Overline in-phase cascading fault detection method and related equipment

Abstract

The invention belongs to the technical field of power system power distribution network relay protection, and discloses an overline in-phase cascading fault detection method and related equipment, and the method comprises the steps: monitoring a bus zero-sequence voltage effective value in real time, and starting a fault detection process when the bus zero-sequence voltage effective value exceeds a preset threshold value; collecting the zero-sequence current of the head end of each feeder line and removing the fundamental frequency component of the zero-sequence current of the head end of each feeder line to obtain the pure transient component of the zero-sequence current of each feeder line; calculating the skewness value of the pure transient component of the zero-sequence current of each feeder line at the first fault moment, and determining an overline in-phase first fault feeder line according to the symbol difference of the skewness value of the pure transient component of the zero-sequence current of each feeder line; and calculating the skewness value of the pure transient component of the zero-sequence current of each feeder at the moment of the second fault, and determining the cross-line in-phase secondary fault feeder according to the positive and negative change relation of the skewness values of the pure transient components of the zero-sequence current of the first fault feeder and the zero-sequence current of other feeders. The objective of the invention is to solve the problem of difficult detection caused by weak fault features during cross-line in-phase cascading faults.

Description

Technical Field

[0001] The present invention belongs to the technical field of relay protection of power system distribution network, and in particular relates to a method for detecting cross-line same-phase successive faults and related equipment. Background Art

[0002] In a low-current grounding system, when a single-phase ground fault occurs, relevant technical guidelines allow the system to operate with the fault for one to two hours. This regulation, to a certain extent, takes into account the inherent characteristics of low-current grounding systems and the need for power continuity, but it also carries hidden risks during this period. Specifically, during this period of operation, the original single-phase ground fault can easily evolve into a more serious, cross-line, same-phase, sequential ground fault. This fault evolution process is highly uncertain, and if not detected and addressed promptly, it can lead to a series of serious consequences. First, the fault could cause a fire in the cable trench, which often houses numerous cables. Once a fire breaks out, it not only burns the cables, causing direct economic losses, but can also spread to surrounding equipment, causing a larger-scale fire and seriously threatening the safety of power facilities such as substations. Second, the fault could also cause widespread power outages, disrupting normal power supply for numerous users, causing inconvenience to social production and life, and resulting in immeasurable indirect economic losses.

[0003] More critically, because the fault current in a low-current grounding system is relatively small when a fault occurs, conventional overcurrent protection devices have difficulty responding effectively to such weak fault currents. This results in the failure to detect and eliminate the fault in a timely manner, causing the fault to persist. During this process, the continued arc burning will cause serious damage to the equipment in the distribution network, accelerate equipment aging, and reduce the service life of the equipment. It will also pose a serious threat to the overall safety of the distribution network, affecting the stable operation of the power system and the reliable power supply to users. At present, for the cross-line same-phase sequential faults that may occur in low-current grounding systems, due to the weak fault characteristics, conventional detection methods have difficulty in accurately capturing the fault signal, resulting in detection difficulties, the inability to locate the fault location in a timely and accurate manner, and thus the inability to take effective measures to deal with it. Summary of the Invention

[0004] In response to the problems existing in the prior art, the present invention provides a method and related equipment for detecting cross-line same-phase successive faults, which aims to solve the problem that the fault characteristics of cross-line same-phase successive faults are weak, making detection difficult.

[0005] In order to solve the above technical problems, the present invention is implemented through the following technical solutions:

[0006] According to a first aspect of the present invention, a method for detecting consecutive same-phase cross-line faults is provided, comprising:

[0007] Real-time monitoring of the busbar zero-sequence voltage effective value. When the busbar zero-sequence voltage effective value exceeds the preset threshold, the fault detection process is initiated;

[0008] Collect the zero-sequence current at the head end of each feeder and remove the fundamental frequency component of the zero-sequence current at the head end of each feeder to obtain the pure transient component of the zero-sequence current of each feeder;

[0009] Calculate the skewness of the pure transient component of the zero-sequence current of each feeder at the time of the first fault, and determine the first fault feeder in the same phase across the line based on the sign difference of the skewness of the pure transient component of the zero-sequence current of each feeder;

[0010] The skewness of the pure transient component of the zero-sequence current of each feeder at the moment of the second fault is calculated, and the feeder with the simultaneous fault across the line is determined based on the positive and negative change relationship between the skewness of the pure transient component of the zero-sequence current of the first fault feeder and other feeders.

