CN104166788A - Overhead transmission line optimal economic life range assessment method - Google Patents

Abstract

The invention provides an overhead transmission line optimal economic life range assessment method. The error of a failure rate prediction result of electric transmission and transformation equipment and the subjectivity of rough calculation of partial parameters of the full-life cycle cost cause an economic life result obtained by the adoption of setting calculation to have certain deviation. The overhead transmission line optimal economic life range assessment method comprises the steps that the fuzzy comprehensive evaluation method and the analytic hierarchy process are used for calculating membership degrees of all indexes and weights of all the indexes respectively; then, training output and error calculation are conducted on three failure rates of a transmission line through a least square support vector machine together with the relevant data of the service age, the external operation environment and the quality condition of the transmission line respectively, and a failure rate prediction model of the transmission line is obtained; finally, the interval analysis method is introduced into the life cycle cost theory and the optimal economic life range of the transmission line is obtained at last. According to the overhead transmission line optimal economic life range assessment method, the characteristics that the wild operation environment of the transmission line is poor and the regional span of the transmission line is wide are fully considered, and meanwhile, the problem that for different transmission lines, a uniform life ending standard is hard to provide is solved.

Description

A Method for Optimum Economic Life Interval Evaluation of Overhead Transmission Lines

technical field

The invention belongs to the field of power systems, in particular to a method for evaluating the optimal economic life interval of an overhead power transmission line.

Background technique

As an important part of the power grid, the transmission line has been in the harsh environment for a long time and the operating conditions are complex and diverse. Therefore, there may be high failure rates and frequent component replacement before reaching the expected design life. The life assessment of transmission lines with a certain service age can effectively avoid a large number of direct economic losses caused by excessive failure rates or frequent maintenance and repairs, and reduce the consequences of high-risk operation of the power grid and indirect economic losses caused by power outages. more immeasurable. In the life cycle asset management of the power grid, the life prediction of the transmission line can realize the life matching between the power grid equipment, improve the utilization rate of the equipment, and reduce the operating cost of the power enterprise. In addition, with the continuous expansion of the scale of my country's power grid and the increasingly complex structure of the power grid, the reasonable decommissioning time of transmission lines can also be used to guide the planning, upgrading and transformation of the future power grid.

In the past, the failure rate prediction model based on Weibull distribution or exponential distribution only used service age as the main variable, and did not consider the influence of other factors on the failure rate, and did not distinguish the severity of failure consequences, making it difficult to finely calculate the failure cost and Maintenance costs.

The errors in the prediction results of the failure rate of power transmission and transformation equipment and the subjectivity of the rough calculation of some parameters of the life cycle cost make the economic life results calculated by fixed values have certain deviations, which in turn have an impact on the decommissioning of power transmission and transformation equipment.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the defects of the above-mentioned prior art, and provide a method for evaluating the optimal economic life interval of overhead transmission lines, which fully considers the influence of uncertain information on the evaluation results of the economic life of the line, so as to improve the accuracy of the results. credibility and plausibility.

For this reason, the present invention adopts the following technical solutions: a method for evaluating the optimal economic life interval of overhead transmission lines, characterized in that,

Firstly, according to the historical statistical data, sort out and classify the external operation environment and self-quality evaluation indicators of the transmission line, and use the fuzzy comprehensive evaluation method and the analytic hierarchy process to calculate the membership degree and weight of each indicator;

Then, according to the severity of the fault consequences, the faults are divided into general faults (line defects, equipment abnormalities, minor faults), major faults (causing seven to eight power grid accidents or equivalent serious faults) and serious faults (causing one to six power grid accidents) Accidents or equally serious faults) three types, through the least squares support vector machine combined with the service age of the transmission line, the external operating environment and the relevant data of its own quality, the three failure rates of the transmission line are respectively trained and output and the error calculation is obtained. Failure rate prediction model for transmission lines;

Finally, the interval analysis method is introduced into the life cycle cost theory, the failure cost and maintenance cost are calculated from the failure rate interval of the line to be evaluated, and each cost index is intervalized, and the optimal decommissioning of the transmission line is solved with the goal of minimizing the annual average cost Time range, eliminate the deviation of a single constant value, and finally get the best economic life interval of the transmission line.

The line decommissioning standard can be formulated by using the optimum economic life interval of the line judged by the present invention. If the running time of the line exceeds the optimal economic life interval, the line will be decommissioned; if it does not exceed the optimal economic life interval, the line will continue to operate.

The invention fully considers the characteristics of harsh field operating environment and large geographical span of the transmission line, and simultaneously solves the problem that it is difficult to provide a unified service life end standard for different types of transmission lines.

