Numerical Simulation And Dynamic Response Of Ice-Accreting And Ice-Shedding On Transmission Lines

Overhead transmission line is a lifeline project used to transport, regulate and distribute electric power. External loads acting on transmission lines include wind load, seismic load, temperature load and uneven settlement of the foundation. Previous ice hazard investigations show that, ice load is one of the greatest threaten to transmission lines. Therefore, the study of loads induced by ice accreting and ice shedding on transmission lines is of great significance.On the basis of an existing transmission line, a three dimensional finite element model of tower-line system is built. At first, three finite element methods, namely adjunctive ice element method, density changing method and additional force method are employed to simulate ice accreting and ice shedding on transmission lines. Using the same case, the results obtained by using these three methods are compared. Based on the comparison, appropriate values of parameters used in different methods are suggested. Then, the influence of different parameters, such as element number per span, span number and tower stiffness, is determined to establish the appropriate finite element model of tower-line system. Moreover, time domain analysis is carried out to calculate the response of shield wires and conductors due to ice shedding. Finally, the method to calculate the dynamic amplification factors of the unbalanced force is proposed and the formula to calculate jump height due to ice shedding is fitted.Results from this study show that, he elastic modulus of ice should be less than 107Pa when using adjunctive ice element method. And the number of simulating forces should be more than 20 per span when using additional force method. The element number per span is an important factor in accurately simulating the transmission-line system. As for the response of transmission lines due to ice shedding, the vibration modes of shield wires and conductors are quite different. However, in both cases the jump height of transmission line due to ice shedding is proportional to the sag of the line. Based on the transient analysis, the dynamic amplification factors of unbalanced force acting on the tower due to ice shedding of the line are carried out. The dynamic amplification factor is about 1.5-2.0 when ice sheds from shield wires and about 1.1-1.5 when ice sheds from conductors. When considering the ice-shedding problem from bundled conductors, the method to combine the bundlend conductors to an equivalent single conductor is developed. The equivalent diameter of conductor and ice thickness is both (?) times to that of bundled conductors.