Interstation power mutual aid method and system for low-voltage power distribution network

Abstract

The invention relates to a low-voltage power distribution network inter-station power mutual aid method and system. The method comprises the following steps: monitoring the load state of each transformer area of the low-voltage power distribution network and the low-voltage side current of the transformer area; when an overload transformer area is detected, searching the adjacent transformer area meeting a load capacity margin condition and a low-voltage side current margin condition as a target light-load transformer area, and if the adjacent transformer areas are both overloaded, starting an orderly power utilization three-level progressive transfer scheme; and determining a target unloading load according to a transfer strategy, controlling the section switch to execute switching operation, and switching the target unloading load from the overload platform area to the target light-load platform area. According to the invention, load balance between stations can be effectively optimized, the power supply safety and reliability are improved, and the method has the characteristics of low investment cost, high automation degree and strong adjustment capability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of low-voltage power distribution networks, in particular to a low-voltage power distribution network inter-substation power mutual assistance method and system. BACKGROUND

[0002] With the rapid development of the energy internet, the low-voltage distribution substation as the terminal link of the power system, its operation efficiency, power supply reliability and power supply quality directly affect the user's power experience, and higher requirements are put forward for the load balancing management between substations. In view of the high-quality and high-reliability power supply requirements, realizing the rapid switching of loads between substations is a necessary measure to enhance system stability, reliability, optimize resource allocation and reduce economic losses. In the actual operation process, there are factors that restrict the improvement of switching speed. First, the performance of load switching equipment directly affects the switching speed. For example, the response time, action reliability and service life of the switch will affect the speed and effect of load switching. Secondly, the topology structure of the distribution network has an important influence on the speed of load switching. Complex network structure may lead to longer switching path, thereby increasing the switching time. Thirdly, the volatility and uncertainty of the load will also affect the speed of load switching. For example, during the peak load period, it may be more difficult to switch the load, because more constraints need to be met. Finally, load switching needs to rely on advanced communication and control systems. If the communication delay or the control system fails, it will directly affect the speed and accuracy of load switching.

[0003] In view of the unbalanced load between substations or seasonal load fluctuation, the existing method mainly uses flexible interconnection devices to realize power mutual assistance and capacity sharing, and improves the flexibility and efficiency of the power grid. However, flexible interconnection devices still face a series of challenges and problems in practical application, especially in terms of economy and reliability.

[0004] First, technological maturity is a crucial factor affecting the economic viability of flexible interconnection devices. Compared to traditional high-voltage direct current (HVDC) transmission technology, low-voltage flexible DC interconnection devices have lower technological maturity and require further research and development. This lack of maturity can lead to higher initial investment costs, thus impacting their economic viability. Second, equipment costs cannot be ignored. While low-voltage equipment reduces costs to some extent, the manufacturing costs of key equipment such as voltage source converters (VSCs) remain high, hindering the promotion and application of flexible interconnection devices. Third, the lack of unified technical standards and specifications is also a reason for the poor economic viability of flexible interconnection devices. Currently, unified technical standards and specifications for low-voltage flexible interconnection devices have not only limited the promotion and application of the technology but also increased the complexity of design and implementation, thereby raising costs. Fourth, the difficulty and cost of operation and maintenance management are also important factors affecting the economic viability of flexible interconnection devices. Due to the system complexity and the characteristics of new technologies, operation and maintenance management is difficult, requiring the training of professional operation and maintenance teams, which also increases costs. Finally, although flexible interconnection devices can reduce transmission losses and improve energy efficiency by optimizing grid structure and operation, thus bringing economic benefits, in practice, due to the aforementioned challenges, their economic benefits are not as significant as expected. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method and system for power mutual assistance between low-voltage distribution network stations, which can realize power mutual assistance between stations in an economical, efficient and rapid manner.

[0006] The technical solution adopted by this invention to solve its technical problem is: providing a method for power mutual assistance between low-voltage distribution network sections, wherein the low-voltage distribution network is equipped with multiple sectionalizing switches, and the multiple sectionalizing switches divide the low-voltage feeder into multiple sections, including the following steps:

[0007] Monitor the load status of each transformer substation and the low-voltage side current of each substation;

[0008] When an overloaded area is detected, the load status of adjacent areas of the overloaded area is analyzed, and adjacent areas that meet the load capacity margin condition and the low-voltage side current margin condition are searched as target light-load areas.

[0009] If all adjacent transformer substations are overloaded, a three-tiered, progressive power transfer system will be activated:

[0010] First-level transfer: Search for cross-level substations within the same feeder that meet the load capacity margin and low-voltage side current margin from the non-directly adjacent substations within the second-level range of the overload substation area as the target light-load substation area.

