Single-phase earth fault judgment method and computer equipment
By calculating the electrical measurement parameters and capacitance ratio at the boundary switch, the single-phase grounding fault is automatically judged, which solves the problem of false movement and refusal of the boundary switch, and improves the stability and fault sensitivity of the system.
Patent Information
- Application Number
- CN202510343130.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-21
- Publication Date
- 2025-07-11
AI Technical Summary
In the prior art, the zero-sequence current setting value of the boundary switch is unreasonable, resulting in erroneous movement of the protection device or refusal, affecting the system reliability and sensitivity.
By calculating the electrical measurement parameters at the delimiting switch, calculating the measurement capacitance of each phase, and using three ratios to determine the single-phase grounding fault, avoiding the unreasonable setting of manual setting values, and using computer equipment to perform these steps to achieve automatic judgment.
It improves the stability and fault sensitivity of the system, avoids the mismoval and refusal of the boundary switch, and accurately determines the occurrence location of a single-phase grounding fault.
Smart Images
Figure CN120294620A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of distribution networks in power systems, and particularly relates to a method for judging single-phase grounding faults and a computer device. Background Art
[0002] The sectionalizing switch is an electrical device in the distribution network that can automatically isolate grounding faults, avoiding power outages affecting the entire line due to problems in a single user line, thus greatly improving the power supply management efficiency. Currently, the sectionalizing switch generally adopts zero-sequence current protection, and the setting value of the zero-sequence current for the sectionalizing switch to operate is generally set by avoiding the capacitive current of the three phases to the ground of the users downstream of the sectionalizing switch and upstream. When the fault point is upstream of the sectionalizing switch, the actual zero-sequence current is less than the setting value of the zero-sequence current; when the fault point is downstream of the sectionalizing switch, the actual zero-sequence current is greater than the setting value of the zero-sequence current, thereby diagnosing the location of the fault, sending a signal, and automatically isolating it. The problem is that the setting of the setting value should comprehensively consider information such as the grounding method of the distribution network, the detuning degree of the arc suppression coil, and the magnitude of the capacitive current upstream and downstream of the sectionalizing switch. And due to the large number of sectionalizing switches and incomplete distribution network information and other complex situations, the manually set setting value may be inappropriate. When the setting value of the zero-sequence current is too large, the protection sensitivity is not high, and the protection may refuse to operate; when the setting value of the zero-sequence current is too small, the protection may malfunction when a fault or disturbance occurs upstream, reducing the system reliability. Summary of the Invention
[0003] The purpose of the present invention is to provide a method for judging single-phase grounding faults and a computer device to solve the problems of misoperation and refusal to operate of the sectionalizing switch caused by inappropriate manually set setting values.
[0004] To solve the above technical problems, the present invention provides a method for judging single-phase grounding faults, including the following steps:
[0005] 1) Calculate the measured capacitance of each phase according to the electrical measurement parameters at the sectionalizing switch;
[0006] 2) Calculate three ratios based on the measured capacitance of each phase. The ratio is the ratio of the difference between the measured capacitances of two phases to the sum of the measured capacitances of these two phases, and the phases selected for the three ratios are not completely the same;
[0007] 3) If the absolute value of one of the ratios is 0 or close to 0, and the absolute values of the other two ratios are greater than 1, it is determined that a single-phase grounding fault has occurred downstream of the sectionalizing switch, and the fault phase is the common phase included in the two ratios greater than 1.
[0008] Further, the three ratios are respectively D ab 、D bc 、D ca , and their calculation formulas are respectively:
[0009]
[0010] Wherein, C a , C b , C c are three-phase measurement capacitors.
[0011] Further, the measurement capacitor of each phase is the average value of the measurement capacitors at M moments, where M≥2.
[0012] Further, the calculation of the measurement capacitor of each phase in step 1) is performed only after determining that a single-phase ground fault may occur, and it is determined that a single-phase ground fault may occur when the voltage mutation at any phase boundary switch is greater than 0.05 times the line voltage.
