Distributed single-phase grounding fault detection method based on power transformer

Abstract

The distributed single-phase ground fault detection method based on power transformer measures all voltages and zero-sequence currents of the power transformer measurement system, and converts the neutral point to ground voltage V n The neutral point to ground voltage threshold V th Comparison is performed to detect faults; if V n Greater than the threshold V th , determine that the system has failed; otherwise, calculate the slope of the neutral voltage dV n , and check whether it is greater than the slope threshold dV dth ; If dV n <dV dth , it indicates that the system has no fault; otherwise, record the current time as t1 and check dV again within △t0 time n To confirm whether the system is faulty or subject to other interference; if the neutral point to ground voltage slope dV during △t0 n The average value dV n Greater than dV dth , then check the neutral point to ground voltage V again n , if V n Less than V th , the value of t1 is cleared and the system is deemed normal; otherwise, the system is deemed faulty. Based on the method of the present invention, single-phase grounding faults in an RG system can be independently detected by the power transformer, improving the reliability of fault detection and enabling distributed fault detection.

Description

Technical Field

[0001] The present invention relates to the technical field of single-phase grounding fault detection, and in particular to a distributed single-phase grounding fault detection method based on a power transformer. Background Art

[0002] Fault detection is a crucial issue in power systems. Reliable and rapid fault detection ensures the safety and reliability of power systems and prevents accidents, equipment damage, and unnecessary power outages. There are four main types of faults in power systems: single-phase ground faults, phase-to-phase faults, two-phase ground faults, and three-phase ground faults. Single-phase ground faults are the most common of these faults, making research on single-phase ground fault detection crucial. The most common single-phase ground fault detection technology relies on overcurrent relays to detect faults in distribution systems. These relays track feeder currents and return a fault signal when the current exceeds a predetermined threshold. This area has been extensively researched by numerous experts. However, in RG systems (grounded via arc suppression coils), this results in very low fault currents, making the existing simple threshold method significantly limited. Furthermore, fault diagnosis requires coordinated measurement data from various components, resulting in significant process errors. The application of power transformers to accurately diagnose single-phase ground faults in RG systems has become an urgent technical challenge. Summary of the Invention

[0003] To address the problem of inaccurate fault detection in neutral-point arc-suppression coil grounding systems (RG systems) due to low fault currents and the need for coordinated measurement data from various components, the present invention provides a distributed single-phase ground fault detection method based on power transformers. Based on the present method, single-phase ground faults in RG systems can be independently detected using power transformers, improving both the reliability of fault detection and the distributed nature of fault detection, thereby enhancing system stability.

[0004] The technical solution adopted by the present invention is:

[0005] The distributed single-phase ground fault detection method based on power transformer includes the following steps:

[0006] Step 1: Based on the power transformer measurement system, measure all the voltages and zero-sequence currents, and convert the neutral point to ground voltage V n The neutral point to ground voltage threshold V th performing comparisons to detect faults;

[0007] Step 2: If V in step 1 n Greater than the threshold V th , determine that the system has failed; otherwise, calculate the slope of the neutral voltage dVn , and check whether it is greater than the slope threshold dV dth ;

[0008] Step 3: If dV in step 2 n <dV dth , it indicates that the system has no fault; otherwise, record the current time as t1 and check dV again within △t0 time n to confirm whether the system has failed or is subject to other interference;

[0009] Step 4: If the neutral point to ground voltage slope dV during △t0 in step 3 n Average value Greater than dV dth , then check the neutral point to ground voltage V again n , if V n Less than V th , then the value of t1 is cleared and the system is judged to be normal; otherwise, the system is judged to be faulty;

[0010] Step 5: If the system fails according to step 4 or step 2, estimate the time of failure and record it as t fe =min[t,t1].

[0011] Step 6: Record time t in step 5 fe Based on this, △t c After the time delay, V n With V th Compare: If V n >V th , then △t c After the time delay, V n With V th Compare: If V n >V th , then the system is judged to have a permanent fault, otherwise it is judged to have a transient fault;

[0012] Step 7: If the system is determined to have a permanent fault in step 6, calculate the deviation △V of all phase voltages when the fault occurs p , if △V p If it is negative, it is determined to be a faulty phase and the other phases are normal phases;

[0013] After the fault phase is identified, the zero sequence current is calculated. if If it is positive, the feeder is determined to be a faulty feeder, otherwise it will be identified as a normal feeder.