The present invention adopts following specific steps:

Step 1), the establishment of the external operating environment of the transmission line and its own quality assessment factor set, index set and comment set,

Divide the factor set and each lower-level index into 4 comment levels, that is, the comment set is V={v ₁ ,v ₂ ,v ₃ ,v ₄ }={good, fair, average, bad};

Step 2), the calculation of the membership degree and weight of the external operating environment of the transmission line and its own quality assessment index,

The calculation of the index membership degree is as follows: by making an evaluation table for each expert, the membership degree of each index is calculated according to the evaluation of the experts. The calculation formula of the index membership degree r _ij is as follows:

${\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; ij</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; ij</span>}}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; total</span>}}}$

In the formula, P _ij represents the number of experts who believe that the index i in the factor set belongs to the comment v _j , P _total represents the total number of experts participating in the evaluation, i=1, 2,..., u, u is the number of indicators in the factor set, j =1-4, after obtaining the membership degree of the index set, the fuzzy membership degree matrix R of the factor set can be obtained;

The determination of the index weight adopts the "9-graduation method" in the Analytic Hierarchy Process (AHP). After sorting and calculating by experts, the weight vector W of each index in the factor set can be obtained;

Step 3), the comprehensive evaluation and scoring of the external operating environment and its own quality status, the calculation formula of the fuzzy comprehensive evaluation vector B is as follows:

B=WoR

In the formula, R is the fuzzy membership degree matrix of the factor set, W is the weight vector of each index of the factor set, "o" is the operator, which represents the synthesis operation, and the M(·,+) operator is used, that is

${\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; u</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; ij</span>}}$

In the formula, b _j is the membership degree of the factor set to the comment v _j , w _i is the weight of the index i in the factor set, r _ij is the index membership degree;

After calculating the fuzzy comprehensive evaluation vector of the factor set, according to the principle of maximum membership degree, the comprehensive evaluation result of the factor set is the comment v _j corresponding to the maximum membership degree; assuming that the rating set corresponding to the comment set is That is, the corresponding comment level corresponds to the corresponding score, and the comprehensive evaluation result is that the factor set score of comment v _j is

Step 4), sample line historical data training and error analysis:

Service age T and operating environment score at the general stage and quality status rating The same transmission line is defined as the same type of line, and the historical data of the same type of line during the period of service age T is analyzed, and the three types of failure rates are respectively counted as a sample (because the line has different types of failures in different seasons of the year and different years Due to the fluctuation of the failure rate caused by a major disaster, it is more scientific to set the statistical period for the number of failures of similar lines to 5 years accordingly),

The formula for calculating the annual failure rate λ of the service age of similar lines is as follows, the unit is times/year · 100 kilometers, $\mathrm{\&lambda;}=\frac{{\mathrm{\&Sigma;}}_{5\mathrm{years}}{Q}^{(T,S_{{\mathrm{E.}}_1},S_{{\mathrm{E.}}_2},S_{h_1},S_{h_2})}}{5\&times;\mathrm{\&Sigma;}{l}^{(T,S_{{\mathrm{E.}}_1},S_{{\mathrm{E.}}_2},S_{h_1},S_{h_2})}},$

In the formula, It is the total number of faults of the same type of line faults within 5 years, and the general faults, major faults and serious faults are counted separately. is the sum of the lengths of similar lines at the end of 5 years;

In the transmission line failure rate prediction model, the sample line data is the line basic information vector x _m = (x _m1 , x _m2 , x _m3 , x _m4 , x _m5 ) and the actual line failure rate vector λ _m = (λ _m1 , λ _m2 , λ _m3 ), where, m=1, 2,..., M+N, M+N is the number of samples; x _m1 , x _m2 , x _m3 , x _m4 , x _m5 represent the service age T and factor set score λ _m1 , λ _m2 , and λ _m3 are the failure rates of general faults, major faults, and serious faults of the sample line respectively; M groups of samples are used for training, and N groups of samples are used for checking calculation. The error calculation formula is as follows:

$\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\frac{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; re</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; pre</span>}}<span\; class="notranslate">\; |</span>}{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; re</span>}}}$

In the formula, is the actual statistical value of the sample line failure rate used for checking calculation, is the predicted value of the sample line failure rate used for checking calculation, N is the number of samples used for checking calculation, and ε is the average value of error;

Step 5), the interval prediction of the failure rate of the line to be evaluated:

When predicting the failure rate of the line to be evaluated, the score of the line's operating environment factor set and Judgment is based on the environmental status of the line corridor over the years after it is put into operation, and the quality status factor set is scored and Evaluate according to the line's operation and maintenance records and status assessment results over the years;

Step 6), line life cycle cost analysis:

When the transmission line is decommissioned in year L, its annual average cost is as follows:

${\mathrm{<span\; class="notranslate">\; NF</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; IC</span>}<span\; class="notranslate">\; +</span>\underset{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; L</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; OC</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; MC</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; FC</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; )</span>{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; R</span>}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; DC</span>}{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; R</span>}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1,2</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; L</span>}$

