A precise hierarchical protection method for distribution network lines

Abstract

The present invention belongs to the field of power system control technology, and is aimed at the problem that the distribution protection in the prior art involves too many parameters, and the distribution network cannot be adjusted to a safe working state in time. To this end, the present invention includes a method for accurate hierarchical protection of distribution network lines, which constructs a hierarchical module of the target distribution network object through the comprehensive data information of the system, and divides the hierarchical module of the target distribution network object into three sub-modules: local, station domain and regional. After the fault is detected, the location of the fault is analyzed, and the impact value generated by the DG grid-connected access system is added. According to the fault situation, a corresponding sub-module is selected to calculate the corresponding adaptive current setting value, and a protection response is executed in the corresponding sub-module based on the calculated adaptive current setting value. The present invention is applied to the latest distribution system containing DG. The access of distributed power sources has greatly changed the system structure of the traditional distribution network, and the distribution network is protected quickly and effectively.

Description

Technical Field

[0001] The present invention belongs to the technical field of power control systems, and in particular relates to a method for hierarchical protection of precise distribution network lines. Background Art

[0002] The distribution network is the link directly facing users in the power system, including overhead lines, cables, towers, distribution transformers, reactive power compensation devices, disconnectors, circuit breakers and other equipment. Its main function is to distribute the electric energy transmitted by the transmission network to each user. There are many shortcomings in the distribution network in the prior art. In terms of grid structure, some grids are not flexible enough, the line layout in old urban areas or remote areas is unreasonable, there are few connecting lines, the ability to cope with emergencies such as load changes and equipment failures is poor, the power supply reliability is easily affected, the power outage range is easy to expand and the power supply restoration time is long, and there is also the problem of too long power supply radius, especially in rural and remote mountainous areas, which will reduce the voltage at the end of the line, reduce the power quality, affect the user's electricity consumption and increase line losses. In terms of equipment, the quality of equipment is uneven, the old equipment has a long operating life, the performance is reduced, and the failure occurs frequently. For example, transformers and circuit breakers have insulation aging and poor contact problems, and the number of equipment is large and the distribution is wide, which makes maintenance difficult and costly. Outdoor equipment is easily damaged by the natural environment, and it is difficult to detect and repair hidden faults. In terms of automation and intelligence levels, the overall degree of automation is low, and some areas still rely on manual operations. The coverage of automated monitoring and control equipment is limited, and real-time monitoring and remote control are impossible, which affects the timeliness of fault handling, operational efficiency and reliability. Intelligent applications are also insufficient, and the application of technologies such as big data, cloud computing, and artificial intelligence is still in its early stages. It is difficult to fully tap the value of data to provide support for the optimized operation and management of distribution networks.

[0003] The hierarchical protection of distribution network lines is composed of three sub-modules: local, station and regional. First, the local current protection is used to handle the fault, and then the intelligent terminal unit STU and the protection unit cooperate to establish an information set. Through the comprehensive judgment of the master station and regional protection, the newly connected non-fault area lines are adaptively adjusted to form a complete local-station-regional hierarchical protection. In this regard, the applicant has also applied for an invention patent with patent number 20231030122827451, "A hierarchical protection method for distribution network lines aimed at improving power supply reliability", which records a hierarchical protection method for distribution network lines aimed at improving power supply reliability, solving the shortcomings of the prior art, including: setting a hierarchical protection construction strategy, the construction strategy includes three layers of sub-strategies: on-site protection strategy, station protection strategy and regional protection strategy; setting a specific protection plan for each sub-strategy, the on-site protection plan uses multi-level switches for protection settings, mainly including outgoing lines, sections, branches, user distribution transformers and DG branch switches, which divide the distribution network lines into different protection areas; the station protection plan sets up independent transformers and transformer outgoing line switch protection; the regional protection plan relies on distribution components and a complete network system, so that the protection and distribution automation systems cooperate with each other, and use the line information collected in the network for analysis and decision-making.

