CN102622711B - Power distribution network planning method based on maximum power supply capacity - Google Patents

Abstract

A distribution network planning method based on the maximum power supply capacity, which obtains the current grid data and load forecast data; judges whether the distance between the new load and the existing substation is greater than the first threshold, and if so, there is a power supply blind area, and adopts Class C If not, calculate the maximum power supply capacity of the current power grid; when the maximum power supply capacity is greater than the planned total load, each main transformer load matches the maximum power supply capacity and each load level meets the main transformer N-1 safety check, the process Otherwise, adopt measures of type B and type C to adjust the total power supply capacity; or adopt measures of type A to adjust the distribution of load among the main transformers; this method reduces the dependence on capacity-load ratio indicators and fully utilizes existing The potential of the network can delay the construction of the power grid and solve the problems of land shortage and high cost of power grid construction; this method can provide a distribution scheme that matches the distribution of load and maximum power supply capacity, so as to achieve the purpose of fully utilizing the power supply capacity of the power grid.

Description

A distribution network planning method based on maximum power supply capacity

technical field

The invention relates to the field of power distribution systems, in particular to a distribution network planning method based on maximum power supply capacity.

Background technique

my country has experienced more than ten years of large-scale urban and rural power grid planning and construction, and traditional planning based on the steps of status analysis, load forecasting, substation and network planning has played an important role. For the distribution network areas that have been built so far, the load density is high and the load growth is slow, and the traditional planning methods are facing challenges.

The advantage of the traditional planning method lies in the medium and long-term target network structure planning, which is more suitable for the rapid development of distribution network and new districts. For the distribution network that has been basically developed, the traditional distribution network planning has the following deficiencies: First, in the traditional planning stage of substation site selection and capacity determination, only the N-1 safety principle is considered when determining the main variable capacity configuration of the substation. The mutual support of the main transformers in the station does not take into account the impact of load mutual supply in the distribution network. Secondly, traditional planning is greatly affected by the accuracy of load forecasting, while load development involves many factors, there are uncertainties, and accurate forecasting is very difficult. Finally, traditional planning mainly uses N-1 simulation verification to evaluate safety, that is, to verify whether the power grid can continue to supply power safely when components exit at a given load level, and then process the verification results of all cases The security index is obtained to evaluate the security of the distribution network at a certain load level.

The power supply capacity of distribution network is a very important new indicator in the planning and construction of distribution network in recent years, and it has been applied in the practice of distribution network construction and transformation in many cities in my country. The power supply capability referred to in the current literature is precisely defined as TSC (Total Supply Capability, maximum power supply capability). TSC refers to the TSC of a given distribution network under the condition that the distribution network in a certain power supply area satisfies the N-1 criterion, taking into account the transfer capacity of the main transformer in the substation and the distribution network and the maximum load supply capacity under the actual operation constraints. For the calculation method, please refer to the literature [1]. The current research on power supply capacity mainly focuses on the accurate calculation and modeling of the power supply capacity of a given distribution network. Literature [2] analyzed the theoretical maximum space for mining the potential of TSC through an example, and defined the TSC index family, pointing out that many new optimization methods can be generated based on these new indexes and giving examples.

In the process of realizing the present invention, the inventor finds that at least the following disadvantages and deficiencies exist in the prior art:

The existing technology is based on the empirical value of capacity-load ratio, and the results tend to be conservative, and are greatly affected by the accuracy of load forecasting. They do not fully consider the improvement of power supply capacity brought about by network interconnection, and do not give full play to the potential of the existing network. In many areas, there are problems of power grid land shortage and high cost.

references

[1] Xiao Jun, Wang Chengshan, Ge Shaoyun, etc. An accurate calculation method for the maximum power supply capacity of medium-voltage distribution network. Patent Publication No. CN102025153A, published on April 20, 2011;

[2] Jun Xiao, Fangxing Li, Wenzhuo Gu, et al, "Total Supply Capability and its Extended Indices for Distribution Systems: Definition, Model Calculation and Applications", IET Generation, Transmission&Distribution, Volume 5, Issue 8, pp.869-876, August 2011.

