A method and system for ground fault protection for active distribution networks

Abstract

The application discloses a kind of ground fault protection and system for active distribution network, belong to active distribution network protection control technical field.The method of the present application comprises: with preset sampling length and sampling frequency, the three-phase voltage instantaneous value at the bus of active distribution network power supply side is collected, the three-phase voltage is synthesized into the zero sequence voltage of active distribution network node, and the unit value of the zero sequence voltage is determined, if the unit value is greater than the preset threshold, the zero sequence voltage is filtered to obtain the instantaneous value matrix of zero sequence voltage;Based on the instantaneous value matrix, the energy value of zero sequence voltage is determined, and based on the energy value, generate zero sequence voltage energy array, determine whether there is a fault latent line or fault line in active distribution network according to the zero sequence voltage energy array;According to preset criterion, for the fault latent line or fault line determined to exist, execute protection action.The present application provides an important condition for safe and reliable operation of distribution network.

Description

Technical Field

[0001] This invention relates to the field of active power distribution network protection and control technology, and more specifically, to a ground fault protection method and system for active power distribution networks. Background Technology

[0002] my country's 6-66kV distribution network is a low-current grounding system. For a long time, the investigation of single-phase grounding faults has relied on fault location and manual line inspection, and the relevant technologies are now relatively mature. With the continuous advancement of smart distribution network construction, in order to reduce the workload of line inspection and improve the automation level of the distribution network, the requirements for fault investigation accuracy are also increasing, namely, achieving section location and even fault distance measurement. Currently, commonly used methods in engineering include the first half-wave method, the S-injection method, and the medium-resistance switching method. The former is greatly affected by the transition resistance and the initial phase angle of the fault, resulting in lower accuracy. The latter two rely on the injection signal or the abrupt change signal generated during the switching process of the neutral point parallel medium-value resistor, respectively, solving the problem of establishing a location method. However, they have a series of drawbacks, such as huge investment, susceptibility to interharmonics affecting smart equipment, and disruption of the original neutral point grounding properties of the power grid. Summary of the Invention

[0003] To address the above problems, this invention proposes a ground fault protection method for active power distribution networks, comprising:

[0004] The instantaneous values ​​of three-phase voltage at the power supply side bus of the active distribution network are collected with a preset sampling duration and sampling frequency. The three-phase voltages are combined into the zero-sequence voltage of the active distribution network node, and the per-unit value of the zero-sequence voltage is determined. If the per-unit value is greater than a preset threshold value, the zero-sequence voltage is filtered to obtain the instantaneous value matrix of the zero-sequence voltage.

[0005] Based on the instantaneous value matrix, the energy value of the zero-sequence voltage is determined, and based on the energy value, a zero-sequence voltage energy array is generated. Based on the zero-sequence voltage energy array, it is determined whether there are latent fault lines or fault lines in the active distribution network.

[0006] Based on preset criteria, protection actions are performed on the identified faulty or latent faulty lines.

[0007] Optionally, determining the per-unit value of the zero-sequence voltage includes:

[0008] Perform a Discrete Fourier Transform on the zero-sequence voltage to obtain the amplitude and phase of the zero-sequence voltage at a preset frequency. Based on the amplitude and phase, determine the amplitude of the zero-sequence voltage at a preset power frequency component.

[0009] The per-unit value of the zero-sequence voltage is determined based on the amplitude of the zero-sequence power frequency component of the voltage.

[0010] Optionally, the filtering process can be wavelet transform or discrete wavelet transform.

[0011] Optionally, the zero-sequence voltage is filtered, including:

[0012] For zero-sequence voltage, wavelet transform processing is performed to eliminate interference from high-frequency noise, third harmonic and fifth harmonic, and zero-sequence voltage with frequency components within the first preset frequency range is selected.

[0013] For the zero-sequence voltage of the frequency component within the first preset frequency range, discrete wavelet transform processing is performed to filter out the zero-sequence voltage of the frequency component within the second preset frequency range.

[0014] Optionally, determining whether there are latent fault lines or faulty lines in the active distribution network based on the zero-sequence voltage energy array includes:

[0015] Determine whether the energy value information in the zero-sequence voltage energy array contains missing values;

[0016] If no numerical values ​​are missing, the active distribution network node corresponding to the maximum value in the zero-sequence voltage energy array is marked as a fault node. The three-phase current of the line connected to the fault node is collected and converted into zero-sequence current. After filtering the zero-sequence current, the energy value of the zero-sequence current is determined to obtain the zero-sequence current energy array of the line connected to the fault node. If the energy value information in the zero-sequence current energy array is not missing, the line corresponding to the maximum value in the zero-sequence current energy array is marked as a fault line. If the energy value information in the zero-sequence current energy array is missing, the line corresponding to the maximum value in the zero-sequence current energy array is marked as a latent fault line.

[0017] If there are missing values, the active distribution network node corresponding to the maximum value in the zero-sequence voltage energy array and the active distribution network node corresponding to the missing value are marked as fault-prone nodes. The three-phase current of the line connected to the fault-prone node is collected and converted into zero-sequence current. After filtering the zero-sequence current, the energy value of the zero-sequence current is determined to obtain the zero-sequence current energy array of the line connected to the fault-prone node. If the energy value information in the zero-sequence current energy array is not missing, the line corresponding to the maximum value in the zero-sequence current energy array and the line connected to the fault-prone node are marked as fault lines. If the energy value information in the zero-sequence current energy array is missing, the line corresponding to the maximum value in the zero-sequence current energy array, the line corresponding to the missing information, and the line connected to the fault-prone node are marked as fault-prone lines.