In the formula, L is the number of years of transmission line operation, NF _L is the annual average cost of transmission line operation for L years, IC is the initial input cost, r is the social discount rate, waste cost DC is income-type cost, and R is the increase in labor and material costs OC _t , MC _t , FC _t are the operation cost, maintenance cost and failure cost of the transmission line in year t, respectively;

Step 7), route cost interval calculation:

After the line is completed and put into operation, the one-time input cost IC is fixed, and the operating cost OC is determined in the operation plan, and the annual expenditure fluctuates within a range; after the line is decommissioned, the calculation formula for the abandonment cost is as follows:

DC=p×IC

In the formula, p is the range of waste cost percentage;

After obtaining various cost intervals, the optimal economic life interval of the transmission line can be obtained by finding the range of operating years when the annual average cost NF _L is the smallest.

Further, in step 5), assuming that the transmission line can run up to the stage service age T _max , the stage service age of the line to be evaluated is substituted in order from "1" to "T _max ", and the service age of each stage of the line is calculated The three types of annual failure rates; then, the conversion of the stage service-year failure rate to the actual service-year failure rate is carried out. It is determined as the annual failure rate when the line has been in operation for 3 years (1 to 5 years), 8 years (6 to 10 years), ..., 5T _max -2 years (5T _max -4 to 5T _max years), using cubic splines Interpolate to calculate the annual failure rate of the transmission line for 1-5T _max years of operation; finally, the failure rate is intervalized according to the error ε, and the failure rate range of the three types of faults is calculated. The formula for the intervalization of the failure rate is as follows:

$<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}^{\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}^{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; [</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; ]</span>$

are the lower limit and upper limit of the line failure rate in the t-th year, respectively, and _λt is the predicted value of the line failure rate in the t-th year after interpolation.

Further, in step 6), the maintenance cost MC _t and the failure cost FC _t of the transmission line in year t are related to the failure rate, and the calculation formula is as follows:

${\mathrm{<span\; class="notranslate">\; MC</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; l</span>}$

${\mathrm{<span\; class="notranslate">\; FC</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; l</span>}$

The subscript k=1, 2, and 3 represent general faults, major faults, and severe faults respectively, λ _k (t) is the failure rate of the line, l is the length of the transmission line, and M _k is the average component replacement cost for each fault of the transmission line and labor maintenance costs, F _k is the average comprehensive loss caused by transmission line faults.

Further, in step 6), the social discount rate r, the maintenance cost M _k , the failure cost F _k , and the growth rate R of labor and material costs are all represented by interval numbers.

Further, in step 4), when training and calculating the failure rate of the transmission line, the data of the transmission line with the same voltage level is used (the voltage level of the transmission line is different, and the failure rate is very different).

Further, in step 4), the service age statistics are carried out on the basis of the initial commissioning year of the line, and the stage service age T is calculated in units of 5 years. Assuming that a certain line has been put into operation for Z years, its stage service age is in is the upper integer symbol. For example, a route with a service age of "6-10 years" has a stage service age of "2".

The present invention combines the complex characteristics of transmission line aging and failure "influenced by multiple factors, multi-consequences" and failure rate error analysis. The prediction result of line failure rate is more reasonable. Carry out life-cycle cost analysis and intervalization of transmission lines, and use the minimum annual average cost as the criterion to obtain the optimal economic life interval of the line with comprehensive reliability and economic indicators, fully considering the uncertain information for the evaluation of the economic life of the line The impact of the results increases the credibility and plausibility of the results. The invention fully considers the characteristics of harsh field operating environment and large geographical span of the transmission line, and simultaneously solves the problem that it is difficult to provide a unified service life end standard for different types of transmission lines.

Description of drawings

Fig. 1 is a flow chart of the line failure rate prediction model of the present invention.

Figure 2a~c are the failure rate curves of common faults, major faults, and severe faults of the example lines (line 1 and line 2) in the application example (the upper curve in the figure is line 1, and the lower curve is line 2) , where Fig. 2a is the failure rate curve of common faults on line 1 and line 2, Fig. 2b is the failure rate curve of relatively large faults on line 1 and line 2, and Fig. 2c is the failure rate curve of serious faults on line 1 and line 2.

Figures 3a-b are the average annual life-cycle cost curves of Line 1 and Line 2 in the application example. Figure 3a is the upper and lower limit curve of the annual average life cycle cost of Line 1, and Figure 3b is the upper and lower limit curve of the annual average life cycle cost of Line 2.

Detailed ways

Below in conjunction with accompanying drawing, the present invention will be further described, and the present invention comprises the following steps:

Step (1), the establishment of line operating environment and quality evaluation factor sets, index sets and comment sets. specifically is:

Table 1 shows the set of factors and indicators for the evaluation of transmission line operating environment and quality status.

