A method for detecting single-phase broken conductor grounding fault of a neutral point ungrounded system

Abstract

The application belongs to the technical field of power system distribution network relay protection, and provides a neutral point ungrounded system single-phase broken line grounding fault detection method, which comprises the following steps: step 1, collecting three-phase current signals of each feeder; step 2, performing morphological filtering processing on the obtained negative sequence current signals; step 3, mapping the filtered negative sequence current signals to a time-frequency space with u as a variable; and step 4, finding an optimal rotation factor according to the energy focusing characteristics of the time-frequency current signals. By combining the symmetric component method, morphological filtering and coordinate transformation technology, the application significantly enhances the accuracy and stability of the feature extraction of the neutral point ungrounded system single-phase broken line grounding fault, greatly improves the precision and reliability of the fault detection, and simultaneously determines the optimal rotation factor based on the feeder energy concentration degree, so that the detection strategy can flexibly adapt to different fault conditions, and effectively improves the fault detection efficiency and success rate under the complex power grid structure and variable operating conditions.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of power system distribution network relay protection, in particular to a neutral point ungrounded system single-phase broken line grounding fault detection method. BACKGROUND

[0002] As the terminal link of the power system and the user, the safe and stable operation of the distribution network is of great importance. Single-phase broken line grounding fault is one of the common faults of the distribution network, which is often caused by lightning, icing, external damage and other factors. When a single-phase broken line grounding fault occurs, if it is not detected and handled in time, it will not only affect the stability of power supply and cause user power outage, but also cause human and animal electric shock accidents due to broken line grounding, and even develop into inter-phase short circuit, expand the power outage range, and seriously threaten the personal safety and reliable operation of the power grid.

[0003] However, at present, the distribution network is generally not equipped with a dedicated broken line fault detection device, and the traditional short-circuit protection principle is not capable of effectively detecting the single-phase broken line grounding fault, and a reliable single-phase broken line grounding fault detection method is urgently needed to ensure the safe and stable operation of the distribution network. SUMMARY

[0004] In order to solve the above technical problems, the present application provides a neutral point ungrounded system single-phase broken line grounding fault detection method to solve the problems in the prior art that the current distribution network is generally not equipped with a dedicated broken line fault detection device, and the traditional short-circuit protection principle is difficult to effectively detect the single-phase broken line grounding fault.

[0005] In the first aspect, the present application provides a neutral point ungrounded system single-phase broken line grounding fault detection method, comprising the following steps:

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

[0007] Step 2: Morphological filtering processing is performed on the obtained negative sequence current signals;

[0008] Step 3: Through coordinate transformation, the filtered negative sequence current signals are mapped to the time-frequency space with u as the variable, and the time-frequency current signals containing the rotation factor parameter are obtained;

[0009] Step 4: On the basis of step 3, for each feeder, the optimal rotation factor is found according to the energy focusing characteristics of the time-frequency current signals, and then the optimal rotation factor is substituted into the time-frequency current signal expression to generate the time-frequency current signals under the optimal rotation factor of each feeder;

[0010] Step 5: Calculate the peak amplitude of the time-frequency current signals of 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, a single-phase broken-ground fault detection criterion is constructed; the peak amplitude of the time-frequency current signal under the optimal rotation factor of each feeder is compared with a threshold value, and when the peak amplitude is greater than the threshold value, it is determined that the single-phase broken-ground fault occurs in the feeder.

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

[0013] Step 1.1: Collecting three-phase current signals i ak (t) of each feeder for a period from the moment of fault occurrence bk (t) of each feeder for a period from the moment of fault occurrence ck (t), k = 1, 2, …, m, k represents line number, i ak (t) of each feeder for a period from the moment of fault occurrence bk (t) of each feeder for a period from the moment of fault occurrence ck (t) represents the a, b, c phase current of the kth feeder;

[0014] Step 1.2: Calculating the negative sequence current signal i k (t) of the A phase of the three-phase current signal collected in step 1.1 through the following formula

[0015]

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

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

[0018] The negative sequence current signal i k (t) obtained in step 1 is processed by using the alternating hybrid filter in morphological filtering to obtain the filtered negative sequence current signal i k '(t).