[0018] Optionally, based on preset criteria, protection actions are performed on the identified faulty or latent faulty lines, including:

[0019] If there are no potential fault lines and only a faulty line exists, disconnect the circuit breaker of the faulty line.

[0020] If there are multiple potential fault lines and no fault lines exist, then the protection of all lines in the active distribution network except for the potential fault lines is blocked, and the protection of the potential fault lines is opened. After the protection of the potential fault lines is opened, the protection of the potential fault lines whose circuit breakers have not been disconnected is blocked.

[0021] This invention also proposes a ground fault protection system for active power distribution networks, comprising:

[0022] The acquisition unit is used to acquire the instantaneous values ​​of three-phase voltage at the power supply side bus of the active distribution network with a preset sampling duration and sampling frequency, synthesize the three-phase voltage into the zero-sequence voltage of the active distribution network node, and determine the per-unit value of the zero-sequence voltage. If the per-unit value is greater than a preset threshold value, the zero-sequence voltage is filtered to obtain the instantaneous value matrix of the zero-sequence voltage.

[0023] The calculation unit is used to determine the energy value of the zero-sequence voltage based on the instantaneous value matrix, generate a zero-sequence voltage energy array based on the energy value, and determine whether there are latent fault lines or fault lines in the active distribution network based on the zero-sequence voltage energy array.

[0024] The control unit is used to perform protection actions on the identified faulty or latent faulty lines based on preset criteria.

[0025] Optionally, the acquisition unit determines the per-unit value of the zero-sequence voltage, including:

[0026] Perform a Discrete Fourier Transform on the zero-sequence voltage to obtain the amplitude and phase of the zero-sequence voltage at a preset frequency. Based on the amplitude and phase, determine the amplitude of the zero-sequence voltage at a preset power frequency component.

[0027] The per-unit value of the zero-sequence voltage is determined based on the amplitude of the zero-sequence power frequency component of the voltage.

[0028] Optionally, the filtering process can be wavelet transform or discrete wavelet transform.

[0029] Optionally, the acquisition unit performs filtering processing on the zero-sequence voltage, including:

[0030] For zero-sequence voltage, wavelet transform processing is performed to eliminate interference from high-frequency noise, third harmonic and fifth harmonic, and zero-sequence voltage with frequency components within the first preset frequency range is selected.

[0031] For the zero-sequence voltage of the frequency component within the first preset frequency range, discrete wavelet transform processing is performed to filter out the zero-sequence voltage of the frequency component within the second preset frequency range.

[0032] Optionally, the calculation unit determines whether there are latent fault lines or fault lines in the active distribution network based on the zero-sequence voltage energy array, including:

[0033] Determine whether the energy value information in the zero-sequence voltage energy array contains missing values;

[0034] If no numerical values ​​are missing, the active distribution network node corresponding to the maximum value in the zero-sequence voltage energy array is marked as a fault node. The three-phase current of the line connected to the fault node is collected and converted into zero-sequence current. After filtering the zero-sequence current, the energy value of the zero-sequence current is determined to obtain the zero-sequence current energy array of the line connected to the fault node. If the energy value information in the zero-sequence current energy array is not missing, the line corresponding to the maximum value in the zero-sequence current energy array is marked as a fault line. If the energy value information in the zero-sequence current energy array is missing, the line corresponding to the maximum value in the zero-sequence current energy array is marked as a latent fault line.

[0035] If there are missing values, the active distribution network node corresponding to the maximum value in the zero-sequence voltage energy array and the active distribution network node corresponding to the missing value are marked as fault-prone nodes. The three-phase current of the line connected to the fault-prone node is collected and converted into zero-sequence current. After filtering the zero-sequence current, the energy value of the zero-sequence current is determined to obtain the zero-sequence current energy array of the line connected to the fault-prone node. If the energy value information in the zero-sequence current energy array is not missing, the line corresponding to the maximum value in the zero-sequence current energy array and the line connected to the fault-prone node are marked as fault lines. If the energy value information in the zero-sequence current energy array is missing, the line corresponding to the maximum value in the zero-sequence current energy array, the line corresponding to the missing information, and the line connected to the fault-prone node are marked as fault-prone lines.

[0036] Optionally, the control unit performs protection actions on the identified potential fault lines or faulty lines based on preset criteria, including:

[0037] If there are no potential fault lines and only a faulty line exists, disconnect the circuit breaker of the faulty line.

[0038] If there are multiple potential fault lines and no fault lines exist, then the protection of all lines in the active distribution network except for the potential fault lines is blocked, and the protection of the potential fault lines is opened. After the protection of the potential fault lines is opened, the protection of the potential fault lines whose circuit breakers have not been disconnected is blocked.

[0039] In another aspect, the present invention also provides a computing device, comprising: one or more processors;

[0040] A processor is used to execute one or more programs;

[0041] When the one or more programs are executed by the one or more processors, the method described above is implemented.

