A power system accurate fault research and judgment method and system

Abstract

The present application relates to the technical field of power system protection, in particular to a kind of power system accurate fault research and judgment method and system, method includes: after receiving comprehensive intelligent alarm signal, distinguish real fault and false alarm signal, then through multidimensional feature analysis, accurate identification of line fault, main transformer fault and bus fault is realized, finally line fault, main transformer fault and bus fault are differentially handled.The intelligent classification research and judgment mechanism based on fault feature difference of the present application not only breaks through the limitations of traditional single research and judgment mode, and through various fault handling strategies, the research and judgment accuracy and efficiency are significantly improved, which provides core technical support for building a new generation of intelligent power grid fault defense system.The present application has strong practicability, and can effectively meet the urgent needs of modern power system for rapid and accurate disposal of faults.

Description

Technical Field

[0001] This invention relates to the field of power system protection technology, specifically to a method and system for accurate fault diagnosis in power systems. Background Technology

[0002] With the expansion of power grid scale and the improvement of intelligence level, power system fault diagnosis faces new challenges. Traditional fault assessment methods have the following limitations: over-reliance on a single protection criterion makes it difficult to accurately identify complex faults; the functions of protection devices and waveform recording systems are disconnected, making it impossible to achieve collaborative analysis of real-time data and historical waveforms; fault feature extraction is insufficient, and there is a lack of multi-source data fusion capabilities; the assessment process has time delays, making it difficult to meet the rapid response requirements of smart grids.

[0003] In summary, existing data technologies in power systems cannot guarantee the comprehensive extraction and real-time analysis of fault characteristics, and there is still a lack of effective solutions to meet the needs of smart grids for rapid and accurate fault location. Summary of the Invention

[0004] To address the technical problem of the contradiction between accuracy and real-time performance in existing technologies, this invention provides the following solution:

[0005] A method for accurate fault assessment in power systems includes the following steps: receiving a comprehensive intelligent alarm signal and determining whether it is a real fault signal; if it is a real fault signal, identifying the fault type as a line fault, main transformer fault, or bus fault based on the protection action type and electrical quantity characteristics; when the fault type is a line fault, further determining whether the line type is a closed-loop operation line, a charging operation line, or an electric railway line, and performing in-zone / out-zone fault assessment based on the line type: if it is an electric railway line, determining whether the fault is located within or outside the protection zone by judging whether the three-phase current triggers the current change quantity element; if it is a charging operation line, determining whether the fault is located within or outside the protection zone based on the judgment result of the directional element; if it is a closed-loop operation line, determining whether the fault is located within or outside the protection zone by analyzing single-sided or double-sided waveform data and using directional elements or differential elements.

[0006] Furthermore, the system receives integrated intelligent alarm signals and determines whether they are genuine fault signals, including: determining whether a genuine fault signal is a signal by detecting whether there is a zero current segment in the waveform.

[0007] Furthermore, if it is an electric railway line, the location of the fault within or outside the protection zone is determined by whether the three-phase current triggers the current change measurement element. This includes: if the three-phase current triggers the current change measurement element, it is determined to be an internal fault, and the triggering phase is identified as the faulty phase; if the zero-sequence current triggers the current change measurement element, it is determined to be a ground fault; if the faulty phase involves two or more phases, it is determined to be a phase-to-phase fault; if none of the three-phase currents trigger the current change measurement element, it is determined to be an external fault.

[0008] Furthermore, if it is a charging operation line, the fault location is determined to be within or outside the protection zone based on the judgment result of the directional element. This includes: if it is a charging operation line, calculating the zero-sequence directional element and the power frequency change directional element, and then, based on the judgment result of the zero-sequence directional element and the power frequency change directional element, if the power direction is displayed as the bus pointing to the line, it is determined to be a fault within the zone; otherwise, it is determined to be a fault outside the zone.

[0009] Furthermore, if it is a closed-loop operation line, by analyzing single-sided or double-sided waveform data, directional elements or differential elements are used to determine whether the fault is located inside or outside the protection zone. This includes: performing waveform scanning on the fault waveform data, identifying and describing the fault characteristics of the waveform; distinguishing whether it is a line break fault or a short circuit fault based on the fault characteristics; if it is a short circuit fault, judging whether it is an inside / outside fault based on the transmission status of the fault waveform data; wherein the fault characteristics include, but are not limited to: abrupt change point, maximum fault current point, clearing point, reclosing point, abrupt change point after reclosing, maximum fault current point after reclosing, and clearing point after reclosing.

[0010] Furthermore, if it is a short-circuit fault, the fault determination (whether it is inside or outside the zone) is based on the transmission of fault recording data, including:

[0011] If the fault recording data on both sides of the closed loop line is not sent up, the judgment result requiring manual processing will be output.

[0012] If only waveform data from one station is uploaded, the fault diagnosis should be performed as follows:

[0013] For the side where the waveform data is sent, if the CT on that side has been checked, the single-sided directional element is used for judgment: if the analysis result of the single-sided directional element shows reverse movement, it is judged as an external fault; if it shows positive movement, it is judged as a suspected internal fault.

[0014] If the CT on that side is not calibrated, the polarity of the CT is calibrated by comparing the calculated active power of the steady-state section with the real-time power flow. If the calibration is successful, the calculation of the directional element on one side is performed. If the power direction on that side is from the bus to the line and only the line corresponding to that side is faulty within 5 minutes, it is judged as a suspected fault in the area. Otherwise, the judgment result requiring manual processing is output.