Table 1 The evaluation factor set and index set of transmission line operating environment and quality status

Divide the factor set and each lower-layer index into 4 comment grades, that is, the comment set is: V={v ₁ ,v ₂ ,v ₃ ,v ₄ }={good, good, average, bad}.

Step (2), calculating the membership degree and weight of the line operating environment and quality status evaluation indicators. specifically is:

The calculation of index membership degree adopts fuzzy comprehensive evaluation method. By making an evaluation table for each expert, calculate the degree of membership of each index according to the evaluation of the experts. The formula for calculating the degree of membership r _ij of the index is as follows:

${\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; ij</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; ij</span>}}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; total</span>}}}$

In the formula, P _ij represents the number of experts who believe that the index i in the factor set belongs to the comment v _j , P _total represents the total number of experts participating in the evaluation, i=1, 2,..., u, u is the number of indicators in the factor set, j = 1-4. After obtaining the membership degree of the index set, the fuzzy membership degree matrix R of the factor set can be obtained.

The determination of index weight adopts the "9-graduation method" in the Analytic Hierarchy Process (AHP). After sorting and calculating by experts, the weight vector W of each index in the factor set can be obtained.

An example of a factor set fuzzy membership degree matrix and index weight vector is shown below:

Step (3), the comprehensive evaluation and scoring of the operating environment and quality status. specifically is:

B is the fuzzy comprehensive evaluation vector, and its calculation formula is as follows:

B=WoR

In the formula, "o" is an operator, representing a composite operation, and the present invention adopts the M( ,+) operator, namely

${\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; u</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; ij</span>}}$

In the formula, b _j is the membership degree of the factor set to the comment v _j , and w _i is the weight of the index i in the factor set.

After calculating the fuzzy comprehensive evaluation vector of the factor set, according to the principle of maximum membership degree, the comprehensive evaluation result of the factor set is the comment v _j corresponding to the maximum membership degree. The present invention assumes that the score set corresponding to the comment set is That is, the corresponding comment level corresponds to the corresponding score, and the comprehensive evaluation result is that the factor set score of comment v _j is

Step (4), sample line historical data training and error analysis. specifically is:

The input information of the training sample line is described as follows.

1) The voltage level of the transmission line is different, and the failure rate is quite different. Therefore, when training and calculating the failure rate of the transmission line, the transmission line data of the same voltage level is used.

2) Referring to the standards on the consequences of transmission line failures promulgated by the State Grid, according to the severity, the faults are divided into general faults (line defects, equipment abnormalities, minor faults), major faults (causing seven to eight power grid accidents or equivalent serious faults) ), serious faults (causing power grid accidents of grades 1 to 6 or equivalent serious faults), and the failure rates of the three types of lines are counted separately.

3) The service age statistics are carried out based on the initial commissioning year of the line, and the stage service age T is calculated in units of 5 years. Assuming that a certain line has been put into operation for Z years, its stage service age is in is the upper integer symbol. For example, a line with a service age of "6 to 10 years" has a stage service age of "2".

4) Score the stage service age T and operating environment and quality status rating The same transmission line is defined as the same type of line, and the historical data of the same type of line during the phase service age T is analyzed, and the three types of failure rates are counted as a sample. Since lines have different types of failures in different seasons of the year and the failure rate fluctuates due to a major disaster in different years, it is more scientific to set the statistical period for the number of failures of similar lines to 5 years accordingly.

The formula for calculating the annual failure rate λ of the service age of similar lines is as follows, and the unit is times/year · 100 kilometers.

$\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}\mathrm{<span\; class="notranslate">\; years</span>}}{\mathrm{<span\; class="notranslate">\; Q</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span>}}{\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}{\mathrm{<span\; class="notranslate">\; l</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span>}}$

In the formula, It is the total number of failures of similar line failures within 5 years (general failures, major failures and serious failures are counted separately), It is the sum of the lengths of similar lines at the end of 5 years.

In the transmission line failure rate prediction model, the sample line data is the line basic information vector x _m = (x _m1 , x _m2 , x _m3 , x _m4 , x _m5 ) and the actual line failure rate vector λ _m = (λ _m1 , λ _m2 ,λ _m3 ), where m=1, 2, ..., M+N (M+N is the sample size). x _m1 , x _m2 , x _m3 , x _m4 , x _m5 denote the stage service age T and factor set score of the sample line respectively λ _m1 , λ _m2 , and λ _m3 are the failure rates of general faults, major faults and serious faults of the sample lines, respectively. The present invention adopts M group of samples to do training, and N group of samples to do checking calculation, and the calculation formula of error is as follows:

$\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\frac{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; re</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; pre</span>}}<span\; class="notranslate">\; |</span>}{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; re</span>}}}$

In the formula, is the actual statistical value of the sample line failure rate used for checking calculation, is the predicted value of the sample line failure rate used for checking calculation, N is the number of samples used for checking calculation, and ε is the average value of error.

