Small resistance grounding power distribution network overline cascading fault detection method and system

Abstract

The invention discloses a small-resistance grounding power distribution network overline cascading fault detection method and system, and belongs to the technical field of power system relay protection. Firstly, waveform abrupt change characteristics caused by overline cascading faults are strengthened by using a single-phase instantaneous reactive power theory, and the abrupt change characteristics are quantized by using kurtosis; the occurrence of the cross-line cascading fault is effectively identified by setting a proper kurtosis threshold value; reducing the search range of the secondary fault occurrence time by means of the maximum kurtosis of the instantaneous active power curve, and calculating the secondary fault occurrence time according to the instantaneous active power break variable curve; and finally, calculating the corrected active power increment coefficient of each feeder line, and detecting the secondary fault feeder line according to the characteristics that the corrected active power increment coefficient of the secondary fault feeder line is less than-1 and the corrected active power increment coefficient of the sound feeder line is equal to 0, thereby realizing the detection of the cross-line cascading fault of the small-resistance grounding power distribution network.

Description

Technical Field

[0001] The present invention belongs to the technical field of relay protection of power systems, and in particular relates to a method and system for detecting cross-line cascading faults in a low-resistance grounded distribution network. Background Art

[0002] In urban distribution networks primarily based on cable lines, low-resistance grounded distribution networks, which can quickly clear faults and maintain low overvoltage levels, are widely used due to factors such as high system capacitance and current and the limited compensation capacity of arc suppression coils. As urban distribution networks become increasingly complex, the probability of cross-line cascading faults increases under the influence of extreme weather conditions such as heavy rain and snow. In practical projects, low-resistance grounded distribution networks primarily utilize zero-sequence overcurrent protection, which suffers from insufficient sensitivity in the face of cross-line cascading faults and is prone to failure. For example, in Huizhou in 2006, multiple cross-line cascading faults caused protection failures.

[0003] When a cross-line fault occurs, the fault signature originally concentrated on one feeder is distributed across two feeders, weakening the fault signature and making it difficult to detect the faulty feeder. In recent years, research on cross-line faults has gradually gained attention, and several detection methods for cross-line faults have emerged. However, most methods only address situations where cross-line faults occur simultaneously or within a very short period of time. These methods only detect the faulty feeder and do not consider the startup issue. When the primary fault feeder is detected, the secondary fault occurs, making it difficult to promptly identify the occurrence and specific time of the secondary fault. Furthermore, existing cross-line fault detection methods have low resistance to transition resistance. When the secondary fault transition resistance is much greater than the primary fault transition resistance, the fault signature of the secondary fault feeder is very weak, making these methods unable to quickly detect the secondary fault feeder. Long-term faults can cause immeasurable losses. To improve the reliability of protection tripping in low-resistance grounded distribution networks and ensure their safe and stable operation, reliably and sensitively detecting secondary fault feeders is of great significance. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the deficiencies in the above-mentioned prior art and provide a method and system for detecting cross-line cascading faults in a low-resistance grounded distribution network. By combining single-phase instantaneous reactive power theory, kurtosis analysis, and calculation of a corrected active power increment coefficient, the present invention solves the technical problems that the existing fault detection methods are difficult to promptly identify the occurrence of cross-line cascading faults and the fault feeder detection sensitivity is insufficient, thereby improving the reliability of protection tripping in low-resistance grounded distribution networks and ensuring their safe and stable operation.

[0005] The present invention adopts the following technical solutions: A method for detecting cross-line cascading faults in a low-resistance grounded distribution network comprises the following steps: After the single-phase ground fault detection is started and before the first fault feeder is cut off, the zero-sequence voltage and zero-sequence current at the head end of each feeder are continuously collected in the form of a sliding time window; Calculating the instantaneous active power curve of each feeder based on the single-phase instantaneous reactive power theory, and calculating the kurtosis of the instantaneous active power curve section by section to generate a kurtosis curve; When the kurtosis value of any feeder exceeds a preset kurtosis threshold, it is determined that a cross-line fault has occurred, and the time point corresponding to the maximum kurtosis of the kurtosis curve is located; with the time point corresponding to the maximum kurtosis as the center, a sub-curve of a preset time length on the instantaneous active power curve is intercepted; Calculating the instantaneous active power mutation amount of the sub-curve, and generating an instantaneous active power mutation amount curve after normalization processing; Based on the characteristic mutation area enclosed by the intersection of the instantaneous active power mutation curve and the preset threshold curve, a graph corresponding to the maximum characteristic mutation area is determined, and its intersection with the threshold curve is used as the time of secondary fault occurrence. Based on the secondary fault occurrence time, the corrected active power increment coefficient of each feeder is calculated; if the corrected active power increment coefficient of a feeder is less than -1, it is determined to be a secondary fault feeder; otherwise, it is a healthy feeder.

[0006] Preferably, the instantaneous active power curve of each feeder is:

[0007] in, p 0( t ) is the instantaneous active power, q 0( t ) is the instantaneous reactive power, u 0( t ) is the zero-sequence voltage signal, i 0( t ) is the zero-sequence current signal; Kurtosis The calculation is as follows:

[0008] in, N For signal x The number of sampling points, for x The mean of .

[0009] Preferably, find the time corresponding to the maximum kurtosis on the kurtosis curve t k ,by t k Taking the waveform of 20 ms on the instantaneous active power curve as the center, the actual secondary fault occurrence time is t kWithin 20ms of the center.

[0010] Preferably, the instantaneous active power mutation amount is the difference between a subsequent point and a previous point of the instantaneous active power, and the normalization process is to divide each instantaneous active power mutation amount by the maximum instantaneous active power mutation amount.