[0015] Furthermore, if it is a short-circuit fault, the fault determination (whether it is inside or outside the zone) is based on the transmission of fault recording data, including:

[0016] If fault waveform data from both sides are uploaded, the fault assessment shall be performed as follows:

[0017] If both CT scans have been calibrated, then the differential element and the two-sided directional element are used for accurate judgment: the action of the differential element is the standard. If the differential element is activated, it is judged as an in-zone fault; otherwise, it is judged as an out-of-zone fault.

[0018] If one side of the CT has been checked while the other side has not, then try to check the polarity of the CT on the unchecked side; if the check is successful, then make a judgment as described above for the case where "both sides of the CT have been checked"; otherwise, calculate the directional element information of the checked side. If the power direction of the checked side is from the bus to the line, and the difference in current amplitude at the fault points on both sides is less than 15% or only the line corresponding to the checked side has a fault within 5 minutes, then it is determined to be a suspected fault within the zone.

[0019] If neither CT on either side is checked, then attempt to check the polarity of both CTs; if one side is successfully checked, then proceed with the judgment as described above for the case where "CT has been checked on one side, but not on the other side"; if neither side can be checked, then further judgment is made: if the difference in current amplitude between the two sides is less than 15%, then it is judged as a suspected fault within the zone; if there is only a line fault between the two sides within 5 minutes, then it is judged as a suspected fault within the zone; if neither of the above conditions are met, then a judgment result requiring manual processing is output.

[0020] Furthermore, when the fault type is a main transformer fault, it also includes:

[0021] Based on the algorithms of the directional and differential elements, the differential current value and braking current value of the main transformer are calculated, and based on the preset ratio differential action characteristic curve, the fault area is initially identified as being within or outside the protection zone.

[0022] Determine the consistency between the actual installation location of the CT winding connected to the fault recorder on the high-voltage side of the main transformer and the protection range of the main transformer.

[0023] If the CT winding position is consistent with the protection range of the main transformer, then a final judgment is made based on the preliminary identification results;

[0024] If the location of the CT winding is inconsistent with the protection range of the main transformer, the preliminary identification result is corrected: if the preliminary identification result is an in-zone fault, it is corrected to an in-zone fault; if the preliminary identification result is an out-of-zone fault and the high-voltage side CT winding is located on the line side, it is further corrected to an out-of-zone fault or a suspected in-zone fault by judging whether the fault phase voltage is greater than the rated voltage threshold.

[0025] Furthermore, when the fault type is a bus fault, it also includes:

[0026] Based on the algorithms of directional and differential elements, as well as fault recording data, the differential current value and braking current value of the bus are calculated, and the fault area is initially identified according to the preset ratio differential action characteristic curve.

[0027] Based on the operation of the bus differential and the tripped bus differential, or based on the situation where the bus differential does not operate but there is an interval fault and the fault duration exceeds the time threshold, the fault or circuit breaker failure within the bus zone is further judged.

[0028] Determine the consistency between the actual installation position of the CT winding connected to each branch fault recorder and the bus protection range; if the CT winding position is consistent with the bus protection range, then make a final judgment based on the preliminary identification results.

[0029] If the location of the CT winding is inconsistent with the bus protection range, a correction judgment shall be made based on the preliminary identification results:

[0030] If the initial identification result is a fault within the zone, then the determination is corrected to a fault within the busbar zone;

[0031] If the initial identification result is an external fault, the determination is further revised to an external fault or a suspected internal fault by judging whether the voltage of the faulty phase on the bus is greater than the rated voltage threshold.

[0032] The present invention also provides a power system accurate fault assessment system, including a processor and a memory, wherein the memory stores a computer program, and the processor executes the computer program to implement the above-mentioned power system accurate fault assessment method.

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] This invention first performs preliminary screening based on current waveform characteristics, and then combines this with a comprehensive judgment based on multiple dimensions of electrical quantities such as voltage and power. By establishing a multi-level verification process, it effectively reduces the risk of malfunctions caused by interference signals. Tests show that this method significantly improves the identification accuracy in typical fault scenarios compared to traditional single-criteria methods, especially demonstrating better stability in distinguishing between real faults and false alarms.

[0035] This invention innovatively employs a hierarchical processing strategy and intelligent feature matching technology. The system first rapidly determines the direction of fault analysis based on protection action signals and changes in basic electrical quantities, and then applies corresponding in-depth analysis strategies for different types of faults. This layered and progressive analysis architecture ensures both rapid response to critical faults and accurate analysis of complex faults. While maintaining the quality of analysis, this invention significantly improves overall processing time compared to traditional serial processing modes, better meeting the needs of modern power grids for rapid fault handling.

[0036] The system's adaptability has been comprehensively enhanced: Differentiated judgment strategies have been designed for different types of lines (loop operation, charging operation, electric railway lines, etc.) and power equipment (busbars, main transformers, etc.), and precise analysis has been carried out based on the ratio differential action characteristic curve, which has significantly improved the system's adaptability to various complex fault scenarios.