[0042] In another aspect, the present invention also provides a computer-readable storage medium having a computer program stored thereon, which, when executed, implements the method described above.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0044] This invention provides a ground fault protection method for active distribution networks, comprising: acquiring instantaneous three-phase voltage values ​​at the power supply side bus of the active distribution network at a preset sampling duration and sampling frequency; synthesizing the three-phase voltages into a zero-sequence voltage of the active distribution network node and determining the per-unit value of the zero-sequence voltage; if the per-unit value is greater than a preset threshold value, filtering the zero-sequence voltage to obtain an instantaneous value matrix of the zero-sequence voltage; determining the energy value of the zero-sequence voltage based on the instantaneous value matrix and generating a zero-sequence voltage energy array based on the energy value; determining whether there is a latent fault line or a faulty line in the active distribution network based on the zero-sequence voltage energy array; and executing protection actions on the determined latent fault line or faulty line according to a preset criterion. This invention can determine the faulty line based on the energy array and then execute protection actions on the determined faulty line according to the criterion, exhibiting high adaptability and providing crucial conditions for the safe and reliable operation of the distribution network. Attached Figure Description

[0045] Figure 1 This is a flowchart of the method of the present invention;

[0046] Figure 2 This is a flowchart of an embodiment of the method of the present invention;

[0047] Figure 3 This is a graph showing the zero-sequence voltage energy values ​​measured on each line under fault F1 in an embodiment of the present invention.

[0048] Figure 4 This is a graph showing the zero-sequence current energy values ​​measured on each line under fault F1 in an embodiment of the present invention.

[0049] Figure 5 This is a typical 10kV distribution network structure diagram constructed according to an embodiment of the present invention.

[0050] Figure 6 This is a structural diagram of the system of the present invention. Detailed Implementation

[0051] Exemplary embodiments of the invention will now be described with reference to the accompanying drawings. However, the invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to fully and completely disclose the invention and to fully convey its scope to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the drawings is not intended to limit the invention. In the drawings, the same units / elements are referred to by the same reference numerals.

[0052] Unless otherwise stated, the terms used herein (including technical terms) have their common meaning as understood by one of ordinary skill in the art. Furthermore, it is understood that terms defined in commonly used dictionaries should be understood to have a meaning consistent with the context of their relevant field, and not to be interpreted as having an idealized or overly formal meaning.

[0053] Example 1:

[0054] This invention provides a ground fault protection method for active power distribution networks, such as... Figure 1 As shown, it includes:

[0055] Step 1: Collect the instantaneous values ​​of the three-phase voltage at the power supply side bus of the active distribution network with a preset sampling duration and sampling frequency. Combine the three-phase voltages into the zero-sequence voltage of the active distribution network node and determine the per-unit value of the zero-sequence voltage. If the per-unit value is greater than a preset threshold value, filter the zero-sequence voltage to obtain the instantaneous value matrix of the zero-sequence voltage.

[0056] Step 2: Based on the instantaneous value matrix, determine the energy value of the zero-sequence voltage, and based on the energy value, generate a zero-sequence voltage energy array. Based on the zero-sequence voltage energy array, determine whether there are latent fault lines or fault lines in the active distribution network.

[0057] Step 3: Based on preset criteria, perform protection actions on the identified faulty or latent faulty lines.

[0058] Determining the per-unit value of the zero-sequence voltage includes:

[0059] Perform a Discrete Fourier Transform on the zero-sequence voltage to obtain the amplitude and phase of the zero-sequence voltage at a preset frequency. Based on the amplitude and phase, determine the amplitude of the zero-sequence voltage at a preset power frequency component.

[0060] The per-unit value of the zero-sequence voltage is determined based on the amplitude of the zero-sequence power frequency component of the voltage.

[0061] The filtering process includes wavelet transform and discrete wavelet transform.

[0062] The filtering process for the zero-sequence voltage includes:

[0063] For zero-sequence voltage, wavelet transform processing is performed to eliminate interference from high-frequency noise, third harmonic and fifth harmonic, and zero-sequence voltage with frequency components within the first preset frequency range is selected.

[0064] For the zero-sequence voltage of the frequency component within the first preset frequency range, discrete wavelet transform processing is performed to filter out the zero-sequence voltage of the frequency component within the second preset frequency range.

[0065] The determination of whether a latent fault line or a faulty line exists in the active distribution network based on the zero-sequence voltage energy array includes:

[0066] Determine whether the energy value information in the zero-sequence voltage energy array contains missing values;

[0067] If no numerical values ​​are missing, the active distribution network node corresponding to the maximum value in the zero-sequence voltage energy array is marked as a fault node. The three-phase current of the line connected to the fault node is collected and converted into zero-sequence current. After filtering the zero-sequence current, the energy value of the zero-sequence current is determined to obtain the zero-sequence current energy array of the line connected to the fault node. If the energy value information in the zero-sequence current energy array is not missing, the line corresponding to the maximum value in the zero-sequence current energy array is marked as a fault line. If the energy value information in the zero-sequence current energy array is missing, the line corresponding to the maximum value in the zero-sequence current energy array is marked as a latent fault line.

[0068] If there are missing values, the active distribution network node corresponding to the maximum value in the zero-sequence voltage energy array and the active distribution network node corresponding to the missing value are marked as fault-prone nodes. The three-phase current of the line connected to the fault-prone node is collected and converted into zero-sequence current. After filtering the zero-sequence current, the energy value of the zero-sequence current is determined to obtain the zero-sequence current energy array of the line connected to the fault-prone node. If the energy value information in the zero-sequence current energy array is not missing, the line corresponding to the maximum value in the zero-sequence current energy array and the line connected to the fault-prone node are marked as fault lines. If the energy value information in the zero-sequence current energy array is missing, the line corresponding to the maximum value in the zero-sequence current energy array, the line corresponding to the missing information, and the line connected to the fault-prone node are marked as fault-prone lines.

[0069] Specifically, based on preset criteria, protection actions are performed on the identified potential fault lines or faulty lines, including:

[0070] If there are no potential fault lines and only a faulty line exists, disconnect the circuit breaker of the faulty line.

