CN109888748B

CN109888748B - Distribution line three-level protection optimal configuration method based on power failure capacity minimum

Info

Publication number: CN109888748B
Application number: CN201910188386.6A
Authority: CN
Inventors: 郭亮; 胡柳; 安义; 徐在德; 邓才波; 李升健
Original assignee: Nanchang Kechen Electric Power Test Research Co ltd; State Grid Corp of China SGCC; Electric Power Research Institute of State Grid Jiangxi Electric Power Co Ltd
Current assignee: Nanchang Kechen Electric Power Test Research Co ltd; State Grid Corp of China SGCC; Electric Power Research Institute of State Grid Jiangxi Electric Power Co Ltd
Priority date: 2019-03-13
Filing date: 2019-03-13
Publication date: 2021-07-02
Anticipated expiration: 2039-03-13
Also published as: CN109888748A

Abstract

A three-level protection optimal configuration method for a distribution line based on minimum power outage capacity is characterized in that a three-level protection configuration scheme is used for establishing an expected failure power outage distribution transformation total capacity calculation formula in consideration of line failure probability, wherein the three-level protection configuration scheme is corresponding to the three-level protection configuration scheme aiming at the three conditions that the distribution line only has a main line, the distribution line has a main line and branch lines, and the distribution line has the main line, the branch lines and secondary branch lines. Respectively giving specific calculation processes by calculating the fault power failure distribution and transformation capacity of the limited protection configuration schemes; and finally finding the switch setting position and the number corresponding to the minimum power failure capacity of the distribution line, thereby obtaining an optimized three-level protection configuration scheme. The attached figure shows the second and third switch distances and distribution transformation distribution of the main line. The method solves the problems of the three-level protection optimization configuration of the distribution line in the aspects of principle, algorithm, calculation flow and the like, can realize computer software programming, and provides possibility for automatic and rapid calculation of the three-level protection configuration of the distribution line.

Description

Distribution line three-level protection optimal configuration method based on power failure capacity minimum

Technical Field

The invention relates to a distribution line three-level protection optimal configuration method based on power failure capacity minimization, and belongs to the technical field of power distribution network protection.

Background

For a 10kV distribution line powered by a 110kV transformer substation, under the conditions of longer line lead and larger line impedance, three-level protection can be configured to realize the coordination of upper and lower-level protection: the transformer substation outgoing switch is used as first-stage protection of a circuit, second-stage protection is arranged at a position where impedance is larger than a certain limit value, and third-stage protection is arranged at a position where impedance is larger than another limit value at the rear side of the second-stage protection according to the impedance of the second-stage protection on the basis of determining the position of the second-stage protection. The second and third-level protection is performed by a pole-mounted switch or a ring main unit switch on a line. The circuit of the three-level protection is configured, the fault at the rear side of the third-level protection only trips off the corresponding third-level switch, the circuit between the second-level protection and the third-level protection has a fault, only the corresponding second-level switch trips off, and only the circuit between the first-level protection and the second-level protection has a fault, the outgoing line switch trips, so that the partition isolation of the fault (particularly the rear-side fault) is realized, and the fault power failure range is reduced.

Because the distribution line generally has branches and secondary branches, and a plurality of second-level and third-level protections are possible according to the branch structure characteristics, if the impedance of a certain position is equal to the required impedance limit value, a second-level switch can be arranged at any position at the rear side of the position, the positions of the second-level switches are different, and the corresponding fixed values are also different; for each second level protection setting position, a third level switch can be set at any position on the rear side where the impedance value is larger than the impedance limit value of the third level protection. Therefore, theoretically, there are an infinite number of schemes for the three-level protection configuration

Disclosure of Invention

The invention aims to obtain an optimized three-level protection configuration scheme, and provides a distribution line three-level protection optimization configuration method based on the minimum power outage capacity.

The invention discloses a distribution line three-level protection optimal configuration method based on the minimum power outage capacity, which aims at the situation that a distribution line only has a main line, the distribution line has the main line and branch lines, and the distribution line has the main line, the branch lines and secondary branch lines, respectively establishes an expected failure power outage distribution transformation total capacity calculation formula corresponding to the three-level protection configuration scheme and considering the line failure probability based on distribution transformation capacity and position information, and finally finds the switch setting position and the number corresponding to the minimum power outage capacity by calculating the failure power outage distribution transformation capacity of the limited protection configuration scheme and respectively giving specific calculation flows according to the characteristic that the power outage distribution transformation capacity is attached to the distribution transformation position, thereby obtaining the optimized three-level protection configuration scheme.

The total capacity Q of the distribution line is only the total capacity Q of the distribution transformer in the expected failure power failure of the main line:

in the formula, λ_ZThe unit length failure probability of the trunk line; l is_ZIs the length of the main line of the distribution line; l is_K2ZThe distance between the position of the second-stage switch of the main line and the starting end of the main line is set; l is_K3ZThe distance between the third-level switch position of the main line and the starting end of the main line is set; s_jThe capacity of the jth distribution transformer; l_jThe distance from the position connected with the jth distribution transformer to the starting end of the trunk line;

the total capacity of all distribution transformers on the distribution line;

the total capacity of the distribution transformer between the second-stage switch of the main line and the tail end of the main line is changed;

the total capacity of the distribution transformer between the third-level switch of the main line and the tail end of the main line;

the second-stage switch and the third-stage switch divide the distribution line into three sections, the total capacity of all distribution transformers on the distribution line is equal to the sum of the distribution transformers connected with each section of line, namely,

in the formula (I), the compound is shown in the specification,

the total capacity of all distribution transformers on the distribution line;

the total capacity of the distribution transformer between the starting end of the main line and the second-stage switch of the main line;

the total capacity of the distribution transformer from the main line second-stage switch to the main line third-stage switch;

the total capacity of the distribution transformer between the third-level switch of the main line and the tail end of the main line; thus, Q can be transformed into:

the selection algorithm flow of the total capacity of the distribution transformer for the expected failure power failure of the distribution line only with the main line is as follows:

(1) obtaining the minimum impedance Z of the second-stage switch in a large formula_2minAnd corresponding minimum distance L_K2ZminAnd minimum impedance Z in a large equation at the third stage switch setting_3minAnd corresponding minimum distance L_K3Zmin；

(2) Judgment of L_K3ZminWhether it is in the length range (0, 0.8L)_Z) In the method, L is the judgment method_K3ZminAnd the upper limit value of the range is 0.8L_ZBy comparison, if L_K3Zmin＞0.8L_ZIf the line can not be configured with three-level protection, entering other process treatment; if L is_K3Zmin≤0.8L_ZThe circuit can be configured with three-level protection;

(3) the serial number j of the rear side distribution transformer of the second-stage switch is 1, and the serial number k of the rear side distribution transformer of the third-stage switch is 1;

(4) let L₂＝L_K2Zmin，L₃＝L_K3Zmin；

(5) Judgment of L₃Whether it is in the length range (0, 0.8L)_Z) In, if L₃＞0.8L_ZIllustrating that the second stage switch is fixedly positioned at L after the traversal is completed₂When the third-stage switch is in all possible distribution positions, entering the step (8) to change the fixed position of the second-stage switch; if L is₃≤0.8L_ZThe third stage switch is at L₃Three-stage protection can be configured, and the distance between the position of the second-stage switch of the main line and the starting end of the main line is L₂I.e. L_K2Z＝L₂The distance between the position of the third-stage switch and the starting end of the main line is L₃I.e. L_K3Z＝L₃；

(6) Calculating L from Q_K2Z、L_K3ZCorresponding expected failure power failure distribution transformer total capacity Q (L)_K2Z,L_K3Z) (ii) a If Q_bestIs an initial value or Q (L)_K2Z,L_K3Z)＜Q_bestThen the minimum expected fault is cut off and the total capacity Q is distributed_bestAssigned value of Q (L)_K2Z,L_K3Z) Corresponding second stage switch optimum position (L)_K2Zbest,L_K3Zbest) Is assigned a value of (L)_K2Z,L_K3Z)；

(7) The position of the second-stage switch is fixed and arranged at L_K2ZTo find L_K3ZThe j-th distribution transformer on the rear side makes an intermediate quantity L₃Equal to the distance l between the distribution and transformation position and the beginning of the trunk line_jI.e. L₃＝l_jAdding 1 to the counting quantity j, then entering the step (5), and circularly traversing all the distribution transformation positions meeting the conditions;

