Nonlinear Numerical Simulation Method And Wind Tunnel Test For Galloping Of Iced Conductors

Galloping of an electrical transmission line is characterized by large amplitude, low frequency, self-excited oscillation under aerodynamic forces. It may deduce flashover between different phase conductors and cause damage to the conductors and even collapsing of transmission tower, which may in turn severely imperils the safe operation of the high voltage transmission line. Therefore, the study on galloping of iced transmission lines behaves great significance in power supply engineering.The curves of aerodynamic coefficients, including drag, lift and moment coefficients, of quad-bundled conductors accreted ices with typical cross-section shapes versus wind attck angle under different wind speeds were determined by wind tunnel test. It is shown that the ice thick has obvious effect on the aerodynamic characteristics of the ice conductors but the wind speed has a slightly effect. The wake of the upwind iced sub-conductor greatly affects the aerodynamic characteristics of the leeward iced sub-conductor. The difference of the aerodynamic loads on all the sub-conductors should be considered in the analysis of galloping of iced bundle conductors.Galloping of iced conductor is a typical nonlinear problem.In this thesis, the study on the nonlinear numerical simulation method for galloping of iced conductor is performed. Based on the principle of virtual work, an updated Lagrangian finite element formulation for the geometrical large deformation analysis of galloping of the iced conductor in an overhead transmission line is developed. In the procedure of numerical simulation, a three-node isoparametric cable element with three translational and one torsional degrees-of-freedom at each node is, are employed to discretize the transmission line; and the nonlinear dynamic system equation is solved by the Newmark time integration method and the Newton-Raphson nonlinear iteration strategy. Numerical examples are employed to demonstrate the efficiency of the presented method and the developed finite element program. Furthermore, a new possible galloping mode, which may reflect the saturation phenomenon of nonlinear dynamic system, is discovered on the condition that the lowest order of vertical natural frequency of the transmission line is approximately two times of the horizontal one.Based on the obtained nonliear finite element formulation for galloping of iced single conductor, a numerical method, in which the spacers are simulated with Euler beam, for galloping of iced bundle conductors is obtained, and the corresponding computer program is also developed. A numerical example is used to demonstrate the efficiency of the presented method and the developed finite element program. Furthermore, the galloping of the quad-bundled conductors with different span lengths is numerically investigated. It is observed that the transmission lines with shorter length of span gallope mainly with lower vibraion modes, and higher modes may occure for the lines with larger span when galloping takes place, which provides some references for the development of anti-galloping technology. In addition, the galloping of iced quad-bundled conductors in the case of considering and without considering the inference of wake around the iced sub-conductors is compared. The results indicate that the galloping amplitude as the wake inference being considered is lager than that as the wake inference not being considered.Galloping of iced qua-bundled conductor in stochastic wind field is firstly investigated by the numerical method developed in this paper. The stochastic wind fields are simulated by the Kaimal spectrum, with which the variation of wind velocity fluctuation with height above ground is taken into account, and the Davenport mutual spectrum. The correlation simples of stochastic wind at the points along the line direction are numerically simulated by means of the WAWS, based on which the aerodynamic loads of iced conductor are calculated. The galloping of iced quad-bundled conductor in stochastic wind filed with different span length is then numerically investigated, and some meaningful conclusions are obtained.The results show that galloping characteristics of the iced transmission lines in stochastic wind field are similar to those of the line in steady wind field. Moreover, the vibration amplitudes of the lines with smaller span length in stochastic wind are bigger than those of the line in steady wind field, but the vibration amplitudes of the lines with larger span in stochastical wind are less than those of the lines in steady wind.To verify the numerical simulation method of nonlinear galoping of iced onductor, two wind tunnel tests of typical galloping models, one for siced single conductor and the other for quad-bundled conductor, were performed, in which the galloping tracks of iced single conductor and iced quad-bundled conductor were obtained. The finite element models of the two tests are set up by the nonlinear finite element simulation methods presented in this paper, and they are used to simulate galloping of the test conductor models. The concidence between the numerical simulation results and wind tunnel tests demonstrate the correctness and efficiency of the presented numerical methods. Research results in this paper provides necessary test data and effective numerical method for the study on galloping of iced bundle conductor, so as to found the theory bases for anti-galloping method of iced bundle conductor.