| Icing has an important i MPact on the safe operation of the line.In the southern region of China,serious electricity grid accidents have been caused by icing for many times,including ice flashes,line breaks and tower collapse.Transmission lines have the characteristics of harsh service environment and long service time.The strength of transmission line will gradually deteriorate under the erosion of environmental loads over a long period of time.In view of this,this paper investigates the dynamic system reliability of transmission lines under short-time icing load and the time-varying system reliability of transmission lines under icing load when considering long-time fretting wear,so as to analyze the service safety of transmission lines.In this paper,the Makkonen icing model and its parameters are analyzed,and the analytical calculation method and finite element calculation method of transmission line tension are derived,the influencing factors of lineshape and tension of transmission line are analyzed from both environmental factors and line parameters.The results show that icing has an important influence on lineshape and tension of transmission line.In this paper,the theories related to the stochastic reliability and the transmission line dynamic system reliability are analyzed,the response surface method and Laplace asymptotic integration method for the stochastic reliability calculation are derived,the Laplace asymptotic second order moment method based on the response surface to analyze the transmission line icing dynamic system reliability is proposed.Some of the factors influencing the icing dynamic system reliability of the transmission line are analyzed in combination with the Makkonen icing model.The results show that wind speed has a large influence on the reliability of transmission line among the environmental loads;the service safety of the transmission line can be improved by reasonable selection of transmission line diameters.In this paper,a finite element model of the transmission tower line system with one tower and two lines in a transmission line in central China is established,and the dynamic characteristics of the tower line system are analyzed;the reliability calculation method of the transmission tower under external loading is proposed,and the reliability analysis of the transmission tower under displacement failure mode is carried out using the equal probability normal transformation method.The method of calculating the stress of the continuous transmission lines is derived,and the method of calculating the reliability of the transmission lines with the tandem structure system is proposed,and the icing dynamic system reliability of the above-mentioned line is analyzed.The results show that the transmission tower has reached the Class III damage standard of ductile damage under the combined effect of wind load and icing load.In this paper,the theory related to transmission lines breeze vibration is analyzed,the influencing factors of breeze vibration based on the analytical model are studied,a transmission line strength degradation model considering fretting wear is proposed,the time-varying system reliability of isolated transmission lines and continuous transmission lines under the action of icing load after considering fretting wear are calculated.The results show that the reliability of the line decreases significantly after considering the fretting wear;the reliability index calculated for the continuous transmission lines is on the safe side,and the calculation theory is more in line with the design requirements of the line. |
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