Method for evaluating main transformer capacity expansion scheme of 500 kV substation power supply area

Abstract

The application discloses a kind of main transformer capacity expansion scheme evaluation methods of 500 kilovolt substation power supply area, including obtaining grid data and expansion scheme;Load rate safety margin under existing state is calculated and judged;Short-circuit current safety margin, line limit transmission capacity safety margin minimum value and the standard deviation of load in the network are calculated;Evaluation objective function is constructed and the main transformer capacity expansion scheme to be evaluated is evaluated.The 500 kilovolt substation power supply area main transformer capacity expansion scheme evaluation method provided by the application is comprehensively evaluated from four aspects of transformer load rate safety margin, bus short-circuit current safety margin, line limit transmission capacity safety margin and the standard deviation of load in the network of main transformer, which not only realizes more comprehensive and objective scheme evaluation, but also has higher reliability, better stability, and is more objective and scientific.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of electrical automation, and particularly relates to a main transformer capacity expansion scheme evaluation method for a 500 kV substation power supply area. BACKGROUND

[0002] With the development of economy and technology and the improvement of people's living standards, electric energy has become an essential secondary energy in people's production and life, bringing endless convenience to people's production and life. Therefore, guaranteeing the stable and reliable supply of electric energy has become one of the most important tasks of the power system.

[0003] At present, the scale of China's power grid continues to expand, and the power grid load continues to increase. In the case of maintaining the same power grid transformer capacity, the ratio between the power grid transformer capacity and the load will decrease year by year. When the main transformer of a substation fails, the load carried by the transformer will be transferred to other transformers. At this time, if the transformer capacity of other transformers is insufficient, it will lead to equipment overload or power failure, thereby threatening the safe and stable operation of the power grid and increasing the difficulty of power grid operation control. The power grid capacity-load ratio has always been a key factor restricting the safe operation of the power grid. Maintaining the power grid capacity-load ratio within a certain range will be conducive to guaranteeing the safe and stable power consumption of users and improving the power supply reliability of the power grid.

[0004] At present, the provincial power grids are usually interconnected through 500 kV voltage level tie lines. When there is a power shortage in a certain region, mutual support between regions can be realized through 500 kV tie lines, thereby improving the safe and stable operation ability of the regional power grid. The main transformer capacity of the 500 kV substation directly determines its load carrying capacity as a power support carrier. According to the safety and stability operation regulations of the power system, when a main transformer in the power supply area fails, the remaining transformers are required to maintain reliable power supply without power failure. Therefore, the 500 kV substation must maintain sufficient power supply capacity to meet the demand of load development.

[0005] However, with the rapid development of society, the power load of the power system also increases rapidly, and the load of the main transformer of the 500kV substation also increases rapidly. In order to ensure the load capacity of the 500kV substation and ensure that other transformers do not overload or power off in the case of main transformer failure, increasing the transformer capacity of the 500kV substation supply area becomes the primary task. For different 500kV substation power supply area main transformer capacity expansion scheme, the power system needs to comprehensively evaluate from the aspects of system operation safety and stability, so as to select the best scheme. However, in actual operation, the current power system only evaluates the pros and cons of the scheme through engineering experience and subjective judgment of the expert group. This subjective judgment method has the defects of low reliability and poor stability, and this method is not scientific, which also brings certain safety hazards to the power system. SUMMARY

[0006] The purpose of the present application is to provide a 500kV substation power supply area main transformer capacity expansion scheme evaluation method with high reliability, good stability and objectivity.

[0007] The 500kV substation power supply area main transformer capacity expansion scheme evaluation method provided by the present application comprises the following steps:

[0008] S1. Obtain the power grid data of the 500kV substation power supply area and the main transformer capacity expansion scheme to be evaluated;

[0009] S2. According to the data obtained in step S1, calculate the load rate safety margin of the remaining main transformer when any one transformer fails and stops running in the existing state;

[0010] S3. According to the load rate safety margin of the remaining main transformer obtained in step S2, make the following judgment:

[0011] If the load rate safety margin of the remaining main transformer meets the set condition, it is determined that the 500kV substation power supply area does not need to be expanded in main transformer capacity, and the evaluation is ended;

[0012] If the load rate safety margin of the remaining main transformer does not meet the set condition, it is determined that the 500kV substation power supply area needs to be expanded in main transformer capacity, and the subsequent steps are continued;