[0004] This technical solution has achieved very good technical results, but in order to improve the power supply reliability of the distribution network, it is necessary not only to coordinate the multi-level protection of the line switch, but also to coordinate the line protection with the feeder automation system. Therefore, the cumbersome calculation method and data acquisition method may lead to slow response speed and increase the deviation of the calculation results. Summary of the invention

[0005] The purpose of the present invention is to improve the power supply reliability of the distribution network line in the existing technology. It is not only necessary to coordinate the multi-level protection of the line switch, but also to coordinate the line protection with the feeder automation system. Therefore, it is possible that the response speed is slow due to the cumbersome calculation method and data acquisition method, and the deviation of the calculation result is increased. To this end, the present invention includes a method for hierarchical protection of precise distribution network lines, a distribution system containing DG is selected as the target distribution network object, a hierarchical module of the target distribution network object is constructed through the comprehensive data information of the system, and the hierarchical module of the target distribution network object is divided into three sub-modules: local, station domain and regional. After the fault is detected, the location of the fault is analyzed, and the impact value generated by the DG grid connection system is added. According to the fault situation, a corresponding sub-module is selected to calculate the corresponding adaptive current setting value, and the protection response is executed in the corresponding sub-module according to the calculated adaptive current setting value.

[0006] The processing modes of the local, station and regional submodules are completely different. The local level protection is mainly configured around the protected object. By establishing the main and backup protection schemes for the protected object, a local protection strategy that does not rely on communication is implemented. In the 10kV distribution network, the main protected objects are branch lines at all levels, and the corresponding protection scheme is a three-stage overcurrent protection.

[0007] The establishment of station-level protection can realize the information integration of each substation and its internal parts. Through the interface of multiple digital transmission channels, the electrical quantity and switch information sent from the local level are received in real time, and the received information is transmitted to the regional decision-making unit to establish a database architecture based on the object data model. Therefore, station-level protection not only needs to establish a real-time database design, but also serves as an information transmission medium for local protection and regional protection.

[0008] Station protection is the basis for regional protection. When the regional protection receives the global information of each substation, its corresponding protection module can determine the operation mode of the entire system, the topological structure of network changes, the fault type of each level of line and the change of load area. Regional protection uses the information collected by the entire network to make comprehensive decisions and realize regional protection control.

[0009] Preferably, the adaptive current setting value calculation includes adaptive current segment I setting value calculation and adaptive current segment II setting value calculation.

[0010] Preferably, when a three-phase short-circuit fault occurs in the line, since the fault is a symmetrical short-circuit and the DG connected to the system can only output the positive sequence current component, the three-phase short-circuit current generated in the entire system is also symmetrical; the corresponding protection position current I segment setting value is:

[0011]

[0012] Where: U3 is the measured value of the phase voltage of protection 3 during fault, Z CD is the impedance corresponding to line CD, α is the line protection range coefficient, The superscript (3) indicates a three-phase short-circuit fault.

[0013] Preferably, when a two-phase metallic short circuit fault occurs in the line, phase A is taken as the non-fault phase, and the symmetrical component method can be applied to analyze and calculate the asymmetrical fault. At this time, the fault current only exists in the positive sequence and negative sequence networks; the corresponding protection position current I segment setting value is:

[0014]

[0015] Z Δ =Z s +Z AB +Z BC

[0016] Where: U 3(1) is the positive sequence voltage value of protection 3 when a fault occurs, The superscript (2) indicates a two-phase short circuit fault, U 3(1) The subscript (1) of represents the positive sequence component.

[0017] Preferably, when the protection line is full length, the setting value of the current section II of the corresponding protection position is set to:

[0018]

[0019] The superscript (3) indicates a three-phase short circuit fault. U3 is the measured value of the phase voltage of protection 3 during the fault. Z CD is the impedance corresponding to line CD, Z DE is the impedance corresponding to line DE, and α is the line protection range coefficient.

[0020] Preferably, when a two-phase short circuit fault occurs in the line, the setting value of the current stage II of the corresponding protection position is set to:

[0021]

[0022] Where: U 3(1) is the positive sequence voltage value of protection 3 when a fault occurs, The superscript (2) indicates a two-phase short-circuit fault, Z CD is the impedance corresponding to line CD, Z DE is the impedance corresponding to line DE, and α is the line protection range coefficient.

[0023] Preferably, STU is installed in the distribution line in units of switches, which are responsible for monitoring the current, voltage and switch status information at the switch. Adjacent STU units are interconnected through optical fiber Ethernet, and the local detection information is transmitted to the station area and regional master station in real time.

