Small current grounding system fault line selection method and system based on transient information fusion

Abstract

The invention discloses a small current grounding system fault line selection method and system based on transient information fusion, and relates to the field of small current grounding system fault detection, and the method comprises the steps: carrying out the signal decomposition and reconstruction through employing a VMD algorithm, and calculating the transient energy of a reconstructed current signal; calculating a transient energy measure according to a transient energy value in a power frequency period; according to the second current decomposition result, the second voltage decomposition result, the first current decomposition result and the fundamental component, the fifth harmonic component and the seventh harmonic component corresponding to the first voltage decomposition result, the sum of admittance phase angle difference coefficients in a power frequency period is calculated, and the transient information fusion criterion measure is further calculated; and determining the fault power transmission line. According to the invention, the reliability of fault line selection criteria can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of small current grounding system fault detection, in particular to a small current grounding system fault line selection method and system based on transient information fusion. BACKGROUND

[0002] As an important node connecting the power system and users, the safety and stability of the distribution network is an important prerequisite to ensure the quality of life and production. The voltage level of the distribution network in China is mainly 10kV and 35kV, and in order to ensure the continuity and stability of user power supply, small current grounding mode is mainly used, including neutral point grounding and arc suppression coil grounding. The distribution network fault accounts for a large proportion in the power system fault, and the single-phase grounding fault accounts for 80% of the distribution network fault. However, due to the small grounding fault current, it will not cause excessive damage to the equipment and system, and it will not affect the continuous power supply in a short time. The system can continue to operate for 1-2 hours after the fault occurs. However, as users pay more and more attention to the power experience, and long-time fault operation can cause multi-point fault to expand the fault range, affecting the reliability of the distribution network power supply. Therefore, the line of single-phase grounding fault in small current grounding system must be found and isolated in time, so the line selection of quickly and accurately judging the fault line has important significance to ensure the safe, stable and reliable power supply of the distribution network.

[0003] The traditional "pull line line selection" method for handling grounding faults is no longer suitable for the current needs of the development of the power system. At present, the line selection method for small current grounding system fault can be divided into steady-state component and transient component methods according to the signal type. The method based on steady-state component, such as group amplitude and phase comparison method, active power method and fifth harmonic method, has low requirements for data acquisition hardware and software and is widely used. However, due to the zero sequence asymmetry of the distribution network itself and the high-frequency transient interference, the fault information is not obvious, especially in the arc suppression coil grounding fault, the fault current is smaller, and the steady-state component line selection method cannot accurately select the fault line. From the current application point of view, the accuracy of the transient component line selection method is higher than that of the steady-state component line selection method, such as the first half wave method, transient energy method and wavelet transform method. The main advantage is that the electrical characteristics of the transient component are more obvious than those of the steady-state component, and it is easier to select lines. And most of the transient component processing needs to go through digital signal processing, and the main frequency transient information will be more obvious.

[0004] With the continuous development of China's power system, the topology structure of the distribution network is becoming more and more complex. In such a huge system, a single line selection method has low line selection accuracy and is prone to line selection failure when the required characteristics are not obvious. Multi-criteria fusion combines the different characteristics of multiple fault and non-fault lines as new judgment basis, making the criterion more stable and reliable. SUMMARY

[0005] The purpose of this invention is to provide a fault selection method and system for low-current grounding systems based on transient information fusion. By using a multi-criteria fusion approach, the different characteristics obtained from various faulty and non-faulty lines are combined as new judgment criteria, making the resulting criteria more stable and reliable.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] A fault location method for low-current grounding systems based on transient information fusion, the fault location method comprising:

[0008] The system acquires the first zero-sequence current signal and the first bus voltage signal of the target line during a first preset time period before a ground fault occurs, and the second zero-sequence current signal and the second bus voltage signal during a second preset time period after the ground fault occurs. The target line includes multiple transmission lines, including multiple normal transmission lines and one faulty transmission line. The first preset time period and the second preset time period are continuous in time. The length of the first preset time period is greater than or equal to one-quarter of a power frequency cycle. The length of the second preset time period is greater than or equal to one power frequency cycle.

[0009] The VMD algorithm is applied to decompose the first zero-sequence current signal, the first bus voltage signal, the second zero-sequence current signal, and the second bus voltage signal of the multiple transmission lines respectively, to obtain the first current decomposition result, the first voltage decomposition result, the second current decomposition result, and the second voltage decomposition result corresponding to each of the transmission lines.

[0010] The first current decomposition result and the second current decomposition result of the multiple transmission lines are reconstructed to obtain the reconstructed first zero-sequence current signal and the reconstructed second zero-sequence current signal.

[0011] The first transient energy of the reconstructed first zero-sequence current signal during a third preset time period before the ground fault occurs, and the second transient energy of the reconstructed second zero-sequence current signal during a fourth preset time period after the ground fault occur, are calculated respectively. The first transient energy and the second transient energy are used as the transient energy values ​​of each transmission line within one power frequency cycle. The third preset time period and the fourth preset time period are continuous in time and constitute a complete power frequency cycle.

[0012] Based on the transient energy values ​​of multiple transmission lines within one power frequency cycle, calculate the transient energy measure of each transmission line.

[0013] Based on the second current decomposition results, second voltage decomposition results, first current decomposition results, and first voltage decomposition results of the multiple transmission lines, the sum of the admittance phase angle difference coefficients of each transmission line in the first power frequency cycle after the ground fault occurs is calculated, and the sum of the admittance phase angle difference coefficients of each transmission line is obtained.