[0011] Secondary transfer: if the overload area is still overloaded after the first transfer, search for a neighboring feeder area that meets the load capacity margin condition and low-voltage side current margin as the target light load area;

[0012] Third bottom-up: if the overload area is still overloaded after the secondary transfer, orderly cut off the area load;

[0013] According to the transfer strategy, the target unloading load is determined, the segmented switch is controlled to perform switch operation, and the target unloading load is switched from the overload area to the target light load area.

[0014] Further, when searching for the target light load area, the adjacent areas in the same low-voltage feeder range are preferentially searched.

[0015] Further, it also includes:

[0016] After detecting the load state of the overload area after load switching, if the load is still overloaded, the load state of the adjacent area of the overload area is analyzed again.

[0017] Further, the target unloading load is determined according to the transfer strategy, which includes:

[0018] When the orderly power utilization three-stage progressive transfer is not needed to be started, the target unloading load is a III type load;

[0019] When the first transfer is adopted, the target unloading load is a II type load;

[0020] When the secondary transfer is adopted, the target unloading load is a I type load;

[0021] When the third transfer is adopted, the target unloading load is a III type load.

[0022] Further, the load state of each area is monitored by calculating the corresponding area load rate based on the load current and the maximum carrying current of each area.

[0023] Further, the overload area is an area whose area load rate is greater than or equal to a set load rate threshold and whose low-voltage side current is greater than or equal to a set current threshold.

[0024] Further, the segmented switch adopts a line circuit breaker or a combined structure of a bidirectional thyristor and a load switch in parallel.

[0025] Further, the line circuit breaker includes a time delay device.

[0026] The application also provides a low-voltage power distribution network area power mutual aid system, which comprises:

[0027] A low-voltage distribution network is provided with a plurality of sectional switches, which divide a low-voltage feeder into a plurality of sections.

[0028] A detection module is configured to monitor the load state of each transformer area and the low-voltage side current of the transformer area.

[0029] An analysis module is configured to, when an overload transformer area is detected, analyze the load state of adjacent transformer areas of the overload transformer area, search for the adjacent transformer areas that meet the load capacity margin condition and the low-voltage side current margin condition as target light-load transformer areas, and start a three-stage progressive power transfer scheme for orderly power utilization if all the adjacent transformer areas are overloaded.

[0030] First-stage power transfer: searching for a cross-stage transformer area that meets the load capacity margin condition and the low-voltage side current margin condition in the same feeder from non-directly adjacent transformer areas within the second-stage range of the overload transformer area as the target light-load transformer area.

[0031] Second-stage power transfer: if the overload transformer area is still overloaded after the first-stage power transfer, searching for a transformer area that meets the load capacity margin condition and the low-voltage side current margin condition from adjacent feeders as the target light-load transformer area.

[0032] Third-stage backup: if the overload transformer area is still overloaded after the second-stage power transfer, orderly cutting off the load of the transformer area.

[0033] The analysis module is further configured to determine the target unloaded load according to the power transfer strategy.

[0034] A control module is configured to control the sectional switches to perform switching operations to switch the target unloaded load from the overload transformer area to the target light-load transformer area.

[0035] Further, the detection module, the analysis module, and the control module are all deployed in a cloud master station to implement a three-stage architecture of edge collection, cloud decision-making, and terminal execution.

[0036] Advantages

[0037] Compared with the prior art, the present application has the following advantages and positive effects: by monitoring the load state of the transformer area in real time, by analyzing the load state of the adjacent transformer area of the overloaded transformer area, searching for the adjacent transformer area meeting the load capacity margin condition as the target light-load transformer area, and controlling the sectionalizing switch to perform load switching, the load distribution dynamic adjustment can be realized, the local overload can be avoided, and the operation efficiency and reliability of the low-voltage power distribution network are significantly improved; the target light-load transformer area and the target unloaded load can be obtained based on the existing current transformer data analysis, and the sectionalizing switch is used to realize the inter-transformer area load switching, so that the fast and automatic load switching is realized at low cost, and the uninterrupted power supply of the user is ensured; in addition, the present application controls the load switching based on the sectionalizing switch, and the load switching process is completed seamlessly, which not only reduces the manual intervention, but also ensures the power stability, and provides an efficient and economic solution for the intelligent upgrading of the power distribution network; the present application can support multi-level transfer function, can flexibly expand the adjustment range, further enhances the adaptability of the power grid, has the characteristics of low investment cost, high automation degree and strong adjustment capacity, can effectively optimize the load balance between the transformer areas, and improves the power supply safety and reliability. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 is a flow chart of the first embodiment of the present application;

[0039] Figure 2 is an implementation flow chart of preferred embodiment 1 and preferred embodiment 2 of the present application;

[0040] Figure 3 is a low-voltage power distribution network structure diagram of preferred embodiment 1 and preferred embodiment 2 of the present application. DETAILED DESCRIPTION

[0041] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application. In addition, it should be understood that after reading the content taught by the present application, those skilled in the art can make various modifications or modifications to the present application, and these equivalent forms also fall within the scope defined by the claims attached hereto.

