Single-phase broken line grounding fault detection method for neutral ungrounded system

Abstract

The invention belongs to the technical field of relay protection of a power distribution network of a power system, and provides a single-phase broken line grounding fault detection method for an ungrounded neutral system, which comprises the following steps of: 1, acquiring three-phase current signals of each feeder line; step 2, performing morphological filtering processing on the acquired negative sequence current signal; step 3, mapping the filtered negative sequence current signal to a time-frequency space with u as a variable; 4, searching an optimal twiddle factor according to the energy focusing characteristic of the time-frequency current signal; according to the method, the symmetric component method, the morphological filtering and the coordinate transformation technology are combined, so that the accuracy and the stability of single-phase broken line grounding fault feature extraction of the neutral ungrounded system are remarkably enhanced, and the precision and the reliability of fault detection are greatly improved; and meanwhile, the optimal twiddle factor is adaptively determined based on the feeder energy concentration ratio, so that the detection strategy can flexibly adapt to different fault conditions, and the fault detection efficiency and success rate under a complex power grid structure and variable operation conditions are effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of power system distribution network relay protection technology, specifically a method for detecting single-phase open-circuit grounding faults in a neutral point ungrounded system. Background Technology

[0002] As the terminal link connecting the power system to users, the safe and stable operation of the distribution network is crucial. Single-phase open-circuit grounding faults are among the common faults in distribution networks, often caused by factors such as lightning strikes, icing, and external damage. If a single-phase open-circuit grounding fault is not detected and handled in a timely manner, it will not only affect the stability of power supply and cause power outages for users, but may also cause electric shock accidents to people and animals due to the open-circuit grounding, or even develop into phase-to-phase short circuits, expanding the scope of the power outage and seriously threatening personal safety and the reliable operation of the power grid.

[0003] However, currently, power distribution networks are generally not equipped with dedicated open-circuit fault detection devices. Traditional short-circuit protection principles are inadequate when faced with single-phase open-circuit grounding faults and are difficult to detect effectively. There is an urgent need for a reliable method for detecting single-phase open-circuit grounding faults to ensure the safe and stable operation of power distribution networks. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method for detecting single-phase open-circuit grounding faults in a neutral-point ungrounded system. This method solves the problems that currently, power distribution networks generally lack dedicated open-circuit fault detection devices, and traditional short-circuit protection principles are insufficient for effective detection.

[0005] In a first aspect, the present invention provides a method for detecting a single-phase open-circuit grounding fault in a neutral-point ungrounded system, comprising the following steps:

[0006] Step 1: Collect the three-phase current signals of each feeder, and then use the symmetrical component method to calculate the negative sequence current signal of phase A of each feeder;

[0007] Step 2: Perform morphological filtering on the acquired negative sequence current signal;

[0008] Step 3: Through coordinate transformation, the filtered negative sequence current signal is mapped to a time-frequency space with u as the variable to obtain a time-frequency current signal containing the rotation factor parameter;

[0009] Step 4: Based on Step 3, for each feeder, find the optimal rotation factor according to the energy focusing characteristics of the time-frequency current signal, and then substitute the optimal rotation factor into the expression of the time-frequency current signal to generate the time-frequency current signal under the optimal rotation factor for each feeder.

[0010] Step 5: Calculate the peak amplitude of the time-frequency current signal for each feeder under the optimal rotation factor;

[0011] Step 6: Based on the peak amplitude of the time-frequency current signal under the optimal rotation factor, construct a single-phase open-circuit grounding fault detection criterion; compare the peak amplitude of the time-frequency current signal under the optimal rotation factor of each feeder with the threshold. When the peak amplitude is greater than the threshold, it is determined that a single-phase open-circuit grounding fault has occurred in the feeder.

[0012] Preferably, step 1 includes the following specific steps:

[0013] Step 1.1: Collect the three-phase current signal i within one cycle from the time of the fault occurrence of each feeder. ak (t), i bk (t), i ck (t), k = 1, 2, ..., m, where k represents the line number, i ak (t), i bk (t), i ck (t) represents the phase currents of the k-th feeder (a, b, c);

[0014] Step 1.2: Calculate the negative sequence current signal i of phase A of the three-phase current signal acquired in step 1.1 using the following formula. k (t):

[0015]

[0016] In the formula, α = e j120° It is a characteristic operator of the symmetric component method.

[0017] Preferably, the morphological filtering process in step 2 is as follows:

[0018] For the negative sequence current signals i of each feeder obtained in step 1 k (t) is processed using an alternating hybrid filter in morphological filtering to obtain the filtered negative sequence current signal i. k '(t).

[0019] Preferably, step 3 includes the following specific process:

[0020] The filtered negative sequence current signal i k '(t) is mapped to a time-frequency space with u as the variable through coordinate transformation, resulting in a time-frequency current signal i containing a rotation factor parameter. k (p,u):

[0021]

[0022] In the formula, the kernel function h p The specific expression for (t,u) is as follows:

[0023]

[0024] In the formula, u = tcosβ + fsinβ is the coordinate transformation formula, where f is the frequency. Let β be the rotation angle, p be the rotation factor, and p ∈ real numbers; and when the rotation angle β = 2nπ, the kernel function h p (t,u) is the impact function δ(t+u); when the rotation angle β=(2n+1)π, the kernel function h p (t,u) is the impulse function δ(t+u); where p∈real is a common mathematical symbol, and its meaning is as follows: p represents a variable, ∈ means "belongs to", real number refers to the set of real numbers; p∈real number means that the range of values ​​of variable p is the set of real numbers.