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

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

[0021]

[0022] In the formula, the specific expression of the kernel function h p (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 Substitute into the time-frequency current signal expression, the time-frequency current signal i k_opt (p k ,u k_opt ) of each feeder under the optimal rotation factor p k_opt is obtained

[0034]

[0035] In the formula, u k_opt is the variable corresponding to the optimal rotation factor p k_opt , is the kernel function corresponding to the optimal rotation factor p k_opt .

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

[0037] The peak amplitude I k_opt of the time-frequency current signal i k (p k_opt ,u k_opt ) of each feeder under the optimal rotation factor p peak,k is calculated

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

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

[0040] Step 6.1: Collect the three-phase current signals in a cycle under the normal operation state of the system, denoted as: i ak0 (t), i bk0 (t), i ck0 (t);

[0041] Step 6.2: For the three-phase current signals collected in step 6.1 under the normal operation state of the system, reuse steps 1 to 5 to calculate the peak value of the time-frequency current signal of each feeder, denoted as the peak reference under the normal operation state of the system: I peak,k0 ;

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

[0043] Step 6.4: Set the threshold value as I h =μ+3σ, compare the peak amplitude I peak,k of the time-frequency current signal of each feeder with the threshold value I h , and when I peak,k >Ih When the peak amplitude is greater than the threshold value, it is determined that the feeder has a single-phase broken-line grounding fault.

[0044] A neutral point ungrounded system single-phase broken-line grounding fault detection system suitable for the neutral point ungrounded system single-phase broken-line grounding fault detection method, the system comprises:

[0045] A three-phase current signal acquisition module for acquiring three-phase current signals i ak (t) of each feeder at a fault occurrence moment for one cycle. bk (t) of each feeder at a fault occurrence moment for one cycle. ck (t), wherein k=1, 2, …, m, k represents a line number.

[0046] A negative sequence current calculation module for calculating the A-phase negative sequence current signal i k (t) of each feeder through the symmetrical component method according to the acquired three-phase current signals.

[0047] A morphological filtering module for performing morphological filtering processing on the obtained negative sequence current signal to obtain a filtered negative sequence current signal.

[0048] A coordinate transformation module for mapping the filtered negative sequence current signal to a time-frequency space with u as a variable through coordinate transformation to obtain a time-frequency current signal i k (p, u) containing a rotation factor parameter.

[0049] An optimal rotation factor determination module for determining the optimal rotation factor p k_opt of each feeder according to the energy concentration degree of each feeder.

[0050] A time-frequency current signal peak value calculation module for calculating the peak amplitude I peak,k of the time-frequency current signal of each feeder under the optimal rotation factor.

[0051] A fault detection module for comparing the peak amplitude of the time-frequency current signal of each feeder with a threshold value I h When the peak amplitude is greater than the threshold value, it is determined that the feeder has a single-phase broken-line grounding fault.

[0052] A computer device comprising a memory and a processor, the memory stores a computer program, and the processor implements the above method when executing the computer program.

[0053] A computer readable storage medium having a computer program stored thereon, wherein the computer program is executed by a processor to implement the above method.

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

[0055] 1. The application innovatively combines the symmetric component method, morphological filtering and coordinate transformation technology; first, the negative sequence current signal is focused through the symmetric component method, then the noise is effectively suppressed by using morphological filtering, and finally the time-frequency current signal is obtained through coordinate transformation; this series of processing significantly enhances the accuracy and stability of fault feature extraction; compared with the traditional method, the application can accurately capture the fault signal characteristics, greatly improves the accuracy and reliability of fault detection, and effectively avoids the problems of missed judgment and misjudgment caused by improper signal processing.

[0056] 2. The application determines the optimal rotation factor based on the feeder energy concentration degree, 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, so that the application can still quickly and accurately detect faults under complex power grid structure, different fault positions and transition resistance, etc. The application overcomes the poor adaptability of traditional methods and effectively improves the fault detection efficiency and success rate in various operating environments.