(8) changing the position of the second stage switch to find L_K2ZUpdating the minimum distance L of the second-stage switch in the kth distribution transformer at the rear side_K2ZminThe distance l between the distribution and transformation position and the beginning of the trunk line_kInstant L_K2Zmin＝l_kJudgment of L_K2ZminWhether it is in the length range (0, 0.8L)_Z) In, if L_K2Zmin＞0.8L_ZDescription of the inventionIf the traversal is completed, the step (9) is entered to output the final optimization calculation result; if L is_K2Zmin≤0.8L_ZExplaining the possibility of further optimization of the line protection configuration, recalculating to obtain the minimum distance L of the third-stage switch_K3ZminJudgment of L_K3ZminWhether it is in the length range (0, 0.8L)_Z) In, if L_K3Zmin＞0.8L_ZIf L is the final result of the optimization calculation, the step (9) is entered to output the final result of the optimization calculation_K3Zmin≤0.8L_ZIf the situation that the calculation is not carried out exists, adding 1 to the counting quantity k, reassigning the counting quantity j to be 1, then entering the step (4), and circularly traversing and calculating;

(9) through the calculation of the procedures, the total capacity Q of the minimum expected failure power failure distribution transformer is finally obtained_bestAnd its corresponding second stage switch optimum position (L)_K2Zbest,L_K3Zbest) And outputting a calculation result.

The distribution line has expected failure outage distribution transformation total capacity Q (L) of main line and branch line_K2Fi,L_K3Fi,L_K2Zi,L_K3Z) The following were used:

in the formula (I), the compound is shown in the specification,

the front end probability power failure capacity of all distribution transformers of the whole distribution line is calculated by the formula

Wherein S is_{General assembly}The sum of all distribution and transformation capacities of the whole distribution line; l is_FiIs the length of each branch line; lambda [ alpha ]_FiThe unit length fault probability of each branch line; l is_K2FiIs K_2FiDistance between position and beginning of branch line, K_2FiA second stage switch on a branch line; the other parameters have the same meanings as described above;

for the second-stage switch failure probability power failure distribution capacity, the calculation formula is as follows:

wherein S is_ZBThe sum of all distribution capacity from the second-stage switch of the main line to the tail end; s_m3The sum of all distribution capacity on the third branch line; s_m42The sum of all distribution and transformation capacities on the fourth type 2 branch line; s_m43The sum of all distribution and transformation capacities on the fourth type 3 branch line; s_FiBThe sum of all distribution transformation capacities from the second-stage switch to the tail end of the i branch line; the other parameters have the same meanings as described above;

for the third-level switch failure probability power failure distribution capacity, the calculation formula is as follows:

wherein S is_ZCThe sum of all distribution capacity from the third-stage switch of the main line to the tail end; s_m43The sum of all distribution and transformation capacities on the fourth type 3 branch line; s_FiCThe sum of all distribution capacity between the third-stage switch and the tail end of the i branch line, and other parameters are as defined above.

When the distribution line has a main line and a branch line, the flow of the selection algorithm of the total capacity of the distribution transformer in the expected failure power failure is as follows:

(1) obtaining line information, and calculating 0.8l from the start end to the end of the effective end corresponding to the trunk line and the branch line according to the line information_mImpedance range (Z)_mi0，Z_mi) (ii) a Determining minimum impedance at the second stage switch settingZ_2min(ii) a Minimum impedance Z at third stage switch setting_3min；

(2) Judging whether a certain impedance range satisfying Z exists_3min∈(Z_mi0,Z_mi) If the protection circuit does not exist, the circuit cannot be configured with three-level protection, and other processes are carried out; if the three-level protection exists, the circuit can be configured with three-level protection, and a lead capable of being provided with a three-level switch is determined; calculating the length L of each three-level switch from the initial end of the main line_K3Zmin、L_K3FiminSimultaneously judging Z_2min∈(Z_mi0,Z_mi) Calculating the length L of each two-stage switch from the initial end of the main line_K2Zmin、L_K2Fimin；

(3) Order to

(4) Judgment of

Whether each element of (1) exceeds the maximum range of the corresponding line by 0.8l_miIf, if

In the presence of less than 0.8l_miElement(s) of (1), illustrating that the second level switch has been pinned in place after traversal has been completed

The case when the third level switch is in all possible distribution positions; at this time, the step (7) is carried out, and the fixed position of the second-stage switch is changed; if it is

In the presence of less than 0.8l_miElement(s) of (2), illustrating the third level switch is located

Three-level protection can be configured, then updating

Deleting more than 0.8l_miOf less than 0.8l_miWhen the position of each second-stage switch is taken

Each element of (1), i.e.

Each third stage switch position fetch

Each element of (1), i.e.

(5) According to the preset position of the switch position, classifying the leads according to Q (L)_K2Fi,L_K3Fi,L_K2Zi,L_K3Z) Formula calculation

Corresponding expected failure power failure distribution transformer total capacity Q (L)_K2Fi,L_K3Fi,L_K2Zi,L_K3Z) (ii) a If Q_bestIs an initial value or Q (L)_K2Fi,L_K3Fi,L_K2Zi,L_K3Z)＜Q_bestThen the minimum expected fault is cut off and the total capacity Q is distributed_bestAssigned value of Q (L)_K2Fi,L_K3Fi,L_K2Zi,L_K3Z) Optimized position of corresponding second stage switch

Is assigned a value of

(6) Fix the position of the second-stage switch at

To find

Calculating the impedance of each distribution transformer after the 1 st distribution transformer of each line position corresponding to each element; the minimum impedance is obtained, and the distance from the position of each line corresponding to the impedance to the start end of the trunk line is calculated and recorded as

Make an intermediate amount

Then, the step (5) is entered, and all the distribution transformation positions which meet the conditions are circularly traversed;

(7) the position of the second-stage switch is changed to find

The impedance of the 1 st distribution position after each line position corresponding to each element is taken as the minimum impedance Z_P2The distance between the position of each line corresponding to the impedance and the start of the trunk line is calculated and recorded as

Updating the minimum distance L of the second-stage switch_K2Zmin、L_K2FiminIs composed of

Corresponding elements, judging

Whether it is in the length range (0,0.8 l)_mi) Within; if it is

All elements are greater than 0.8l_miIf all the traversals are completed, the step (8) is carried out to output the result of the final optimization calculation; if it is

The presence of less than 0.8l of elements_miIllustrates the possibility of further optimization of the line protection configuration, according to the second stageImpedance Z at switch_P2The minimum impedance Z corresponding to the third-stage switch is obtained through recalculation_P3The distance between the position of each line corresponding to the impedance and the start of the trunk line is calculated and recorded as

Updating the minimum distance L of the third stage switch_K3Zmin、L_K3FiminIs composed of

Corresponding elements, judging

Whether it is in the length range (0,0.8 l)_mi) In, if

All elements are greater than 0.8l_miAfter the second-stage switch bit is changed, the third-stage protection cannot be configured continuously, all traversal is completed, and the step (8) is carried out to output the final optimization calculation result; if it is

The presence of less than 0.8l of elements_miAfter the second-stage switch position is changed, three-stage protection can be configured, and the step (3) is entered for circular traversal calculation;

(8) through the calculation of the procedures, the total capacity Q of the minimum expected failure power failure distribution transformer is finally obtained_bestAnd its corresponding second stage switch optimum position

And outputting a calculation result.