[0014] The transient energy measurement and admittance phase angle difference coefficient of each of the multiple transmission lines are normalized, and the normalized transient energy measurement and admittance phase angle difference coefficient are summed to obtain the transient information fusion criterion measurement of each of the transmission lines.

[0015] The faulty transmission line is determined by measuring the transient information fusion criteria of multiple transmission lines.

[0016] Optionally, the length of the third preset time period is one-quarter of a complete power frequency cycle, and the third preset time period ends at the time corresponding to the grounding fault of the faulty transmission line.

[0017] Optionally, the length of the fourth preset time period is three-quarters of a complete power frequency cycle, and the fourth preset time period begins at the moment when the faulty transmission line experiences a ground fault.

[0018] Optionally, the step of calculating the transient energy measure of each of the multiple transmission lines based on their transient energy values ​​within one power frequency cycle specifically includes:

[0019] The transient energy values ​​of the multiple transmission lines are sampled within one power frequency cycle to obtain multiple transient energy sample values ​​for each of the transmission lines.

[0020] The energy value of each of the multiple transmission lines is determined based on multiple transient energy sampling values ​​of the multiple transmission lines.

[0021] Based on the energy values ​​of the multiple transmission lines, the transient energy measure of each transmission line is calculated using a summation and normalization method.

[0022] Optionally, the energy value of the transmission line is the largest sample value among multiple transient energy sample values ​​of the transmission line.

[0023] Optionally, based on the fundamental, fifth, and seventh harmonic components corresponding to the second current decomposition results, second voltage decomposition results, first current decomposition results, and first voltage decomposition results of the multiple transmission lines, the sum of the admittance phase angle difference coefficients of each transmission line in the first power frequency cycle after the ground fault occurs is calculated to obtain the sum of the admittance phase angle difference coefficients of each transmission line, specifically including:

[0024] Based on the second current decomposition results and the first current decomposition results of the multiple transmission lines, calculate the phasors of the fundamental component, fifth harmonic component and seventh harmonic component of the zero-sequence current of each of the transmission lines.

[0025] Based on the second voltage decomposition results and the first voltage decomposition results of the multiple transmission lines, calculate the phasors of the fundamental component, fifth harmonic component and seventh harmonic component of the zero-sequence voltage of each of the transmission lines.

[0026] Based on the phasors of the fundamental, fifth, and seventh harmonic components of the zero-sequence current of the multiple transmission lines and the phasors of the fundamental, fifth, and seventh harmonic components of the zero-sequence voltage of the multiple transmission lines, calculate the total admittance of the fundamental, fifth, and seventh harmonic components of each of the transmission lines.

[0027] Based on the total admittance of the fundamental component, fifth harmonic component and seventh harmonic component of the multiple transmission lines, calculate the phase angle of the total admittance of the fundamental component, fifth harmonic component and seventh harmonic component of each of the transmission lines.

[0028] Calculate the difference between the total admittance phase angle of the fundamental, fifth, and seventh harmonic components of each transmission line and the total admittance phase angle of the fundamental, fifth, and seventh harmonic components of the other transmission lines, and obtain the total admittance phase angle difference coefficient of the fundamental, fifth, and seventh harmonic components of each transmission line.

[0029] The sum of the total admittance phase angle difference coefficients of the fundamental component, fifth harmonic component and seventh harmonic component of the multiple transmission lines is calculated within the first power frequency cycle after the ground fault occurs, so as to obtain the sum of the admittance phase angle difference coefficients of each of the transmission lines.

[0030] Optionally, a transmission line whose transient information fusion criterion measure is greater than a preset threshold is selected from the multiple transmission lines as the faulty transmission line.

[0031] A fault location system for low-current grounding systems based on transient information fusion, applying the aforementioned fault location method for low-current grounding systems based on transient information fusion, wherein the fault location system includes:

[0032] The acquisition module is used to acquire the first zero-sequence current signal and the first bus voltage signal of the target line during a first preset time period before the ground fault occurs, and the second zero-sequence current signal and the second bus voltage signal during a second preset time period after the ground fault occurs; wherein, the target line includes multiple transmission lines; the multiple transmission lines include multiple normal transmission lines and one faulty transmission line; the first preset time period and the second preset time period are continuous in time; the length of the first preset time period is greater than or equal to one-quarter of the power frequency cycle; the length of the second preset time period is greater than or equal to one power frequency cycle;

[0033] The decomposition module is used to apply the VMD algorithm to decompose the first zero-sequence current signal, the first bus voltage signal, the second zero-sequence current signal, and the second bus voltage signal of the multiple transmission lines respectively, so as to obtain the first current decomposition result, the first voltage decomposition result, the second current decomposition result, and the second voltage decomposition result corresponding to each of the transmission lines.

[0034] The reconstruction module is used to reconstruct the first current decomposition result and the second current decomposition result of the multiple transmission lines to obtain the reconstructed first zero-sequence current signal and the reconstructed second zero-sequence current signal.

[0035] The first calculation module is used to calculate the first transient energy of the reconstructed first zero-sequence current signal during a third preset time period before the ground fault occurs and the second transient energy of the reconstructed second zero-sequence current signal during a fourth preset time period after the ground fault occurs, and to use the first transient energy and the second transient energy as the transient energy values ​​of each transmission line within one power frequency cycle; wherein the third preset time period and the fourth preset time period are continuous in time and the third preset time period and the fourth preset time period constitute a complete power frequency cycle;

[0036] The second calculation module is used to calculate the transient energy measure of each of the multiple transmission lines based on the transient energy values ​​of the multiple transmission lines within one power frequency cycle.