[0057] 3. The application forms a complete and coordinated fault detection process through multiple steps such as collecting three-phase current signals of 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 to ensure the comprehensiveness and accuracy of fault detection from signal acquisition to fault determination. This multi-step coordinated approach enables the application to provide reliable detection results for different types of single-phase broken-line grounding faults. BRIEF DESCRIPTION OF DRAWINGS

[0058] Figure 1 The flow chart of the single-phase broken-line grounding fault detection method of the application;

[0059] Figure 2 The broken-line grounding fault analysis model diagram of the ungrounded system of the application;

[0060] Figure 3 The load sequence network diagram of the single-phase broken-line grounding fault of the application;

[0061] Figure 4 The negative sequence equivalent network diagram of the power supply side broken-line grounding fault of the application;

[0062] Figure 5 The negative sequence equivalent network diagram of the load side broken-line grounding fault of the application;

[0063] Figure 6 The 10kV ungrounded system distribution network simulation model diagram of the application;

[0064] Figure 7Fig. 1 is a diagram of each feeder negative sequence current when a single-phase power side open-line grounding fault occurs at a 10Ω transition resistance 3km away from the online circuit l2 head end of the bus 3 of the present application. DETAILED DESCRIPTION

[0065] The embodiments of the present application will be further described below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present application, but cannot be used to limit the scope of the present application.

[0066] Embodiment: The present application provides a neutral point ungrounded system single-phase open-line grounding fault detection method, comprising the following steps:

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

[0068] Step 1.1: Collecting three-phase current signals i ak (t) of each feeder for one cycle from the time of fault occurrence; bk (t) of each feeder for one cycle from the time of fault occurrence; ck (t), k = 1, 2, …, m, k represents the line number, i ak (t) of each feeder for one cycle from the time of fault occurrence; bk (t) of each feeder for one cycle from the time of fault occurrence; ck (t) of each feeder for one cycle from the time of fault occurrence;

[0069] Step 1.2: Calculating the A-phase negative sequence current signal i k (t) of each feeder by the following formula:

[0070]

[0071] wherein, α = e j120° is the characteristic operator of the symmetrical component method;

[0072] In step 1, first, three-phase current signals i ak (t) of each feeder for one cycle from the time of fault occurrence are collected; bk (t) of each feeder for one cycle from the time of fault occurrence; ck (t), wherein k = 1, 2, …, m, k represents the line number, i k (t) of each feeder are calculated by using the characteristic operator of the symmetrical component method; the above steps can effectively extract the fault characteristics, because the negative sequence current signal will show a specific change rule when a single-phase open-line grounding fault occurs, thereby 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 of step 2 is as follows:

[0074] For each feeder negative sequence current signal i k (t) acquired in step 1, an alternating mixed filter in morphological filtering is used for processing to obtain the filtered negative sequence current signal i k '(t);

[0075] In step 2, for each feeder negative sequence current signal i k (t) acquired in step 1, an alternating mixed filter in morphological filtering is used for processing; the specific operation is to use the alternating mixed filter to perform open operation and closed operation combination processing on the signal to effectively suppress noise in the signal and enhance fault features; the effect of the above step is to significantly improve the clarity of the signal, reduce the interference of background noise on subsequent fault detection, and thus ensure the accuracy and stability of fault feature extraction.

[0076] Step 3: Map the filtered negative sequence current signal to the time-frequency space with u as the variable through coordinate transformation to obtain 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 the time-frequency space with u as the variable through coordinate transformation to obtain a time-frequency current signal i k (p,u) containing a rotation factor parameter:

[0078]

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

[0080]

[0081] In the formula, u=tcosβ+fsinβ is the coordinate transformation formula, where f is the frequency, is the rotation angle, p is the rotation factor, p∈real number; and when the rotation angle β=2nπ, the kernel function h p (t,u) is an impulse function δ(t+u); when the rotation angle β=(2n+1)π, the kernel function h p (t,u) is an impulse function δ(t+u); where p∈real number is a common mathematical symbol, and its meaning is as follows: p represents a variable, ∈ represents the "belongs to" symbol, and real number refers to the real number set; p∈real number means that the variable p takes values in the real number set;