[0037] In summary, this invention aims to address the problems of insufficient accuracy and slow response speed in fault assessment in existing technologies. First, after receiving comprehensive intelligent alarm signals, the system performs preliminary screening using waveform scanning technology, effectively distinguishing between real faults and false alarms, significantly improving the reliability of fault identification. Second, through multi-dimensional feature analysis, the system achieves accurate identification and differentiated processing of line faults, main transformer faults, and bus faults. This intelligent classification and assessment mechanism based on fault characteristic differences not only overcomes the limitations of traditional single assessment modes but also significantly improves assessment accuracy and efficiency through various fault handling strategies, providing core technical support for building a new generation of smart grid fault defense systems. This invention is highly practical and can effectively meet the urgent needs of modern power systems for rapid and accurate fault handling. Attached Figure Description

[0038] Figure 1 This is a schematic flowchart illustrating a method for accurate fault assessment of a power system according to an embodiment of the present invention;

[0039] Figure 2 This is a schematic flowchart illustrating a method for judging faults in electric railway lines according to an embodiment of the present invention;

[0040] Figure 3 This is a schematic flowchart illustrating a method for judging faults in a charging operation line according to an embodiment of the present invention;

[0041] Figure 4 This is a schematic flowchart illustrating the fault assessment method for closed-loop operation lines according to an embodiment of the present invention;

[0042] Figure 5 This is a schematic flowchart illustrating a main transformer fault assessment method according to an embodiment of the present invention;

[0043] Figure 6This is a schematic flowchart illustrating a bus fault assessment method according to an embodiment of the present invention. Detailed Implementation

[0044] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0045] A method for accurate fault diagnosis in power systems, such as Figure 1 As shown, it includes the following steps:

[0046] S1. Receive integrated intelligent alarm signals and determine whether they are genuine fault signals.

[0047] Specifically, upon receiving a comprehensive intelligent alarm signal, the system first performs a waveform scan to determine if it is a false alarm. If it is a genuine tripping fault, there will definitely be a segment in the waveform where the current drops to zero. Otherwise, it is a false tripping signal caused by interference, hardware failure, software defects, or other reasons, where no actual fault has occurred and the circuit breaker has not tripped.

[0048] In other embodiments, in addition to detecting whether there is a zero current segment in the waveform, it is also possible to determine whether it is a real fault signal by relying on circuit breaker position signals, protection action reports, real-time electrical quantity changes, adjacent protection action status, and SCADA system data; of course, it is also possible to make a judgment by combining these information.

[0049] S2. If it is a real fault signal, the fault type will be identified as a line fault, main transformer fault or bus fault based on the protection action type and electrical quantity characteristics.

[0050] Specifically, the identification of electric railway lines is as follows: Lines with the keyword "traction station" in their station names are all electric railway lines. The identification of charging operation lines is as follows: For lines where the voltage leads the current by 90 degrees, the status of the switch on the opposite side of the line is read in real time. If it is in the open position, then the line is a charging operation line. The identification of closed-loop operation lines is as follows: If it is neither an electric railway line nor a charging operation line, then it is a closed-loop operation line.

[0051] In this context, "loop-connected lines" typically refer to a segment of a power distribution or transmission network that operates in a closed-loop topology. "Charging lines" refer to power distribution lines that provide electricity to charging facilities for large electric vehicles (such as electric bus charging stations and electric vehicle charging pile clusters). "Electric rail lines" refer to dedicated power supply lines that provide traction power to rail transit systems (including railways, subways, light rail, and trams).

[0052] S3. When the fault type is a line fault, further determine whether the line belongs to a closed-loop operation line, a charging operation line, or an electric railway line, and perform intra-area / extra-area fault assessment according to the line type:

[0053] If it is an electric railway line, the location of the fault can be determined by whether the three-phase current triggers the current change measurement element;

[0054] If it is a charging operation line, the fault location is determined to be inside or outside the protection zone based on the judgment result of the directional element.

[0055] If it is a closed-loop line, by analyzing the single-sided or double-sided waveform data, directional elements or differential elements are used to determine whether the fault is located inside or outside the protection zone.

[0056] In one embodiment, if it is an electric railway line, the location of the fault within or outside the protection zone is determined by judging whether the three-phase current triggers the current change measurement element. This includes: if it is an electric railway line, if the three-phase current triggers the current change measurement element, it is determined to be an internal fault, and the triggering phase is identified as the fault phase; if the zero-sequence current triggers the current change measurement element, it is determined to be a ground fault; otherwise, if the fault phase involves two or more phases, it is determined to be a phase-to-phase fault; if none of the three-phase currents trigger the current change measurement element, it is determined to be an external fault.

[0057] Specifically, such as Figure 2 As shown, it includes:

[0058] First, analyze whether the current in each phase of the line reached the preset operating threshold of the current change quantity element during the time when the alarm signal occurred and the time period before and after it. The current change quantity element is specifically used to detect rapid changes in current.

[0059] If a three-phase current triggers the current change indicator, it is determined to be a fault within the protection zone. In this case, the drastic change in current indicates a short-circuit fault has occurred within the line itself or its protected zone. Simultaneously, the phase that triggered the current change indicator is identified as the fault phase. If multiple phases are triggered, all triggered phases are considered fault phases.

[0060] After identifying the faulty phase, further determine whether the zero-sequence current triggers the current change indicator. If the zero-sequence current also exhibits a significant abrupt change and reaches its activation threshold, it indicates that the fault involves a ground path and is classified as a ground fault, such as single-phase grounding or two-phase grounding. If the zero-sequence current does not trigger the current change indicator, and the faulty phase involves two or more phases, it is classified as a phase-to-phase short-circuit fault, meaning the fault does not involve a ground path. If none of the three-phase currents trigger the current change indicator, it is classified as an external fault.

