A method for generating load balancing strategy for regional power grid main network

Abstract

The present invention proposes a method for generating a load balancing strategy for a regional power grid main network, which belongs to the field of power system operation control technology. When a 220 kV overloaded plant or station exists in a regional power grid, the method comprehensively considers the operation modes such as the 110 kV busbar split operation of the 220 kV substation, the busbar reversal of the 110 kV line switch, and the adjustment of the operation mode of the 110 kV and 35 kV substations, and uses the plant or station that transfers the load that meets the requirements as the adjustment unit. The strategy calculation unit is used to obtain the current adjustment unit combination, and then the result after the load transfer is completed according to the combination is verified through the historical load curve, thereby obtaining the optimal load balancing strategy for the regional power grid main network. When the emergency power outage of the 110 kV and above main transformer or line in the regional power grid causes the 220 kV main equipment or section of the upper power source to be overloaded, the present invention can quickly form the optimal power grid operation mode adjustment plan to achieve load balancing of the entire network and ensure the safe and stable operation of the regional power grid.

Description

Technical Field

[0001] The present invention belongs to the technical field of power system operation control, and in particular relates to a method for generating a load balancing strategy for a regional power grid main network. Background Art

[0002] Emergency outages of 110 kV and higher main transformers or lines in the regional power grid cause overloads on 220 kV main equipment or sections of the upstream power source, necessitating rapid elimination of the overload to maintain safe and stable operation of normal equipment. Load shifting can alleviate equipment overloads, but current transfer plans rely primarily on dispatchers' operational experience, making it difficult to quickly arrive at an optimal solution. Furthermore, during peak summer load periods, most 220 kV substations are heavily loaded, with low capacity margins. Multiple load shifts are typically required to achieve load balance across the entire network, increasing the number and duration of switching operations and heightening operational risks for the grid.

[0003] Parallel operation of 220 kV substations plays a crucial role in improving power supply reliability. However, during peak load periods, the main transformer N-1 can cause severe equipment overload. In these situations, the 110 kV busbars of 220 kV substations are often operated in parallel to improve substation power supply capacity, at the expense of grid reliability. Therefore, when 220 kV main equipment or sections of a regional power grid are overloaded, it is necessary to comprehensively consider the safety, reliability, and economic efficiency of grid operation and select an appropriate adjustment plan to achieve load balancing across the entire network. Summary of the Invention

[0004] The present invention aims to overcome the shortcomings of existing technologies by proposing a method for generating a load balancing strategy for a regional power grid. This method can rapidly generate an optimal grid operation adjustment plan when an emergency power outage of a 110 kV or higher main transformer or line in a regional power grid causes an overload of a 220 kV main device or section of the upstream power source. This strategy achieves load balancing across the entire grid and ensures the safe and stable operation of the regional power grid.

[0005] An embodiment of the present invention provides a method for generating a load balancing strategy for a regional power grid main network, comprising:

[0006] 1) Determine the current regional power grid: If there is a 220 kV overloaded power station, enter the first round of regional power grid main grid load balancing optimization;

[0007] 2) Based on the result of step 1), determine whether the 110 kV busbars of the 220 kV overloaded power plants and substations in the regional power grid are in parallel operation:

[0008] If they are operated in parallel, proceed to step 3) to eliminate overload on the central main transformer section; if they are operated in separate columns, proceed to step 6) to eliminate overload on the central main transformer section;

[0009] 3) Taking the 220 kV overloaded central main transformer section as the current overload target, a load transfer solution is sought through a preset strategy calculation unit to eliminate the overload of the central main transformer section. The specific steps of the strategy calculation unit are as follows:

[0010] 3-1) Determine the overload load of the overload object;

[0011] 3-2) Obtain the adjustment unit combination sequence under the overload object. The specific steps are as follows:

[0012] 3-2-1) Obtain the 110 kV power substation and 35 kV power substation under the overload object;

[0013] 3-2-2) Screening out empty charging lines, single power source plants and stations, line transformer groups, power plants, and important users from the load plants and stations obtained in step 3-2-1) to obtain screened load plants and stations;

[0014] 3-2-3) sequentially traverse the selected load plants obtained in step 3-2-2) and determine whether their high-voltage side buses are operating in separate or parallel order to determine the load transfer mode; wherein:

[0015] If any of the selected load plants is a split-operation plant, half of the load of the load plant under the overload object is transferred to form an adjustment unit corresponding to the load plant;

[0016] If any of the selected load plants is a parallel operation plant, then half of the load of the plant directly connected to the main transformer or under the section directly connected to the main transformer is transferred to form an adjustment unit corresponding to the load plant, or the entire load of the load plant is transferred to form an adjustment unit corresponding to the load plant;

[0017] 3-2-4) Based on the results of step 3-2-3), the adjustment units corresponding to each selected load station are combined into 1 unit, 2 units, ..., X units to form an adjustment unit combination, where X is the total number of selected load stations, and all the obtained adjustment unit combinations are then combined into an adjustment unit combination sequence;

[0018] Among them, in the combination of a single adjustment unit, any parallel operation plant station selects an adjustment unit formed by transferring half of the load of the plant station directly connected to the main transformer or under the main transformer section, or an adjustment unit formed by transferring the entire station load for combination;

[0019] 3-3) Selecting, from the adjustment unit combination sequence obtained in step 3-2), adjustment unit combinations whose transferable load is greater than or equal to the overload load of the overload object, and then sorting the selected adjustment unit combinations in ascending order of transferable load to form a subsequence;

[0020] 3-4) From the subsequence obtained in step 3-3), select the first adjustment unit combination as the current candidate combination;

[0021] 3-5) Perform corresponding load transfer according to each adjustment unit in the current candidate combination;

[0022] 3-6) Using the preset historical load curve, perform a superposition calculation and verification on the load of the overloaded object after the load transfer in step 3-5) to determine whether the overloaded object is still overloaded after the load transfer according to the current selected combination:

[0023] If not overloaded, keep the current candidate combination and go to step 3-7);

[0024] If the overload still exists, the next adjustment unit combination in the subsequence obtained in step 3-3) is selected as the new current candidate combination, and then the process returns to step 3-5) until the overload phenomenon of the overloaded object can be eliminated by load transfer according to the current candidate combination. The current candidate combination is then retained and the process proceeds to step 3-7);

[0025] 3-7) Using the preset historical load curve, perform a superposition calculation and verification on the directly connected main transformer or directly connected main transformer section after the load transfer of the current candidate combination retained in step 3-6) to determine whether the directly connected main transformer or main transformer section is overloaded after the load transfer according to the current candidate combination:

[0026] If it does not exist, the overload of the overload object is eliminated successfully and does not cause overload of the directly connected main transformer or the directly connected main transformer section, and the current candidate combination is output as a perfect combination;

[0027] If so, ignore the load transfer according to the current candidate combination, continue to select the next adjustment unit combination in the subsequence obtained in step 3-3) as the new current candidate combination, and then return to step 3-5);

[0028] If, after sequentially traversing all the adjustment unit combinations in the subsequence obtained in step 3-3), no combination exists that can eliminate the overload of the overloaded object without causing overload of the directly connected main transformer or the directly connected main transformer section after performing the corresponding load transfer according to each adjustment unit in any combination, then the adjustment unit combination in the subsequence obtained in step 3-3) that eliminates the overload of the overloaded object and has the smallest transferable load is output as a non-perfect combination;

[0029] 4) Judgment:

[0030] 4-1) If the output of step 3) is a perfect combination, then the perfect combination is the current load balancing strategy of the main power grid in the region, and the method ends;

[0031] 4-2) If the output of step 3) is a non-perfect combination, the operating mode of the overloaded 110 kV busbar directly connected to the power plant station resulting from the corresponding load transfer according to each adjustment unit in the non-perfect combination is read, where:

[0032] 4-2-1) If the overloaded 110 kV busbar of the directly connected power plant station is in parallel operation, the overloaded directly connected main transformer section is regarded as the current overload target, and the above strategy calculation unit is repeated to find a load transfer solution to eliminate the overload of the directly connected main transformer section;

[0033] Among them, if a perfect combination for eliminating the overload of the directly connected main transformer section is found, then the load balancing strategy of the main grid of the current regional power grid is generated, including: a non-perfect combination for eliminating the overload of the central main transformer section and a perfect combination for eliminating the overload of the directly connected main transformer section, and the method ends; if a non-perfect combination for eliminating the overload of the directly connected main transformer section is found, then the non-perfect combination for eliminating the overload of the central main transformer section and the non-perfect combination for eliminating the overload of the directly connected main transformer section are ignored, and then the process proceeds to step 5);

[0034] 4-2-2) If the overloaded 110 kV busbar of the direct-connected power plant / station is in separate operation, the overloaded direct-connected main transformer is treated as the current overloaded object, and the above strategy calculation unit is repeated to find a load transfer solution to eliminate the overload of the direct-connected main transformer;

[0035] Among them, if a perfect combination for eliminating overload of the directly connected main transformer is found, then the load balancing strategy of the main grid of the current regional power grid is generated, including: a non-perfect combination for eliminating overload of the central main transformer section and a perfect combination for eliminating overload of the directly connected main transformer, and the method ends; if a non-perfect combination for eliminating overload of the directly connected main transformer is found, then the non-perfect combination for eliminating overload of the central main transformer section and the non-perfect combination for eliminating overload of the directly connected main transformer are ignored, and then the process proceeds to step 5);