[0082] In step 3, the specific operation is to map the negative sequence current signal obtained after filtering to a time-frequency space with u as a variable through coordinate transformation, and a kernel function containing a rotation factor p is introduced for transformation in the process, the kernel function presents in the form of an impact function according to different rotation angles, so that a time-frequency current signal containing a rotation factor parameter is obtained; the effect of the above step is that through coordinate transformation and the introduction of the rotation factor, the distribution characteristics of the signal at different times and frequencies can be more flexibly analyzed, and the extraction ability of the time-frequency characteristics of the fault signal is enhanced, which provides a more accurate basis for subsequent optimal rotation factor finding and fault detection based on energy focusing characteristics.

[0083] Step 4: On the basis of step 3, for each feeder, the optimal rotation factor is found according to the energy focusing characteristics of the time-frequency current signal, and then the optimal rotation factor is substituted into the time-frequency current signal expression to generate the time-frequency current signal of each feeder under the optimal rotation factor; step 4 includes the following specific steps:

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

[0085]

[0086] The corresponding time-frequency current signal i k (p s ,u) is calculated, and a "rotation factor-time-frequency signal" mapping relationship is constructed;

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

[0088]

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

[0090] Step 4.3: For each feeder, all the sampling rotation factors p s in step 4.1 are traversed respectively, the corresponding energy concentration C k (p s ) is calculated, and the rotation factor that makes C k (p s ) maximum is selected as the optimal rotation factor p k_opt;

[0091] Step 4.4: Substitute the optimal rotation factor p k_opt into the time-frequency current signal expression to obtain the time-frequency current signal i k_opt of each feeder under the optimal rotation factor p k (p k_opt , u k_opt ):

[0092]

[0093] wherein u k_opt is the variable corresponding to the optimal rotation factor p k_opt , and K is the kernel function corresponding to the optimal rotation factor p k_opt .

[0094] In step 4, first, the rotation factor range is sampled at intervals of 0.1 to construct a discrete rotation factor set, and the time-frequency current signal formula in step 3 is used to calculate the time-frequency current signal corresponding to each sampling point, thereby establishing a “rotation factor-time-frequency signal” mapping relationship; then, to quantify the energy concentration degree of the time-frequency current signal under different rotation factors, the energy concentration index C k (p) of each feeder is defined, and the greater the value, the more concentrated the signal is under the variable u; then, for each feeder, all the sampling rotation factors are traversed to calculate the corresponding energy concentration, and the rotation factor that maximizes C k (p s ) is selected as the optimal rotation factor p k_opt of the feeder; finally, the optimal rotation factor p k_opt is substituted into the time-frequency current signal expression to generate the time-frequency current signal of each feeder under the optimal rotation factor; the effect of the above operation steps is that the optimal time-frequency analysis parameters for each feeder can be adaptively found, thereby more accurately extracting fault features and improving the sensitivity and accuracy of fault detection.

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

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

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

[0098] In step 5, the specific operation is to calculate the peak amplitude of the time-frequency current signal of each feeder under the optimal rotation factor p k_opt ; the effect lies in that the signal strength of each feeder under specific time-frequency analysis parameters can be accurately quantified, thereby providing a key comparison benchmark for subsequent fault detection criterion based on peak amplitude, which helps to accurately identify the feeder where single-phase broken-line grounding fault occurs.

[0099] Step 6: Based on the peak amplitude of the time-frequency current signal under the optimal rotation factor, a single-phase broken-line grounding fault detection criterion is constructed; the peak amplitude of the time-frequency current signal of each feeder under the optimal rotation factor is compared with the threshold value, and when the peak amplitude is greater than the threshold value, it is determined that the single-phase broken-line grounding fault occurs in the feeder.

[0100] Step 6 includes the following specific steps:

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

[0102] Step 6.2: For the three-phase current signal collected in step 6.1 under the normal operation of the system, reuse steps 1 to 5 to calculate the peak value of the time-frequency current signal of each feeder, denoted as the peak reference under the normal operation condition of the system: I peak,k0 ;

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

[0104] Step 6.4: The threshold value is set as I h = μ + 3σ, and the peak amplitude I peak,k of the time-frequency current signal of each feeder is compared with the threshold value I h ; when I peak,k >I h , it is determined that the single-phase broken-line grounding fault occurs in the feeder.