[0071] If there are multiple potential fault lines and no fault lines exist, then the protection of all lines in the active distribution network except for the potential fault lines is blocked, and the protection of the potential fault lines is opened. After the protection of the potential fault lines is opened, the protection of the potential fault lines whose circuit breakers have not been disconnected is blocked.

[0072] The invention will be further described below with reference to specific implementation applications:

[0073] like Figure 2 As shown, it includes:

[0074] Step 1: Activation of the activation criterion: Sample the instantaneous three-phase voltage values ​​at the first-level bus, i.e., the power supply side bus. Subscript B indicates the electrical quantity at the bus terminal, a, b, and c represent electrical quantities a, b, and c respectively, and N0 is the total number of sampling points, calculated using the following formula:

[0075] Synthesize the three-phase voltages into a zero-sequence voltage. Among them, zero-sequence voltage The method for calculating the nth data is as follows:

[0076]

[0077] For zero-sequence voltage The discrete Fourier transform formula is as follows:

[0078]

[0079] In equation (2), the subscript n represents the value of the nth sampling point, and k represents k times the frequency domain resolution of the signal system. When the sampling frequency is fs, the system frequency domain resolution is fs / N. In this invention, the sampling rate fs is 20kHz. This characterizes the amplitude and phase of the signal at frequencies that are k times the system resolution. Therefore, the amplitude of the zero-sequence power frequency component of the bus terminal voltage connected to the power supply at a 50Hz power frequency can be calculated as follows:

[0080]

[0081] The voltage level of the distribution network constructed in this invention is 10kV, from which the per-unit value can be further calculated as follows:

[0082]

[0083] In equation (4), U sThe calculated per-unit value is denoted as "start-up voltage". When equation (5) is satisfied, the start-up criterion is activated:

[0084] U s >K s (5)

[0085] K s The threshold value for initiating the criterion is set to 0.1 in this invention.

[0086] Step 2: Startup Criteria After startup, the data acquisition devices at each level of the distribution network collect the instantaneous values ​​of the three-phase voltage at each bus node. The total number of voltage nodes is M, and the three-phase voltage collected at the m-th bus is u. ma =[u ma1 ,u ma2 ,…,u maN ]、u mb =[u mb1 ,u mb2 ,…,u mbN ]、u mc =[u mc1 ,u mc2 ,…,u mcN [N] represents the number of sampling points. In this invention, the sampling duration is 100ms. Therefore, in a scenario where the sampling frequency fs is 20kHz, the total number of sampling points N = 2000. Similarly, the three-phase voltages at each node are synthesized into a zero-sequence voltage. The zero-sequence voltage collected at the m-th node is... The calculation method is the same as the calculation method of the zero-sequence voltage at the power supply side bus terminal (Equation (1)) mentioned above, and will not be repeated here.

[0087] Subsequently, wavelet transform is used for filtering. To eliminate high-frequency noise interference as well as interference from the third and fifth harmonics, frequency components no higher than 50Hz need to be selected. Therefore, discrete wavelet transform is used to filter out high-frequency components above 50Hz, retaining low-frequency components between 0 and 50Hz. The calculation method of the wavelet coefficients of the zero-sequence voltage at the m-th node is illustrated as an example:

[0088]

[0089] In equation (6), j is the wavelet decomposition level, n is the index of the wavelet coefficients of the j-th level, and j and n are both integers. Let Ψ be the nth wavelet coefficient of the j-th layer. j,k (n) represents the selected wavelet basis function. Considering that the Har wavelet supports bioorthogonality, compact support, and symmetry, and has the shortest required filter length, the Har wavelet is chosen as the wavelet basis function. The sampling frequency is 20kHz. According to the sampling theorem, the maximum frequency in wavelet decomposition is 10kHz. A 7-level decomposition is performed, resulting in 8 sets of wavelet coefficients. These represent wavelet coefficients from 0Hz to 78.125Hz, 78.125Hz to 156.25Hz, 156.25Hz to 312.5Hz, 312.5Hz to 625Hz, 625Hz to 1250Hz, 1.25kHz to 2.5kHz, 2.5kHz to 5kHz, and 5kHz to 10kHz, respectively. To filter out high-frequency noise and harmonic interference, only the wavelet coefficients from 0Hz to 78.125Hz are retained. As the filtered zero-sequence voltage; the above operations are performed on the zero-sequence voltage of each node in the distribution network according to the aforementioned steps to obtain the N×M order instantaneous value matrix of the zero-sequence voltage of each node after filtering:

[0090]

[0091] In the matrix represented by equation (7), the m-th column vector Represents the values ​​of all sampled points of the m-th node, and the n-th row vector. This represents the value of the nth sampling point of each node.

[0092] Step 3: Based on the instantaneous value matrix of zero-sequence voltage at each node obtained in Step 2 after filtering. The energy value of the zero-sequence voltage at each node after filtering is calculated. Taking the m-th node as an example, the calculation method for its energy value is as follows:

[0093]

[0094] Step 4: Based on equation (8), the energy value of the voltage of each node can be calculated. The zero-sequence voltage energy value of each node is transmitted to the centralized control and decision-making center via 5G communication to obtain an energy array composed of the zero-sequence voltage energy values ​​of each node (M in total):

[0095] E U =[E U (1),E U (2),…,E U (M)] (9)

[0096] Subsequently, the centralized control and decision-making center checks whether there are any missing zero-sequence voltage energy values ​​transmitted by each node. Specifically, the centralized control and decision-making center records the node information of each downstream voltage node. When information from a downstream voltage node is successfully received, that node is marked as having successfully transmitted. Only when all downstream voltage nodes are marked as having successfully transmitted can the data transmission of the voltage nodes be considered intact; otherwise, the zero-sequence voltage transmission is considered lost, and nodes not marked as having successfully transmitted are considered to have lost information. If the zero-sequence voltage energy values ​​of all nodes are intact, proceed to Step 5; if the zero-sequence voltage energy values ​​of any node are lost, proceed to Step 6.

