A method and system for successive fault judgment by using line switching impedance variation

Abstract

This invention provides a method and system for determining successive faults using impedance changes before and after line switching. The system includes: a data acquisition module for real-time detection of the zero-sequence voltage and zero-sequence current of each line in the system; a fault initiation module for initiating the judgment process after a ground fault is detected; an impedance calculation module for calculating the impedance changes of each line; a logic judgment module for comparing the impedance changes with a preset threshold and outputting the successive fault judgment result; and an action execution module for performing subsequent fault line tripping and reclosing operations based on the fault judgment result. This invention effectively overcomes the influence of transition resistance, is unaffected by the neutral point grounding method, and improves the accuracy and reliability of successive fault judgment.

Description

Technical Field

[0001] This invention relates to the field of power system relay protection technology, specifically a method and system for determining successive faults by utilizing the impedance changes before and after line switching. Background Technology

[0002] Power distribution networks typically have a radial or ring structure and operate in complex ways. Under severe weather conditions (such as lightning strikes and strong winds) or due to equipment aging, distribution lines are prone to "sequential faults." A sequential fault occurs when a fault occurs on one line (such as a single-phase ground fault), and within a very short time, a new fault occurs on another line, either in the same or a different phase. If not handled properly, such faults can cause electric shocks, fires, or widespread power outages, seriously threatening power grid stability and the safety of life and property.

[0003] Currently, ground fault detection and isolation technologies for single lines are relatively mature, such as zero-sequence overcurrent protection, group amplitude and phase ratio protection, and transient directional protection. However, most of these methods are designed for single ground fault points and are difficult to effectively handle successive fault scenarios. Existing successive fault judgment schemes mainly utilize changes in zero-sequence admittance or active power components caused by the fault as criteria. However, these methods have significant drawbacks:

[0004] 1. Highly affected by transition resistance: Fault points often have large transition resistance (such as tree contact or fallen wires), which can severely reduce the measured value of zero-sequence admittance, causing the criterion to fail and resulting in misjudgment or rejection.

[0005] 2. Low proportion of active component: In power distribution lines, especially in single-phase grounding faults in neutral ungrounded systems or high-impedance grounding faults of arc suppression coils, the active component in the fault current is very weak and easily drowned out by measurement noise and system imbalance, resulting in insufficient judgment sensitivity and low accuracy.

[0006] Therefore, there is an urgent need for a reliable successive fault diagnosis method that is not significantly affected by transition resistance. Summary of the Invention

[0007] To address the shortcomings of the existing technology, this invention provides a method and system for determining successive faults by utilizing the impedance change before and after line switching. This method can effectively overcome the influence of transition resistance, is unaffected by the neutral grounding method, and improves the accuracy and reliability of successive fault determination.

[0008] The technical solution provided by this invention is a method for determining successive faults based on impedance changes before and after line switching, comprising the following steps:

[0009] Step 1: Ground Fault Initiation: Real-time monitoring of the grid's zero-sequence voltage and zero-sequence current. When a single-phase ground fault is detected (the zero-sequence voltage or zero-sequence current exceeds the set value, which is a conventional detection method), the judgment process is initiated.

[0010] Step 2: First line trips: Detect a faulty line and trip it using conventional grounding fault detection methods, or use manual circuit breaking to disconnect one of the lines;

[0011] Step 3: Zero-sequence impedance detection: The fault diagnosis program automatically records the impedance value Z measured at the protection installation points of all other remaining lines (i.e., lines that were not disconnected) in the system before and after the disconnection operation. before and Z after ;

[0012] Step 4: Calculate the impedance change: For each remaining line, calculate the impedance change ΔZ = Z before and after the switching. after - Z before ;

[0013] Step 5: Determine the faulty line: If the impedance change ΔZ ≥ ΔZ set, or ΔZ is the maximum, the line is determined to be faulty.

[0014] Step 6: Disconnect the faulty line: Disconnect the selected successor faulty line;

[0015] Step 7: Continuous detection and judgment: Determine whether the ground fault has been eliminated (zero-sequence voltage and zero-sequence current are lower than the set values, which is a conventional detection method). If it has not been eliminated, continue to execute steps 3 to 7. If the ground fault has been eliminated, proceed to step 8.

[0016] Step 8: Reclosing the tripped line: The ground fault has been eliminated, and the tripped line is reclosing.

[0017] Step 9: Permanent Fault Handling: Determine if the grounding fault reappears. If the fault reappears after reclosing, disconnect the line again, inspect the fault point, and handle it. If the fault does not reappear after reclosing, the handling of this line is complete.

[0018] Step 10: Fault handling completed: Continue to reconnect other lines until all lines are powered back on, and the fault handling is complete.