[0024] Preferably, the on-site protection sets two sets of protection settings, A and B, in each protection unit. During normal operation, the setting A or B is selected according to the clear upstream and downstream relationship. When the power supply of the original network system changes, the real-time information of each substation is transmitted to the station area protection by STU, and the regional protection makes a comprehensive decision to select and determine the protection setting after reconstruction of the non-fault area in the network. When the protection measurement value after monitoring each line fault is greater than the set value, and the maximum branch current on both sides of the line is located on the same line, the protection action will cut off the fault.

[0025] The present invention also includes an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps of the method for hierarchical protection of precise distribution network lines are implemented.

[0026] The present invention is applied in the latest power distribution system containing DG. The access of distributed power sources has greatly changed the system structure of the traditional distribution network. The development of intelligent feeder automation has brought technical support to the protection of distribution networks. Therefore, in combination with the construction method of hierarchical protection described in the present invention, in-depth exploration of the protection implementation scheme of the distribution network containing distributed power sources is the basis for establishing a new type of protection for intelligent distribution networks.

[0027] The above invention content is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented according to the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Other features, objects and advantages of the present invention will become more apparent by reading the detailed description of non-limiting embodiments made with reference to the following drawings. The drawings are only for the purpose of illustrating preferred embodiments and are not to be considered as limiting the present invention. Also, the same reference symbols are used throughout the drawings to represent the same parts.

[0029] Figure 1 It is a schematic diagram of a strategy for constructing hierarchical protection in a method for hierarchical protection of precise distribution network lines provided in an embodiment of the present invention.

[0030] Figure 2 It is a schematic diagram of the power flow direction of the distribution network where the fault point is located downstream of the DG in the precise hierarchical protection method for distribution network lines provided by an embodiment of the present invention.

[0031] Figure 3 It is a composite sequence network diagram of two-phase short circuit in the precise hierarchical protection method for distribution network lines provided in an embodiment of the present invention.

[0032] Figure 4 It is a flow chart of an on-site protection method of the precise hierarchical protection method for distribution network lines provided in an embodiment of the present invention.

[0033] Figure 5 It is a schematic diagram of the distribution network structure in the precise distribution network line hierarchical protection method provided in an embodiment of the present invention.

[0034] Figure 6 It is a schematic diagram of a flow chart of an on-site protection method in a precise hierarchical protection method for distribution network lines provided in an embodiment of the present invention.

[0035] Figure 7 It is a schematic diagram of a distribution network with a photovoltaic power station in a specific scenario in the precise hierarchical protection method for distribution network lines provided in an embodiment of the present invention.

[0036] Figure 8 It is a schematic diagram of current simulation results of different fault types in the precise hierarchical protection method for distribution network lines provided in an embodiment of the present invention.

[0037] Fig. 9 It is a schematic diagram of current simulation results after line adaptive adjustment in the precise hierarchical protection method for distribution network lines provided in an embodiment of the present invention.

[0038] Fig.10 It is a schematic diagram of the simulation results of the current difference of different DG capacities in the precise hierarchical protection method for distribution network lines provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0039] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific implementation method described herein is only an optimal embodiment of the present invention, which is only used to explain the present invention and does not limit the scope of protection of the present invention. All other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0040] Before discussing the exemplary embodiments in more detail, it should be mentioned that some exemplary embodiments are described as processes or methods depicted as flow charts. Although the flow charts describe the operations (or steps) as sequential processes, many of the operations (or steps) therein can be implemented in parallel, concurrently, or simultaneously. In addition, the order of the operations can be rearranged. A process can be terminated when its operations are completed, but can also have additional steps not included in the accompanying drawings; a process can correspond to a method, function, procedure, subroutine, subprogram, etc.

[0041] The terms "first", "second", "third", "fourth", etc. (if any) in the specification of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. It should also be understood that in various embodiments of the present invention, the size of the sequence number of each process does not mean the order of execution, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present invention.

[0042] It should be understood that, in the present invention, "multiple" means two or more. "And / or" is only a variable relationship that describes associated objects, indicating that three relationships may exist. It should be understood that, in the present invention, "B corresponding to A", "B corresponding to A", "A corresponds to B" or "B corresponds to A" means that B is associated with A, and B can be determined based on A. Determining B based on A does not mean determining B based only on A, but B can also be determined based on A and / or other information. The match between A and B means that the similarity between A and B is greater than or equal to a preset threshold.