[0097] Step 5: The centralized control and decision-making center compares the zero-sequence voltage energy values ​​of each node to obtain the maximum value E in the zero-sequence voltage energy value array. Umax =[E U (1),E U (2),…,E U (M)] max The node corresponding to this value is the node associated with the faulty line, denoted as the "faulty node". Proceed to Step 7.

[0098] Step 6: The centralized control decision center compares the zero-sequence voltage energy values ​​of each node after the loss of zero-sequence voltage energy values ​​to obtain the maximum value E in the zero-sequence voltage energy value array. Umax =[E U (1),E U (2),…,E U (M)] max The nodes corresponding to the maximum value and the nodes with missing energy data are all recorded as "fault-latent nodes", and proceed to Step 8;

[0099] Step 7: The data acquisition device at the "fault node" collects the three-phase current of all lines connected to the "fault node," converts it into zero-sequence current, filters it, and then calculates its zero-sequence current energy value. This energy value is transmitted to the centralized control and decision-making center, resulting in an array of zero-sequence current energy values ​​from the lines connected to the "fault node."

[0100] E I =[E I (1),E I (2),…,E I (L)] (10)

[0101] In equation (10), L is the total number of lines connected to the "fault node". The filtering method for zero-sequence current and the calculation method for zero-sequence current energy are exactly the same as those for zero-sequence voltage, and have been explained in detail in Step 2 and Step 3, so they will not be repeated here. Each element of this array is the zero-sequence current energy value of each line connected to the "fault node", proceed to Step 9;

[0102] Step 8: Data acquisition devices at multiple "latent fault nodes" collect the three-phase current of all lines connected to each "latent fault node," convert them into zero-sequence currents, filter them, and then calculate their zero-sequence current energy values. These energy values ​​are transmitted to the centralized control and decision-making center, resulting in multiple zero-sequence current energy arrays for the lines connected to the "fault nodes," with each zero-sequence current energy array corresponding one-to-one with each "latent fault node."

[0103] Step 9: The 5G communication device at each line of the "fault node" or each "fault latent node" transmits the zero-sequence current energy array obtained in Step 7 or Step 8 to the centralized control and decision-making center.

[0104] Step 10: The centralized control decision center checks whether the data in the zero-sequence voltage energy value array corresponding to the node is missing. When the energy value information is not missing, that is, there is only one "fault node" and no "fault latent node": if the zero-sequence current energy value information is not missing, the centralized control decision center sorts the zero-sequence current energy value array by size. The line with the largest zero-sequence current energy value is the line that has experienced a ground fault, and is recorded as the "fault line".

[0105] If the zero-sequence current energy value information is missing, the line corresponding to the maximum zero-sequence current energy value in this array and the line with missing zero-sequence current energy value information are collectively referred to as "fault-latent lines".

[0106] When voltage energy value information is missing, there are multiple "fault latent nodes" and no "fault node": for "fault latent nodes" with missing current energy value information, the line corresponding to the maximum current energy value in the array and the line corresponding to the missing current energy value information are collectively referred to as "fault latent lines". For "fault latent nodes" with not missing current energy value information, the line corresponding to the maximum current energy value in the array is referred to as "fault latent lines".

[0107] Step 11: If there are no "latent fault lines" and only "fault lines", it means that the voltage energy value information and current energy value information are not missing. In this case, directly disconnect the circuit breaker of the "fault line" to isolate the fault. If there are multiple "latent fault lines" and no "fault lines", it means that the voltage energy value information or current energy value information is missing. In this case, lock out the protection of all lines except the "latent fault lines" and open the protection of the "latent fault lines". The "latent fault line" that first disconnects the circuit breaker is the real fault line. Then lock out the protection of the remaining "latent fault lines".

[0108] The invention will be further explained below in different scenarios:

[0109] Scenario 1: F1 fault, zero-sequence voltage and current energy values ​​are collected normally.

[0110] Assuming that within a 100ms time window after the activation criterion is activated, the centralized control decision center can receive the zero-sequence current and network node zero-sequence voltage energy transmitted through the 5G network, and no data anomalies occur.

[0111] When a short circuit occurs at point F1 (3km from bus line BUS3), the zero-sequence current energy at both ends of each line and the zero-sequence voltage energy at each node are as follows: Figure 3 and 4 As shown, the maximum zero-sequence voltage energy at node BUS3 is 5.58. Among the associated lines L2, L5, L6, and L11, the maximum zero-sequence current energy is 1.48, corresponding to line L5. Based on the protection scheme mentioned above, it can be determined that a short-circuit fault has occurred on line L5, and the protection device can correctly trip and clear the fault.

[0112] Further simulations show that when the transition resistance increases to 100Ω, the maximum zero-sequence voltage energy at the node is 1.39 and the maximum zero-sequence current energy is 0.46. Line L5 can still be identified as a faulty line, and the analysis is the same as above.

[0113] Scenario 2: When the zero-sequence current energy value is partially missing, but the zero-sequence voltage energy value is collected normally.

[0114] Assume that due to communication network congestion or transmission over a 5G communication network, some zero-sequence current energy value information is missing, causing the centralized control and decision-making center to be unable to collect complete zero-sequence current energy value information within the time window. Figure 5 As shown, taking a short-circuit fault at point F1 as an example, the performance of the protection action is analyzed.