[0011] In a possible implementation of the first aspect, removing the fundamental frequency component of the zero-sequence current at the head end of each feeder to obtain the pure transient component of the zero-sequence current of each feeder includes:

[0012] The frequency shift algorithm is used to remove the fundamental frequency component of the zero-sequence current at the head end of each feeder to obtain the pure transient component of the zero-sequence current of each feeder.

[0013] In a possible implementation of the first aspect, the frequency shift algorithm is used to remove the fundamental frequency component of the zero-sequence current at the head end of each feeder to obtain the pure transient component of the zero-sequence current of each feeder, specifically:

[0014] Perform Hilbert transform on the zero-sequence current at the head end of each feeder to obtain the analytical signal of each feeder;

[0015] The pure transient component of the zero-sequence current of each feeder is obtained by multiplying the analytical signal of each feeder by the fundamental frequency shift factor.

[0016] In a possible implementation of the first aspect, determining the first-fault feeder in the same phase across the lines according to the sign difference of the skewness values ​​of the pure transient components of the zero-sequence currents of the feeders is specifically as follows:

[0017] When the skewness value of the pure transient component of the zero-sequence current of a feeder is greater than 0, and the skewness values ​​of the pure transient components of the zero-sequence current of the other feeders are all less than 0, the feeder with the skewness value greater than 0 is determined to be the feeder with the first cross-line same-phase fault.

[0018] In a possible implementation of the first aspect, determining the feeder with simultaneous cross-line faults based on the positive and negative change relationship between the skewness values ​​of the pure transient components of the zero-sequence currents of the first fault feeder and other feeders is specifically as follows:

[0019] The skewness value of the pure transient component of the zero-sequence current of the first fault feeder changes from greater than 0 to less than 0;

[0020] The skewness value of the pure transient component of the zero-sequence current of a certain feeder changes from less than 0 to greater than 0;

[0021] The skewness values ​​of the pure transient components of the zero-sequence currents of the remaining feeders remain unchanged and are all less than 0;

[0022] When all the above conditions are met, the feeder whose skewness value changes from negative to positive is determined to be a feeder with simultaneous cross-line faults.

[0023] In a possible implementation of the first aspect, a calculation formula for the skewness value of the pure transient component of the feeder zero-sequence current is:

[0024]

[0025] Where S is the skewness value of the pure transient component of the feeder zero-sequence current; μ is the mean; σ is the standard deviation; N is the total number of sampling points in the time window of the pure transient component of the zero-sequence current selected when calculating the skewness value; and x(n) is the nth sample value in the sample sequence.

[0026] In a possible implementation manner of the first aspect, the preset threshold is 15% of the system nominal phase voltage.

[0027] According to a second aspect of the present invention, a computer device is provided, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the method for detecting cross-line in-phase sequential faults when executing the computer program.

[0028] According to a third aspect of the present invention, a computer-readable storage medium is provided, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the method for detecting cross-line in-phase sequential faults is implemented.

[0029] According to a fourth aspect of the present invention, a computer program product is provided, which implements the method for detecting cross-line in-phase sequential faults when executed by a processor.

[0030] Compared with the prior art, the present invention has at least the following beneficial effects:

[0031] The present invention provides a method for detecting cross-line same-phase successive faults. The method starts the fault detection process by real-time monitoring of the effective value of the busbar zero-sequence voltage, collects and processes the zero-sequence current at the head end of each feeder to obtain the pure transient component of the zero-sequence current, and then uses the sign difference of the skewness value to determine the cross-line same-phase first-fault feeder and the cross-line same-phase successive fault feeder. This solves the problem that the fault characteristics are weak and cause detection difficulties during cross-line same-phase successive faults, and can detect such faults in a timely and accurate manner. The present invention calculates the skewness value of each obtained pure transient component of the zero-sequence current of each feeder, and realizes cross-line same-phase successive fault detection based on the sign difference of the skewness value. The skewness value is simple to calculate, which reduces the computational complexity. Fault detection can be realized by only using the polarity difference of the skewness value. The criterion execution is simpler, and only the positive and negative judgment of the obtained value needs to be performed. This simple and efficient detection method not only ensures the detection accuracy, but also improves the detection rate, can quickly locate the fault, and reduce the impact time of the fault on the system. The present invention can timely and accurately detect cross-line same-phase successive faults, and then take measures to deal with them, reducing the risk of fire in the cable trench and large-scale power outages, and ensuring the safety of power facilities and normal power supply to users.