[0036] 5) Based on the initial operating mode of the central main transformer section overload, the overloaded central plant station 110 kV busbar is separated and calculated and verified according to the preset historical load curve to determine whether the central main transformer is overloaded:

[0037] If it does not exist, then generate the current load balancing strategy of the main grid of the regional power grid, which is to split the 110 kV busbar of the overloaded central plant station, and the method ends;

[0038] If it exists, go to step 6);

[0039] 6) Taking the 220 kV overloaded central main transformer as the current overloaded object, repeat the strategy calculation unit to find a load transfer solution to eliminate the overload of the central main transformer, where:

[0040] If a perfect combination for eliminating the overload of the central main transformer is found, the current load balancing strategy for the main grid of the regional power grid is generated, including: split operation of the 110 kV busbar of the overloaded central plant station and a perfect combination for eliminating the overload of the central main transformer, and the method ends; if a non-perfect combination for eliminating the overload of the central main transformer is found, the process proceeds to step 7);

[0041] 7) Based on the imperfect combination for eliminating overload of the central main transformer outputted in step 6), the operation mode of the overloaded direct-connected plant / station 110 kV bus resulting from the corresponding load transfer according to each adjustment unit in the imperfect combination is read, wherein:

[0042] If the overloaded 110 kV busbar directly connected to the plant station is in separate operation, proceed to step 9);

[0043] If the overloaded 110 kV busbar of the directly connected power plant station is in parallel operation, the overloaded directly connected main transformer section is taken as the current overload object, and the load transfer scheme is found to eliminate the overload of the directly connected main transformer section by repeating the strategy calculation unit; wherein, if a perfect combination for eliminating the overload of the directly connected main transformer section is found, the current load balancing strategy of the main network of the power grid in the region is generated, including: separate operation of the overloaded central power plant station 110 kV busbar, a non-perfect combination for eliminating the overload of the central main transformer, and a perfect combination for eliminating the overload of the directly connected main transformer section; if a non-perfect combination for eliminating the overload of the directly connected main transformer section is found, the non-perfect combination for eliminating the overload of the directly connected main transformer section is ignored, and based on the separate operation of the overloaded central power plant station 110 kV busbar and the non-perfect combination for eliminating the overload of the central main transformer, step 8 is then entered;

[0044] 8) After separating the overloaded 110 kV busbars of the directly connected power plant and substation, calculate and verify based on the preset historical load curve to determine whether there is an overload on the directly connected main transformer:

[0045] If it does not exist, then generate the current load balancing strategy of the main grid of the power grid in the region, including: split operation of the overloaded central plant station 110 kV bus, an imperfect combination of eliminating overload of the central main transformer, and split operation of the 110 kV bus of the directly connected plant station, and the method ends; if it exists, proceed to step 9);

[0046] 9) taking the overloaded directly connected main transformer as the current overload object, and finding a load transfer solution to eliminate the overload of the directly connected main transformer by repeating the strategy calculation unit;

[0047] If a perfect combination is found to eliminate overload of the directly connected main transformer, the load balancing strategy for the current regional power grid will include: split operation of the overloaded central power plant 110 kV busbar, an imperfect combination to eliminate overload of the central main transformer, and split operation of the directly connected power plant 110 kV busbar, a perfect combination to eliminate overload of the directly connected main transformer;

[0048] If a non-perfect combination is found to eliminate the overload of the directly connected main transformer, the non-perfect combination to eliminate the overload of the directly connected main transformer, the direct-connected plant and substation 110 kV busbar splitting, and the non-perfect combination to eliminate the overload of the central main transformer are ignored, and then based on the overloaded central plant and substation 110 kV busbar splitting operation mode, proceed to step 10);

[0049] 10) Load balancing is achieved by switching the 110 kV outgoing line to the overloaded central main transformer. The specific steps are as follows:

[0050] 10-1) Obtain the 110 kV load plant and 35 kV load plant under the main transformer of the same station;

[0051] 10-2) Eliminate empty charging lines, single power source plants, line transformer groups, power plants, and important users from the load plants obtained in step 10-1), and sort out the load plants that have a unique connection relationship between the main transformer at the same station and the directly connected plants, to obtain sorted load plants;

[0052] 10-3) sequentially traverse the sorted load stations obtained in step 10-2) and determine whether their high-voltage side busbars are operating in separate or parallel order to determine the load transfer mode; wherein:

[0053] If any of the sorted load stations is a split-operation station, half of the load of the station under the main transformer at the same station will be transferred to form an adjustment unit corresponding to the load station;

[0054] If any of the sorted load stations is a parallel operation station, half of the load of the station under the directly connected station will be transferred to form an adjustment unit corresponding to the load station, or the entire load of the load station will be transferred to form an adjustment unit corresponding to the load station;

[0055] 10-4) Based on the results of step 10-3), the adjustment units corresponding to the sorted load plants are combined into 1 unit, 2 units, ..., Y units to form a combination of interconnected adjustment units, where Y is the total number of load plants sorted in step 10-2); all the obtained interconnected adjustment unit combinations are then sorted from largest to smallest according to their corresponding transferable load amounts to obtain a sequence of interconnected adjustment unit combinations;

[0056] Among them, in a single interconnected adjustment unit combination, any parallel-operating power station chooses to transfer half of the load of the power station under the directly connected power station to form an adjustment unit or transfer the entire station load to form an adjustment unit for combination;

[0057] 10-5) Sequentially selecting each interconnection adjustment unit combination in the interconnection adjustment unit combination sequence obtained in step 10-4), performing corresponding load transfer according to each adjustment unit in the combination, and performing superposition calculation verification using a preset historical load curve after the transfer to determine whether the transfer causes overload on the opposite main transformer or the opposite main transformer section, wherein:

[0058] If the transfer does not cause overload of the opposite main transformer or the opposite main transformer section, the current contact adjustment unit combination is output and the process goes to step 10-6);

[0059] If the transfer causes the opposite main transformer or the opposite main transformer section to be overloaded, the next contact adjustment unit combination in the contact adjustment unit combination sequence is continuously selected for load transfer until the corresponding load transfer is performed according to the current contact adjustment unit combination and it is verified that the opposite main transformer or the opposite main transformer section is not overloaded, then the current contact adjustment unit combination is output and the process proceeds to step 10-6);

[0060] If, after traversing all the interconnection adjustment unit combinations in the sequence in step 10-4), no load transfer according to each adjustment unit in any interconnection adjustment unit combination does not cause overload of the opposite main transformer or the opposite main transformer section, no load transfer is performed under the same-station main transformer, and the process proceeds to step 10-6);

[0061] 10-6) Select non-zero load outgoing lines under the central main transformer, excluding the power plant, and then combine the selected load outgoing lines into 1 outgoing line, 2 outgoing lines, ..., Z outgoing lines to form an outgoing line combination, where Z is the total number of outgoing lines after screening. Then, all outgoing line combinations are combined into an outgoing line combination sequence;

[0062] 10-7) selecting, from the outgoing line combination sequence obtained in step 10-6), outgoing line combinations under the central main transformer that are less than or equal to the acceptable capacity of the main transformer at the same station, and sorting the combinations from large to small according to their load levels to form an outgoing line subsequence;

[0063] 10-8) Select each outgoing line combination from the outgoing line subsequence obtained in step 10-7) as the current outgoing line combination for bus switching, and then use the preset historical load curve to perform superposition calculation verification to calculate whether the main transformer at the same station is overloaded after bus switching:

[0064] If it is not overloaded, the current outgoing line combination is output and the process goes to step 11);

[0065] If overloaded, the next outgoing line combination is selected from the outgoing line subsequence as the new current outgoing line combination for bus switching, and then the preset historical load curve is used for superposition calculation verification until the bus switching is performed according to the current outgoing line combination and it is verified that it does not cause overload of the main transformer at the same station, then the current outgoing line combination is output and the process goes to step 11);

[0066] If, after traversing all outgoing line combinations in the outgoing line subsequence, no outgoing line combination reverses the busbar and after verification, it is not caused to overload the main transformer at the same station, then the busbar reverse operation is not performed and the load transfer operation of the main transformer at the same station is ignored; then, based on the overloaded central plant station 110 kV busbar split operation mode, proceed to step 12);

[0067] 11) Perform superposition calculation and verification based on the preset historical load curve to determine whether the central main transformer is overloaded after the mother is switched off:

[0068] If the central main transformer overload is eliminated, the current load balancing strategy of the regional power grid main network is generated, including: separate operation of the central plant station 110 kV busbar, load combination of the same station main transformer transferred to the external station, and load combination of the central main transformer to the same station main transformer busbar, and the method ends;

[0069] If the central main transformer is still overloaded, go to step 12);

[0070] 12) Taking the overloaded central main transformer as the current overload object, repeating the strategy calculation unit to find a load transfer solution to eliminate the overload of the central main transformer;

[0071] Among them, if the perfect combination for eliminating the overload of the central main transformer is found, the load balancing strategy of the current regional power grid main network is generated, including: split operation of the overloaded central plant station 110 kV busbar, load combination of transferring the main transformer at the same station to the external station, load combination of the central main transformer to the main transformer at the same station, and the perfect combination for eliminating the overload of the central main transformer, and the method ends;

[0072] If a non-perfect combination that eliminates the overload of the central main transformer is found, and the current process is the first round of regional power grid main network load balancing optimization, then proceed to step 13); if a non-perfect combination that eliminates the overload of the central main transformer is found, and the current process is the second round of regional power grid main network load balancing optimization, then proceed to step 14); if a non-perfect combination that eliminates the overload of the central main transformer is found, and the current process is the third round of regional power grid main network load balancing optimization, then proceed to step 18);

