| In the power system,long-distance transmission lines usually span geographical areas that have different environmental conditions,and the environmental conditions of different seasons in the same geographical area also have considerable change.However,the variation of environmental conditions will lead to changes in the size of the current and resistance of the overhead transmission line.If the influence of ambient factors is ignored,the calculation results will introduce a large error.Based on this,this paper has researched the analysis method of transmission capacity of power grid affected by ambient factors,and the main research contents are as follows:(1)This paper proposes an effective analysis model and algorithm for the impact of meteorological and geographic factors on the power transmission characteristics of the power grid.Firstly,combining the heat balance equation of the transmission line with the conventional power flow equation,this paper presents an electro-thermal coupled unified power flow model and its solution algorithm considering environmental factors,in which meteorological and geographic information around overhead transmission lines is introduced into power flow calculations as variables and the extended Jacobian matrix and the Newton iterative format are derived.Secondly,the influence degree of the difference of wind speed,altitude and ambient temperature on line temperature,resistance,active power and reactive power loss is comparatively analyzed.The case studies show that environmental factors affect the electrothermal balance of overhead conductors and change the resistance of the line,which has a significant impact on the power flow distribution,active and reactive power losses.Relying on the temperature data of 14 locations in Xinjiang,the Pearson correlation coefficient is used to measure the temporal and spatial correlation characteristics of the daily average temperature of different locations,and the changes and differences of the power transmission characteristics of the power grid in different seasons are analyzed.(2)Although the traditional static voltage stability analysis model can quickly judge the stability of the system node voltage,its mathematical model only considers the electrical model of the line,and ignores the electric and thermal coupling relationship of the line in the actual situation.Therefore,the calculation results of the traditional model have a large deviation as the reference of the actual voltage stability judgment.Against this background,based on the research content of improving the Jacobian matrix in the power flow model,a V-Q sensitivity analysis method and a modal analysis method considering environmental factors are proposed to evaluate the static voltage stability situation of the power grid.Finally,an improved IEEE 14node test system is tested and analyzed to verify the effectiveness and feasibility of the proposed method.(3)The available transfer capacity(ATC)of the power grid is an important measure to evaluate the security and stability margin of the power grid.If the calculation results of ATC without considering the maximum allowable operating temperature of the line and the impact of environmental factors are taken as a reference for grid dispatching operation.The important power transmission channel may have a permanent fault due to high temperature.Against this background,this chapter introduces the dynamic electrothermal coupling equation of the transmission line into the traditional optimal power flow model,takes the line temperature as the state variable and the maximum load in the receiving area as the objective function,and constructs the optimal power flow model suitable for the calculation of transmission capacity.Then,the proposed model is decomposed into several different subproblems and a parallel computing program is designed by using the optimality condition decomposition method.Finally,based on the environmental data of different locations and different typical days in China,the improved IEEE6-bus test system is simulated and tested.The calculation results show that the ATC time evaluation curve of the power grid has significant temporal and spatial differences.Considering the temporal and spatial differences of environmental factors can effectively improve the accuracy of the calculation of ATC. |
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