Contents of the invention

The invention provides a distribution network planning method based on the maximum power supply capacity. The invention fully exploits the potential of the existing network, fully utilizes the existing network to accommodate new loads, improves the asset efficiency of the power grid, and solves the problem of land shortage and For issues with higher costs, see the description below:

A distribution network planning method based on maximum power supply capacity, said method comprising the following steps:

(1) Based on the planning measures of the maximum power supply capacity TSC, according to the degree of change to the power grid, define the priority of the power supply capacity adjustment measures A-type measures, B-type measures and C-type measures;

(2) Obtain current grid data and load forecast data;

(3) Judging whether the distance between the newly added load and the existing substation is greater than the first threshold, if yes, there is a power supply blind area, and step (4) is performed; if not, there is no power supply blind area, and step (5) is performed;

(4) Adopt the measures of category C, add a substation, and re-execute step (3);

(5) Calculate the maximum power supply capacity TSC of the current grid;

(6) Determine whether the maximum power supply capacity TSC is greater than the planned total load, if yes, perform step (7); if not, perform step (8);

(7) Determine whether each main transformer load matches the maximum power supply capacity TSC, if yes, perform step (9); if not, perform step (10);

(8) Adjust the total power supply capacity by adopting the B-category measures and the C-category measures, and re-execute step (5);

(9) Determine whether each load level meets the main transformer N-1 safety check, if yes, perform step (11); if not, perform step (12);

(10) adopt described A class measures to adjust the distribution of load among the main transformers, and re-execute step (7);

(11) The process ends;

(12) Adopting the above-mentioned type A measures or the above-mentioned type B measures to transform the line, or adopting the above-mentioned type B measures to increase the feeder, and re-execute step (9).

The priority A-type measures, B-type measures, and C-type measures for defining power supply capacity adjustment measures are specifically:

A-type measures: load redistribution measures, A-type measures are divided into four measures according to priority: A1 adjust switch status, A2 adjust switch position, A3 new load access and A4 load cut;

Type B measures: Measures for feeder planning. Type B measures are divided into three measures according to priority: B1 replacement of conductors, B2 new connection and B3 new feeder measures;

Type C measures: Measures planned for substations. Type C measures are divided into three measures according to priority: C1 new main transformer, C2 replacement of main transformer and C3 new substation.

The adjustment of the total power supply capacity by adopting the B-category measures and the C-category measures is specifically:

1) Calculate the TSC when all main transformers are interconnected in pairs, that is, when the current grid reaches full connection and the connection capacity reaches the second threshold;

2) Determine whether the maximum power supply capacity TSC is greater than the planned total load, if yes, perform step 3); if not, perform step 4);

3) adopt the B class measures to optimize the grid structure, recalculate the new TSC, and perform step 5);

4) Adopt the measures of category C, increase the variable capacity, and re-execute step 1);

5) Judging whether the new maximum power supply capacity TSC is greater than the planned total load, re-executing step 3) or 4) according to the judgment result, and finally making the new TSC greater than the planned total load.

The distribution of the adjustment load among the main transformers by using the A-type measures is specifically:

1) Establish a load redistribution model that matches the maximum power supply capacity TSC;

Max F＝w ₁ SDI-w ₂ VAT (1)

1) Objective function F

The objective function F uses the weight vector W(w ₁ , w ₂ ) to describe two sub-objectives: main transformer N-1 safety and load rate balance;

(1) Safety of main transformer N-1;

The main transformer N-1 safety index SDI takes the minimum value of the N-1 safety distance and main transformer load margin among all main transformers, SD _i refers to the safety distance of main transformer i, and the range is [0, +∞) , that is, the difference between the total potential transferable load of all main transformers connected with main transformer i and the actual load value of main transformer i; AL _i refers to the load of main transformer i after load distribution; k when the main transformer is short Allowable overload factor; and Respectively represent the set of main transformers connected in the station and the set of connected main transformers outside the station in the main transformer contact unit centered on the main transformer i; R _i and T _i are respectively the rated capacity of the main transformer i and the maximum load that satisfies the load balance under TSC Rate;

(2) load rate balance V _VLR ;

2) Constraints

Constraint 1: N-1 load transfer constraint;

Formulas 2, 3, 4 and 5 are the constraints of load transfer, which means that when the main transformer i fails, the normal load of the main transformer i before the accident will be transferred jointly by the rest of the main transformers in the station and the main transformers in other stations; Tri _{, j} The size of the load transferred to the main transformer j when the main transformer i fails;

Constraint 2: load distribution constraint;

Formulas 6, 7, 8 and 9 are load distribution constraints; the existing load distribution refers to the change and redistribution of the main transformer load caused by the change of the open-loop point position between the contact lines; the new load distribution refers to the consideration of the substation The scope of power supply, the new load will be distributed to each main transformer.