[0013] S4. According to the data obtained in step S1, calculate the short-circuit current safety margin of the 220kV bus in the 500kV substation in the 500kV substation power supply area in the existing state;

[0014] S5. According to the data obtained in step S1, the minimum value of the line limit transmission capacity safety margin of each 220 kV transmission line in the 500 kV substation power supply area when a certain 500 kV main transformer fails is calculated under the existing state;

[0015] S6. According to the data obtained in step S1, the standard deviation of the 500 kV main transformer off-network load in the 500 kV substation power supply area is calculated under each main transformer capacity expansion scheme to be evaluated;

[0016] S7. Based on the calculated load rate safety margin, short-circuit current safety margin, minimum value of line limit transmission capacity safety margin and standard deviation of 500 kV main transformer off-network load, an evaluation objective function is constructed;

[0017] S8. According to the value of the evaluation objective function obtained in step S7, the main transformer capacity expansion scheme to be evaluated is evaluated.

[0018] According to the data obtained in step S1, the load rate safety margin of the remaining main transformer when any one transformer fails is calculated under the existing state, and the specific steps are as follows:

[0019] The load rate safety margin of the remaining main transformer when any one transformer fails is calculated by the following formula:

[0020]

[0021] In the formula, α i is the load rate safety margin of the i-th main transformer; P load,N,i is the rated capacity of the i-th main transformer; P load,i is the load of the i-th main transformer when any one transformer in the supply area fails; i is 1, 2,..., n, and n is the number of main transformers in the 500 kV substation power supply area; α i > 0 indicates that the main transformer load rate is in a safe state, α i < 0 indicates that the main transformer load rate is in an unsafe state, and α i = 0 indicates that the main transformer load rate is in a critical safe state.

[0022] The step S3 specifically includes the following steps:

[0023] If the load rate safety margin α i of the remaining main transformer satisfies α i > 0.2, it is determined that the 500 kV substation power supply area does not need to be expanded in main transformer capacity, and the evaluation is ended;

[0024] If the load rate safety margin αi satisfies a i ≤0.2, it is determined that the current 500 kV substation power supply area needs to be expanded in main transformer capacity, and the subsequent steps are continued.

[0025] Step S4 calculates the short-circuit current safety margin of the 220 kV bus in the 500 kV substation in the 500 kV substation power supply area under the existing state according to the data obtained in step S1, and specifically includes the following steps:

[0026] The short-circuit current safety margin of the 220 kV bus is calculated by the following formula:

[0027]

[0028] In the formula, β j is the short-circuit current safety margin of the jth 220 kV bus in the 500 kV substation; I N is the breaking capacity of the 220 kV circuit breaker; I is the short-circuit current when the 220 kV bus is in three-phase short circuit; j takes the value of 1, 2, …, m, and m is the number of 220 kV buses in the 500 kV substation; the greater the short-circuit current safety margin β j , the greater the safety margin for short-circuit current, and β j > 0 indicates that the short-circuit current level is in a safe state, β j < 0 indicates that the short-circuit current level is in an unsafe state.

[0029] Step S5 calculates the minimum value of the line limit transmission capacity safety margin of each 220 kV transmission line in the 500 kV substation power supply area when a certain 500 kV main transformer fails under the existing state according to the data obtained in step S1, and specifically includes the following steps:

[0030] The minimum value of the line limit transmission capacity safety margin of each 220 kV transmission line in the 500 kV substation power supply area when a certain main transformer fails is calculated by the following formula:

[0031]

[0032] In the formula, P k,line,N is the limit transmission capacity of the kth 220 kV transmission line; P k,line is the actual transmission capacity of the kth 220 kV transmission line.