[0042] The first embodiment of the present application relates to a low-voltage power distribution network inter-transformer area power mutual aid method, wherein the low-voltage power distribution network is provided with a plurality of sectionalizing switches, and the sectionalizing switches divide the low-voltage feeder into a plurality of sections.

[0043] As shown in Figure 1 , the low-voltage power distribution network inter-transformer area power mutual aid method comprises the following steps:

[0044] When monitoring the load state of each transformer area, the real-time current at the low-voltage side of the transformer area is synchronously collected, and a "current threshold-load rate" double-parameter cooperative judgment mechanism is constructed:

[0045] Set three current threshold: warning threshold I1, switching threshold I2, safety upper limit I3, respectively 75%, 80%, 90% of transformer rated current; overload determination needs to meet load rate ≥ 80% and real-time current ≥ switching threshold, target light load area needs to meet load rate ≤ 60% and real-time current ≤ 60% of rated current at the same time, to avoid misjudgment of a single parameter;

[0046] When detecting the overload area, analyze the load state of the adjacent area of the overload area, and search for the adjacent area that meets the load capacity margin condition and the low-voltage side current margin condition as the target light load area;

[0047] Determine the target unloading load, control the sectional switch to perform switching operation, and switch the target unloading load from the overload area to the target light load area.

[0048] Wherein, the load state of each area can be judged by calculating the load rate of the area, and the load rate of the area can be calculated based on the load current and the maximum carrying current of the line. Specifically, the existing low-voltage current transformer of each area can be used to form a data acquisition module to monitor the load rate of the low-voltage side in real time. Then the load rate information of each load point is uploaded to the control module through the communication module to realize full coverage of load rate monitoring in low-voltage distribution network.

[0049] The overload area can be determined by comparing the load rate of the area and the low-voltage side current margin condition with the corresponding set threshold. When searching for the target light load area, the adjacent areas within the same low-voltage feeder range are searched first. If all the adjacent areas are overloaded, the orderly power utilization scheme is started, otherwise the system controls the closing and opening operation of the sectional switch through the distribution automation master station to realize the safe transfer of load.

[0050] As shown in Figure 2 , which is one preferred embodiment 1 of the present embodiment, the core of which is to realize the low-cost regulation of power mutual aid between different section areas of low-voltage distribution network through multiple sectional switches and intelligent control modules.

[0051] The technical principle mainly includes:

[0052] 1. Multi-sectional switch control: by controlling the closing and opening of the multi-sectional switch, the connection mode of the area load is changed to realize power mutual aid;

[0053] 2. Intelligent control module: use the intelligent control module to monitor the load rate of the area in real time, optimize the load switching strategy, and ensure the continuity and stability of power supply;

[0054] 3. Low-cost design: by reducing equipment investment and operation and maintenance cost, improve the economy and reliability of the power grid.

[0055] The method comprises the following main steps:

[0056] 1. Data acquisition: using existing low-voltage current transformers in each transformer area to form a data acquisition module to monitor the load rate of the low-voltage side of the transformer area in real time;

[0057] 2. Communication transmission: uploading the load rate information of each load point to the control module through the communication module to achieve full coverage of load rate monitoring in the low-voltage distribution network;

[0058] 3. Intelligent control: the control module is composed of a transformer area intelligent fusion terminal (TTU) with a new type of distribution network voltage optimization control function, and based on a voltage optimization algorithm and control strategy, the control of the execution module is realized;

[0059] 4. Load switching: the execution module is a distribution switch that can realize phase sequence discrimination, and through the phase sequence discrimination function, orderly execution in the case of phase sequence disorder in the load switching process is realized.

[0060] As shown in Figure 3 , the low-voltage distribution network comprises an intelligent fusion terminal TTU, sectional switches CB1, CB2, CB3, etc., and a communication line. The intelligent terminal is an intelligent control module, contains a new type of distribution network load fast switching control function, and realizes control of the sectional switch based on a load rate optimization algorithm and control strategy. The communication line contains multiple communication modes such as low-voltage distribution network carrier wave communication, optical fiber communication, and 4G, and one or a combination of multiple modes can be used to realize communication between the intelligent terminal and the sectional switch.

