefficients are calculated. To minimize the sum of squared errors within the event window And from this, we obtain the closed-form solution: ,in The fitting coefficients for the k-th feeder within the event window are used to characterize the capacitive response strength of the zero-sequence current of that feeder, which changes from the same source as the zero-sequence voltage difference component of the bus. This is the cumulative correlation between the zero-sequence current and the zero-sequence voltage difference components within the event window. This represents the accumulated energy of the zero-sequence voltage difference component within the event window. It is a non-zero correction value, and it is preferred to take one to avoid the denominator being zero when the bus zero-sequence voltage difference component is close to zero within the event window, which would lead to indeterminate fitting.

[0024] Based on the fitting coefficients, the residual calculation module generates a fitted sequence of capacitive current components for each sampling time t within the event window: ,in, This represents the instantaneous value of the capacitive current component of the k-th feeder at sampling time t within the event window. This component corresponds to the charging and discharging displacement current of the cable-to-ground distributed capacitance under the bus-to-ground voltage transition, conforming to the natural law that the capacitive current is proportional to the rate of voltage change. Therefore, it is used in conjunction with... Proportional linear fits have clear physical interpretability.

[0025] Finally, the difference between the feeder zero-sequence current and the capacitor current component is calculated for each sampling time within the event window to obtain the residual zero-sequence current sequence: ,in, This represents the instantaneous value of the residual zero-sequence current after the capacitor displacement current is stripped from the k-th feeder within the event window. This residual zero-sequence current sequence serves as the direct input for the subsequent fault selection module to calculate the comprehensive score, thus preventing the capacitor first peak of a healthy feeder from being mistakenly identified as evidence of a fault even when the first peak inversion phenomenon exists.

[0026] It should be noted that the capacitive current component refers to the displacement current component formed by the charging and discharging of the feeder cable's ground capacitance and the parallel branch's ground capacitance when the common component of the bus voltage to ground undergoes a rapid transition in a low-current grounded underground cable ring network. This component is positively correlated with the rate of change of the bus zero-sequence voltage, manifested as multiple feeder zero-sequence currents simultaneously exhibiting spikes at the beginning of a fault event, with the spike amplitude increasing as the feeder's equivalent capacitance to ground increases. Therefore, it mainly reflects the response of the line's capacitive structure to voltage transitions and does not necessarily point to the fault location. The residual zero-sequence current refers to the remaining zero-sequence current component after stripping the capacitive current component from the feeder zero-sequence current that can be explained by the bus zero-sequence voltage difference component. This residual component reflects more the ground conduction current introduced by the fault path and the non-stationary current component caused by arcing instability. Therefore, compared to the capacitive current component, it can better characterize the true contribution of the faulty feeder and faulty section and is used to suppress the misleading effect of the first peak inversion phenomenon on fault diagnosis.

[0027] In an embodiment of the present invention, based on the residual zero-sequence current sequence and the zero-sequence current sequence of each feeder within all event windows, a comprehensive score for each feeder is calculated, and the feeder with the highest comprehensive score is identified as the faulty feeder, including: After the residual calculation module outputs the residual zero-sequence current sequence of each feeder within each event window, the fault selection module performs a comprehensive scoring calculation for each feeder using feeder number k as an index. First, it obtains the event window set from the window generation module and represents it as a set composed of several window segments. The j-th event window is then denoted as... Where j is the event window number, which increments in the order of its creation. It consists of a set of sampling time indices, where any sampling time index is denoted as t and satisfies Read the k-th feeder in the event window The instantaneous value of the residual zero-sequence current within is denoted as Simultaneously read the k-th feeder in the event window. The instantaneous value of the zero-sequence current within is denoted as ,in This represents the instantaneous value of the remaining zero-sequence current of the k-th feeder after stripping the capacitive current component within the j-th event window. This represents the instantaneous value of the original zero-sequence current of the k-th feeder within the event window; subsequently, the residual zero-sequence current of the k-th feeder within all event windows is squared and accumulated to obtain the total residual energy. The formula for its calculation is: ,in This represents the cumulative zero-sequence current energy of the k-th feeder that cannot be explained by capacitive response across all event windows. The sum of squares is used to convert the alternating positive and negative instantaneous current into a non-negative metric and enhance sensitivity to peak amplitudes, making the abnormal components introduced by the fault path more prominent in terms of energy. Simultaneously, the original total energy is obtained by summing the squares of the original zero-sequence current of the k-th feeder across all event windows. Its calculation formula is ,in This represents the total zero-sequence current energy observed in the k-th feeder across all event windows, including the capacitive current component and the fault path component.