[0043] It can be seen that in order to achieve effective distribution network line protection, the current optimal protection scheme includes the following steps:

[0044] (1) First, the protection start-up criterion is established by using the current mutation in the local layer protection. The local protection scheme uses multi-level switches for protection settings, mainly including outgoing line, section, branch, user distribution transformer and DG branch switches. These switches divide the distribution network lines into different protection areas; the station protection scheme sets up independent transformers and transformer outgoing line switch protection; then the measured fault current is converted into positive and negative zero-sequence components for the judgment of fault symmetry, and then the local level adaptive current protection is performed according to different fault types.

[0045] (2) For line protection in non-fault areas, the intelligent terminal unit STU is used to effectively cooperate with each protection unit to establish information interaction with the station and regional protection. Then, as the basis for the implementation of regional layer protection, the station layer protection will receive the information sent from the local level and transmit it to the regional decision-making unit, while forming a database architecture.

[0046] (3) Finally, the regional layer protection reuses the comprehensive information between stations to make decision analysis on the faulty line and realizes the effective isolation of the faulty area through the overall coordination of hierarchical protection.

[0047] The key point is that in order to cover the overall performance, the overall distribution network needs to be divided into different protection areas when calculating faults, and the coordination relationship between the protection areas should be comprehensively considered. For example, in the technical solution recorded in the background technology, the protection of the outgoing line switch section I should be coordinated with the protection of the upper main transformer section II. From an overall perspective, such a technical solution must be more accurate and comprehensive. However, in actual use, it is found that there are still some disadvantages. For example, sometimes the distribution network structure is more complex, and more protection areas are allocated, which leads to inaccurate calculation of faults. And the corresponding response time is too long.

[0048] In the present invention, by grasping the key nodes for abnormal calculation, the response time of fault analysis can be significantly reduced, and in particular, too many influencing factors that reduce the effect of fault analysis can be avoided.

[0049] Some abbreviations used in the present invention are explained here:

[0050] DG in this invention is the abbreviation of Distributed Generation, which means "distributed power source", specifically refers to a small-scale power generation device distributed near the load and connected to the distribution network nearby. It includes many types, such as micro gas turbines, fuel cells, solar photovoltaic cells, wind power generation and energy storage devices.

[0051] The STU in the distribution network described in the present invention is the abbreviation of Smart Terminal Unit, which means "intelligent terminal unit". It is a key device in the distribution network automation system, which can collect various electrical quantity data in the distribution network in real time, such as current, voltage, power, etc., as well as switch status and other information. STU has powerful communication capabilities, can exchange information with the master station and other intelligent terminals, upload the collected data to the master station, and receive control instructions from the master station. When a fault occurs, STU can quickly detect and identify the fault, and through collaborative work with other intelligent terminals, it can achieve fault location, isolate the faulty section, and restore power supply to the non-faulty section.

[0052] The present invention includes a method for accurate hierarchical protection of distribution network lines, wherein a distribution system containing DG is selected as a target distribution network object, and a hierarchical module of the target distribution network object is constructed through the comprehensive data information of the system, such as Figure 1 As shown, the present invention divides the hierarchical module of the target distribution network object into three sub-modules: local, station domain and regional. After the fault is detected, the location of the fault is analyzed, and the impact value generated by the DG grid-connected access system is added. According to the fault situation, a corresponding sub-module is selected to calculate the corresponding adaptive current setting value, and the protection response is executed in the corresponding sub-module according to the calculated adaptive current setting value. In terms of protection setting principles, with the continuous development of computer network technology, the application of adaptive protection in protection scheme setting has been promoted. Adaptive current protection can rely on the powerful computing power and memory capacity of the computer system to monitor the operating status of the power system in real time, and can complete the protection of protection setting measurement online.

[0053] In the traditional adaptive current protection setting process, the impact of DG grid connection to the system is not considered. However, DG will produce auxiliary or external absorption effects when a fault occurs, and the existing equivalent impedance calculation method cannot obtain the real-time changing fault current value. In this regard, the present invention relates to an improved adaptive current I stage setting value:

[0054] Condition 1: When a three-phase short-circuit fault occurs in the line, since the fault is a symmetrical short-circuit and the DG connected to the system can only output the positive sequence current component, the three-phase short-circuit current generated in the entire system is also symmetrical.