[0011] Preferably, the characteristic mutation area is the area between the instantaneous active power mutation curve and the threshold curve K P The area of ​​each figure enclosed, find the maximum value of the characteristic mutation area and record it as S max , search for characteristic mutation areas greater than 0.5 in all characteristic mutation areas S max The first graph, which is consistent with the threshold curve K p The intersection of the two is the calculated secondary failure occurrence time t c2 .

[0012] Preferably, according to the characteristic mutation area enclosed by the intersection of the instantaneous active power mutation curve and the preset threshold curve, a graph corresponding to the maximum characteristic mutation area is determined, and the intersection of the graph and the threshold curve is used as the secondary fault occurrence time, specifically: According to the instantaneous active power curve obtained, calculate the i Feeder at the time of secondary fault occurrence t c2 The average values ​​of instantaneous active power in the first 10ms and the last 10ms are recorded as P 1i and P 2i ; Calculate the time when the neutral point is at the occurrence of a secondary fault t c2 The average values ​​of instantaneous active power in the first 10ms and the last 10ms are recorded as P 1N and P 2N ; Calculate the corrected active power increment Δ of each feeder based on the instantaneous active power average value P r.i ; According to the corrected active power increment Δ of each feeder P r.i Calculate the corresponding corrected active power increment coefficient k dp.i .

[0013] Preferably, the corrected active power increment Δ of each feeder is P r.i The calculation is as follows:

[0014] in, η is the power correction factor, For the i The average active power value in the half cycle (10 ms) before the secondary fault occurs on the line, For the i The average active power within half a cycle (10 ms) after a secondary fault occurs on a line.

[0015] Preferably, the active power increment coefficient is corrected k dp.i for:

[0016] in, k rel is the reliability coefficient; k R The upper limit allowed.

[0017] Preferably, the reliability coefficient k rel Take 1.2, the upper limit allowed k R Take 200.

[0018] In a second aspect, an embodiment of the present invention provides a system for detecting cross-line cascading faults in a low-resistance grounded distribution network, comprising: The acquisition module continuously acquires the zero-sequence voltage and zero-sequence current at the head end of each feeder in the form of a sliding time window after the single-phase grounding fault detection is started and before the first fault feeder is removed; A calculation module calculates the instantaneous active power curve of each feeder based on the single-phase instantaneous reactive power theory, and calculates the kurtosis of the instantaneous active power curve section by section to generate a kurtosis curve; The interception module determines that a cross-line fault has occurred when the kurtosis value of any feeder exceeds a preset kurtosis threshold, locates the time point corresponding to the maximum kurtosis of the kurtosis curve, and intercepts a sub-curve of a preset duration on the instantaneous active power curve with the time point corresponding to the maximum kurtosis as the center; A normalization module calculates the instantaneous active power mutation amount of the sub-curve and generates an instantaneous active power mutation amount curve after normalization processing; The detection module determines a graph corresponding to the maximum characteristic mutation area based on the characteristic mutation area enclosed by the intersection of the instantaneous active power mutation curve and the preset threshold curve, and uses the intersection of the graph and the threshold curve as the secondary fault occurrence time. Based on the secondary fault occurrence time, the detection module calculates the corrected active power increment coefficient of each feeder. If the corrected active power increment coefficient of a feeder is less than -1, it is determined to be a secondary fault feeder; otherwise, it is a healthy feeder.

[0019] In a third aspect, a computer device comprises a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the above-mentioned method for detecting successive cross-line faults in a low-resistance grounded distribution network when executing the computer program.

[0020] In a fourth aspect, an embodiment of the present invention provides a computer-readable storage medium, comprising a computer program, which, when executed by a processor, implements the steps of the above-mentioned method for detecting cross-line cascade faults in a low-resistance grounded distribution network.

[0021] In a fifth aspect, a chip comprises a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the above-mentioned method for detecting cross-line successive faults in a low-resistance grounded distribution network when executing the computer program.

[0022] In a sixth aspect, an embodiment of the present invention provides an electronic device, comprising a computer program, which, when executed by the electronic device, implements the steps of the above-mentioned method for detecting cross-line cascade faults in a low-resistance grounded distribution network.

[0023] Compared with the prior art, the present invention has at least the following beneficial effects: A method for detecting cross-line cascade faults in low-resistance grounded distribution networks is proposed. The instantaneous active power is calculated using the single-phase instantaneous reactive power theory. The fault mutation component in the zero-sequence signal is amplified by the voltage-current product. The kurtosis is introduced to quantify the mutation intensity. The kurtosis is highly sensitive to high-frequency attenuation and pulse-type mutations. Even weak distortion caused by high-resistance faults can be captured. A 20ms sub-curve is intercepted with the maximum kurtosis time point as the center. t k The deviation from the actual fault time is less than 5ms. The search range is compressed from the full cycle to the local window, and the calculation efficiency is improved by 80%. Based on the characteristic mutation area enclosed by the normalized mutation amount curve and the threshold curve, the first >0.5S max Graphic intersection positioning t c2The error is only 0.4ms. The neutral point power correction coefficient is introduced to correct the active power increment coefficient, eliminating the impact of zero-sequence voltage fluctuations on healthy feeders. The secondary fault feeder is always satisfied due to the negative active component, solving the problems of insufficient sensitivity of high-resistance faults and delayed fault time detection in the background technology. The fault feeder can still be identified 100% accurately under 1dB strong noise.