[0061] In this situation, the three-phase current of the line does not experience a drastic change sufficient to trigger a sudden change in the current change element, indicating that the fault did not occur within the protection zone of the current protection device, but rather in an area outside the protection zone, such as a fault on an adjacent line, busbar, or other equipment. Although the protection device may issue an alarm for other reasons, analysis based on the current change element can rule out a short-circuit fault within the protection zone of this line.

[0062] Through the above steps, faults on electric railway lines can be accurately located within / outside the designated area, and the phase and type of the fault can be further refined, providing crucial information for subsequent fault handling and system restoration.

[0063] In one embodiment, if it is a charging operation line, the fault is determined to be located inside or outside the protection zone based on the judgment result of the directional element. This includes: if it is a charging operation line, calculating the zero-sequence directional element and the power frequency change directional element, and then, based on the judgment result of the directional element, if the power direction is displayed as the bus pointing to the line, it is determined to be an internal fault; otherwise, it is determined to be an external fault.

[0064] In another embodiment, the fault can be confirmed first, including: if it is a charging line, after performing CT polarity verification based on the line characteristic of voltage leading current by 90 degrees, the fault feature scan is used to determine whether there is a sudden change point to confirm the fault. Here, current transformers are usually simply referred to as CTs in the power industry.

[0065] When a charging line is operating normally and without faults, it typically connects to a large number of power electronic conversion devices, such as chargers. These devices exhibit specific electrical quantity characteristics during operation. Under certain operating modes or simplified models, due to the inductive or capacitive characteristics of the charging load, there may be a certain phase relationship between the voltage and current at the connection point. The 90-degree voltage-current lead here should be understood as the phase characteristic of the line voltage relative to the current under normal operation or a specific equivalent model. This can serve as a basis for verifying the line condition.

[0066] Specifically, such as Figure 3 As shown, it includes:

[0067] Since correct CT polarity is fundamental for relay protection devices to accurately determine fault direction and calculate differential current, this verification process aims to ensure that the acquired current signal correctly reflects the actual power flow direction and fault characteristics, providing reliable data for subsequent fault analysis. In other embodiments, other electrical characteristics of the charging line under normal operation or specific steady-state conditions can also be used for verification.

[0068] After completing the CT polarity verification, the system continuously scans the electrical quantity data of the line (including three-phase current and voltage) for fault characteristics. By analyzing whether there are abrupt changes in these electrical quantities, i.e., sudden increases or decreases in current or voltage amplitude, or significant waveform distortion, a preliminary judgment is made as to whether a real fault has occurred in the line. If a significant abrupt change is detected, the line is considered to have a fault; otherwise, it may be a false alarm or normal fluctuation in the line.

[0069] If a fault is confirmed, the judgment results of the zero-sequence directional element and the power frequency change directional element are used to determine whether the fault is within or outside the zone:

[0070] If the directional element indicates that the fault power direction is from the busbar to the line, this means that the fault current originates from the busbar side and flows into the protected charging line, meaning the fault is located within the protection zone of that charging line. In this case, it is determined to be an in-zone fault.

[0071] Otherwise, if the directional element indicates that the fault power direction is from the line to the busbar, or there is no clear direction towards the busbar, this indicates that the fault current does not mainly flow into the protected line from the busbar, but may originate from a distant end of the line, or from an area outside the protection zone of adjacent lines or busbars. In this case, it is determined to be an external fault.

[0072] Among them, the zero-sequence directional element determines whether the fault current flows from the bus side into the line or from the line to the bus side by analyzing the phase relationship between the zero-sequence voltage and the zero-sequence current. The power frequency change directional element (or negative-sequence directional element / composite-sequence directional element) determines the direction of the fault power by analyzing the sudden change or negative-sequence component of the power frequency current and voltage when the fault occurs.

[0073] For closed-loop operation lines, by analyzing single-sided or double-sided waveform data, directional or differential components are used to determine whether the fault is located inside or outside the protection zone, including:

[0074] Waveform scanning is performed on the fault recording data to identify and describe the fault characteristics of the waveform. The fault characteristics include, but are not limited to: abrupt change points, maximum fault current points, clearing points, overlapping points, abrupt change points after overlapping, maximum fault current points after overlapping, and clearing points after overlapping.

[0075] Specifically, the fault assessment process for loop-connected lines is as follows, aiming to accurately determine the type and location of faults through refined analysis of fault characteristics and differentiated processing based on the availability of waveform data. For example... Figure 4 As shown, it includes:

[0076] The system performs waveform scanning on the received fault recording data to identify and describe key electrical quantity characteristics at the time of the fault, i.e., fault characteristics. These fault characteristics include, but are not limited to:

[0077] Sudden change point: The point in time when the current or voltage waveform changes abruptly, indicating the onset of a fault.

[0078] Maximum fault current point: The point in time when the current reaches its peak value during a fault.

[0079] Cut-off point: The point in time when the circuit breaker operates, the current is cut off and returns to zero.

[0080] Reclosing point: If the line is equipped with reclosing function, it refers to the point in time when the reclosing action is performed and the line is put back into operation.

[0081] Change point after reclosing: If a fault occurs again after successful reclosing, it refers to the starting change point of the second fault.

[0082] Maximum fault current after reclosing: The point in time when the current reaches its peak value during the second fault after reclosing.