[0073] 13) Based on the load combinations of the overloaded central power plant station 110 kV busbar split operation, the load transfer from the same-station main transformer to the external station, the load transfer from the central main transformer to the same-station main transformer, and the imperfect combination of eliminating the overload of the central main transformer in the first round of regional power grid main network load balancing optimization, determine the overloaded central main transformer or central main transformer section in the second round of regional power grid main network load balancing optimization, select the load level corresponding to the moment of maximum overload in the historical curve verification of the overloaded central main transformer or central main transformer section in the second round of regional power grid main network load balancing optimization as the initial load for the second round of regional power grid main network load balancing optimization, and return to step 2) to perform the second round of regional power grid main network load balancing optimization;

[0074] 14) Based on the split operation of 110 kV busbars at overloaded central power plants and substations, the load combinations of transferring the main transformers at the same station to external stations, the load combinations of transferring the main transformers from the central main transformers to the main transformers at the same station, and the imperfect combinations of eliminating overload of the central main transformers in the second round of regional power grid main grid load balancing optimization, the overloaded central main transformers or central main transformer sections in the third round of regional power grid main grid load balancing optimization are determined, and the overloaded central main transformers or central main transformer sections in the third round of regional power grid main grid load balancing optimization are compared with the overloaded central main transformers or central main transformer sections in the first round of regional power grid main grid load balancing optimization:

[0075] If the main transformers or main transformer sections are different, the load level corresponding to the moment of maximum overload of the overloaded central main transformer or central main transformer section in the historical curve verification in the third round of regional power grid main network load balancing optimization is selected as the initial load of the third round of regional power grid main network load balancing optimization, and the process returns to step 2) to perform the third round of regional power grid main network load balancing optimization;

[0076] If the main transformer or main transformer section is the same, the imperfect combination for eliminating the overload of the central main transformer in the second round of regional power grid main grid load balancing optimization is ignored, and the process goes to step 15);

[0077] 16) Based on the load combination of the overloaded central power plant station 110 kV busbar in separate operation, the load combination of the same-station main transformer transferring to the external station, and the load combination of the central main transformer transferring to the same-station main transformer in the second round of regional power grid load balancing optimization, the overloaded central main transformer in the second round of regional power grid load balancing optimization is taken as the overload object, and steps 3-2) are repeated to obtain an adjustment unit combination sequence under the overloaded central main transformer in the second round of regional power grid load balancing optimization. Then, from the adjustment unit combination sequence, an adjustment unit combination with a transferable load greater than or equal to the overload load of the central main transformer in the second round of regional power grid load balancing optimization is selected and a subsequence is formed in ascending order of transferable load; adjustment unit combinations are sequentially selected from the subsequence, and corresponding load transfer is performed according to each adjustment unit in the combination. After each transfer, a preset historical load curve is used for row superposition calculation verification to determine whether the central main transformer in the second round of regional power grid load balancing optimization is overloaded after the transfer according to the load combination corresponding to the current adjustment unit combination:

[0078] If not overloaded, output the current adjustment unit combination and go to step 16);

[0079] If it is still overloaded, the next adjustment unit combination in the subsequence is selected to continue load transfer, verification, and judgment until the corresponding load transfer is performed according to each adjustment unit in the current adjustment unit combination to eliminate the overload of the central main transformer in the second round of regional power grid main network load balancing optimization, and then the current adjustment unit combination is output and the process goes to step 16);

[0080] 16) Based on the adjustment unit combination output from step 15), determine the current overloaded main transformer or main transformer section, and judge whether the overloaded main transformer or main transformer section is the same as the initial central main transformer or central main transformer section in the first round of regional power grid main network load balancing optimization:

[0081] If different, proceed to step 17);

[0082] If they are the same, then continue to select the next adjustment unit combination in the subsequence obtained in step 15) to continue load transfer, verification, and judgment until the corresponding load transfer according to each adjustment unit in the new current adjustment unit combination can eliminate the overload of the central main transformer in the second round of regional power grid main network load balancing optimization, and the overloaded main transformer or main transformer section caused by the corresponding load transfer according to each adjustment unit in the current adjustment unit combination is different from the initial central main transformer or central main transformer section in the first round of regional power grid main network load balancing optimization, then output the current adjustment unit combination and enter step 17);

[0083] 17) Determining the central main transformer or central main transformer section for the third round of regional power grid load balancing optimization based on the adjustment unit combination output from step 16), selecting the load level corresponding to the moment of maximum overload of the overloaded central main transformer or central main transformer section in the third round of regional power grid load balancing optimization in historical curve verification as the initial load for the third round of regional power grid load balancing optimization, and returning to step 2) to perform the third round of regional power grid load balancing optimization;

[0084] 18) Based on the load combinations of split operation of 110 kV busbars at overloaded central power plants and substations, transfer of loads from the same-station main transformer to an external station, transfer of loads from the central main transformer to the same-station main transformer, and imperfect combinations for eliminating overloads on the central main transformer in the third round of regional power grid main grid load balancing optimization, determine the current overloaded main transformer or main transformer section, and compare the current overloaded main transformer or main transformer section with the overloaded central main transformer or central main transformer section in the first round of regional power grid main grid load balancing optimization and the second round of regional power grid main grid load balancing optimization:

[0085] If the main transformers or main transformer sections are different, the generated regional power grid main network load balancing strategy includes: the output results of the first and second rounds of regional power grid main network load balancing optimization, and the overloaded central power station 110 kV busbar split operation in the third round of regional power grid main network load balancing optimization, the load combination of the main transformer at the same station transferred to the external station, the load combination of the central main transformer to the main transformer at the same station reverse bus, and the imperfect combination of eliminating the overload of the central main transformer. The method ends;

[0086] If the main transformer or main transformer section is the same, the imperfect combination for eliminating the overload of the central main transformer in the third round of regional power grid main grid load balancing optimization is ignored, and the process goes to step 19);

[0087] 19) Based on the load combinations of the overloaded central power plant station 110 kV busbar split operation, the transfer of the same-station main transformer to the external station, and the transfer of the central main transformer to the same-station main transformer in the third round of regional power grid load balancing optimization, the overloaded central main transformer in the third round of regional power grid load balancing optimization is taken as the overload object, and step 3-2) is repeated to obtain the adjustment unit combination sequence of the overloaded central main transformer in the third round of regional power grid load balancing optimization. Then, from the current adjustment unit combination sequence, an adjustment unit combination with a transferable load greater than or equal to the overload load of the central main transformer in the third round of regional power grid load balancing optimization is selected and a subsequence is formed in ascending order of transferable load; adjustment unit combinations are sequentially selected from the subsequence, and corresponding load transfer is performed according to each adjustment unit in the combination. After each transfer, a preset historical load curve is used for row superposition calculation verification to determine whether the central main transformer in the third round of regional power grid load balancing optimization is overloaded after the transfer according to the load combination corresponding to the current adjustment unit combination:

[0088] If it is not overloaded, the current adjustment unit combination is output and the process goes to step 20);

[0089] If it is still overloaded, the next adjustment unit combination in the subsequence is selected to continue load transfer, verification, and judgment until the overload of the central main transformer in the third round of regional power grid main network load balancing optimization is eliminated after corresponding load transfer according to each adjustment unit of the current adjustment unit combination. Then, the current adjustment unit combination is output and the process goes to step 20);

[0090] 20) Based on the adjustment unit combination output from step 19), determine the current overloaded main transformer or main transformer section, and determine whether the overloaded main transformer or main transformer section is the same as the central main transformer or central main transformer section in the first or second round of regional power grid main network load balancing optimization:

[0091] If they are different, the current adjustment unit combination is output, and the load balancing strategy of the regional power grid main network is generated, including: the output results of the first and second rounds of regional power grid main network load balancing optimization, and the load combination of the overloaded central power station 110 kV busbar split operation, the load transfer of the main transformer at the same station to the external station, the load transfer of the central main transformer to the main transformer at the same station, and the current adjustment unit combination for eliminating the overload of the central main transformer in the third round of regional power grid main network load balancing optimization, and the method ends;

[0092] If they are the same, continue to select the next adjustment unit combination in the subsequence obtained in step 19) to continue load transfer, verification and judgment, until the corresponding load transfer is performed according to each adjustment unit in the new current adjustment unit combination, and the overloaded main transformer or main transformer section caused by the corresponding load transfer according to each adjustment unit in the current adjustment unit combination is different from the central main transformer or central main transformer section in the first or second round, then output the current adjustment unit combination, and generate a regional power grid main grid load balancing strategy including: the output results of the first and second rounds of regional power grid main grid load balancing optimization, and the third round of overloaded regional power grid main grid load balancing optimization 110 kV busbar separate operation of the central plant station, the load combination of the main transformer at the same station transferred to the external station, the load combination of the central main transformer to the main transformer at the same station, and the current adjustment unit combination that eliminates the overload of the central main transformer, and the method ends.

[0093] The characteristics and beneficial effects of the present invention are:

[0094] Compared with relying on the dispatcher's operating experience to formulate a load balancing plan, the present invention comprehensively considers the advantages and disadvantages of operating modes such as the separate operation of the 110 kV busbar of the 220 kV substation, the reversal of the busbar of the 110 kV line switch, and the adjustment of the operating mode of the 110 kV and 35 kV substations, and takes into account the long-term load level of the power grid. By combining multiple adjustment methods, a regional power grid load balancing strategy is quickly generated, eliminating the problem of overload of main equipment or sections. The results are more accurate, the number of switch operations is reduced, and the safety, reliability and economy of the large power grid operation are guaranteed. BRIEF DESCRIPTION OF THE DRAWINGS

[0095] Figure 1 The figure is an overall flow chart of a method for generating a load balancing strategy for a regional power grid main network in a specific implementation of the present invention.

