A small current grounding line selection method, system and device

Abstract

A method, system, and apparatus for selecting ground faults with low current is disclosed. The method includes: acquiring the zero-sequence voltage of the busbar of a power distribution system; determining the grounding status of the busbar based on the zero-sequence voltage; if the grounding status indicates an abnormal grounding, sending a grounding characteristic discrimination command to multiple selection units; the selection units determining the branch grounding characteristics based on the direction of voltage and current changes; receiving multiple branch grounding characteristics sent one-to-one by the selection units; and determining the branch outlet where the grounding fault occurred based on the multiple branch grounding characteristics and the line network topology diagram. This invention allows the selection host to quickly identify the faulty branch by utilizing various selection units when a grounding fault is detected, enabling rapid fault elimination measures and ensuring the grounding performance of the entire power distribution system, thus providing better safety and practicality.

Description

Technical Field

[0001] This invention belongs to the field of power supply and distribution, and specifically relates to a method, system and device for selecting grounding lines with low current. Background Technology

[0002] A power system whose center point is ungrounded or whose neutral point is grounded through a resistor and arc suppression coil is called a low-current grounding system. Low-current grounding systems do not generate large short-circuit currents during single-phase grounding faults, and the line voltages between phases remain symmetrical. Therefore, it is not necessary to immediately disconnect the faulty circuit, and the power supply to the load is not affected. Thus, low-current grounding is widely used in my country's 3kV to 66kV distribution networks. More than 90% of faults in power distribution systems are single-phase grounding faults. If the system operates for a prolonged period after a single-phase grounding fault, the fault is prone to developing into a two-point or multi-point grounding short circuit. Arcing grounding can also cause overvoltage throughout the system, damaging equipment and jeopardizing safe system operation. Furthermore, overvoltage near the grounding point can easily cause casualties. Therefore, it is essential to locate and disconnect the faulty line promptly. Thus, the ability to quickly determine the location of a grounding fault and eliminate it is an important current research direction.

[0003] Traditionally, centralized grounding fault location devices are installed at the substation side. These devices can detect the zero-sequence voltage of the cable entering the substation's low-voltage busbar and the zero-sequence current of each outgoing line. This allows for direct data sampling by the centralized low-current grounding fault location device to perform this function. However, because centralized grounding fault location devices can only access voltage and current signals from the substation outlet, they cannot pinpoint the faulty branch in complex power distribution network topologies. Consequently, they cannot accurately locate or eliminate grounding faults. Summary of the Invention

[0004] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a method for selecting ground fault locations with low current, capable of accurately determining ground faults. This invention also proposes a low-current ground fault location system and a low-current ground fault location device.

[0005] According to a first aspect of the present invention, a low-current grounding fault location method is applied to a fault location host, wherein the fault location host is communicatively connected to multiple fault location units, and the multiple fault location units are used to collect the branch zero-sequence voltage and branch zero-sequence current of multiple branch outlets in a one-to-one correspondence.

[0006] The method for selecting grounding lines with low current includes the following steps:

[0007] Collect the zero-sequence voltage of the power distribution system's busbars;

[0008] The bus grounding status of the power distribution system is determined based on the bus zero-sequence voltage. If the bus grounding status indicates an abnormal bus grounding, a grounding characteristic discrimination command is sent to multiple selection units. The selection unit responds to the grounding characteristic discrimination command to determine the branch grounding characteristic. The branch grounding characteristic is determined by the corresponding selection unit based on the voltage change direction of the corresponding branch zero-sequence voltage and the current change direction of the branch zero-sequence current. Wherein, if the voltage change direction and the current change direction are the same, the branch grounding characteristic is confirmed as having the same grounding characteristic direction, meaning neither this branch nor its subordinate branches are grounded; if the voltage change direction and the current change direction are opposite, the branch grounding characteristic is confirmed as having opposite characteristic directions, meaning either this branch or its subordinate branches are grounded.

[0009] Receive multiple branch grounding characteristics sent one-to-one by the multiple line selection units;

[0010] Based on the grounding characteristics of multiple branches and the line network topology diagram, the grounding characteristics of the branch at the very end of the power distribution system are identified as the branch outlet with opposite characteristic directions, and the branch outlet where the grounding fault occurs is determined. The line network topology diagram represents the topological connection relationship between the bus and multiple branch outlets in the power distribution system.

[0011] The low-current grounding fault location method according to embodiments of the present invention has at least the following technical advantages: By acquiring the bus zero-sequence voltage, the fault location host can quickly determine whether a grounding fault exists. Furthermore, because fault location units are set at the outlets of each branch in the power distribution system, when the fault location host determines that a grounding fault has occurred, each fault location unit can quickly determine whether its own fault has occurred. Since there is a unique correspondence between the branch outlet and the fault location unit, once the fault location unit is determined, the specific fault location is essentially determined. Compared to traditional methods, the low-current grounding fault location method of the present invention can determine the grounding fault location segment and assist in preliminary automatic fault elimination, possessing better safety and practicality, and is suitable for industrial-scale promotion.

[0012] According to some embodiments of the present invention, determining the bus grounding state of the power distribution system based on the bus zero-sequence voltage includes the following steps:

[0013] The steady-state value of the bus zero-sequence voltage is determined using the aforementioned bus zero-sequence voltage and based on the Fourier algorithm.