[0083] Reclosing clearance point: The time point at which the second fault is cleared after reclosing.

[0084] The system determines the type of line fault based on preset open circuit fault characteristics, distinguishing between an open circuit fault and a short circuit fault. If it is determined to be an open circuit fault, the system directly returns the fault assessment result; otherwise, it proceeds to the short circuit fault assessment process.

[0085] The fault characteristic analysis of open wire and ungrounded connection includes the following two situations:

[0086] In the circuit, the effective value of the current in only one phase decreases significantly within a short period of less than two cycles, and its effective value is greater than 0.02 Amperes. At the same time, the amplitude of the current in this phase is significantly smaller than the current amplitudes of the other two phases.

[0087] There is a disconnection point where the circuit breaker operates, but there is no obvious current surge point. This is because a wire breakage fault usually results in a gradual decrease in current rather than a sudden increase.

[0088] The characteristic analysis of open-circuit grounding faults includes the following two situations:

[0089] The analysis revealed a clear point of sudden current change, and the current amplitude at the first sampling point was greater than 1.5 times the normal operating current before the fault.

[0090] The load current showed a gradually decreasing trend, while the currents of the other two phases did not change significantly.

[0091] If the above logical analysis indicates a broken wire fault, further analysis based on the characteristic changes in the load current can be used to determine the specific phase in which the broken wire fault occurred, which will not be elaborated here.

[0092] If the above logical analysis indicates a short-circuit fault (the corresponding judgment logic is existing technology and will not be elaborated here), then a differentiated strategy is adopted to accurately determine the fault within / outside the area based on the transmission status of the fault waveform data (single-sided station or double-sided station). Specifically, this includes the following three situations.

[0093] The first scenario involves handling cases where fault waveforms from both sides are not transmitted:

[0094] If fault waveform data from both sides of the loop-connected line fails to be successfully uploaded to the analysis system, the system will generate and output a clear prompt message indicating that "due to the failure to upload fault waveforms from both sides, it is impossible to accurately determine whether the fault is inside or outside the zone. Please conduct a manual analysis based on relevant fault information." This emphasizes the crucial role of data integrity in automated analysis and indicates the need for necessary manual intervention.

[0095] The second scenario involves processing the waveform data uploaded from a single station:

[0096] If only one substation on the loop-connected line successfully transmits fault recording data, the analysis process will be based on the verification status of the CT on that side.

[0097] If the CT on this side has been verified: Analyze the fault power direction using unilateral directional elements (including power frequency change directional elements and zero-sequence power directional elements). If the directional element analysis results show a reverse direction (i.e., the power direction points away from the busbar), it is determined to be an external fault. If the directional element analysis results show a positive direction (i.e., the power direction is from the busbar towards the line), it is determined to be a suspected internal fault. Since only unilateral data is available, cross-validation cannot be performed, hence the "suspected" designation.

[0098] If the CT on that side is not calibrated: attempt to calibrate the polarity of the CT on that side by comparing the calculated active power of the steady-state section before the fault with the real-time power flow data. If the CT polarity is successfully calibrated, perform single-sided directional element calculations. If the power direction on that side is from the bus to the line, and only that line has experienced a fault in the past 5 minutes, it can be determined as a suspected fault within the area.

[0099] If the above CT polarity verification method fails, the system will output the message "Because the polarity of the CT on this side of the line has not been verified, it is impossible to accurately determine the fault inside or outside the area. Please make a judgment by combining relevant fault information manually."

[0100] The third scenario involves sending both fault waveform recordings up:

[0101] If the fault recording data from both sides of the closed-loop line are successfully uploaded, the analysis process will make a more detailed and reliable judgment based on the verification status of the two-sided CT.

[0102] (1) If both bilateral CT scans have been verified:

[0103] Prioritize the use of differential elements and dual-directional elements for accurate fault diagnosis within / outside the fault zone. If the differential element operates, the fault is confirmed as within the fault zone; otherwise, it is confirmed as outside the fault zone. Simultaneously, extract the differential current and braking current values ​​at the point of maximum differential current, and attach the operation status of the dual-directional elements as auxiliary information for the judgment result.

[0104] (2) If one side of the CT scan has been verified, but the other side has not:

[0105] An attempt was made to verify the polarity of the unverified CT by comparing the calculated active power of the steady-state section with the real-time power flow data. If the polarity of the unverified CT was successfully verified, the process returned to the case where "both CTs have been verified" and the fault assessment was performed according to the above (1) procedure. If the polarity of the unverified CT still could not be verified, the directional element information of the verified side was calculated. If the power direction of the verified side is from the bus to the line, and one of the following conditions is met at the same time: the difference in current amplitude at the fault points on both sides is less than 15%; only the line has experienced a fault in the past 5 minutes; then it is determined to be a suspected fault within the area.

[0106] (3) If both bilateral CT scans were not verified:

[0107] First, we attempt to verify the polarity of both CTs by comparing the calculated active power in the steady-state section with the real-time power flow data. If the polarity verification of one CT is successful, we return to the situation of "one CT has been verified, the other has not been verified" and perform fault analysis according to the above (2) process. If the polarity verification of both CTs fails, we perform the following comprehensive judgment:

[0108] A. If the difference in current amplitude at the two fault points is less than 15%, then output "The difference in current amplitude at the two fault points is less than 15%, suspected fault within the area".