Among them, m is the number of main transformers; l is the number of newly added loads; OL _i is the load of main transformer i before distribution; SL _ij is the load value cut from main transformer i to main transformer j; The actual possibility of switch position operation, there is an upper limit value SL _{ij Max} for the load value; DL _li is the load value distributed by the new load l to the main transformer i, and the sum of all DL _il related to the new load l is equal to the new The load value NL _l of the increased load l; the load value borne by each main transformer after distribution should be less than or equal to R _i T _i , that is, the constraint condition of load transfer between main transformers needs to be satisfied; R _j and T _j are respectively the rated capacity and the maximum load rate that satisfies load balancing under TSC; AL _j refers to the load of main transformer j after load distribution.

(2) According to the load redistribution model, the distribution of load among the main variables is adjusted through the linear programming method.

The beneficial effect of the technical solution provided by the present invention is: the method first considers optimizing the structure and operation mode of the distribution network to improve the TSC to meet the load, and then considers adding new variable capacity, so as to fully utilize the existing network to accommodate the new load 1. The purpose of improving the efficiency of power grid assets is very suitable for the planning of complex power distribution networks in urban built-up areas; With the potential of the network, it can delay the construction of the power grid and solve the problems of land shortage and high cost of power grid construction; this method can realize the calculated maximum power supply capacity under the actual power grid load level, that is, the distribution of the given load and the maximum power supply capacity can be matched distribution scheme to achieve the purpose of fully utilizing the power supply capacity of the power grid.

Description of drawings

Fig. 1 is a flow chart of a distribution network planning method based on maximum power supply capacity provided by the present invention;

Fig. 2 is the flow chart that adopts B type measure and C type measure to adjust the total amount of power supply capacity provided by the present invention;

Fig. 3 is the schematic diagram of the current power grid provided by the present invention;

Fig. 4 is the schematic diagram that is based on TSC total amount check adjustment that the present invention provides;

Fig. 5 is a schematic diagram of a traditional planning solution provided by the prior art.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the implementation manner of the present invention will be further described in detail below in conjunction with the accompanying drawings.

In order to give full play to the potential of the existing network, make full use of the existing network to accommodate new loads, improve the efficiency of grid assets, and solve the problems of grid land shortage and high cost, see Figure 1. The embodiment of the present invention provides a The distribution network planning method for power supply capacity is described in detail below:

101: Based on the planning measures of the maximum power supply capacity TSC, according to the degree of change to the power grid, define the priority of the power supply capacity adjustment measures A-type measures, B-type measures and C-type measures;

Among them, the priority levels of measures are defined as 3 major categories and 10 subcategories from high to low, that is, measures of category A have the highest priority and measures of category C have the lowest priority. The specific priority of power supply capacity adjustment measures is defined as follows:

(1) Type A measures: measures for load redistribution. Type A measures are further divided into four measures according to priority: A1 to adjust the switch state, A2 to adjust the switch position, A3 to connect new loads and A4 to change loads.

Among them, type A measures do not change the grid structure, but only change the redistribution of load between feeders and main transformers.

(2) Type B measures: Measures for feeder planning. Type B measures are divided into three types according to priority: B1 replacement of wires, B2 new connection and B3 new feeder.

(3) Category C measures: measures for substation planning, and category C measures are divided into three measures according to priority: C1 new main transformer, C2 replacement of main transformer and C3 new substation.

The above measures can be used in combination, and the order of priority is not absolute. If it is really not necessary to take the next-level measures first to achieve the planning goal, the measures at this level should be adopted first according to the order of priority; if the next-level measures need to be used first, such as when building a new substation, the actual order should be C3 first Measures for the new substation, and then consider the construction of the grid structure on the basis of the outgoing line of the substation.

102: Obtain current grid data and load forecast data;

Among them, the current grid data includes: the area covered by the grid, the structure of the grid frame, and the load type, etc.; the load forecast data includes: the growth of the existing load, the size and location of the new load, and possible access points in the current grid, etc. .

103: Determine whether the distance between the newly added load and the existing substation is greater than the first threshold, if yes, there is a power supply blind area, and perform step 104; if not, there is no power supply blind area, perform step 105;

Wherein, the first threshold is set according to requirements in practical applications, and is not limited in this embodiment of the present invention during specific implementation.

104: Adopt C-type measures, add new substations, and re-execute step 103;

That is, when the distance between the new load and the existing substation is greater than the first threshold, a power supply blind zone is formed, and C3 new substation in category C measures is adopted.