[0096] Figure 2 The figure is a flow chart of a strategy calculation unit in a specific implementation of the present invention.

[0097] Figure 3 The present invention is a flowchart of load balancing of 110 kV load outgoing lines in a 220 kV substation in a specific implementation of the present invention.

[0098] Specific implementation instructions

[0099] The present invention proposes a method for generating a load balancing strategy for a regional power grid main network. The content of the present invention will be further explained below in conjunction with the accompanying drawings and specific embodiments, and the technical solutions therein will be described clearly and completely.

[0100] The embodiment of the present invention proposes a method for generating a load balancing strategy for a regional power grid main network. In this embodiment, a certain 220 kV overloaded main transformer is defined as a central main transformer, a non-overloaded 220 kV main transformer at the same station as the central main transformer is defined as a co-station main transformer, a 220 kV main transformer that has a 110 kV or 35 kV connection relationship with the central main transformer is defined as a directly connected main transformer, and a 220 kV main transformer that has a 110 kV or 35 kV connection relationship with the directly connected main transformer is defined as a secondary connected main transformer. The overall process is as follows: Figure 1 As shown, the following steps are included:

[0101] 1) Read the current regional power grid operation mode, model, parameters, and expected fault information. If there is a 220 kV overloaded plant or station, enter the first round of regional power grid main network load balance optimization.

[0102] 2) Based on the result of step 1), determine whether the 110 kV busbars of the 220 kV overloaded power plants and substations in the regional power grid are in parallel operation:

[0103] If they are operated in parallel, proceed to step 3) to eliminate overload on the central main transformer section; if they are operated in separate columns, proceed to step 6) to eliminate overload on the central main transformer section;

[0104] 3) Taking the 220 kV overloaded central main transformer section as the current overload target, a load transfer scheme is sought through a preset strategy calculation unit to eliminate the overload of the central main transformer section; the overall process of the strategy calculation unit is as follows: Figure 2 The specific steps are as follows:

[0105] 3-1) Determine the overload load of the overload object;

[0106] 3-2) Obtain the adjustment unit combination sequence under the overload object. The specific steps are as follows:

[0107] 3-2-1) Obtain the 110 kV load plant and station and the 35 kV load plant and station under the overload object;

[0108] 3-2-2) Screening out empty charging lines, single power source plants and stations, line transformer groups, power plants, and important users from the load plants and stations obtained in step 3-2-1) to obtain screened load plants and stations;

[0109] 3-2-3) sequentially traverse the selected load plants obtained in step 3-2-2) and determine whether their high-voltage side buses are operating in separate or parallel order to determine the load transfer mode; wherein:

[0110] If the high-voltage side busbar of any selected load plant is in split operation, half of the load of the load plant under the overload object will be transferred to form an adjustment unit corresponding to the load plant;

[0111] If the high-voltage side busbar of any selected load station is in parallel operation, half of the load of the load station is transferred to the directly connected main transformer or under the directly connected main transformer section to form an adjustment unit corresponding to the load station, or the entire station load of the load station is transferred to form an adjustment unit corresponding to the load station;

[0112] 3-2-4) Based on the results of step 3-2-3), the adjustment units corresponding to each screened load station are combined into 1 unit, 2 units, ..., X units to form an adjustment unit combination, where X is the total number of screened stations. All the obtained adjustment unit combinations are then combined into an adjustment unit combination sequence.

[0113] It should be noted that, in this embodiment, in a single adjustment unit combination, any parallel-operating plant station can only choose to combine with one adjustment unit formed by transferring half of the load of the plant station directly connected to the main transformer or under the main transformer section, or one adjustment unit formed by transferring the entire station load. These two methods cannot appear in the same combination at the same time.

[0114] 3-3) Selecting an adjustment unit combination whose transferable load is greater than or equal to the overload load of the overload object from the adjustment unit combination sequence obtained in step 3-2), and then sorting the selected adjustment unit combinations in ascending order of transferable load to form a subsequence.

[0115] 3-4) From the subsequence obtained in step 3-3), the first adjustment unit combination is selected as the current candidate combination.

[0116] 3-5) Perform corresponding load transfer according to each adjustment unit in the current candidate combination;

[0117] 3-6) Using a preset historical load curve, a superimposed calculation is performed on the load of the overloaded object after the load transfer in step 3-5) (in this embodiment, the historical load curve of the 220 kV overloaded object is obtained by superimposing the historical load curve of the 110 kV main transformer it carries based on the grid operation mode adjusted in step 3-5). In this embodiment, the historical load curve can be selected by date and time period. In specific implementation, the selection is made by comprehensively considering factors such as temperature, humidity, work and rest, and production period) to determine whether the overloaded object is still overloaded after load transfer according to the currently selected combination:

[0118] If not overloaded, keep the current candidate combination and go to step 3-7);

[0119] If it is still overloaded, continue to select the next adjustment unit combination in the subsequence obtained in step 3-3) as the new current candidate combination, and then return to step 3-5) until the overload phenomenon of the overloaded object can be eliminated after load transfer according to the current candidate combination, then retain the current candidate combination and enter step 3-7).

[0120] 3-7) Using a preset historical load curve, superimposed calculation and verification are performed on the directly connected main transformer or directly connected main transformer section after load transfer of the current candidate combination retained in step 3-6) (in this embodiment, the historical load curve of the 220 kV directly connected main transformer or directly connected main transformer section is obtained by superimposing the historical load curve of the 110 kV main transformer it carries based on the grid operation mode adjusted in step 3-5)) to determine whether the directly connected main transformer or main transformer section is overloaded after load transfer according to the current candidate combination:

[0121] If it does not exist, the overload of the overload object is eliminated successfully and does not cause overload of the directly connected main transformer or the directly connected main transformer section, and the current candidate combination is output as a perfect combination;

[0122] If so, ignore the load transfer according to the current candidate combination, continue to select the next adjustment unit combination in the subsequence obtained in step 3-3) as the new current candidate combination, and then return to step 3-5);

[0123] If, after sequentially traversing all the adjustment unit combinations in the subsequence obtained in step 3-3), there is no combination that can eliminate the overload of the overloaded object without causing overload of the directly connected main transformer or the directly connected main transformer section after performing the corresponding load transfer according to each adjustment unit in any combination, then the adjustment unit combination in the subsequence obtained in step 3-3) that eliminates the overload of the overloaded object and has the smallest transferable load is output as a non-perfect combination.

[0124] 4) Judgment:

[0125] 4-1) If the output of step 3) is a perfect combination, then the perfect combination is the current load balancing strategy of the main power grid in the region, and the method ends;

[0126] 4-2) If the output of step 3) is a non-perfect combination, the operating mode of the overloaded 110 kV busbar directly connected to the power plant station resulting from the corresponding load transfer according to each adjustment unit in the non-perfect combination is read, where:

[0127] 4-2-1) If the overloaded 110 kV busbar of the directly connected power plant station is in parallel operation, the overloaded directly connected main transformer section is regarded as the current overload target, and the above strategy calculation unit is repeated to find a load transfer solution to eliminate the overload of the directly connected main transformer section;

[0128] Among them, if a perfect combination for eliminating the overload of the directly connected main transformer section is found, then the load balancing strategy of the main grid of the current regional power grid is generated, including: a non-perfect combination for eliminating the overload of the central main transformer section and a perfect combination for eliminating the overload of the directly connected main transformer section, and the method ends; if a non-perfect combination for eliminating the overload of the directly connected main transformer section is found, then the non-perfect combination for eliminating the overload of the central main transformer section and the non-perfect combination for eliminating the overload of the directly connected main transformer section are ignored, and then the process proceeds to step 5);

[0129] 4-2-2) If the overloaded 110 kV busbar of the direct-connected power plant / station is in separate operation, the overloaded direct-connected main transformer is treated as the current overloaded object, and the above strategy calculation unit is repeated to find a load transfer solution to eliminate the overload of the direct-connected main transformer;

[0130] Among them, if a perfect combination for eliminating overload of the directly connected main transformer is found, the load balancing strategy of the main grid of the current regional power grid is generated, including: a non-perfect combination for eliminating overload of the central main transformer section and a perfect combination for eliminating overload of the directly connected main transformer, and the method ends; if a non-perfect combination for eliminating overload of the directly connected main transformer is found, the non-perfect combination for eliminating overload of the central main transformer section and the non-perfect combination for eliminating overload of the directly connected main transformer are ignored, and then step 5 is entered).

[0131] 5) Based on the initial operating mode of the central main transformer section overload, the overloaded central plant station 110 kV busbar is separated and calculated and verified according to the preset historical load curve to determine whether the central main transformer is overloaded:

[0132] If it does not exist, then generate the current load balancing strategy of the main grid of the regional power grid, which is to split the 110 kV busbar of the overloaded central plant station, and the method ends;

[0133] If it exists, go to step 6).