[0032] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the specific embodiments of the present invention, the following is a brief introduction to the drawings required for use in the description of the specific embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0034] Figure 1 This is a flow chart of a method for detecting cross-line same-phase successive faults according to the present invention;

[0035] Figure 2 This is a flow chart of a method for detecting consecutive same-phase cross-line faults according to the present invention;

[0036] Figure 3 This is a fourth-order transient equivalent circuit diagram when a cross-line fault occurs in the resonant grounding system of the present invention;

[0037] Figure 4 Schematic diagram of the skewness test signal of the present invention;

[0038] Figure 5 Schematic diagram of a simulation model of a 10kV resonant grounding system according to an embodiment of the present invention;

[0039] Figure 6(a) is the zero-sequence current of each feeder before and after the first fault occurs under typical working conditions in the embodiment of the present invention;

[0040] Figure 6 (b) is the zero-sequence current of each feeder before and after the secondary fault occurs under typical working conditions in the embodiment of the present invention;

[0041] Figure 6 (c) is the pure transient component of the zero-sequence current of each feeder obtained by using the frequency shift algorithm under typical working conditions in an embodiment of the present invention;

[0042] Figure 7 (a) and (b) are curves showing the variation of the feeder skewness values ​​with the secondary fault transition resistance under working conditions 1 and 2, respectively, in an embodiment of the present invention;

[0043] Figure 8 : This is the transient zero-sequence current of the healthy feeder l2 and the faulty feeder l4 after adding noise when a secondary fault occurs in the embodiment of the present invention. DETAILED DESCRIPTION

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0045] In this implementation, a corresponding monitoring and data processing system is established within the low-current grounding system. First, a zero-sequence voltage sensor is installed at the system's busbars to monitor the effective zero-sequence voltage of the busbars in real time. Furthermore, a zero-sequence current sensor is installed at the headend of each feeder to collect zero-sequence current data.

[0046] Combine Figure 1 and Figure 2 As shown, an embodiment of the present invention provides a method for detecting consecutive same-phase cross-line faults, which is mainly intended to solve the problem that the fault characteristics of consecutive same-phase cross-line faults in a low-current grounding system are weak, resulting in difficulty in detection. The method specifically includes the following steps:

[0047] Step 1: Monitor the effective value of the bus zero-sequence voltage in real time. When the effective value of the bus zero-sequence voltage exceeds a preset threshold, start the fault detection process.

[0048] In one implementation, the setting of the preset threshold is calculated based on the nominal phase voltage of the system. Assuming that the nominal phase voltage of the system is U n , the preset threshold is 0.15U nFor example, if the system nominal phase voltage is 10kV, the preset threshold is 1.5kV.

[0049] That is to say, when the bus zero sequence voltage RMS value U0(t1) is greater than the system nominal phase voltage U n 0.15 times of U0(t1)>15%U n When the system determines that a fault may have occurred, it starts the fault detection process.

[0050] Step 2: Collect the zero-sequence current at the head end of each feeder and remove the fundamental frequency component of the zero-sequence current at the head end of each feeder to obtain the pure transient component of the zero-sequence current of each feeder.

[0051] That is, after the fault detection process is started, the system begins to collect zero-sequence current data at the head end of each feeder.

[0052] In one possible implementation, in order to remove the fundamental frequency component in the zero-sequence current at the head end of each feeder and obtain the pure transient component of the zero-sequence current of each feeder, a frequency shift algorithm is used for processing. The specific steps are as follows:

[0053] First, the collected zero-sequence current at the head end of each feeder is Hilbert transformed to obtain the analytical signal of each feeder;

[0054] Finally, the analytical signal of each feeder is multiplied by the fundamental frequency shift factor to obtain the pure transient component of the zero-sequence current of each feeder.

[0055] For example, the original zero-sequence current signal x(t) of a feeder is analyzed as follows:

[0056] a. Calculate the analytical signal of the original zero-sequence current x(t) through Hilbert transform The specific transformation process is shown in the following formula:

[0057]

[0058] Where H(·) represents the Hilbert transform; j is the imaginary unit, The imaginary part lags the real part by π / 2; t is the time point of the Hilbert transform; ξ is the dummy variable in the Hilbert transform integration process, which is used to traverse all time points to calculate the convolution integral; x(ξ) is the instantaneous value of the original zero-sequence current x(t) at time ξ.

[0059] b. Define the fundamental frequency shift factor e -jωt , for the analytical signal Multiplying by the frequency shift factor, we can get the function after removing the fundamental component The specific formula is as follows:

[0060]

[0061] Where, This is the desired pure transient component of the zero-sequence current.

[0062] c. Perform steps a and b on the original zero-sequence current signal of each feeder to obtain the pure transient component of the zero-sequence current of each feeder.

[0063] Step 3: Calculate the skewness of the pure transient component of the zero-sequence current of each feeder at the time of the first fault, and determine the first inter-line in-phase fault feeder based on the sign difference of the skewness of the pure transient component of the zero-sequence current of each feeder.