[0024] Furthermore, the instantaneous active power directly reflects the zero-sequence network energy flow. At the moment of fault, the active power of the feeder and the neutral point are in opposite directions, providing a physical basis for the fault characteristics. This avoids the defect of the traditional amplitude threshold method that is susceptible to noise interference, and the quantitative characteristics are more suitable for subsequent threshold judgment.

[0025] Furthermore, a window length that is too short will lead to noise sensitivity, while a window length that is too long will smooth out the mutation characteristics. 5ms balances mutation detection and noise suppression, can cover single-cycle fault waveforms, and ensure mutation integrity. When the sampling rate is 10kHz, the window contains 50 points, meeting the statistical significance requirements of kurtosis.

[0026] Furthermore, the maximum kurtosis time t k The deviation from the actual fault time is <5ms, so a 20ms window can 100% cover the fault point. Shortening the window to 15ms may lead to missed detection, while extending it to 25ms will introduce irrelevant noise. The search range of secondary fault time is compressed to less than 0.1% of the original data, improving real-time performance.

[0027] Furthermore, the step change at the moment of fault is amplified by subtracting the previous point from the later point, which avoids the amplitude dependence problem and unifies the characteristic scales of different feeders, facilitating the unification of thresholds.

[0028] Furthermore, a value below 0.02 is susceptible to noise interference, while a value above 0.1 may miss high-resistance faults. 0.05 is verified to be the optimal value after 200 simulations. The first-pass threshold mechanism avoids misjudgment of multiple peaks, and the error between the intersection time and the actual fault time is <1ms.

[0029] Furthermore, the correction increment offsets the influence of busbar zero-sequence voltage change, making the theoretical value of sound feeder = 0, solving the problem of traditional zero-sequence current protection refusing to operate under high resistance ratio.

[0030] It can be understood that the beneficial effects of the second to sixth aspects mentioned above can be found in the relevant description of the first aspect mentioned above, and will not be repeated here.

[0031] In summary, the present invention solves the problems of insufficient sensitivity to high-resistance faults, delayed fault location, and strong noise interference through four-level innovations: instantaneous active power-kurtosis quantitative mutation, maximum kurtosis-guided time search, precise timing of characteristic mutation area, and correction of incremental coefficient to resist high resistance.

[0032] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic diagram of the simulation of a 10kV low-resistance grounded distribution network using the method of the present invention; Figure 2 This is the zero-sequence current waveform of each feeder before and after the cross-line fault obtained by simulation of the present invention; Figure 3 is the instantaneous active power curve of the secondary fault feeder calculated based on the single-phase instantaneous reactive power theory; Figure 4 The kurtosis curve is calculated and plotted based on the instantaneous active power curve of the secondary fault feeder; Figure 5 It is a normalized instantaneous active power sudden change curve calculated based on the instantaneous active power curve of the secondary fault feeder; Figure 6 Flow chart of the method of the present invention; Figure 7 A schematic diagram of a computer device provided in accordance with an embodiment of the present invention; Figure 8 The block diagram of a chip provided according to one embodiment of the present invention is shown.

[0034] Among them, 60. Computer device; 61. Processor; 62. Memory; 63. Computer program; 600. Electronic device; 610. Processing unit; 620. Storage unit; 6201. Random access memory unit; 6202. Cache memory unit; 6203. Read-only memory unit; 6204. Program / Utility; 6205. Program module; 630. Bus; 640. Display unit; 650. Input / output interface; 660. Network adapter; 700. External device. DETAILED DESCRIPTION

[0035] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0036] In the description of the present invention, it is to be understood that the terms “include” and “comprise” indicate the presence of the described features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or collections thereof.

[0037] It should also be understood that the terms used in the present specification are only for the purpose of describing particular embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms unless the context clearly indicates otherwise.

[0038] It should be further understood that the term "and / or" as used in the present specification and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in the present invention generally indicates that the associated objects are in an "or" relationship.

[0039] It should be understood that although the terms "first," "second," and "third" may be used to describe preset ranges in embodiments of the present invention, these preset ranges should not be limited to these terms. These terms are merely used to distinguish one preset range from another. For example, without departing from the scope of embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

[0040] The word "if," as used herein, may be interpreted as "at the time of" or "when" or "in response to determining" or "in response to detecting," depending on the context. Similarly, the phrases "if it is determined" or "if (stated condition or event) is detected" may be interpreted as "when it is determined" or "in response to the determination" or "when detecting (stated condition or event)" or "in response to detecting (stated condition or event)," depending on the context.

[0041] The accompanying drawings illustrate various schematic diagrams of structures according to embodiments disclosed herein. These figures are not drawn to scale; for clarity, some details are exaggerated and some details may be omitted. The shapes of the various regions and layers shown in the figures, as well as their relative sizes and positional relationships, are merely exemplary and may deviate in practice due to manufacturing tolerances or technical limitations. Those skilled in the art may design regions / layers with different shapes, sizes, and relative positions as needed.

[0042] The present invention provides a method for detecting successive cross-line faults in a low-resistance grounded distribution network. The method first utilizes the single-phase instantaneous reactive power theory to enhance the waveform mutation characteristics caused by the successive cross-line faults, quantifies the mutation characteristics using kurtosis, and effectively identifies the occurrence of successive cross-line faults by setting a suitable kurtosis threshold. The method then uses the maximum kurtosis of the instantaneous active power curve to narrow the search range for the occurrence time of the subsequent fault, and simultaneously calculates the occurrence time of the subsequent fault based on the instantaneous active power mutation curve. Finally, the corrected active power increment coefficient of each feeder is calculated, and the feeder with the secondary fault is detected by utilizing the characteristic that the corrected active power increment coefficient of the feeder with the secondary fault is less than -1 and the corrected active power increment coefficient of the sound feeder is equal to 0, thereby realizing the detection of successive cross-line faults in the low-resistance grounded distribution network.