[0134] 6) Taking the 220 kV overloaded central main transformer as the current overloaded object, repeat the strategy calculation unit to find a load transfer solution to eliminate the overload of the central main transformer, where:

[0135] If a perfect combination for eliminating the overload of the central main transformer is found, the load balancing strategy for the current power grid in the region is generated, including: separate operation of the 110 kV busbar of the overloaded central plant station and a perfect combination for eliminating the overload of the central main transformer, and the method ends; if a non-perfect combination for eliminating the overload of the central main transformer is found, proceed to step 7).

[0136] 7) Based on the imperfect combination for eliminating overload of the central main transformer outputted in step 6), the operation mode of the overloaded direct-connected plant / station 110 kV bus resulting from the corresponding load transfer according to each adjustment unit in the imperfect combination is read, wherein:

[0137] If the overloaded 110 kV busbar directly connected to the plant station is in separate operation, proceed to step 9);

[0138] If the overloaded 110 kV busbar of the direct-connected plant station is operated in parallel, the overloaded direct-connected main transformer section is taken as the current overload object, and the load transfer scheme is found to eliminate the overload of the direct-connected main transformer section by repeating the strategy calculation unit; wherein, if a perfect combination for eliminating the overload of the direct-connected main transformer section is found, the current load balancing strategy of the main grid of the power grid in the region is generated, including: the overloaded central plant station 110 kV busbar is operated in parallel, the non-perfect combination for eliminating the overload of the central main transformer, and the perfect combination for eliminating the overload of the direct-connected main transformer section; if a non-perfect combination for eliminating the overload of the direct-connected main transformer section is found, the non-perfect combination for eliminating the overload of the direct-connected main transformer section is ignored, and based on the overloaded central plant station 110 kV busbar being operated in parallel and the non-perfect combination for eliminating the overload of the central main transformer, step 8 is entered).

[0139] 8) After separating the overloaded 110 kV busbars of the directly connected power plant and substation, calculate and verify based on the preset historical load curve to determine whether there is an overload on the directly connected main transformer:

[0140] If it does not exist, the current load balancing strategy of the main grid of the power grid in the region is generated, including: split operation of the 110 kV busbar of the overloaded central plant station, an imperfect combination of eliminating overload of the central main transformer, and split operation of the 110 kV busbar of the directly connected plant station, and the method ends; if it exists, go to step 9).

[0141] 9) taking the overloaded directly connected main transformer as the current overload object, and finding a load transfer solution to eliminate the overload of the directly connected main transformer by repeating the strategy calculation unit;

[0142] If a perfect combination is found to eliminate overload of the directly connected main transformer, the load balancing strategy for the current regional power grid will include: split operation of the overloaded central power plant 110 kV busbar, an imperfect combination to eliminate overload of the central main transformer, and split operation of the directly connected power plant 110 kV busbar, a perfect combination to eliminate overload of the directly connected main transformer;

[0143] If a non-perfect combination that eliminates the overload of the directly connected main transformer is found, ignore the non-perfect combination that eliminates the overload of the directly connected main transformer, the direct-connected plant station 110 kV busbar split, and the non-perfect combination that eliminates the overload of the central main transformer, and then proceed to step 10 based on the overloaded central plant station 110 kV busbar split operation mode.

[0144] 10) Load balancing is achieved by switching the 110 kV outgoing line to the overloaded central main transformer. The overall process of switching the 110 kV outgoing line to the overloaded central main transformer is as follows: Figure 3 The specific steps are as follows:

[0145] 10-1) Obtain the 110 kV load plant and 35 kV load plant under the main transformer of the same station;

[0146] 10-2) Eliminate unused charging lines, single-source power plants, line transformer groups, power plants, and important users from the load plants obtained in step 10-1), and then sort out the load plants that have a unique connection between the main transformer and the directly connected plant at the same station (i.e., if there is only a single 110 kV or 35 kV connecting plant between the main transformer and the directly connected plant at the same station, then sort out such load plants), to obtain sorted load plants;

[0147] 10-3) sequentially traverse the sorted load stations obtained in step 10-2) and determine whether their high-voltage side busbars are operating in separate or parallel order to determine the load transfer mode; wherein:

[0148] If any of the sorted load stations is a split-operation station, half of the load of the station under the main transformer at the same station will be transferred to form an adjustment unit corresponding to the load station;

[0149] If any of the sorted load stations is a parallel operation station, half of the load of the station under the directly connected station will be transferred to form an adjustment unit corresponding to the load station, or the entire load of the load station will be transferred to form an adjustment unit corresponding to the load station;

[0150] 10-4) Based on the result of step 10-3), the adjustment units corresponding to each load plant after sorting are respectively combined into 1 unit, 2 units, ..., Y units to form a communication adjustment unit combination, where Y is the total number of load plants after sorting in step 10-2); then all the obtained communication adjustment unit combinations are sorted from large to small according to their corresponding transferable load amounts to obtain a communication adjustment unit combination sequence.

[0151] It should be noted that, in this embodiment, in a single interconnected adjustment unit combination, any parallel-operating plant station can only choose to combine with one adjustment unit formed by transferring half of the load of the plant station under the directly connected plant station or one adjustment unit formed by transferring the entire station load. These two methods cannot appear in the same combination at the same time.

[0152] 10-5) Sequentially selecting each interconnection adjustment unit combination in the interconnection adjustment unit combination sequence obtained in step 10-4), performing corresponding load transfer according to each adjustment unit in the combination, and performing superposition calculation verification using a preset historical load curve after the transfer to determine whether the transfer causes overload of the opposite-side power station main transformer or main transformer section, wherein:

[0153] If the transfer does not cause overload of the opposite main transformer or the opposite main transformer section, the current contact adjustment unit combination is output and the process goes to step 10-6);

[0154] If the transfer causes the opposite main transformer or the opposite main transformer section to be overloaded, the next contact adjustment unit combination in the contact adjustment unit combination sequence is continuously selected for load transfer until the corresponding load transfer is performed according to each adjustment unit in the current contact adjustment unit combination and it is verified that the opposite main transformer or the opposite main transformer section is not overloaded, then the current contact adjustment unit combination is output and the process goes to step 10-6);

[0155] If, after traversing all the interconnection adjustment unit combinations in the sequence in step 10-4), there is no load transfer according to each adjustment unit in any interconnection adjustment unit combination that does not cause overload of the opposite main transformer or the opposite main transformer section, then no load transfer is performed under the main transformer at the same station, and the process goes to step 10-6).

[0156] 10-6) Select non-zero load outgoing lines under the central main transformer except for the power plant, and then combine the selected load outgoing lines into 1 outgoing line, 2 outgoing lines, ..., Z outgoing lines to form an outgoing line combination, where Z is the total number of outgoing lines after screening. Then, all outgoing line combinations are combined into an outgoing line combination sequence.

[0157] 10-7) Selecting outgoing line combinations with load levels less than or equal to the acceptable capacity of the main transformer at the same station from the outgoing line combination sequence obtained in step 10-6) and sorting them from large to small according to load levels to form an outgoing line subsequence.

[0158] 10-8) Select each outgoing line combination from the outgoing line subsequence obtained in step 10-7) as the current outgoing line combination for bus switching, and then use the preset historical load curve to perform superposition calculation verification to calculate whether the main transformer at the same station is overloaded after bus switching:

[0159] If it is not overloaded, the current outgoing line combination is output and the process goes to step 11);

[0160] If overloaded, the next outgoing line combination is selected from the outgoing line subsequence as the new current outgoing line combination for bus switching, and then the preset historical load curve is used for superposition calculation verification until the bus switching is performed according to the current outgoing line combination and it is verified that it does not cause overload of the main transformer at the same station, then the current outgoing line combination is output and the process goes to step 11);

[0161] If after traversing all the outgoing line combinations in the outgoing line sub-sequence in turn, no outgoing line combination reverses the bus and after verification does not cause overload of the main transformer at the same station, the bus reverse operation will not be performed and the load transfer operation of the main transformer at the same station will be ignored; then based on the 110 kV busbar split operation mode of the overloaded central plant station, enter step 12).

[0162] 11) Perform superposition calculation and verification based on the preset historical load curve to determine whether the central main transformer is overloaded after the mother is switched off:

[0163] If the central main transformer overload is eliminated, the current load balancing strategy of the regional power grid main network is generated, including: separate operation of the central plant station 110 kV busbar, load combination of the same station main transformer transferred to the external station, and load combination of the central main transformer to the same station main transformer busbar, and the method ends;

[0164] If the central main transformer is still overloaded, go to step 12).

[0165] 12) Taking the overloaded central main transformer as the current overload object, repeating the strategy calculation unit to find a load transfer solution to eliminate the overload of the central main transformer;

[0166] Among them, if the perfect combination for eliminating the overload of the central main transformer is found, the load balancing strategy of the current regional power grid main network is generated, including: split operation of the overloaded central plant station 110 kV busbar, load combination of transferring the main transformer at the same station to the external station, load combination of the central main transformer to the main transformer at the same station, and the perfect combination for eliminating the overload of the central main transformer, and the method ends;

[0167] If a non-perfect combination that eliminates the overload of the central main transformer is found, and the current process is the first round of regional power grid main network load balancing optimization, then proceed to step 13); if a non-perfect combination that eliminates the overload of the central main transformer is found, and the current process is the second round of regional power grid main network load balancing optimization, then proceed to step 14); if a non-perfect combination that eliminates the overload of the central main transformer is found, and the current process is the third round of regional power grid main network load balancing optimization, then proceed to step 18).