[0064] In one embodiment, the calculation formula for the skewness value of the pure transient component of the feeder zero-sequence current is:

[0065]

[0066] Where S is the skewness value of the pure transient component of the feeder zero-sequence current; μ is the mean; σ is the standard deviation; N is the total number of sampling points in the time window of the pure transient component of the zero-sequence current selected when calculating the skewness value. For example, when calculating the skewness value at a certain moment, N data points in a certain time window before and after the moment can be selected; x(n) is the nth sample value in the sample sequence.

[0067] In one implementable method, the feeder with the first cross-line same-phase fault is determined based on the sign difference of the skewness values ​​of the pure transient components of the zero-sequence current of each feeder. Specifically, when the skewness value of the pure transient component of the zero-sequence current of a certain (only) feeder is greater than 0, and the skewness values ​​of the pure transient components of the zero-sequence current of the remaining feeders are all less than 0, the feeder with the skewness value greater than 0 is determined to be the feeder with the first cross-line same-phase fault.

[0068] Step 4: Calculate the skewness of the pure transient component of the zero-sequence current of each feeder at the time of the second fault, and determine the feeder with the simultaneous fault across the line based on the positive and negative change relationship between the skewness of the pure transient component of the zero-sequence current of the first fault feeder and other feeders.

[0069] That is, the system continues to be monitored, and when a second fault occurs, the skewness value of the pure transient component of the zero-sequence current of each feeder at the moment of the second fault is calculated.

[0070] In one possible implementation, the feeder with the simultaneous cross-line fault is determined based on the positive and negative change relationship between the skewness of the pure transient component of the zero-sequence current of the first fault feeder and other feeders. The specific judgment conditions are as follows:

[0071] The skewness value of the pure transient component of the zero-sequence current of the first fault feeder changes from greater than 0 to less than 0;

[0072] The skewness value of the pure transient component of the zero-sequence current of a certain feeder changes from less than 0 to greater than 0;

[0073] The skewness values ​​of the pure transient components of the zero-sequence currents of the remaining feeders remain unchanged and are all less than 0.

[0074] When all the above conditions are met, the feeder whose skewness value changes from negative to positive is determined to be the feeder with simultaneous cross-line faults, and the other feeders are all healthy feeders.

[0075] Preferably, after identifying the first faulty feeder in the same phase across the line and the subsequent faulty feeders in the same phase across the line, the system can promptly issue an alarm signal to notify the operation and maintenance personnel to handle the problem. At the same time, the system continues to monitor the real-time zero-sequence voltage of the busbar and the zero-sequence current of each feeder, so that new faults can be discovered and handled in a timely manner during subsequent operation.

[0076] Through the above implementation, the cross-line same-phase successive fault detection method provided by the present invention can effectively detect cross-line same-phase successive faults in a low-current grounding system, solve the problem of detection difficulty caused by weak fault characteristics, and ensure the stable operation of the power system and reliable power supply to users.

[0077] The working principle of the present invention is explained in detail below:

[0078] For the equivalent circuit of cross-line faults, the fourth-order transient equivalent circuit when a cross-line fault occurs in a resonant grounding system can be simplified to: Figure 3 The second-order circuit shown in the figure. There are n feeders in the system, of which line 1 is the first fault feeder and line 2 is the second fault feeder. R1 and R2 are the first and second grounding resistances R respectively. f1 With R f2 3 times of C 01 and C 02 is the zero-sequence distributed capacitance of the corresponding fault feeder to ground; u 0f2 It is the virtual power supply at the secondary fault grounding point. 0k and C 0k (k=3,4,···,n) are the zero-sequence current at the head end of the healthy feeder and the zero-sequence distributed capacitance to the ground respectively; i 0Lp is the zero-sequence current flowing through the arc suppression coil; C 0sum It is the sum of the zero-sequence distributed capacitance of each feeder to the ground.

[0079] according to Figure 3 For the circuit shown, write the differential equation:

[0080]

[0081] The characteristic roots of the above equation are:

[0082]

[0083] The present invention focuses on analyzing the underdamped resonance process of high-resistance working conditions.

[0084] For transient zero-sequence current polarity analysis, when the fault resistances R1 and R2 of the primary and secondary faults satisfy the following equations, the resonant system is underdamped.

[0085]

[0086] Most high-resistance ground faults are in an underdamped state, where the attenuation factor δ and the damped oscillation angular frequency ω are d Satisfies the following equation

[0087]

[0088] At the moment of secondary fault occurrence, set i 0Lp =I m2 sin(ω0t+θ), where I m2 and θ are the amplitude and initial phase angle of the arc suppression coil inductance current at this time, respectively, and ω0 is the angular frequency of the power frequency.