[0061] The specific implementation process is shown in Figure 2 :

[0062] First, the current data of the low-voltage distribution network transformer area is collected in real time by the intelligent monitoring equipment, the current load rate is calculated and compared with the preset threshold;

[0063] When the load is detected to be over the limit, the system automatically analyzes the load state of the adjacent transformer area, and preferentially searches for a lightly loaded transformer area with capacity margin within the same feeder range, and if all adjacent transformer areas are overloaded, an orderly power utilization scheme is started;

[0064] Secondly, after determining the target lightly loaded transformer area, the system controls the closing and opening operation of the sectional switch through the distribution automation master station to realize safe transfer of the load, and simultaneously monitors the power flow distribution and voltage quality in real time;

[0065] Thirdly, after the load transfer is completed, the system continuously tracks key indicators such as the load rate, voltage qualification rate, and line loss changes of each transformer area to ensure that the operating parameters are within a safe range;

[0066] Finally, for the case of adjacent areas being overloaded under complex conditions, the three-level progressive power transfer scheme for orderly power utilization is started:

[0067] First-level power transfer: search for non-directly adjacent areas within the 2-level range of the overloaded area (across 1 intermediate area), screen for lightly loaded areas with load rate ≤ 60% and residual current margin ≥ 1.2 times the target unloaded load, preferentially select cross-level areas within the same feeder as the power transfer node, control the sectionalization switch to close to form the power transfer path, and transfer the Class II load (non-essential commercial load);

[0068] Second-level power transfer: if the load rate of the original overloaded area is still ≥ 80% after the first-level power transfer, issue the contactor closing instruction through the cloud master station to open the cross-feeder power transfer channel, and transfer the Class I transferable load (such as non-core livelihood load) of the overloaded area to the lightly loaded area of the adjacent feeder. The path line loss needs to be calculated before power transfer, and only when the line loss is ≤ 5% is it executed;

[0069] Third-level backup: if the load rate is still ≥ 90% after the first two levels of power transfer, start the hierarchical orderly load shedding, preferentially cut off the Class III load (industrial auxiliary load), until the load rate is reduced to below 75%, and upload the overload warning to the cloud master station to trigger the on-site verification of the operation and maintenance personnel. This scheme, through the cooperation of intelligent decision-making algorithms and automation equipment, can realize the whole-process closed-loop management from fault detection to load adjustment.

[0070] For Area 1, a 10kV / 0.4kV transformer (rated capacity 200kVA, rated voltage 0.4kV) is configured, the current transformer CT1 has a transformation ratio of 1000 / 5 (transformation ratio coefficient 200), and the low-voltage side contains 4 parts of load including production equipment, lighting equipment, etc. Each group has a normal operating power of 45kW and a power factor of 0.85.

[0071] According to the double-parameter collaborative judgment mechanism, the transformer rated current In≈340.1A is calculated first, and the three-level current threshold is set simultaneously: the warning threshold I1=In×75%≈255.1A, the switching threshold I2=In×80%≈272.1A, and the safety upper limit I3=In×90%≈306.1A. It is also clear that the overload determination needs to meet the conditions of "load rate ≥ 80% and real-time current ≥ I2", and the target lightly loaded area needs to meet the conditions of "load rate ≤ 60% and real-time current ≤ In×60%≈204.1A".

[0072] Initial state CB1, CB2 closed (CB2 with all 4 groups of load), CB3 open, measure CT1 secondary current 1.22A, the actual load current is calculated to be 1.22A x 200 = 244A through the transformation ratio, the load rate 244A / 340.1A ≈ 0.717, as the double conditions of overload determination are not met at the same time, the intelligent terminal does not trigger switching; After the subsequent load is superimposed, the CT1 secondary current is measured to be 1.38A, the actual load current is calculated to be 276A, and the load rate is 276A / 340.1A ≈ 0.812. At this time, the conditions of "load rate ≥ 80% and real-time current ≥ I2 (272.1A)" are met at the same time, and the strategy is executed to adjust "single group load transfer, minimum operation amount": close CB3 (confirm that the station area 2 meets the light load double condition), open CB2, and switch the load 3 to the station area 2.

[0073] After the state is stable, the CT1 secondary current is measured to be 0.98A, the actual load current is calculated to be 196A, and the load rate is 196A / 340.1A ≈ 0.576. It does not exceed the determination standard and meets the safety operation requirement, and the load switching stops. The rest of the station areas are executed according to the double parameter cooperative judgment and closed loop operation process.