105: Calculate the maximum power supply capacity TSC of the current grid;

Among them, the calculation method of the maximum power supply capacity TSC of the power grid is as follows: establish a mathematical model with the maximum power supply capacity of the distribution network as the objective function, convert the calculation into a linear programming problem, and use the linear programming software to calculate the objective function, which is the existing " For the exact maximum power supply capacity under the N-1" constraint, refer to reference [1] for details, and the embodiments of the present invention will not be repeated here.

106: Determine whether the maximum power supply capacity TSC is greater than the planned total load, if yes, go to step 107; if not, go to step 108;

Among them, a certain margin can be considered according to the needs in practical applications during specific implementation, that is, to judge whether the sum of the maximum power supply capacity TSC and the margin is greater than the planned total load, and the value of the margin is determined through specific calculations, which is not done in the embodiment of the present invention. limit.

107: Determine whether each main transformer load matches the maximum power supply capacity TSC, if yes, perform step 109; if not, perform step 110;

108: Adjust the total power supply capacity by adopting B-category measures and C-category measures, and re-execute step 105;

Wherein, referring to Fig. 2, this step includes: digging potential power supply capacity, performing verification and adjustment of the total power supply capacity, specifically:

(1) Calculate the TSC when all main transformers are interconnected in pairs, that is, when the current grid reaches full connection and the connection capacity reaches the second threshold;

Wherein, the second threshold is set according to requirements in practical applications, which is not limited in this embodiment of the present invention during specific implementation.

(2) Determine whether the maximum power supply capacity TSC is greater than the planned total load, if yes, perform step (3); if not, perform step (4);

Wherein, a certain margin may also be considered in the specific judgment.

(3) adopt B type measures to optimize the grid structure, recalculate the new TSC, and perform step (5);

That is, B1, B2 and B3 measures can be used to optimize the grid structure.

(4) Adopt C-type measures, increase the variable capacity, and re-execute step (1);

That is, the measures of C1, C2 and C3 can be adopted to increase the variable capacity.

(5) Determine whether the new maximum power supply capacity TSC is greater than the planned total load, and re-execute step (3) or (4) according to the judgment result, and finally make the new TSC greater than the planned total load.

109: Determine whether each load level meets the main transformer N-1 safety check, if yes, go to step 111; if not, go to step 112;

110: Adopt A-type measures to adjust the distribution of load among the main transformers, and re-execute step 107;

Among them, adjusting the load distribution among the main transformers is a problem of implementing the calculated maximum power supply capacity TSC results in the actual power grid. When the maximum power supply capacity TSC of the entire network is greater than the total load, it does not mean that the local grid can meet the N-1 safety check. At this time, the load is redistributed in the grid to achieve all N-1 checks. The steps are:

(1) Establish a load redistribution model that matches the maximum power supply capacity TSC;

The problem of load redistribution matching TSC is described as: under the condition of definite substation and network structure, satisfying the N-1 safety criterion of the main transformer, by changing the position and state of the tie switch in the tie line, and optimizing the distribution of the newly added load, the The line where the existing load is located is cut and modified, and finally a solution that satisfies N-1 security and load rate balance is formed.

The specific load redistribution model is:

Max F＝w ₁ SDI-w ₂ VAT (1)

1) Objective function F

The load redistribution model is a multi-objective programming problem. The objective function F in Formula 1 uses the weight vector W(w ₁ , w ₂ ) to describe two sub-objectives: the safety of the main transformer N-1 and the balance of load ratio.

(1) Safety of main transformer N-1;

The main transformer N-1 safety index SDI takes the minimum value of the N-1 safety distance and main transformer load margin among all main transformers, as shown in formulas (11) and (12). SD _i refers to the safety distance of main transformer i, and the range is [0, +∞). That is, the difference between the total potential transferable load of all main transformers connected with main transformer i and the actual load value of main transformer i. AL _i refers to the load of main transformer i after load distribution. The overload factor is allowed when k is the main variable. and Respectively denote the set of connected main transformers in the station and the set of connected main transformers outside the station in the main transformer connection unit centered on the main transformer i. R _i and T _i are respectively the rated capacity of the main transformer i and the maximum load rate that satisfies load balancing under TSC.

(2) Load rate balance V _VLR .

The balance of load rate refers to the balance degree of the load rate of the main transformer, which prevents the simultaneous occurrence of partial main transformer overload and part of the main transformer light load, and obtains a reasonable load distribution scheme. The load rate balance VAT is calculated according to formula (10).