[0089] Then, the zero-sequence current flowing through the arc suppression coil can be set as:

[0090]

[0091] in

[0092]

[0093] Where, I m1 is the amplitude of the zero-sequence current of the arc suppression coil during the initial ground fault; It is the initial phase angle of the zero-sequence current of the arc suppression coil when a secondary fault occurs.

[0094] The busbar transient zero-sequence voltage is

[0095] u 02-t =L p e -δt (B1cosω d t-B2sinω d t)

[0096] in

[0097]

[0098] The transient zero-sequence current at the head end of a healthy feeder is:

[0099] i c0k-t =C 0k L p e -δt (B3cosω d t+B4sinω d t)

[0100] in

[0101]

[0102] The transient zero-sequence current at the first end of the feeder with the initial fault is:

[0103]

[0104] The transient zero-sequence current at the head end of the secondary fault feeder is:

[0105]

[0106] Through the above analysis, the expressions of busbar transient zero-sequence voltage and each feeder transient zero-sequence current when a secondary fault occurs are obtained.

[0107] In order to measure the polarity relationship of the transient zero-sequence current of each feeder, the inner product of the transient zero-sequence current of each feeder and the transient zero-sequence voltage of the bus is defined as:

[0108]

[0109] Where: i 0k (t) and u 02 (t) are the transient zero-sequence current of feeder k and the transient zero-sequence voltage of busbar; t is the duration of transient process. When the inner product is greater than 0, it means that i 0k (t) and u 02 (t) is of the same polarity; otherwise, it is of opposite polarity. Based on this formula, the inner products of the transient zero-sequence voltages of the healthy feeder, the first fault feeder, the secondary fault feeder, and the busbar are calculated respectively.

[0110]

[0111]

[0112] It can be seen that the sign of each feeder's inner product is affected by factors such as the first fault resistance and system capacitance. When the first fault resistance approaches infinity, the inner product of the healthy feeder and the first fault feeder is negative, while the inner product of the secondary fault feeder is positive. Furthermore, it is shown that the polarity of the healthy feeder and the first fault feeder is the same, while the polarity of the secondary fault feeder is opposite.

[0113] Regarding the frequency shift algorithm, the specific process of the fundamental frequency shift algorithm is explained by taking the transient zero-sequence current at the head end of a healthy feeder as an example. According to the trigonometric function transformation relationship, it can be organized into the form of real part plus imaginary part, as shown in the following formula:

[0114] i 0k =x RS cosω0t-x IS sinω0t

[0115] +xRT (t)cosω d tx IT (t)sinω d t

[0116] Where: x RS Real amplitude coefficient of fundamental component; x IS The imaginary (orthogonal) amplitude coefficient of the fundamental component; x RT The real part of the frequency-shifted component is the time-varying amplitude coefficient; x IT The time-varying amplitude coefficient of the imaginary (orthogonal) part of the frequency-shifted component.

[0117] The analytical signal of the original signal can be obtained by Hilbert transform The transformation process is shown in the following formula.

[0118]

[0119] Where H(·) represents the Hilbert transform; j is the imaginary unit; The imaginary part lags the real part by π / 2; t is the time point of the Hilbert transform; ξ is the dummy variable in the Hilbert transform integration process, which is used to traverse all time points to calculate the convolution integral; x(ξ) is the instantaneous value of the original zero-sequence current signal x(t) at time ξ.

[0120] Bring in to get:

[0121]

[0122] It can be seen that the fundamental component of the original signal still exists after the Hilbert transform. At this time, the fundamental frequency shift factor e is defined as -jωt By multiplying both sides by the frequency shift factor, we can get the function after removing the fundamental component, as shown in the following formula:

[0123]

[0124] in, The real part of is the signal after removing the fundamental component. Therefore, the transient zero-sequence current of a healthy feeder is:

[0125] i 0k-t =C 0k L p e -δt [B3cos(ω d t-ω0t)+B4sin(ω d t-ω0t)]

[0126] In summary, the combination of Hilbert transform and fundamental frequency shift factor can effectively remove the fundamental component in the zero-sequence current of each feeder, further highlight the transient characteristics of weak signals, and facilitate fault detection.