[0168] 13) Based on the load combinations of the overloaded central plant station 110 kV busbar split operation, the transfer of the same-station main transformer to the external station, the load combination of the central main transformer to the same-station main transformer, and the non-perfect combination of eliminating the overload of the central main transformer in the first round of regional power grid main grid load balancing optimization, determine the overloaded central main transformer or central main transformer section in the second round of regional power grid main grid load balancing optimization, select the load level corresponding to the moment of maximum overload of the overloaded central main transformer or central main transformer section in the historical curve verification in the second round of regional power grid main grid load balancing optimization as the initial load of the second round of regional power grid main grid load balancing optimization, and return to step 2) to perform the second round of regional power grid main grid load balancing optimization.

[0169] 14) Based on the split operation of 110 kV busbars at overloaded central power plants and substations, the load combinations of transferring the main transformers at the same station to external stations, the load combinations of transferring the main transformers from the central main transformers to the main transformers at the same station, and the imperfect combinations of eliminating overload of the central main transformers in the second round of regional power grid main grid load balancing optimization, the overloaded central main transformers or central main transformer sections in the third round of regional power grid main grid load balancing optimization are determined, and the overloaded central main transformers or central main transformer sections in the third round of regional power grid main grid load balancing optimization are compared with the overloaded central main transformers or central main transformer sections in the first round of regional power grid main grid load balancing optimization:

[0170] If the main transformers or main transformer sections are different, the load level corresponding to the moment of maximum overload of the overloaded central main transformer or central main transformer section in the historical curve verification in the third round of regional power grid main network load balancing optimization is selected as the initial load of the third round of regional power grid main network load balancing optimization, and the process returns to step 2) to perform the third round of regional power grid main network load balancing optimization;

[0171] If the main transformer or main transformer section is the same, the imperfect combination for eliminating overload of the central main transformer in the second round of regional power grid main grid load balancing optimization is ignored, and the process goes to step 15).

[0172] 15) Based on the load combination of the overloaded central power plant station 110 kV busbar in separate operation, the load combination of the same-station main transformer transferring to the external station, and the load combination of the central main transformer transferring to the same-station main transformer in the second round of regional power grid load balancing optimization, the overloaded central main transformer in the second round of regional power grid load balancing optimization is taken as the overload object, and steps 3-2) are repeated to obtain an adjustment unit combination sequence under the overloaded central main transformer in the second round of regional power grid load balancing optimization. Then, from the adjustment unit combination sequence, an adjustment unit combination with a transferable load greater than or equal to the overload load of the central main transformer in the second round of regional power grid load balancing optimization is selected and a subsequence is formed in ascending order of transferable load; adjustment unit combinations are sequentially selected from the subsequence, and corresponding load transfer is performed according to each adjustment unit in the combination. After each transfer, a preset historical load curve is used for row superposition calculation verification to determine whether the central main transformer in the second round of regional power grid load balancing optimization is overloaded after load transfer according to the current adjustment unit combination:

[0173] If not overloaded, output the current adjustment unit combination and go to step 16);

[0174] If it is still overloaded, the next adjustment unit combination in the subsequence is selected to continue load transfer, verification and judgment until the corresponding load transfer is performed according to each adjustment unit in the current adjustment unit combination, and the overload of the central main transformer in the second round of regional power grid main network load balancing optimization can be eliminated. Then the current adjustment unit combination is output and step 16 is entered).

[0175] 16) Based on the adjustment unit combination output from step 15), determine the current overloaded main transformer or main transformer section, and judge whether the overloaded main transformer or main transformer section is the same as the central main transformer or central main transformer section in the first round of regional power grid main network load balancing optimization:

[0176] If different, proceed to step 17);

[0177] If they are the same, continue to select the next adjustment unit combination in the subsequence obtained in step 15) to continue load transfer, verification and judgment until the corresponding load transfer is performed according to each adjustment unit in the new current adjustment unit combination, and the overload of the central main transformer in the second round of regional power grid main network load balancing optimization can be eliminated, and the overloaded main transformer or main transformer section caused by the corresponding load transfer according to each adjustment unit in the current adjustment unit combination is different from the central main transformer or central main transformer section in the first round of regional power grid main network load balancing optimization, then output the current adjustment unit combination and enter step 17).

[0178] 17) Based on the adjustment unit combination output from step 16), determine the central main transformer or central main transformer section for the third round of regional power grid main network load balancing optimization, select the load level corresponding to the moment of the largest overload of the overloaded central main transformer or central main transformer section in the third round of regional power grid main network load balancing optimization in the historical curve verification as the initial load for the third round of regional power grid main network load balancing optimization, and return to step 2) to perform the third round of regional power grid main network load balancing optimization.

[0179] 18) Based on the load combinations of split operation of 110 kV busbars at overloaded central power plants and substations, transfer of loads from the same-station main transformer to an external station, transfer of loads from the central main transformer to the same-station main transformer, and imperfect combinations for eliminating overloads on the central main transformer in the third round of regional power grid main grid load balancing optimization, determine the current overloaded main transformer or main transformer section, and compare the current overloaded main transformer or main transformer section with the overloaded central main transformer or central main transformer section in the first round of regional power grid main grid load balancing optimization and the second round of regional power grid main grid load balancing optimization:

[0180] If the main transformers or main transformer sections are different, the generated regional power grid main network load balancing strategy includes: the output results of the first and second rounds of regional power grid main network load balancing optimization, and the overloaded central power station 110 kV busbar split operation in the third round of regional power grid main network load balancing optimization, the load combination of the main transformer at the same station transferred to the external station, the load combination of the central main transformer to the main transformer at the same station reverse bus, and the imperfect combination of eliminating the overload of the central main transformer. The method ends;

[0181] If the main transformer or main transformer section is the same, the imperfect combination for eliminating overload of the central main transformer in the third round of regional power grid main grid load balancing optimization is ignored, and the process goes to step 19).

[0182] 19) Based on the load combinations of the overloaded central power plant station 110 kV busbar split operation, the load transfer from the same-station main transformer to the external station, and the load transfer from the central main transformer to the same-station main transformer in the third round of regional power grid load balancing optimization, the overloaded central main transformer in the third round of regional power grid load balancing optimization is taken as the overload object, and step 3-2) is repeated to obtain the adjustment unit combination sequence of the overloaded central main transformer in the third round of regional power grid load balancing optimization. Then, from the current adjustment unit combination sequence, adjustment unit combinations with a transferable load greater than or equal to the overload load of the central main transformer in the third round of regional power grid load balancing optimization are selected and formed into a subsequence in ascending order of transferable load. Adjustment unit combinations are sequentially selected from the subsequence, and corresponding load transfers are performed according to each adjustment unit in the combination. After each transfer, a superposition calculation is performed using a preset historical load curve to verify whether the central main transformer in the third round of regional power grid load balancing optimization is overloaded after the load transfer according to the current adjustment unit combination:

[0183] If it is not overloaded, the current adjustment unit combination is output and the process goes to step 20);

[0184] If it is still overloaded, the next adjustment unit combination in the subsequence is selected to continue load transfer, verification and judgment until the corresponding load transfer is performed according to each adjustment unit in the current adjustment unit combination, and the overload of the central main transformer in the third round of regional power grid main network load balancing optimization can be eliminated. Then the current adjustment unit combination is output and step 20 is entered).

[0185] 20) Based on the adjustment unit combination output from step 19), determine the current overloaded main transformer or main transformer section, and determine whether the overloaded main transformer or main transformer section is the same as the central main transformer or central main transformer section in the first or second round of regional power grid main network load balancing optimization:

[0186] If they are different, the current adjustment unit combination is output, and the load balancing strategy of the regional power grid main network is generated, including: the output results of the first and second rounds of regional power grid main network load balancing optimization, and the load combination of the overloaded central power station 110 kV busbar split operation, the load transfer of the main transformer at the same station to the external station, the load transfer of the central main transformer to the main transformer at the same station, and the current adjustment unit combination for eliminating the overload of the central main transformer in the third round of regional power grid main network load balancing optimization, and the method ends;

[0187] If they are the same, the next adjustment unit combination in the subsequence obtained in step 19) is selected to continue load transfer, verification and judgment until the overload of the central main transformer in the third round of regional power grid main network load balancing optimization can be eliminated after the corresponding load transfer is performed according to each adjustment unit in the new current adjustment unit combination, and the overloaded main transformer or main transformer section caused by the corresponding load transfer according to each adjustment unit in the current adjustment unit combination is different from the central main transformer or central main transformer section in the first or second round, then the current adjustment unit combination is output, and the regional power grid main network load balancing strategy is generated, including: the output results of the first and second rounds of regional power grid main network load balancing optimization, and the third round of overloaded regional power grid main network load balancing optimization 110 kV busbar separate operation of the central plant station, the load combination of the main transformer at the same station transferred to the external station, the load combination of the central main transformer to the main transformer at the same station reverse bus, and the current adjustment unit combination that eliminates the overload of the central main transformer, and the method ends.