[0033] Step S6 calculates the standard deviation of the 500 kV main transformer grid-connected load in the 500 kV substation power supply area under each main transformer capacity expansion scheme to be evaluated according to the data obtained in step S1, and specifically includes the following steps:

[0034] The average value P of the 500 kV main transformer off-network load in the 500 kV substation power supply area is calculated Train,i ;

[0035] The average value P of the 500 kV main transformer off-network load in the 500 kV substation power supply area is calculated ave Wherein n1 is the number of 500 kV main transformers in the power supply area after the current to be evaluated scheme is adopted;

[0036] According to the average value P ave , the standard deviation σ of the 500 kV main transformer off-network load in the 500 kV substation power supply area is calculated

[0037] Step S7: Based on the calculated minimum values of the load rate safety margin, the short-circuit current safety margin, the line limit transmission capacity safety margin and the standard deviation of the 500 kV main transformer off-network load, an evaluation objective function is constructed, which specifically includes the following steps:

[0038] The following formula is used as the evaluation objective function:

[0039]

[0040] In the formula, F is the objective function value of the evaluation objective function; β is the minimum value of the current safety margin and β = min(β j ), β j is the short-circuit current safety margin of the jth 220 kV bus in the 500 kV substation; α is the minimum value of the load rate safety margin and α = min(α i ), α i is the load rate safety margin of the ith main transformer; η is the minimum value of the line limit transmission capacity safety margin η of each 220 kV bus in the 500 kV substation power supply area when a certain main transformer fails; σ is the standard deviation of the 500 kV main transformer off-network load in the 500 kV substation power supply area; k is a variable coefficient, and the value rule is: if α, β and η are all greater than 0, then k = 0, otherwise k = 1.

[0041] Step S8: According to the value of the evaluation objective function obtained in step S7, the main transformer capacity expansion scheme to be evaluated is evaluated, which specifically includes the following steps:

[0042] If the value F of the evaluation objective function is greater than 0, it means that the main transformer capacity expansion scheme to be evaluated is feasible; at the same time, the greater the value of F, the better the performance of the corresponding main transformer capacity expansion scheme to be evaluated;

[0043] ​If the value of the evaluation objective function F is less than or equal to 0, it indicates that the main transformer capacity expansion scheme to be evaluated is not feasible.

[0044] The main transformer capacity expansion scheme evaluation method for the 500 kV substation power supply area provided by the application comprehensively evaluates the main transformer capacity expansion scheme from four aspects of transformer load rate safety margin, bus short-circuit current safety margin, line limit transmission capacity safety margin and standard deviation of the load of the main transformer, realizes more comprehensive and objective scheme evaluation, and has higher reliability, better stability and more objectivity and science. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 The figure is a method flowchart of the method of the application.

[0046] Figure 2 The figure is a power supply area power grid geographical connection schematic diagram of the embodiment of the method of the application. DETAILED DESCRIPTION

[0047] As Figure 1 The figure is a method flowchart of the method of the application: the main transformer capacity expansion scheme evaluation method for the 500 kV substation power supply area provided by the application includes the following steps:

[0048] S1. obtaining power grid data of the 500 kV substation power supply area and a main transformer capacity expansion scheme to be evaluated;

[0049] S2. calculating the load rate safety margin of the remaining main transformer when any one transformer fails and stops running in the existing state according to the data obtained in step S1; specifically including the following steps:

[0050] The load rate safety margin of the remaining main transformer when any one transformer fails and stops running is calculated by using the following formula:

[0051]

[0052] In the formula, α i is the load rate safety margin of the i th main transformer; P load,N,i is the rated capacity of the i th main transformer; P load,i is the load of the i th main transformer when any one transformer in the power supply area fails and stops running; the value of i is 1, 2,..., n, and n is the number of main transformers in the 500 kV substation power supply area; α i > 0 indicates that the main transformer load rate is in a safe state, α i < 0 indicates that the main transformer load rate is in an unsafe state, α i = 0 indicates that the main transformer load rate is in a critical safe state; when the main transformer load rate is less than or equal to 0.2, it indicates that the transformer is in a heavy load state;

[0053] S3. According to the load rate safety margin of the remaining main transformer obtained in step S2, the following judgment is made:

[0054] If the load rate safety margin of the remaining main transformer meets the set condition, it is determined that the 500 kV substation power supply area does not need to be expanded in main transformer capacity, and the evaluation ends.

[0055] If the load rate safety margin of the remaining main transformer does not meet the set condition, it is determined that the 500 kV substation power supply area needs to be expanded in main transformer capacity, and the subsequent steps are continued.

[0056] In specific implementation, the following steps are specifically included:

[0057] If the load rate safety margin of the remaining main transformer α i meets α i > 0.2, it is determined that the 500 kV substation power supply area does not need to be expanded in main transformer capacity, and the evaluation ends.