[0115] Let's assume for a moment that the zero-sequence current energy value of line L4 cannot be transmitted to the centralized control decision center. Based on the previous analysis, after sorting the zero-sequence voltage energy values, we can see that the bus corresponding to BUS0 is BUS3, and L2, L5, L6, and L11 are associated with it. Since there is no missing zero-sequence current energy value information in the lines associated with BUS3, the maximum value after sorting must be the zero-sequence current energy value corresponding to the actual faulty line. At this time, the zero-sequence current energy value is 1.38, corresponding to line L5. Therefore, it can be determined that line L5 has a fault, and the centralized control decision center immediately issues a trip signal to the lower-level protection, satisfying both the protection speed and selectivity requirements.

[0116] If the zero-sequence current energy of line L5 cannot be collected by the centralized control decision center, and because there is a lack of zero-sequence current energy in the lines associated with BUS3, the line corresponding to the maximum zero-sequence current energy obtained after sorting is considered a "fault-latent line". At this time, the maximum zero-sequence current energy is 0.99, corresponding to line L6. Therefore, among the lines for which zero-sequence current energy has been received, the protection of line L6 is opened while L2, L5, and L11 are blocked. In this case, the protection of line L6 will compete with that of line L5. For the same type of protection device, L5 will trip first, ensuring selectivity.

[0117] Scenario 3: If the zero-sequence voltage energy value information is partially missing, the zero-sequence current energy value information is not missing.

[0118] Assume that due to 5G communication network congestion, some zero-sequence current energy value information is missing, causing the centralized control decision center to be unable to collect complete zero-sequence voltage energy value information within the specified time window. This will be illustrated using fault F1 as an example.

[0119] Assuming the zero-sequence voltage energy of bus BUS3 cannot be obtained by the centralized control decision center, after sorting the collected zero-sequence voltage energy, it is easy to find that the bus corresponding to the maximum zero-sequence voltage energy is BUS2. Among the lines connected to it, the line corresponding to the maximum zero-sequence current energy value of 0.63 is L1. According to the previous analysis, the protection of line L5 and the line L1 directly connected to bus BUS5 is opened at this time, while the protection of lines L3, L4, and L9 is blocked. Although only the zero-sequence current protection of three lines is blocked, the selectivity has been greatly improved compared to the uncoordinated action of the entire network.

[0120] Example 2:

[0121] The present invention also provides a ground fault protection system 200 for active power distribution networks, such as... Figure 6 As shown, it includes:

[0122] The acquisition unit 201 is used to acquire the instantaneous values ​​of the three-phase voltage at the power supply side bus of the active distribution network with a preset sampling duration and sampling frequency, synthesize the three-phase voltage into the zero-sequence voltage of the active distribution network node, and determine the per-unit value of the zero-sequence voltage. If the per-unit value is greater than a preset threshold value, the zero-sequence voltage is filtered to obtain the instantaneous value matrix of the zero-sequence voltage.

[0123] The calculation unit 202 is used to determine the energy value of the zero-sequence voltage based on the instantaneous value matrix, generate a zero-sequence voltage energy array based on the energy value, and determine whether there are any latent fault lines or fault lines in the active distribution network based on the zero-sequence voltage energy array.

[0124] The control unit 203 is used to perform protection actions on the identified faulty latent line or faulty line according to preset criteria.

[0125] The acquisition unit determines the per-unit value of the zero-sequence voltage, including:

[0126] Perform a Discrete Fourier Transform on the zero-sequence voltage to obtain the amplitude and phase of the zero-sequence voltage at a preset frequency. Based on the amplitude and phase, determine the amplitude of the zero-sequence voltage at a preset power frequency component.

[0127] The per-unit value of the zero-sequence voltage is determined based on the amplitude of the zero-sequence power frequency component of the voltage.

[0128] The filtering process includes wavelet transform and discrete wavelet transform.

[0129] The acquisition unit performs filtering on the zero-sequence voltage, including:

[0130] For zero-sequence voltage, wavelet transform processing is performed to eliminate interference from high-frequency noise, third harmonic and fifth harmonic, and zero-sequence voltage with frequency components within the first preset frequency range is selected.

[0131] For the zero-sequence voltage of the frequency component within the first preset frequency range, discrete wavelet transform processing is performed to filter out the zero-sequence voltage of the frequency component within the second preset frequency range.

[0132] The calculation unit determines whether there are latent fault lines or faulty lines in the active distribution network based on the zero-sequence voltage energy array, including:

[0133] Determine whether the energy value information in the zero-sequence voltage energy array contains missing values;

[0134] If no numerical values ​​are missing, the active distribution network node corresponding to the maximum value in the zero-sequence voltage energy array is marked as a fault node. The three-phase current of the line connected to the fault node is collected and converted into zero-sequence current. After filtering the zero-sequence current, the energy value of the zero-sequence current is determined to obtain the zero-sequence current energy array of the line connected to the fault node. If the energy value information in the zero-sequence current energy array is not missing, the line corresponding to the maximum value in the zero-sequence current energy array is marked as a fault line. If the energy value information in the zero-sequence current energy array is missing, the line corresponding to the maximum value in the zero-sequence current energy array is marked as a latent fault line.