[0025] Preferably, step 4 includes the following specific steps:

[0026] Step 4.1: Within the rotation factor range p∈[0,2], sample at equal intervals with a step size of 0.1 to obtain the discrete rotation factor set {p s}, s=1,2,…,S, for each sampling point p s Using the time-frequency current signal formula defined in step 3:

[0027]

[0028] Calculate the corresponding time-frequency current signal i k (p s Construct a mapping relationship between the rotation factor and the time-frequency signal (u).

[0029] Step 4.2: Quantize the time-frequency current signal i k (p,u) represents the degree of energy concentration under different rotation factors p, and the energy concentration of each feeder is defined as C. k (p):

[0030]

[0031] That is, C k The larger (p) is, the greater the time-frequency current signal i k (p,u) is more concentrated under variable u;

[0032] Step 4.3: For each feeder, iterate through all sampling rotation factors p from Step 4.1. s Calculate the corresponding energy concentration C k (p s Select C k (p s The largest rotation factor is denoted as the optimal rotation factor p of the feeder. k_opt ;

[0033] Step 4.4: Apply the optimal rotation factor p determined in Step 4.3k_opt Substituting into the time-frequency current signal expression, we obtain the optimal rotation factor p for each feeder. k_opt The time-frequency current signal i k (p k_opt ,u k_opt ):

[0034]

[0035] In the formula, u k_opt For the corresponding optimal rotation factor p k_opt The variables under, For the corresponding optimal rotation factor p k_opt The kernel function below.

[0036] Preferably, step 5 includes the following specific process:

[0037] Calculate the optimal rotation factor p for each feeder k_opt Lower time-frequency current signal i k (p k_opt ,u k_opt Peak amplitude I peak,k :

[0038] I peak,k =max|i k (p k_opt ,u k_opt )|.

[0039] Preferably, step 6 includes the following specific steps:

[0040] Step 6.1: Under normal system operation, acquire the three-phase current signal within one cycle, denoted as: i ak0 (t), i bk0 (t), i ck0 (t);

[0041] Step 6.2: For the three-phase current signals acquired in Step 6.1 during normal system operation, reuse Steps 1 to 5 to calculate the peak value of the time-frequency current signal of each feeder, and record it as the peak value reference under normal system operation conditions: I peak,k0 ;

[0042] Step 6.3: Calculate the mean μ and standard deviation σ of the normal peak values. m is the number of feeders, and the standard deviation is...

[0043] Step 6.4: Set the threshold to I h =μ+3σ, where I is the peak amplitude of the time-frequency current signal of each feeder. peak,k With threshold I h Comparison, when I peak,k >Ih At that time, it was determined that a single-phase open-circuit ground fault had occurred in the feeder.

[0044] A single-phase open-circuit grounding fault detection system for a neutral-point ungrounded system, applicable to the aforementioned single-phase open-circuit grounding fault detection method for a neutral-point ungrounded system, the system comprising:

[0045] The three-phase current signal acquisition module is used to acquire the three-phase current signal i within one cycle from the time of the fault occurrence of each feeder. ak (t), i bk (t), i ck (t), where k = 1, 2, ..., m, and k represents the line number;

[0046] The negative sequence current calculation module is used to calculate the A-phase negative sequence current signal i of each feeder based on the acquired three-phase current signals using the symmetrical component method. k (t);

[0047] The morphological filtering module is used to perform morphological filtering on the acquired negative sequence current signal to obtain the filtered negative sequence current signal.

[0048] The coordinate transformation module is used to map the filtered negative-sequence current signal to a time-frequency space with u as the variable, thereby obtaining a time-frequency current signal i containing a rotation factor parameter. k (p,u);

[0049] The optimal rotation factor determination module is used to determine the optimal rotation factor p for each feeder based on the energy concentration of each feeder. k_opt ;

[0050] The time-frequency current signal peak value calculation module is used to calculate the peak amplitude I of the time-frequency current signal of each feeder under the optimal rotation factor. peak,k ;

[0051] The fault detection module is used to compare the peak amplitude of the time-frequency current signal of each feeder with the threshold I. h The comparison is performed, and when the peak amplitude is greater than the threshold, it is determined that a single-phase open-circuit ground fault has occurred in the feeder.

[0052] A computer device includes a memory and a processor, the memory storing a computer program, the processor executing the computer program to implement the method described above.

[0053] A computer-readable storage medium having a computer program stored thereon, characterized in that the computer program, when executed by a processor, implements the above-described method.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] 1. This invention innovatively combines the symmetrical component method, morphological filtering, and coordinate transformation techniques. First, the negative sequence current signal is focused using the symmetrical component method. Then, morphological filtering is used to effectively suppress noise. Finally, the time-frequency current signal is obtained through coordinate transformation. This series of processes significantly enhances the accuracy and stability of fault feature extraction. Compared with traditional methods, this invention can accurately capture fault signal features, greatly improve the accuracy and reliability of fault detection, and effectively avoid the problems of missed or false judgments caused by improper signal processing.

[0056] 2. This invention determines the optimal rotation factor based on the energy concentration of the feeder, adaptively adjusts the detection parameters according to the actual situation of each feeder, and flexibly optimizes the time-frequency current signal analysis strategy for different fault conditions. As a result, this invention can still detect faults quickly and accurately in scenarios such as complex power grid structures, different fault locations, and transition resistances. It overcomes the shortcomings of poor adaptability of traditional methods and effectively improves the fault detection efficiency and success rate in various operating environments.