[0188] Regarding the description of the present invention, it should be noted that the above-described embodiments are only specific implementation methods of the present invention, which are used to illustrate the technical solutions of the present invention, rather than to limit them. The scope of protection of this application is not limited thereto. Although this application is described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that any person skilled in the art who is familiar with this technical field can still modify the technical solutions described in the aforementioned embodiments within the technical scope disclosed in this application, or can easily think of changes, or make equivalent replacements for some of the technical features therein; and these modifications, changes or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A method for generating a load balancing strategy for a regional power grid main network, characterized in that: include: 1) When there is a 220 kV overloaded power plant in the current regional power grid, the first round of regional power grid main grid load balancing optimization begins; 2) Determine whether the 110 kV busbars of the 220 kV overloaded power plants and substations in the regional power grid are operating in parallel: If the 110 kV busbars of the 220 kV overloaded power plant and station in the regional power grid are operated separately, proceed to step 3); 3) Taking the 220 kV overloaded central main transformer as the current overload object, a load transfer solution is found to eliminate the overload of the central main transformer through the preset strategy calculation unit, where: If the load transfer according to the load transfer scheme eliminates the overload of the overloaded object and does not cause overload of the directly connected main transformer or the main transformer section, the load transfer combination corresponding to the scheme is a perfect combination, and the method ends; If there is no perfect combination, the load transfer combination corresponding to the load transfer scheme that eliminates the overload of the overloaded object and minimizes the transferable load is selected as the imperfect combination, and then proceed to step 4); 4) Reading the operating mode of the overloaded direct-connected 110 kV busbar of the power plant station caused by the corresponding load transfer according to the imperfect combination output in step 3), wherein: If the overloaded 110 kV busbar directly connected to the plant station is in separate operation, proceed to step 5); 5) taking the overloaded directly connected main transformer as the current overload object, and finding a load transfer solution to eliminate the overload of the directly connected main transformer by repeating the strategy calculation unit; If a perfect combination for eliminating the overload of the directly connected main transformer is found, the method ends; otherwise, proceed to step 6); 6) Based on the 110 kV busbar split operation mode of the overloaded central plant station, load balancing is achieved by reversing the 110 kV outgoing busbars of the overloaded central main transformer; if the outgoing busbar combination is found to eliminate the overload of the main transformer at the same station, the process proceeds to step 7); otherwise, the process proceeds to step 8); 7) Based on the outgoing line combination found in step 6), perform superposition calculation and verification according to the preset historical load curve to determine whether the central main transformer is overloaded after the mother is switched: If the central main transformer is not overloaded, the method ends; otherwise, proceed to step 8); 8) Taking the overloaded central main transformer as the current overload object, repeat the strategy calculation unit to find a load transfer solution to eliminate the overload of the central main transformer; If a perfect combination is found to eliminate the overload of the central main transformer, the method ends; otherwise, in the first round of regional power grid main network load balancing optimization, step 9 is entered; 9) Based on the results of the first round of regional power grid main network load balancing optimization, determine the overloaded central main transformer or central main transformer section in the second round of regional power grid main network load balancing optimization, select the load level corresponding to the moment of the maximum overload of the overloaded central main transformer or central main transformer section in the second round of regional power grid main network load balancing optimization in the historical curve verification as the initial load of the second round of regional power grid main network load balancing optimization, and return to step 2) to perform the second round of regional power grid main network load balancing optimization.

2. The method according to claim 1, characterized in that The strategy calculation unit includes: 3-1) Determine the overload load of the overload object; 3-2) Obtain the adjustment unit combination sequence under the overload object. The specific steps are as follows: 3-2-1) Obtain the 110 kV power substation and 35 kV power substation under the overload object; 3-2-2) Screening out empty charging lines, single power source plants and stations, line transformer groups, power plants, and important users from the load plants and stations obtained in step 3-2-1) to obtain screened load plants and stations; 3-2-3) sequentially traverse the selected load plants obtained in step 3-2-2) and determine whether their high-voltage side buses are operating in separate or parallel order to determine the load transfer mode; wherein: If any of the selected load plants is a split-operation plant, half of the load of the load plant under the overload object is transferred to form an adjustment unit corresponding to the load plant; If any of the selected load plants is a parallel operation plant, then half of the load of the plant directly connected to the main transformer or under the section directly connected to the main transformer is transferred to form an adjustment unit corresponding to the load plant, or the entire load of the load plant is transferred to form an adjustment unit corresponding to the load plant; 3-2-4) Based on the results of step 3-2-3), the adjustment units corresponding to each selected load station are combined into 1 unit, 2 units, ..., X units to form an adjustment unit combination, where X is the total number of selected load stations, and all the obtained adjustment unit combinations are then combined into an adjustment unit combination sequence; 3-3) Selecting, from the adjustment unit combination sequence obtained in step 3-2), adjustment unit combinations whose transferable load is greater than or equal to the overload load of the overload object, and then sorting the selected adjustment unit combinations in ascending order of transferable load to form a subsequence; 3-4) From the subsequence obtained in step 3-3), select the first adjustment unit combination as the current candidate combination; 3-5) Perform corresponding load transfer according to each adjustment unit in the current candidate combination; 3-6) Using the preset historical load curve, perform a superposition calculation and verification on the load of the overloaded object after the load transfer in step 3-5) to determine whether the overloaded object is still overloaded after the load transfer according to the current selected combination: If not overloaded, keep the current candidate combination and go to step 3-7); If the overload still exists, the next adjustment unit combination in the subsequence obtained in step 3-3) is selected as the new current candidate combination, and then the process returns to step 3-5) until the overload phenomenon of the overloaded object can be eliminated by load transfer according to the current candidate combination. The current candidate combination is then retained and the process proceeds to step 3-7); 3-7) Using the preset historical load curve, perform a superposition calculation and verification on the directly connected main transformer or directly connected main transformer section after the load transfer of the current candidate combination retained in step 3-6) to determine whether the directly connected main transformer or main transformer section is overloaded after the load transfer according to the current candidate combination: If it does not exist, the overload of the overload object is eliminated successfully and does not cause overload of the directly connected main transformer or the directly connected main transformer section, and the current candidate combination is output as a perfect combination; If so, ignore the load transfer according to the current candidate combination, continue to select the next adjustment unit combination in the subsequence obtained in step 3-3) as the new current candidate combination, and then return to step 3-5); If, after sequentially traversing all the adjustment unit combinations in the subsequence obtained in step 3-3), there is no combination that can eliminate the overload of the overloaded object without causing overload of the directly connected main transformer or the directly connected main transformer section after performing the corresponding load transfer according to each adjustment unit in any combination, then the adjustment unit combination in the subsequence obtained in step 3-3) that eliminates the overload of the overloaded object and has the smallest transferable load is output as a non-perfect combination.

3. The method according to claim 2, characterized in that The method of determining whether the 110 kV busbars of the 220 kV overloaded power plant and substation in the regional power grid are in parallel operation also includes: 2-1) If a 220 kV overloaded power plant and station in the regional power grid operates in parallel with a 110 kV bus, the 220 kV overloaded central main transformer section is considered the current overload target, and a load transfer solution is sought through a preset strategy calculation unit to eliminate the overload at the central main transformer section; If a perfect combination is found, the method ends; otherwise, an imperfect combination is found, and the operating mode of the overloaded 110 kV busbar directly connected to the power plant station resulting from the corresponding load transfer according to each adjustment unit in the imperfect combination is read, and the process proceeds to step 2-2). 2-2) If the 110 kV busbar of the overloaded directly connected power plant station is in parallel operation, the overloaded directly connected main transformer section is treated as the current overload target, and the strategy calculation unit is repeated to find a load transfer solution to eliminate the overload of the directly connected main transformer section; if a perfect combination that eliminates the overload of the directly connected main transformer section is found, the method ends; otherwise, the method proceeds to step 2-3); If the 110 kV busbar of the overloaded direct-connected plant / station is in separate operation, the overloaded direct-connected main transformer is treated as the current overloaded object, and the strategy calculation unit is repeated to find a load transfer solution to eliminate the overload of the direct-connected main transformer; if a perfect combination to eliminate the overload of the direct-connected main transformer is found, the method ends; otherwise, the method proceeds to step 2-3); 2-3) Based on the initial operating mode of the central main transformer section overload, the overloaded central plant station 110 kV busbar is separated and calculated and verified according to the preset historical load curve to determine whether the central main transformer is overloaded: If it does not exist, the method ends; otherwise, proceed to step 3).

4. The method according to claim 3, characterized in that Also includes: When reading the operation mode of the overloaded direct-connected plant and station 110 kV busbar caused by the corresponding load transfer according to the imperfect combination output in step 3), if the overloaded direct-connected plant and station 110 kV busbar is in parallel operation, the overloaded direct-connected main transformer section is taken as the current overload object, and the load transfer scheme is found to eliminate the overload of the direct-connected main transformer section by repeating the strategy calculation unit; wherein, If a perfect combination is found to eliminate the overload of the directly connected main transformer section, the method ends; Otherwise, when the overloaded central plant station 110 kV busbar is operated in split mode, based on the imperfect combination of eliminating the overload of the central main transformer, the overloaded direct-connected plant station 110 kV busbar is split, and verification is performed to determine whether the direct-connected main transformer is overloaded: if not, the method ends; if so, proceed to step 5).