The distribution line has expected failure outage distribution transformation total capacity Q of main line, branch line and secondary branch line_fcThe following were used:

in the formula, N_CIs the sum of the total number of secondary branches, i.e.:

wherein N is_iThe number of secondary branches on the ith branch line;

the calculation formula of the probability outage capacity of the front end of all distribution transformers of the whole distribution line is as follows:

wherein S is_{General assembly}The sum of all distribution and transformation capacities of the whole distribution line, and the meanings of other parameters are as described above;

the power failure distribution and transformation capacity is the power failure distribution and transformation capacity of the second-stage switch failure probability of the main line, and the calculation formula is as follows:

wherein, Sigma lambda L_K3CZThe sum of the product of the length of a third-stage switch of all third-stage secondary branches connected to the main line to the starting end of the third-stage switch and the fault probability; sigma lambda L_b0The sum of the products of the lengths and the failure probabilities of all the fourth type 2 secondary branches positioned between the second level switch and the third level switch of the main line; s_ZBThe sum of all distribution capacity from the second-stage switch of the main line to the tail end; s_mf3The sum of all the distribution capacity on all the third-class branch lines; s_mf42The sum of all distribution and transformation capacities on all fourth type 2 branch lines; s_mf43The sum of all distribution and transformation capacities on all fourth type 3 branch lines; s_mc3ZThe sum of all distribution transformation capacities on all the third type secondary branches connected to the main trunk line; s_b0All between the second and third stage switches of the main lineThe sum of all distribution transformation capacities on the fourth type 2 secondary branch; s_c0The sum of all distribution transformation capacities on the fourth type 3 secondary branches connected with the main trunk line; the other parameters have the same meanings as described above;

the power failure distribution capacity is the power failure distribution capacity of the second-stage switch failure probability of the branch line, and the calculation formula is as follows:

wherein, Sigma lambda L_K3CFiThe sum of the product of the length from the third-stage switch of the third-class secondary branch line to the initial end of the third-class secondary branch line after the second-stage switch of the first-class or second-class branch line with the serial number of i and the fault probability; sigma lambda L_b1iThe sum of the product of the length and the failure probability of a fourth 2 nd-type secondary branch line positioned between second and third-level switches of the first-type branch line with the number i is obtained; sigma lambda L_b2iThe sum of the product of the length and the failure probability of a fourth 2 nd-type secondary branch line positioned between second and third-level switches of a second-type branch line with the number of i is taken as the sum; s_FiBThe sum of all the distribution capacity from the second-stage switch connected with the ith branch line to the tail end; s_mc3FiThe sum of all distribution capacity on the third type secondary branch line connected with the ith branch line; s_b1iThe sum of all distribution transformation capacities on a fourth type 2 secondary branch line connected with the first type branch line with the number of i; s_b2iThe sum of all distribution transformation capacities on a fourth type 2 secondary branch line connected with a second type branch line with the number of i; the other parameters have the same meanings as described above;

the power failure distribution capacity is the power failure distribution capacity of the fault probability of the third-level switch of the secondary branch line, and the calculation formula is as follows:

wherein S is_CiCThe sum of all distribution capacity from the third class secondary branch third level switch with the number i to the tail end, and the meaning of other parameters are as described above.

The method is characterized in that when the distribution line has a main line, branch lines and secondary branch lines, the flow of the selection algorithm of the total capacity of the distribution transformer in the expected failure power failure is as follows:

(1) obtaining line information, and calculating 0.8l from the initial end to the end of the effective end corresponding to the trunk line, the branch line and the secondary branch line according to the line information_mImpedance range (Z)_mi0，Z_mi) (ii) a Determining the minimum impedance Z at the second stage switch setting_2min(ii) a Minimum impedance Z at third stage switch setting_3min；

(2) Judging whether a certain impedance range satisfying Z exists_3min∈(Z_mi0,Z_mi) (ii) a If the protection circuit does not exist, the circuit cannot be configured with three-level protection, and other processes are carried out; if the three-level protection exists, the circuit can be configured with three-level protection, and a lead capable of being provided with a three-level switch is determined; calculating the length L of each three-level switch from the initial end of the main line_K3Zmin、L_K3Fimin、L_K3CiminSimultaneously judging Z_2min∈(Z_mi0,Z_mi) (ii) a Calculating the length L of each two-stage switch setting position from the starting end of the main line_K2Zmin、L_K2Fimin、L_K2Cimin；

(3) Order to

(4) Judgment of

Whether each element of (1) exceeds the maximum range of the corresponding line by 0.8l_mi(ii) a If it is

The case when the third level switch is in all possible distribution positions; at the moment, entering the step (7) to change the fixed position of the second-stage switch; if it is

Three-level protection can be configured, then updating

Each element of (1), i.e.

Each third stage switch position fetch

Each element of (1), i.e.

(5) Classifying the leads according to Q according to the preset position of the switch position_fcEquation, calculate

Corresponding expected failure power failure distribution transformer total capacity Q_fcIf Q is_bestIs an initial value or Q_fc＜Q_bestThen the minimum expected fault is cut off and the total capacity Q is distributed_bestAssigned a value of Q_fcOptimized position of corresponding second stage switch

Is assigned a value of

(6) Fix the position of the second-stage switch at

To find

Calculating the impedance of each distribution transformer after the 1 st distribution transformer of each line position corresponding to each element, and taking the minimum impedance; the distance between the position of each line corresponding to the impedance and the start end of the trunk line is calculated and recorded as

Make an intermediate amount

Then step (4) is entered, and all the distribution transformation positions meeting the conditions are circularly traversed;

(7) the position of the second-stage switch is changed to find

Updating the minimum distance L of the second-stage switch_K2Zmin、L_K2Fimin、L_K2CiminIs composed of

Corresponding elements, judging

Whether it is in the length range (0,0.8 l)_mi) In, if

The presence of less than 0.8l of elements_miIllustrates the possibility of further optimization of the line protection configuration, depending on the impedance Z at the second stage switch_P2The minimum impedance Z corresponding to the third-stage switch is obtained through recalculation_P3The distance between the position of each line corresponding to the impedance and the start of the trunk line is calculated and recorded as

Updating the minimum distance L of the third stage switch_K3Zmin、L_K3Fimin、L_K3CiminIs composed of

Corresponding elements, judging

Whether it is in the length range (0,0.8 l)_mi) In, if

(8) through the calculation of the process, the total capacity Q of the minimum expected failure power failure distribution transformer is finally obtained_bestAnd its corresponding second stage switch optimum position

And outputting a calculation result.

The method has the advantages that the problems of the three-level protection optimal configuration of the distribution line in the aspects of principle, algorithm, calculation flow and the like are solved based on the three-level protection optimal configuration method of the distribution line with the minimum power outage capacity, computer software programming can be realized, and the possibility is provided for automatic and rapid calculation of the three-level protection configuration of the distribution line.

Drawings

FIG. 1 is a schematic diagram of the second and third level switching distances and distribution transformation distribution of a main line;

FIG. 2 is a schematic diagram of the effect of the relative position of the third stage switch and the distribution transformer on the expected outage capacity;

FIG. 3 is a schematic diagram of the relative positions of the second and third stage switches and the distribution transformer affecting the expected outage capacity;

FIG. 4 is a flow chart of a calculation algorithm for the total capacity of the distribution transformer in case of an expected failure power outage when the three-level protection configuration is only a main line;

FIG. 5 is a schematic diagram of a line classification after a three-level protection setting for a distribution line including branch lines;

FIG. 6 is a flow chart of a selection algorithm for anticipating total capacity of a faulted power distribution transformer with a trunk line and branch lines;

FIG. 7 is a schematic diagram of a line classification after a three-level protection setting for a distribution line including secondary branches;

fig. 8 is a flow chart of a selection algorithm for anticipating total capacity of a power distribution transformer in the case of a fault with a trunk line, branch lines and secondary branches.

Detailed Description

According to the three-level protection optimal configuration method for the distribution line with the minimum power outage capacity, firstly, according to the principle of three-level protection coordination, after the minimum impedance at the setting position of the second-level switch or the shortest distance from the setting position to the starting end is determined, the minimum impedance at the setting position of the third-level switch or the shortest distance from the setting position to the starting end can be calculated and obtained, then, the expected power outage distribution transformer total capacity of various protection schemes under different conditions in the fault processing process is calculated, and the optimal configuration scheme corresponding to the minimum expected power outage distribution transformer total capacity is found.

The setting position of the second-stage switch meets the following conditions:

impedance Z in a large square at the setting position of the second stage switch₂The following relationship should be satisfied:

Z₂≥1.5Z_small

In the formula, Z_SmallThe impedance of the system at the beginning of the line, namely the minimum mode of the 10kV bus, which satisfies the above formula is Z₂Is the position in which the second stage switch can be set.

The third-stage switch setting position satisfies the following conditions:

impedance Z in a large square at the third-stage switch setting position₃The following relationship should be satisfied:

Z₃≥1.5Z_{2 small}

In the formula, Z_{2 small}The system impedance in the minimum mode is set for the second-stage switch, and the impedance satisfying the above formula is Z₃Is the position in which the third stage switch can be set.