[0057] 3. This invention forms a complete and coordinated fault detection process through multiple steps, including acquiring three-phase current signals from each feeder, calculating negative-sequence current signals, morphological filtering, coordinate transformation, finding the optimal rotation factor, calculating the peak amplitude of time-frequency current signals, and constructing fault detection criteria. Each step is optimized for different aspects of fault detection, ensuring the comprehensiveness and accuracy from signal acquisition to fault determination. This multi-step coordinated approach enables the invention to provide reliable detection results when facing different types of single-phase open-circuit grounding faults. Attached Figure Description

[0058] Figure 1 This is a flowchart of the single-phase open-circuit grounding fault detection method of the present invention;

[0059] Figure 2 This is a diagram of the open-circuit grounding fault analysis model for an ungrounded system according to the present invention;

[0060] Figure 3 This is the load sequence diagram for a single-phase open-circuit grounding fault according to the present invention;

[0061] Figure 4 This is the negative sequence equivalent network diagram of the power supply side open-circuit grounding fault of the present invention;

[0062] Figure 5 This is the negative sequence equivalent network diagram of the load-side open-circuit grounding fault of the present invention;

[0063] Figure 6 This is a simulation model diagram of a 10kV ungrounded distribution network according to the present invention;

[0064] Figure 7This is a diagram of the negative sequence current of each feeder when a single-phase power supply side open-circuit grounding fault occurs 3km from the head end of line l2, according to the present invention. Detailed Implementation

[0065] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0066] Example: This invention provides a method for detecting single-phase open-circuit grounding faults in a neutral-point ungrounded system, comprising the following steps:

[0067] Step 1: Acquire the three-phase current signals of each feeder, and then use the symmetrical component method to calculate the A-phase negative sequence current signal of each feeder; Step 1 includes the following specific steps:

[0068] Step 1.1: Collect the three-phase current signal i within one cycle from the time of the fault occurrence of each feeder. ak (t), i bk (t), i ck (t), k = 1, 2, ..., m, where k represents the line number, i ak (t), i bk (t), i ck (t) represents the phase currents of the k-th feeder (a, b, c);

[0069] Step 1.2: Calculate the negative sequence current signal i of phase A of the three-phase current signal acquired in step 1.1 using the following formula. k (t):

[0070]

[0071] In the formula, α = e j120° It is a characteristic operator of the symmetric component method;

[0072] In step 1, the three-phase current signal i is first acquired within one cycle from the time of the fault occurrence of each feeder. ak (t), i bk (t), i ck (t), where k = 1, 2, ..., m, k represents the line number, and these signals represent the a, b, and c phase currents of the k-th feeder, respectively; then, in step 1.2, the collected three-phase current signals are processed using the symmetrical component method characteristic operator, specifically by calculating the A-phase negative sequence current signal i of each feeder using the formula. k (t); The above steps can effectively extract fault characteristics because the negative sequence current signal will show a specific change pattern when a single-phase open-circuit ground fault occurs, thus providing an accurate basis for subsequent fault detection.

[0073] Step 2: Perform morphological filtering on the acquired negative sequence current signal; the morphological filtering process in Step 2 is as follows:

[0074] For the negative sequence current signals i of each feeder obtained in step 1 k (t) is processed using an alternating hybrid filter in morphological filtering to obtain the filtered negative sequence current signal i. k '(t);

[0075] In step 2, for each feeder negative sequence current signal i obtained in step 1 k (t) is processed using an alternating hybrid filter in morphological filtering; specifically, the alternating hybrid filter is used to perform a combination of opening and closing operations on the signal to effectively suppress noise in the signal and enhance fault features; the effect of the above steps is to significantly improve the clarity of the signal and reduce the interference of background noise on subsequent fault detection, thereby ensuring the accuracy and stability of fault feature extraction.

[0076] Step 3: Through coordinate transformation, the filtered negative-sequence current signal is mapped to a time-frequency space with u as the variable, resulting in a time-frequency current signal containing a rotation factor parameter. Step 3 includes the following specific process:

[0077] The filtered negative sequence current signal i k '(t) is mapped to a time-frequency space with u as the variable through coordinate transformation, resulting in a time-frequency current signal i containing a rotation factor parameter. k (p,u):

[0078]

[0079] In the formula, the kernel function h p The specific expression for (t,u) is as follows:

[0080]

[0081] In the formula, u = tcosβ + fsinβ is the coordinate transformation formula, where f is the frequency. Let β be the rotation angle, p be the rotation factor, and p ∈ real numbers; and when the rotation angle β = 2nπ, the kernel function h p (t,u) is the impact function δ(t+u); when the rotation angle β=(2n+1)π, the kernel function h p (t,u) is the impulse function δ(t+u); where p∈real is a common mathematical notation, and its meaning is as follows: p This represents a variable, where ∈ signifies "belongs to", and real numbers refer to the set of real numbers; p∈real numbers means that the range of values ​​for variable p is the set of real numbers.

[0082] In step 3, the specific operation involves mapping the filtered negative-sequence current signal to a time-frequency space with u as the variable through coordinate transformation. During this process, a kernel function containing a rotation factor p is introduced for transformation. This kernel function takes the form of an impulse function depending on the rotation angle, thereby obtaining a time-frequency current signal with rotation factor parameters. The effect of the above steps is that, through coordinate transformation and the introduction of rotation factors, the distribution characteristics of the signal at different times and frequencies can be analyzed more flexibly, enhancing the ability to extract the time-frequency characteristics of the fault signal, and providing a more accurate basis for subsequent optimal rotation factor search and fault detection based on energy focusing characteristics.

[0083] Step 4: Based on Step 3, for each feeder, find the optimal rotation factor according to the energy focusing characteristics of the time-frequency current signal, and then substitute this optimal rotation factor into the time-frequency current signal expression to generate the time-frequency current signal under the optimal rotation factor for each feeder; Step 4 includes the following specific steps:

[0084] Step 4.1: Within the rotation factor range p∈[0,2], sample at equal intervals with a step size of 0.1 to obtain the discrete rotation factor set {p s}, s=1,2,…,S, for each sampling point p s Using the time-frequency current signal formula defined in step 3:

[0085]

[0086] Calculate the corresponding time-frequency current signal i k (p s Construct a mapping relationship between the rotation factor and the time-frequency signal (u).