In step (5), the interval prediction of the failure rate of the line to be evaluated is performed. specifically is:

When predicting the failure rate of the line to be evaluated, the score of the line's operating environment factor set and Judgment is based on the environmental status of the line corridor over the years after it is put into operation, and the quality status factor set is scored and The evaluation is based on the line's operation and maintenance records and status assessment results over the years.

Assuming that the transmission line can be operated up to the stage service age T _max , the stage service age of the line to be evaluated is substituted in order from "1" to "T _max ", and the three types of annual failure rates of each stage service age of the line are obtained. Then, the failure rate of the stage service age is transformed into the actual service age failure rate. The transformation process is as follows: the average value of the upper and lower limits of the service age of the transmission line at each stage is taken, and the stage service age failure rate is respectively set as the line operation for 3 years (1 to 5 years), 8 years (6 to 10 years)... The annual failure rate at 5T _max -2 years (5T _max -4 to 5T _max years), using cubic spline interpolation, calculates the transmission line running 1 ~5T _max annual failure rate. Finally, the failure rate is intervalized according to the error ε, and the failure rate range of the three types of failures is calculated. The interval formula of the failure rate is as follows:

$<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}^{\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}^{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; [</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; ]</span>$

are the lower limit and upper limit of the line failure rate in the t-th year, respectively, and _λt is the predicted value of the line failure rate in the t-th year after interpolation.

The flow chart of the failure rate prediction model for the evaluation line is shown in Figure 1.

Step (6), line life cycle cost analysis. specifically is:

When the transmission line is decommissioned in year L, its annual average cost is as follows:

${\mathrm{<span\; class="notranslate">\; NF</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; IC</span>}<span\; class="notranslate">\; +</span>\underset{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; L</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; OC</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; MC</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; FC</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; )</span>{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; R</span>}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; DC</span>}{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; R</span>}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1,2</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; L</span>}$

In the formula, L is the number of years of transmission line operation, NF _L is the annual average cost of transmission line operation for L years, IC is the initial input cost, r is the social discount rate, waste cost DC is income-type cost, and R is the increase in labor and material costs Rate. OC _t , MC _t , FC _t are the operation cost, maintenance cost and failure cost of the transmission line in year t, respectively.

The maintenance cost MC _t and the failure cost FC _t of the transmission line in year t are related to the failure rate, and the calculation formula is as follows:

${\mathrm{<span\; class="notranslate">\; MC</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; l</span>}$

${\mathrm{<span\; class="notranslate">\; FC</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; l</span>}$

The subscript k=1, 2, and 3 represent general faults, major faults, and severe faults respectively, λ _k (t) is the failure rate of the line, l is the length of the transmission line, and M _k is the average component replacement cost for each fault of the transmission line and labor maintenance costs, F _k is the average comprehensive loss caused by transmission line faults.

In step (7), the route cost is calculated in intervals. specifically is:

After the line is completed and put into operation, the one-time input cost IC is fixed. The operating cost OC basically fluctuates within a range every year under the condition that the operation plan is determined (the present invention does not consider the line loss). After the line is decommissioned, the formula for calculating the abandonment cost is as follows:

DC=p×IC

In the formula, p is the percentage interval of the discarded cost. In addition, the social discount rate r, maintenance cost M _k , failure cost F _k , and labor and material cost growth rate R are all represented by interval numbers.

After obtaining various cost intervals, the optimal economic life interval of the transmission line can be obtained by finding the range of operating years when the annual average cost NF _L is the smallest.

Application example

In order to verify the feasibility of the evaluation method for the optimal economic life interval of overhead transmission lines. Two 220kV overhead transmission lines in a certain area are selected to evaluate the best economic life interval. Line 1 has a total length of 42.9km and was put into operation in July 2005 with a total price of 21.433 million yuan when it was completed; Line 2 has a total length of 37.8km and was put into operation in November 2004 with a total price of 18.735 million yuan when it was completed.