[0058] If the load rate safety margin of the remaining main transformer α i meets α i ≤ 0.2, it is determined that the 500 kV substation power supply area needs to be expanded in main transformer capacity, and the subsequent steps are continued.

[0059] S4. According to the data obtained in step S1, the short-circuit current safety margin of the 220 kV bus in the 500 kV substation in the 500 kV substation power supply area under the existing state is calculated; specifically including the following steps:

[0060] The short-circuit current safety margin of the 220 kV bus is calculated by the following formula:

[0061]

[0062] In the formula, β j is the short-circuit current safety margin of the jth 220 kV bus in the 500 kV substation; I N is the breaking capacity of the 220 kV circuit breaker; I is the short-circuit current when the 220 kV bus is in three-phase short circuit; j takes the value of 1, 2,..., m, and m is the number of 220 kV buses in the 500 kV substation; the larger the short-circuit current safety margin β j , the greater the safety margin for short-circuit current, β j > 0 indicates that the short-circuit current level is in a safe state, and β j < 0 indicates that the short-circuit current level is in an unsafe state.

[0063] S5. According to the data obtained in step S1, the minimum value of the line limit transmission capacity safety margin of each 220 kV transmission line in the 500 kV substation power supply area when a certain 500 kV main transformer fails is calculated under the existing state; specifically comprising the following steps:

[0064] The minimum value of the line limit transmission capacity safety margin of each 220 kV transmission line in the 500 kV substation power supply area when a certain 500 kV main transformer fails is calculated by the following formula:

[0065]

[0066] In the formula, P k,line,N is the limit transmission capacity of the kth 220 kV transmission line; P k,line is the actual transmission capacity of the kth 220 kV transmission line;

[0067] S6. According to the data obtained in step S1, the standard deviation of the 500 kV main transformer off-network load in the 500 kV substation power supply area is calculated under each main transformer capacity expansion scheme to be evaluated; specifically comprising the following steps:

[0068] The off-network load P Train,i of each main transformer after the capacity of the 500 kV main transformer is increased in the 500 kV substation power supply area under each main transformer capacity expansion scheme to be evaluated is calculated by power flow calculation under the given year and operation mode.

[0069] The average value P ave of the 500 kV main transformer off-network load in the 500 kV substation power supply area is calculated as where n1 is the number of 500 kV main transformers in the power supply area after the current to be evaluated scheme is adopted;

[0070] According to the average value P ave , the standard deviation σ of the 500 kV main transformer off-network load in the 500 kV substation power supply area is calculated as

[0071] S7. Based on the calculated load rate safety margin, short-circuit current safety margin, minimum value of line limit transmission capacity safety margin, and standard deviation of 500 kV main transformer off-network load, an evaluation objective function is constructed; specifically comprising the following steps:

[0072] The following formula is used as the evaluation objective function:

[0073]

[0074] In the formula, F is the objective function value; β is the minimum value of the current safety margin and β = min(βj ), β j is the short-circuit current safety margin of the jth 220 kV bus in the 500 kV substation; α is the minimum load rate safety margin and α = min(α i ), α i is the load rate safety margin of the ith main transformer; η is the minimum line limit transmission capacity safety margin of each 220 kV bus in the 500 kV substation power supply area when a main transformer fails; σ is the standard deviation of the 500 kV main transformer grid load in the 500 kV substation power supply area; k is a variable coefficient, and the value is as follows: if α, β and η are all greater than 0, then k = 0, otherwise k = 1;

[0075] S8. Evaluate the main transformer capacity expansion scheme to be evaluated according to the value of the evaluation target function obtained in step S7; specifically including the following steps:

[0076] If the value F of the evaluation target function is greater than 0, it indicates that the main transformer capacity expansion scheme to be evaluated is feasible; at the same time, the greater the value of F, the better the performance of the corresponding main transformer capacity expansion scheme to be evaluated;

[0077] If the value F of the evaluation target function is less than or equal to 0, it indicates that the main transformer capacity expansion scheme to be evaluated is not feasible.