[0074] When the adjacent station areas are all overloaded, take the example of station area 1 (200kVA transformer, rated current ≈ 343A, switching threshold I2 ≈ 274A) being overloaded and the directly adjacent station area 2 being overloaded. The multi-level transfer is executed as follows:

[0075] First level cross-level transfer: first search the 2nd level adjacent station area 3 of station area 1 (load rate 55%, real-time current 206A, remaining margin 137A), determine that the load current 80A needs to be transferred, control the sectional switch CB6 to close and CB2 to open, and transfer the load 3 (60A) of station area 1 to station area 3. After switching, the load rate of station area 1 is reduced to 72%, and the real-time current is 252A (≤ I2);

[0076] If the load rate of station area 1 is still 78% (real-time current 268A ≈ I2) after transfer, start the second level cross-feed line transfer: the cloud host station closes the tie switch LK1, transfers the load 4 (40A) of station area 1 to the station area 4 of the adjacent feed line (load rate 50%), and the transfer path line loss is calculated to be 3.2% (≤ 5%). After switching, the load rate of station area 1 is reduced to 68%;

[0077] The current is monitored in real time through the current transformer monitoring loop throughout the process. When switching, the sectional switch is controlled to act at the current zero crossing point, ensuring that the current fluctuation is ≤ ± 5A.

[0078] The sectional switch can adopt a combination form of a line circuit breaker or a high-precision bidirectional thyristor in parallel with a load switch. When a common circuit breaker is adopted, a delay device needs to be configured to avoid misoperation caused by circulating current interference due to the overcurrent protection function of the outlet circuit breaker at the end of the transformer area. When a high-precision bidirectional thyristor is adopted in parallel with a load switch, the thyristor can realize rapid and accurate cutting of the line, and a short-circuit path is formed by closing the parallel load switch, which can not only take advantage of the rapid response of the thyristor, but also protect the thyristor from the influence of conduction voltage drop. The design scheme comprehensively considers key factors such as protection reliability, action rapidity and equipment economy, and can flexibly select and configure the scheme according to the actual application scene.

[0079] The second embodiment of the present application relates to a low-voltage distribution network transformer area interconnection power mutual assistance system for realizing the above method, comprising:

[0080] A low-voltage distribution network is provided with a plurality of sectional switches, which divide the low-voltage feeder into a plurality of sections;

[0081] A detection module is used to monitor the load state of each transformer area and the low-voltage side current of the transformer area;

[0082] An analysis module is used to analyze the load state of the adjacent transformer area of the overloaded transformer area when the overloaded transformer area is detected, search for an adjacent transformer area that meets the load capacity margin condition and the low-voltage side current margin condition as a target light-load transformer area, and start a three-level progressive power transfer scheme for orderly power utilization if all the adjacent transformer areas are overloaded:

[0083] First-level power transfer: search for a cross-level transformer area that meets the load capacity margin condition and the low-voltage side current margin in the same feeder from the non-directly adjacent transformer area in the second level range of the overloaded transformer area as the target light-load transformer area;

[0084] Second-level power transfer: if the overloaded transformer area is still overloaded after the first-level power transfer, search for a transformer area that meets the load capacity margin condition and the low-voltage side current margin from the adjacent feeder as the target light-load transformer area;

[0085] Third-level backup: if the overloaded transformer area is still overloaded after the second-level power transfer, orderly cut off the transformer area load;

[0086] The analysis module is also used to determine the target unloaded load according to the power transfer strategy; when the first-level power transfer is adopted, the target unloaded load is a type II load; when the second-level power transfer is adopted, the target unloaded load is a type I load; and when the third-level power transfer is adopted, the target unloaded load is a type III load;

[0087] A control module is used to control the sectional switch to perform switching operation and switch the target unloaded load from the overloaded transformer area to the target light-load transformer area.

[0088] Among them, the intelligent control function including the detection module, the analysis module and the control module can be realized on the cloud master station platform, the load rate data is processed centrally through the cloud to generate control instructions. In specific implementation, the load data collected by the current transformers of each district is directly uploaded to the cloud master station through 4G / 5G or optical fiber channel, the load rate analysis, adjacent district capacity matching and switching strategy optimization are completed by the cloud algorithm, and then the sectionalizing switch operation instructions are issued through the distribution automation system. This scheme eliminates the local calculation link of the district intelligent fusion terminal (TTU), realizes the collaborative optimization of multiple districts by using the computing power of the cloud master station platform, and at the same time retains the sectionalizing switch control architecture and load switching logic of the original invention, thereby improving the system expansibility and data analysis capability.