Through the evaluation of many experts, the fuzzy comprehensive evaluation results of each factor set of line 1 and line 2 are as follows:

$\begin{array}{cc}{\mathrm{<span\; class="notranslate">\; B</span>}}_{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; line</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\left[\begin{array}{cccc}\mathrm{<span\; class="notranslate">\; 0.0948</span>}& \mathrm{<span\; class="notranslate">\; 0.2080</span>}& \mathrm{<span\; class="notranslate">\; 0.5907</span>}& \mathrm{<span\; class="notranslate">\; 0.1065</span>}\end{array}\right]& {\mathrm{<span\; class="notranslate">\; B</span>}}_{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; line</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\left[\begin{array}{cccc}\mathrm{<span\; class="notranslate">\; 0.1436</span>}& \mathrm{<span\; class="notranslate">\; 0.4925</span>}& \mathrm{<span\; class="notranslate">\; 0.2211</span>}& \mathrm{<span\; class="notranslate">\; 0.1428</span>}\end{array}\right]\\ {\mathrm{<span\; class="notranslate">\; B</span>}}_{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}^{\mathrm{<span\; class="notranslate">\; line</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\left[\begin{array}{cccc}\mathrm{<span\; class="notranslate">\; 0.2260</span>}& \mathrm{<span\; class="notranslate">\; 0.5314</span>}& \mathrm{<span\; class="notranslate">\; 0.2122</span>}& \mathrm{<span\; class="notranslate">\; 0.0304</span>}\end{array}\right]& {\mathrm{<span\; class="notranslate">\; B</span>}}_{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}^{\mathrm{<span\; class="notranslate">\; line</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\left[\begin{array}{cccc}\mathrm{<span\; class="notranslate">\; 0.4640</span>}& \mathrm{<span\; class="notranslate">\; 0.2682</span>}& \mathrm{<span\; class="notranslate">\; 0.2009</span>}& \mathrm{<span\; class="notranslate">\; 0.0669</span>}\end{array}\right]\\ {\mathrm{<span\; class="notranslate">\; B</span>}}_{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; line</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\left[\begin{array}{cccc}\mathrm{<span\; class="notranslate">\; 0.1333</span>}& \mathrm{<span\; class="notranslate">\; 0.4662</span>}& \mathrm{<span\; class="notranslate">\; 0.2471</span>}& \mathrm{<span\; class="notranslate">\; 0.1534</span>}\end{array}\right]& {\mathrm{<span\; class="notranslate">\; B</span>}}_{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; line</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\left[\begin{array}{cccc}\mathrm{<span\; class="notranslate">\; 0.5035</span>}& \mathrm{<span\; class="notranslate">\; 0.2664</span>}& \mathrm{<span\; class="notranslate">\; 0.1524</span>}& \mathrm{<span\; class="notranslate">\; 0.0777</span>}\end{array}\right]\\ {\mathrm{<span\; class="notranslate">\; B</span>}}_{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}^{\mathrm{<span\; class="notranslate">\; line</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\left[\begin{array}{cccc}\mathrm{<span\; class="notranslate">\; 0.1508</span>}& \mathrm{<span\; class="notranslate">\; 0.2358</span>}& \mathrm{<span\; class="notranslate">\; 0.5142</span>}& \mathrm{<span\; class="notranslate">\; 0.0992</span>}\end{array}\right]& {\mathrm{<span\; class="notranslate">\; B</span>}}_{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}^{\mathrm{<span\; class="notranslate">\; line</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\left[\begin{array}{cccc}\mathrm{<span\; class="notranslate">\; 0.1662</span>}& \mathrm{<span\; class="notranslate">\; 0.5098</span>}& \mathrm{<span\; class="notranslate">\; 0.2248</span>}& \mathrm{<span\; class="notranslate">\; 0.0992</span>}\end{array}\right]\end{array}$

The evaluation results of E ₁ , E ₂ , H ₁ , and H ₂ of line 1 and line 2 are general, good, good, and general, that is, S _line1 = {3,2,2,3} and good, good, good, Still good, that is, S _line2 ={2,1,1,2}.

After the training output and interpolation operation of the failure rate prediction model, the failure rate curves of the three types of faults of line 1 and line 2 are obtained, as shown in Figure 2a~c. According to the error calculation of the checking result, the error ε of the failure rate is 7.5%.

Referring to the relevant historical data of local power companies, the cost of transmission lines and the range of related economic parameters are shown in Table 2.

Table 2 Costs of transmission lines and ranges of related economic parameters

Costs and related economic parameters Range Operating cost _OC (10,000 yuan/year·100 kilometers) [13,16] Sum of the average maintenance and failure costs of general failures (10,000 yuan/time) [10,12] The sum of the average maintenance and failure costs of major failures (10,000 yuan/time) [121,128] The sum of the average maintenance and failure costs of serious failures (10,000 yuan/time) [406,419] social discount rate _r [0.055,0.06] Labor material cost growth rate _R [0.053,0.058] Abandoned cost percentage _p [0.35,0.4]

From the data in Table 2, the upper and lower limits of the annual average cost of Line 1 and Line 2 with different operating years are calculated and drawn as curves, as shown in Figure 3a-b.