[0087] Step 4.2: Quantize the time-frequency current signal i k (p,u) represents the degree of energy concentration under different rotation factors p, and the energy concentration of each feeder is defined as C. k (p):

[0088]

[0089] That is, C k The larger (p) is, the greater the time-frequency current signal i k (p,u) is more concentrated under variable u;

[0090] Step 4.3: For each feeder, iterate through all sampling rotation factors p from Step 4.1. s Calculate the corresponding energy concentration C k (p s Select C k (p s The largest rotation factor is denoted as the optimal rotation factor p of the feeder. k_opt;

[0091] Step 4.4: Apply the optimal rotation factor p determined in Step 4.3 k_opt Substituting into the time-frequency current signal expression, we obtain the optimal rotation factor p for each feeder. k_opt The time-frequency current signal i k (p k_opt ,u k_opt ):

[0092]

[0093] In the formula, u k_opt For the corresponding optimal rotation factor p k_opt The variables under, For the corresponding optimal rotation factor p k_opt The kernel function below;

[0094] In step 4, sampling is first performed at equal intervals with a step size of 0.1 within the rotation factor range to construct a discrete rotation factor set. Then, the time-frequency current signal corresponding to each sampling point is calculated using the time-frequency current signal formula from step 3, thereby establishing a "rotation factor-time-frequency signal" mapping relationship. Next, to quantify the energy concentration degree of the time-frequency current signal under different rotation factors, an energy concentration index C for each feeder is defined. k (p), the larger the value, the more concentrated the signal is under variable u; then, for each feeder, all sampling rotation factors are traversed, the corresponding energy concentration is calculated, and the factor that makes C the most concentrated is selected. k (p s The largest rotation factor is taken as the optimal rotation factor p for this feeder. k_opt Finally, the optimal rotation factor p is... k_opt Substituting the time-frequency current signal expression, the time-frequency current signal of each feeder under the optimal rotation factor is generated. The effect of the above operation steps is that the optimal time-frequency analysis parameters for each feeder can be adaptively found, thereby extracting fault characteristics more accurately and improving the sensitivity and accuracy of fault detection.

[0095] Step 5: Calculate the peak amplitude of the time-frequency current signal for each feeder under the optimal rotation factor; Step 5 includes the following specific process:

[0096] Calculate the optimal rotation factor p for each feeder k_opt Lower time-frequency current signal i k (p k_opt ,u k_opt Peak amplitude I peak,k :

[0097] I peak,k =max|i k (p k_opt ,uk_opt )|;

[0098] In step 5, the specific operation is to calculate the optimal rotation factor p for each feeder. k_opt The peak amplitude of the time-frequency current signal under the action is obtained by extracting the maximum amplitude of the time-frequency current signal under the optimal rotation factor condition. Its effect is that it can accurately quantify the signal strength of each feeder under specific time-frequency analysis parameters, thereby providing a key comparison benchmark for subsequent fault detection criteria based on peak amplitude, which helps to accurately identify feeders that have experienced single-phase open-circuit grounding faults.

[0099] Step 6: Based on the peak amplitude of the time-frequency current signal under the optimal rotation factor, construct a single-phase open-circuit grounding fault detection criterion; compare the peak amplitude of the time-frequency current signal under the optimal rotation factor of each feeder with the threshold. When the peak amplitude is greater than the threshold, it is determined that a single-phase open-circuit grounding fault has occurred in the feeder.

[0100] Step 6 includes the following specific steps:

[0101] Step 6.1: Under normal system operation, acquire the three-phase current signal within one cycle, denoted as: i ak0 (t), i bk0 (t), i ck0 (t);

[0102] Step 6.2: For the three-phase current signals acquired in Step 6.1 during normal system operation, reuse Steps 1 to 5 to calculate the peak value of the time-frequency current signal of each feeder, and record it as the peak value reference under normal system operation conditions: I peak,k0 ;

[0103] Step 6.3: Calculate the mean μ and standard deviation σ of the normal peak values. m is the number of feeders, and the standard deviation is...

[0104] Step 6.4: Set the threshold to I h =μ+3σ, where I is the peak amplitude of the time-frequency current signal of each feeder. peak,k With threshold I h Comparison, when I peak,k >I h At that time, it was determined that a single-phase open-circuit ground fault had occurred in the feeder.

[0105] In step 6, the three-phase current signal within one cycle is first collected as reference data under normal system operation (step 6.1); then, the method of steps 1 to 5 is reused to calculate the peak value of the time-frequency current signal of each feeder under normal system operation, forming the peak value reference under normal operating conditions (step 6.2); next, the mean and standard deviation of these normal peak values ​​are calculated to quantify the signal fluctuation range under normal operation (step 6.3); finally, the threshold is set to the mean plus three times the standard deviation. When the peak value amplitude of the time-frequency current signal of a feeder exceeds the threshold, it is determined that a single-phase open-circuit grounding fault has occurred in that feeder (step 6.4). The above steps effectively avoid the problem of insufficient adaptability of fixed thresholds to changes in system operating conditions by establishing a dynamic threshold reference based on normal operating data, and significantly improve the accuracy and reliability of fault detection.

[0106] As can be seen from the above, this method, by combining the symmetrical component method, morphological filtering, and coordinate transformation techniques, significantly enhances the accuracy and stability of single-phase open-circuit grounding fault feature extraction in neutral-point ungrounded systems. It can accurately capture fault signal features and greatly improve the accuracy and reliability of fault detection. At the same time, based on the adaptive determination of the optimal rotation factor according to the feeder energy concentration, the detection strategy can flexibly adapt to different fault conditions, effectively improving the fault detection efficiency and success rate under complex power grid structures and variable operating conditions, and overcoming the shortcomings of poor adaptability of traditional methods.