[0019] Furthermore, the conventional grounding fault judgment methods include the zero-sequence overcurrent method, the transient direction method, and the group amplitude and phase comparison method.

[0020] Furthermore, in step (3), the measured impedance value is the zero-sequence impedance of each circuit measured at the protection installation location.

[0021] Furthermore, the impedance change in step (4) is calculated using the effective values ​​of the zero-sequence voltage and the effective value of the zero-sequence current forward and backward, with the tripping moment as the reference point:

[0022] ΔZ =Z after - Z before =U 0before / I 0before -U 0after / I 0after ,

[0023] Among them, U 0before I is the effective value of the zero-sequence voltage before tripping. 0before U is the effective value of the zero-sequence current before tripping. 0after I is the effective value of the zero-sequence voltage after tripping. 0after This is the effective value of the zero-sequence current after the trip.

[0024] Another technical solution provided by this invention: a fault judgment system utilizing the impedance change before and after line switching, used to implement the above method, the system comprising:

[0025] The data acquisition module is used to detect the zero-sequence voltage and zero-sequence current of each line in the system in real time.

[0026] The fault initiation module is used to initiate the judgment process after a ground fault is detected.

[0027] Impedance calculation module, used to calculate the impedance change of each line;

[0028] The logic judgment module is used to compare the impedance change with a preset threshold and output successive fault judgment results;

[0029] The action execution module is used to perform subsequent fault line tripping and reclosing operations based on the fault diagnosis results.

[0030] Another technical solution provided by the present invention is a computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the aforementioned fault judgment method based on the impedance changes before and after line switching.

[0031] The basic principle of this invention is as follows: When a series of faults occur in a distribution network, the disconnection of the first faulty line (through protection operation or manual circuit breaking) alters the system's topology and zero-sequence network. This change significantly affects the measured impedance of other faulty lines, while having negligible impact on non-faulty lines. By calculating and comparing the impedance changes before and after the line disconnection, the successive faulty lines can be accurately identified.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] 1. Strong resistance to transition resistance: This invention utilizes the impedance change caused by system topology changes. This change is mainly determined by the parameters of the line itself and the network structure, and is less affected by the transition resistance at the fault point, which significantly improves the reliability of the criterion.

[0034] 2. High sensitivity: It uses impedance change for judgment, which is accurate and the change is obvious, avoiding the problem of insufficient sensitivity caused by the weak active component of different systems.

[0035] 3. Clear logic and simple implementation: The method has clear criteria, simple calculation, and is easy to implement in existing ground fault line selection protection devices.

[0036] 4. High adaptability: It can adapt to different neutral grounding methods, effectively distinguish different successive fault scenarios (including multiple line faults), and make accurate judgments. Attached Figure Description

[0037] Figure 1 This is a flowchart of the sequential fault judgment method of the present invention;

[0038] Figure 2 This is a schematic diagram of the circuit and faults in Embodiment 1 of the present invention, wherein line L1 and line L2 successively fail;

[0039] Figure 3 This is a flowchart of the fault diagnosis process in Embodiment 1 of the present invention. Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] Example 1

[0042] like Figure 2 As shown, assume a 10kV distribution network has four outgoing lines: L1, L2, L3, and L4. First, a high-resistance single-phase-to-ground fault occurs on line L1, followed by a low-resistance successive fault on line L2.

[0043] like Figure 3 As shown, a method for determining successive faults using impedance changes before and after line switching includes the following steps:

[0044] Step 1: The successive fault judgment system monitors the zero-sequence voltage and zero-sequence current of the power grid in real time. If the zero-sequence voltage exceeds the set value, it is judged that a single-phase ground fault has occurred.

[0045] Step 2: Determine that line L2 is a faulty line by using the group amplitude and phase comparison method, and execute a trip to disconnect the faulty line L2.

[0046] Step 3: If the ground fault is not cleared, initiate the successive fault judgment process. The successive fault judgment program automatically records the impedance values ​​of all other remaining lines in the system, L1, L3, and L4, measured at their protection installation points two cycles before the disconnection operation, and denoted as Z. -before-1 Z before-3 Z before-4 Record the impedance value of the wave two weeks after the resection operation, denoted as Z. afte-1 Z afte-3 Z after-4 .

[0047] Step 4: Calculate the impedance changes ΔZL1, ΔZL3, and ΔZL4 of L1, L3, and L4 before and after the switching of line L2.

[0048] Step 5: The impedance changes ΔZL3 and ΔZL4 are close to 0, while ΔZL1 is the largest, so L1 is judged to be the faulty line.

[0049] Step 6: Disconnect the selected successor faulty line L1.

[0050] Step 7: Determine that the ground fault has been eliminated, and perform a reclosing operation on the tripped line, reclosing line L1.