A calculation formula and a calculation process of the total capacity of the expected failure power failure distribution transformer are implemented by considering the following three conditions.

In the first case, the distribution line has only the main line:

setting the length of the main line of the power distribution line to be L_ZThe main lines have the same fault probability, and the fault probability per unit length is lambda_Z(ii) a For a distribution line with only a main line, the second-stage switch is positioned on the main line and only one, the third-stage switch is also positioned on the main line and only one, and the distance between the position of the second-stage switch of the main line and the starting end of the main line is set to be L_K2ZThe distance between the third-level switch position of the main line and the starting end of the main line is L_K3ZThe j-th distribution transformer on the main line has a capacity S_jAs shown in fig. 1.

The expected total capacity Q of the fault power failure distribution transformer is as follows:

in the formula, λ_ZIs the failure probability of the main line per unit length, L_ZIs the main line length, L of the distribution line_K2ZThe distance between the position of the second-stage switch of the main line and the starting end of the main line, L_K3ZThe distance between the third-level switch position of the main line and the starting end of the main line is set; s_jFor the j-th distribution capacity, l_jThe distance from the position connected with the jth distribution transformer to the starting end of the trunk line;

the total capacity of all distribution transformers on the distribution line;

the total capacity of the distribution between the third stage switch of the main line and the end of the main line is changed.

The second-stage and third-stage switches divide the distribution line into three sections, and the total capacity of all distribution transformers on the distribution line is equal to the sum of the distribution transformers connected with each section of line, namely

In the formula (I), the compound is shown in the specification,

for the total capacity of all distribution transformers on the distribution line,

for the total capacity of the distribution between the mains start and the mains second stage switch,

for the total capacity of the distribution between the main line second stage switches to the main line third stage switches,

the total capacity of the distribution between the third stage switch of the main line and the end of the main line is changed. Thus equation (1) can be transformed into:

taking the distribution line of fig. 1 as an example, the distribution transformers are distributed among three segments of conductors, and the quantities related to the transformer capacity in equation (2) are:

from the equation (2), it can be seen that, under the condition that the distribution of three lines into which the second and third-stage switches on the main line are divided is not changed, the size of the total capacity Q of the distribution transformer in the expected fault and power failure is determined by the distance L between the positions of the second and third-stage switches and the start end of the main line_K2Z、L_K3ZIt is clear that with the distribution and second stage switch positions unchanged, L_K3ZThe minimum value is taken, so that the total capacity Q of the distribution transformer in the expected failure power failure can be minimized; under the condition of unchanged distribution situation, the distance L between the second-level switch position and the third-level switch position and the starting end of the main line_K2Z、L_K3ZAnd meanwhile, the minimum is achieved, and the total capacity Q of the distribution transformer in the expected failure power failure can be minimized.

The case of a constant distribution and second stage switch position is described with reference to fig. 2.

As shown in FIG. 2, the position of the second stage switch is fixed, and the position of the third stage switch can be any position between the distribution transformers j-1 and j, obviously, when the third stage switch is positioned at the position closest to the previous distribution transformer j-1, the corresponding L is_K3ZMinimum, at this time corresponding to expected failure power outage distribution transformer total capacity Q_j-1And minimum.

For the case where the distribution profile is constant and the second and third stage switch positions are variable, it is described with reference to fig. 3.

As shown in fig. 3 at 2, assuming that the second stage switch may be inThe position of the third stage switch can be any position between the distribution transformers j-1 and j at any position between k-1 and k, obviously, when the second stage switch is positioned at the position closest to the distribution transformer k-1 and the third stage switch is positioned at the position closest to the distribution transformer j-1, the total capacity Q of the distribution transformer corresponding to the expected failure and outage₁And minimum.

Meanwhile, because the minimum impedance at the position of the third-stage switch is influenced by the impedance at the position of the second-stage switch, the impedance at a certain position of the wire is determined by the distance from the position to the starting end, and the larger the impedance is, the larger the corresponding distance is; thus L_K3ZIs located by L_K2ZLimit of each L_K2ZCorresponding one L_K3ZAfter the second-stage switch is determined, the total capacity of the third-stage switch, which corresponds to the position of each distribution transformer meeting the distance limit requirement and is located near each distribution transformer position, of the expected fault power failure distribution transformer is obtained according to the formula (1), and the minimum expected total capacity of the fault power failure distribution transformer corresponding to the position of the second-stage switch is obtained through comparison; when the position of the second-stage switch changes, the second-stage switch is sequentially arranged near each distribution transformer position meeting the distance limiting requirement, the expected failure power-off distribution transformer total capacity corresponding to the third-stage switch arranged near each distribution transformer position meeting the distance limiting requirement is continuously obtained according to the formula (1), and the corresponding minimum expected failure power-off distribution transformer total capacity is obtained through comparison; and (4) exhausting all possible switch position setting conditions, and finally obtaining the minimum expected fault power failure distribution transformer total capacity under all conditions.

In summary, when the distribution line has only a main line, there are infinite switch position setting situations within the selectable range of the second and third-level switch positions, wherein the expected failure outage distribution transformer total capacity Q of each situation when each switch position is located near the distribution transformer position only needs to be calculated and compared according to equation (1), and the minimum value is found, and the second and third-level switch positions corresponding to the minimum value and the corresponding protection configuration scheme are the optimal scheme of the distribution line three-level protection configuration.

On the basis, the flow of the selection algorithm of the total capacity of the expected failure power failure distribution transformer is as follows:

1) to find the size of the second stage switchMinimum impedance Z under mode_2minAnd corresponding minimum distance L_K2ZminAnd minimum impedance Z in a large equation at the third stage switch setting_3minAnd corresponding minimum distance L_K3Zmin；

2) Judgment of L_K3ZminWhether it is in the length range (0, 0.8L)_Z) In the method, L is the judgment method_K3ZminAnd the upper limit value of the range is 0.8L_ZBy comparison, if L_K3Zmin＞0.8L_ZIf the line can not be configured with three-level protection, entering other process treatment; if L is_K3Zmin≤0.8L_ZThe circuit can be configured with three-level protection;

3) the serial number j of the rear side distribution transformer of the second-stage switch is 1, and the serial number k of the rear side distribution transformer of the third-stage switch is 1;

4) let L₂＝L_K2Zmin，L₃＝L_K3Zmin；

5) Judgment of L₃Whether it is in the length range (0, 0.8L)_Z) In, if L₃＞0.8L_ZIllustrating that the second stage switch is fixedly positioned at L after the traversal is completed₂When the third-stage switch is in all possible distribution positions, entering the step 8) to change the fixed position of the second-stage switch; if L is₃≤0.8L_ZThe third stage switch is at L₃Three-stage protection can be configured, and the distance between the position of the second-stage switch of the main line and the starting end of the main line is L₂I.e. L_K2Z＝L₂The distance between the position of the third-stage switch and the starting end of the main line is L₃I.e. L_K3Z＝L₃；

6) Calculating L according to equation (1)_K2Z、L_K3ZCorresponding expected failure power failure distribution transformer total capacity Q (L)_K2Z,L_K3Z) If Q is_bestIs an initial value or Q (L)_K2Z,L_K3Z)＜Q_bestThen the minimum expected fault is cut off and the total capacity Q is distributed_bestAssigned value of Q (L)_K2Z,L_K3Z) Corresponding second stage switch optimum position (L)_K2Zbest,L_K3Zbest) Is assigned a value of (L)_K2Z,L_K3Z)；

7) Fixed second level switch position settingIn L_K2ZTo find L_K3ZThe j-th distribution transformer on the rear side makes an intermediate quantity L₃Equal to the distance l between the distribution and transformation position and the beginning of the trunk line_jI.e. L₃＝l_jAdding 1 to the counting quantity j, and then entering the step 5), and circularly traversing all the distribution transformation positions meeting the conditions;

8) changing the position of the second stage switch to find L_K2ZUpdating the minimum distance L of the second-stage switch in the kth distribution transformer at the rear side_K2ZminThe distance l between the distribution and transformation position and the beginning of the trunk line_kInstant L_K2Zmin＝l_kJudgment of L_K2ZminWhether it is in the length range (0, 0.8L)_Z) In, if L_K2Zmin＞0.8L_ZIf all the traversals are completed, the step 9) is carried out to output the final optimization calculation result; if L is_K2Zmin≤0.8L_ZExplaining the possibility of further optimization of the line protection configuration, recalculating to obtain the minimum distance L of the third-stage switch_K3ZminJudgment of L_K3ZminWhether it is in the length range (0, 0.8L)_Z) In, if L_K3Zmin＞0.8L_ZIf L shows that all traversals of the three-level protection configuration are finished, the step 9) is carried out to output the result of the final optimization calculation_K3Zmin≤0.8L_ZIf the situation that the calculation is not carried out exists, adding 1 to the counting quantity k, reassigning the counting quantity j to be 1, and then entering the step 4) to carry out circular traversal calculation;

9) through the calculation of the procedures, the total capacity Q of the minimum expected failure power failure distribution transformer is finally obtained_bestAnd its corresponding second stage switch optimum position (L)_K2Zbest,L_K3Zbest) And outputting a calculation result.