2) Constraints

Constraint 1: N-1 load transfer constraint;

Formulas 2, 3, 4 and 5 are the constraints of load transfer, which means that when the main transformer i fails, the normal load of the main transformer i before the accident will be transferred jointly by the rest of the main transformers in the station and the contacting main transformers of other stations. Tri _{, j} is the size of the load transferred to the main transformer j when the main transformer i fails.

Constraint 2: load distribution constraints;

Equations 6, 7, 8 and 9 are load distribution constraints. Existing load distribution refers to the change and redistribution of the load borne by the main transformer caused by the change of the open-loop point position between the tie lines. New load distribution refers to the distribution of new loads to each main transformer considering the power supply range of the substation.

Among them, m is the number of main transformers; l is the number of newly added loads; OL _i is the load of main transformer i before distribution; SL _ij is the load value cut from main transformer i to main transformer j; The actual possibility of switch position operation, there is an upper limit value SL _{ij Max} for the load value; DL _li is the load value distributed by the new load l to the main transformer i, and the sum of all DL _il related to the new load l is equal to the new The load value NL _l of the increased load l; the load value borne by each main transformer after distribution should be less than or equal to R _i T _i , that is, the constraint condition of load transfer between main transformers needs to be satisfied; R _j and T _j are respectively the rated capacity and the maximum load rate that satisfies load balancing under TSC; AL _j refers to the load of main transformer j after load distribution.

(2) According to the load redistribution model, the distribution of load among the main variables is adjusted through the linear programming method.

The linear programming method may use a general linear programming method, such as the linear programming software Lingo, and other linear programming methods may also be used in specific implementation, which is not limited in the embodiment of the present invention.

111: the process ends;

112: Use type A measures or type B measures to transform the line, or use type B measures to add feeders, and re-execute step 109.

Among them, this method is used to solve the problem of realizing the TSC obtained by theoretical calculation in the actual power grid, and can find the optimal load distribution method that satisfies the main transformer N-1 under the condition that the basic structure of the distribution network remains unchanged.

The following is a specific experiment to verify the feasibility of a distribution network planning method based on the maximum power supply capacity provided by the embodiment of the present invention, see the following description for details:

Referring to Figure 3, the basic situation of the current 10kV distribution network is as follows: 3 110kV substations with a total capacity of 240MVA, the current load is 128MVA, and the capacity-to-load ratio is 1.875. The planned annual total load is 188MVA, the new total load is 60MVA, the new load of L1～L4 is 6MVA, and the new load of L5～L7 is 12MVA. Table 1 shows the status of the main transformer in the current network, Table 2 shows the newly added load, and Table 3 shows the upper limit value SL _ij·Max of load switching between main transformers.

Table 1 Current status of power grid main transformer

Table 2 New load situation

Table 3 Upper limit value of load switching between main transformers SL _{ij Max} (MVA)

The TSC-based planning steps of this example are as follows:

(1) The new load is within the power supply range of the existing station, so the new substation is not considered.

(2) Total power supply capacity verification: use the calculation method of the maximum power supply capacity TSC to calculate the maximum power supply capacity and the allowable load of each main transformer, as shown in Table 4. TSC = 180MVA, which is less than the planned total load of 188MVA, and the total power supply capacity needs to be adjusted.

Table 4 Main transformer load under the condition of maximum power supply capacity

(3) Adjustment of the total power supply capacity: first calculate the maximum power supply capacity of full connection TSC = 252MVA, which is greater than the total load of 188MVA, that is, the current main transformer capacity can meet the planned load requirements with the support of sufficient network connection. Part of the line cut and changed in the plan is shown by the dotted line in Figure 4. The planned network TSC is 200MVA, which is greater than the total load of 188MVA, passing the total load verification.

(4) Power supply capacity distribution verification: call the load optimization distribution method based on power supply capacity, set the weight W = (0.5, 0.5) and use Lingo to solve the formula (1~12), and obtain the load redistribution scheme as shown in Table 5 and Table 6 shown. After distribution, the load of each main transformer is less than the allowable load of the main transformer under TSC, as shown in Table 7.

Table 5 Existing load redistribution among main transformers

Table 6 New load distribution

Table 7 Main transformer load based on TSC planning scheme

3. Compared with the traditional planning scheme

According to the traditional planning guidelines, it is determined that the capacity-load ratio of the planned power grid will reach about 2.0, and a new substation capacity of 120MVA is required. Therefore, according to the current main transformer configuration of the power grid, a new 3×40MVA substation will be built. After site selection and planning of the substation, and new construction and reconstruction of outgoing lines, the planning scheme is shown in Figure 5. The comparison between the traditional planning and the planning method proposed by this method is shown in Table 8.