[0107] Working principle of this invention:

[0108] 1. Load sequence network diagram for open-circuit grounding fault in ungrounded system

[0109] Figure 2 For the open-circuit grounding fault model of an ungrounded system, where Let C be the three-phase electromotive force of the system, L and R be the equivalent inductance and resistance of the line, respectively. A1 C B1 C C1 For the phase-to-ground capacitance of each phase of the faulty feeder, C Ai C Bi C Ci (i = 2, 3, ..., n) represents the phase-to-ground capacitance of each phase of the healthy feeder, Z AB =Z BC =Z CA The impedance of the three-phase load; This is a virtual voltage source for the grounding point, equal to the steady-state reverse voltage amplitude of the grounding point before the open-circuit fault occurred; The virtual current source at the fault point is equal to the phase current amplitude before the fault occurred, R. fLet be the grounding resistance. Assuming a single-phase open-circuit fault occurs at a distance x from the busbar, with breaks at points M and N, the system is grounded on the single-phase power supply side when K1 is closed and K2 is open; when K1 is open and K2 is closed, it is grounded on the single-phase load side.

[0110] Assume the voltage between each phase break is The current in each phase on the power supply side of the break is The phase-to-ground voltages and grounding currents on side M of the break are as follows: and The phase-to-ground voltages and grounding currents on the N side of the break are as follows: and The boundary conditions for a single-phase power supply side open-circuit ground fault are given by equations (1), (2), (3), and (4), as follows:

[0111]

[0112] The boundary conditions for a single-phase load-side open-circuit grounding fault are given by equations (1), (2), (5), and (6), as follows:

[0113]

[0114] Analysis using the symmetrical component method yields the boundary conditions for power supply side grounding and load side grounding as shown in equations (7) and (8), respectively:

[0115]

[0116] In the formula: subscripts A1, A2, and A0 represent the positive, negative, and zero-order components, respectively.

[0117] Combining boundary conditions (7) and (8), the load sequence network diagram for a single-phase open-circuit grounding fault in an ungrounded system is as follows: Figure 3 As shown; Z M1 Z M2 Z M0 and Z N1 Z N2 Z N0 These are the positive-sequence, negative-sequence, and zero-sequence equivalent impedances on the M and N sides of the faulty feeder break, respectively.

[0118] 2. Analysis of negative sequence current characteristics in single-phase open-circuit grounding faults

[0119] From the perspective of negative sequence impedance characteristics, both the system and the load exhibit inductive behavior, and the negative sequence impedance of the load is nearly a hundred times that of the system, while the negative sequence impedance of the line is much smaller than that of the load. Figure 4 This is the negative sequence equivalent network diagram for a ground fault on the power supply side, where Z... i2 (i = 2, 3, ..., n), ZS2 These are the equivalent negative sequence impedances referred to the low-voltage side for the robust feeder and the high-voltage system, respectively; i ni (i = 2, 3, ..., n) represents the negative sequence current flowing through the healthy feeder i. ns i n and i nM i nN These are the negative sequence currents flowing through the system, the disconnected branch, and the M and N sides of the break point, respectively; i Rf This is the negative sequence current flowing through the grounding resistor; For a grounded virtual voltage source, U m For virtual voltage source u n The amplitude.

[0120] Combination Figure 3 Therefore, the negative sequence current flowing downstream of the faulty feeder is:

[0121]

[0122] In equation (9):

[0123] Z X =[Z M0 ·3R f +Z N0 (Z M0 +3R f )]·Z N1 (10)

[0124] Z Y =(Z N1 ·Z N2 +Z N0 ·Z1)·Z M0 (11)

[0125] The negative sequence current flowing upstream of the faulty feeder is:

[0126]

[0127] according to Figure 4 The negative sequence current flowing through a healthy feeder is:

[0128]

[0129] In equation (13), Simplifying equation (13) yields:

[0130]

[0131] Synthetic (14) and Figure 4 From the negative sequence network diagram, it can be seen that the negative sequence current amplitude of the faulty feeder is the largest, and its direction is opposite to that of the normal feeder.

[0132] The negative sequence equivalent network of a load-side open-circuit ground fault is as follows: Figure 5 The equivalent current source is:

[0133]

[0134] In equation (15):

[0135] Z X1 =[Z N0 ·3R f +Z M0 (Z N0 +3R f )]·Z M1 (16)

[0136] Z Y1 =(Z M1 ·Z M2 +Z M0 ·Z1)·Z N0 (17)

[0137] Similarly, in a single-phase load-side open-circuit grounding fault, the negative sequence current amplitude of the faulty feeder is the largest, and its direction is opposite to that of the normal feeder.