[0089] The preferred embodiment 2 of the present application aims to provide a transformer inter-district power mutual aid low-cost regulation system based on sectionalizing switches, to solve the problems of low technical maturity, high equipment cost and complex operation and maintenance of existing flexible interconnection devices. By using an economical and efficient sectionalizing switch to replace the traditional high-cost converter (VSC), the equipment investment and operation and maintenance cost are significantly reduced; at the same time, the load switching mechanism is optimized to realize the rapid mutual aid of inter-district power, effectively cope with the problems of load imbalance and insufficient power supply capacity, and improve the continuity and reliability of power supply. The system can adapt to the challenge of bidirectional power flow caused by complex distribution network topology and new load access, realize automatic regulation through an intelligent control module, and reduce the difficulty of operation and maintenance. In addition, by dynamically adjusting the inter-district power distribution to balance the load rate, the overall operation efficiency and economy of the power grid are improved, providing a low-cost, efficient and reliable solution for urban distribution networks, old city reconstruction and new energy high penetration scenarios, and promoting the development of distribution networks towards intelligence and economy.

[0090] The core of the present embodiment is to realize low-cost regulation of inter-district power mutual aid in different sections of low-voltage distribution networks through multiple sectionalizing switches and an intelligent control module. The technical principles mainly include:

[0091] 1. Multi-sectionalizing switch control: by controlling the closing and opening of multiple sectionalizing switches, the connection mode of district load is changed to realize power mutual aid;

[0092] 2. Intelligent control module: the intelligent control module is used to monitor the district load rate in real time, optimize the load switching strategy, and ensure the continuity and stability of power supply;

[0093] 3. Low-cost design: by reducing equipment investment and operation and maintenance cost, the economy and reliability of the power grid are improved.

[0094] The main steps include:

[0095] 1. Data acquisition: use the existing low-voltage end current transformers of each district to form a data acquisition module to monitor the load rate of the low-voltage side of the district in real time;

[0096] 2. Communication transmission: upload the load rate information of each load point to the control module through the communication module to realize full coverage of load rate monitoring in the low-voltage distribution network;

[0097] 3. Intelligent control: the control module is composed of a transformer area intelligent fusion terminal (TTU) with a new type of distribution network voltage optimization control function, and based on a voltage optimization algorithm and control strategy, the control of the execution module is realized;

[0098] 4. Load switching: the execution module is a distribution switch that can realize phase sequence discrimination, and through the phase sequence discrimination function, orderly execution in the case of phase sequence disorder during load switching is realized.

[0099] As shown in Figure 3 , the low-voltage distribution network includes intelligent fusion terminals TTU, sectional switches CB1, CB2, CB3, etc., and communication lines. The intelligent terminal is an intelligent control module, which contains a new type of distribution network load fast switching control function, and realizes control of the sectional switch based on a load rate optimization algorithm and control strategy. The communication line includes low-voltage distribution network carrier communication, optical fiber communication, 4G, etc. Various communication methods can be used alone or in combination to realize communication between the intelligent terminal and the sectional switch.

[0100] The specific implementation process is shown in Figure 2 :

[0101] First, real-time current data of the low-voltage distribution network transformer area is collected by the intelligent monitoring equipment, the current load rate is calculated and compared with the preset threshold;

[0102] When the load is detected to be over limit, the system automatically analyzes the load state of the adjacent transformer area, and preferentially searches for a lightly loaded transformer area with capacity margin within the same feeder range. If all adjacent transformer areas are overloaded, the orderly power utilization scheme is started;

[0103] Secondly, after determining the target lightly loaded transformer area, the system controls the closing and opening operation of the sectional switch through the distribution automation master station to realize safe transfer of the load, while monitoring the power flow distribution and voltage quality in real time;

[0104] Thirdly, after the load transfer is completed, the system continuously tracks key indicators such as load rate, voltage qualification rate and line loss change of each transformer area to ensure that the operating parameters are within a safe range;

[0105] Finally, for the case where all adjacent transformer areas are overloaded under complex conditions, the orderly power utilization three-stage progressive transfer scheme is started;

[0106] Primary transfer: search for non-direct adjacent substation in the 2nd level range of the overloaded substation (cross 1 intermediate substation), screen the light load substation with load rate ≤ 60% and residual current margin ≥ 1.2 times of the target unloaded load, preferentially select the cross-level substation in the same feeder as the transfer node, control the sectionalizing switch to close to form the transfer path, and transfer the class II load (non-essential commercial load);