5. The method according to claim 4, characterized in that The load balancing is achieved by switching the 110 kV outgoing line to the overloaded central main transformer, including: 6-1) Obtain the 110 kV load plant and 35 kV load plant under the main transformer of the same station; 6-2) Eliminate empty charging lines, single power supply plants, line transformer groups, power plants, and important users from the load plants obtained in step 6-1), and sort out the load plants that have a unique connection relationship between the main transformer and the directly connected plant at the same station, to obtain sorted load plants; 6-3) sequentially traverse the sorted load stations obtained in step 6-2) and determine whether their high-voltage side busbars are operating in separate or parallel order to determine the load transfer mode; wherein: If any of the sorted load stations is a split-operation station, half of the load of the station under the main transformer at the same station will be transferred to form an adjustment unit corresponding to the load station; If any of the sorted load stations is a parallel operation station, half of the load of the station under the directly connected station will be transferred to form an adjustment unit corresponding to the load station, or the entire load of the load station will be transferred to form an adjustment unit corresponding to the load station; 6-4) Based on the results of step 6-3), the adjustment units corresponding to the sorted load plants are combined into 1 unit, 2 units, ..., Y units to form a combination of interconnected adjustment units, where Y is the total number of load plants sorted in step 10-2); all the obtained interconnected adjustment unit combinations are then sorted from largest to smallest according to their corresponding transferable load amounts to obtain a sequence of interconnected adjustment unit combinations; 6-5) Sequentially selecting each interconnection adjustment unit combination in the interconnection adjustment unit combination sequence obtained in step 6-4), performing corresponding load transfer according to each adjustment unit in the combination, and performing superposition calculation verification using a preset historical load curve after the transfer to determine whether the transfer causes overload on the opposite side main transformer or the opposite side main transformer section, wherein: If the transfer does not cause overload of the opposite main transformer or the opposite main transformer section, the current contact adjustment unit combination is output and the process goes to step 6-6); If the transfer causes the opposite main transformer or the opposite main transformer section to be overloaded, the next contact adjustment unit combination in the contact adjustment unit combination sequence is continuously selected for load transfer until the corresponding load transfer is performed according to the current contact adjustment unit combination and it is verified that the opposite main transformer or the opposite main transformer section is not overloaded, then the current contact adjustment unit combination is output and the process goes to step 6-6); If, after traversing all the interconnection adjustment unit combinations in the sequence obtained in step 6-4), no load transfer according to each adjustment unit in any interconnection adjustment unit combination does not cause overload of the opposite main transformer or the opposite main transformer section, then no load transfer is performed under the same-station main transformer, and the process proceeds to step 6-6); 6-6) Select non-zero load outgoing lines under the central main transformer, excluding the power plant, and then combine the selected load outgoing lines into 1 outgoing line, 2 outgoing lines, ..., Z outgoing lines to form an outgoing line combination, where Z is the total number of outgoing lines after screening. Then, all outgoing line combinations are combined into an outgoing line combination sequence; 6-7) Selecting, from the outgoing line combination sequence obtained in step 6-6), outgoing line combinations under the central main transformer that are less than or equal to the acceptable capacity of the main transformer at the same station and sorting the combinations from large to small according to their load levels to form an outgoing line subsequence; 6-8) Select each outgoing line combination from the outgoing line subsequence obtained in step 6-7) as the current outgoing line combination for bus switching, and then use the preset historical load curve to perform superposition calculation verification to calculate whether the main transformer at the same station is overloaded after bus switching: If it is not overloaded, the current output line combination is output and the process goes to step 7); If overloaded, the next outgoing line combination is selected from the outgoing line subsequence as the new current outgoing line combination for bus switching, and then the preset historical load curve is used for superposition calculation verification until the bus switching is performed according to the current outgoing line combination and it is verified that it does not cause overload of the main transformer at the same station. Then the current outgoing line combination is output and the process goes to step 7); If after traversing all the outgoing line combinations in the outgoing line sub-sequence in turn, no outgoing line combination is reversed and after verification, it does not cause overload of the main transformer at the same station, the reverse operation will not be performed and the load transfer operation of the main transformer at the same station will be ignored; then based on the 110 kV busbar split operation mode of the overloaded central plant station, go to step 8).

6. The method according to claim 5, characterized in that Also includes: In the second round of regional power grid main network load balancing optimization, when executing step 8), if a non-perfect combination that eliminates the overload of the central main transformer is found, further executing steps 10)-13); in: 10) Based on the results of the second round of regional power grid main network load balancing optimization, determine the overloaded central main transformer or central main transformer section in the third round of regional power grid main network load balancing optimization, and compare the overloaded central main transformer or central main transformer section in the third round of regional power grid main network load balancing optimization with the overloaded central main transformer or central main transformer section in the first round of regional power grid main network load balancing optimization: If the main transformers or main transformer sections are different, the load level corresponding to the moment of maximum overload of the overloaded central main transformer or central main transformer section in the historical curve verification in the third round of regional power grid main network load balancing optimization is selected as the initial load of the third round of regional power grid main network load balancing optimization, and the process returns to step 2) to perform the third round of regional power grid main network load balancing optimization; If the main transformer or main transformer section is the same, the imperfect combination for eliminating the overload of the central main transformer in the second round of regional power grid main grid load balancing optimization is ignored, and the process goes to step 11); 11) Taking the overloaded central main transformer in the second round of regional power grid main network load balancing optimization as the overloaded object, obtaining the adjustment unit combination sequence under the overloaded central main transformer in the second round of regional power grid main network load balancing optimization, then selecting adjustment unit combinations with transferable loads greater than or equal to the overloaded load of the central main transformer in the second round of regional power grid main network load balancing optimization from the adjustment unit combination sequence and forming a subsequence in ascending order of transferable loads; sequentially selecting adjustment unit combinations from the subsequence, performing corresponding load transfers according to each adjustment unit in the combination, and after each transfer, using a preset historical load curve for superposition calculation verification to determine whether the central main transformer in the second round of regional power grid main network load balancing optimization is overloaded after the transfer according to the load combination corresponding to the current adjustment unit combination: If it is not overloaded, the current adjustment unit combination is output and the process goes to step 12); If it is still overloaded, the next adjustment unit combination in the subsequence is selected to continue load transfer, verification, and judgment until the corresponding load transfer is performed according to each adjustment unit in the current adjustment unit combination to eliminate the overload of the central main transformer in the second round of regional power grid main network load balancing optimization, and then the current adjustment unit combination is output and the process goes to step 12); 12) Based on the adjustment unit combination output from step 11), determine the current overloaded main transformer or main transformer section, and judge whether the overloaded main transformer or main transformer section is the same as the initial central main transformer or central main transformer section in the first round of regional power grid main network load balancing optimization: If different, go to step 13); If they are the same, then continue to select the next adjustment unit combination in the subsequence obtained in step 11) to continue load transfer, verification, and judgment until the corresponding load transfer according to each adjustment unit in the new current adjustment unit combination can eliminate the overload of the central main transformer in the second round of regional power grid main network load balancing optimization, and the overloaded main transformer or main transformer section caused by the corresponding load transfer according to each adjustment unit in the current adjustment unit combination is different from the initial central main transformer or central main transformer section in the first round of regional power grid main network load balancing optimization, then output the current adjustment unit combination and enter step 13); 13) Based on the adjustment unit combination output from step 12), determine the central main transformer or central main transformer section for the third round of regional power grid main network load balancing optimization, select the load level corresponding to the moment of maximum overload of the overloaded central main transformer or central main transformer section in the third round of regional power grid main network load balancing optimization in the historical curve verification as the initial load for the third round of regional power grid main network load balancing optimization, and return to step 2) to perform the third round of regional power grid main network load balancing optimization.

7. The method according to claim 6, characterized in that Also includes: 14) After the third round of regional power grid main network load balancing optimization is completed, based on the results of the third round of regional power grid main network load balancing optimization, the current overloaded main transformer or main transformer section is determined, and the current overloaded main transformer or main transformer section is compared with the overloaded central main transformer or central main transformer section obtained in the first round of regional power grid main network load balancing optimization and the second round of regional power grid main network load balancing optimization: If it is a different main transformer or main transformer section, the method ends; If the main transformer or main transformer section is the same, the imperfect combination for eliminating the overload of the central main transformer in the third round of regional power grid main grid load balancing optimization is ignored, and the process goes to step 15); 15) Taking the overloaded central main transformer in the third round of regional power grid main network load balancing optimization as the overloaded object, obtaining the adjustment unit combination sequence under the overloaded central main transformer in the third round of regional power grid main network load balancing optimization, then selecting from the current adjustment unit combination sequence an adjustment unit combination whose transferable load is greater than or equal to the overload load of the central main transformer in the third round of regional power grid main network load balancing optimization and forming a subsequence in ascending order of transferable load; sequentially selecting adjustment unit combinations from the subsequence, performing corresponding load transfer according to each adjustment unit in the combination, and after each transfer, using a preset historical load curve for superposition calculation verification to determine whether the central main transformer in the third round of regional power grid main network load balancing optimization is overloaded after the transfer according to the load combination corresponding to the current adjustment unit combination: If not overloaded, output the current adjustment unit combination and go to step 16); If it is still overloaded, the next adjustment unit combination in the subsequence is selected to continue load transfer, verification, and judgment until the overload of the central main transformer in the third round of regional power grid main network load balancing optimization is eliminated after corresponding load transfer according to each adjustment unit of the current adjustment unit combination. Then, the current adjustment unit combination is output and the process goes to step 16); 16) Based on the adjustment unit combination output from step 15), determine the current overloaded main transformer or main transformer section, and determine whether the overloaded main transformer or main transformer section is the same as the central main transformer or central main transformer section in the first or second round of regional power grid main network load balancing optimization: If different, the method ends; If they are the same, continue to select the next adjustment unit combination in the subsequence obtained in step 15) to continue load transfer, verification and judgment until the corresponding load transfer is performed according to each adjustment unit in the new current adjustment unit combination, which can eliminate the overload of the central main transformer in the third round of regional power grid main network load balance optimization, and the overloaded main transformer or main transformer section caused by the corresponding load transfer according to each adjustment unit in the current adjustment unit combination is different from the central main transformer or central main transformer section in the first or second round, and the method ends.

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