The flow of the calculation algorithm of the total capacity of the distribution transformer in the case of the anticipated fault power failure when the three-level protection configuration only has the main line is shown in the figure 4.

In the second case, the distribution line has a trunk line and a branch line:

for distribution lines having trunk and branch lines, the second and third stage switches may be present on both the trunk and branch lines, i.e., the number of second and third stage switches may be greater than 1. Setting the length of the main line of the power distribution line to be L_ZFault probability per unit lengthA ratio of λ_Z(ii) a The branch lines on the trunk line have M (M is more than or equal to 0) lines, and the length of the position where each branch line is connected with the trunk line and the starting end of the trunk line is l_F1、l_F2、…、l_FMEach branch line has a length L_F1、L_F2、…、L_FMThe unit length fault probability of each branch line is lambda_F1、λ_F2、…、λ_FM(ii) a The number of distribution transformers hooked on the distribution line is R, and the j (j is more than or equal to 0 and less than or equal to R) th capacity is S_jThe distance between the main line and the branch line is l_j。

According to the distribution line information, the line has 1 main line and M branch lines in total, and each conducting wire corresponds to one tail end, so that M +1 tail ends are in total. Numbering each end, recording the length from each end to the beginning of the trunk as l_mi(i is more than or equal to 1 and less than or equal to M +1), before the positions of the second-level switch and the third-level switch are determined, the positions of the contact points of all branch lines and the corresponding l_miIs compared with 0.8 times, if the distance from the contact point to the start end of the main line is more than 0.8l_miThe branch line shares one end with the trunk line, called the active end.

On the basis, the corresponding end number of the trunk line is 1, and the start end is calculated to be 0.8l_m1The range of impedance variation therebetween is expressed as (Z)_m10，Z_m1) (ii) a For a branch line, the number of the corresponding tail end is recorded as i, and the initial end of the branch line is calculated to be 0.8l_miRange of impedance variation (Z) therebetween_mi0，Z_mi). Setting the impedance of the second-stage switch at the position obtained by calculation of the power distribution line to be Z₂Judgment of Z₂Whether within the respective impedance range, for Z₂At the end of each range, it indicates that the second stage switch can be set on the wire corresponding to the end. Let the second switch on the main line be K_2Z，K_2ZThe distance between the position and the starting end of the trunk line is L_K2ZIf there is a second switch on a branch line, it is marked as K_2FiI is a counting parameter, K_2FiThe distance between the position and the initial end of the branch line is L_K2Fi. Setting the impedance of the third-stage switch setting position obtained by calculating the power distribution line to be Z₃If Z is₃And if the impedance is within a certain range, the impedance indicates that the wire corresponding to the end can be provided with the third-stage switch. Let the third switch on the main line denote K_3Z，K_3ZThe distance between the position and the starting end of the trunk line is L_K3ZIf there is a third switch on a branch line, it is marked as K_3FiI is a counting parameter, K_3FiThe distance between the position and the initial end of the branch line is L_K3Fi。

According to whether the grading switch is arranged on each line or not and the number of the grading switches, the wires of the whole line are divided into four types:

(1) the circuit is simultaneously provided with a second stage switch and a third stage switch

(2) Only a second-stage switch is arranged on the circuit;

(3) only a third-stage switch is arranged on the circuit;

(4) the circuit is not provided with a switch, and the type of the circuit only comprises branch lines which can be subdivided into 3 small types, wherein the small types are all positioned in front of the second-stage switch, are all positioned between the second-stage switch and the third-stage switch, are all positioned behind the third-stage switch, and the like;

the distribution line containing branch lines is classified after the three-level protection setting, as shown in fig. 5.

The number of branch lines in the first type of wire is recorded as m₁The number of branch lines in the second type of wire is m₂The number of branch lines in the third type of wire is m₃Number m of branch lines of class 4

wire

1, 2, 3₄₁、m₄₂、m₄₃Branch line numbering in m₁，m₂，m₃，m₄₁、m₄₂、m₄₃By sequential addition of (i.e. M ═ M)₁+m₂+m₃+m₄₁+m₄₂+m₄₃Then, the expected failure power failure distribution transformation total capacity Q (L)_K2Fi,L_K3Fi,L_K2Zi,L_K3Z) Comprises the following steps:

in the formula (I), the compound is shown in the specification,

wherein S is_ZBIs the sum of all distribution capacities between the second stage switch of the main line to the end, S_m3Is the sum of all distribution capacity on the third branch line, S_m42Is the sum of all distribution capacities, S, on the fourth class 2 branch line_m43Is the sum of all distribution capacities, S, on the fourth class 3 branch line_FiBThe sum of all distribution transformation capacities from the second-stage switch to the tail end of the i branch line, and the meanings of other parameters are as described above;

wherein S is_ZCIs the sum of all distribution capacities from the third stage of the main line switch to the end, S_m43Is the sum of all distribution capacities, S, on the fourth class 3 branch line_FiCThe sum of all distribution capacity between the third-stage switch and the tail end of the i branch line, and the othersThe meaning of the parameters is as described above.

When the distribution line capable of configuring the three-level protection has a main line and a branch line, infinite switch position setting conditions exist in the selectable range of the second-level switch position and the third-level switch position, wherein the minimum value is found by only comparing the expected failure power failure distribution transformer total capacity Q of each condition when each switch is positioned near the distribution transformer position, and the second-level switch position and the third-level switch position corresponding to the minimum value and the corresponding protection configuration scheme are the protection configuration optimal scheme.

1) obtaining line information, and calculating 0.8l from the start end to the end of the effective end corresponding to the trunk line and the branch line according to the line information_mImpedance range (Z)_mi0，Z_mi) (ii) a Determining the minimum impedance Z at the second stage switch setting_2min(ii) a Minimum impedance Z at third stage switch setting_3min。

2) Judging whether a certain impedance range satisfying Z exists_3min∈(Z_mi0,Z_mi) If the protection circuit does not exist, the circuit cannot be configured with three-level protection, and other processes are carried out; if the three-level switch exists, the circuit can be configured with three-level protection, a lead wire capable of being provided with the three-level switch is determined, and the length L of the setting position of each three-level switch from the starting end of the main line is calculated_K3Zmin、L_K3FiminSimultaneously judging Z_2min∈(Z_mi0,Z_mi) Calculating the length L of each two-stage switch from the initial end of the main line_K2Zmin、L_K2Fimin。

3) Order to

4) Judgment of

When the third-stage switch is in all possible distribution positions, entering the step 7) to change the fixed position of the second-stage switch; if it is

Three-level protection can be configured, then updating

Each element of (1), i.e.

Each third stage switch position fetch

Each element of (1), i.e.

5) According to the preset position of the switch position, classifying the leads and calculating according to the formula (3)

Corresponding expected failure power failure distribution transformer total capacity Q (L)_K2Fi,L_K3Fi,L_K2Zi,L_K3Z) If Q is_bestIs an initial value or Q (L)_K2Fi,L_K3Fi,L_K2Zi,L_K3Z)＜Q_bestThen the minimum expected fault is cut off and the total capacity Q is distributed_bestAssigned value of Q (L)_K2Fi,L_K3Fi,L_K2Zi,L_K3Z) Optimized position of corresponding second stage switch

Is assigned a value of

6) Fix the position of the second-stage switch at

To find

The impedance of each distribution transformer is calculated after the 1 st distribution transformer corresponding to each element, the minimum impedance is taken, and the distance from the position of each line corresponding to the impedance to the start end of the trunk line is calculated and recorded as

Make an intermediate amount

And entering the step 5), and circularly traversing all the qualified distribution positions.