[0013] Further, if the absolute value of one of the ratios is 0 or close to 0 and the absolute values of the other two ratios are greater than 1 do not hold, it is determined that no single-phase ground fault has occurred, or a single-phase ground fault has occurred upstream of the boundary switch.
[0014] Further, the calculation method of the measurement capacitor at a certain moment is:
[0015]
[0016] Wherein, C φ is the measurement capacitor of phase φ; Δi φ (n) = {i φ (n) - i φ (n - N)}, Δu φ (n) = {u φ (n) - u φ (n - N)}, i φ is the current value at the phase φ boundary switch, Δi φ is the mutation of the phase φ current value, u φ is the voltage value at the phase φ boundary switch, Δu φ is the mutation of the phase φ voltage value, φ is phases a, b, c, n is a certain sampling time point, N is the number of interval sampling points for each signal sampling, and t is the time variable.
[0017] Further, when it is determined that a single-phase ground fault has occurred downstream of the boundary switch, the boundary switch is tripped. To solve the above technical problems, the present invention also provides a computer device, including a processor, and the processor is used to execute a computer program to implement the steps of the above method.
[0018] To solve the above technical problems, the present invention also provides a method for judging a single-phase ground fault, including the following steps:
[0019] 1) When it is determined that a single-phase grounding fault may occur, calculate the measured capacitance of each phase according to the electrical measurement parameters at the sectionalizing switch.
[0020] 2) Calculate three ratios based on the measured capacitance of each phase. The ratio is the ratio of the difference in the measured capacitance of two phases to the sum of the measured capacitance of these two phases, and the phases selected for the three ratios are not completely the same.
[0021] 3) If the absolute value of one of the ratios is 0 or close to 0, and the absolute values of the other two ratios are greater than 1, it is determined that a single-phase grounding fault has occurred downstream of the sectionalizing switch and the faulty phase is the common phase contained in the two ratios greater than 1.
[0022] Furthermore, when the sudden change in the voltage of any phase at the sectionalizing switch is greater than 0.05 times the line voltage, it is determined that a single-phase grounding fault may occur.
[0023] To solve the above technical problems, the present invention also provides a computer device, including a processor, and the processor is used to execute a computer program to implement the steps of the above-mentioned method.
[0024] The beneficial effects are as follows: The present invention is an innovative invention. The present invention analyzes the measured capacitance values of each phase upstream and downstream of the power distribution network when a fault occurs upstream and downstream. When a single-phase grounding fault occurs downstream of the sectionalizing switch, the measured capacitance of the two non-faulty phases is the actual capacitance to the ground of the two non-faulty phases downstream of the sectionalizing switch. The measured capacitance of the two phases is approximately equal and the value is small. The measured capacitance of the faulty phase is approximately the negative value of the sum of the capacitances to the ground of each phase downstream of the sectionalizing switch. Due to the obvious difference in the measured capacitance between the faulty phase and the non-faulty phases, three ratios are calculated using this characteristic. The ratio is the ratio of the difference in the measured capacitance of two phases to the sum of the measured capacitance of these two phases, and the phases selected for the three ratios are not completely the same. Using the ratio for determination does not require manual setting, avoiding misoperation and refusal to operate of the sectionalizing switch caused by unreasonable manual setting values, and improving the system stability and fault sensitivity. Description of the Drawings
[0025] Figure 1 It is a schematic flowchart of the method example of the present invention for judging a single-phase grounding fault. Detailed Embodiments
[0026] The present invention calculates the measured capacitance of each phase according to the electrical measurement parameters at the sectionalizing switch; further calculates three ratios based on the measured capacitance of each phase, where the ratio is the ratio of the difference in the measured capacitance of two phases to the sum of the measured capacitance of these two phases, and the phases selected for the three ratios are not completely the same; further, if the absolute value of one of the ratios is 0 or close to 0 (here, close to 0 means a value very close to 0, for example, by determining whether the absolute value of the ratio is less than a set threshold to determine whether it meets the condition of being close to 0), and the absolute values of the other two ratios are greater than 1, it is determined that a single-phase grounding fault has occurred downstream of the sectionalizing switch and the faulty phase is the common phase included in the two ratios greater than 1. Different from the prior art that requires manual setting values, no manual setting is needed, avoiding misoperation and refusal to operate of the sectionalizing switch caused by unreasonable manual setting values, and improving the system stability and fault sensitivity.