[0028] Finally, the ratio of the residual total energy to the original total energy is used as the feeder comprehensive score. Its calculation formula is ,in This represents the comprehensive score of the k-th feeder. Adding one to the denominator is used to avoid indeterminate ratios and ensure the score is calculable when the original total energy is very small or even zero in extreme cases. The ratio form is used to normalize the difference in the original zero-sequence current amplitude caused by the difference in the cable length and equivalent capacitance to ground of different feeders, so that the score focuses more on reflecting the proportion of the residual component in the original observation. This helps to suppress healthy feeders with large capacitance to ground from being mistakenly selected as faulty feeders due to the large original first peak when the first peak inversion phenomenon exists, and outputs the feeder with the highest comprehensive score as the faulty feeder.

[0029] It should be noted that the residual total energy refers to the cumulative amount obtained by squaring and summing the instantaneous values ​​of the residual zero-sequence current for the same feeder across all event windows. It is used to characterize the total zero-sequence current intensity of the feeder that cannot be explained by the capacitive current component in fault-related events. The residual zero-sequence current is the remaining zero-sequence current after removing the capacitive current component. The residual total energy is obtained by squaring and summing to transform the alternating positive and negative instantaneous current values ​​into a non-negative metric and enhance the sensitivity to peak amplitudes and continuous fluctuations. This makes the abnormal zero-sequence current component introduced by the fault channel more easily highlighted on the energy scale and facilitates the cumulative statistics across different event windows. The original total energy refers to the cumulative amount obtained by squaring and summing the instantaneous values ​​of the original zero-sequence current for the same feeder across all event windows. It is used to characterize the total intensity of the zero-sequence current observed in fault-related events for that feeder. The original zero-sequence current includes the capacitive current component formed by the charging and discharging of the feeder's equivalent capacitance to ground and the ground current component formed by the conduction of the fault channel. The original total energy is also obtained by squaring and summing to obtain an intensity characterization independent of the current direction and to provide a denominator benchmark for subsequent normalization scoring, thereby offsetting the differences in the original amplitude caused by differences in feeder length and equivalent capacitance to ground.

[0030] It should be noted that the comprehensive score of a feeder refers to the score obtained by comparing the total residual energy with the original total energy of the same feeder. It is used to quantify the proportion of the residual component in the zero-sequence current of the feeder and serves as a basis for fault selection. The higher the comprehensive score, the lower the proportion of the zero-sequence current that can be explained by the capacitor response and the higher the proportion of the zero-sequence current that cannot be explained by the capacitor response within the event window. Therefore, it is more likely to correspond to the abnormal zero-sequence current contribution introduced by the actual fault channel. The comprehensive score, through ratio normalization, can suppress the risk of misjudgment caused by the large first peak of the original zero-sequence current in the case of inverted first peak of healthy feeders with large equivalent capacitance to ground. It also makes the comparability between different feeders stronger.