[0014] In step 1, V n The calculation formula is:

[0015]

[0016] Where: Z ASC is the impedance across the arc suppression coil (ASC); Z l is the inductive reactance of the distribution line under test; Z c is the capacitive reactance of the distribution line under test; Z f is the fault ground impedance; Z c ||Z f Represents Z c With Z f Parallel; V pn It is the phase voltage of the distribution line under test.

[0017] In step 2, dV n The neutral point-to-ground voltage V of the distribution line under test n The derivative with respect to time t;

[0018] dV dth is a given constant, which is typically a few milliseconds.

[0019] In the steps 3 and 6, Δt0, Δt c is the delay detection time, which is typically a few milliseconds.

[0020] In the step 7,

[0021] △V p The calculation formula is:

[0022]

[0023] in: The phase voltage to ground of the distribution line under test after the fault; It is the phase voltage to ground of the distribution line under test before the fault.

[0024] The calculation formula is:

[0025]

[0026] in: is the zero sequence current at t fe Closing Opening Difference Operation (CODO) output at the moment; t fe Transient fault voltage signal at time t r To calculate y CODOb The length of time, and it satisfies: y CODOb (i0(t)) is the CODO output at time i0(t) to determine the faulty feeder.

[0027] y CODOb The calculation formula is:

[0028]

[0029] in: To detect the CODO output in the positive direction; is the CODO output for detecting the negative direction; g(m) is the structuring element; y CODO (n) is the detected CODO output; y c (n) is the front component; y0(0) is the back component;

[0030] It is the symbol of erosion and dilation in morphological mathematics; f is the front measurand; g is the back measurand.

[0031] The present invention provides a distributed single-phase ground fault detection method based on power transformers, and the technical effects are as follows:

[0032] 1) Compared with the existing technology, the present invention solves the defect of inaccurate fault detection in a neutral point arc suppression coil grounding system (RG system) due to the small fault current and the need for coordination of various components for measurement data.

[0033] 2) Single-phase grounding faults in the RG system of the present invention can be detected independently by power transformers, which not only improves the reliability of fault detection but also enables distributed fault detection, thereby improving system stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The present invention will be further described below with reference to the accompanying drawings and examples:

[0035] Figure 1 Schematic diagram of the method of the present invention.

[0036] Figure 2 This is a 13-node system diagram. DETAILED DESCRIPTION

[0037] In such Figure 1 The method of the present invention is applied to the 13-node system shown in FIG. Figure 2 As shown, a distributed single-phase ground fault detection technology based on power transformers includes the following steps:

[0038] Step 1: Use power transformers to measure all voltages and zero-sequence currents in the system, and convert the neutral point to ground voltage V n The neutral point to ground voltage threshold V thPerform comparisons to detect faults;

[0039] Step 2: If V in step 1 n If the voltage is greater than the threshold, the system is judged to be faulty; otherwise, the slope dV of the neutral voltage is calculated. n , and check whether it is greater than the slope threshold dV dth ;

[0040] Step 3: If dV in step 2 n <dV dth , it indicates that the system has no fault; otherwise, record the current time as t1 and check dV again within △t0 n to confirm whether the system has failed or is subject to other interference;

[0041] Step 4: If in step 3, the neutral point to ground voltage slope dV during △t0 n Average value Greater than dV dth , then check V again n If V n Less than V th , then the value of t1 is cleared and the system is judged to be normal; otherwise, the system is judged to be faulty;

[0042] Step 5: If the system is judged to have failed in step 4 or step 2, the time of failure is estimated and recorded as t fe =min[t,t1];

[0043] Step 6: Record time t in step 5 fe Based on this, △t c After the time delay, V n With V th For comparison: If V n >V th , then △t c After the time delay, V n With V th For comparison: If V n >V th , then the system is judged to have a permanent fault, otherwise it is judged to have a transient fault.

[0044] Step 7: If the system is determined to have a permanent fault in step 6, calculate the deviation △V of all phase voltages when the fault occurs p If △V p If it is negative, it is determined to be the fault phase and the other phases are healthy phases. After the fault phase is identified, the zero sequence current is calculated. if If it is positive, the feeder is determined to be a faulty feeder, otherwise it will be identified as a normal feeder.

[0045] In step 1, V n The calculation formula is:

[0046]

[0047] where Z ASC is the impedance across the arc suppression coil (ASC); Z l is the inductive reactance of the distribution line under test; Z c is the capacitive reactance of the distribution line under test; Z f is the fault ground impedance; Z c ||Z f Represents Z c With Z f Parallel; V pn It is the phase voltage of the distribution line under test.