[0014] The bus grounding status is determined based on the steady-state value of the zero-sequence voltage of the bus and a preset grounding voltage determination threshold. If the steady-state value of the zero-sequence voltage of the bus is higher than the grounding voltage determination threshold, the bus grounding status is used to characterize an abnormal bus grounding. If the steady-state value of the zero-sequence voltage of the bus is equal to or lower than the grounding voltage determination threshold, the bus grounding status is used to characterize a normal bus grounding.

[0015] According to some embodiments of the present invention, the above-described low-current grounding line selection method further includes the following steps:

[0016] The fault abnormal time segment is determined based on the branch zero-sequence voltage and the branch zero-sequence current. The fault abnormal time segment includes the moment when the branch zero-sequence current exceeds a preset current change threshold. The moment when the branch zero-sequence current exceeds the preset current change threshold is the moment when the branch outlet grounding occurs.

[0017] Obtain multiple zero-sequence voltages and multiple zero-sequence currents of each branch outlet within the fault abnormal time period, and construct a fault waveform file based on the multiple zero-sequence voltages and multiple zero-sequence currents of each branch outlet.

[0018] According to a second aspect of the present invention, a low-current grounding fault location system is applied to a fault location host, wherein the fault location host is communicatively connected to multiple fault location units, and the multiple fault location units are used to collect the branch zero-sequence voltage and branch zero-sequence current of multiple branch outlets in a one-to-one correspondence.

[0019] The low-current grounding fault location system includes:

[0020] Bus status acquisition unit, used to collect the zero-sequence voltage of the bus in the power distribution system;

[0021] A bus grounding determination unit is used to determine the bus grounding status of the power distribution system based on the bus zero-sequence voltage. If the bus grounding status indicates an abnormal bus grounding, a grounding characteristic discrimination command is sent to multiple selection units. The selection units respond to the grounding characteristic discrimination command to determine branch grounding characteristics. The branch grounding characteristics are determined by the corresponding selection unit based on the voltage change direction of the corresponding branch zero-sequence voltage and the current change direction of the corresponding branch zero-sequence current. Wherein, if the voltage change direction and the current change direction are the same, the branch grounding characteristic is confirmed as having the same grounding characteristic direction, meaning that neither the branch nor its downstream branches are grounded; if the voltage change direction and the current change direction are opposite, the branch grounding characteristic is confirmed as having the opposite characteristic direction, meaning that either the branch or its downstream branches are grounded.

[0022] A grounding feature receiving unit is used to receive multiple branch grounding features sent one-to-one by the multiple line selection units;

[0023] The line selection and determination unit is used to search for the grounding characteristics of the branch at the end of the power distribution system based on the grounding characteristics of multiple branches and the line network topology diagram, confirm the branch outlet with the opposite characteristic direction, and determine the branch outlet where a grounding fault has occurred. The line network topology diagram represents the topological connection relationship between the bus and multiple branch outlets in the power distribution system.

[0024] The low-current grounding fault location system according to embodiments of the present invention has at least the following technical advantages: By acquiring the busbar zero-sequence voltage through the busbar status acquisition unit, the busbar grounding determination unit can quickly determine whether a grounding fault exists. Furthermore, because fault location units are set at the outlets of each branch of the power distribution system, when the fault location determination unit determines that a grounding fault has occurred, each fault location unit can quickly determine whether its own grounding fault has occurred. Since there is a unique correspondence between the branch outlet and the fault location unit, determining the fault location of the fault location unit essentially determines the specific fault location. Compared to traditional methods, the low-current grounding fault location system of the present invention can achieve segmental determination of the grounding fault location and assist in preliminary automatic fault elimination, possessing better safety and practicality, and is suitable for industrial-scale promotion.

[0025] According to some embodiments of the present invention, the above-described low-current grounding fault location system further includes:

[0026] An abnormal time determination unit is used to determine the fault abnormal time segment based on the branch zero-sequence voltage and the branch zero-sequence current. The fault abnormal time segment includes the moment when the branch zero-sequence current exceeds a preset current change threshold value. The moment when the branch zero-sequence current exceeds the preset current change threshold value is the moment when the branch outlet grounding occurs.

[0027] The waveform recording information generation unit is used to acquire multiple branch zero-sequence voltages and multiple branch zero-sequence currents corresponding to each branch outlet within the fault abnormal time period, and to construct a fault waveform recording file based on the multiple branch zero-sequence voltages and multiple branch zero-sequence currents corresponding to each branch outlet.

[0028] A low-current grounding fault location device according to a third aspect embodiment of the invention includes:

[0029] Multiple line selection units are used to collect the branch zero-sequence voltage and branch zero-sequence current of multiple branch outlets one by one;

[0030] The line selection host is communicatively connected to multiple line selection units, and the line selection host is used to perform the low-current grounding line selection method described above.

[0031] The low-current grounding fault location device according to embodiments of the present invention has at least the following technical advantages: By acquiring the zero-sequence voltage of the busbar through the fault location host, it is easy to quickly determine whether a grounding fault exists. Furthermore, because fault location units are set at the outlets of each branch of the power distribution system, when the fault location host determines that a grounding fault has occurred, each fault location unit can quickly determine whether its own grounding fault has occurred. Since there is a unique correspondence between the branch outlet and the fault location unit, once the fault of the fault location unit is determined, the specific fault location is essentially determined. Compared with traditional methods, the low-current grounding fault location device of the present invention can achieve segmental determination of the grounding fault location and assist in preliminary automatic fault elimination, possessing better safety and practicality, and is suitable for industrial promotion.