[0105] In step 6, firstly, the three-phase current signals in a cycle are collected in the normal operation state of the system as the reference data (step 6.1); then the method of steps 1 to 5 is reused to calculate the time-frequency current signal peak values of each feeder in the normal operation of the system, and the peak reference in the normal operation condition is formed (step 6.2); then the mean and standard deviation of the normal peak values are calculated to quantify the signal fluctuation range in the normal operation (step 6.3); finally, the threshold value is set as the mean plus three times the standard deviation, and when the time-frequency current signal peak value amplitude of a certain feeder exceeds the threshold value, it is determined that the single-phase broken-line grounding fault occurs in the feeder (step 6.4); the above steps effectively avoid the problem of insufficient adaptability of the fixed threshold value to the system operation condition change by establishing a dynamic threshold reference based on the normal operation data, and significantly improve the accuracy and reliability of fault detection.

[0106] As can be seen from the above, the method significantly enhances the accuracy and stability of the feature extraction of the single-phase broken-line grounding fault of the neutral point ungrounded system by combining the symmetric component method, morphological filtering and coordinate transformation technology, can accurately capture the fault signal features, and greatly improves the accuracy and reliability of fault detection; at the same time, the optimal rotation factor is adaptively determined based on the feeder energy concentration degree, so that the detection strategy can flexibly adapt to different fault conditions, effectively improves the fault detection efficiency and success rate under complex power grid structure and variable operation conditions, and overcomes the poor adaptability of the traditional method.

[0107] The working principle of the application is as follows:

[0108] 1. Load sequence network diagram of broken-line grounding fault of ungrounded system

[0109] Figure 2 It is a broken-line grounding fault model of ungrounded system, wherein is the three-phase electromotive force of the system, L and R are the equivalent inductance and resistance of the line respectively, C A1 , C B1 , C C1 is the capacitance of each phase of the fault feeder to the ground, C Ai , C Bi , C Ci (i=2,3,...,n) is the capacitance of each phase of the healthy feeder to the ground, Z AB =Z BC =Z CA is the three-phase load impedance; is a virtual voltage source at the grounding point, equal to the steady-state reverse voltage amplitude of the grounding point before the broken-line fault occurs; is a virtual current source at the broken point, equal to the phase current amplitude before the fault occurs, R fR is the grounding resistance; assuming that a single-phase broken line fault occurs at a distance x from the bus, the fault points are M and N, in the case of K1 closing and K2 opening, the system is single-phase power side broken line grounding; in the case of K1 opening and K2 closing, it is single-phase load side broken line grounding.

[0110] Assuming that the voltage between the fault points of each phase is The phase current of the power side of the fault point is The phase-to-ground voltage and ground current of the M side of the fault point are and The phase-to-ground voltage and ground current of the N side of the fault point are and The boundary conditions of the single-phase power side broken line grounding fault are formula (1), formula (2), formula (3) and formula (4), as follows:

[0111]

[0112] The boundary conditions of the single-phase load side broken line grounding fault are formula (1), formula (2), formula (5) and formula (6), as follows:

[0113]

[0114] The boundary conditions of the power side grounding and the load side grounding obtained by the symmetrical component method are formula (7) and formula (8) respectively:

[0115]

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

[0117] Combined with the boundary conditions of formula (7) and formula (8), the load sequence network diagram of the single-phase broken line grounding fault of the ungrounded system is shown in Figure 3 M1 , Z M2 , Z M0 and Z N1 , Z N2 , Z N0 are the positive sequence, negative sequence and zero sequence equivalent impedances of the fault feeder fault points M and N respectively.