[0055] Due to the different lengths of the protected lines in the distribution network, when setting the traditional protection current value, if it is still set according to the full length of the line, the protection range of each section will be reduced to a certain extent. In order to enable the current section I to protect this section of the line as much as possible, the line protection range coefficient is introduced during the protection setting. Figure 2 Taking the three-phase short circuit fault of the middle line CD as an example, the setting value of stage I at protection 3 is:

[0056]

[0057] Where: U3 is the measured value of the phase voltage of protection 3 during fault, Z CD is the impedance corresponding to line CD, and α is the line protection range coefficient.

[0058] It should be noted that in the definition of protection, "three-phase short-circuit fault, two-phase short-circuit fault" are represented by "(3)", (2)" respectively.

[0059] Taking into account the reliability of line protection and the accuracy of transformer measuring elements, the line protection range factor can be taken as 0.8.

[0060] Condition 2: After the DG is connected to the grid, the system potential will change with the operation mode, so the fault current in the minimum operation mode is no longer the fault current in the maximum operation mode. If the setting calculation is still performed in the original way, the protection range will change significantly.

[0061] by Figure 2 Taking the two-phase metallic short circuit fault in the middle line CD as an example, phase A is regarded as the non-fault phase, and its corresponding composite sequence network diagram is shown in Figure 3. The two-phase short circuit in the line belongs to the asymmetric fault type. According to the content of the transient analysis of the power system, the symmetrical component method can be used to analyze and calculate the asymmetric fault. Since there is no grounding in the two-phase short circuit fault, the fault current only exists in the positive sequence and negative sequence networks.

[0062] according to Figure 3 In the composite sequence network diagram of two-phase short circuit, the setting value of the adaptive current stage I of protection 3 is:

[0063]

[0064] Z Δ =Z s +Z AB +Z BC

[0065] Where: U 3(1) It is the positive sequence voltage value of protection 3 when a fault occurs.

[0066] The present invention also includes an improved adaptive current II stage setting value:

[0067] Condition 3: Since the protection range of the adaptive current protection section I does not reach the full length of the line, the protection section I cannot be used alone as the main line protection. Therefore, in order to protect the full length of the line, the adaptive protection current section II is set. Figure 4 Shown

[0068] according to Figure 4 The protection range diagram shown in the figure shows that the setting value of section II at protection 3 is:

[0069]

[0070] In order to ensure the selectivity of current protection, the stage II protection of protection 3 needs to set a time difference Δt, which is generally taken as 0.5s.

[0071] Condition 4: Two-phase short circuit fault is similar to three-phase short circuit fault. The setting principle of current stage II protection should consider the impedance of the current line and the next adjacent line, and the protection range extends to the next line stage I protection range. Therefore, when a two-phase short circuit fault occurs on the line, the setting value of stage II of protection 3 is set to:

[0072]

[0073] The access of distributed power sources has greatly changed the system structure of traditional distribution networks. The development of intelligent feeder automation has brought technical support to the protection of distribution networks. Therefore, combining the construction method of hierarchical protection and deeply exploring the protection implementation scheme of distribution networks containing distributed power sources is the basis for establishing new protection for intelligent distribution networks.

[0074] According to the construction method of hierarchical protection, the decision information obtained by the station domain and regional protection comes from the local protection. STU is installed in the distribution line in units of switches, which is responsible for monitoring the current, voltage and switch status information at the switch. Adjacent STU units are interconnected through optical fiber Ethernet to transmit the local detection information to the station domain and regional master station in real time. Figure 5 The figure shows the schematic diagram of the distribution network structure including DG, where S1 and S2 represent the power supplies on both sides. With the tie switch 00 as the boundary, the positive direction of the current is defined from the power supply side to the load side. During normal operation, the power supplies on each side supply power to the corresponding load, and the tie switch 00 is in the disconnected state.

[0075] When formulating a protection plan, it is necessary to consider the upstream and downstream relationships of the switches on the same side. However, when a power supply on one side stops operating due to a fault, the entire network structure will change. If the fault judgment continues according to the original setting, it will affect the normal operation of the protection. Figure 5As shown, a permanent fault occurs on line AB. The protection operates normally, causing switch 11 to disconnect and isolate the fault. The system will order the tie switch to close, and the non-fault area will be powered by power supply S2. At this time, the upstream and downstream relationship of the line has changed, and switch 12 has become the downstream switch of switch 22. If the protection setting is not changed accordingly, when the fault occurs again, the line cannot be protected normally.