[0138] 3. Morphological filtering

[0139] Mathematical morphology in signal processing mainly utilizes gray value morphology, and its basic operations include gray value dilation and gray value erosion; f(n) is the one-dimensional signal to be processed, and its domain is D. f = {0,1,2,...,N}; the structuring element sequence is g(n), and the domain is D. g ={0,1,2,...,P}; where P and N are both integers, and N≥P; the operational expressions for gray value dilation and gray value erosion are respectively:

[0140]

[0141] (fΘg)(n)=min{f(n+x)-g(x)|(n+x)∈D f ,x∈D g} (19)

[0142] In equations (18) and (19), Θ represents the dilation operation, and θ represents the erosion operation. Erosion followed by dilation is called grayscale opening, and dilation followed by erosion is called grayscale closing. Opening is suitable for eliminating spike noise at the top of a signal and removing glitches; closing helps suppress trough noise at the bottom and fill in small depressions. Morphological filtering achieves signal noise suppression and feature enhancement through dilation or erosion and their combinations. The definition of an alternating hybrid filter is:

[0143] [(f)altmix(g)](n)=[(f)OC(g)+(f)CO(g)](n) / 2 (20)

[0144] In summary, the present invention has the following beneficial effects:

[0145] 1) High-precision signal processing enhances fault feature extraction capability: Traditional methods often fail to accurately extract signal features when processing single-phase open-circuit grounding fault signals in ungrounded systems due to weak fault features and background noise interference. This invention innovatively combines symmetrical component method, morphological filtering, and coordinate transformation technology. First, the symmetrical component method is used to focus the negative sequence current signal, then morphological filtering is used to effectively suppress noise, and finally, the time-frequency current signal is obtained through coordinate transformation, which significantly enhances the accuracy and stability of fault feature extraction. In comparison, this invention can accurately capture fault signal features, greatly improve the accuracy and reliability of fault detection, and avoid the problems of missed or false judgments caused by improper signal processing.

[0146] 2) Adaptive optimization of detection strategy to improve applicability in complex scenarios: Existing detection technologies mostly use fixed thresholds or simple parameter settings, which are difficult to adapt to the complex and ever-changing operating conditions in ungrounded systems. This invention determines the optimal rotation factor based on the energy concentration of the feeder and adaptively adjusts the detection parameters according to the actual situation of each feeder. It flexibly optimizes the time-frequency current signal analysis strategy for different fault conditions. This feature enables the invention to quickly and accurately detect faults in complex power grid structures, different fault locations, and transition resistance scenarios, overcoming the shortcomings of poor adaptability of traditional methods and effectively improving the fault detection efficiency and success rate in various operating environments.

[0147] Application example: Building using PSCAD, such as Figure 6 The simulation model of a 10kV ungrounded distribution network is shown. The model uses a 110 / 10.5kV step-down transformer with a rated capacity of 31.5MVA. The system is configured with 6 outgoing lines, of which line l1 is a cable line and the rest are overhead lines. Each feeder end uses a 0.5MW constant impedance load. The length of each line is clearly marked in the figure, and the specific parameters of the line are shown in Table 1.

[0148] Table 1 System Specific Parameters

[0149]

[0150] Simulation Analysis 1

[0151] Assuming a single-phase power supply side open-circuit grounding fault occurs 3km from the busbar at the beginning of feeder l2, with a grounding resistance of 10Ω and an initial phase angle of 0°, this case is analyzed. The system sampling frequency is f = 20kHz, the simulation duration is 0.2s, and the fault occurrence time is set to 0.12s.

[0152] Figure 1 This is a flowchart of the single-phase open-circuit grounding fault detection method for an ungrounded system according to the present invention. According to the method of the present invention, firstly, the three-phase current signals of each feeder within one cycle after the fault occurs are collected. The negative sequence current signals of each feeder are then calculated using the symmetrical component method, as shown below. Figure 7 As shown; then for Figure 7 The negative sequence current of each feeder is subjected to morphological filtering, and the time-frequency current signal of each feeder under the variable u is obtained by coordinate transformation. Then, according to the energy concentration of each feeder, the optimal rotation factor corresponding to each feeder is determined, and the peak amplitude of the time-frequency current signal under the optimal rotation factor of each feeder is calculated. The peak amplitude results of the time-frequency current signal of each feeder are [0.0014, 26.0649, 0.0017, 0.0021, 0.0017, 0.0017], indicating that a single-phase open-circuit ground fault has occurred in feeder l2, and the open-circuit ground fault detection is accurately realized.

[0153] Simulation Analysis 2

[0154] Assuming a single-phase load-side open-circuit ground fault occurs 10km from the busbar at the beginning of feeder l4, with a grounding resistance of 100Ω and an initial phase angle of 0°, this case is analyzed. The system sampling frequency is f = 20kHz, the simulation duration is 0.2s, and the fault occurrence time is set to 0.12s.

[0155] Following the same steps as a method for detecting single-phase open-circuit grounding faults in a neutral-point ungrounded system, the peak amplitude results of the time-frequency current signals of each feeder are [0.0013, 0.0019, 0.0016, 24.6328, 0.0016, 0.0016], indicating that a single-phase open-circuit grounding fault occurred in feeder l4, thus accurately realizing the detection of open-circuit grounding faults.

[0156] To further demonstrate the reliability of this method, using Figure 6 The topology shown was subjected to multiple sets of simulations under different fault locations and different initial phase angles.

[0157] use Figure 6The system topology of the 10kV ungrounded system shown is simulated for different fault locations. The peak amplitude results of the time-frequency current signal of each feeder are shown in Table 2. With the grounding resistance set to 1Ω and the fault initiation phase angle set to 0°, detailed simulation calculations were performed for power supply side open-circuit grounding fault and load side open-circuit grounding fault of line 5 at l = 1 to 20km (distance from the busbar).

[0158] Table 2 Simulation results for different fault locations

[0159]

[0160]

[0161] Analysis of Table 2 shows that the same type of single-phase open-circuit grounding fault occurred at different fault locations. By comparing the peak amplitude results of each group of time-frequency current signals, it can be found that the feeder where the maximum value is located is the faulty feeder.

[0162] use Figure 6 The 10kV ungrounded system topology is shown. Simulations were performed for different grounding resistances at the same fault location. The peak amplitude results of the time-frequency current signals for each feeder are shown in Table 3. The fault was set to occur at 6km along line 3, with a fault initiation phase angle of 0°. The simulations were performed for grounding resistance R... f For power supply side open-circuit grounding faults and load side open-circuit grounding faults occurring at 10Ω, 500Ω, and 1000Ω respectively, the accuracy of the line selection result of this method is determined by analyzing the peak amplitude of the time-frequency current signal of each feeder.

