| Galloping of iced power transmission lines is a type of low frequency and large amplitude nonlinear vibration excited by natural wind. Galloping is one of the major disaster for high voltage power transmission lines, which will induce various mechanical and electrical failures to the overhead power transmission lines. The computation and governing of the galloping are still an unsolved complex engineering problems covering many engineering fields and there is no any mature analytical method for them currently. Numerical simulation is the only practical way to deal with such kind of problems in present power engineering. Some dynamic characteristics of the galloping are discussed theoretically and a virtual reality (VR) simulation platform for the galloping of power transmission lines is established in this thesis. The main contents and achievements are as follows:Based on the analysis of the galloping status in China and the research status around the world, some dominating galloping mechanisms are summarized and the existing limitations and developing directions are therefore pointed out in the thesis. Relating to the galloping problem, some ice-prevention methods together with the galloping prevention measures are also discussed in the thesis.Accoring to the established transverse-vertical coupling model for iced conductor and the relevant2-D coupling equations, some dynamic response properties are discussed in-depth and a more precision and universal critical-wind-speed formula and system instability criterion is put out in the thesis. The analysis shows that the vertical instability of iced conductors is not only related to the slope of the lift curve but also that of the resistance curve and depending on the matching partnership of the two curves. Galloping can happen disregarding the value of the slope of the resistance curve if the corresponding lift curve was matched, which extends the limitation of Den Hartog mechanism.In contrast with tranditional mechanics methods, a3-D differential equation for iced conductor is deduced from the perspective of energy, and detailed analysis of the dynamic responses is carried out in a numerical way in the thesis. It is pointed out that the birth of galloping is a process of energy accumulation, there are two different critical-wind-speeds corresponding to the transverse and torsional galloping, and the galloping of the conductor can be induced by both net energy accumulation and torsional vibration excitation. Galloping can be induced by torsional vibration (when torsional vibration frequency is near to that of tranverse vibration) if the wind speed is low, while in condition of high wind speed, galloping will be induced by net energy accumulation where transverse and torsional resonance are both excited at the same time.Tranditionally the aerodynamic coefficients (ADC) of iced conductor can only be obtained by wind-tunnel tests, which is non-economical and unable to obtain all the values for practical random conditions needed for engineering computation. Therefore a computer simulation method for ADC of iced conductor is systematically discussed in the thesis for the first time, and relevant computation formulae and values are also presented. Based on the theory of computational fluid dynamics (CFD) and FLUENT software, a CFD simulation model for the computation of ADC of crescent iced conductor is established, the model is then modified with the existing wind-tunnel test data. Relevant computation softwares are programmed and a set of ADC of crescent iced conductor under the typical work conditions are calculated. A computation method and its relevant formulae for the calculation of ADC of crescent iced conductor for practical random work conditions are brought out. Based on the above results, a CFD simulation model for the computation of ADC of D-shape iced conductor is further established, a computation theory for the calculation of ADC of D-shape iced conductor based on the crescent ice wind-tunnel test data is put forward. Relevant computation formule is induced, a set of ADC of D-shape iced conductor under the typical work conditions are calculated, and all the ADC modifying factors of D-shape iced conductor for practical random work conditions are presented. For bundled conductors, a concept of wake correction factor is induced and relevant definition and calculation formula is presented, and finally some values are listed for the two bundle conductor. The theory and method put out in the thesis has not only laid the foundation for the galloping numerical simulation, but also offered a way to reduce the number of ADC wind-tunnel tests for engineering, which presents its huge potential applicable value. It is possible, with the method and theory mentioned in the thesis, to calculate the ADC for any type of icing shape conductors with the existing crescent iced conductor wind-tunnel data without more extra relevant tsets. It can also be extended to the calculations of ADC of other types of fluid-object coupling conditions.As the foundation and precondition of galloping simulation, some typical technical problems in the process of numerical simulation are also discussed in the thesis, including the construction of finite element model of iced conductors, the influence and exertation of fluctuating wind to the galloping of power transmission lines, the influence of Ampere force to the galloping of power transmission lines, and the real-time exertation of dynamic loads in the simulation process.A virtual reality numerical simulation platform for the galloping of power transmission lines is then developed in the thesis based on the above researches. Taking the practical engineering application into consideration, a general frame for the galloping simulation platform is first constructed, more than12sub-modules under the Galloping Simulation Module, Galloping Prevention Module and Virtual Reality Module are designed and programmed, and all the modules and simulation processes are parametrically designed. The platform has good interactive feature and meet the requirements of engineering applications.An engineering application with the application of the developed platform for a practical power transmission line galloping is finally presented in the thesis. The application results shows that the error of galloping amplitudes between the simulation result and the practical observation value is only about8.9%, other results are in consistance with each other. It means that the platform system is designed reasonablely and correctly, the simulation results are high precision and trustable.The results and achevements of the thesis can either be applied in various power grid companies for thier existing power transmission line evaluation and galloping prevention designing, or be applied to power design instutes for their new line selection and design. It can also be extended to the calculation and analysis of other kinds of fluid induced virations, with a huge engineering application foreground. |
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