[0031] In an embodiment of the present invention, automated measurement points on the faulty feeder line are acquired, and a comprehensive score for the automated measurement points is calculated. Based on the difference in comprehensive scores between adjacent automated measurement points, the faulty section is determined, including: After the fault location module outputs the faulty feeder, it first reads the electrical connection sequence of the faulty feeder from the topology configuration of the distribution automation master station or feeder terminal, and then obtains the set of automated measuring points sequentially deployed along the faulty feeder. The m-th automated measuring point is then denoted as... Where m is the measurement point number, increasing sequentially from the busbar side to the load side based on electrical connection order, and within the same event window set as the fault location, for each automated measurement point... The zero-sequence current sequence and its corresponding residual zero-sequence current sequence are used to calculate a comprehensive score. Specifically, the section positioning module reads the measurement points. The instantaneous value of the zero-sequence current at sampling time t is denoted as... Read the measurement points In the event window The instantaneous value of the residual zero-sequence current within is denoted as ,in Indicates the measuring point The original zero-sequence current, Indicates the measuring point The residual zero-sequence current after stripping the capacitive current component within the j-th event window, followed by measurements at the measurement points. The total residual energy is obtained by summing the squares of the residual zero-sequence currents across all event windows. and the measuring points The original total energy is obtained by squaring and summing the original zero-sequence currents within all event windows. The ratio of the residual total energy to the original total energy is then used as the measurement point. Overall rating Its calculation formula is ,in Indicates the measuring point The comprehensive score is calculated by adding one to the denominator to avoid the ratio being uncertain due to the extremely small original total energy and to ensure that the score can be calculated. The ratio form makes the score of the measurement point unaffected by the difference between the cable-to-ground equivalent capacitance and the measurement amplitude scale at different measurement points, and focuses more on reflecting the proportion of the residual component.

[0032] After completing the comprehensive scoring of all measuring points, the adjacent measuring points are compared according to the electrical connection sequence of the faulty feeder. and Calculate the section score of the line segment Its calculation formula is ,in The section score represents the line segment located between adjacent measuring points. Taking the absolute value ensures that the section score reflects only the magnitude of the difference in the overall score, unaffected by the direction of the difference. Furthermore, when the fault is located within a section between adjacent measuring points, the residual component introduced by the fault path, which cannot be explained by the capacitive response, will cause a more significant differentiation in the overall scores of the upstream and downstream measuring points of the fault point, thus affecting the corresponding... The larger the score, the higher the score. Finally, the section scores of all adjacent measuring points are compared and the highest score is selected. The line section between the adjacent measuring points with the highest section score is determined as the fault section. The identifiers of the upstream and downstream measuring points corresponding to the fault section and the section score are output for maintenance location and isolation recovery decision-making.

[0033] It should be noted that the topology configuration of the distribution automation master station or feeder terminal refers to the set of configuration data used to describe the electrical connection relationship between the bus and each feeder, as well as their sectionalizing switches and tie switches in the distribution network. The configuration data is used to clarify the electrical connection sequence of the faulty feeder from the bus side to the load side and the position identifier of each automation measuring point in the electrical connection sequence. The topology configuration may include the association relationship between feeder number and switch number, the correspondence between measuring point and line section, the upstream and downstream adjacency relationship of measuring point, and the switch status information related to the measuring point, so that the section positioning module can determine the adjacent automation measuring point pairs and the line section range between them based on the topology configuration and output the location of the faulty section.

[0034] It should be noted that automated measuring points refer to monitoring nodes deployed along the faulty feeder that have the ability to collect electrical parameters. They are used to provide zero-sequence current observation data corresponding to the line section in the distribution automation system. The automated measuring points can be set on both sides of the sectionalizing switch, at the incoming and outgoing ends of the ring main unit, near the feeder branch node or important cable joint, and their zero-sequence current sequence is collected and uploaded by the feeder terminal or local monitoring unit. The automated measuring points have unique identifiers in the topology configuration and are arranged in the order of electrical connection, so that the section location module can determine the line section where the fault occurs based on the scoring difference between adjacent measuring points.