[0037] The third calculation module is used to calculate the sum of the admittance phase angle difference coefficients of each of the multiple transmission lines in the first power frequency cycle after the ground fault occurs, based on the second current decomposition results, the second voltage decomposition results, the first current decomposition results, and the fundamental component, fifth harmonic component, and seventh harmonic component corresponding to the first voltage decomposition results of the multiple transmission lines, and to obtain the sum of the admittance phase angle difference coefficients of each of the transmission lines.

[0038] The normalization module is used to normalize the transient energy measurement and admittance phase angle difference coefficient of the multiple transmission lines respectively, and to sum the normalized transient energy measurement and admittance phase angle difference coefficient to obtain the transient information fusion criterion measurement of each transmission line.

[0039] The comparison module is used to determine the faulty transmission line by fusing judgment criteria based on transient information of multiple transmission lines.

[0040] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0041] This invention obtains transient parameters with large amplitude and abundant content by extracting fault transient information. Signal processing is performed on the extracted transient quantities to obtain their modal components, first, fifth, and seventh harmonic components, and a new admittance composed of the sum of the first, fifth, and seventh harmonic admittances is further calculated. The modal components with more prominent energy are reconstructed, and their transient modal energy and modal energy measure are calculated as criterion one. The phase difference coefficient of the new admittance is calculated as criterion two. Using a multi-criterion fusion method, the different characteristics obtained from various faulty and non-faulty lines are combined as new judgment criteria, making the resulting criteria more stable and reliable. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 This is a flowchart of VMD optimization;

[0044] Figure 2 This is a simplified schematic diagram of a 10kV distribution network simulation line selection model;

[0045] Figure 3 This is a schematic diagram of the VMD decomposition results for line 1 with the neutral point ungrounded;

[0046] Figure 4 This is a schematic diagram of the VMD decomposition results for line 2 with the neutral point ungrounded;

[0047] Figure 5 This is a schematic diagram of the VMD decomposition results of the high-resistance grounding system in the neutral point ungrounded system of line 1;

[0048] Figure 6 This is a schematic diagram of the VMD decomposition results of the high-resistance grounding system in the neutral point ungrounded system of line 2;

[0049] Figure 7 This is a schematic diagram of the VMD decomposition results of the arc suppression coil grounding system of Line 1;

[0050] Figure 8 This is a schematic diagram of the VMD decomposition results of the arc suppression coil grounding system of line 2;

[0051] Figure 9 This is a schematic diagram of the VMD decomposition results of the high-resistance grounding system of the arc suppression coil grounding system of Line 1;

[0052] Figure 10 This is a schematic diagram of the VMD decomposition results of the high-resistance grounding system of the arc suppression coil grounding system of line 2;

[0053] Figure 11 This is a schematic diagram of the reconfiguration signal of an ungrounded system;

[0054] Figure 12 This is a schematic diagram of the reconfiguration signal of the arc suppression grounding system;

[0055] Figure 13 This is a flowchart of a fault location method for low-current grounding systems based on transient information fusion. Detailed Implementation

[0056] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0057] The purpose of this invention is to provide a fault selection method and system for low-current grounding systems based on transient information fusion. By using a multi-criteria fusion approach, the different characteristics obtained from various faulty and non-faulty lines are combined as new judgment criteria, making the resulting criteria more stable and reliable.

[0058] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0059] Example 1

[0060] like Figure 13 As shown, this invention provides a fault location method for low-current grounding systems based on transient information fusion, the fault location method comprising:

[0061] Step S1: Acquire the first zero-sequence current signal and the first bus voltage signal of the target line during a first preset time period before the ground fault occurs, and the second zero-sequence current signal and the second bus voltage signal during a second preset time period after the ground fault occurs; wherein, the target line includes multiple transmission lines; the multiple transmission lines include multiple normal transmission lines and one faulty transmission line; the first preset time period and the second preset time period are continuous in time; the length of the first preset time period is greater than or equal to one-quarter of the power frequency cycle; the length of the second preset time period is greater than or equal to one power frequency cycle.

[0062] Specifically, the third preset time period is one-quarter of a complete power frequency cycle, and the third preset time period ends at the moment when the faulty transmission line experiences a ground fault.

[0063] Furthermore, the fourth preset time period is three-quarters of a complete power frequency cycle, and the fourth preset time period begins at the moment when the faulty transmission line experiences a ground fault.

[0064] In practical applications, when the system is running normally, it collects the zero-sequence current I0 and the bus zero-sequence voltage U0 of each line and records the data for 1 / 4 power frequency cycle. It determines whether a ground fault has occurred by whether the bus zero-sequence voltage exceeds the limit. If it does not exceed the limit, the data of the previous 1 / 4 cycle is cleared. If the zero-sequence voltage exceeds the limit, the zero-sequence voltage and zero-sequence current data of the cycle after the fault are collected. These data, together with the voltage and current data of the 1 / 4 cycle before the fault, are used as signals to be processed.

[0065] Because this invention uses transient signals as the signals to be processed, and the transient process is very short, generally 0.5-1 power frequency cycles, experiments have shown that the difference between the transient signals of the fault and the normal line is more obvious and stable within 3 / 4 of the power frequency cycles after the fault. It was also found that there is a certain difference between the transient signals and the transient signals of the 1 / 4 cycle before the fault. Compared with recording the data of the 1 / 4 cycle before the fault, recording the data of the 1 / 4 cycle is less and more conducive to preservation. Therefore, the 1 / 4 cycle before the fault is selected.

