| GIL is widely used in power system due to its advantages of large transmission capacity,small footprint,low maintenance cost and high operation stability.With the increase of GIL usage,the development direction of GIL is to be compact,lightweight,reduce greenhouse effect and improve economic benefit under the condition of ensuring insulation level.Therefore,a complete GIL model is established and based on that,this thesis carries out a research on GIL multi-objective optimization.The main research contents are as follows:(1)Based on the breakdown criterion of mixed gas,an evaluation model of the internal insulation level in the GIL is established including basin insulators,post insulators and shield case.The calculation results of electric field,temperature field and flow field are analyzed and the weak point of insulation is also analyzed.(2)The influence of reliability growth model and maintenance strategy on GIL life cycle cost model is analyzed.The GIL life cycle cost model is improved and the GIL carbon emission cost model is proposed.On this basis,a comprehensive economic model of GIL is established.(3)According to the experimental design and random forest algorithm,the dimension reduction of GIL structural parameters is completed and the structural parameters which have great influence on electric field intensity and temperature rise are selected.Then,the constraint conditions of GIL multi-objective optimization are determined according to the design criteria of GIL,such as electric field strength and structural strength.(4)Based on the above research,GIL multi-objective optimization research can be divided into the following steps: GIL optimization objectives are determined and specific objective function expressions(surrogate model)are established.The NSGA-II algorithm is used for GIL multi-objective optimization,and the optimization scheme set is obtained.According to the improved TOPSIS comprehensive evaluation method,the final optimization scheme is obtained and verified.The main conclusions of the thesis are as follows:(1)In the GIL,the distribution of electric field intensity and temperature rise between the basin insulator and the post insulator shows obviously different trends.The maximum electric field intensity is 4.95 k V/mm,which appears at the shield case near the basin insulator,and the variation of electric field intensity on the concave surface of the basin insulator is very drastic.The temperature rise in the air chamber tends to be larger at the top and smaller at the bottom,and the maximum temperature rise can reach 45℃.The stress distribution at post insulators and basin insulators is uniform and the value is small,with the maximum value not exceeding 4.95 MPa.The distribution of breakdown criterion is similar to that of the mixed gas density.The lowest breakdown criterion appears directly above the conductor,with a value of18.2k V/mm.The minimum of the mixed gas density is located at the same position,with a minimum value of 9.1 kg/m3.(2)The calculation results of the economic comprehensive model show that the maintenance degree of GIL gradually deepens with the increase of GIL running time.According to the three-time maintenance plan set in this thesis,the maintenance time should be 14～15 years,25～16 years and 36～37 years.(3)The R2＿adjusted of polynomial response surface model and radial basis neural network model is above 0.9,indicating that the two models have better nonlinear data fitting accuracy.In the polynomial response surface model,the R2,R2＿adjusted and root mean squared error of E,Tm are 0.961,0.979,0.041 and 0.991,0.991,0.031,respectively,indicating that the polynomial response surface model fully meets the accuracy requirements of the surrogate model.(4)The final optimization results are obtained by using NSGA-II algorithm and TOPSIS comprehensive evaluation method based on fuzzy comprehensive weight.The results show that the maximum electric field intensity,maximum temperature rise,material cost and carbon emission cost in GIL decrease by 34.5%,19.0%,34.6% and17.8% respectively,while the minimum density and minimum breakdown margin increase by 2.75% and 6% respectively.The innovation points of the thesis are as follows:(1)The evaluation criteria for GIL internal insulation is proposed,and the complete GIL multi-physical field coupling model including basin insulators,post insulators,shield case and other components is established.The model is helpful for quantitative evaluation of GIL internal insulation,and lays a foundation for GIL multi-objective optimization.(2)A comprehensive GIL economic model is proposed,which includes life cycle cost model and carbon emission cost model.Moreover,GIL carbon emission cost model is an exploration of realizing "dual carbon" goal of electrical equipment.(3)For the research on the GIL multi-objective optimization,this thesis adopted the optimization method combining multi-objective optimization algorithm and comprehensive evaluation method.And the TOPSIS comprehensive evaluation method based on fuzzy comprehensive weight is proposed.This method could make full use of GIL multi-objective optimization data set information and target weight,which is helpful to find the optimal optimization result efficiently. |
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