[0163] Table 3 Simulation results for different grounding resistances

[0164]

[0165] Table 3 lists the simulation results under varying grounding resistance. As shown in Table 3, when the fault location remains unchanged and only the grounding resistance changes, the peak amplitude of the time-frequency current signal of line l3 in each simulation is the maximum value. Therefore, it can be determined that line l3 is the faulty feeder.

[0166] A single-phase open-circuit grounding fault detection system for a neutral-point ungrounded system, applicable to the aforementioned single-phase open-circuit grounding fault detection method for a neutral-point ungrounded system, the system comprising:

[0167] The three-phase current signal acquisition module is used to acquire the three-phase current signal i within one cycle from the time of the fault occurrence of each feeder. ak (t), i bk (t), i ck (t), where k = 1, 2, ..., m, and k represents the line number;

[0168] The negative sequence current calculation module is used to calculate the A-phase negative sequence current signal i of each feeder based on the acquired three-phase current signals using the symmetrical component method. k (t);

[0169] The morphological filtering module is used to perform morphological filtering on the acquired negative sequence current signal to obtain the filtered negative sequence current signal.

[0170] The coordinate transformation module is used to map the filtered negative-sequence current signal to a time-frequency space with u as the variable, thereby obtaining a time-frequency current signal i containing a rotation factor parameter. k (p,u);

[0171] The optimal rotation factor determination module is used to determine the optimal rotation factor p for each feeder based on the energy concentration of each feeder. k_opt ;

[0172] The time-frequency current signal peak value calculation module is used to calculate the peak amplitude I of the time-frequency current signal of each feeder under the optimal rotation factor. peak,k ;

[0173] The fault detection module is used to compare the peak amplitude of the time-frequency current signal of each feeder with the threshold I. h The comparison is performed, and when the peak amplitude is greater than the threshold, it is determined that a single-phase open-circuit ground fault has occurred in the feeder.

[0174] As can be seen from the above, this single-phase open-circuit grounding fault detection system for a neutral-point ungrounded system integrates three-phase current signal acquisition, negative sequence current calculation, morphological filtering, coordinate transformation, optimal rotation factor determination, time-frequency current signal peak value calculation, and fault detection modules to form a complete and coordinated fault detection process. This system not only significantly enhances the accuracy and stability of fault feature extraction, but also effectively improves the fault detection efficiency and success rate under complex power grid structures and variable operating conditions through an adaptive optimal rotation factor determination mechanism, thereby ensuring the safe and stable operation of the distribution network.

[0175] This application provides an electronic device applicable to the above-described method for detecting single-phase open-circuit grounding faults in a neutral-point ungrounded system, comprising:

[0176] Memory is used to protect computer programs and data;

[0177] A processor is used to run system programs.

[0178] This application provides a computer storage medium applicable to the above-described method for detecting single-phase open-circuit grounding faults in a neutral-point ungrounded system, and in accordance with confidentiality management requirements, classifies and manages the above-described system and data for confidentiality.

[0179] Those skilled in the art will understand that embodiments of this application can be provided as a system or a computer program product. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0180] This application is described with reference to flowchart illustrations and / or block diagrams of apparatus (systems) and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create a machine for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0181] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0182] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0183] In a typical configuration, a computing device includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.

[0184] Memory may include non-persistent memory in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM. Memory is an example of computer-readable media.

[0185] Computer-readable media include both permanent and non-permanent, removable and non-removable media, which can store information using any method or technology. Information can be computer-readable instructions, data structures, modules of programs, or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, CD-ROM, digital versatile optical disc (DVD) or other optical storage, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other non-transferable medium that can be used to store information accessible by a computing device. As defined herein, computer-readable media does not include transient computer-readable media, such as modulated data signals and carrier waves.

[0186] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, article, or apparatus that includes that element.

[0187] The embodiments of the present invention are given for the purposes of illustration and description. Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for detecting single-phase open-circuit grounding faults in a neutral-point ungrounded system, characterized in that, Includes the following steps: Step 1: Collect the three-phase current signals of each feeder, and then use the symmetrical component method to calculate the negative sequence current signal of phase A of each feeder; Step 2: Perform morphological filtering on the acquired negative sequence current signal; Step 3: Through coordinate transformation, the filtered negative sequence current signal is mapped to a time-frequency space with u as the variable to obtain a time-frequency current signal containing the rotation factor parameter; Step 4: Based on Step 3, for each feeder, find the optimal rotation factor according to the energy focusing characteristics of the time-frequency current signal, and then substitute the optimal rotation factor into the expression of the time-frequency current signal to generate the time-frequency current signal under the optimal rotation factor for each feeder. Step 5: Calculate the peak amplitude of the time-frequency current signal for each feeder under the optimal rotation factor; Step 6: Based on the peak amplitude of the time-frequency current signal under the optimal rotation factor, construct a single-phase open-circuit grounding fault detection criterion; compare the peak amplitude of the time-frequency current signal under the optimal rotation factor of each feeder with the threshold. When the peak amplitude is greater than the threshold, it is determined that a single-phase open-circuit grounding fault has occurred in the feeder.

2. The method for detecting single-phase open-circuit grounding faults in a neutral-point ungrounded system as described in claim 1, characterized in that: Step 1 includes the following specific steps: Step 1.1: Collect the three-phase current signal i within one cycle from the time of the fault occurrence of each feeder. ak (t), i bk (t), i ck (t), k = 1, 2, ..., m, represents the line number, i ak (t), i bk (t), i ck (t) represents the phase currents of the k-th feeder (a, b, c); Step 1.2: Calculate the negative sequence current signal i of phase A of the three-phase current signal acquired in step 1.1 using the following formula. k (t): In the formula, α = e j120° It is a characteristic operator of the symmetric component method.