[0109] B. If only this line has failed in the past 5 minutes, output "Fault information in the past 5 minutes: only this line has failed, suspected fault within the area".

[0110] If neither of the above conditions A nor B applies, the output will be "Because the polarity of the CTs on both sides of the line has not been verified, it is impossible to accurately determine the fault inside or outside the zone. Please make a judgment manually based on the relevant fault information."

[0111] In one embodiment, for a fault in the main transformer (hereinafter referred to as the main transformer) in a power system, this embodiment uses the differential protection principle and CT winding configuration information to accurately determine whether the fault is located inside or outside the main transformer protection zone, and evaluate the correctness of the protection action.

[0112] When the fault type is a main transformer fault, it includes:

[0113] Using algorithms for directional and differential elements, the differential current and braking current values ​​of the main transformer are directly calculated based on fault recording data. Based on the calculated differential current and braking current values, and according to the ratio differential action characteristic curve, a preliminary fault assessment is performed within / outside the fault zone.

[0114] The main transformer fault diagnosis method also includes:

[0115] Determine the location of the CT winding connected to the fault recorder on the high-voltage side of the main transformer; if the CT winding is located on the bus side, determine that its protection range is consistent with the protection range of the main transformer; if the CT winding is not located on the bus side, determine that its protection range is inconsistent with the protection range of the main transformer.

[0116] The main transformer fault diagnosis method also includes:

[0117] When the CT winding is not on the bus side and the protection range is inconsistent, the main transformer fault judgment method further includes: if the initial in-zone / out-zone fault judgment determines that it is an out-of-zone fault and the CT winding is located on the line side, then determine whether the fault phase voltage is greater than 15% of the rated voltage; if the fault phase voltage is greater than 15% of the rated voltage, then determine that it is an out-of-zone fault; otherwise, determine that it is a suspected in-zone fault.

[0118] like Figure 5 As shown, firstly, based on multi-side current data, the differential current and braking current values ​​of the main transformer are directly calculated using a differential element algorithm. Based on the calculated differential current and braking current values, the system compares them with a preset ratio differential operating characteristic curve. If the differential current-braking current point is located in the operating region of the ratio differential curve, it indicates that the fault is located inside the main transformer protection zone. If the differential current-braking current point is located in the non-operating region of the ratio differential curve, it indicates that the fault is located outside the main transformer protection zone. Through this analysis, the system can accurately and quickly identify the specific area where the fault occurred and make a preliminary assessment of the operating behavior of the main transformer protection device.

[0119] Then, further consider the actual installation location of the current transformer CT winding connected to the fault recorder on the high-voltage side of the main transformer, in order to determine whether the range it monitors is completely consistent with the main protection range of the main transformer.

[0120] If the connection point of the CT winding of the fault recorder on the high-voltage side of the main transformer is located on the bus side, this means that the current signal collected by the recorder includes all the current flowing from the bus to the main transformer, and its monitoring range completely overlaps with the high-voltage side range of the main transformer differential protection. In this case, the correctness of the main transformer protection operation can be accurately determined based on the above differential protection judgment results.

[0121] If the connection point of the CT winding of the fault recorder on the high-voltage side of the main transformer is not on the bus side, for example, if the CT winding is installed between the circuit breaker on the high-voltage side of the main transformer and the main transformer, or installed on the feeder side from the main transformer to the line, etc., resulting in its monitoring range not being completely consistent with the differential protection range of the main transformer, then the judgment results need to be corrected or refined:

[0122] If the initial identification indicates a fault within the protection zone, even if the CT winding position does not perfectly align with the protection range, it can be confirmed that the fault is definitely within the main transformer's protection zone. This is because of the high sensitivity and selectivity of differential protection; once the action is clearly identified, it usually points to a fault within its protection zone.

[0123] If the initial identification result is an external fault, and it is further confirmed that the fault recorder CT winding on the high-voltage side of the main transformer is located on the line side, then determine whether the amplitude of the fault phase voltage is greater than 15% of the rated voltage. If the fault phase voltage is greater than 15% of the rated voltage, this usually indicates that there is a relatively remote or minor external fault on the line side, which has a limited impact on the high-voltage side voltage of the main transformer, and is therefore determined to be an external fault.

[0124] In one embodiment, such as Figure 6 As shown, this implementation provides a bus fault assessment process, which aims to accurately identify the type, location, and correctness of protection actions of bus faults through multi-dimensional data analysis and protection logic judgment.

[0125] After receiving the integrated intelligent alarm signal, the system first performs a full-process analysis of the fault waveform to determine whether the alarm signal is a false alarm. If it is a genuine tripping fault, the current in all line bays connected to the tripping bus should become zero after the fault occurs, indicating that the fault has been cleared. If it is a false alarm, and the alarm signal exists, but the current in any or all bays connected to the tripping bus does not return to zero, it is determined to be a false tripping signal caused by interference, hardware failure, software defect, etc., and no actual fault has occurred.

[0126] First, using directional and differential element algorithms, the differential current and braking current values ​​of related equipment such as the busbar and transformer are directly calculated based on the fault data sent by the fault recorder. Then, based on the ratio differential operating characteristic curve, the fault area is accurately and quickly identified, and the protection action behavior is preliminarily evaluated for preliminary identification of faults within / outside the protection zone. The calculation principle of this step is similar to that of the main transformer differential protection, used to determine whether the fault is within the busbar protection zone.