[0127] Regarding the skewness feature, skewness is used to measure the degree to which the probability density distribution function deviates from the center of the normal distribution, reflecting the asymmetry of the signal distribution relative to its mean. The calculation formula is as follows:

[0128]

[0129] Where μ is the mean, σ is the standard deviation, and N is the total number of sampling points within the time window of the pure transient component of the zero-sequence current used to calculate the skewness. Based on the data distribution, skewness can be categorized as follows: normal distribution, with skewness (S = 0); right-skewed distribution (also known as positive skewness), with skewness (S > 0); and left-skewed distribution (also known as negative skewness), with skewness (S < 0). x(n) is the nth sample value in the sample sequence.

[0130] In order to further analyze the characteristics of skewness, the discrete signals s1(t) and s2(t) were tested, and their expressions are as follows:

[0131]

[0132] In a low-current grounding system, when a single-phase grounding fault occurs, the transient zero-sequence current polarity of the fault feeder is opposite to that of the healthy feeder, and exhibits an oscillation attenuation characteristic. Figure 4 As shown in Figure 3, the waveform characteristics of the discrete signals s1(t) and s2(t) are highly consistent with their fault characteristics.

[0133] The area above the mean of a discrete signal is defined as the positive region, and the area below the mean is defined as the negative region. According to the definition of the mean, when the discrete data points in the positive region are far from the mean, the data points in that region are sparsely distributed; conversely, when the data points in the negative region are sparsely distributed, the data points in that region are densely distributed. From the expressions for the discrete signals s1(t) and s2(t), we can see that, for a constant standard deviation σ, when the data points in the positive region are sparse, the calculated skewness is positive; conversely, when the data points in the negative region are sparse, the calculated skewness is negative.

[0134] like Figure 4 As shown in , s1(t) first increases and then decreases at t = 0. The data points in the positive region are far from the mean, indicating that the data points in this region are sparsely distributed. The calculated skewness value S1 = 0.75 > 0, so s1(t) is positively skewed. On the other hand, s2(t) first decreases and then increases at t = 0. The data points in the negative region are far from the mean, indicating that the data points in this region are sparsely distributed. The calculated skewness value S2 = -0.75 < 0, so s2(t) is negatively skewed. In summary, by analyzing the distribution characteristics of the data points in the positive and negative regions of the discrete signal, the skewness values ​​at the time of the two faults can be determined, thereby realizing the detection of cross-line in-phase sequential faults.

[0135] In one embodiment, if Figure 5As shown in Figure 1, a 10kV active resonant grounded distribution network with DGs is built. The line parameters are shown in Table 1. The system sampling rate is 10kHz, and m1-m5 represent the current transformers at the head end of each feeder. The system uses overcompensation. When the overcompensation degree is 10%, the arc suppression coil inductance L p =0.2569H, damping resistor R L =4.0352Ω.

[0136] Table 1 Line specific parameters

[0137]

[0138]

[0139] A simulation analysis was conducted for a typical operating condition: Phase A ground faults occurred successively on feeders L1 and L3, with ground resistances of 500Ω and 2000Ω, respectively. The initial fault occurred at 0.4s, and the subsequent faults at 0.6s.

[0140] Figure 6 (a) in FIG6 is the zero-sequence current of each feeder before and after the occurrence of the first fault. As can be seen from (a) in FIG6, the polarity of the healthy feeder and the faulty feeder are opposite, and the fault characteristics are obvious. Figure 6 The skewness values ​​of the feeders in (a) are [0.251, -0.160, -0.145, -0.197, -0.126]. By comparison, it can be seen that the sign of the skewness value of feeder l1 is opposite to that of other feeders, and thus the first fault feeder is determined to be l1.

[0141] The frequency shift algorithm is used to Figure 6 The power frequency component of the zero sequence current of each feeder in (b) is filtered out, and the result is as follows Figure 6 As shown in (c) of the figure, the algorithm effectively filters out the power frequency components of each feeder and reveals the transient characteristics of secondary faults. Specifically, the transient current polarity of the healthy and faulty feeders is opposite, which is consistent with theoretical analysis. Based on this characteristic, skewness can be used to detect secondary faults. Figure 6 In (c), the skewness values ​​of each feeder are [-0.650, -0.420, 0.127, -0.478, -0.425], respectively. Comparing the skewness changes during the two faults, we see that the sign of the skewness of feeder l1 changes from positive to negative, while the sign of the skewness of feeder l3 changes from negative to positive. The signs of the skewness values ​​of the other feeders remain unchanged and are all negative. Therefore, feeder l3 is identified as the secondary fault. The results demonstrate that this method can accurately detect both primary and secondary cross-line in-phase faults.

[0142] For adaptability analysis, for different transition resistance combinations, based on the relationship between the initial and subsequent fault transition resistances, the subsequent fault transition resistance combinations can be divided into two typical operating conditions: initial low resistance, subsequent high resistance, and initial high resistance, subsequent low resistance. To verify the adaptability of this method under different transition resistance combinations, a phase A grounding fault was sequentially applied to feeders L1 and L3. The specific combination relationships are shown in Operating Conditions 1 and 2.