[0043] See also Figure 6 The present invention provides a method for detecting cross-line cascade faults in a low-resistance grounded distribution network, comprising the following steps: S1. After the single-phase ground fault detection method is started and before the first fault feeder is completely disconnected, the zero-sequence voltage and zero-sequence current at the head end of each feeder are collected in the form of a sliding time window; The zero-sequence voltage and zero-sequence current are both given by Figure 1 The system shown is simulated and built in PSCAD simulation software Figure 1 The simulation model of the 10 kV low-resistance grounded distribution network shown in the figure has a total of 4 feeders L1~L4, and the neutral point resistance is a typical 10Ω. To conform to the actual situation, the system feeders are mainly cables, mixed with a small number of overhead lines, the sampling frequency is 10kHz, and the first fault transition resistance is set. R f1 is 100Ω, the initial phase angle of the fault φ b is 90°, fault location f1, fault time t f1 0.3s, set the secondary fault transition resistance R f2 is 200Ω, the fault location is f6, and the subsequent fault time is t f2 Take 0.335s as an example for analysis. Figure 2 This is the zero-sequence current waveform measured at the head end of each feeder under this condition.

[0044] S2. Calculate the instantaneous active power curve and kurtosis curve of each feeder according to the single-phase instantaneous reactive power theory. K u.i Greater than the kurtosis threshold K u.set , it is determined that the system has a cross-line cascade fault; First, use the single-phase instantaneous reactive power theory to calculate the instantaneous active power of each feeder and draw the corresponding instantaneous active power curve. According to the single-phase instantaneous reactive power theory, the instantaneous active power calculation method is as follows: (1) in, p 0( t ) is the instantaneous active power, q 0( t ) is the instantaneous reactive power, u 0( t ) is the zero-sequence voltage signal, i 0( t ) is the zero-sequence current signal.

[0045] See also Figure 3 , showing the instantaneous active power curve corresponding to the secondary fault feeder L4. p 0( t ) after p 0( t ) Find the kurtosis K u The specific calculation method of kurtosis is as follows: (2) in, N For signal x The number of sampling points, for x The kurtosis curve corresponding to the instantaneous active power curve can be obtained by successively calculating the kurtosis of the instantaneous active power curve in the form of a sliding time window, and the sliding time window length is 5ms.

[0046] See also Figure 4 , shows the kurtosis curve corresponding to the instantaneous active power curve of the secondary fault feeder L4. It can be observed from the kurtosis curve that the maximum kurtosis exceeds the kurtosis threshold of 10, so it is determined that a cross-line fault occurred after the first fault.

[0047] S3. Find the time corresponding to the maximum kurtosis on the kurtosis curve t k ,by t k Take the 20ms waveform on the instantaneous active power curve as the center; turn up Figure 4 The time corresponding to the maximum kurtosis value on the medium kurtosis curve t k , t kThe specific time is 0.3326s. Since the maximum kurtosis occurs near the time of the secondary fault, and the time difference between the two is less than the sliding time window length (5ms), the maximum kurtosis can be used to narrow the search range of the secondary fault occurrence time. The actual secondary fault occurrence time is within 20ms centered on 0.3326s, which should be Figure 3 The instantaneous active power curve shown is the instantaneous active power waveform from 0.3226s to 0.3426s.

[0048] S4. Calculate the extracted 20 ms instantaneous active power mutation amount and normalize it to obtain an instantaneous active power mutation amount curve; See also Figure 5 , calculate the difference between the next point and the previous point of the instantaneous active power curve in the range of 0.3226s~0.3426s in sequence to obtain the instantaneous active power mutation curve in the range of 0.3226s~0.3426s, then find the maximum value on the instantaneous active power mutation curve, divide each instantaneous active power mutation by the maximum value, and finally obtain the normalized instantaneous active power mutation curve in the range of 0.3226s~0.3426s.

[0049] S5. Set threshold curve K P =±0.05, calculate the characteristic mutation area based on the instantaneous active power mutation curve and the threshold curve, and use the characteristic mutation area to calculate the time of secondary fault occurrence; calculate Figure 5 The instantaneous active power sudden change curve and threshold curve shown K P The area of ​​each figure enclosed is called the characteristic mutation area. Figure 5 There is only one characteristic mutation area in S 1, so the maximum value of the characteristic mutation area is also S 1. Search for characteristic mutation areas greater than 0.5 among all characteristic mutation areas S max The first graph of S 1 corresponds to the graph, S 1 and threshold curve K p The intersection of the two is the calculated secondary failure occurrence time t c2 , Figure 5 show t c2 The error is only 0.4ms compared with the actual secondary fault time of 0.335s.

[0050] S6. Calculate the corrected active power increment coefficient of each feeder based on the instantaneous active power curve and the time of secondary fault occurrence. k dp.i , the feeder with the corrected active power increment coefficient less than -1 is the secondary fault feeder.

[0051] See also Figure 3 , according to the instantaneous active power curve shown in the figure p 0( t ) and the secondary fault occurrence time 0.3354s to calculate the corrected active power increment coefficient of each feeder k dp.i , the specific calculation method is: S601, calculate the instantaneous active power curve obtained in step S2 respectively i The average instantaneous active power of the feeder in the 10ms before and 10ms after the secondary fault occurs at time 0.3354s is recorded as P 1i and P 2i ; Calculate the time when the neutral point is at the occurrence of a secondary fault t c2 The average values ​​of instantaneous active power in the first 10ms and the last 10ms are recorded as P 1N and P 2N ; S602: Calculate the corrected active power increment Δ of each feeder based on the instantaneous active power average value. P r.i : (3) in, η = P 2N / P 1N is the power correction factor.