[0118] 2. Analysis of negative sequence current characteristics of single-phase broken line grounding fault

[0119] From the negative sequence impedance characteristics, the system and the load both show inductive, and the negative sequence impedance value of the load is about one hundred times that of the system, and the line negative sequence impedance value is much smaller than the load impedance; Figure 4 is the negative sequence equivalent network diagram of the power side broken line grounding fault, wherein, Z i2 (i=2, 3,..., n), Z​S2 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 the load side open line to ground fault is as follows Figure 5 ; wherein the equivalent current source is:

[0133]

[0134] In formula (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 the single-phase load side open line to ground fault, the negative sequence current amplitude of the fault feeder is the largest, and is opposite to the direction of the normal feeder.

[0138] 3. Morphological filtering

[0139] The mathematical morphology mainly uses gray value morphology in signal processing, and the basic operations include gray value dilation and gray value erosion; f(n) is a one-dimensional signal to be processed, and the definition domain is D f ={0, 1, 2,..., N}; the structure element sequence is g(n), and the definition domain is D g ={0, 1, 2,..., P}; wherein P and N are integers, and N≥P; the operation expressions of 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 formula (18), (19), Θ represents the erosion operation; the open operation after erosion and then dilation is called gray value opening operation, and the closed operation after dilation and then erosion is called gray value closing operation; the opening operation is suitable for eliminating the peak noise at the top of the signal and removing burrs; the closing operation is helpful to suppress the wave trough noise at the bottom and fill the small concave area; the morphological filtering realizes signal noise suppression and feature enhancement through dilation or erosion and their combination operation; wherein the definition of the alternating hybrid filter is:

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

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

[0145] 1) High-precision signal processing, enhanced fault feature extraction capability: Traditional methods often fail to accurately extract signal features when dealing with single-phase broken conductor grounding fault signals in ungrounded systems due to weak fault features and background noise interference. The present application innovatively combines the symmetric component method, morphological filtering, and coordinate transformation technology. First, the symmetric component method is used to focus on the negative sequence current signal. Then, morphological filtering is used to effectively suppress noise. Finally, coordinate transformation is used to obtain time-frequency current signals, significantly enhancing the accuracy and stability of fault feature extraction. Compared with traditional methods, the present application can accurately capture fault signal features, greatly improving the precision and reliability of fault detection, and avoiding misjudgment and false positives caused by improper signal processing.

[0146] 2) Self-adaptive optimization detection strategy, improving the applicability of complex scenarios: Existing detection techniques often use fixed thresholds or simple parameter settings, making it difficult to adapt to complex and variable operating conditions in ungrounded systems. The present application determines the optimal rotation factor based on the feeder energy concentration degree, 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 present application to quickly and accurately detect faults in complex power grid structures, different fault locations, and transition resistances, overcoming the poor adaptability of traditional methods and effectively improving the fault detection efficiency and success rate in various operating environments.

[0147] Application example: A 10kV ungrounded system distribution network simulation model is built using PSCAD as shown in the figure. Figure 6 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 the l1 line is a cable line, and the rest are overhead lines. Each feeder end uses a 0.5MW constant impedance load. The lengths of each line are clearly marked in the figure, and the specific parameters of the lines are shown in Table 1.

[0148] Table 1 System specific parameters

[0149]

[0150] Simulation analysis 1

[0151] Assume that single-phase power side broken line grounding fault occurs at 3km from the bus of feeder l2, the grounding resistance is 10Ω, and the initial phase angle is 0°, and the case is analyzed; the system sampling frequency f=20kHz, the simulation duration is 0.2s, and the fault occurrence time is set to 0.12s.

[0152] Figure 1 It is a single-phase broken line grounding fault detection method flow chart of the ungrounded system, according to the method, first, the three-phase current signals within one cycle of each feeder after the fault occurs are collected, and the negative sequence current signals of each feeder are calculated according to the symmetrical component method, as shown in Figure 7 ; then the morphological filtering processing is carried out on the negative sequence current of each feeder in Figure 7 ; the time-frequency current signals under the variable u of each feeder are obtained by using coordinate transformation; then, according to the energy concentration degree 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 result of the time-frequency current signal of each feeder is [0.0014, 26.0649, 0.0017, 0.0021, 0.0017, 0.0017], which indicates that the single-phase broken line grounding fault occurs in feeder l2, and the broken line grounding fault detection is accurately realized.