[0027] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Therefore, the detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed present invention, but only represents the selected embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.
[0028] An embodiment 1 of a method for judging a single-phase grounding fault:
[0029] An embodiment of a method for judging a single-phase grounding fault of the present invention has a process as Figure 1 shown and is described in words as follows:
[0030] Step 1: Collect the three-phase current i φ (n) and three-phase voltage u φ (n) at the sectionalizing switch installed at the demarcation point between the user power supply system and the public distribution network under the jurisdiction of the power supply enterprise, and calculate the three-phase current mutation amount Δi φ (n) and three-phase voltage mutation amount Δu φ (n).
[0031] Specifically, the mutation amount can be obtained from the following formula:
[0032] Δi φ (n) = {i φ (n) - i φ (n - N)}
[0033] Δu φ (n) = {uφ (n) - u φ (n - N)}
[0034] Where φ = a, b, c phases, N is the number of sampling points of each signal in one power frequency cycle, and in this embodiment, N is set to 64.
[0035] Step 2, after determining that a ground fault may occur, proceed to Step 3; otherwise, proceed to Step 1.
[0036] Among them, when there is a certain phase |Δu φ (n)| > 0.05U N , it is determined that a ground fault may occur.
[0037] Where U N is the line voltage, and φ = a, b, c phases.
[0038] Step 3, sample multiple times and calculate the average value of the three-phase measured capacitance.
[0039] Specifically, the measured capacitance can be obtained from the following formula:
[0040]
[0041] Where φ = a, b, c phases, and t is defined as time.
[0042] Similarly, calculate the measured capacitances C φ (n + 1), C φ (n + 2), …, C φ (n + M - 1) at times n + 1, n + 2, …, n + M - 1, where M takes an integer from 10 to 20.
[0043] The formula for obtaining the average value is as follows:
[0044]
[0045] Where φ = a, b, c phases, and n is the first sampling point.
[0046] Step 4, calculate D ab , D bc , D ca from the measured capacitances of the three phases obtained. The descriptions of the three ratios are as follows: The ratio is the ratio of the difference between the measured capacitances of two phases to the sum of the measured capacitances of the two phases, and the phases selected for the three ratios are not completely the same. In this embodiment, the three ratios D ab , D bc , D ca are as follows:
[0047]
[0048] Step 5: Use D ab , D bc , D ca to determine whether a single-phase grounding fault has occurred downstream of the sectionalizing switch based on the relationship with the set value. The criterion for a single-phase grounding fault downstream of the sectionalizing switch is shown in Table 1, and the textual description is as follows:
[0049] If D ab > 1 and -0.2 < D bc < 0.2 and D ca < -1, it is determined that a phase A grounding fault has occurred downstream of the sectionalizing switch, and proceed to Step 6;
[0050] If D ab < -1 and D bc > 1 and -0.2 < D ca < 0.2, it is determined that a phase B grounding fault has occurred downstream of the sectionalizing switch, and proceed to Step 6;
[0051] If -0.2 < D ab < 0.2 and D bc < -1 and D ca > 1, it is determined that a phase C grounding fault has occurred downstream of the sectionalizing switch, and proceed to Step 6;
[0052] Otherwise, it is determined that no single-phase grounding fault has occurred, or the single-phase grounding fault has occurred upstream of the sectionalizing switch, and enter Step 1.