[0032] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0033] The above or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0034] Figure 1 This is a flowchart of the low-current grounding line selection method according to an embodiment of the present invention;

[0035] Figure 2 This is a system block diagram of the low-current grounding line selection system according to an embodiment of the present invention;

[0036] Figure 3 This is a structural block diagram of the low-current grounding line selection device according to an embodiment of the present invention;

[0037] Figure 4 This is a system diagram of the power distribution system according to an embodiment of the present invention.

[0038] Figure labels;

[0039] Line selection host 100, line selection unit 200. Detailed Implementation

[0040] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0041] In the description of this invention, the use of terms such as first, second, third, fourth, etc., is for the purpose of distinguishing technical features only and should not be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated or the order of the technical features indicated.

[0042] In the description of this invention, unless otherwise explicitly defined, terms such as "setup" and "connection" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0043] The following is for reference. Figures 1 to 4 A method for selecting a low-current grounding line according to an embodiment of the first aspect of the present invention is described. The method for selecting a low-current grounding line according to the embodiment of the present invention is applied to a line selection host 100, which is communicatively connected to multiple line selection units 200. The multiple line selection units 200 are used to collect the branch zero-sequence voltage and branch zero-sequence current of multiple branch outlets in a one-to-one correspondence.

[0044] The method for selecting grounding lines with low current includes the following steps:

[0045] Collect the zero-sequence voltage of the power distribution system's busbars;

[0046] The bus grounding status of the power distribution system is determined based on the bus zero-sequence voltage. If the bus grounding status indicates an abnormal bus grounding, a grounding characteristic discrimination command is sent to multiple line selection units 200. The line selection unit 200 responds to the grounding characteristic discrimination command to determine the branch grounding characteristics. The branch grounding characteristics are determined by the corresponding line selection unit 200 based on the voltage change direction of the zero-sequence voltage and the current change direction of the zero-sequence current of the corresponding branch. Wherein, if the voltage change direction and the current change direction are the same, the branch grounding characteristics are confirmed as having the same grounding characteristic direction, that is, neither this branch nor its subordinate branches are grounded; if the voltage change direction and the current change direction are opposite, the branch grounding characteristics are confirmed as having opposite characteristic directions, that is, either this branch or its subordinate branches are grounded.

[0047] Receives multiple branch grounding characteristics transmitted one-to-one by multiple line selection units 200;

[0048] Based on the grounding characteristics of multiple branches and the line network topology, the grounding characteristics of the last branch in the power distribution system are identified as the branch outlet with the opposite characteristic direction, and the branch outlet of the grounding fault is determined. The line network topology diagram represents the topological connection relationship between the bus and multiple branch outlets in the power distribution system.

[0049] refer to Figures 1 to 4A communication network is constructed between the line selection host 100 and multiple line selection units 200 based on 5G communication. 5G communication ensures high bandwidth and low latency. Simultaneously, to ensure time synchronization between the line selection host 100 and the multiple line selection units 200, the line selection host 100 continuously sends time synchronization messages to each other at equal intervals. These time synchronization messages carry standard time information, allowing all line selection units 200 to maintain time synchronization with the line selection host 100, thus ensuring the accuracy of subsequent calculations and control.

[0050] After the line selection host 100 and multiple line selection units 200 establish communication, the line selection host 100 and multiple line selection units 200 all begin high-speed sampling at a sampling frequency of 4000Hz, that is, there are 80 sampling points in each cycle.

[0051] When a ground fault occurs, because the entire power distribution system is interconnected, a ground fault will be detected at the busbar regardless of which branch experiences the fault. The fault location unit 100 is installed at the substation busbar, allowing it to directly collect the zero-sequence voltage of the power distribution system busbar and use this voltage to determine the busbar grounding status. Furthermore, when the busbar grounding status indicates an abnormal grounding condition, a grounding characteristic discrimination command will be generated.

[0052] This section briefly describes the process by which the line selection host 100 determines the faulty branch after detecting a bus grounding anomaly. After confirming the grounding anomaly, the line selection host 100 generates a grounding characteristic discrimination command and sends it to each line selection unit 200 via the 5G network. Upon receiving the grounding characteristic discrimination command, each line selection unit 200 determines whether its collected branch zero-sequence voltage and zero-sequence current during the period when the line selection host 100 determined the grounding fault occurred show any grounding anomalies. Based on the determination result, it generates branch grounding characteristics and transmits these characteristics to the line selection host 100. After receiving the branch grounding characteristics from all line selection units 200, the line selection host 100, in conjunction with the line network topology diagram, searches for the branch grounding characteristics at the very end of the power distribution system and identifies it as the branch outlet with the opposite characteristic direction, thus determining the specific branch where the grounding fault occurred. To ensure the ground fault detection capabilities of the fault location host 100 and fault location unit 200, a sampling buffer is set up in both hosts for storing zero-sequence current and zero-sequence voltage data. Once the fault location host 100 determines a bus ground fault anomaly, it can freeze the data in the sampling buffers of each fault location unit 200, using the frozen data to determine the branch ground fault characteristics. It should also be noted that the line network topology diagram illustrates the connection relationships between various levels of power equipment in the wiring system. Furthermore, by establishing a correspondence between each fault location unit 200 and each branch in the line network topology diagram, the specific location of the fault can be quickly determined after a ground fault occurs.