[0078] The following further illustrates the method of the application in combination with a specific embodiment:

[0079] Taking a certain 500 kV power supply area power grid as an example, the necessity of increasing the capacity of the 500 kV main transformer in the area power grid is analyzed, and different main transformer capacity expansion schemes are comprehensively evaluated. The geographical connection diagram of the power supply area power grid is as shown in Figure 2 ; the 500 kV power supply area main transformer N-1 checking data under the given year operation mode is as shown in Table 1:

[0080] Table 1 shows the 500 kV power supply area main transformer N-1 checking data under the given year operation mode

[0081]

[0082] As can be seen from the results in Table 1, when the main transformers of 500 kV substation A and 500 kV substation B fail, the load rate safety margin of the main transformer of 500 kV substation C is less than 0, therefore, the 500 kV substation power supply area needs to increase the capacity of the 500 kV voltage level main transformer under the given year operation mode. According to the analysis, the following three solutions are obtained.

[0083] Solution one, expand one main transformer (1x100 million kVA) of 500 kV substation C.

[0084] Scheme two, expand 500 kV substation A one main transformer (1 x 100 million kVA).

[0085] Scheme three, expand 500 kV substation B one main transformer (1 x 100 million kVA).

[0086] For the above different schemes, the different schemes can be obtained under the power supply area within the 500 kV substation main transformer N-1 checking table, as shown in table 2, table 3, table 4 and table 5:

[0087] Table 2 after taking scheme one area 500 kV main transformer N-1 checking data schematic table (unit: million kVA)

[0088]

[0089] Table 3 after taking scheme two area 500 kV main transformer N-1 checking data schematic table (unit: million kVA)

[0090]

[0091] Table 4 after taking scheme three area 500 kV main transformer N-1 checking data schematic table (unit: million kVA)

[0092]

[0093] Table 5 different scheme 500 kV substation 220 kV bus short circuit current comparison table (unit: kA)

[0094] Bus name Scheme 1 Scheme 2 Scheme 3 C station I section bus 37.3 49.3 48.6 C station II section bus 33.0 / / A station II section bus 44.7 48.9 45.8 B station I section bus 42.2 43.9 50.4 B station II section bus 38.1 38.1 38.12

[0095] According to the power flow calculation results and the data of table 2 to table 5, the maximum value of the load rate of other main transformers when any one transformer in the 500 kV substation power supply area fails (N-1) under different schemes can be calculated, the minimum value of the short circuit current safety margin of the 220 kV bus in the 500 kV substation, the maximum load rate of the 220 kV line in the power supply area when a main transformer in the 500 kV substation fails, the standard deviation of the 500 kV main transformer grid load in the power supply area, the specific data is shown in table 6:

[0096] Table 6 different scheme parameters and objective function value table

[0097]

[0098] According to the above analysis, the objective function value F of the first scheme is 0.033, the objective function value F of the second scheme is 0.002, and the objective function value of the third scheme is less than 0. Therefore, the first and second schemes are feasible schemes, and the third scheme is an infeasible scheme. In the feasible schemes, the F value of the first scheme is larger, and therefore the first scheme is selected as the 500 kV power supply area main transformer capacity expansion scheme.