[0143] Working condition 1: The transition resistance of the first fault is 500Ω, and the transition resistance of the subsequent faults gradually increases from 1000Ω to 5000Ω;

[0144] Working condition 2: The transition resistance of the first fault is 5000Ω, and the transition resistance of the subsequent faults gradually decreases from 4500Ω to 500Ω.

[0145] Figure 7 Figures (a) and (b) show the curves of feeder skewness as a function of secondary fault transition resistance under operating conditions 1 and 2, respectively. As can be seen, under both operating conditions, the skewness of the feeder with the initial fault changes from positive to negative, while the skewness of the feeder with the secondary fault changes from negative to positive. The skewness of the other feeders remains unchanged and remains negative. This demonstrates that this method can accurately detect both initial and secondary faults across the same phase of the line and is unaffected by the transition resistance combination.

[0146] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples without contradiction.

[0147] To verify the adaptability of this method under noise interference, phase A grounding faults are set on feeders l2 and l4 successively, with transition resistances of 1000Ω and 2000Ω respectively, and Gaussian white noise with a signal-to-noise ratio of 40dB is superimposed. Figure 8 is the transient zero-sequence current of the healthy feeder l2 and the faulty feeder l4 when a secondary fault occurs. Figure 8It can be seen that the transient current of the healthy feeder L2 fluctuates significantly due to noise, but its transient characteristics remain stable. By calculating the skewness, it is still possible to detect secondary faults. The skewness values ​​for each feeder are calculated as [-0.294, -0.419, -0.309, 0.096, -0.338]. By comparison, the sign of the skewness value of feeder L4 is opposite to that of the other feeders, thus determining that feeder L4 is the secondary fault. To further verify the noise immunity of this method, the initial fault feeder is L2, and the transition resistance is 1000Ω. The secondary fault operating conditions are shown in Table 2. Table 2 shows the secondary fault detection results of this method under Gaussian white noise with different signal-to-noise ratios. Table 2 shows that this method can detect secondary faults even in the presence of strong noise of 30dB.

[0148] Table 2 Detection results under noise interference

[0149] feeder Secondary / Ω SNR / dB Skewness value <![CDATA[l1]]> 500 60 [0.468,-0.339,-0.242,-0.241,-0.256] <![CDATA[l3]]> 1000 50 [-0.292,-0.400,0.162,-0.329,-0.323] <![CDATA[l4]]> 2000 40 [-0.294,-0.419,-0.309,0.096,-0.338] <![CDATA[l5]]> 3000 30 [-0.085,-0.568,-0.102,-0.289,0.268]

[0150] In another embodiment of the present invention, a computer device is provided, comprising a processor and a memory, wherein the memory is used to store a computer program, wherein the computer program includes program instructions, and the processor is used to execute the program instructions stored in the computer storage medium. The processor may be a central processing unit (CPU), or may be other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, and is suitable for implementing one or more instructions, specifically suitable for loading and executing one or more instructions in the computer storage medium to implement the corresponding method flow or corresponding function; the processor described in the embodiment of the present invention can be used for the operation of a cross-line same-phase sequential fault detection method.

[0151] In another embodiment of the present invention, a storage medium is provided, specifically a computer-readable storage medium (Memory). The computer-readable storage medium is a memory device in a computer device, used to store programs and data. It is understood that the computer-readable storage medium herein may include both built-in storage media in the computer device and, of course, extended storage media supported by the computer device. The computer-readable storage medium provides storage space, which stores the terminal's operating system. Furthermore, the storage space also stores one or more instructions suitable for being loaded and executed by a processor. These instructions may be one or more computer programs (including program code). It should be noted that the computer-readable storage medium herein may be a high-speed RAM memory or a non-volatile memory, such as at least one disk storage device. The processor may load and execute the one or more instructions stored in the computer-readable storage medium to implement the corresponding steps of the method for detecting cross-line in-phase sequential faults in the above-mentioned embodiment.

[0152] It will be understood by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Thus, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0153] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts 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, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowcharts and / or block diagrams. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0154] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0155] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0156] The present invention further provides a computer program product, which is configured to execute any of the aforementioned methods for detecting consecutive same-phase faults across a line. Since the computer program product provided by the present invention and the aforementioned method for detecting consecutive same-phase faults across a line are based on the same inventive concept, the computer program product provided by the present invention possesses all the advantages of the aforementioned method for detecting consecutive same-phase faults across a line. Therefore, the beneficial effects of the computer program product provided by the present invention will not be detailed here.