7) The position of the second-stage switch is changed to find

Corresponding elements, judging

Whether it is in the length range (0,0.8 l)_mi) In, if

All elements are greater than 0.8l_miIf all the traversals are completed, the step 8) is carried out to output the final optimization calculation result; if it is

Corresponding elements, judging

Whether it is in the length range (0,0.8 l)_mi) In, if

All elements are greater than 0.8l_miAfter the second-stage switch bit is changed, the third-stage protection cannot be configured continuously, all traversal is completed, the step 8) is carried out, and the result of final optimization calculation is output, if the result is not changed, the step

The presence of less than 0.8l of elements_miAfter the second-stage switch position is changed, three-stage protection can be configured, and the step 3) is carried out to carry out circular traversal calculation.

8) Through the calculation of the procedures, the total capacity Q of the minimum expected failure power failure distribution transformer is finally obtained_bestAnd its corresponding second stage switch optimum position

And outputting a calculation result.

The flow of the selection algorithm for anticipating the total capacity of the power distribution transformer in case of a fault with a trunk line and a branch line is shown in fig. 6.

In the third case, the distribution line has a trunk line, branch lines and secondary branch lines:

for distribution lines having trunks, branches and secondary branches, the second level switches may be present on the trunks, branches or secondary branches at the same time, i.e., the number of second level switches may be greater than 1.

Setting the length of the main line of the power distribution line to be L_ZFault probability per unit length of λ_Z(ii) a The branch lines on the trunk line have M (M is more than or equal to 0) lines, and the length of the position where each branch line is connected with the trunk line and the starting end of the trunk line is l_F1、l_F2、…、l_FMEach branch line has a length L_F1、L_F2、…、L_FMThe unit length fault probability of each branch line is lambda_F1、λ_F2、…、λ_FM(ii) a The number of secondary branches on the ith (i is more than or equal to 0 and less than or equal to M) branch line is N_i(N_iNot less than 0), each branch is connected to the ith branch line, and the length of the position of each branch connected to the ith branch line from the beginning end of the branch line is l_iC1、l_iC2、…、l_iCNiEach branch line has a length L_iC1、L_iC2、…、L_iCNiThe unit length failure probability of each branch line is lambda_iC1、λ_iC2、…、λ_iCNi. The number of distribution transformers hooked on the power distribution line is R, and the j (j is more than or equal to 0 and less than or equal to R) th capacity is S_jIts position is l from the beginning of the trunk line_j. The number of distribution transformers hooked on the distribution line is R, and the j (j is more than or equal to 0 and less than or equal to R) th capacity is S_jPosition of whichThe initial end of the main line or branch line at which the distance is arranged is l_j。

The optimal setting method and calculation formula of the second-stage switch of the two-stage protection configuration of the distribution line containing the main line, the branch line and the secondary branch line are approximately the same, and the difference is the processing of the secondary branch line. Since the line structure including the sub-branch is complex, it is complicated and difficult to perform the calculation with the length, and all the comparison processes are performed with impedance.

According to the distribution line information, the line has 1 trunk line, M branch lines and

a secondary branch line, each conductor line corresponding to one end, and having a common structure

And (4) an end. Numbering each end, recording the length from each end to the beginning of the trunk as l_mi

Before the calculation is carried out, the contact positions and the corresponding l for all branch lines and sub-branch lines_miIs compared with 0.8 times, if the distance from the contact point to the start end of the main line is more than 0.8l_miThen the branch line shares an end with the trunk line, or the sub-branch line shares an end with the branch line, called the active end.

On the basis, the corresponding end number of the trunk line is 1, and the start end is calculated to be 0.8l_m1The range of impedance variation therebetween is expressed as (Z)_m10，Z_m1) (ii) a For a branch line, the number of the corresponding tail end is recorded as i, and the initial end of the branch line is calculated to be 0.8l_miRange of impedance variation (Z) therebetween_mi0，Z_mi) (ii) a For a branch line, the corresponding end number is recorded as j, and the value from the beginning of the branch line to 0.8l is calculated_miRange of impedance variation (Z) therebetween_mj0，Z_mj). Setting the impedance of the second-stage switch at the position obtained by calculation of the power distribution line to be Z₂Judgment of Z₂Whether within the respective impedance range, for Z₂At the end of each range, it indicates that the second stage switch can be set on the wire corresponding to the end. Let the second switch on the main line be K_2Z，K_2ZThe distance between the position and the starting end of the trunk line is L_K2ZIf there is a second switch on a branch line, it is marked as K_2FiI is a counting parameter, K_2FiThe distance between the position and the initial end of the branch line is L_K2FiIf there is a second switch on a branch, it is marked as K_2CjJ is a counting parameter, K_2CjThe distance between the position and the initial end of the branch line is L_K2Cj. Setting the impedance of the third-stage switch setting position obtained by calculating the power distribution line to be Z₃If Z is₃And if the impedance is within a certain range, the impedance indicates that the wire corresponding to the end can be provided with the third-stage switch. Let the third switch on the main line denote K_3Z，K_3ZThe distance between the position and the starting end of the trunk line is L_K3ZIf there is a third switch on a branch line, it is marked as K_3FiI is a counting parameter, K_3FiThe distance between the position and the initial end of the branch line is L_K3FiIf a third switch is also on a branch line, it is marked as K_3CjJ is a counting parameter, K_3CjThe distance between the position and the initial end of the branch line is L_K3Cj。

According to whether the grading switch is arranged on each line or not and the number of the grading switches, the conducting wires of the whole line are divided into five types:

(1) the circuit is simultaneously provided with a second-stage switch and a third-stage switch;

(2) only a second-stage switch is arranged on the circuit;

(3) only a third-stage switch is arranged on the circuit;

(4) the circuit is not provided with a switch, and the type can be divided into 3 small types, wherein the branch line and the secondary branch line are possible, and the 3 small types are all positioned in front of the second-stage switch, are all positioned between the second-stage switch and the third-stage switch, and are all positioned behind the third-stage switch;

the distribution line containing the secondary branch is classified after the three-level protection setting, as shown in fig. 7.

Note the first kind of midsplit of the wireThe number of branch lines is m_f1The number of secondary branches is m_c1The number of branch lines in the second type of wire is m_f2The number of secondary branches is m_c2The number of branch lines in the third type of wire is m_f3The number of secondary branches is m_c3Number m of branch lines of class 4

wire

1, 2, 3_f41、m_f42、m_f43Number of minor branches m_c41、m_c42、m_c43Branch line numbering in m_f1，m_f2，m_f3，m_f41、m_f42、m_f43By sequential addition of (i.e. M ═ M)_f1+m_f2+m_f3+m_f41+m_f42+m_f43The number of the minor branch is m_c1，m_c2，m_c3，m_c41、m_c42、m_c43By sequential addition, i.e.

At m_c42In the 2 nd secondary branch of the fourth type wire, the number of the secondary branches between the second and third level switches of the main line is b0, and the secondary branches are m_f1The number between the second and third switches of the first branch line is b1_iAt m position_f2The number of the rear sides of the second stage switches of the second type branch line is b2_iThus, therefore, it is

At m_c43In the 3 rd secondary branch of the fourth type wire, the number of the secondary branches behind the third level switch of the main line is c0, and the secondary branches behind the third level switch of the main line is m_f1The number of the rear sides of the third stage switch of the branch line of the first type is c1_iAt m position_f3The number of the rear sides of the third-stage switch of the third-type branch line is c3_i(ii) a Thus, it is possible to provide

Expected failure power outage distribution transformer total capacity Q_fcIs composed of

In the formula, N_CIs the sum of the total number of secondary branches, i.e.