[0066] Step S2: Apply the VMD algorithm to decompose the first zero-sequence current signal, the first bus voltage signal, the second zero-sequence current signal, and the second bus voltage signal of the multiple transmission lines respectively, to obtain the first current decomposition result, the first voltage decomposition result, the second current decomposition result, and the second voltage decomposition result corresponding to each of the transmission lines.

[0067] In practical applications, the VMD algorithm is used to optimize and solve the problem, and the optimal parameters K and α are finally obtained. The optimized VMD algorithm is then used to decompose the zero-sequence current signals of each transmission line.

[0068] The specific implementation steps of optimizing VMD with the genetic algorithm can be summarized as follows: Set the genetic algorithm parameters, determine the parameters [K, α] to be optimized in the VMD algorithm and their ranges, and select the evaluation criterion. Part of the program is described as follows:

[0069] while gen < MAXGEN % less than the number of evolutionary generations

[0070] FitnV = ranking(-ObjV); % Assign fitness values

[0071] SelCh = select('sus', Chrom, FitnV, GGAP); % Selection

[0072] SelCh = recombin('xovsp', SelCh, px); % Recombination

[0073] SelCh = mut(SelCh, pm); % Mutation

[0074] XY = bs2rv(SelCh, FieldD); % Decimal conversion of offspring individuals

[0075] Input the individuals of the sub-band population into VMD to obtain the evaluation criterion, and save the parameters [K, α] corresponding to the optimal evaluation criterion

[0076] end

[0077] k, a <- [K, α] corresponding to the minimum value of the optimal evaluation criterion in all iteration times

[0078] Output [K, α]

[0079] The flowchart of the implementation steps of optimizing VMD with the genetic algorithm is as Figure 1 shown, specifically including:

[0080] Step 1. Select the fitness function.

[0081] Step 2. Initialize the population parameters [K, α].

[0082] Step 3. Perform VMD decomposition on the signal under the population conditions.

[0083] Step 4. Calculate the individual fitness values.

[0084] Step 5. Judge whether the termination condition is satisfied.

[0085] Step 6. When the termination condition is not satisfied, perform selection, crossover, and mutation operations to form a new population, and return to Step 5.

[0086] Step 7. When the termination condition is satisfied, output the optimal parameters [K, α].

[0087] Step S3: Reconstruct the first current decomposition results and the second current decomposition results of the multiple transmission lines to obtain the reconstructed first zero-sequence current signal and the reconstructed second zero-sequence current signal.

[0088] Step S4: Calculate the first transient energy of the reconstructed first zero-sequence current signal during the third preset time period before the ground fault and the second transient energy of the reconstructed second zero-sequence current signal during the fourth preset time period after the ground fault, and use the first transient energy and the second transient energy as the transient energy values ​​of each transmission line within one power frequency cycle; wherein the third preset time period and the fourth preset time period are continuous in time and constitute a complete power frequency cycle.

[0089] The following application example further illustrates steps S2 through S4.

[0090] The required voltage and current signals are acquired by building a 10kV distribution network low-current grounding simulation model, the structure of which is as follows: Figure 2 As shown:

[0091] The zero-sequence current was decomposed under four conditions: neutral point ungrounded, neutral point grounded through an arc suppression coil (overcompensated), and neutral point grounded through a high-resistance ground (grounding resistance 2000Ω). For each condition, a faulty line (line 1) and a normal line (line 2) were compared. The decomposition results are as follows: Figures 3-10 As shown.

[0092] By comparing the above decomposition results, it can be seen that the energy amplitude of the modal components in the faulty line is higher in both the ungrounded neutral point and the neutral point through the arc suppression coil system, which is significantly different from that of the normal line. Although the amplitude is lower in the high-resistance grounded case, the faulty line is still significantly different from the normal line. Therefore, to reduce the compensation effect of the arc suppression coil, the frequency of the reconstructed fault transient components should be as high as possible. Thus, one or more modal components with higher frequency or more prominent energy are selected for reconstruction as the signal to be processed for transient energy judgment. The reconstructed signal is as follows: Figures 11-12 As shown.

[0093] The reconstructed signal shows that the energy of the faulty line is significantly higher than that of the normal line within one cycle after the fault occurs, which can be used as a basis for line selection.

[0094] The transient energy method described above effectively eliminates the influence of arc suppression coil compensation by extracting the high-frequency transient components of the faulty line. To make the line selection more accurate and improve the accuracy of line selection under high-resistance grounding conditions, a phase angle difference criterion based on the 1st, 5th, and 7th harmonic admittances of transient quantities is constructed. Therefore, the collected zero-sequence voltage and zero-sequence current signals are processed to decompose the fundamental component, the fifth harmonic component, and the seventh harmonic component as signals for constructing the phase angle difference criterion.

[0095] Step S5: Calculate the transient energy measure of each of the multiple transmission lines within one power frequency cycle.

[0096] S5 specifically includes:

[0097] Step S51: Sample the transient energy values ​​of the multiple transmission lines within one power frequency cycle to obtain multiple transient energy sample values ​​for each transmission line.

[0098] Step S52: Determine the energy value of each of the multiple transmission lines based on the multiple transient energy sampling values ​​of the multiple transmission lines.

[0099] Specifically, the energy value of the transmission line is the largest sample value among multiple transient energy sample values ​​of the transmission line.

[0100] In practical applications, after mode decomposition and reconstruction of the zero-sequence current, the transient energy criterion is constructed using the signals from the 1 / 4 cycle before the fault and the 3 / 4 cycle after the fault. The maximum value of the transient energy of each line within one power frequency cycle is taken as the energy value of that line, i.e.:

[0101] E i =max E n ,(n=1…T·f s (1)

[0102] In the formula: E i Let E be the transient energy of the i-th line. n f represents the nth sampled data. s Where n is the sampling frequency, and n is the number of samples taken within one power frequency cycle.