In Figure 3a-b, the economic life of line 1 and line 2 under high failure rate and high operation and maintenance failure cost is 27 years and 30 years, and the economic life of line 1 and line 2 is 29 years and 32 years under low failure rate and low operation and maintenance failure cost , that is, the optimal economic life intervals of Line 1 and Line 2 are 27-29 years and 30-32 years, respectively. This shows that the operating environment and quality conditions of different transmission lines are different, and the optimal economic life span will change.

Claims (7)

1. A method for evaluating the best economic life interval of overhead transmission lines, characterized in that, First, according to the historical statistical data, sort out and classify the evaluation indicators of the external operating environment and the quality status of the transmission line, and use the fuzzy comprehensive evaluation method and the analytic hierarchy process to calculate the membership degree and weight of each indicator; Then, according to the severity of the fault consequences, the faults are divided into three types: general faults, major faults, and serious faults. The least squares support vector machine is used to analyze the data of the transmission line's service age, external operating environment, and its own quality status. The three failure rates of the transmission line are respectively trained and output and error calculated to obtain the failure rate prediction model of the transmission line; Finally, the interval analysis method is introduced into the life cycle cost theory, the fault cost and maintenance cost are calculated from the fault rate interval of the line to be evaluated, and each cost index is intervalized, and the optimal decommissioning of the transmission line is solved with the goal of minimizing the annual average cost Time range, eliminate the deviation of a single constant value, and finally get the best economic life interval of the transmission line. 2. The method for assessing the optimal economic life span of overhead transmission lines according to claim 1, characterized in that it adopts the following specific steps: Step 1), the establishment of the external operating environment of the transmission line and its own quality assessment factor set, index set and comment set, Divide the factor set and each lower-level index into 4 comment levels, that is, the comment set is V={v ₁ ,v ₂ ,v ₃ ,v ₄ }={good, fair, average, bad}; Step 2), the calculation of the membership degree and weight of the external operating environment of the transmission line and its own quality assessment index, The calculation of the index membership degree is as follows: by making an evaluation table for each expert, the membership degree of each index is calculated according to the evaluation of the experts. The calculation formula of the index membership degree r _ij is as follows: ${\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; ij</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; ij</span>}}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; total</span>}}}<span\; class="notranslate">\; ,</span>$ In the formula, P _ij represents the number of experts who believe that the index i in the factor set belongs to the comment v _j , P _total represents the total number of experts participating in the evaluation, i=1, 2,..., u, u is the number of indicators in the factor set, j =1-4, after obtaining the membership degree of the index set, the fuzzy membership degree matrix R of the factor set can be obtained; The determination of the index weight adopts the "9 division method" in the analytic hierarchy process. After the expert sorting and calculation, the weight vector W of each index of the factor set can be obtained; Step 3), the comprehensive evaluation and scoring of the external operating environment and its own quality status, the calculation formula of the fuzzy comprehensive evaluation vector B is as follows: B=WoR In the formula, R is the fuzzy membership degree matrix of the factor set, W is the weight vector of each index of the factor set, "o" is an operator, which represents the synthesis operation, and the M(·,+) operator is used, that is ${\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; u</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; ij</span>}}$ In the formula, b _j is the membership degree of the factor set to the comment v _j , w _i is the weight of the index i in the factor set, r _ij is the index membership degree; After calculating the fuzzy comprehensive evaluation vector of the factor set, according to the principle of maximum membership degree, the comprehensive evaluation result of the factor set is the comment v _j corresponding to the maximum membership degree; assuming that the rating set corresponding to the comment set is That is, the corresponding comment level corresponds to the corresponding score, and the comprehensive evaluation result is that the factor set score of comment v _j is Step 4), sample line historical data training and error analysis: Score the stage service age T and operating environment and quality status rating The same transmission line is defined as the same type of line, and the historical data of the same type of line during the phase service age T is analyzed, and the three types of failure rates are counted as a sample. The formula for calculating the annual failure rate λ of the service age of similar lines is as follows, the unit is times/year · 100 kilometers, $\mathrm{\&lambda;}=\frac{{\mathrm{\&Sigma;}}_{5\mathrm{years}}{Q}^{(T,S_{{\mathrm{E.}}_1},S_{{\mathrm{E.}}_2},S_{h_1},S_{h_2})}}{5\&times;\mathrm{\&Sigma;}{l}^{(T,S_{{\mathrm{E.}}_1},S_{{\mathrm{E.