[0053] Table 1
[0054] <![CDATA[D ab > <![CDATA[D bc > <![CDATA[D ca > Phase A ground fault >1 Is 0 or approximately 0 <-1 Phase B ground fault <-1 >1 Is 0 or approximately 0 Phase C ground fault Is 0 or approximately 0 <-1 >1
[0055] Among them, the specific judgment process of the embodiment is as follows:
[0056] Assume that a phase A grounding fault has occurred downstream of the sectionalizing switch. Then measure the capacitance C b (n), C c (n) are the actual capacitances downstream of the sectionalizing switch, whose signs are positive and the values are small; the measured capacitance C a (n) has a negative sign, and its absolute value is the sum of the capacitances of the entire system to the ground minus the capacitance of the downstream phase A to the ground. Its absolute value is much larger than C b (n), C c (n). Therefore, D ab > 1; D ca < -1. Since the three-phase parameters of the 10kV voltage level distribution network are generally balanced, C b (n) is approximately equal to C c (n), and D bc is close to 0 and its absolute value is much less than 1. Fully considering the possible maximum imbalance of the three-phase parameters of the distribution network, -0.2 < D bc < 0.2 also holds.
[0057] Similarly, for phase B and phase C when a ground fault occurs, the faulty phase can also be accurately determined.
[0058] When a high-resistance ground fault occurs, the above criteria also hold, with high judgment sensitivity and the sectionalizing switch not failing to operate.
[0059] Step Six: The sectionalizing switch trips, isolating the fault and sending out a signal.
[0060] In addition, the following two forms of criteria can also be deduced:
[0061] One, when occurs, the faulty phase of the ground fault can also be judged, and the corresponding criteria change, as shown in Table 2:
[0062] Table 2
[0063] <![CDATA[D ab > <![CDATA[D bc > <![CDATA[D ca <!-- 4 -->]]> Phase A ground fault >1 Is 0 or approximately 0 >1 Phase B ground fault >1 >1 Is 0 or approximately 0 Phase C ground fault Is 0 or approximately 0 >1 >1
[0064] Two, when occurs, the faulty phase of the ground fault can also be judged, and the corresponding criteria change, as shown in Table 3:
[0065] Table 3
[0066] <![CDATA[D ba > <![CDATA[D cb > <![CDATA[D ac > Phase A ground fault <-1 Is 0 or approximately 0 >1 Phase B ground fault >1 <-1 Is 0 or approximately 0 Phase C ground fault Is 0 or approximately 0 >1 <-1
[0067] An embodiment 2 of a method for judging single-phase ground faults:
[0068] The difference between this embodiment and embodiment 1 of the method for judging single-phase ground faults lies only in that after the required data is collected in step one, the judgment in step two is not carried out, and step three is directly executed to calculate the average value of the three-phase measured capacitance and the corresponding judgment processing. This method can also accurately discriminate single-phase ground faults.
[0069] An embodiment 1 of a computer device:
[0070] An embodiment of a computer device according to the present invention includes a memory, a processor, an internal bus, and a computer program stored on the memory. The processor and the memory complete mutual communication and data interaction through the internal bus. The processor executes the computer program to implement the steps of the method described in embodiment 1 of a method for judging single-phase ground faults of the present invention. Among them, the processor can be a microprocessor MCU, a programmable logic device FPGA, etc.; the memory can be various memories that store information in an electrical energy manner, such as RAM, ROM, etc., or can also be a memory using other methods.
[0071] An embodiment 2 of a computer device:
[0072] An embodiment of a computer device according to the present invention includes a memory, a processor, an internal bus, and a computer program stored in the memory. The processor and the memory communicate and exchange data with each other through the internal bus. The processor executes the computer program to implement the steps of the method introduced in Embodiment 2 of a single-phase grounding fault judgment method according to the present invention. Among them, the processor can be a processing device such as a microprocessor MCU or a field programmable gate array FPGA; the memory can be various memories that store information in the form of electric energy, such as RAM, ROM, etc., or can also be a memory using other methods.
