Stability Of Iced Quad Bundled Conductor Considering Wake Effect

Under the action of ice and wind load,the low frequency and large amplitude selfexcited vibration are very easy to occur in the overhead transmission line.We call this self-excited vibration as transmission line galloping.The galloping of iced transmission lines will cause the wear of hardware,the damage of conductor,and even the collapse of transmission tower,which will cause the power transmission system to be paralyzed,which will bring inconvenience to people’s lives and cause huge economic losses.With the construction and operation of UHV transmission project in China,the study of the galloping stability of iced transmission lines provides guidance for the anti-galloping of transmission lines.In this paper,the influence of the wake of the upwind side conductor on the aerodynamic parameters of the conductor at the back wind side is considered,and the corresponding critical wind speed calculation method is proposed.Firstly,a three degree of freedom galloping model of iced quad bundle conductor is established based on quasistatic assumption,and the typical crescent shape is selected for the iced shape.In the wind field,considering the different aerodynamic coefficients of each sub conductor of quad bundle conductor due to the influence of wake effect,the whole aerodynamic equation of quad bundle conductor is listed.At the initial angle of attack,Taylor expansion is carried out for the whole aerodynamic coefficient.The dynamic equilibrium equation of three degrees of freedom of quad bundle conductor is established,and the aerodynamic damping matrix of transmission line system is derived.According to the Routh Hurwitz criterion,the formula for the stability of the three degree of freedom and quad bundle conductor is derived.The judgment formula shows that the criterion of the transmission line galloping is a complex mechanism,and the galloping of the transmission line is related to the external conditions and the physical parameters of the conductor itself.In order to simulate the weather conditions encountered in the actual project,the aerodynamic coefficients of the iced quad bundle conductor under different wind speed,different ice thickness,different ice shape and different wind attack angle are tested.The influence of wind speed and ice type on the aerodynamic coefficient of the conductor is analyzed.The results show that the wind speed has little influence on the aerodynamic coefficient of transmission lines.The ice thickness has a great influence on the aerodynamic coefficient of transmission lines,and the aerodynamic coefficient increases with the increase of the ice thickness.The aerodynamic parameters of crescent and sector ice are significantly different.The experimental results provide reference for the analysis of the galloping characteristics of transmission lines and provide the original data for judging the stable state of transmission line galloping.According to the formula of the iced quad bundle conductor galloping,the paper uses MATLAB software to write the cycle calculation program and brings in the aerodynamic coefficient corresponding to wind tunnel test under different working conditions and the physical parameters of the quad bundle conductor and calculates the critical wind speed of the quad bundle conductor starting to gallop.The three degree of freedom stability criterion established in this paper is compared with the traditional Den Hartog and Nigol stability criteria.The results show that the critical wind speed increases first and then decrease with the increase of the ratio of in-plane to out of plane frequency.With the decrease of the torsional frequency of the conductor,the critical wind speed of the conductor galloping decreases.With the increase of ice thickness,the critical wind speed of conductor galloping decreases.In the design,we should consider the most likely to galloping,as the standard of transmission line anti-galloping design.The research methods and experimental data provide a reference for the study of the galloping characteristics of iced transmission lines.The research results have important theoretical guidance significance for the stability judgment of iced quad bundle transmission lines.