[0135] If there are missing values, the active distribution network node corresponding to the maximum value in the zero-sequence voltage energy array and the active distribution network node corresponding to the missing value are marked as fault-prone nodes. The three-phase current of the line connected to the fault-prone node is collected and converted into zero-sequence current. After filtering the zero-sequence current, the energy value of the zero-sequence current is determined to obtain the zero-sequence current energy array of the line connected to the fault-prone node. If the energy value information in the zero-sequence current energy array is not missing, the line corresponding to the maximum value in the zero-sequence current energy array and the line connected to the fault-prone node are marked as fault lines. If the energy value information in the zero-sequence current energy array is missing, the line corresponding to the maximum value in the zero-sequence current energy array, the line corresponding to the missing information, and the line connected to the fault-prone node are marked as fault-prone lines.

[0136] The control unit, based on preset criteria, performs protection actions on the identified potential fault lines or faulty lines, including:

[0137] If there are no potential fault lines and only a faulty line exists, disconnect the circuit breaker of the faulty line.

[0138] If there are multiple potential fault lines and no fault lines exist, then the protection of all lines in the active distribution network except for the potential fault lines is blocked, and the protection of the potential fault lines is opened. After the protection of the potential fault lines is opened, the protection of the potential fault lines whose circuit breakers have not been disconnected is blocked.

[0139] This invention is based on the amplitude distribution characteristics of zero-sequence electrical quantities in the zero-sequence protection zones naturally formed in the power distribution system. It utilizes the convenient real-time data acquisition and transmission capabilities of 5G to implement this invention. This invention can effectively identify the location of grounding faults occurring in various locations within a complex active power distribution network area, and has high adaptability, providing crucial conditions for the safe and reliable operation of the power distribution network.

[0140] Example 3:

[0141] Based on the same inventive concept, this invention also provides a computer device, which includes a processor and a memory. The memory stores a computer program, which includes program instructions. The processor executes the program instructions stored in the computer storage medium. The processor may be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing and control core of the terminal, suitable for implementing one or more instructions, specifically suitable for loading and executing one or more instructions in the computer storage medium to implement corresponding method flows or corresponding functions, thereby implementing the steps of the methods in the above embodiments.

[0142] Example 4:

[0143] Based on the same inventive concept, this invention also provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a computer device used to store programs and data. It is understood that the computer-readable storage medium here can include both the built-in storage medium in the computer device and extended storage media supported by the computer device. The computer-readable storage medium provides storage space that stores the terminal's operating system. Furthermore, this storage space also stores one or more instructions suitable for loading and execution by a processor. These instructions can be one or more computer programs (including program code). It should be noted that the computer-readable storage medium here can be high-speed RAM or non-volatile memory, such as at least one disk storage device. The processor can load and execute one or more instructions stored in the computer-readable storage medium to implement the steps of the method in the above embodiments.

[0144] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of the present invention can be implemented using various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0145] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0146] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0147] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0148] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the invention.

[0149] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A ground fault protection method for active power distribution networks, characterized in that, The method includes: The instantaneous values ​​of three-phase voltage at the power supply side bus of the active distribution network are collected with a preset sampling duration and sampling frequency. The instantaneous values ​​of the three-phase voltage are synthesized into the zero-sequence voltage of the active distribution network node, and the per-unit value of the zero-sequence voltage is determined. If the per-unit value is greater than a preset threshold value, the zero-sequence voltage is filtered to obtain the instantaneous value matrix of the zero-sequence voltage. Based on the instantaneous value matrix, the energy value of the zero-sequence voltage is determined, and based on the energy value, a zero-sequence voltage energy array is generated. Based on the zero-sequence voltage energy array, it is determined whether there are latent fault lines or fault lines in the active distribution network. Based on preset criteria, protection actions are performed on the identified faulty or latent faulty lines. The step of determining whether there are latent fault lines or fault lines in the active distribution network based on the zero-sequence voltage energy array includes: Determine whether the energy value information in the zero-sequence voltage energy array contains missing values; If no numerical values ​​are missing, the active distribution network node corresponding to the maximum value in the zero-sequence voltage energy array is marked as a fault node. The three-phase current of the line connected to the fault node is collected and converted into zero-sequence current. After filtering the zero-sequence current, the energy value of the zero-sequence current is determined to obtain the zero-sequence current energy array of the line connected to the fault node. If the energy value information in the zero-sequence current energy array is not missing, the line corresponding to the maximum value in the zero-sequence current energy array is marked as a fault line. If the energy value information in the zero-sequence current energy array is missing, the line corresponding to the maximum value in the zero-sequence current energy array is marked as a latent fault line. If there are missing values, the active distribution network node corresponding to the maximum value in the zero-sequence voltage energy array and the active distribution network node corresponding to the missing value are marked as fault-prone nodes. The three-phase current of the line connected to the fault-prone node is collected and converted into zero-sequence current. After filtering the zero-sequence current, the energy value of the zero-sequence current is determined to obtain the zero-sequence current energy array of the line connected to the fault-prone node. If the energy value information in the zero-sequence current energy array is not missing, the line corresponding to the maximum value in the zero-sequence current energy array and the line connected to the fault-prone node are marked as fault lines. If the energy value information in the zero-sequence current energy array is missing, the line corresponding to the maximum value in the zero-sequence current energy array, the line corresponding to the missing information, and the line connected to the fault-prone node are marked as fault-prone lines.

2. The method according to claim 1, characterized in that, Determining the per-unit value of the zero-sequence voltage includes: Perform a Discrete Fourier Transform on the zero-sequence voltage to obtain the amplitude and phase of the zero-sequence voltage at a preset frequency. Based on the amplitude and phase, determine the amplitude of the zero-sequence voltage at a preset power frequency component. The per-unit value of the zero-sequence voltage is determined based on the amplitude of the zero-sequence power frequency component of the voltage.

