Analysis Of The Response Of Iced Transmission Lines Due To Wind And Ice Shedding

Transmission lines，as the lifeline project，are always exposed outside andseriously affected by weather loads. From times of studies of ice disasters, it’s foundthat ice shedding and wind are the two important factors leading to the whole linesfailure. Therefore, the study of dynamic behaviors of transmission lines under windand ice shedding is very meaningful.In this thesis，numerical experiment was adopted to analyze the effects of windspeed, initial wind angle, elevation difference and ice thickness on longitudinalunbalance tension of transmission tower. Harmony-superposition method was used tosimulate fluctuating wind speed time series acting on transmission tower line and thelaw of unbalance tension was derived through changing elevation difference and icethickness. Through numerical simulating method, the dynamic response of theconductor system after ice shedding was studied with various rate of ice shedding, icethickness, span number of the system. The following conclusions were drawn throughanalyzing the results obtained from the experiments:(1) Under the same wind speed, the greater ice thickness, the higher ra te oflongitudinal unbalance tension growth of transmission tower with the increasingelevation difference. Under the same wind speed, the greater ice thickness, the higherrate of growth of the average displacement growth of the tower’s top with theincreasing elevation difference. Under the same elevation difference, longitudinalunbalance tension growth of transmission tower under wind grows increasingly withthe increasing ice thickness. When elevation difference is in sequence of30m,60m,90m, unbalance tension growth of transmission tower under wind grows increasinglywith the increasing ice thickness. The results show that, in some cases, the value oflongitudinal unbalance tension of tower in existing electricity industry standard issmall.(2) The thesis proposed the formula of longitudinal unbalance tension oftransmission tower under wind by statistical analysis. This formula is applicable tothe transmission line whose tower style is5B-ZBC1under the maximum wind speedof30m/s. The errors of the formula are within±6%compared to numericalsimulation and can provide references for related design.(3) By comparing the ice shedding induced dynamic response of all conductor systems, it is found that the differences between the response of3-span system andthose of5-span and7-span are large, while the jump height derived from5-spansystem is basically identical with that from7-span system. Thus modeling5-spansystem to study jump height is reasonable. The maximum unbalance tensions underdifferent ice shedding rates have deviations to different degrees, indicating thatmodeling7-span system to study the maximum unbalance tension is reasonable.(4) By comparing the ice shedding induced dynamic response of all conductorsystems, it is found that the maximum jump height of the system under no wind is thegreatest among those under various load cases, and the maximum jump height of thesystem decreases with the increasing wind speed. The maximum unbalance tension ofthe system grows with the increasing wind speed, and the minimum occurs when thereis no wind. At the same time, by using the finite element method to simulatetransmission wire models under various loads conditions, the curve and time historycurve of the tension of wire, jump height and the longitudinal unbalance tension.vs.ice thickness, ice-shedding rate, wind speed was drawn. The influence of variousfactors on target physical variables then were analyzed.