}}_2},S_{h_1},S_{h_2})}},$ In the formula, It is the total number of faults of the same type of line faults within 5 years, and the general faults, major faults and serious faults are counted separately. is the sum of the lengths of similar lines at the end of 5 years; In the transmission line failure rate prediction model, the sample line data is the line basic information vector x _m = (x _m1 , x _m2 , x _m3 , x _m4 , x _m5 ) and the actual line failure rate vector λ _m = (λ _m1 , λ _m2 , λ _m3 ), where, m=1, 2,..., M+N, M+N is the number of samples; x _m1 , x _m2 , x _m3 , x _m4 , x _m5 represent the service age T and factor set score λ _m1 , λ _m2 , and λ _m3 are the failure rates of general faults, major faults, and serious faults of the sample line respectively; M groups of samples are used for training, and N groups of samples are used for checking calculation. The error calculation formula is as follows: $\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\frac{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; re</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; pre</span>}}<span\; class="notranslate">\; |</span>}{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; re</span>}}}$ In the formula, is the actual statistical value of the sample line failure rate used for checking calculation, is the predicted value of the sample line failure rate used for checking calculation, N is the number of samples used for checking calculation, and ε is the average value of error; Step 5), the interval prediction of the failure rate of the line to be evaluated: When predicting the failure rate of the line to be evaluated, the score of the line's operating environment factor set and Judgment is based on the environmental status of the line corridor over the years after it is put into operation, and the quality status factor set is scored and Evaluate according to the line's operation and maintenance records and status assessment results over the years; Step 6), line life cycle cost analysis: When the transmission line is decommissioned in year L, its annual average cost is as follows: ${\mathrm{<span\; class="notranslate">\; NF</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; IC</span>}<span\; class="notranslate">\; +</span>\underset{\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; L</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; OC</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; MC</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; FC</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; )</span>{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; R</span>}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; DC</span>}{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; R</span>}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1,2</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; L</span>}$ In the formula, L is the number of years of transmission line operation, NF _L is the annual average cost of transmission line operation for L years, IC is the initial input cost, r is the social discount rate, waste cost DC is income-type cost, and R is the increase in labor and material costs OC _t , MC _t , FC _t are the operation cost, maintenance cost and failure cost of the transmission line in year t, respectively; Step 7), route cost interval calculation: After the line is completed and put into operation, the one-time input cost IC is fixed, and the operating cost OC is determined in the operation plan, and the annual expenditure fluctuates within a range; after the line is decommissioned, the calculation formula for the abandonment cost is as follows: DC=p×IC In the formula, p is the percentage interval of the discarded cost; After obtaining various cost intervals, the optimal economic life interval of the transmission line can be obtained by finding the range of operating years when the annual average cost NF _L is the smallest. 3. The method for assessing the optimal economic life interval of overhead transmission lines according to claim 2, characterized in that in step 5), assuming that the transmission line can run up to the stage service age T _max at the longest, the stage service life of the line to be evaluated is Ages are substituted in order from "1" to "T _max ", and the annual failure rates of the three types of service ages at each stage of the line are calculated; then, the annual failure rate of the stage service age is transformed into the actual service age annual failure rate, and the conversion process is as follows : Take the average value of the upper and lower limit years of service life of the transmission line at each stage, and set the annual failure rate of the service age of the stage as the annual failure rate of the line operation for 3 years, 8 years, ..., 5T _max -2 years, using cubic splines Interpolate to calculate the annual failure rate of the transmission line for 1-5T _max years of operation; finally, the failure rate is intervalized according to the error ε, and the failure rate range of the three types of faults is calculated. The formula for the intervalization of the failure rate is as follows: $<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}^{\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}^{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; [</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; ]</span>$ are the lower limit and upper limit of the line failure rate in the t-th year, respectively, and _λt is the predicted value of the line failure rate in the t-th year after interpolation. 4. The method for assessing the optimal economic life interval of overhead transmission lines according to claim 3, characterized in that, in step 6), the required maintenance cost MC _t and failure cost FC _t of the transmission line in year t are related to the failure rate ,Calculated as follows: ${\mathrm{<span\; class="notranslate">\; MC</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; l</span>}$ ${\mathrm{<span\; class="notranslate">\; FC</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; l</span>}$ The subscript k=1, 2, and 3 represent general faults, major faults, and severe faults respectively, λ _k (t) is the failure rate of the line, l is the length of the transmission line, and M _k is the average component replacement cost for each fault of the transmission line and labor maintenance costs, F _k is the average comprehensive loss caused by transmission line faults. 5. The method for assessing the optimal economic life interval of overhead transmission lines according to claim 4, characterized in that, in step 6), social discount rate r, maintenance cost M _k , failure cost F _k , artificial material cost growth rate R All are represented by interval numbers. 6. The method for evaluating the optimal economic life interval of overhead transmission lines according to claim 1, characterized in that, in step 4), when performing training calculations on the failure rate of transmission lines, transmission line data of the same voltage level are used. 7. The method for assessing the optimal economic life interval of overhead transmission lines according to claim 1, characterized in that, in step 4), the service age statistics are carried out based on the year and month of the initial investment of the line, and the statistics are calculated in units of 5 years Stage service age T, assuming that a line has been put into operation for Z years, its stage service age is in is the upper integer symbol.