[0053] According to the low-current grounding fault location method of this invention, by acquiring the zero-sequence voltage of the busbar, the fault location host 100 can quickly determine whether a grounding fault exists. Simultaneously, because fault location units 200 are set at the outlets of each branch in the power distribution system, when the fault location host 100 determines that a grounding fault has occurred, each fault location unit 200 can quickly determine whether a grounding fault has occurred within itself and its downstream branches. Furthermore, because there is a unique correspondence between the branch outlet and the fault location unit 200, determining the fault in the fault location unit 200 essentially determines the specific fault location. Compared to traditional methods, the low-current grounding fault location method of this invention can achieve segmental determination of the grounding fault location and assist in preliminary automatic fault elimination, possessing better safety and practicality, and is suitable for industrial-scale promotion.

[0054] It should be noted that a grounding anomaly on the busbar may be caused by a grounding anomaly in a branch, and a grounding fault in a higher-level branch may be caused by a grounding anomaly in a lower-level branch. Therefore, identifying branch grounding anomalies is fundamental to determining the specific location of a grounding fault. At the moment of a grounding fault, if the direction of the sudden change in the branch's zero-sequence voltage is consistent with the direction of the sudden change in the branch's zero-sequence current, the branch is not grounded; if the direction of the sudden change in the branch's zero-sequence voltage is opposite to the direction of the sudden change in the branch's zero-sequence current, the branch or its lower-level branch is grounded.

[0055] Specifically, taking a sampling frequency of 4000Hz as an example, the grounding characteristics of this branch can be determined according to the following formula:

[0056] C L =(di) k *(du) k ;

[0057] In the above formula: the corresponding k value is the grounding time, (di) k =i k -i k-4 ,(du) k =u k -u k-4 In the formula, i k u k The zero-sequence current and zero-sequence voltage sampled values ​​collected by the line selection unit 200 and the line selection host 100, i k-4 u k-4 This represents the sampled values ​​from the four sampling intervals preceding the corresponding sampling point. C L This is the grounding characteristic value of branch L. Then, based on branch C... L The task is to determine whether the branch grounding is normal. Specific judgment rules are as follows:

[0058] If branch C L If the value is >0, then the direction of the sudden change in the zero-sequence voltage of the branch is consistent with the direction of the sudden change in the zero-sequence current of the branch, and the grounding is normal.

[0059] If branch C L <0, and the direction of the abrupt change of the zero-sequence voltage of at least one of the subordinate branches of this branch is opposite to the direction of the abrupt change of the zero-sequence current of the branch (i.e., the direction of the abrupt change of the zero-sequence voltage of the subordinate branch C). L If <0), then the grounding of this branch is normal;

[0060] If branch C L <0, and all subordinate branches C of this branch L A value greater than 0 indicates an abnormal grounding condition in that branch.

[0061] In some embodiments of the present invention, determining the bus grounding state of the power distribution system based on the bus zero-sequence voltage includes the following steps:

[0062] The steady-state value of the zero-sequence voltage of the bus is determined using the bus zero-sequence voltage and based on the Fourier algorithm.

[0063] The bus grounding status is determined based on the steady-state value of the bus zero-sequence voltage and the preset grounding voltage judgment threshold. If the steady-state value of the bus zero-sequence voltage is higher than the grounding voltage judgment threshold, the bus grounding status is used to characterize the bus grounding abnormality. If the steady-state value of the bus zero-sequence voltage is equal to or lower than the grounding voltage judgment threshold, the bus grounding status is used to characterize the bus grounding normal.

[0064] The Fourier algorithm is used to obtain the steady-state value of the bus zero-sequence voltage. Since the steady-state value of the bus zero-sequence voltage changes when a ground fault occurs in actual engineering, it can be used to determine whether a branch grounding anomaly has occurred by comparing the steady-state value with a preset grounding voltage threshold. It should be noted that, to ensure accuracy and prevent erroneous judgments due to individual values, after the steady-state value of the bus zero-sequence voltage exceeds the grounding voltage threshold, it is continuously checked whether the steady-state value of the bus zero-sequence voltage remains above the grounding voltage threshold for a specific time period. If it remains consistently above the threshold, a bus grounding anomaly is confirmed. In some embodiments, the check is maintained for 20ms, i.e., one cycle.

[0065] In some embodiments of the present invention, the above-described low-current grounding line selection method further includes the following steps:

[0066] The fault abnormal time segment is determined based on the branch zero-sequence voltage and branch zero-sequence current. The fault abnormal time segment includes the moment when the branch zero-sequence current exceeds the preset current change threshold. The moment when the branch zero-sequence current exceeds the preset current change threshold is the moment when the branch outlet grounding occurs.

[0067] Obtain the zero-sequence voltage and zero-sequence current of each branch outlet within the fault abnormal time period, and construct a fault waveform file based on the zero-sequence voltage and zero-sequence current of each branch outlet.