Claims

1. A method for evaluating the expansion scheme of the main transformer capacity in a 500 kV substation power supply area, comprising the following steps: S1. Obtain power grid data for the 500 kV substation's power supply area and the proposed expansion plan for the main transformer capacity to be evaluated; S2. Based on the data obtained in step S1, calculate the load rate safety margin of the remaining main transformers under the current conditions when any transformer fails and stops operating; specifically including the following steps: The load factor safety margin of the remaining main transformers when any one transformer fails and goes out of service is calculated using the following formula: In the formula Let be the load factor safety margin of the i-th main transformer; Let be the rated capacity of the i-th main transformer; Let be the load of the i-th main transformer when any transformer in the supply area fails and goes out of service; The value is , The number of main transformers within the power supply area of ​​a 500 kV substation; This indicates that the main transformer load rate is in a safe state. This indicates that the main transformer load rate is in an unsafe state. This indicates that the main transformer load rate is at a critical safety state; S3. Based on the load factor safety margin of the remaining main transformer obtained in step S2, make the following judgment: If the load rate safety margin of the remaining main transformers meets the set conditions, it is determined that the current 500 kV substation power supply area does not require expansion of the main transformer capacity, and the assessment ends. If the load rate safety margin of the remaining main transformer does not meet the set conditions, it is determined that the current 500 kV substation power supply area needs to expand the main transformer capacity, and the subsequent steps will continue. S4. Based on the data obtained in step S1, calculate the short-circuit current safety margin of the 220 kV busbar within the 500 kV substation supply area under the current conditions; specifically including the following steps: The short-circuit current safety margin of the 220 kV busbar is calculated using the following formula: In the formula The short-circuit current safety margin for the j-th 220 kV busbar in a 500 kV substation; The breaking capacity of a 220 kV circuit breaker; The short-circuit current is given by the given value when a three-phase short circuit occurs on a 220 kV busbar; the value of j is... , This refers to the number of 220 kV busbars within a 500 kV substation. Short-circuit current safety margin The larger the value, the greater the safety margin for short-circuit current. This indicates that the short-circuit current level is in a safe condition. This indicates that the short-circuit current level is in an unsafe condition; S5. Based on the data obtained in step S1, calculate the minimum safety margin of the ultimate transmission capacity of each 220 kV transmission line in the power supply area of ​​the 500 kV substation under the current conditions when a certain 500 kV main transformer fails and stops operating. Specifically, the steps include the following: The minimum safety margin of the ultimate transmission capacity of each 220 kV transmission line within the power supply area of ​​a 500 kV substation when a main transformer fails and is out of service is calculated using the following formula. : In the formula This represents the maximum transmission capacity of the kth 220 kV transmission line. This represents the actual transmission capacity of the kth 220 kV transmission line. S6. Based on the data obtained in step S1, calculate the standard deviation of the load on the grid connection of the 500 kV main transformer within the power supply area of ​​the 500 kV substation under each proposed expansion scheme for the main transformer capacity to be evaluated; specifically including the following steps: By using power flow calculations, the grid load of each main transformer in the power supply area of ​​the 500 kV substation is calculated under various main transformer capacity expansion schemes to be evaluated, given the increase in the capacity of the 500 kV main transformer in a given year and operating mode. ; Calculate the average load of the 500 kV main transformer in the power supply area of ​​the 500 kV substation. for ,in This refers to the number of 500 kV main transformers in the power supply area after adopting the current scheme to be evaluated; According to the average The standard deviation of the load on the grid from the 500 kV main transformer within the power supply area of ​​the 500 kV substation was calculated. for ; S7. Based on the calculated load factor safety margin, short-circuit current safety margin, minimum safety margin of line ultimate transmission capacity, and standard deviation of the load disconnected from the grid by the 500 kV main transformer, construct the evaluation objective function; specifically including the following steps: The following formula is used as the evaluation objective function: In the formula The objective function value; The minimum current safety margin and , The short-circuit current safety margin for the j-th 220 kV busbar in a 500 kV substation; The minimum safety margin of load rate and , Let be the load factor safety margin of the i-th main transformer; The minimum safety margin of the ultimate transmission capacity of each 220 kV busbar within the power supply area of ​​a 500 kV substation when a main transformer fails and is out of service. ; The standard deviation of the load on the grid of the 500 kV main transformer within the power supply area of ​​the 500 kV substation; For the coefficients of the variables, and the rules for their values ​​are as follows: If , and If all are greater than 0, then ,otherwise ; S8. Based on the value of the evaluation objective function obtained in step S7, evaluate the main transformer capacity expansion scheme to be evaluated.

2. The evaluation method for the main transformer capacity expansion scheme of the 500 kV substation power supply area according to claim 1, characterized in that... Step S3 specifically includes the following steps: If the remaining main transformer has a safety margin in load rate satisfy If the current 500 kV substation power supply area is deemed not to require expansion of the main transformer capacity, the assessment is concluded. If the remaining main transformer has a safety margin in load rate satisfy If so, it is determined that the current 500 kV substation power supply area needs to expand the main transformer capacity, and subsequent steps will continue.

3. The evaluation method for the main transformer capacity expansion scheme of a 500 kV substation power supply area according to claim 2, characterized in that... Step S8, which evaluates the main transformer capacity expansion scheme based on the value of the evaluation objective function obtained in step S7, specifically includes the following steps: If we evaluate the value of the objective function This indicates that the proposed expansion plan for the main transformer capacity is feasible; at the same time... The larger the value, the better the performance of the corresponding transformer capacity expansion scheme to be evaluated; If we evaluate the value of the objective function If the result is negative, it means that the proposed expansion plan for the main transformer capacity is not feasible.

Images