[0107] Secondary transfer: if the load rate of the original overloaded substation is still ≥ 80% after primary transfer, issue the interlocking switch closing instruction through the cloud master station to open the cross-feeder transfer channel, and transfer the class I transferable load (such as non-core livelihood load) of the overloaded substation to the light load substation of the adjacent feeder. The path line loss needs to be calculated before transfer, and only when the line loss is ≤ 5% is it executed;

[0108] Third-level backup: if the load rate is still ≥ 90% after the first two levels of transfer, start the hierarchical and orderly load shedding, preferentially cut off the class III load (industrial auxiliary load), until the load rate is reduced to below 75%, and upload the overload warning to the cloud master station to trigger the on-site verification of the operation and maintenance personnel. This scheme can realize the whole-process closed-loop management from fault detection to load adjustment through the cooperation of intelligent decision algorithm and automatic equipment.

[0109] For substation 1, a 10kV / 0.4kV transformer (rated capacity 200kVA, rated voltage 0.4kV) is configured, the current transformer CT1 has a transformation ratio of 1000 / 5 (transformation ratio coefficient 200), and the low-voltage side contains 4 parts of load such as production equipment and lighting equipment. Each group has a normal operating power of 45kW and a power factor of 0.85.

[0110] According to the double-parameter cooperative judgment mechanism, the rated current of the transformer In≈340.1A is calculated, and the three-level current threshold is set simultaneously: the warning threshold I1=In×75%≈255.1A, the switching threshold I2=In×80%≈272.1A, and the safety upper limit I3=In×90%≈306.1A. It is clear that the overload determination needs to meet the conditions of "load rate ≥ 80% and real-time current ≥ I2", and the target light load substation needs to meet the conditions of "load rate ≤ 60% and real-time current ≤ In×60%≈204.1A".

[0111] Initial state CB1, CB2 closed (CB2 with all 4 groups of load), CB3 open, measure CT1 secondary current 1.22A, the actual load current is calculated to be 1.22A x 200 = 244A through the transformation ratio, the load rate 244A / 340.1A ≈ 0.717, as the double conditions of overload determination are not met at the same time, the intelligent terminal does not trigger switching; After the subsequent load is superimposed, the CT1 secondary current is measured to be 1.38A, the actual load current is calculated to be 276A, and the load rate is 276A / 340.1A ≈ 0.812. At this time, the conditions of "load rate ≥ 80% and real-time current ≥ I2 (272.1A)" are met at the same time, and the strategy is executed to adjust "single group load transfer, minimum operation amount": close CB3 (confirm that the station area 2 meets the light load double condition), open CB2, and switch the load 3 to the station area 2.

[0112] After the state is stable, the CT1 secondary current is measured to be 0.98A, the actual load current is calculated to be 196A, and the load rate is 196A / 340.1A ≈ 0.576. It does not exceed the determination standard and meets the safety operation requirement, and the load switching stops. The rest of the station areas are executed according to the double parameter cooperative judgment and closed loop operation process.

[0113] When the adjacent station areas are all overloaded, take the example of station area 1 (200kVA transformer, rated current ≈ 343A, switching threshold I2 ≈ 274A) being overloaded and the directly adjacent station area 2 being overloaded. The multi-level transfer is executed as follows:

[0114] First level cross-level transfer: first search the 2nd level adjacent station area 3 of station area 1 (load rate 55%, real-time current 206A, remaining margin 137A), determine that the load current 80A needs to be transferred, control the sectional switch CB6 to close and CB2 to open, and transfer the load 3 (60A) of station area 1 to station area 3. After switching, the load rate of station area 1 is reduced to 72%, and the real-time current is 252A (≤ I2);

[0115] If the load rate of station area 1 is still 78% (real-time current 268A ≈ I2) after transfer, start the second level cross-feed line transfer: the cloud host station closes the tie switch LK1, transfers the load 4 (40A) of station area 1 to the station area 4 of the adjacent feed line (load rate 50%), and the transfer path line loss is calculated to be 3.2% (≤ 5%). After switching, the load rate of station area 1 is reduced to 68%;

[0116] The current is monitored in real time through the current transformer monitoring loop throughout the process. When switching, the sectional switch is controlled to act at the current zero crossing point, ensuring that the current fluctuation is ≤ ± 5A.