Wherein N is_iThe number of secondary branches on the ith branch line;

in the formula (I), the compound is shown in the specification,

wherein, Sigma lambda L_K3CZSum of the product of the length of all third-stage switches connected to the third-stage secondary branch on the main line to the beginning and the probability of failure, Σ λ L_b0For all located in the trunk lineSum of product of length and probability of failure of a fourth class 2 sub-branch between second and third class switches, S_ZBIs the sum of all distribution capacities between the second stage switch of the main line to the end, S_mf3For the sum of all distribution capacities, S, on all third-class branches_mf42For the sum of all distribution capacities, S, on all fourth class 2 branch lines_mc3ZFor the sum of all distribution capacities, S, on all the third-class secondary branches connected to the main trunk_b0The sum of all distribution transformation capacities on the fourth type 2 sub-branch between the second and third class switches of the main line, S_c0The sum of all distribution transformation capacities on the fourth type 3 secondary branches connected with the main trunk line; the other parameters have the same meanings as described above;

wherein, Sigma lambda L_K3CFiSum of the product of the length of the third-stage switch of the third-class secondary branch to the beginning of the third-class secondary branch after the second-stage switch of the first-class or second-class branch with the number i and the fault probability ∑ λ L_b1iSum of the product of the length and the probability of failure of all the fourth 2 nd sub-branches between the second and third switches of the first branch of the number i_b2iThe sum of the products of the lengths and the failure probabilities of all the fourth 2 nd sub-branches between the second and third class switches of the second branch line with the number i, S_FiBIs the sum of all distribution capacities from the second stage switch to the end connected to the i-th branch line, S_mc3FiIs the sum of all distribution capacities, S, on a third class of secondary branches connected to the ith branch_b1iIs the sum of all distribution transformation capacities, S, on the fourth class 2 secondary branch line connected to the first class branch line with the number i_b2iTo branch lines of the second type numbered iThe sum of all distribution transformation capacities on the fourth type 2 secondary branch; the other parameters have the same meanings as described above;

for the power failure distribution capacity of the secondary branch line secondary switch failure probability, the calculation formula is as follows:

wherein S is_CiBThe sum of all distribution transformation capacities from the second-stage switch of the first-class or second-class secondary branch line with the number of i to the tail end, and the meanings of other parameters are as described above;

the power failure distribution and transformation capacity is the power failure distribution and transformation capacity of the third-level switch failure probability of the main line, and the calculation formula is as follows:

wherein, Sigma lambda L_c0The sum of the products of the length and the probability of failure of all the fourth class 3 type secondary branches located after the main three-level switch, S_ZCIs the sum of all distribution capacities from the third stage of the main line switch to the end, S_mf42For the sum of all distribution capacities, S, on all fourth class 3 branch lines_c0The sum of all distribution transformation capacities on the fourth type 3 secondary branches connected with the main trunk line; the other parameters have the same meanings as described above;

the power failure distribution capacity is the power failure distribution capacity of the third-level switch failure probability of the branch line, and the calculation formula is as follows:

wherein, Sigma lambda L_c1iFor all at the number iSum of product of length and fault probability of fourth 3 kinds of secondary branches after third-stage switch of branch line_c3iThe sum of the product of the length and the probability of failure of all the fourth 3 rd sub-branches after the third class branch third-stage switch with the number i, S_FiBIs the sum of all distribution capacities from the second stage switch to the end connected to the i-th branch line, S_c1iIs the sum of all distribution transformation capacities, S, on the fourth 3 rd branch line connected to the first branch line with the number i_c3iThe sum of all distribution transformation capacities on a fourth 3 rd branch line connected with a second branch line with the number of i; the other parameters have the same meanings as described above;

wherein S is_CiCThe sum of all distribution transformation capacities from the third-class secondary branch third-stage switch with the number i to the tail end is shown, and other parameters have the meanings as described above.

When the distribution line has a main line, a branch line and a secondary branch line, infinite switch position setting conditions exist in the selectable range of the second-level switch position and the third-level switch position, wherein the total capacity Q of the distribution transformer for power failure in expected faults of various conditions when the switches are located near the distribution transformer position only needs to be compared, the minimum value is found, and the second-level switch position and the third-level switch position corresponding to the minimum value and the corresponding protection configuration scheme are the optimal protection configuration scheme.

When the distribution line has a main line, a branch line and a secondary branch line, the flow of the selection algorithm of the total capacity of the distribution transformer in the expected fault power failure is as follows:

1) obtaining line information, and calculating 0.8l from the initial end to the end of the effective end corresponding to the trunk line, the branch line and the secondary branch line according to the line information_mImpedance range (Z)_mi0，Z_mi) (ii) a For obtaining the position of the second-stage switchMinimum impedance Z_2min(ii) a Minimum impedance Z at third stage switch setting_3min。

2) Judging whether a certain impedance range satisfying Z exists_3min∈(Z_mi0,Z_mi) If the protection circuit does not exist, the circuit cannot be configured with three-level protection, and other processes are carried out; if the three-level switch exists, the circuit can be configured with three-level protection, a lead wire capable of being provided with the three-level switch is determined, and the length L of the setting position of each three-level switch from the starting end of the main line is calculated_K3Zmin、L_K3Fimin、L_K3CiminSimultaneously judging Z_2min∈(Z_mi0,Z_mi) Calculating the length L of each two-stage switch from the initial end of the main line_K2Zmin、L_K2Fimin、L_K2Cimin。

3) Order to

4) Judgment of

Three-level protection can be configured, then updating

Each element of (1), i.e.

Each third stage switch position fetch

Each element of (1), i.e.

5) According to the preset position of the switch position, classifying the leads and calculating according to the formula (4)

Is assigned a value of

6) Fix the position of the second-stage switch at

To find

Calculating impedance of each distribution transformer after 1 st distribution transformer corresponding to each element, taking minimum impedance, and calculating each impedance corresponding to the impedanceThe distance from the location of the line to the beginning of the trunk is recorded as

Make an intermediate amount

And 4), circularly traversing all the qualified distribution positions.

7) The position of the second-stage switch is changed to find

Corresponding elements, judging

Whether it is in the length range (0,0.8 l)_mi) In, if

Corresponding elements, judging

Whether it is in the length range (0,0.8 l)_mi) In, if

And outputting a calculation result.

The flow of the selection algorithm for anticipating the total capacity of the power distribution transformer in case of a fault with a trunk line, a branch line and a secondary branch line is shown in fig. 8.

After the setting optimization positions of the second-stage switch and the third-stage switch are determined, setting calculation is carried out on the protection fixed values of the switches according to a protection coordination principle, and the setting calculation is the optimization configuration.

Claims

1. A three-level protection optimal configuration method for a distribution line based on the minimum power outage capacity is characterized in that the method aims at the situation that the distribution line only has a main line, the distribution line has a main line and a branch line, and the distribution line has the main line, the branch line and a secondary branch line; respectively establishing an expected failure power failure distribution transformer total capacity calculation formula which is corresponding to the three-level protection configuration scheme and takes the line failure probability into consideration; respectively giving specific calculation processes by calculating the fault power failure distribution and transformation capacity of the limited protection configuration schemes; finally, finding out the switch setting position and the number corresponding to the minimum power failure capacity of the distribution line, thereby obtaining an optimized three-level protection configuration scheme;

the total capacity of all distribution transformers on the distribution line;

in the formula (I), the compound is shown in the specification,

the total capacity of all distribution transformers on the distribution line;

(4) let L₂＝L_K2Zmin，L₃＝L_K3Zmin；

(8) changing the position of the second stage switch to find L_K2ZUpdating the minimum distance L of the second-stage switch in the kth distribution transformer at the rear side_K2ZminThe distance l between the distribution and transformation position and the beginning of the trunk line_kInstant L_K2Zmin＝l_kJudgment ofBroken L_K2ZminWhether it is in the length range (0, 0.8L)_Z) In, if L_K2Zmin＞0.8L_ZIf all the traversals are completed, the step (9) is carried out to output the result of the final optimization calculation; if L is_K2Zmin≤0.8L_ZExplaining the possibility of further optimization of the line protection configuration, recalculating to obtain the minimum distance L of the third-stage switch_K3ZminJudgment of L_K3ZminWhether it is in the length range (0, 0.8L)_Z) In, if L_K3Zmin＞0.8L_ZIf L is the final result of the optimization calculation, the step (9) is entered to output the final result of the optimization calculation_K3Zmin≤0.8L_ZIf the situation that the calculation is not carried out exists, adding 1 to the counting quantity k, reassigning the counting quantity j to be 1, then entering the step (4), and circularly traversing and calculating;