[0048] V th is a given constant, which is typically a few milliseconds.

[0049] In step 2, dV n 、dV dth for:

[0050] dV n : Neutral point to ground voltage V of the distribution line under test n , the derivative with respect to time t.

[0051] dV dth : A given constant.

[0052] △t0, △t c is the delay detection time, which is typically a few milliseconds.

[0053] In step 7, ΔV p The calculation formula is:

[0054]

[0055] in: The phase voltage to ground of the distribution line under test after the fault; It is the phase voltage to ground of the distribution line under test before the fault.

[0056] The calculation formula is:

[0057]

[0058] in: is the zero sequence current at t feClosing Opening Difference Operation (CODO) output at the moment; t fe Transient fault voltage signal at time t r To calculate y CODOb The length of time, and it satisfies: y CODOb (i0(t)) is the CODO output at time i0(t) to determine the faulty feeder.

[0059] where y CODOb The calculation formula is:

[0060]

[0061] in: To detect the CODO output in the positive direction; is the CODO output for detecting the negative direction; g(m) is the structuring element; y CODO (n) is the detected CODO output; y c (n) is the front component; y0(0) is the back component;

[0062] It is the symbol of erosion and dilation in morphological mathematics; f is the front measurand; g is the back measurand.

[0063] The fault detection effect in the 13-power-saving system is shown in Table 1:

[0064] Table 1 CCPP-P2G parameters

[0065]

[0066] In Table 1, P: permanent fault; T: transient fault.

[0067] In this example, according to the fault detection effect table, it can be seen that the faults are successfully detected by adopting the detection method of the solution of the present invention, which is beneficial to the stable operation of the power grid and the timely detection and positioning of the faults.

Claims

1. A distributed single-phase ground fault detection method based on power transformers, characterized in that The following steps are involved: Step 1: Based on the power transformer measurement system, measure all voltages and zero-sequence currents, and convert the neutral point voltage to ground Neutral point to ground voltage threshold performing comparisons to detect faults; Step 2: If the Greater than threshold , determine that the system fails; Otherwise, calculate the slope of the neutral-to-ground voltage , and check whether it is greater than the slope threshold ; Step 3: If the , it indicates that the system has no fault; otherwise, record the current time as , and check again within the time to confirm whether the system has failed or is subject to other interference; Step 4: If in step 3 Neutral point to ground voltage slope during Average value Greater than , then check the neutral point to ground voltage again ,if Less than , then clear If the value of is equal to , the system is judged to be normal; otherwise, the system is judged to be faulty; Step 5: If the system fails according to step 4 or step 2, estimate the time of failure and record it as ; Step 6: Record Time in Step 5 On the basis of After the time delay, and To compare: If , then proceed After the time delay and To compare: If , then the system is judged to have a permanent fault, otherwise it is judged to have a transient fault; Step 7: If the system is determined to have a permanent fault in step 6, calculate the deviation of all phase voltages at the time of the fault. ,if If it is negative, it is determined to be a faulty phase and the other phases are normal phases; After the fault phase is identified, the zero sequence current is calculated. ,if If is positive, the feeder corresponding to the fault is determined to be a faulty feeder, otherwise it will be identified as a normal feeder; In the step 7, The calculation formula is: ； in: The phase voltage to ground of the distribution line under test after the fault; The phase-to-ground voltage of the distribution line under test before the fault; The calculation formula is: ； in: The zero sequence current is Closing Opening Difference Operation (CODO) output at the moment; for The transient fault voltage signal at the moment; To calculate The length of time, and it satisfies: ; for CODO output at the moment to determine the faulty feeder; The calculation formula is: ； in: To detect the CODO output in the positive direction; To detect the CODO output in the negative direction; For structural elements; CODO output for detection; For the front portion; For the posterior portion; It is the symbol for erosion and dilation in morphological mathematics; For the former measured; To be measured later.

2. The distributed single-phase ground fault detection method based on power transformer according to claim 1 is characterized in that: In the step 1, The calculation formula is: ； in: is the impedance across the arc suppression coil (ASC); is the inductive reactance of the distribution line under test; is the capacitive reactance of the distribution line under test; is the fault ground impedance; Z c ||Z f express and in parallel; It is the phase voltage of the distribution line under test.

3. The distributed single-phase ground fault detection method based on power transformer according to claim 1 is characterized in that: In the step 2, The neutral point-to-ground voltage of the distribution line under test About time The derivative of is a given constant.

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