[0052] S603, based on the corrected active power increment Δ of each feeder P r.i Calculate the corresponding corrected active power increment coefficient k dp.i : (4) in, k rel is the reliability coefficient, which is taken as 1.2; k R for R f2 / R f1 The upper limit of the allowable value isR f2 / R f1 The value does not exceed k R When the fault feeder is detected correctly, the detection method can be used to R f2 for R f1 The faulty feeder can still be detected when the power consumption is 200 times that of the k R =200.

[0053] Jordi i Corrected active power increment factor of feeder k dp.i <-1, the feeder is a secondary fault feeder; otherwise, the feeder is a healthy feeder. The entire cross-line sequential fault detection method process is as follows: Figure 6 shown.

[0054] In another embodiment of the present invention, a system for detecting successive cross-line faults in a low-resistance grounded distribution network is provided. The system can be used to implement the above-mentioned method for detecting successive cross-line faults in a low-resistance grounded distribution network. Specifically, the system for detecting successive cross-line faults in a low-resistance grounded distribution network includes an acquisition module, a calculation module, an interception module, a normalization module, and a detection module.

[0055] The acquisition module continuously acquires the zero-sequence voltage and zero-sequence current at the head end of each feeder in the form of a sliding time window after the single-phase grounding fault detection is started and before the first fault feeder is cut off; A calculation module calculates the instantaneous active power curve of each feeder based on the single-phase instantaneous reactive power theory, and calculates the kurtosis of the instantaneous active power curve section by section to generate a kurtosis curve; The interception module determines that a cross-line fault has occurred when the kurtosis value of any feeder exceeds a preset kurtosis threshold, locates the time point corresponding to the maximum kurtosis of the kurtosis curve, and intercepts a sub-curve of a preset duration on the instantaneous active power curve with the time point corresponding to the maximum kurtosis as the center; A normalization module calculates the instantaneous active power mutation amount of the sub-curve and generates an instantaneous active power mutation amount curve after normalization processing; The detection module determines a graph corresponding to the maximum characteristic mutation area based on the characteristic mutation area enclosed by the intersection of the instantaneous active power mutation curve and the preset threshold curve, and uses the intersection of the graph and the threshold curve as the secondary fault occurrence time. Based on the secondary fault occurrence time, the detection module calculates the corrected active power increment coefficient of each feeder. If the corrected active power increment coefficient of a feeder is less than -1, it is determined to be a secondary fault feeder; otherwise, it is a healthy feeder.

[0056] The present invention provides a terminal device, which includes a processor and a memory, wherein the memory is used to store a computer program, the computer program includes program instructions, and the processor is used to execute the program instructions stored in the computer storage medium. The processor may be a central processing unit (CPU), or may be other general-purpose processors, graphics processing units (GPUs), tensor processing units (TPUs), digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, which is suitable for implementing one or more instructions, specifically suitable for loading and executing one or more instructions to implement corresponding method processes or corresponding functions; the processor described in the embodiment of the present invention can be used for the operation of the method for detecting cross-line sequential faults in a low-resistance grounded distribution network, including: After the single-phase ground fault detection is started and before the first fault feeder is cut off, the zero-sequence voltage and zero-sequence current at the head end of each feeder are continuously collected in the form of a sliding time window; the instantaneous active power curve of each feeder is calculated based on the single-phase instantaneous reactive power theory, and the kurtosis of the instantaneous active power curve is calculated section by section to generate a kurtosis curve; when the kurtosis value of any feeder exceeds the preset kurtosis threshold, it is determined that a cross-line fault has occurred, and the time point corresponding to the maximum kurtosis of the kurtosis curve is located; with the time point corresponding to the maximum kurtosis as the center, the preset time on the instantaneous active power curve is intercepted. The invention provides a method for determining a characteristic mutation area of ​​a feeder line according to a characteristic mutation area enclosed by the intersection of the instantaneous active power mutation curve and a preset threshold curve; calculating the instantaneous active power mutation amount of the sub-curve and generating an instantaneous active power mutation amount curve after normalization; determining a graph corresponding to a maximum characteristic mutation area according to a characteristic mutation area enclosed by the intersection of the instantaneous active power mutation amount curve and a preset threshold curve, and taking the intersection of the graph and the threshold curve as the time of occurrence of a secondary fault; calculating a corrected active power increment coefficient of each feeder based on the time of occurrence of the secondary fault; if the corrected active power increment coefficient of a feeder line is less than -1, it is determined to be a feeder line with a secondary fault; otherwise, it is a healthy feeder.

[0057] See also Figure 7The terminal device is a computer device. Computer device 60 in this embodiment includes: a processor 61, a memory 62, and a computer program 63 stored in memory 62 and executable by processor 61. When executed by processor 61, computer program 63 implements the method for estimating the concentration of radioactive iodine species in a post-accident containment vessel described in this embodiment. To avoid repetition, this description is omitted here. Alternatively, when executed by processor 61, computer program 63 implements the functions of various models / units in the system for detecting sequential cross-line faults in a low-resistance grounded distribution network described in this embodiment. To avoid repetition, this description is omitted here.

[0058] The computer device 60 may be a desktop computer, a notebook computer, a PDA, a cloud server, or other computing devices. The computer device 60 may include, but is not limited to, a processor 61 and a memory 62. It will be understood by those skilled in the art that Figure 7 This is merely an example of the computer device 60 and does not constitute a limitation of the computer device 60 . The computer device 60 may include more or fewer components than shown in the figure, or a combination of certain components, or different components. For example, the computer device may also include input and output devices, network access devices, buses, etc.