[0076] When the fault point f is located downstream of the DG, since the fault area can be regarded as a single power radiation area, no directional element is required in this area, and the fault can be removed by using adaptive current protection based on local information. When the fault point f is located upstream of the DG or in an adjacent line, the protection upstream of the DG may malfunction. Since the current of the fault branch is significantly greater than the current of the non-fault branch at the same node, when the maximum branch currents on both sides are located in the same line, it can be judged that the fault is located inside the line, and the protection action trips the line circuit breaker to remove the fault.

[0077] Therefore, in order to cope with changes in network structure, it is necessary to adaptively switch the protection settings. The local protection sets two sets of protection settings, A and B, in each protection unit. During normal operation, the setting A or B is selected according to the clear upstream and downstream relationship. When the power supply of the original network system changes, the real-time information of each substation transmitted to the station area protection by STU is used, and the regional protection makes a comprehensive decision to select and determine the protection setting after reconstruction of the non-fault area in the network. When the protection measurement value after monitoring each line fault is greater than the set value, and the maximum branch current on both sides of the line is on the same line, the protection action will cut off the fault. Among them, the flow chart of the local main protection method is as follows: Figure 6 shown.

[0078] The present invention selects the distribution network of a 10kV area in Taizhou City containing the Yilida photovoltaic power station as the basic data, and builds a simulation model in Simulink according to the actual network parameters. Figure 7 shown.

[0079] (1) Analysis of protection action under different fault types

[0080] When the fault point is located within the protection range of the switch P5140Ⅰ of Liulin P167 line, and the proportion of the total length of the line β (0<β<1) is 0.3, 0.6 and 0.9, different fault types are assumed, and the corresponding simulation results are as follows: Figure 8 By comparison Figure 8 The current simulation results of different fault types show that when different fault types occur at the same fault location, the short-circuit current of a three-phase short circuit is the largest, and the short-circuit current of a two-phase short circuit is the smallest. At the same time, as the proportion of the fault point in the protected line increases, the setting value set at the protection installation increases, and the protection measurement value shows a decreasing trend.

[0081] In addition, when the photovoltaic power station in the line is off-grid, since the protection measurement value is less than the measurement value of the DG grid-connected operation, the DG is connected to the grid in the power supply state. When different fault types occur at different locations on the line, the measurement values ​​at the protection installation are all greater than the protection setting value, and the protection can operate reliably. Therefore, it can be explained that the hierarchical protection scheme proposed in this paper can still maintain grid-connected operation under the support of the low-voltage ride-through operation capability of DG. Although DG has an increasing effect on the fault current, the protection scheme can adaptively adjust the protection setting value as the fault location changes, and the protection scheme is not affected by the operation mode.

[0082] Analysis of adaptive protection action after fault occurs: When switch P5140 is disconnected to isolate the fault, the distributed power source connected to the switch and the adjacent load branch will form an island operation. If the line part has not been put into anti-island protection, it will cause damage to the relevant loads and equipment.

[0083] At this time, the 10kV busbar sectionalizer is closed and operated, and the entire distribution network will be reconstructed. The farm transformer and Chenguang transformer master stations integrate data through the associated STU, and pass the information to the regional protection for comprehensive analysis, determine the new downstream load branch, and adaptively switch the protection setting. Assuming that the newly connected downstream load fails, β is still selected to be 0.3, 0.6 and 0.9, and the corresponding simulation results are as follows Fig. 9 As shown. Fig. 9 The data shows that when different fault types occur at the same location, the three-phase short-circuit fault current is greater than the short-circuit current when other faults occur, and the two-phase short-circuit current value is the smallest. As the fault point gets closer to the end of the line, the protection measurement value tends to decrease. However, in all fault types, the protection measurement value is still greater than the setting value, so the protection can be reliably operated.

[0084] It shows that after the power supply or line on one side of the system changes, the network structure can adaptively adjust the protection setting according to the instructions of the master station and regional protection to adapt to the new load access, avoid the impact of distributed power sources on the protection, and make the reconstructed distribution network protection able to operate reliably, thereby improving the power supply reliability of the distribution network.