[0103] Step S53: Based on the energy values ​​of the multiple transmission lines, calculate the transient energy measure of each transmission line using the summation and normalization method.

[0104] The faulty line is the line with the largest amplitude among all transient energies, i.e.:

[0105] E j =max E i ,(i=1…k) (2)

[0106] To improve the distinction margin between faulty and normal lines and increase the accuracy of line selection, a transient energy measure is formed using summation and normalization, namely:

[0107]

[0108] In the formula: e i The transient energy measure of the i-th outgoing line, where k is the total number of outgoing lines in the system.

[0109] The faulty line is the one whose energy measurement differs the most from other lines. This difference includes, but is not limited to, taking the maximum value or the difference.

[0110] Taking the maximum value as an example, the transient energy measure of the faulty line is:

[0111] e j =max e i ,(i=1…k) (4)

[0112] In this application, formula (3) means calculating the transient energy E of each line. i Transient energy of all lines The proportion e i This proportion makes the difference between normal lines and faulty lines more obvious. Then, the line with the largest difference from other lines is determined by formula (4), which is the faulty line. Therefore, there are two steps: formula (3) to calculate the proportion and formula (4) to calculate the difference. The max operation in formula (4) is just an example of calculating the difference.

[0113] Step S6: Based on the fundamental component, fifth harmonic component, and seventh harmonic component corresponding to the second current decomposition result, second voltage decomposition result, first current decomposition result, and first voltage decomposition result of the multiple transmission lines, calculate the sum of the admittance phase angle difference coefficients of each transmission line in the first power frequency cycle after the ground fault occurs, and obtain the sum of the admittance phase angle difference coefficients of each transmission line.

[0114] S6 specifically includes:

[0115] Step S61: Based on the second current decomposition results and the first current decomposition results of the multiple transmission lines, calculate the phasors of the fundamental component, fifth harmonic component and seventh harmonic component of the zero-sequence current of each of the transmission lines.

[0116] In practical applications, the phasors of the fundamental component and the 5th and 7th harmonic components of the zero-sequence current of each line are calculated after processing:

[0117]

[0118] In the formula: i is the i-th outgoing line, h (h=1, 5, 7) are the fundamental, fifth harmonic and seventh harmonic components respectively, and α, β represent the phase angles of the h-component of the i-th line respectively.

[0119] Step S62: Based on the second voltage decomposition results and the first voltage decomposition results of the multiple transmission lines, calculate the phasors of the fundamental component, fifth harmonic component and seventh harmonic component of the zero-sequence voltage of each of the transmission lines.

[0120] In practical applications, the phasors of the fundamental component and the 5th and 7th harmonic components of the zero-sequence voltage of each line are calculated after processing:

[0121]

[0122] In the formula: i is the i-th outgoing line, h (h=1, 5, 7) are the fundamental, fifth harmonic and seventh harmonic components respectively, and α, β represent the phase angles of the h-component of the i-th line respectively.

[0123] In this invention, the zero-sequence voltage of each line after processing is the zero-sequence voltage of each line after VMD decomposition. The analysis and calculation involved in this invention are all based on the signals after VMD decomposition and reconstruction.

[0124] Step S63: Based on the phasors of the fundamental, fifth, and seventh harmonic components of the zero-sequence current of the multiple transmission lines and the phasors of the fundamental, fifth, and seventh harmonic components of the zero-sequence voltage of the multiple transmission lines, calculate the total admittance of the fundamental, fifth, and seventh harmonic components of each transmission line.

[0125] In practical applications, calculate the total transient harmonic admittance of the 1st, 5th, and 7th orders for the i-th outgoing line:

[0126]

[0127] Step S64: Calculate the phase angle of the total admittance of the fundamental component, fifth harmonic component and seventh harmonic component of each of the multiple transmission lines based on the total admittance of the fundamental component, fifth harmonic component and seventh harmonic component.

[0128] In practical applications, the phase angles of the total transient admittance of the 1st, 5th, and 7th transient harmonics of the i-th outgoing line are calculated as follows:

[0129]

[0130] At this point, the line can be selected based on the quadrant in which the phase angle is located. The total admittance phase angle of a normal line is located in the first quadrant, while the total admittance phase angle of a faulty line is located in the second and third quadrants.

[0131] Step S65: Calculate the difference between the total admittance phase angle of the fundamental component, fifth harmonic component and seventh harmonic component of each transmission line and the total admittance phase angle of the fundamental component, fifth harmonic component and seventh harmonic component of the other transmission lines, and obtain the total admittance phase angle difference coefficient of the fundamental component, fifth harmonic component and seventh harmonic component of each transmission line.

[0132] In practical applications, to further distinguish faulty lines, the total admittance phase angles of each line are subtracted and accumulated, i.e., the admittance phase angle difference coefficient of the i-th line:

[0133]

[0134] Defined by the admittance phase angle difference coefficient, the phase angle difference coefficient of the i-th line is the total transient harmonic admittance phase angle of the line minus the sum of the total transient harmonic admittance phase angles of all outgoing lines excluding the line itself. As can be seen from the quadrants where the normal line and the faulty line are located, the coefficient is negative for the normal line and positive for the faulty line.

[0135] Step S66: Calculate the sum of the total admittance phase angle difference coefficients of the fundamental component, fifth harmonic component and seventh harmonic component of the multiple transmission lines in the first power frequency cycle after the ground fault occurs, and obtain the sum of the admittance phase angle difference coefficients of each of the transmission lines.