[0117] Among them, the sectional switch can adopt the combination form of line circuit breaker or high-precision bidirectional thyristor in parallel with load switch. When using ordinary circuit breaker, due to the over-current protection function of the outlet circuit breaker at the end of the transformer area, a delay device needs to be configured to avoid the interference of circulating current leading to misoperation. When using high-precision bidirectional thyristor in parallel with load switch, the thyristor can realize the fast and accurate cut-off of the line, and at the same time, through closing the parallel load switch to form a short circuit path, it can not only play the advantages of fast response of thyristor, but also protect the thyristor from the influence of conduction voltage drop. The design scheme comprehensively considers the key factors such as protection reliability, action rapidity and equipment economy, and can flexibly select the configuration scheme according to the actual application scene.

Claims

1. A method for power mutual assistance between low-voltage distribution network substations, characterized in that, The low-voltage distribution network is equipped with multiple sectionalizing switches, which divide the low-voltage feeder into multiple sections, including the following steps: Monitor the load status of each transformer substation and the low-voltage side current of each substation; When an overloaded area is detected, the load status of adjacent areas of the overloaded area is analyzed, and adjacent areas that meet the load capacity margin condition and the low-voltage side current margin condition are searched as target light-load areas. If all adjacent transformer substations are overloaded, a three-tiered, progressive power transfer system will be activated: First-level transfer: Search for cross-level substations within the same feeder that meet the load capacity margin and low-voltage side current margin from the non-directly adjacent substations within the second-level range of the overload substation area as the target light-load substation area. Secondary transfer: If the overloaded area is still overloaded after the primary transfer, then the target light-load area is selected from the adjacent feeders that meet the load capacity margin condition and the low-voltage side current margin. Level 3 backup: If the overloaded transformer area is still overloaded after Level 2 transfer, the load of the transformer area will be systematically cut off; The target unloading load is determined according to the transfer strategy, and the segmented switch is controlled to perform a switching operation to switch the target unloading load from the overload station area to the target light load station area.

2. The method according to claim 1, characterized in that, When searching for the target lightly loaded transformer area, adjacent transformer areas within the same low-voltage feeder range are searched first.

3. The method according to claim 1, characterized in that, Also includes: After the load switch is detected, the load status of the overloaded area is checked. If the load is still overloaded, the load status of the adjacent areas of the overloaded area is analyzed again.

4. The method according to claim 1, characterized in that, The step of determining the target offloading load according to the transfer strategy includes: When it is not necessary to initiate the orderly three-level progressive power transfer, the target unloaded load is a Class III load; When using Level 1 power transfer, the target unloaded load is a Class II load; When a two-level transfer method is used, the target unloaded load is a Class I load; When a three-level transfer system is used, the target unloaded load is a Class III load.

5. The method according to claim 1, characterized in that, The monitoring of the load status of each transformer substation is achieved by calculating the corresponding substation load rate based on the load current of each substation and the maximum line carrying current.

6. The method according to claim 5, characterized in that, The overloaded transformer area is a transformer area whose load rate is greater than or equal to a set load rate threshold and whose low-voltage side current is greater than or equal to a set current threshold.

7. The method according to claim 1, characterized in that, The sectionalizing switch is a line circuit breaker or a combination structure of bidirectional thyristors and load switches connected in parallel.

8. The method according to claim 7, characterized in that, The circuit breaker includes a time delay device.

9. A power mutual assistance system between low-voltage distribution network substations, characterized in that, include: The low-voltage distribution network is equipped with multiple sectionalizing switches, which divide the low-voltage feeder into multiple sections. The detection module is used to monitor the load status of each transformer area and the low-voltage side current of the transformer area. The analysis module is used to analyze the load status of adjacent transformer stations when an overloaded transformer station is detected, and search for adjacent transformer stations that meet the load capacity margin condition and the low-voltage side current margin condition as target light-load transformer stations. If all adjacent transformer stations are overloaded, a three-level progressive power transfer scheme is activated. First-level transfer: Search for cross-level substations within the same feeder that meet the load capacity margin and low-voltage side current margin from the non-directly adjacent substations within the second-level range of the overload substation area as the target light-load substation area. Secondary transfer: If the overloaded area is still overloaded after the primary transfer, then the target light-load area is selected from the adjacent feeders that meet the load capacity margin condition and the low-voltage side current margin. Level 3 backup: If the overloaded transformer area is still overloaded after Level 2 transfer, the load of the transformer area will be systematically cut off; The analysis module is also used to determine the target offloading load based on the transfer strategy; The control module is used to control the segmented switch to perform a switching operation, switching the target unloaded load from the overload station area to the target light load station area.

10. The system according to claim 9, characterized in that, The detection module, the analysis module, and the control module are all deployed on the cloud main station, realizing a three-level architecture of edge acquisition, cloud decision-making, and terminal execution.

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