[0085] In traditional overcurrent protection, the protection setting is set according to the coordination of the upper and lower levels, and the setting value and time limit are not adjusted according to the changes in the network structure. Therefore, when the power supply is restored in the non-fault area, in the new power supply network, the traditional protection may not be able to achieve fault isolation through the protection closest to the fault point, and the protection may malfunction, or even cause a power outage on the entire line.

[0086] As the DG capacity increases, the boost or external draw effect it produces becomes stronger, which is more likely to cause protection misoperation or refusal to operate. In order to verify the impact of increased DG capacity on fault current, the photovoltaic power capacity is set to 5MVA. Figure 7 The simulation results are shown in Table 1.

[0087] Table 1 Current simulation results of DG capacity of 5MVA

[0088]

[0089]

[0090] It can be seen from Table 1 that when the DG access capacity is 5MVA, when faults occur at different locations of the line, the closer the fault point is to the end of the line, the lower the current value gradually decreases. When different fault types occur at the same fault location, the fault current of the three-phase short circuit is the largest, and the fault current of the two-phase short circuit is the smallest. In addition, at different fault points of the line, the protection measurement values ​​are all greater than the protection setting values, so the protection can achieve reliable action.

[0091] In order to more clearly compare the changes in short-circuit current after the DG capacity increases, the fault current differences generated by DG capacities of 2.5MVA and 5MVA are compared based on the fault type and fault point location. Fig.10 It can be obtained that when different fault types occur in the line, due to the increase in DG capacity, the minimum difference in fault current is about 12A and the maximum does not exceed 60A. In the case of three-phase short circuit, the increase in short-circuit current difference is most obvious, and the difference change in two-phase short circuit is the smallest. When the same fault type occurs at the same fault location, the difference in the measured value is greater than the setting difference. Since the protection measurement value is still greater than the setting value at this time, the protection can operate reliably.

[0092] This means that as the DG capacity increases, the short-circuit current at the fault point will also increase. Hierarchical protection adjusts the protection setting value according to the size of the short-circuit current at the protection installation location, realizing adaptive adjustment of the protection setting value under different DG access capacities.

[0093] When the DG capacity is 5MVA, different fault types are set at different positions of the line to test the ability to withstand transition resistance. The transition resistance is 5Ω, 10Ω and 20Ω respectively.

[0094] When a fault occurs at the same location, as the transition resistance increases, the difference between the protection measurement value and the setting value gradually decreases, and as the fault point gets closer to the end of the line, the difference between the protection measurement value and the setting value shows a decreasing trend.

[0095] Therefore, in terms of protection setting, when the transition resistance increases further, the difference between the protection measurement value and the setting value will gradually decrease, and as the DG capacity continues to increase, the protection measurement value may be closer to the setting value, and the protection will not be able to achieve reliable action. Since the 10kV distribution network line is generally short, the hierarchical protection scheme proposed in the present invention can achieve reliable action. In this way, for the protection and handling of faults, only part of the distribution network needs to be paid attention to, and there is no need to calculate the relationship between the modules in the entire network.

[0096] The embodiment of the present invention further provides a computer device, which includes: a processor, a memory, and a computer program stored in the memory and executable on the processor. The processor calls the computer program stored in the memory to execute each step of the asymmetric flexible interconnected AC / DC hybrid distribution network optimization method provided in the embodiment of the present invention, and can achieve the same technical effect, refer to the description in the above embodiment, which will not be repeated here.

[0097] It should be pointed out that those skilled in the art can understand that the electronic device in the embodiment of the present invention is a device that can automatically perform numerical calculations and / or information processing according to pre-set or stored instructions, and its hardware includes but is not limited to microprocessors, application specific integrated circuits (ASIC), field-programmable gate arrays (FPGA), digital signal processors (DSP), embedded devices, etc. The electronic device can be a computing device such as a desktop computer, a notebook, a handheld computer, and a cloud server. The electronic device can perform human-computer interaction through a keyboard, a mouse, a remote control, a touchpad, or a voice-controlled device.

[0098] An embodiment of the present invention also provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the various processes and steps in the asymmetric flexible interconnected AC / DC hybrid distribution network optimization method provided in the embodiment of the present invention are implemented, and the same technical effect can be achieved. To avoid repetition, it will not be repeated here.