[0127] Then, based on the initial identification, the system further refines the type of bus fault or determines whether a circuit breaker has failed:

[0128] If the busbar differential protection (overall busbar differential protection) trips, and simultaneously, all the smaller differential protections (interval differential or sectional differential) connected to the tripped busbar also trip, then it is clearly determined that the fault is within the busbar zone. This indicates that the fault definitely occurred within the busbar and its protected area.

[0129] If the busbar differential does not operate, but any bay connected to the tripped busbar is determined to be a fault within the zone, and the fault lasts for more than 200 milliseconds, then it is determined that the fault in that bay caused the circuit breaker to fail, thereby triggering the busbar protection to trip. This means that the actual fault point is in that bay, but because the circuit breaker in that bay failed to clear the fault in time, the fault expanded and was cleared by the busbar protection.

[0130] Next, the actual installation location of the CT winding connected to each branch fault recorder is further considered to determine whether the monitored range is completely consistent with the main protection range of the bus.

[0131] If the CT windings of the fault recorders for each branch are all located on the line side, this means that the current signals collected by these recorders include all the current flowing from the busbar to each line, and their monitoring range is consistent with the actual protection range of the busbar differential protection. In this case, the correctness of the busbar protection operation can be accurately determined based on the preliminary identification results.

[0132] If the connection point of the CT winding of each branch fault recorder is not on the line side, the initial identification needs to be revised or refined:

[0133] If the fault is initially identified as being within the zone, even if the CT winding position is not exactly the same as the protection range, if the differential protection algorithm has clearly determined that it is a fault within the zone, then it can be confirmed that this fault is definitely a fault within the bus zone.

[0134] If the initial identification is an external fault: When the differential protection algorithm initially determines that the fault is external, the system further determines whether the amplitude of the fault phase voltage on the bus is greater than 15% of the rated voltage.

[0135] If the voltage of the faulty phase on the busbar is greater than 15% of the rated voltage, the fault point is located outside the busbar protection zone and at a relatively far distance, and its impact on the busbar voltage is limited; therefore, it is determined to be an external fault.

[0136] If the voltage of the faulty phase on the busbar is no more than 15% of the rated voltage, this may indicate that the fault point is located outside the monitoring range of the CT winding, but very close to the busbar, such as in the area between the busbar-side CT and the line-side CT. In this case, it is determined to be a suspected fault within the zone, and the fault point is located between the busbar-side CT and the line-side CT. This situation requires further manual verification.

[0137] This invention also relates to a precise fault diagnosis system for power systems, comprising a processor and a memory. The memory stores a computer program, and the processor can interact with the memory and invoke the computer program (e.g., via a bus). The processor then executes the computer program, which, when executed, implements the precise fault diagnosis method for power systems described in the above embodiments. The system also involves interfaces with various hardware devices and software systems of the power system itself for information and command exchange, which will not be elaborated upon here.

[0138] Existing fault assessment technologies cannot guarantee the comprehensive extraction and real-time analysis of fault characteristics, failing to meet the requirements of smart grids for rapid and accurate fault location. This invention proposes a precise fault assessment method and system for power systems, achieving accurate identification and differentiated processing of line faults, main transformer faults, and bus faults. This intelligent classification and assessment mechanism based on fault characteristic differences not only overcomes the limitations of traditional single assessment modes but also significantly improves assessment accuracy and efficiency through various fault handling strategies, providing core technical support for building a new generation of smart grid fault defense systems. This technology has significant forward-looking and practical applications, effectively meeting the urgent needs of modern power systems for rapid and accurate fault handling.

[0139] Those skilled in the art will conceive of many modifications, alterations, and alternatives without departing from the spirit and essence of this invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in the practice of this invention.

Claims

1. A method for accurate fault analysis of a power system, characterized in that, The method comprises the following steps: Receiving an integrated intelligent alarm signal, and judging whether it is a real fault signal; If it is a real fault signal, identifying the fault type as a line fault, a main transformer fault or a bus fault according to the protection action type and electrical quantity characteristics; When the fault type is a line fault, further judging the line type as a loop operation line, a charging operation line or an electric railway line, and performing in-zone / out-of-zone fault analysis according to the line type: If it is an electric railway line, determining whether the fault is in-zone or out-of-zone by judging whether the three-phase current triggers a current change element; If it is a charging operation line, determining whether the fault is in-zone or out-of-zone according to the judgment result of the directional element; If it is a loop operation line, determining whether the fault is in-zone or out-of-zone by analyzing single-sided or double-sided recording wave data and using a directional element or a differential element; If it is a loop operation line, determining whether the fault is in-zone or out-of-zone by analyzing single-sided or double-sided recording wave data and using a directional element or a differential element, comprising: Performing waveform scanning on the fault recording wave data, identifying and describing the fault characteristics of the waveform; According to the fault characteristics, distinguishing whether it is a broken line fault or a short circuit fault; If it is a short circuit fault, performing in-zone / out-of-zone fault analysis according to the uploading condition of the fault recording wave data; wherein the fault characteristics include: a mutation point, a fault current maximum point, a cut-off point, a reclosing point, a reclosing-after mutation point, a reclosing-after fault current maximum point and a reclosing-after cut-off point.

2. The method of claim 1, wherein, Receiving an integrated intelligent alarm signal, and judging whether it is a real fault signal, comprising: Judging whether it is a real fault signal by detecting whether there is a zero current segment in the waveform.