2. The method of claim 1, wherein the distribution line has a total capacity Q (L) of the distribution transformer for the expected failure of the main line and the branch line_K2Fi,L_K3Fi,L_K2Z,L_K3Z) The following were used:

in the formula (I), the compound is shown in the specification,

Wherein S is_{General assembly}To be integratedThe sum of all distribution and transformation capacities of the power distribution lines; l is_FiIs the length of each branch line; lambda [ alpha ]_FiThe unit length fault probability of each branch line; l is_K2FiIs K_2FiDistance between position and beginning of branch line, K_2FiA second stage switch on a branch line; l is_K3FiIs K_3FiDistance between position and beginning of branch line, K_3FiA third stage switch on a branch line; the other parameters have the same meanings as described above;

3. The distribution line three-level protection optimal configuration method based on the minimum blackout capacity according to claim 2, wherein when the distribution line has a main line and a branch line, the flow of the selection algorithm of the total capacity of the expected failure blackout distribution transformer is as follows:

(1) obtaining line information, and calculating 0.8l from the start end to the end of the effective end corresponding to the trunk line and the branch line according to the line information_mImpedance range (Z)_mi0，Z_mi) (ii) a Determining the minimum impedance Z at the second stage switch setting_2min(ii) a Minimum impedance Z at third stage switch setting_3min；

(3) Order to

(4) Judgment of

Three-level protection can be configured, then updating

Each element of (1), i.e.

Each third stage switch position fetch

Each element of (1), i.e.

(5) According to the preset position of the switch position, classifying the leads according to Q (L)_K2Fi,L_K3Fi,L_K2Z,L_K3Z) Formula calculation

Corresponding expected failure power failure distribution transformer total capacity Q (L)_K2Fi,L_K3Fi,L_K2Z,L_K3Z) (ii) a If Q_bestIs an initial value orQ(L_K2Fi,L_K3Fi,L_K2Z,L_K3Z)＜Q_bestThen the minimum expected fault is cut off and the total capacity Q is distributed_bestAssigned value of Q (L)_K2Fi,L_K3Fi,L_K2Z,L_K3Z) Optimized position of corresponding second stage switch

Is assigned a value of

(6) Fix the position of the second-stage switch at

To find

Make an intermediate amount

(7) the position of the second-stage switch is changed to find

Corresponding elements, judging

Whether it is in the length range (0,0.8 l)_mi) Within; if it is

Corresponding elements, judging

Whether it is in the length range (0,0.8 l)_mi) In, if

All elements are greater than 0.8l_miAfter the second-stage switch bit is changed, the third-stage protection cannot be configured continuously, all traversal is completed, and the output is input in the step (8)Finally optimizing the calculated result; if it is

And outputting a calculation result.

4. The power distribution line three-level protection optimal configuration method based on outage capacity minimization according to claim 2, wherein when the power distribution line has a main line and a branch line, the second and third level switches are simultaneously present on the main line and the branch line, that is, the number of the second and third level switches may be greater than 1;

(2) only a second-stage switch is arranged on the circuit;

(3) only a third-stage switch is arranged on the circuit;

(4) the line has no switch, and the branch line or secondary branch line can be subdivided into 3 small types which are all positioned in front of the second stage switch, are all positioned between the second stage switch and the third stage switch, and are all positioned behind the third stage switch.

5. The method of claim 2, wherein the distribution line has a total capacity Q of the distribution substation for expected failures including main lines, branch lines and minor branch lines_fcThe following were used:

in the formula, N_CIs the sum of the total number of secondary branches, i.e.:

wherein N is_iThe number of secondary branches on the ith branch line;

wherein S is_{General assembly}Is the sum of all distribution transformation capacities, m, of the whole distribution line_f1The number of branch lines in the first type of wire, m_f2The number of branch lines, m, in the second class of conductors_f3The number of branch lines, m, in the third category of conductors_f41For class 4 wire, number of 1 branch line, m_c1The number of secondary branches in the first type of wire, m_c2The number of secondary branches in the second type of wire, m_c3Number of secondary branches m in third type of conductor_c41The number of the 1 st secondary branch of the 4 th type conductor line, L_CiLength of the minor branch, λ, numbered i_CiThe unit length fault probability of the secondary branch with the number of i is obtained; the other parameters have the same meanings as described above;

wherein, Sigma lambda L_K3CZThe sum of the product of the length of a third-stage switch of all third-stage secondary branches connected to the main line to the starting end of the third-stage switch and the fault probability; sigma lambda L_b0The sum of the products of the lengths and the failure probabilities of all the fourth type 2 secondary branches positioned between the second level switch and the third level switch of the main line; s_ZBThe sum of all distribution capacity from the second-stage switch of the main line to the tail end; s_mf3The sum of all the distribution capacity on all the third-class branch lines; s_mf42The sum of all distribution and transformation capacities on all fourth type 2 branch lines; s_mf43The sum of all distribution and transformation capacities on all fourth type 3 branch lines; s_mc3ZThe sum of all distribution transformation capacities on all the third type secondary branches connected to the main trunk line; s_b0The sum of all the distribution transformation capacities on the fourth type 2 secondary branches between the second level switch and the third level switch of the main line is obtained; s_c0The sum of all distribution transformation capacities on the fourth type 3 secondary branches connected with the main trunk line; m is_c42The number of the 2 nd secondary branches of the 4 th type wire is set; the other parameters have the same meanings as described above;

the power failure distribution capacity is distributed for the second-stage switch failure probability of the secondary branch line, and the calculation formula is

Wherein S is_CiBThe sum of all distribution transformation capacities from the second-stage switch of the first-type or second-type secondary branch line with the number of i to the tail end is shown; l is_K3CiThird level switch K for secondary branch_3CiThe distance between the position and the starting end of the secondary branch line; l is_K2CiFor the second switch K of the secondary branch_2CiThe distance between the position and the starting end of the secondary branch line; the other parameters have the same meanings as described above;

wherein, Sigma lambda L_c1iSum of the product of the length and the probability of failure of all the fourth 3 rd sub-branches after the third stage switch of the first branch line with the number i_c3iThe sum of the product of the length and the probability of failure of all the fourth 3 rd sub-branches after the third class branch third-stage switch with the number i, S_FiBIs the sum of all distribution capacities from the second stage switch to the end connected to the i-th branch line, S_c1iIs the sum of all distribution transformation capacities, S, on the fourth 3 rd branch line connected to the first branch line with the number i_c3iThe sum of all distribution transformation capacities on a fourth 3 rd branch line connected with a second branch line with the number of i; the other parameters have the same meanings as described above;

wherein S is_CiCSum of all distribution capacities from the third class of secondary-third-stage switches to the end, L, of number i_K3CiThird level switch K for secondary branch_3CiThe distance between the position and the starting end of the secondary branch line; the other parameters have the same meanings as described above.

6. The distribution line three-level protection optimal configuration method based on the minimum blackout capacity according to claim 5, wherein when the distribution line has a main line, a branch line and a secondary branch line, the flow of the selection algorithm for predicting the total capacity of the distribution transformer in the case of a fault blackout is as follows:

(3) Order to

(4) Judgment of

Three-level protection can be configured, then updating

Each element of (1), i.e.

Each third stage switch position fetch

Each element of (1), i.e.

Is assigned a value of

(6) Fix the position of the second-stage switch at

To find

Make an intermediate amount

(7) the position of the second-stage switch is changed to find

Corresponding elements, judging

Whether it is in the length range (0,0.8 l)_mi) In, if

Corresponding elements, judging

Whether it is in the length range (0,0.8 l)_mi) In, if

The presence of less than 0.8l of elements_miAfter the second stage switch position is changed, three stages of protection can be configured, and step (a)3) Performing circular traversal calculation;

And outputting a calculation result.

7. The distribution line three-level protection optimal configuration method based on the power outage minimum capacity according to claim 5, wherein when the distribution line has a main line, a branch line and a secondary branch line, the second-level switches are simultaneously present on the main line, the branch line or the secondary branch line, namely the number of the second-level switches is more than 1;

(2) only a second-stage switch is arranged on the circuit;

(3) only a third-stage switch is arranged on the circuit;

(4) the circuit has no switch, and the branch line and the secondary branch line can be subdivided into 3 small types which are all positioned in front of the second-stage switch, are all positioned between the second-stage switch and the third-stage switch, and are all positioned behind the third-stage switch.