Study On The Simulation Experiment Method Of Ice Accretion On Transmission Line Without Torsion

Icing on transmission line seriouly affects the security and stability of power grid.Due to a fact that icing on transmission line is a scientific problem which refers to multidisciplines and multi-specialties,the icing mechanism of conductor is particularly complex.Relevant and basic research is lacked.As icing parameters change,shapes of ice-covered conductor differ from each other.Based on the physical icing process of conductor,the research on numerical simulation method of ice accrection on transmission line and establishing a visual simulation software platform,which can reduce a lot of manpower,material and financial resources for natural icing observation.Therefore,the research in this paper has great academic significance and engineering application value for icing on transmisison line and its disaster prevention.The main work of this thesis,which is shown as follows.(1)Based on the conditions of natural ice formation,ice thickness and ice-shape change in the natural icing process,which have been analyzed.Based on the physical icing process of the conductor,the calculation method for airflow of ice-covered conductor is proposed by using boundary element method and boundary layer theory.The effects of three typical boundary discrete methods on the accuracy and calculation time of airflow velocity distributions are discussed and analyzed.Considering the calculation precision and time,The results show that using constant element as boundary division is optimal.(2)Using Lagrange method to simulate the process of water droplets hitting the wire.When the accuracy is ensured,the selection of time step in the trajectory calculation is optimized.Based on the cross product,an mathematical expression,which is used for judging whether there is collision between the water droplets and the irregular surface boundary of the ice-covered conductor,is proposed.According to the characteristics of Langmiur D distribution,single size droplets are transformed to obtain a variety of droplets with different sizes and used for calculation.The result shows that the local collision coefficient under the condition of multi-size droplets is in good agreement with the experimental values.(3)Considering the effect of ice roughness on the convective heat-transfer coefficient,a certain degree of improvement was made in the thermodynamic model in freezing process on conductor surface.The results show that the maximum value of the local convective heat transfer coefficient appears on both sides of the stationary point,while the stationary point corresponds to the minimum value.Besides,the distribution characteristics of local collision coefficients and local freezing coefficient on conductor surface are also discussed.(4)The mathematical model of boundary dynamic change is proposed.By the dichotomy of the algorithm,the limit point,where the droplet just cannot collide the conductor surface,could be found.Accordingly,the collision region can be determined.Based on the boundary function under the Nth observation time,boundary function expression under the N+1 observation time also can be obtained.On the basis of this boundary function expression,terminal condition of boundary can be updated and used for iteration in the following airflow calculation.(5)Considering the precision and efficiency of numerical calculation,the value of the time step should be adjusted based on the actual icing degree and ice growth rate.The adaptive time step methods were proposed.When the icing degree is increased by about 3.4%,it can be considered as an iterative calculation and the time step is determined by the growth rate of icing under this condition.The ambient temperature,wind speed,median volume diameter(MVD)and liquid water content(LWC)directly affect the ice type and ice shape,which has been discussed.(6)The accuracy of numerical simulation method for icing on conductor has been verified by artificial icing test and natural icing test.For the constant airflow field,the environment parameters remain unchanged,the numerical results highly coincide with the artificial icing experimental results.For non-constant airflow field,the environmental parameters change all the time,the ice shape in short-term is still in good agreement with the numerical calculation results.(7)Based on the programming lauguage,visual simulation software platform for icing on conductor has been independently developed.By setting the parameters of icing environment and conductor structure,the software will automatically carry out numerical calculation without manual intervention.During the operation,the ice mass,the maximum icing thickness and the corresponding shape of ice-covered conductor will be automatically presented in the software interface.At the same time,this data can also be exported for back-end data reuse as needed.