[0099] A person of ordinary skill in the art can understand that the implementation of all or part of the processes in the above-mentioned embodiment method can be completed by instructing the relevant hardware through a computer program, and the program can be stored in a computer-readable storage medium. When the program is executed, it can include the processes of various embodiments of the above-mentioned asymmetric flexible interconnected AC / DC hybrid distribution network optimization method. Among them, the storage medium can be a disk, an optical disk, a read-only memory (ROM) or a random access memory (RAM), etc. The above specific implementation method is a preferred implementation method of the hierarchical protection method for the precise distribution network line of the present invention, and it is not intended to limit the specific implementation scope of the present invention. The scope of the present invention includes but is not limited to the present specific implementation method. All equivalent changes made in accordance with the shape and structure of the present invention are within the protection scope of the present invention.

Claims

1. A precise hierarchical protection method for distribution network lines, which selects a distribution system containing DG as a target distribution network object, and constructs a hierarchical module of the target distribution network object through the comprehensive data information of the system, characterized in that: The hierarchical module of the target distribution network object is divided into three sub-modules: local, station domain and regional. After the fault is detected, the location of the fault is analyzed, and the impact value of the DG grid-connected access system is added. According to the fault situation, a corresponding sub-module is selected to calculate the corresponding adaptive current setting value, and the protection response is executed in the corresponding sub-module according to the calculated adaptive current setting value.

2. The precise distribution network line hierarchical protection method according to claim 1 is characterized in that: The adaptive current setting value calculation includes adaptive current segment I setting value calculation and adaptive current segment II setting value calculation.

3. The precise distribution network line hierarchical protection method according to claim 2 is characterized in that: When a three-phase short-circuit fault occurs in the line, since the fault is a symmetrical short-circuit and the DG connected to the system can only output the positive sequence current component, the three-phase short-circuit current generated in the entire system is also symmetrical; the corresponding protection position current I segment setting value is: Where: U3 is the measured value of the phase voltage of protection 3 during fault, Z CD is the impedance corresponding to line CD, α is the line protection range coefficient, The superscript (3) indicates a three-phase short-circuit fault.

4. The precise distribution network line hierarchical protection method according to claim 2 is characterized in that: When a two-phase metallic short circuit fault occurs in the line, phase A is regarded as the non-fault phase, and the symmetrical component method can be used to analyze and calculate the asymmetrical fault. At this time, the fault current only exists in the positive sequence and negative sequence networks; the corresponding protection position current I segment setting value is: Where: U 3(1) is the positive sequence voltage value of protection 3 when a fault occurs, The superscript (2) indicates a two-phase short circuit fault, U 3(1) The subscript (1) of represents the positive sequence component.

5. The precise distribution network line hierarchical protection method according to claim 4 is characterized in that: When the protection line is full length, the setting value of the corresponding protection position current stage II is: Where: The superscript (3) indicates a three-phase short circuit fault. U3 is the measured value of the phase voltage of protection 3 during the fault. Z CD is the impedance corresponding to line CD, Z DE is the impedance corresponding to line DE, and α is the line protection range coefficient.

6. The precise distribution network line hierarchical protection method according to claim 4 is characterized in that: When a two-phase short circuit occurs in the line, the setting value of the current stage II of the corresponding protection position is set to: Where: U 3(1) is the positive sequence voltage value of protection 3 when a fault occurs, The superscript (2) indicates a two-phase short-circuit fault, Z CD is the impedance corresponding to line CD, Z DE is the impedance corresponding to line DE, and α is the line protection range coefficient.

7. The method for hierarchical protection of precise distribution network lines according to any one of claims 1 to 6, characterized in that: STU is installed in the distribution line in units of switches, which are responsible for monitoring the current, voltage and switch status information at the switch. Adjacent STU units are interconnected through optical fiber Ethernet, and the local detection information is transmitted to the station area and regional master station in real time.

8. The precise distribution network line hierarchical protection method according to claim 7 is characterized in that: The local protection sets two sets of protection settings, A and B, in each protection unit. During normal operation, setting A or B is selected according to the clear upstream and downstream relationship. When the power supply of the original network system changes, the real-time information of each substation is transmitted to the station area protection by STU, and the regional protection makes a comprehensive decision to select and determine the protection setting after reconstruction of the non-fault area in the network. When the protection measurement value after monitoring each line fault is greater than the set value, and the maximum branch current on both sides of the line is located on the same line, the protection action will cut off the fault.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the precise distribution network line hierarchical protection method as described in any one of claims 1 to 8 are implemented.

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