[0035] It should be noted that the section score is a numerical indicator used to quantify the degree of anomaly in a line section between two adjacent automated measuring points. It is calculated from the difference in the comprehensive scores of two adjacent automated measuring points. Specifically, it is the result of taking the absolute value of the difference in the comprehensive scores of adjacent measuring points. The larger the section score, the more significant the difference in the proportion of residual components between the upstream and downstream measuring points of the line section. This reflects that the section is more likely to contain the contribution of zero-sequence current introduced by the fault channel that cannot be explained by the capacitive response. Therefore, the section score can be used as a basis for judging faulty sections and for comparing and ranking multiple candidate sections.

[0036] like Figure 2 The diagram shown is a flowchart illustrating a fault diagnosis method for an automated power distribution network according to an embodiment of the present invention.

[0037] In this embodiment, the steps of the fault diagnosis method for an automated power distribution network are as follows: S1. Collect the three-phase voltage of the power distribution network bus and the three-phase current of each feeder, and calculate the zero-sequence voltage differential sequence of the bus and the zero-sequence current sequence of each feeder. S2. Generate an event window set based on the bus zero-sequence voltage differential component sequence; S3. Within each event window in the event window set, fit the zero-sequence current sequence of each feeder with the zero-sequence voltage difference component sequence of the bus to obtain the residual zero-sequence current sequence of each feeder in the corresponding event window. S4. Based on the residual zero-sequence current sequence and zero-sequence current sequence of each feeder in all event windows, calculate the comprehensive score of each feeder and determine the feeder with the highest comprehensive score as the faulty feeder. S5. Obtain the automated measurement points on the faulty feeder line and calculate the comprehensive score of the automated measurement points. Based on the difference in comprehensive scores between adjacent automated measurement points, determine the faulty section.

[0038] like Figure 3As shown, a fault feeder is led downstream from the busbar of the power distribution network. Automated measuring points P1, P2, and P3 are sequentially installed along the electrical connection sequence on the fault feeder. A ground fault point exists between P2 and P3 on the fault feeder. The system collects zero-sequence current at each automated measuring point and performs linear fitting on the zero-sequence current based on the busbar zero-sequence voltage difference component to obtain the capacitive current component. The residual zero-sequence current is obtained by calculating the difference between the zero-sequence current and the capacitive current component. Then, within each measuring point, a comprehensive score is calculated based on the ratio of the residual total energy of the residual zero-sequence current to the original total energy of the zero-sequence current. Measuring points P1 and P2 have a higher proportion of residual zero-sequence current energy, corresponding to high comprehensive scores F1 and F2, respectively. Measuring point P3 has a lower proportion of residual zero-sequence current energy, corresponding to a low comprehensive score F3. Finally, the absolute value of the difference in comprehensive scores between adjacent measuring points is taken as the segment score, forming the segment score for segment P1 to P2. Furthermore, the segment scores are relatively small, as are the segment scores from P2 to P3. Furthermore, the section with the highest score is identified as the faulty section, thus allowing for the location of the faulty section.

[0039] 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 equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A fault diagnosis system for an automated power distribution network, characterized in that, include: The data construction module is used to collect the three-phase voltage of the distribution network bus and the three-phase current of each feeder, and to calculate the zero-sequence voltage differential component sequence of the bus and the zero-sequence current sequence of each feeder. The window generation module is used to generate a set of event windows based on the bus zero-sequence voltage difference component sequence; The residual calculation module is used to fit the zero-sequence current sequence of each feeder and the zero-sequence voltage difference component sequence of the bus in each event window in the event window set, so as to obtain the residual zero-sequence current sequence of each feeder in the corresponding event window. The fault selection module is used to calculate the comprehensive score of each feeder based on the residual zero-sequence current sequence and zero-sequence current sequence of each feeder in all event windows, and to identify the feeder with the highest comprehensive score as the faulty feeder. The section location module is used to acquire the automated measurement points on the faulty feeder line, calculate the comprehensive score of the automated measurement points, and determine the faulty section based on the difference in comprehensive scores between adjacent automated measurement points.

