Numerical Simulation Of Ice-accreting And Ice-shedding On Transmission Tower-line System

Transmission line system is the lifeline project used to transport the high-voltage electric power. Similar as strong wind load, ice load can make serious damages to the transmission line. Uneven ice-accreting and ice-shedding on transmission lines will result in the longitudinal unbalanced forces on the adjacent transmission towers, which significantly threatens the safety of transmission lines.Take a transmission line for example which was damaged in an ice storm, a three dimensional finite element model of tower-line system is constructed to simulate towers, insulators and cables by beam element, truss element and tension-only truss element, respectively. Pipe element is employed to simulate the accreted ice of transmission line. Ice-shedding is achieved through specifying element's birth and death capability. And the methodology of ice-shedding simulation on transmission lines is validated by comparing the simulation results with those obtained from the model-scale experiments done by previous researchers. Then the sensitivity study on model parameters is performed to determine the appropriate analytical model.With the developed finite element methodology, the phenomena of ice shedding from conductors and shield wires are simulated. Results from this study show that ice-shedding causes low-frequency vibration of the conductors and large-amplitude oscillation of the isolators. Many members of the tower experience high peak impact stresses. At the same time, ice-shedding causes a significant increase of the base shears and base moments of the transmission tower. The impacting effects of the transmission tower-line system due to ice-shedding may increase with the decreasing distance between the tower and ice-shedding span. The parametric study of ice shedding on conductors is carried out. The responses induced by ice-shedding will decrease when the initial stress on conductors is larger and will increase when the length of span, the amount of accreting ice and the ratio of ice-shedding is larger, or the location of ice-shedding is nearer to the middle of span. Ice-shedding on transmission line system considering unzipping effect is studied in which the influences of the velocity of ice-shedding on the responses are investigated. During the analysis of ice-shedding considering unzipping effect, if the velocity of ice-shedding is slower, the responses are much closer to those resulting from the static unloading. And if the velocity of ice-shedding is faster, the responses are much closer to those resulting from the simultaneous ice-shedding.Ice-accreting and ice-shedding on spans with angled transmission line and continuously inclined spans are investigated. Results show that if the angle is larger, the transmission tower undertakes larger forces. The effects of the length of insulators on the dynamic response of tower-line system is also investigated. Results show that under the effects of ice shedding from conductors, the jump height and the axial force of ice-shedding conductors will increase and the unbalanced forces between adjacent spans will decrease when the insulators are longer. Under the effects of earthquake, the peak value of axial forces in the insulators and base reactions on the transmission towers will increase when the insulators are longer.