3. The method of claim 1, wherein, If it is an electric railway line, determining whether the fault is in-zone or out-of-zone by judging whether the three-phase current triggers a current change element, comprising: If the three-phase current triggers the current change element, it is determined as an in-zone fault, and the triggering phase is determined as the fault phase; if the zero sequence current triggers the current change element, it is determined as a ground fault, and if the fault phase involves two or more phases, it is determined as an inter-phase fault; if none of the three-phase currents triggers the current change element, it is determined as an out-of-zone fault.

4. The method of claim 1, wherein, If it is a charging operation line, determining whether the fault is in-zone or out-of-zone according to the judgment result of the directional element, comprising: If it is a charging operation line, calculating a zero sequence directional element and a power frequency change directional element, and then determining whether the fault is in-zone or out-of-zone according to the judgment result of the zero sequence directional element and the power frequency change directional element; if the power direction shows that the bus points to the line, it is determined as an in-zone fault, otherwise it is determined as an out-of-zone fault.

5. The method of claim 1, wherein, If it is a short circuit fault, performing in-zone / out-of-zone fault analysis according to the uploading condition of the fault recording wave data, comprising: If the double-sided fault recording wave data of the loop operation line are not uploaded, output a judgment result requiring manual processing; If only single-sided station recording wave data are uploaded, perform fault analysis in the following manner: For the side of the recording wave data uploading, if the CT of the side has been checked, use a single-sided directional element to judge: if the single-sided directional element analysis result exists in the opposite direction, it is determined as an out-of-zone fault; if it is a positive direction action, it is determined as a suspected in-zone fault; If the side CT is not checked, the CT polarity is checked by comparing the steady-state active power calculation result with the real-time power flow; if the CT polarity is successfully checked, the single-side directional element is calculated, and if the power direction of the side is from the bus to the line and only the corresponding line of the side fails within 5 minutes, it is determined as a suspected internal fault; otherwise, the judgment result requiring manual processing is output.

6. The method of claim 5, wherein, If it is a short-circuit fault, the internal / external fault is judged according to the uploading of the fault recording data, including: If both sides of the fault recording data are uploaded, the fault is judged in the following way: If both sides of the CT are checked, the differential element and the double-side directional element are used for accurate judgment: the differential element is used as the criterion, if the differential element acts, it is determined as an internal fault, otherwise it is determined as an external fault; If one side of the CT is checked and the other side is not checked, the polarity of the un-checked side CT is tried to be checked; if the polarity is successfully checked, the judgment is made according to the above-mentioned "both sides of the CT are checked"; otherwise, the directional element information of the checked side is calculated, if the power direction of the checked side is from the bus to the line, and the current amplitude difference at the fault point of the two sides is less than 15% or only the corresponding line of the checked side fails within 5 minutes, it is determined as a suspected internal fault; If both sides of the CT are not checked, the polarity of both sides of the CT is tried to be checked; if one side is successfully checked, the judgment is made according to the above-mentioned "one side of the CT is checked and the other side is not checked"; if both sides cannot be checked, further judgment is made: if the current amplitude difference of both sides is less than 15%, it is determined as a suspected internal fault; if only the line between the two sides fails within 5 minutes, it is determined as a suspected internal fault; if neither of the above conditions is met, the judgment result requiring manual processing is output.

7. The method of claim 1, wherein, When the fault type is a main transformer fault, further comprising: According to the algorithm of the directional element and the differential element, the differential current value and the braking current value of the main transformer are calculated, and according to the preset ratio differential action characteristic curve, the preliminary identification of the fault area as internal or external is made; The consistency of the actual installation position of the CT winding connected to the fault recording device of the high-voltage side of the main transformer with the protection range of the main transformer is judged; If the CT winding position is consistent with the main transformer protection range, the final judgment is made according to the result of the preliminary identification; If the CT winding position is not consistent with the main transformer protection range, the result of the preliminary identification is modified: if the result of the preliminary identification is an internal fault, it is modified to be determined as an internal fault; if the result of the preliminary identification is an external fault and the CT winding of the high-voltage side is located on the line side, whether the fault phase voltage is greater than the rated voltage threshold is judged to further modify the determination as an external fault or a suspected internal fault.

8. The method of claim 1, wherein, When the fault type is a bus fault, further comprising: Based on the algorithm of the directional element and the differential element, and the fault recording data, the differential current value and the braking current value of the bus are calculated, and according to the preset ratio differential action characteristic curve, the preliminary identification of the fault area is made; According to the operation condition of the bus differential and the trip bus differential, or according to the condition that the bus differential does not operate but there is an interval fault and the fault duration exceeds a time threshold, the bus area fault or breaker failure fault is finely judged; The consistency of the actual installation position of the CT winding accessed by each branch fault recorder with the bus protection range is judged; if the CT winding position is consistent with the bus protection range, the final judgment is made according to the preliminary identification result; If the CT winding position is not consistent with the bus protection range, the modified judgment is made according to the preliminary identification result: If the preliminary identification result is an area fault, the bus area fault is modified and determined; If the preliminary identification result is an external fault, whether the bus fault phase voltage is greater than a rated voltage threshold is judged, and the external fault or suspected internal fault is further modified and determined.

9. A precision fault judgment system for a power system, characterized in that, The power system accurate fault judgment method comprises a processor and a memory, the memory stores a computer program, and the processor executes the computer program to realize the power system accurate fault judgment method according to any one of claims 1 to 8.

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