[0136] In practical applications, to reduce the impact of the number of outgoing lines on the admittance phase angle difference coefficient criterion, the admittance phase angle difference coefficient is summed within the first power frequency cycle after the fault, i.e.:

[0137]

[0138] In the formula: T·f s This represents the number of samples taken within one power frequency cycle.

[0139] Using the above equation θ′ i The largest line is the faulty line.

[0140] In practical applications, although the harmonic phase difference criterion and the transient energy line selection criterion are applied at different time periods, they are both used in formula (11) to calculate δ. i Since the normalization operations are performed separately and then summed, the inconsistency in the timing of the two operations will not affect the final result.

[0141] Step S7: Normalize the transient energy measurement and admittance phase angle difference coefficient of each of the multiple transmission lines, and sum the normalized transient energy measurement and admittance phase angle difference coefficient to obtain the transient information fusion criterion measurement of each transmission line.

[0142] In practical applications, the transient energy selection criterion selects the modes with higher frequencies or more prominent energy after VMD decomposition, reconstructs them, and uses the maximum transient energy value to sum and normalize to form a transient energy measure. This reduces the compensation effect of the arc suppression coil and can effectively select lines. Phase angle difference coefficients of the 1st, 5th, and 7th transient harmonic admittances are constructed. The phase angle difference is less affected by high-resistance grounding and can effectively select lines under high-resistance grounding conditions. Now, the two selection criteria are normalized and summed to form a transient information fusion criterion measure, namely:

[0143] δ i =norm(e i )+norm(θ′ i (11)

[0144] In the formula: norm is the normalization operation, δ i ∈[0,2].

[0145] Step S8: Determine the faulty transmission line based on the transient information fusion criteria of multiple transmission lines.

[0146] Specifically, the line with the largest transient information fusion criterion measure among the multiple transmission lines is selected as the faulty transmission line. In other words, the faulty line's δ... i The value is significantly larger than that of a normal line, when the calculated δ of the line... i Significantly higher δ than other lines i Most of the time, this line experiences a ground fault.

[0147] In practical applications, δ can be calculated using equation (11). i The largest faulty line is the one with the most faults.

[0148] To verify the feasibility of the proposed calculation, a system was constructed as follows: Figure 2 The 10kV low-current distribution network grounding simulation system shown is used for verification. This simulation system includes five transmission lines. Considering the increasingly widespread laying of cable lines in China's distribution network, both overhead lines and cables are considered in this simulation model. Line 1 is a mixed cable and cable line, with a cable length of 4km and an overhead line length of 10km. Lines 2, 3, and 4 are overhead lines with lengths of 20km, 10km, and 5km respectively, primarily considering the impact of overhead line length on line selection. Line 5 is a cable line with a length of 4km.

[0149] 1. Line selection results for ungrounded systems and systems grounded via arc suppression coils.

[0150] In both grounding methods, the fault location is a ground fault in phase A of line 3, 5 km away from the bus. The fault grounding resistance is set to 20 ohms, 200 ohms and 2000 ohms respectively. The simulation line selection results are shown in Table 1 and Table 2. It can be seen that the measure value of the fault line obtained by the multi-criteria fusion based on transient information proposed in this invention is the highest and differs greatly from the measure values ​​of other lines, making it less prone to misjudgment. Furthermore, the change in grounding resistance does not affect the line selection criteria and has high stability.

[0151] Table 1 Simulation results of the neutral point ungrounded system

[0152]

[0153] Table 2 Simulation results of the neutral point arc-suppression coil system

[0154]

[0155] 2. Simulation results for different fault locations.

[0156] To verify the impact of different fault locations on the transient fusion criterion measure value, phase A ground faults were set at distances of 3 km and 7 km from the bus on line 3, with a fault resistance of 200 ohms. The simulation line selection results are shown in Table 3. It can be seen that the transient fusion criterion measure value of the faulty line at different fault locations on the same line is still the highest and differs significantly from the measure values ​​of other lines. Therefore, different fault locations have no impact on this line selection method.

[0157] Table 3 Simulation results for different fault locations

[0158]

[0159] 3. Simulation results of different faulty circuits

[0160] To verify the impact of different fault lines and different types of lines on the transient fusion criterion measure value, phase A grounding faults were set on the shortest overhead line L4, the longest overhead line L2, the cable line L5, and the mixed line L1, respectively, with a fault resistance of 200 ohms. The simulation line selection results are shown in Table 4. It can be seen from the table that the transient fusion criterion measure value proposed in this invention can still accurately and stably select lines for overhead lines, cable lines, and mixed lines of different lengths.

[0161] Table 4 Simulation results for different fault lines

[0162]

[0163] 4. Simulation results of high-resistance grounding fault

[0164] High-resistance grounding in low-current systems has always been a challenge for single-phase grounding fault location due to its low electrical parameters and difficulty in measurement. To verify the impact of high-resistance grounding on the transient fusion criterion measurement value, a three-phase grounding fault was simulated with fault resistances of 2000 ohms and 5000 ohms, respectively. The simulation location results are shown in Table 5. It can be seen that the transient fusion criterion can still accurately locate the fault under high-resistance grounding fault conditions.