3. The method according to claim 1, characterized in that, The filtering process is a discrete wavelet transform process.

4. The method according to claim 1, characterized in that, The filtering process for the zero-sequence voltage includes: For zero-sequence voltage, discrete wavelet transform processing is performed to eliminate interference from high-frequency noise, third harmonic and fifth harmonic, and zero-sequence voltage with frequency components within the first preset frequency range is selected. For the zero-sequence voltage of the frequency component within the first preset frequency range, discrete wavelet transform processing is performed to filter out the zero-sequence voltage of the frequency component within the second preset frequency range.

5. The method according to claim 1, characterized in that, The step of performing protection actions on the identified potential fault lines or fault lines according to preset criteria includes: If there are no potential fault lines and only a faulty line exists, disconnect the circuit breaker of the faulty line. If there are multiple potential fault lines and no fault lines exist, then the protection of all lines in the active distribution network except for the potential fault lines is blocked, and the protection of the potential fault lines is opened. After the protection of the potential fault lines is opened, the protection of the potential fault lines whose circuit breakers have not been disconnected is blocked.

6. A ground fault protection system for active power distribution networks, characterized in that, The system includes: The acquisition unit is used to acquire the instantaneous values ​​of three-phase voltage at the power supply side bus of the active distribution network with a preset sampling duration and sampling frequency, synthesize the instantaneous values ​​of the three-phase voltage into the zero-sequence voltage of the active distribution network node, and determine the per-unit value of the zero-sequence voltage. If the per-unit value is greater than a preset threshold value, the zero-sequence voltage is filtered to obtain the instantaneous value matrix of the zero-sequence voltage. The calculation unit is used to determine the energy value of the zero-sequence voltage based on the instantaneous value matrix, generate a zero-sequence voltage energy array based on the energy value, and determine whether there are latent fault lines or fault lines in the active distribution network based on the zero-sequence voltage energy array. The control unit is used to perform protection actions on the identified faulty latent lines or faulty lines according to preset criteria. The calculation unit determines whether there are latent fault lines or fault lines in the active distribution network based on the zero-sequence voltage energy array, including: Determine whether the energy value information in the zero-sequence voltage energy array contains missing values; If no numerical values ​​are missing, the active distribution network node corresponding to the maximum value in the zero-sequence voltage energy array is marked as a fault node. The three-phase current of the line connected to the fault node is collected and converted into zero-sequence current. After filtering the zero-sequence current, the energy value of the zero-sequence current is determined to obtain the zero-sequence current energy array of the line connected to the fault node. If the energy value information in the zero-sequence current energy array is not missing, the line corresponding to the maximum value in the zero-sequence current energy array is marked as a fault line. If the energy value information in the zero-sequence current energy array is missing, the line corresponding to the maximum value in the zero-sequence current energy array is marked as a latent fault line. If there are missing values, the active distribution network node corresponding to the maximum value in the zero-sequence voltage energy array and the active distribution network node corresponding to the missing value are marked as fault-prone nodes. The three-phase current of the line connected to the fault-prone node is collected and converted into zero-sequence current. After filtering the zero-sequence current, the energy value of the zero-sequence current is determined to obtain the zero-sequence current energy array of the line connected to the fault-prone node. If the energy value information in the zero-sequence current energy array is not missing, the line corresponding to the maximum value in the zero-sequence current energy array and the line connected to the fault-prone node are marked as fault lines. If the energy value information in the zero-sequence current energy array is missing, the line corresponding to the maximum value in the zero-sequence current energy array, the line corresponding to the missing information, and the line connected to the fault-prone node are marked as fault-prone lines.

7. The system according to claim 6, characterized in that, The acquisition unit determines the per-unit value of the zero-sequence voltage, including: Perform a Discrete Fourier Transform on the zero-sequence voltage to obtain the amplitude and phase of the zero-sequence voltage at a preset frequency. Based on the amplitude and phase, determine the amplitude of the zero-sequence voltage at a preset power frequency component. The per-unit value of the zero-sequence voltage is determined based on the amplitude of the zero-sequence power frequency component of the voltage.

8. The system according to claim 6, characterized in that, The filtering process is a discrete wavelet transform process.

9. The system according to claim 6, characterized in that, The acquisition unit performs filtering processing on the zero-sequence voltage, including: For zero-sequence voltage, discrete wavelet transform processing is performed to eliminate interference from high-frequency noise, third harmonic and fifth harmonic, and zero-sequence voltage with frequency components within the first preset frequency range is selected. For the zero-sequence voltage of the frequency component within the first preset frequency range, discrete wavelet transform processing is performed to filter out the zero-sequence voltage of the frequency component within the second preset frequency range.

10. The system according to claim 6, characterized in that, The control unit performs protection actions on the identified potential fault lines or fault lines based on preset criteria, including: If there are no potential fault lines and only a faulty line exists, disconnect the circuit breaker of the faulty line. If there are multiple potential fault lines and no fault lines exist, then the protection of all lines in the active distribution network except for the potential fault lines is blocked, and the protection of the potential fault lines is opened. After the protection of the potential fault lines is opened, the protection of the potential fault lines whose circuit breakers have not been disconnected is blocked.

11. A computer device, characterized in that, include: One or more processors; A processor is used to execute one or more programs; When the one or more programs are executed by the one or more processors, the method described in any one of claims 1-5 is implemented.

12. A computer-readable storage medium, characterized in that, It contains a computer program, which, when executed, implements the method as described in any one of claims 1-5.

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