[0157] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples without contradiction.

[0158] Finally, it should be noted that the above-described embodiments are only specific implementations of the present invention, which are used to illustrate the technical solutions of the present invention, rather than to limit them. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the above-described embodiments, those skilled in the art should understand that any person skilled in the art can modify or easily conceive of changes to the technical solutions described in the above-described embodiments within the technical scope disclosed by the present invention, or replace some of the technical features therein with equivalents. Such modifications, changes, or replacements do not deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for detecting consecutive same-phase cross-line faults, characterized in that: include: Real-time monitoring of the effective value of the busbar zero-sequence voltage. When the effective value of the busbar zero-sequence voltage exceeds the preset threshold, the fault detection process is initiated; Collect the zero-sequence current at the head end of each feeder and remove the fundamental frequency component of the zero-sequence current at the head end of each feeder to obtain the pure transient component of the zero-sequence current of each feeder; Calculate the skewness of the pure transient component of the zero-sequence current of each feeder at the time of the first fault, and determine the first fault feeder in the same phase across the line based on the sign difference of the skewness of the pure transient component of the zero-sequence current of each feeder; The skewness of the pure transient component of the zero-sequence current of each feeder at the moment of the second fault is calculated, and the feeder with the simultaneous fault across the line is determined based on the positive and negative change relationship between the skewness of the pure transient component of the zero-sequence current of the first fault feeder and other feeders.

2. A method for detecting cross-line same-phase sequential faults according to claim 1, characterized in that: The process of removing the fundamental frequency component of the zero-sequence current at the head end of each feeder to obtain the pure transient component of the zero-sequence current of each feeder includes: The frequency shift algorithm is used to remove the fundamental frequency component of the zero-sequence current at the head end of each feeder to obtain the pure transient component of the zero-sequence current of each feeder.

3. A method for detecting cross-line same-phase sequential faults according to claim 2, characterized in that: The frequency shift algorithm is used to remove the fundamental frequency component of the zero-sequence current at the head end of each feeder to obtain the pure transient component of the zero-sequence current of each feeder, specifically: Perform Hilbert transform on the zero-sequence current at the head end of each feeder to obtain the analytical signal of each feeder; The pure transient component of the zero-sequence current of each feeder is obtained by multiplying the analytical signal of each feeder by the fundamental frequency shift factor.

4. A method for detecting cross-line same-phase sequential faults according to claim 1, characterized in that: The method of determining the first-fault feeder in the same phase across the lines according to the sign difference of the skewness value of the pure transient component of the zero-sequence current of each feeder is specifically as follows: When the skewness value of the pure transient component of the zero-sequence current of a feeder is greater than 0, and the skewness values ​​of the pure transient components of the zero-sequence current of the other feeders are all less than 0, the feeder with the skewness value greater than 0 is determined to be the feeder with the first cross-line same-phase fault.

5. The method for detecting cross-line same-phase sequential faults according to claim 1, characterized in that: The method of determining the feeder with simultaneous cross-line faults based on the positive and negative change relationship between the skewness values ​​of the pure transient components of the zero-sequence current of the first fault feeder and other feeders is as follows: The skewness value of the pure transient component of the zero-sequence current of the first fault feeder changes from greater than 0 to less than 0; The skewness value of the pure transient component of the zero-sequence current of a certain feeder changes from less than 0 to greater than 0; The skewness values ​​of the pure transient components of the zero-sequence currents of the remaining feeders remain unchanged and are all less than 0; When all the above conditions are met, the feeder whose skewness value changes from negative to positive is determined to be a feeder with simultaneous cross-line faults.

6. A method for detecting cross-line same-phase sequential faults according to claim 1, characterized in that: The calculation formula for the skewness value of the pure transient component of the feeder zero-sequence current is: Where S is the skewness value of the pure transient component of the feeder zero-sequence current; μ is the mean; σ is the standard deviation; N is the total number of sampling points in the time window of the pure transient component of the zero-sequence current selected when calculating the skewness value; and x(n) is the nth sample value in the sample sequence.

7. A method for detecting cross-line same-phase sequential faults according to claim 1, characterized in that: The preset threshold is 15% of the system nominal phase voltage.

8. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the computer program, the method for detecting cross-line same-phase sequential faults according to any one of claims 1 to 7 is implemented.

9. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the method for detecting cross-line same-phase sequential faults according to any one of claims 1 to 7 is implemented.

10. A computer program product, characterized in that When the computer program product is executed by a processor, the method for detecting cross-line same-phase sequential faults according to any one of claims 1 to 7 is implemented.

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