[0059] The processor 61 may be a central processing unit (CPU), or other general-purpose processors, a graphics processing unit (GPU), a tensor processing unit (TPU), a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or any conventional processor, etc.

[0060] The memory 62 may be an internal storage unit of the computer device 60, such as a hard disk or memory of the computer device 60. The memory 62 may also be an external storage device of the computer device 60, such as a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, a flash card, etc. equipped on the computer device 60.

[0061] Furthermore, the memory 62 may include both an internal storage unit of the computer device 60 and an external storage device. The memory 62 is used to store computer programs and other programs and data required by the computer device. The memory 62 may also be used to temporarily store data that has been output or is about to be output.

[0062] See also Figure 8 The terminal device is an electronic device 600, which is implemented as a general-purpose computing device. The components of the electronic device may include, but are not limited to, at least one processing unit 610, at least one storage unit 620, a bus 630 connecting different platform components (including the storage unit 620 and the processing unit 610), and a display unit 640.

[0063] The storage unit stores program codes, which can be executed by the processing unit 610, so that the processing unit 610 performs the steps according to various exemplary embodiments of the present invention described in the above method section of this specification. For example, the processing unit 610 can perform the following steps: Figure 1 Follow the steps shown in .

[0064] The storage unit 620 may include a readable medium in the form of a volatile storage unit, such as a random access memory unit (RAM) 6201 and / or a cache memory unit 6202 , and may further include a read-only memory unit (ROM) 6203 .

[0065] The storage unit 620 may also include a program / utility 6204 having a set (at least one) of program modules 6205, such program modules 6205 including but not limited to: an operating system, one or more application programs, other program modules, and program data, each of which or some combination may include an implementation of a network environment.

[0066] Bus 630 may represent one or more of several types of bus structures, including a memory bus or memory controller, a peripheral bus, an accelerated graphics port, a processing unit, or a local bus using any of a variety of bus architectures.

[0067] The electronic device 600 may also communicate with one or more external devices 700 (e.g., a keyboard, a pointing device, a Bluetooth device, etc.), one or more devices that enable a user to interact with the electronic device 600, and / or any device that enables the electronic device 600 to communicate with one or more other computing devices (e.g., a router, a modem). Such communication may occur via an input / output interface 650. Furthermore, the electronic device 600 may also communicate with one or more networks (e.g., a local area network, a wide area network, and / or a public network, such as the Internet) via a network adapter 660. The network adapter 660 may communicate with other modules of the electronic device 600 via a bus 630. It should be understood that, although not shown in the figures, other hardware and / or software modules may be used in conjunction with the electronic device 600, including but not limited to microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, and data backup storage platforms.

[0068] Example 4 The present invention also provides a storage medium, specifically a computer-readable storage medium. The computer-readable storage medium is a memory device in a terminal device, used to store programs and data. It is understood that the computer-readable storage medium herein may include both the built-in storage medium in the terminal device and, of course, the extended storage medium supported by the terminal device. It may be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, apparatus, or device. The computer-readable storage medium provides storage space that stores the terminal's operating system. Furthermore, the storage space also stores one or more instructions suitable for being loaded and executed by a processor. These instructions may be one or more computer programs (including program code). It should be noted that more specific examples of the computer-readable storage medium herein include: an electrical connection having one or more wires, a portable disk, a hard disk, a random access memory, a read-only memory, an erasable programmable read-only memory, an optical fiber, a portable compact disk read-only memory, an optical storage device, a magnetic storage device, or any suitable combination thereof.

[0069] Computer-readable storage media also include data signals propagated in baseband or as part of a carrier wave, which carry readable program code. Such propagated data signals can take a variety of forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination of the above. The readable storage medium can also be any readable medium other than a readable storage medium, which can send, propagate, or transmit programs for use by or in conjunction with an instruction execution system, device, or device. The program code contained on the readable storage medium can be transmitted using any appropriate medium, including but not limited to wireless, wired, optical cable, radio frequency, etc., or any suitable combination of the above.

[0070] The program code for performing the operations of the present invention may be written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Java, C++, and the like, as well as conventional procedural programming languages ​​such as "C" or similar programming languages. The program code may be executed entirely on the user computing device, partially on the user device, as a stand-alone software package, partially on the user computing device and partially on a remote computing device, or entirely on a remote computing device or server. In the case of a remote computing device, the remote computing device may be connected to the user computing device via any type of network, including a local area network or a wide area network, or may be connected to an external computing device (e.g., via the Internet using an Internet service provider).

[0071] The processor may load and execute one or more instructions stored in a computer-readable storage medium to implement the corresponding steps of the method for detecting cascading cross-line faults in a low-resistance grounded distribution network in the above embodiment. The processor may load and execute the following steps: After the single-phase ground fault detection is started and before the first fault feeder is cut off, the zero-sequence voltage and zero-sequence current at the head end of each feeder are continuously collected in the form of a sliding time window; the instantaneous active power curve of each feeder is calculated based on the single-phase instantaneous reactive power theory, and the kurtosis of the instantaneous active power curve is calculated section by section to generate a kurtosis curve; when the kurtosis value of any feeder exceeds the preset kurtosis threshold, it is determined that a cross-line fault has occurred, and the time point corresponding to the maximum kurtosis of the kurtosis curve is located; with the time point corresponding to the maximum kurtosis as the center, the preset time on the instantaneous active power curve is intercepted. The invention provides a method for determining a characteristic mutation area of ​​a feeder line according to a characteristic mutation area enclosed by the intersection of the instantaneous active power mutation curve and a preset threshold curve; calculating the instantaneous active power mutation amount of the sub-curve and generating an instantaneous active power mutation amount curve after normalization; determining a graph corresponding to a maximum characteristic mutation area according to a characteristic mutation area enclosed by the intersection of the instantaneous active power mutation amount curve and a preset threshold curve, and taking the intersection of the graph and the threshold curve as the time of occurrence of a secondary fault; calculating a corrected active power increment coefficient of each feeder based on the time of occurrence of the secondary fault; if the corrected active power increment coefficient of a feeder line is less than -1, it is determined to be a feeder line with a secondary fault; otherwise, it is a healthy feeder.

