The Reliability Modeling And Assessment Of Transmission Lines Considering The Wind And Rain Load And Fretting

This paper is supported by Natural Science Foundation of China(The probabilisticrisk assessment and Optimal allocation model research of Flexible AC transmissionsystems50977094) and Natural Science Foundation of Chongqing(Power SystemReliability Assessment Model research considering flexible generation and transmissionequipment,CSTC,2011BB6047).The strength degradation is mainly caused by corrosion and fretting fatigue for thetransmission lines exposing in the atmosphere, and the fretting between steel wirestrands of transmission line caused by wind loads is much more obvious.The long-termfretting fatigue will depress the structural strength of lines and cause steel wire strand、lines broken,and the impact of strong wind and rain loads exacerbated broken risk.Inrecent years,there are a mass of broken tower and lines accident caused by strong windand rain during the typhoon, which causes severe economic losses.Therefore, it isnecessary to study reliability model and reliability assessment of transmission line andpower system under the condition of wind and rain and long-term fretting.There are fretting between steel wire strands of transmission line, long-termfretting fatigue will depress the structural strength and affect the reliability level oftransmission lines.Three factors that influence frettingfatigue is identified and solved.The three factors are fretting frequency, fretting amplitude andcontact stress betweensteel wire strands. Fretting frequency and amplitude are identified through the vibrationcharacteristics of the transmission lines;the finite element model of the transmission lineis established using finite element software and the contact stress is solved throughsimulation analysis. The function which the fretting depth of steel wire strands changesversus time is fitted using theoretical models of fretting and three factors, then thetime-varying function of structural strength is solved. Combined with structuralreliability theory,the time-dependent failure probability modelof transmission lines isestablished considering fretting,which can provide more accuratebasic data forreliability assessment for power system planning guidance. The example shows: thefailure probability of lines increase with running time.The transmission lines exposing in atmosphere are vulnerable to the influence ofvarious meteorological disasters.For example, the typhoon brought strong winds andheavy rainfall is quite a serious impact on the line, which usually cause lines and tower broken. In this paper, the wind loads model is solved according to the design standardsof transmission lines, the rain loads model is solved according to the raindrops modeland conservation of energy. Combined with structural reliability theory, thetime-dependent failure probability modelof transmission lines is established under theimpact of strong wind and rain. The example shows: the heavy rainfall not only triggersgeological disasters and affect the safety of the tower foundation, but also has someimpact for linesstructural strength.The influence of fretting to lines structural reliabilityis long-term accumulation,and the influence strong wind and rain to lines structural reliability is short-term impact.In this paper, the time-dependent reliability model of transmission lines with long-termfretting is established and the power system reliability is assessed under the impact ofstrong wind and rain. The example shows: the fretting is sensitive to the lines reliabilityunder the impact of strong wind and rain; rain loadscannot be ignored under thecombined effect of wind and rain loads.