[0165] Table 5 Simulation results of high-cathode grounding fault

[0166]

[0167] Example 2

[0168] To implement the method corresponding to Embodiment 1 above and achieve the corresponding functions and technical effects, a fault location system for low-current grounding systems based on transient information fusion is provided below. The fault location system includes:

[0169] The acquisition module is used to acquire the first zero-sequence current signal and the first bus voltage signal of the target line during a first preset time period before the ground fault occurs, and the second zero-sequence current signal and the second bus voltage signal during a second preset time period after the ground fault occurs; wherein, the target line includes multiple transmission lines; the multiple transmission lines include multiple normal transmission lines and one faulty transmission line; the first preset time period and the second preset time period are continuous in time; the length of the first preset time period is greater than or equal to one-quarter of the power frequency cycle; the length of the second preset time period is greater than or equal to one power frequency cycle.

[0170] The decomposition module is used to apply the VMD algorithm to decompose the first zero-sequence current signal, the first bus voltage signal, the second zero-sequence current signal, and the second bus voltage signal of the multiple transmission lines, respectively, to obtain the first current decomposition result, the first voltage decomposition result, the second current decomposition result, and the second voltage decomposition result corresponding to each of the transmission lines.

[0171] The reconstruction module is used to reconstruct the first current decomposition results and the second current decomposition results of the multiple transmission lines to obtain the reconstructed first zero-sequence current signal and the reconstructed second zero-sequence current signal.

[0172] The first calculation module is used to calculate the first transient energy of the reconstructed first zero-sequence current signal during a third preset time period before the ground fault occurs and the second transient energy of the reconstructed second zero-sequence current signal during a fourth preset time period after the ground fault occurs, and to use the first transient energy and the second transient energy as the transient energy values ​​of each transmission line within one power frequency cycle; wherein the third preset time period and the fourth preset time period are continuous in time and constitute a complete power frequency cycle.

[0173] The second calculation module is used to calculate the transient energy measure of each of the multiple transmission lines based on the transient energy values ​​of the multiple transmission lines within one power frequency cycle.

[0174] The third calculation module is used to calculate the sum of the admittance phase angle difference coefficients of each of the multiple transmission lines in the first power frequency cycle after the ground fault occurs, based on the second current decomposition results, the second voltage decomposition results, the first current decomposition results, and the first voltage decomposition results corresponding to the fundamental component, the fifth harmonic component, and the seventh harmonic component.

[0175] The normalization module is used to normalize the transient energy measurement and admittance phase angle difference coefficient of the multiple transmission lines respectively, and to sum the normalized transient energy measurement and admittance phase angle difference coefficient to obtain the transient information fusion criterion measurement of each transmission line.

[0176] The comparison module is used to determine the faulty transmission line by fusing judgment criteria based on transient information of multiple transmission lines.

[0177] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple; relevant parts can be referred to the method section.

[0178] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A fault location method for low-current grounding systems based on transient information fusion, characterized in that, The line selection method includes: The system acquires the first zero-sequence current signal and the first bus voltage signal of the target line during a first preset time period before a ground fault occurs, and the second zero-sequence current signal and the second bus voltage signal during a second preset time period after the ground fault occurs. The target line includes multiple transmission lines, including multiple normal transmission lines and one faulty transmission line. The first preset time period and the second preset time period are continuous in time. The length of the first preset time period is greater than or equal to one-quarter of a power frequency cycle. The length of the second preset time period is greater than or equal to one power frequency cycle. The VMD algorithm is applied to decompose the first zero-sequence current signal, the first bus voltage signal, the second zero-sequence current signal, and the second bus voltage signal of the multiple transmission lines respectively, to obtain the first current decomposition result, the first voltage decomposition result, the second current decomposition result, and the second voltage decomposition result corresponding to each of the transmission lines. The first current decomposition result and the second current decomposition result of the multiple transmission lines are reconstructed to obtain the reconstructed first zero-sequence current signal and the reconstructed second zero-sequence current signal. The first transient energy of the reconstructed first zero-sequence current signal during a third preset time period before the ground fault occurs, and the second transient energy of the reconstructed second zero-sequence current signal during a fourth preset time period after the ground fault occur, are calculated respectively. The first transient energy and the second transient energy are used as the transient energy values ​​of each transmission line within one power frequency cycle. The third preset time period and the fourth preset time period are continuous in time and constitute a complete power frequency cycle. Based on the transient energy values ​​of multiple transmission lines within one power frequency cycle, calculate the transient energy measure of each transmission line. Based on the second current decomposition results, second voltage decomposition results, first current decomposition results, and first voltage decomposition results of the multiple transmission lines, the sum of the admittance phase angle difference coefficients of each transmission line in the first power frequency cycle after the ground fault occurs is calculated, and the sum of the admittance phase angle difference coefficients of each transmission line is obtained. The transient energy measurement and admittance phase angle difference coefficient of each of the multiple transmission lines are normalized, and the normalized transient energy measurement and admittance phase angle difference coefficient are summed to obtain the transient information fusion criterion measurement of each of the transmission lines. The faulty transmission line is determined by measuring the transient information fusion criteria of multiple transmission lines.

2. The fault location method for low-current grounding systems based on transient information fusion according to claim 1, characterized in that, The length of the third preset time period is one-quarter of a complete power frequency cycle, and the third preset time period ends at the time corresponding to the grounding fault of the faulty transmission line.

3. The fault location method for low-current grounding systems based on transient information fusion according to claim 1, characterized in that, The fourth preset time period is three-quarters of a complete power frequency cycle, and the fourth preset time period begins at the moment when the faulty transmission line experiences a ground fault.