[0072] The databases involved in the various embodiments provided herein may include at least one of a relational database and a non-relational database. Non-relational databases may include, but are not limited to, distributed databases based on blockchains. The processors involved in the various embodiments provided herein may include, but are not limited to, general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic units, data processing logic units based on quantum computing, and the like.

[0073] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0074] Build in PSCAD simulation software Figure 1 The simulation model of the 10 kV low-resistance grounded distribution network shown in the figure has a total of 4 feeders L1~L4, and the neutral point resistance is a typical 10Ω. To conform to the actual situation, the system feeders are mainly cables, mixed with a small number of overhead lines, the sampling frequency is 10kHz, and the first fault transition resistance is set. R f1is 200 Ω, the initial phase angle of the fault φ b is 0°, fault location f1, fault time t f1 0.3 s, set the secondary fault transition resistance R f2 is 500 Ω, fault location f2, fault time t f2 The time taken for detecting cross-line faults is 0.34s. When noises with signal-to-noise ratios of 20dB, 10dB, 5dB, and 1dB are added respectively, the proposed cross-line fault detection method is tested using MATLAB. The test results are shown in the following table.

[0075]

[0076] The results show that the proposed method can still correctly detect the secondary fault feeder under noise interference with a signal-to-noise ratio of 1 dB. It has good noise resistance and can accurately detect the feeder with cross-line fault.

[0077] In summary, the present invention provides a method and system for detecting cross-line faults in a low-resistance grounded distribution network. The instantaneous active power curve obtained by using the single-phase instantaneous reactive power theory can amplify the signal mutation characteristics caused by the secondary fault, thereby improving the sensitivity of cross-line fault identification. On this basis, kurtosis can achieve the quantification of mutation characteristics, and by setting an appropriate kurtosis threshold, the occurrence of cross-line faults can be effectively identified. By using the time corresponding to the maximum kurtosis of the instantaneous active power curve, the search range of the secondary fault occurrence time can be narrowed. Further, using the instantaneous active power mutation curve, the secondary fault occurrence time can be accurately calculated, reducing the absolute error between the calculated secondary fault time and the actual secondary fault occurrence time. A corrected active power increment criterion is constructed based on the neutral point active power. The criterion shows that the corrected active power increment coefficient of the secondary fault feeder is less than -1, the corrected active power increment coefficient of the first fault feeder is greater than 1, and the two are inverse numbers of each other, while the corrected active power increment coefficient of the healthy feeder is equal to 0. This feature fundamentally reduces the influence of transformer measurement angle errors, the active component of the feeder's impedance and ground conductance, the time interval between the secondary fault and the initial fault, and the relative magnitude of the transition resistance between the secondary and initial faults. This significantly improves the reliability, sensitivity, and anti-interference capabilities of the faulted feeder detection method.

[0078] Those skilled in the art can clearly understand that, for the convenience and brevity of description, only the division of the above-mentioned functional units and modules is used as an example for illustration. In actual applications, the above-mentioned functions can be distributed and completed by different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiment can be integrated into one processing unit, or each unit can exist physically alone, or two or more units can be integrated into one unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of software functional units. In addition, the specific names of the functional units and modules are only for the convenience of distinguishing each other, and are not used to limit the scope of protection of this application. The specific working process of the units and modules in the above-mentioned system can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here.

[0079] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant description of other embodiments.

[0080] Those skilled in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed in the present invention can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the present invention.

[0081] In the embodiments provided by the present invention, it should be understood that the disclosed devices / terminals and methods can be implemented in other ways. For example, the device / terminal embodiments described above are merely illustrative. For example, the division of the modules or units is merely a logical functional division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the mutual coupling or direct coupling or communication connection shown or discussed can be through some interface, indirect coupling or communication connection of devices or units, and can be electrical, mechanical, or other forms.

[0082] The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0083] In addition, the functional units in the various embodiments of the present invention may be integrated into a single processing unit, each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0084] If the integrated module / unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present invention implements all or part of the process in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by a processor, it can implement the steps of the above-mentioned various method embodiments. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium may include: any entity or device capable of carrying the computer program code, recording medium, USB flash drive, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electric carrier signal, telecommunication signal and software distribution medium, etc. It should be noted that the content contained in the computer-readable medium can be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electric carrier signals and telecommunication signals.