[0068] When the bus grounding status is determined to be an abnormal bus grounding, a fault anomaly time segment containing this moment is identified. Simultaneously, the branch zero-sequence voltage and branch zero-sequence current of all selection units 200 within this fault anomaly time segment are transmitted to the selection host 100. The selection host 100 can then synthesize a fault waveform file based on these branch zero-sequence voltages and currents, according to the grounding time indicated by the current abrupt change. The fault waveform file displays the branch zero-sequence voltage and current information collected by all selection units 200, facilitating rapid subsequent fault analysis by the central control center. It should be noted that the frozen data typically freezes data for 60ms before and after the bus grounding anomaly is determined, i.e., freezing three cycles of data before and after. In actual engineering, the length of the frozen data can be appropriately increased according to the actual situation. Furthermore, in a low-latency environment based on 5G transmission, to ensure accurate acquisition of data within the fault anomaly time segment, the sampling buffer is designed to buffer at least 8 cycles of storage space, ensuring that the selection unit can freeze three cycles of data before and after. It should also be noted that when constructing the fault waveform file, the zero-sequence currents of all branch selection units are aligned according to the moment of abrupt change in the branch zero-sequence current (i.e., the moment of grounding). Furthermore, the relationship between the sampling buffer storage length setting and the frozen data length setting of the selection unit can be adjusted appropriately according to actual needs; it is not necessary to strictly constrain the sampling buffer to 8 cycles and the frozen data to 6 cycles.

[0069] In some embodiments of the present invention, after the faulty branch is identified, the branch can be disconnected so that the grounding of the entire wiring system can be restored to normal. After the branch is disconnected, the staff of the central control center can promptly arrange maintenance personnel to go to the corresponding branch for inspection in order to quickly troubleshoot the fault.

[0070] For branches where the grounding is determined to be normal, no further action is required. For branches where the grounding is determined to be abnormal, the switch for that branch needs to be disconnected promptly to allow the electrical equipment affecting the grounding to be removed from the power distribution network as quickly as possible. Specifically, such as... Figure 4 As shown, when conducting grounding tests at points K1 to K6, the line selection host 100 will report grounding faults in branches L1, L2, L2-2, L3-3, L2-2-4, and L3-3-1 respectively. At this time, trip commands can be sent to acquisition units S1, S2, S2-2, S3-3, S2-2-4, and S3-3-1 to disconnect the corresponding switches and clear the grounding fault.

[0071] In some embodiments of the present invention, a certain branch judgment waiting time is intervening between the sending of the grounding feature discrimination command by the line selection host 100 and the receiving of the branch grounding feature by the line selection unit 200, so as to ensure that the line selection unit 200 can complete the determination of the branch grounding feature of the corresponding branch outlet after receiving the grounding feature discrimination command. In the embodiments, the branch judgment waiting time is maintained at more than 100ms.

[0072] According to a second aspect of the present invention, a low-current grounding fault location system is applied to a fault location host 100. The fault location host 100 is communicatively connected to multiple fault location units 200. The multiple fault location units 200 are used to collect the branch zero-sequence voltage and branch zero-sequence current of multiple branch outlets in a one-to-one correspondence.

[0073] The low-current grounding fault location system includes: a busbar status acquisition unit, a busbar grounding determination unit, a grounding characteristic receiving unit, and a fault location determination unit.

[0074] Bus status acquisition unit, used to collect the zero-sequence voltage of the bus in the power distribution system;

[0075] The bus grounding determination unit is used to determine the bus grounding status of the power distribution system based on the bus zero-sequence voltage. If the bus grounding status indicates an abnormal bus grounding, it sends a grounding characteristic discrimination command to multiple line selection units. The line selection unit 200 determines the branch grounding characteristics in response to the grounding characteristic discrimination command. The branch grounding characteristics are determined by the voltage change direction of the zero-sequence voltage and the current change direction of the zero-sequence current of the corresponding line selection unit 200. Wherein, if the voltage change direction and the current change direction are the same, the branch grounding characteristics are confirmed as having the same grounding characteristic direction; if the voltage change direction and the current change direction are opposite, the branch grounding characteristics are confirmed as having opposite characteristic directions.

[0076] A grounding feature receiving unit is used to receive multiple branch grounding features sent by multiple line selection units 200;

[0077] The line selection and determination unit is used to search for the grounding characteristics of the last branch in the power distribution system based on the grounding characteristics of multiple branches and the line network topology diagram, confirm the branch outlet with the opposite characteristic direction, and determine the branch outlet where the grounding fault occurs. The line network topology diagram represents the topological connection relationship between the bus and multiple branch outlets in the power distribution system.

[0078] refer to Figures 1 to 4The line selection host 100 and multiple line selection units 200 can build a communication network based on 5G communication to ensure high bandwidth and low latency. Simultaneously, to ensure time synchronization between the line selection host 100 and the multiple line selection units 200, the line selection host 100 continuously sends time synchronization messages to each other at equal intervals. These time synchronization messages contain standard timestamps, allowing all line selection units 200 to maintain time synchronization with the line selection host 100, ensuring the accuracy of subsequent calculations and control.

[0079] After the line selection host 100 and multiple line selection units 200 establish communication, the line selection host 100 and multiple line selection units 200 all start high-speed sampling. The sampling frequency is 4000Hz, that is, there are 80 sampling points in each cycle.