3. The method for detecting single-phase open-circuit grounding faults in a neutral-point ungrounded system as described in claim 1, characterized in that: The morphological filtering process in step 2 is as follows: For the negative sequence current signals i of each feeder obtained in step 1 k (t) is processed using an alternating hybrid filter in morphological filtering to obtain the filtered negative sequence current signal i. k '(t).

4. The method for detecting single-phase open-circuit grounding faults in a neutral-point ungrounded system as described in claim 1, characterized in that: Step 3 includes the following specific process: The filtered negative sequence current signal i k '(t) is mapped to a time-frequency space with u as the variable through coordinate transformation, resulting in a time-frequency current signal i containing a rotation factor parameter. k (p,u): In the formula, the kernel function h p The specific expression for (t,u) is as follows: In the formula, u = tcosβ + fsinβ is the coordinate transformation formula, where f is the frequency. Let β be the rotation angle and p be the rotation factor. When the rotation angle β = 2nπ, the kernel function h p (t,u) is the impact function δ(t+u); when the rotation angle β=(2n+1)π, the kernel function h p (t,u) is the impact function δ(t+u).

5. The method for detecting single-phase open-circuit grounding faults in a neutral-point ungrounded system as described in claim 1, characterized in that: Step 4 includes the following specific steps: Step 4.1: Within the rotation factor range p∈[0,2], sample at equal intervals with a step size of 0.1 to obtain the discrete rotation factor set {p s }, s=1,2,…,S, for each sampling point p s Using the time-frequency current signal formula defined in step 3: Calculate the corresponding time-frequency current signal i k (p s Construct a "rotation factor-time frequency signal" mapping relationship using the ,u) method. Step 4.2: Quantize the time-frequency current signal i k (p,u) represents the degree of energy concentration under different rotation factors p, and the energy concentration of each feeder is defined as C. k (p): That is, C k The larger (p) is, the greater the time-frequency current signal i k (p,u) is more concentrated under variable u; Step 4.3: For each feeder, iterate through all sampling rotation factors p from Step 4.

1. s Calculate the corresponding energy concentration C k (p s Select C k (p s The largest rotation factor is denoted as the optimal rotation factor p of the feeder. k_opt ; Step 4.4: Apply the optimal rotation factor p determined in Step 4.3 k_opt Substituting into the time-frequency current signal expression, we obtain the optimal rotation factor p for each feeder. k_opt The time-frequency current signal i k (p k_opt ,u k_opt ): In the formula, u k_opt For the corresponding optimal rotation factor p k_opt The variables under, For the corresponding optimal rotation factor p k_opt The kernel function below.

6. The method for detecting single-phase open-circuit grounding faults in a neutral-point ungrounded system as described in claim 1, characterized in that: Step 5 includes the following specific process: Calculate the optimal rotation factor p for each feeder k_opt Lower time-frequency current signal i k (p k_opt ,u k_opt Peak amplitude I peak,k : I peak,k = max|i k (p k_opt ,u k_opt )|。 7. The method for detecting single-phase open-circuit grounding faults in a neutral-point ungrounded system as described in claim 1, characterized in that: Step 6 includes the following specific steps: Step 6.1: Under normal system operation, acquire the three-phase current signal within one cycle, denoted as: i ak0 (t), i bk0 (t), i ck0 (t); Step 6.2: For the three-phase current signals acquired in Step 6.1 during normal system operation, reuse Steps 1 to 5 to calculate the peak value of the time-frequency current signal of each feeder, and record it as the peak value reference under normal system operation conditions: I peak,k0 ; Step 6.3: Calculate the mean μ and standard deviation σ of the normal peak values. m is the number of feeders, and the standard deviation is... Step 6.4: Set the threshold to I h =μ+3σ, where I is the peak amplitude of the time-frequency current signal of each feeder. peak,k With threshold I h Comparison, when I peak,k >I h At that time, it was determined that a single-phase open-circuit ground fault had occurred in the feeder.

8. A single-phase open-circuit grounding fault detection system for a neutral point ungrounded system, characterized in that: The method for detecting single-phase open-circuit grounding faults in a neutral-point ungrounded system as described in any one of claims 1-7, wherein the system comprises: The three-phase current signal acquisition module is used to acquire the three-phase current signal i within one cycle from the time of the fault occurrence of each feeder. ak (t), i bk (t), i ck (t), where k = 1, 2, ..., m, represents the line number; The negative sequence current calculation module is used to calculate the A-phase negative sequence current signal i of each feeder based on the acquired three-phase current signals using the symmetrical component method. k (t); The morphological filtering module is used to perform morphological filtering on the acquired negative sequence current signal to obtain the filtered negative sequence current signal. The coordinate transformation module is used to map the filtered negative-sequence current signal to a time-frequency space with u as the variable, thereby obtaining a time-frequency current signal i containing a rotation factor parameter. k (p,u); The optimal rotation factor determination module is used to determine the optimal rotation factor p for each feeder based on the energy concentration of each feeder. k_opt ; The time-frequency current signal peak value calculation module is used to calculate the peak amplitude I of the time-frequency current signal of each feeder under the optimal rotation factor. peak,k ; The fault detection module is used to compare the peak amplitude of the time-frequency current signal of each feeder with the threshold I. h The comparison is performed, and when the peak amplitude is greater than the threshold, it is determined that a single-phase open-circuit ground fault has occurred in the feeder.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the method of any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the method of any one of claims 1 to 7.

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