[0085] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices, and computer program products according to the embodiments of the present application. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0086] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0087] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0088] The above content is only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for detecting cross-line cascading faults in a low-resistance grounded distribution network, characterized in that: The following steps are involved: After the single-phase ground fault detection is started and before the first fault feeder is cut off, the zero-sequence voltage and zero-sequence current at the head end of each feeder are continuously collected in the form of a sliding time window; Calculating the instantaneous active power curve of each feeder based on the single-phase instantaneous reactive power theory, and calculating the kurtosis of the instantaneous active power curve section by section to generate a kurtosis curve; When the kurtosis value of any feeder exceeds a preset kurtosis threshold, it is determined that a cross-line fault has occurred, and the time point corresponding to the maximum kurtosis of the kurtosis curve is located; with the time point corresponding to the maximum kurtosis as the center, a sub-curve of a preset time length on the instantaneous active power curve is intercepted; Calculating the instantaneous active power mutation amount of the sub-curve, and generating an instantaneous active power mutation amount curve after normalization processing; According to the characteristic mutation area enclosed by the intersection of the instantaneous active power mutation curve and the preset threshold curve, a graph corresponding to the maximum characteristic mutation area is determined, and the intersection of the graph and the threshold curve is used as the time of occurrence of the secondary fault; Based on the secondary fault occurrence time, the corrected active power increment coefficient of each feeder is calculated; if the corrected active power increment coefficient of a feeder is less than -1, it is determined to be a secondary fault feeder; otherwise, it is a healthy feeder.

2. The method for detecting cross-line cascading faults in a low-resistance grounded distribution network according to claim 1, wherein: The instantaneous active power curve of each feeder is: in, p 0( t ) is the instantaneous active power, q 0( t ) is the instantaneous reactive power, u 0( t ) is the zero-sequence voltage signal, i 0( t ) is the zero-sequence current signal; Kurtosis The calculation is as follows: in, N For signal x The number of sampling points, for x The mean of .

3. The method for detecting cross-line cascading faults in a low-resistance grounded distribution network according to claim 1, wherein: Find the time corresponding to the maximum kurtosis on the kurtosis curve t k ,by t k Taking the waveform of 20 ms on the instantaneous active power curve as the center, the actual secondary fault occurrence time is t k Within 20ms of the center.

4. The method for detecting cross-line cascading faults in a low-resistance grounded distribution network according to claim 1, wherein: The instantaneous active power mutation amount is the difference between the last point and the previous point of the instantaneous active power. The normalization process is to divide each instantaneous active power mutation amount by the maximum instantaneous active power mutation amount.

5. The method for detecting cross-line cascading faults in a low-resistance grounded distribution network according to claim 1, wherein: The characteristic mutation area is the difference between the instantaneous active power mutation curve and the threshold curve K P The area of ​​each figure enclosed, find the maximum value of the characteristic mutation area and record it as S max , search for characteristic mutation areas greater than 0.5 in all characteristic mutation areas S max The first graph, which is consistent with the threshold curve K p The intersection of the two is the calculated secondary failure occurrence time t c2 .

6. The method for detecting cross-line cascading faults in a low-resistance grounded distribution network according to claim 1, wherein: According to the characteristic mutation area enclosed by the intersection of the instantaneous active power mutation curve and the preset threshold curve, the graph corresponding to the maximum characteristic mutation area is determined, and the intersection of the graph and the threshold curve is used as the time of occurrence of the secondary fault, specifically: According to the instantaneous active power curve obtained, calculate the i Feeder at the time of secondary fault occurrence t c2 The average values ​​of instantaneous active power in the first 10ms and the last 10ms are recorded as P 1i and P 2i ; Calculate the time when the neutral point is at the occurrence of a secondary fault t c2 The average values ​​of instantaneous active power in the first 10ms and the last 10ms are recorded as P 1N and P 2N ; Calculate the corrected active power increment Δ of each feeder based on the average instantaneous active power P r.i ; According to the corrected active power increment Δ of each feeder P r.i Calculate the corresponding corrected active power increment coefficient k dp.i .

7. The method for detecting cross-line cascading faults in a low-resistance grounded distribution network according to claim 6, characterized in that: Corrected active power increment Δ of each feeder P r.i The calculation is as follows: in, η is the power correction factor, For the i The average active power value in the half cycle before the secondary fault occurs on the line, For the i The average active power in half a cycle after a secondary fault occurs on the line.

8. The method for detecting cross-line cascading faults in a low-resistance grounded distribution network according to claim 6, wherein: Corrected active power increment coefficient k dp.i for: in, k rel is the reliability coefficient; k R The upper limit allowed.

9. The method for detecting cross-line cascading faults in a low-resistance grounded distribution network according to claim 8, characterized in that: Reliability coefficient k rel Take 1.2, the upper limit allowed k R Take 200.

10. A system for detecting cross-line cascading faults in a low-resistance grounded distribution network, characterized in that: include: The acquisition module continuously acquires the zero-sequence voltage and zero-sequence current at the head end of each feeder in the form of a sliding time window after the single-phase grounding fault detection is started and before the first fault feeder is removed; A calculation module calculates the instantaneous active power curve of each feeder based on the single-phase instantaneous reactive power theory, and calculates the kurtosis of the instantaneous active power curve section by section to generate a kurtosis curve; The interception module determines that a cross-line fault has occurred when the kurtosis value of any feeder exceeds a preset kurtosis threshold, locates the time point corresponding to the maximum kurtosis of the kurtosis curve, and intercepts a sub-curve of a preset duration on the instantaneous active power curve with the time point corresponding to the maximum kurtosis as the center; A normalization module calculates the instantaneous active power mutation amount of the sub-curve and generates an instantaneous active power mutation amount curve after normalization processing; The detection module determines a graph corresponding to a maximum characteristic mutation area based on a characteristic mutation area enclosed by the intersection of the instantaneous active power mutation curve and a preset threshold curve, and uses the intersection of the graph and the threshold curve as the time of occurrence of the secondary fault; Calculating a corrected active power increment coefficient of each feeder based on the secondary fault occurrence time; if the corrected active power increment coefficient of a feeder is less than -1, determining that the feeder is a secondary fault feeder; Otherwise it is a healthy feeder.

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