[0080] When a ground fault occurs, because the entire power distribution system is interconnected, a ground fault will be detected at the busbar regardless of which branch experiences the fault. The fault location unit 100 is installed at the substation busbar, allowing it to directly collect the zero-sequence voltage of the power distribution system busbar and use this voltage to determine the busbar grounding status. Furthermore, when the busbar grounding status indicates an abnormal grounding condition, a grounding characteristic discrimination command will be generated.

[0081] Here is a brief description of the process by which the busbar grounding determination unit determines the faulty branch after the busbar grounding determination unit identifies the busbar grounding anomaly. After confirming the grounding anomaly, the busbar grounding determination unit generates a grounding characteristic discrimination command and sends it to each selection unit 200 via the 5G network. Upon receiving the grounding characteristic discrimination command, each selection unit 200 determines whether the zero-sequence voltage and zero-sequence current of the branch it collected during the period when the selection host 100 judged the grounding fault occurred show any grounding anomalies. Based on the judgment result, it generates branch grounding characteristics and transmits these characteristics to the selection host 100. After receiving the branch grounding characteristics sent by all selection units 200, the selection host 100, in conjunction with the line network topology diagram, searches for the branch grounding characteristics at the very end of the power distribution system and identifies it as the branch outlet with the opposite characteristic direction, thus determining the specific branch where the grounding fault occurred. To enable the fault location detection by the fault location host 100 and fault location unit 200, a sampling buffer is set up in both the host 100 and the unit 200 for storing zero-sequence current and zero-sequence voltage data. Once the fault location host 100 determines that a bus grounding anomaly has occurred, it can freeze the data in the sampling buffers of each fault location unit 200, and then use the frozen data to complete the branch grounding characteristic detection. It should also be noted that the line network topology diagram shows the connection relationships between various levels of power equipment in the wiring system. Furthermore, by establishing a correspondence between each fault location unit 200 and each branch in the line network topology diagram, the specific fault location can be quickly determined after a grounding fault occurs.

[0082] The low-current grounding fault location system according to an embodiment of the present invention obtains the busbar zero-sequence voltage through the busbar status acquisition unit, which facilitates the busbar grounding determination unit to quickly determine whether a grounding fault exists. Furthermore, because fault location units 200 are installed at the outlets of each branch of the power distribution system, each fault location unit 200 can quickly determine whether a grounding fault has occurred when the fault location determination unit determines that a grounding fault has occurred. Since there is a unique correspondence between the branch outlet and the fault location unit 200, determining that the fault is in the fault location unit 200 essentially determines the specific fault location. Compared with traditional methods, the low-current grounding fault location system of this embodiment can achieve segmental determination of the grounding fault location and assist in preliminary automatic fault elimination, possessing better safety and practicality, and is suitable for industrial-scale promotion.

[0083] It should be noted that a grounding anomaly on the busbar may be caused by a grounding anomaly in a branch, and a grounding fault in a higher-level branch may be caused by a grounding anomaly in a lower-level branch. Therefore, identifying branch grounding anomalies is fundamental to determining the specific location of a grounding fault. At the moment of a grounding fault, if the direction of the sudden change in the branch's zero-sequence voltage is consistent with the direction of the sudden change in the branch's zero-sequence current, the branch is not grounded; if the direction of the sudden change in the branch's zero-sequence voltage is opposite to the direction of the sudden change in the branch's zero-sequence current, the branch or its lower-level branch is grounded.

[0084] Specifically, taking a sampling frequency of 4000Hz as an example, the grounding characteristics of this branch can be determined according to the following formula:

[0085] C L =(di) k *(du) k ;

[0086] In the above formula: the corresponding k value is the grounding time, (di) k =i k -i k-4 ,(du) k =u k -u k-4 In the formula, i k u k The zero-sequence current and zero-sequence voltage sampled values ​​collected by the line selection unit 200 and the line selection host 100, i k-4 u k-4 This represents the sampled values ​​from the four sampling intervals preceding the corresponding sampling point. C L This is the grounding characteristic value of branch L. Then, based on branch C... L The task is to determine whether the branch grounding is normal. Specific judgment rules are as follows:

[0087] If branch C L If the value is >0, then the direction of the sudden change in the zero-sequence voltage of the branch is consistent with the direction of the sudden change in the zero-sequence current of the branch, and the grounding is normal.

[0088] If branch C L <0, and the direction of the abrupt change of the zero-sequence voltage of at least one of the subordinate branches of this branch is opposite to the direction of the abrupt change of the zero-sequence current of the branch (i.e., the direction of the abrupt change of the zero-sequence voltage of the subordinate branch C). L If <0), then the grounding of this branch is normal;

[0089] If branch C L <0, and all subordinate branches C of this branch L A value greater than 0 indicates an abnormal grounding condition in that branch.

[0090] In some embodiments of the present invention, the above-mentioned low-current grounding fault location system further includes: an abnormal time determination unit and a waveform recording information generation unit;

[0091] The abnormal time determination unit is used to determine the fault abnormal time segment based on the branch zero-sequence voltage and the branch zero-sequence current. The fault abnormal time segment includes the moment when the branch zero-sequence current exceeds the preset current change threshold value. The moment when the branch zero-sequence current exceeds the preset current change threshold value is the moment when the branch outlet grounding occurs.