Table 8 Comparison of traditional planning and planning schemes of this method

It can be seen that the traditional planning method is based on the empirical value of capacity-load ratio, and the result tends to be conservative, without fully considering the improvement of power supply capacity brought about by network interconnection; while this method reduces the dependence on capacity-load ratio indicators and directly supplies power to the entire network. Planning after accurate calculation of the capacity can give full play to the potential of the existing network, delay the construction of the power grid, and solve the problems of land shortage and high cost for power grid construction.

To sum up, the embodiment of the present invention provides a distribution network planning method based on the maximum power supply capacity. This method gives priority to improving the TSC to meet the load by optimizing the structure and operation mode of the distribution network, and then considers adding new variable capacity , so as to make full use of the existing network to accommodate new loads and improve the efficiency of power grid assets, which is very suitable for the planning of complex power distribution networks in urban built-up areas; Planning the power supply capacity after accurate calculation can give full play to the potential of the existing network, delay the construction of the power grid, and solve the problems of land shortage and high cost of power grid construction; this method can calculate the maximum power supply capacity under the actual grid load level The realization of the system is to provide a distribution scheme that matches the load and the maximum power supply capacity distribution, so as to achieve the purpose of fully utilizing the power supply capacity of the grid.

Those skilled in the art can understand that the accompanying drawing is only a schematic diagram of a preferred embodiment, and the serial numbers of the above-mentioned embodiments of the present invention are for description only, and do not represent the advantages and disadvantages of the embodiments.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection of the present invention. within range.

Claims (2)

1. A distribution network planning method based on maximum power supply capacity, characterized in that, the method comprises the following steps: (1) Based on the planning measures of the maximum power supply capacity TSC, according to the degree of change to the power grid, define the priority of the power supply capacity adjustment measures A-type measures, B-type measures and C-type measures; Among them, A-type measures: load redistribution measures, A-type measures are divided into four measures according to priority: A1 adjust switch status, A2 adjust switch position, A3 new load access and A4 load cut; Type B measures: Measures for feeder planning. Type B measures are divided into three measures according to priority: B1 replacement of conductors, B2 new connection and B3 new feeder measures; Type C measures: Measures for substation planning. According to the priority, Type C measures are divided into three measures: C1 new main transformer, C2 replacement of main transformer and C3 new substation; (2) Obtain current grid data and load forecast data; (3) Judging whether the distance between the newly added load and the existing substation is greater than the first threshold, if yes, there is a power supply blind area, and step (4) is performed; if not, there is no power supply blind area, and step (5) is performed; (4) Adopt the measures of category C, add a substation, and re-execute step (3); (5) Calculate the maximum power supply capacity TSC of the current grid; (6) Determine whether the maximum power supply capacity TSC is greater than the planned total load, if yes, perform step (7); if not, perform step (8); (7) Determine whether each main transformer load matches the maximum power supply capacity TSC, if yes, perform step (9); if not, perform step (10); (8) Adjust the total power supply capacity by adopting the B-category measures and the C-category measures, and re-execute step (5); (9) Determine whether each load level meets the main transformer N-1 safety check, if yes, perform step (11); if not, perform step (12); (10) adopt described A class measures to adjust the distribution of load among the main transformers, and re-execute step (7); (11) The process ends; (12) Adopting the above-mentioned type A measures or the above-mentioned type B measures to transform the line, or adopting the above-mentioned type B measures to increase the feeder, and re-execute step (9). 2. A distribution network planning method based on maximum power supply capacity according to claim 1, wherein the adjustment of the total amount of power supply capacity by adopting the B-type measures and the C-type measures is specifically: 1) Calculate the TSC when all main transformers are interconnected in pairs, that is, when the current grid reaches full connection and the connection capacity reaches the second threshold; 2) Determine whether the maximum power supply capacity TSC is greater than the planned total load, if yes, perform step 3); if not, perform step 4); 3) adopt the B class measures to optimize the grid structure, recalculate the new TSC, and perform step 5); 4) Adopt the measures of category C, increase the variable capacity, and re-execute step 1); 5) Judging whether the new maximum power supply capacity TSC is greater than the planned total load, re-executing step 3) or 4) according to the judgment result, and finally making the new TSC greater than the planned total load.