[0153] Simulation analysis 2

[0154] Assume that single-phase load side broken line grounding fault occurs at 10km from the bus of feeder l4, the grounding resistance is 100Ω, and the initial phase angle is 0°, and the case is analyzed; the system sampling frequency f=20kHz, the simulation duration is 0.2s, and the fault occurrence time is set to 0.12s.

[0155] Similarly, according to the steps of a neutral point ungrounded system single-phase broken line grounding fault detection method, the peak amplitude result of the time-frequency current signal of each feeder is [0.0013, 0.0019, 0.0016, 24.6328, 0.0016, 0.0016], which indicates that the single-phase broken line grounding fault occurs in feeder l4, and the broken line grounding fault detection is accurately realized.

[0156] In order to further show the reliability of the method, a plurality of simulation verifications are carried out under different fault positions, different fault initial phase angles and the like working conditions by using the topology shown in Figure 6 .

[0157] The simulation results are shown in Figure 6The 10kV ungrounded system topology is shown, and simulation is performed for different fault locations, and the time-frequency current signal peak amplitude results of each feeder are shown in Table 2; in the case of setting the grounding resistance to 1Ω and the fault initial phase angle to 0°, the power side broken line grounding fault and the load side broken line grounding fault are simulated and calculated in detail for line 5 at l=1-20km (distance from the bus).

[0158] Table 2 simulation results for different fault locations

[0159]

[0160]

[0161] It can be seen from Table 2 that the same type of single-phase broken line grounding fault occurs at different fault locations, and by comparing the peak amplitude of each group of time-frequency current signals, it can be found that the feeder with the maximum value is the fault feeder.

[0162] Using Figure 6 The 10kV ungrounded system topology is shown, and simulation is performed for different fault locations, and the time-frequency current signal peak amplitude results of each feeder are shown in Table 2; in the case of setting the grounding resistance to 1Ω and the fault initial phase angle to 0°, the power side broken line grounding fault and the load side broken line grounding fault are simulated and calculated in detail for line 5 at l=1-20km (distance from the bus). f For 10Ω, 500Ω, 1000Ω, respectively, the power side broken line grounding fault and the load side broken line grounding fault are simulated and calculated in detail for line 5 at l=1-20km (distance from the bus).

[0163] Table 3 simulation results for different grounding resistances

[0164]

[0165] Table 3 lists the results of simulation under varying grounding resistances, and from Table 3 it can be seen that when the fault location remains unchanged and only the grounding resistance changes, the peak amplitude of the time-frequency current signal of each simulated line l3 is the maximum, so it can be judged that line l3 is the fault feeder.

[0166] A neutral point ungrounded system single-phase broken line grounding fault detection system suitable for the above-mentioned neutral point ungrounded system single-phase broken line grounding fault detection method, the system comprises:

[0167] A three-phase current signal acquisition module for acquiring three-phase current signals i ak (t), i bk (t), i ck (t) in a cycle from the moment of fault occurrence of each feeder, where k=1, 2, …, m, k represents the line number;

[0168] a negative sequence current calculation module, configured to calculate, according to the acquired three-phase current signals, an A-phase negative sequence current signal i k (t);

[0169] a morphological filtering module, configured to perform morphological filtering on the acquired negative sequence current signal to obtain a filtered negative sequence current signal;

[0170] a coordinate transformation module, configured to map the filtered negative sequence current signal to a time-frequency space with u as a variable through coordinate transformation to obtain a time-frequency current signal i k (p, u);

[0171] an optimal rotation factor determination module, configured to determine an optimal rotation factor p of each feeder according to an energy concentration degree of each feeder k_opt ;

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

[0173] a fault detection module, configured to compare the peak amplitude of the time-frequency current signal of each feeder with a threshold I h , and determine that a single-phase broken-line grounding fault occurs in the feeder when the peak amplitude is greater than the threshold.

[0174] As can be seen from the above, the neutral point ungrounded system single-phase broken-line grounding fault detection system forms a complete and coordinated fault detection process by integrating the 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. The 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] Embodiments of the present application provide an electronic device suitable for the neutral point ungrounded system single-phase broken-line grounding fault detection method described above, comprising:

[0176] a memory, configured to protect computer programs and data;

[0177] a processor, configured to run system programs.