[0092] The waveform recording information generation unit is used to obtain multiple branch zero-sequence voltages and multiple branch zero-sequence currents corresponding to each branch outlet within the fault abnormal time segment, and to construct a fault waveform recording file based on the multiple branch zero-sequence voltages and multiple branch zero-sequence currents corresponding to each branch outlet.

[0093] When the bus grounding status is determined to be an abnormal bus grounding, the abnormal time determination unit will identify a fault abnormal time segment containing this moment. Simultaneously, the waveform information generation unit will acquire the frozen branch zero-sequence voltage and branch zero-sequence current from all line selection units 200 within this fault abnormal time segment. This allows the waveform information generation unit to synthesize a fault waveform file based on these branch zero-sequence voltages and currents. The fault waveform file will display the branch zero-sequence voltage and current information collected by all line selection units 200, facilitating rapid subsequent fault analysis by the central control center. It should be noted that the frozen data is the data frozen 60ms before and after the bus grounding abnormality is determined, i.e., three cycles of data before and after freezing. In actual engineering, the length of the frozen data can be appropriately increased according to the actual duration. It should also be noted that when constructing the fault waveform file, the branch zero-sequence currents collected by all line selection units will be aligned according to the moment of abrupt change in branch zero-sequence current. Furthermore, the relationship between the setting of the sampling buffer storage length and the setting of the frozen data length of the line selection unit can be adjusted appropriately according to actual needs, and it is not necessary to strictly constrain the sampling buffer to 8 cycles and the frozen data to 6 cycles.

[0094] A low-current grounding fault location device according to a third aspect embodiment of the invention includes:

[0095] Multiple line selection units 200 are used to collect the branch zero-sequence voltage and branch zero-sequence current of multiple branch outlets one by one;

[0096] The line selection host 100 is communicatively connected to multiple line selection units 200. The line selection host 100 is used to perform the low-current grounding line selection method described above.

[0097] refer to Figures 1 to 3The line selection host 100 and multiple line selection units 200 can build a communication network based on 5G communication. By utilizing the high bandwidth and low latency of 5G, the time synchronization between the line selection host 100 and multiple line selection units 200 can be achieved. The line selection host 100 continuously sends time synchronization messages to each line selection host 100 at equal intervals. The time synchronization messages have standard timestamps, so that all line selection units 200 can keep time synchronized with the line selection host 100, ensuring the accuracy of subsequent calculations and control.

[0098] After the line selection host 100 and multiple line selection units 200 establish communication, the line selection host 100 and multiple line selection units 200 all begin high-speed sampling at a sampling frequency of 4000Hz, that is, there are 80 sampling points in each cycle.

[0099] When a ground fault occurs, because the entire power distribution system is interconnected, a ground fault will be detected at the busbar regardless of which branch experiences the fault. The fault location unit 100 is located at the substation busbar, allowing it to directly collect the busbar zero-sequence voltage of the power distribution system and use this voltage to determine the busbar grounding status. Furthermore, when the busbar grounding status indicates an abnormal grounding condition, the faulty branch will be identified. The specific process for determining the faulty branch has been described in the first aspect embodiment and will not be repeated here.

[0100] According to an embodiment of the present invention, the low-current ground fault location device obtains the bus zero-sequence voltage through the fault location host 100, which facilitates rapid determination of whether a ground fault exists. Furthermore, because fault location units 200 are installed at the outlets of each branch in the power distribution system, when the fault location host 100 determines that a ground fault has occurred, each fault location unit 200 can quickly determine whether its own fault has occurred. Since there is a unique correspondence between the branch outlet and the fault location unit 200, determining that the fault is in the fault location unit 200 essentially determines the specific fault location. Compared to traditional methods, the low-current ground fault location device of this embodiment can determine the location segment of a ground fault and assist in preliminary automatic fault elimination, possessing better safety and practicality, and is suitable for industrial-scale promotion.

[0101] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0102] Although the embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to the above embodiments. Those skilled in the art will understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for selecting ground faults with low current, applied to a fault selection host, characterized in that, The line selection host is communicatively connected to multiple line selection units, and the multiple line selection units are used to collect the branch zero-sequence voltage and branch zero-sequence current of multiple branch outlets in a one-to-one correspondence; the line selection host and the multiple line selection units establish a communication network based on 5G communication. The method for selecting grounding lines with low current includes the following steps: Collect the zero-sequence voltage of the power distribution system's busbars; The bus grounding status of the power distribution system is determined based on the bus zero-sequence voltage. If the bus grounding status indicates an abnormal bus grounding, a grounding feature discrimination command is sent to multiple selection units. The selection unit responds to the grounding feature discrimination command to determine the branch grounding feature. The branch grounding feature is determined by the corresponding selection unit based on the voltage change direction of the corresponding branch zero-sequence voltage and the current change direction of the branch zero-sequence current. Wherein, if the voltage change direction and the current change direction are the same, the branch grounding feature is confirmed to have the same grounding feature direction; if the voltage change direction and the current change direction are opposite, the branch grounding feature is confirmed to have opposite feature directions. Receive multiple branch grounding characteristics sent one-to-one by the multiple line selection units; Based on the grounding characteristics of multiple branches and the line network topology diagram, the grounding characteristics of the branch at the very end of the power distribution system are identified as the branch outlet with opposite characteristic directions, and the branch outlet where the grounding fault occurs is determined. The line network topology diagram represents the topological connection relationship between the busbar and multiple branch outlets in the power distribution system. The branch grounding characteristic is determined by the grounding characteristic value, which is constrained by the following formula: ； In the formula, the corresponding k value is the grounding time, (di) k =i k -i k-4 ,(du) k =u k -u k-4 In the formula, i k u k The zero-sequence current and zero-sequence voltage sampled values ​​collected by the line selection unit and the line selection host, i k-4 u k-4 C represents the sampled values ​​from the four sampling intervals preceding the corresponding sampling point. L It is the grounding characteristic value of branch L.