4. The fault location method for low-current grounding systems based on transient information fusion according to claim 1, characterized in that, The calculation of the transient energy measure of each transmission line based on the transient energy values ​​of multiple transmission lines within one power frequency cycle specifically includes: The transient energy values ​​of the multiple transmission lines are sampled within one power frequency cycle to obtain multiple transient energy sample values ​​for each of the transmission lines. The energy value of each of the multiple transmission lines is determined based on multiple transient energy sampling values ​​of the multiple transmission lines. Based on the energy values ​​of the multiple transmission lines, the transient energy measure of each transmission line is calculated using a summation and normalization method.

5. The fault location method for low-current grounding systems based on transient information fusion according to claim 4, characterized in that, The energy value of the transmission line is the largest sample value among multiple transient energy samples of the transmission line.

6. The fault location method for low-current grounding systems based on transient information fusion according to claim 1, characterized in that, Based on the second current decomposition results, second voltage decomposition results, first current decomposition results, and the fundamental, fifth, and seventh harmonic components corresponding to the first voltage decomposition results of the multiple transmission lines, the sum of the admittance phase angle difference coefficients of each transmission line in the first power frequency cycle after the ground fault occurs is calculated, resulting in the sum of the admittance phase angle difference coefficients of each transmission line. Specifically, this includes: Based on the second current decomposition results and the first current decomposition results of the multiple transmission lines, calculate the phasors of the fundamental component, fifth harmonic component and seventh harmonic component of the zero-sequence current of each of the transmission lines. Based on the second voltage decomposition results and the first voltage decomposition results of the multiple transmission lines, calculate the phasors of the fundamental component, fifth harmonic component and seventh harmonic component of the zero-sequence voltage of each of the transmission lines. Based on the phasors of the fundamental, fifth, and seventh harmonic components of the zero-sequence current of the multiple transmission lines and the phasors of the fundamental, fifth, and seventh harmonic components of the zero-sequence voltage of the multiple transmission lines, calculate the total admittance of the fundamental, fifth, and seventh harmonic components of each of the transmission lines. Based on the total admittance of the fundamental component, fifth harmonic component and seventh harmonic component of the multiple transmission lines, calculate the phase angle of the total admittance of the fundamental component, fifth harmonic component and seventh harmonic component of each of the transmission lines. Calculate the difference between the total admittance phase angle of the fundamental, fifth, and seventh harmonic components of each transmission line and the total admittance phase angle of the fundamental, fifth, and seventh harmonic components of the other transmission lines, and obtain the total admittance phase angle difference coefficient of the fundamental, fifth, and seventh harmonic components of each transmission line. The sum of the total admittance phase angle difference coefficients of the fundamental component, fifth harmonic component and seventh harmonic component of the multiple transmission lines is calculated within the first power frequency cycle after the ground fault occurs, so as to obtain the sum of the admittance phase angle difference coefficients of each of the transmission lines.

7. The fault location method for low-current grounding systems based on transient information fusion according to claim 1, characterized in that, Transmission lines whose transient information fusion criterion measurement is greater than a preset threshold are selected from the multiple transmission lines as fault transmission lines.

8. A fault location system for low-current grounding systems based on transient information fusion, characterized in that, The route selection system includes: The acquisition module is used to acquire the first zero-sequence current signal and the first bus voltage signal of the target line during a first preset time period before the ground fault occurs, and the second zero-sequence current signal and the second bus voltage signal during a second preset time period after the ground fault occurs; wherein, the target line includes multiple transmission lines; the multiple transmission lines include multiple normal transmission lines and one faulty transmission line; the first preset time period and the second preset time period are continuous in time; the length of the first preset time period is greater than or equal to one-quarter of the power frequency cycle; the length of the second preset time period is greater than or equal to one power frequency cycle; The decomposition module is used to apply the VMD algorithm to decompose the first zero-sequence current signal, the first bus voltage signal, the second zero-sequence current signal, and the second bus voltage signal of the multiple transmission lines respectively, so as to obtain the first current decomposition result, the first voltage decomposition result, the second current decomposition result, and the second voltage decomposition result corresponding to each of the transmission lines. The reconstruction module is used to reconstruct the first current decomposition result and the second current decomposition result of the multiple transmission lines to obtain the reconstructed first zero-sequence current signal and the reconstructed second zero-sequence current signal. The first calculation module is used to calculate the first transient energy of the reconstructed first zero-sequence current signal during a third preset time period before the ground fault occurs and the second transient energy of the reconstructed second zero-sequence current signal during a fourth preset time period after the ground fault occurs, and to use the first transient energy and the second transient energy as the transient energy values ​​of each transmission line within one power frequency cycle; wherein the third preset time period and the fourth preset time period are continuous in time and the third preset time period and the fourth preset time period constitute a complete power frequency cycle; The second calculation module is used to calculate the transient energy measure of each of the multiple transmission lines based on the transient energy values ​​of the multiple transmission lines within one power frequency cycle. The third calculation module is used to calculate the sum of the admittance phase angle difference coefficients of each of the multiple transmission lines in the first power frequency cycle after the ground fault occurs, based on the second current decomposition results, the second voltage decomposition results, the first current decomposition results, and the fundamental component, fifth harmonic component, and seventh harmonic component corresponding to the first voltage decomposition results of the multiple transmission lines, and to obtain the sum of the admittance phase angle difference coefficients of each of the transmission lines. The normalization module is used to normalize the transient energy measurement and admittance phase angle difference coefficient of the multiple transmission lines respectively, and to sum the normalized transient energy measurement and admittance phase angle difference coefficient to obtain the transient information fusion criterion measurement of each transmission line. The comparison module is used to determine the faulty transmission line by fusing judgment criteria based on transient information of multiple transmission lines.

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