[0073] Compared with the prior art, the present invention uses three ratios defined by the measured capacitances of each phase for judgment, the eigenvalue differences are obvious, the demarcation result reliability is high, and the system stability and fault sensitivity are improved.
[0074] The specific implementation manners are given above, but the present invention is not limited to the described implementation manners. The basic idea of the present invention lies in the above basic solution. For those skilled in the art, according to the teachings of the present invention, it does not require creative labor to design various deformed models, formulas, and parameters. Changes, modifications, substitutions, and variations made to the implementation manners without departing from the principle and spirit of the present invention still fall within the protection scope of the present invention.
Claims
1. A method for judging single-phase grounding faults, characterized in that, It includes the following steps: 1) Calculate the measured capacitance of each phase according to the electrical measurement parameters at the sectionalizing switch; 2) Calculate three ratios based on the measured capacitance of each phase. The ratio is the ratio of the difference in the measured capacitance of two phases to the sum of the measured capacitance of these two phases, and the phases selected for the three ratios are not completely the same; 3) If the absolute value of one of the ratios is 0 or close to 0, and the absolute values of the other two ratios are greater than 1, it is determined that a single-phase grounding fault occurs downstream of the sectionalizing switch and the fault phase is the common phase included in the two ratios greater than 1.
2. The method for judging single-phase grounding faults according to claim 1, characterized in that, The three ratios are D ab , D bc , D ca , and their calculation formulas are respectively: where C a , C b , C c are three-phase measuring capacitors.
3. The method for judging single-phase grounding faults according to claim 1, characterized in that The measured capacitance of each phase is the average value of the measured capacitance at M moments, where M≥2.
4. The method for judging single-phase grounding faults according to claim 1, characterized in that If the condition that the absolute value of one of the ratios is 0 or close to 0, and the absolute values of the other two ratios are greater than 1 does not hold, it is determined that no single-phase grounding fault occurs, or a single-phase grounding fault occurs upstream of the sectionalizing switch.
5. The method for judging single-phase grounding faults according to claim 3, characterized in that The calculation method of the measured capacitance at a certain moment is: Where C φ is the measured capacitance of the φ phase; Δi φ (n) = {i φ (n) - i φ (n - N)}, Δu φ (n) = {u φ (n) - u φ (n - N)}, i φ is the current value at the φ-phase boundary switch, Δi φ is the sudden change in the φ-phase current value, u φ is the voltage value at the φ-phase boundary switch, Δu φ is the sudden change in the φ-phase voltage value, φ is the a, b, c phases, n is a certain sampling time point, N is the number of interval sampling points for each signal sampling, and t is the time variable.
6. The method for judging single-phase grounding faults according to claim 1, characterized in that, When it is determined that a single-phase grounding fault occurs downstream of the sectionalizing switch, trip the sectionalizing switch.
7. A method for judging single-phase grounding faults, characterized in that, It includes the following steps: 1) In the case of determining that a single-phase grounding fault may occur, calculate the measured capacitance of each phase according to the electrical measurement parameters at the sectionalizing switch; 2) Calculate three ratios based on the measured capacitance of each phase. The ratio is the ratio of the difference in the measured capacitance of two phases to the sum of the measured capacitance of these two phases, and the phases selected for the three ratios are not completely the same; 3) If the absolute value of one of the ratios is 0 or close to 0, and the absolute values of the other two ratios are greater than 1, it is determined that a single-phase grounding fault occurs downstream of the sectionalizing switch and the fault phase is the common phase included in the two ratios greater than 1.
8. The method for judging single-phase grounding fault according to claim 7, wherein It is determined that a single-phase grounding fault may occur when the voltage mutation of any phase at the sectionalizing switch is greater than 0.05 times the line voltage.
9. A computer device, comprising a processor, characterized in that, The processor is used to execute a computer program to implement the steps of the method described in any one of claims 1 to 6.
10. A computer device includes a processor, characterized in that, The processor is used to execute a computer program to implement the steps of the method described in claim 7 or 8.