2. The method for selecting grounding lines with low current according to claim 1, characterized in that, Determining the bus grounding status of the power distribution system based on the bus zero-sequence voltage includes the following steps: The steady-state value of the bus zero-sequence voltage is determined using the aforementioned bus zero-sequence voltage and based on the Fourier algorithm. The bus grounding status is determined based on the steady-state value of the bus zero-sequence voltage and the preset grounding voltage determination threshold. If the steady-state value of the bus zero-sequence voltage is higher than the grounding voltage determination threshold, the bus grounding status is used to characterize an abnormal bus grounding. If the steady-state value of the bus zero-sequence voltage is equal to or lower than the grounding voltage determination threshold, the bus grounding status is used to characterize a normal bus grounding.

3. The method for selecting grounding lines with low current according to claim 2, characterized in that, It also includes the following steps: The fault abnormal time segment is determined based on the branch zero-sequence voltage and the branch zero-sequence current. The fault abnormal time segment includes the moment when the branch zero-sequence current exceeds a preset current change threshold. The moment when the branch zero-sequence current exceeds the preset current change threshold is the moment when the branch outlet grounding occurs. Obtain multiple zero-sequence voltages and multiple zero-sequence currents of each branch outlet within the fault abnormal time period, and construct a fault waveform file based on the multiple zero-sequence voltages and multiple zero-sequence currents of each branch outlet.

4. A low-current grounding fault location system, applied to a fault location host, characterized in that, The line selection host is communicatively connected to multiple line selection units, and the multiple line selection units are used to collect the branch zero-sequence voltage and branch zero-sequence current of multiple branch outlets in a one-to-one correspondence. The line selection host and the multiple line selection units establish a communication network based on 5G communication. The low-current grounding fault location system includes: Bus status acquisition unit, used to collect the zero-sequence voltage of the bus in the power distribution system; A bus grounding determination unit is used to determine the bus grounding status of the power distribution system based on the bus zero-sequence voltage. If the bus grounding status indicates a bus grounding anomaly, a grounding feature discrimination command is sent to multiple line selection units. The line selection unit determines the branch grounding feature in response to the grounding feature discrimination command. The branch grounding feature is determined by the corresponding line selection unit based on the voltage change direction of the corresponding branch zero-sequence voltage and the current change direction of the branch zero-sequence current. Wherein, if the voltage change direction and the current change direction are the same, the branch grounding feature is confirmed to have the same grounding feature direction; if the voltage change direction and the current change direction are opposite, the branch grounding feature is confirmed to have opposite feature directions. A grounding feature receiving unit is used to receive multiple branch grounding features sent one-to-one by the multiple line selection units; The line selection and determination unit is used to search for the grounding characteristics of the branch at the end of the power distribution system based on the grounding characteristics of multiple branches and the line network topology diagram, confirm the branch outlet with opposite characteristic directions, and determine the branch outlet where a grounding fault has occurred. The line network topology diagram represents the topological connection relationship between the bus and multiple branch outlets in the power distribution system. The branch grounding characteristic is determined by the grounding characteristic value, which is constrained by the following formula: ； In the formula, the corresponding k value is the grounding time, (di) k =i k -i k-4 ,(du) k =u k -u k-4 In the formula, i k u k The zero-sequence current and zero-sequence voltage sampled values ​​collected by the line selection unit and the line selection host, i k-4 u k-4 C represents the sampled values ​​from the four sampling intervals preceding the corresponding sampling point. L It is the grounding characteristic value of branch L.

5. The low-current grounding fault location system according to claim 4, characterized in that, Also includes: An abnormal time determination unit is used to determine the fault abnormal time segment based on the branch zero-sequence voltage and the branch zero-sequence current. The fault abnormal time segment includes the moment when the branch zero-sequence current exceeds a preset current change threshold value. The moment when the branch zero-sequence current exceeds the preset current change threshold value is the moment when the branch outlet grounding occurs. The waveform recording information generation unit is used to acquire multiple branch zero-sequence voltages and multiple branch zero-sequence currents corresponding to each branch outlet within the fault abnormal time period, and to construct a fault waveform recording file based on the multiple branch zero-sequence voltages and multiple branch zero-sequence currents corresponding to each branch outlet.

6. A low-current grounding fault location device, characterized in that, include: Multiple line selection units are used to collect the branch zero-sequence voltage and branch zero-sequence current of multiple branch outlets one by one; The line selection host is communicatively connected to multiple line selection units, and the line selection host is used to perform the low-current grounding line selection method as described in any one of claims 1 to 3.

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