[0051] Step 8: Determine if the grounding fault has recurred (permanent fault).

[0052] Step 9: Trip L1 line again.

[0053] Step 10: Inspect and troubleshoot fault points on the L1 line.

[0054] Step 11: Overlap L2

[0055] Step 12: The fault did not reappear (transient fault).

[0056] Step 13: L2 line processing completed.

[0057] Step 14: After the fault point on line L1 is dealt with, line L1 is closed.

[0058] Step 15: The fault did not reappear after L1 was reclosed, and the L1 line has been repaired.

[0059] Step 16: All lines have been reclosed, and the entire fault has been resolved.

[0060] As can be seen from the above steps, the present invention can quickly and accurately locate successively faulty lines in different scenarios, providing reliable technical support for the rapid self-healing and power restoration of the power distribution network.

[0061] Embodiments of the present invention also provide a successive fault judgment system utilizing impedance changes before and after line switching, for implementing the aforementioned successive fault judgment method, the system comprising:

[0062] The data acquisition module is used to detect the zero-sequence voltage and zero-sequence current of each line in the system in real time.

[0063] The fault initiation module is used to initiate the judgment process after a ground fault is detected.

[0064] Impedance calculation module, used to calculate the impedance change of each line;

[0065] The logic judgment module is used to compare the impedance change with a preset threshold and output successive fault judgment results;

[0066] The action execution module is used to perform subsequent fault line tripping and reclosing operations based on the fault diagnosis results.

[0067] Another aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the aforementioned method for successive fault judgment using impedance changes before and after line switching.

[0068] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0069] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0070] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0071] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention without departing from the spirit and scope of the present invention.

Claims

1. A method for determining faults by utilizing the successive changes in impedance before and after line switching, characterized in that, Includes the following steps: Step 1: Monitor the zero-sequence voltage and zero-sequence current of the power grid in real time. When a single-phase ground fault is detected, initiate the judgment process. Step 2: Detect a faulty line and trip it using conventional grounding fault detection methods, or use manual circuit breaking to disconnect one of the lines; Step 3: The fault diagnosis program automatically records the impedance value Z measured at the protection installation points of all other remaining lines in the system before and after the disconnection operation. before and Z after ; Step 4: For each remaining line, calculate the impedance change ΔZ = Z before and after switching. after - Z before ; Step 5: If the impedance change ΔZ ≥ ΔZ set, or ΔZ is at its maximum, determine the successive fault lines; Step 6: Disconnect the selected successor faulty line; Step 7: Determine whether the ground fault has been eliminated by checking whether the zero-sequence voltage and zero-sequence current are lower than the set values. If not eliminated, continue to execute steps 2 to 7. If the ground fault has been eliminated, proceed to step 8. Step 8: The ground fault has been cleared; the tripped line is reclosing. Step 9: Determine if the grounding fault reappears. If the fault reappears after reclosing, disconnect the line again, inspect the fault point and handle it. If the fault does not reappear after reclosing, the handling of this line is complete. Step 10: Continue to reconnect other lines until all lines are powered back on, and the fault is resolved.

2. The method for determining faults based on successive impedance changes before and after line switching, as described in claim 1, is characterized in that... The conventional grounding fault judgment methods include the zero-sequence overcurrent method, the transient direction method, and the group amplitude and phase comparison method.

3. The method for determining faults based on successive impedance changes before and after line switching, as described in claim 1, is characterized in that... Its features are, In step (3), the measured impedance value is the zero-sequence impedance of each circuit measured at the protection installation location.

4. The method for determining faults based on successive impedance changes before and after line switching, as described in claim 1, is characterized in that... In step (4), the impedance change is calculated using the effective values ​​of the zero-sequence voltage and the effective value of the zero-sequence current, taken as the tripping moment as the reference point: ΔZ =Z after - Z before =U 0before / I 0before -U 0after / I 0after , Among them, U 0before I is the effective value of the zero-sequence voltage before tripping. 0before U is the effective value of the zero-sequence current before tripping. 0after I is the effective value of the zero-sequence voltage after tripping. 0after This is the effective value of the zero-sequence current after the trip.

5. A fault detection system utilizing the successive impedance changes before and after line switching, characterized in that, The system for implementing the method as described in any one of claims 1-4 includes: The data acquisition module is used to detect the zero-sequence voltage and zero-sequence current of each line in the system in real time. The fault initiation module is used to initiate the judgment process after a ground fault is detected. Impedance calculation module, used to calculate the impedance change of each line; The logic judgment module is used to compare the impedance change with a preset threshold and output successive fault judgment results; The action execution module is used to perform subsequent fault line tripping and reclosing operations based on the fault diagnosis results.

6. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the successive fault judgment method based on the impedance changes before and after line switching as described in any one of claims 1-4.

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