2. The fault diagnosis system for an automated power distribution network according to claim 1, characterized in that, Calculate the zero-sequence voltage difference component of the bus and the zero-sequence current of each feeder, including: The current zero-sequence voltage instantaneous value is obtained by summing and averaging the three-phase bus voltages at the current moment, and the previous zero-sequence voltage instantaneous value is obtained by summing and averaging the three-phase bus voltages at the previous moment. The bus zero-sequence voltage difference component at the current moment is obtained based on the difference between the current instantaneous value of the zero-sequence voltage and the previous instantaneous value of the zero-sequence voltage. Based on the bus zero-sequence voltage difference components at each sampling time, a bus zero-sequence voltage difference component sequence is formed; The zero-sequence current of each feeder is obtained by summing the three-phase currents of each feeder. Based on the zero-sequence current of each feeder at each sampling time, a zero-sequence current sequence for each feeder is formed.

3. The fault diagnosis system for an automated power distribution network according to claim 1, characterized in that, The event window set is generated based on the bus zero-sequence voltage differential component, including: Identify local extreme points in the bus zero-sequence voltage difference component sequence, wherein the local extreme point is a point whose absolute value is greater than or equal to the previous moment and greater than the next moment; Determine the sign-stable segment where each local extremum point is located, with the two adjacent zero-crossing points as boundaries; Each symbol-stable segment is defined as a candidate event window, and overlapping candidate event windows are merged to form an event window set.

4. The fault diagnosis system for an automated power distribution network according to claim 1, characterized in that, Within each event window in the event window set, the zero-sequence current sequence of each feeder is fitted to the bus zero-sequence voltage difference component sequence, including: For each event window in the event window set, the zero-sequence current sequence of each feeder is linearly fitted with the bus zero-sequence voltage difference component sequence within that event window to obtain a fitted capacitor current component sequence. The residual zero-sequence current sequence within the event window is obtained based on the difference between the zero-sequence current sequence of the feeder and the capacitor current component sequence.

5. The fault diagnosis system for an automated power distribution network according to claim 1, characterized in that, Calculate the overall score for each feeder, including: The sum of squares of the residual zero-sequence current sequences of each feeder within all event windows is calculated as the total residual energy. Calculate the sum of squares of the zero-sequence current sequence for each feeder within all event windows, and use it as the original total energy; The ratio of the residual total energy to the original total energy is used as the comprehensive score for the corresponding feeder.

6. The fault diagnosis system for an automated power distribution network according to claim 1, characterized in that, The calculation of the comprehensive score of the automated measuring point is the same as the calculation of the comprehensive score of the feeder, the difference being that the input is the zero-sequence current sequence of the automated measuring point and the corresponding residual zero-sequence current sequence.

7. The fault diagnosis system for an automated power distribution network according to claim 1, characterized in that, Based on the differences in comprehensive scores between adjacent automated measurement points, the faulty sections are determined, including: Based on the electrical connection sequence of the faulty feeder, calculate the absolute value of the difference between the comprehensive scores of two adjacent automated measuring points, and use it as the section score of the line section between adjacent measuring points; Compare the segment scores of all line segments and identify the line segment with the highest segment score as the faulty segment.

8. A fault diagnosis method for an automated power distribution network, characterized in that, The method includes: S1. Collect the three-phase voltage of the power distribution network bus and the three-phase current of each feeder, and calculate the zero-sequence voltage differential sequence of the bus and the zero-sequence current sequence of each feeder. S2. Generate an event window set based on the bus zero-sequence voltage differential component sequence; S3. Within each event window in the event window set, fit the zero-sequence current sequence of each feeder with the zero-sequence voltage difference component sequence of the bus to obtain the residual zero-sequence current sequence of each feeder in the corresponding event window. S4. Based on the residual zero-sequence current sequence and zero-sequence current sequence of each feeder in all event windows, calculate the comprehensive score of each feeder and determine the feeder with the highest comprehensive score as the faulty feeder. S5. Obtain the automated measurement points on the faulty feeder line and calculate the comprehensive score of the automated measurement points. Based on the difference in comprehensive scores between adjacent automated measurement points, determine the faulty section.

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