Research On Anti-icing Critical Current Of Power Grid Based On Dimension Analysis

Ice accretion makes a threat to the safety operation of the power network, affects the safety transportation of electric power, and harasses the daily life of resident people. China is among those countries who suffer the most severe ice damage of overhead lines, which costs enormous financial losses in power system due to the frequent occurrence of icing events. With the construction of the west-east electricity transmission project and extra-high tension transmission lines, a gradually bigger power grid network is founded in China, which adds the possibility of power lines crossing the severe environments, and raises the probability of power lines undergoing the icing events. Together with the gradually more severe global atmosphere condition, the outcomes of ice accretion in overhead lines become worse as well. All of these make the resolution of ice accretion problems in overhead lines an issue with important engineering significance.The influence factors and formation conditions of transmission power lines, couple with the impacts of ice accretion in aircrafts, railway contact line system and transmission lines are introduced in this dissertation. Then, the characteristics of ice accretion in transmission lines, the ice accretion online monitoring and current main de-icing methods deployed over the world are introduced. A review of in-field anti-icing technologies and deficiencies of current research works are presented, the models of critical anti-icing current put forward by specialists and scholars domestically and overseas are introduced, with the brief description of several classical criterion formulas and experimental correlations of convection heat transfer, and on this basis the main contents of this dissertation are presented,In the basis of dimensional analysis modeling theory, the dimensional method is used in the first time, to put forward a series of 5 dimensionless attributions in this dissertation. This is based on the comprehensive analysis of the influence factors to the critical anti-icing current, and by using the method of Pi theorem, specifically, these dimensionless attributions is the combination of meteorological parameters (i.e. air temperature, wind velocity, the LWC and MVD in air, etc.) and conductor parameters. The dimensionless attributions related to the critical anti-icing current are put forward in the further deduction, and the physical significance of each attribution is analyzed.The experiments of ice wind tunnel are introduced, the heat balance equation of the ice accretion critical state in the overhead lines is applied to deduce the calculation model of convective heat transfer coefficient. The numerical values of the coefficient in specific condition are obtained according to the experiment data. Then, the correlation formula between the Nusselt number and the corresponding Reynolds number are fitted using data analysis software. And the difference and relation between this correlation formula and other classical ones are analyzed.And on this basis the variation of each dimensionless attribution is discussed according to the experiment data. The mathematical model of critical anti-icing current is put forward by applying the method of principal component analysis, polynomial fitting and product-of-exponential fitting to the dimensionless attributions, respectively. Then, the relative error and average relative error are calculated and the comparison between the mathematical model and heat balance equation model are made, which confirms the accuracy of the experiment data. The analysis results indicate that it is feasible to study critical anti-icing current by the means of dimensional analysis modeling and product-of-exponential fitting.The dimensional analysis model of critical anti-icing current which is putting forward in this dissertation is the first usage in the domestic field. And the critical current criterion formula provides a theoretical support to the network critical anti-icing process, and therefore should be used in engineering applications.