[0178] Embodiments of the present application provide a computer storage medium suitable for the neutral point ungrounded system single-phase broken-line grounding fault detection method described above, and perform hierarchical security management on the system and data according to security management requirements.

[0179] Those skilled in the art will appreciate that embodiments of the application can be readily used as software, hardware, or a combination of software and hardware. In a typical configuration, a computing device includes one or more processors (CPUs), input / output interfaces, network interfaces, and memory.

[0180] The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks. Figure 1 one or more functions specified in the flowchart block or blocks. Figure 1 means for performing each one or more of the functions specified in the flowchart block or blocks.

[0181] These computer program instructions can also be stored in a computer- readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instructions which implement the functions specified in the flowchart block or blocks. Figure 1 one or more functions specified in the flowchart block or blocks. Figure 1 means for performing each one or more of the functions specified in the flowchart block or blocks.

[0182] The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks. Figure 1 one or more functions specified in the flowchart block or blocks. Figure 1 means for performing each one or more of the functions specified in the flowchart block or blocks.

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

[0184] The memory can include non-persistent memory and / or volatile memory, such as a random access memory (RAM) including a cache area for the temporary storage of data. The memory can also include non-volatile memory, such as read only memory (ROM) for storing structural information and / or instruction code. Both can be within one or more memory devices 1225.

[0185] Computer-readable media includes permanent and non-permanent, movable and non-movable media, which can be implemented by any method or technology to store information. The information can be computer-readable instructions, data structures, program modules 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, compact disc read-only memory (CD-ROM), digital versatile disc (DVD) or other optical storage, magnetic cassette, magnetic tape disk storage or other magnetic storage devices, or any other non-transmission medium that can be used to store information accessible by a computing device. According to the definition herein, computer-readable media does not include transitory media such as modulated data signals and carriers.

[0186] It should also be noted that the terms "comprising", "including", or any other variant thereof are intended to cover non-exclusive inclusions, so that a process, product or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or inherent to such a process, product or device. Without more limitations, the element defined by the statement "including a" does not exclude the presence of other identical elements in the process, product or device including the element.

[0187] The embodiments of the present application are given for example and description, although the embodiments of the present application have been shown and described above, it is understood that the above embodiments are exemplary and cannot be understood as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present application.

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. Step 3 includes the following specific process: The negative sequence current signal obtained after filtering By mapping the coordinates to a time-frequency space with u as the variable, a time-frequency current signal containing a rotation factor parameter is obtained. : ； In the formula, the kernel function The specific expression is as follows: ； In the formula, Here is the coordinate transformation formula, where f is the frequency. Let be the rotation angle, and p be the rotation factor. When the rotation angle is... At that time, kernel function For the impact function When rotating angle At that time, kernel function For the impact function ; Step 4 includes the following specific steps: Step 4.1: Within the range of rotation factors Within this range, sampling is performed 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 Construct a rotation factor-time frequency signal mapping relationship; Step 4.2: Quantize the time-frequency current signal The energy concentration degree under different rotation factors p is defined as C, where C is the energy concentration degree of each feeder. k (p): ； That is, C k The larger (p) is, the stronger the time-frequency current signal. The more concentrated it is 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 below : ； In the formula, 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.

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, 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. .

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 5 includes the following specific process: Calculate the optimal rotation factor p for each feeder k_opt Lower time-frequency current signal peak amplitude : 。 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 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: ; Step 6.3: Calculate the mean of normal peak values. and standard deviation mean m is the number of feeders, and the standard deviation is... ; Step 6.4: Set the threshold to... The peak amplitude of the time-frequency current signal of each feeder With threshold I h When comparing, At that time, it was determined that a single-phase open-circuit ground fault had occurred in the feeder.

6. 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 1-5, 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 containing a rotation factor parameter. ; 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 of the time-frequency current signal of each feeder under the optimal rotation factor. ; The fault detection module is used to compare the peak amplitude of the time-frequency current signal of each feeder with the threshold Ih. 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.

7. 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 5.

8. 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 5.

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