control o galloping in cables

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Information about control o galloping in cables

Published on October 2, 2010

Author: abhay128125


Control of Aerodynamic Galloping in Conductor Cables : Control of Aerodynamic Galloping in Conductor Cables Under the guidance of Prof.T.K.Dutta A.Bhaskar 2009CES2780 Department of Civil Engineering Indian Institute of Technology, Delhi 1 OVER VIEW : OVER VIEW Introduction Literature Review Objective Numerical Example Tentative Schedule References 2 Introduction : Introduction Possible types of wind-induced vibrations of cables Rain/wind-induced vibrations Vortex excitation of an isolated and group of cables Galloping of single cables inclined to wind Galloping cables with ice accumulations Galloping of cables in the wake of other structural components Wake galloping of group of cables Aerodynamic excitation of overall bridge modes of vibration involving cable motion Motion caused by wind turbulence buffeting Motion caused by fluctuating cable tensions 3 Galloping : Galloping Aerodynamic instability in translational motion normal to wind, in which the structural motion itself is the cause of creating the negative aerodynamic damping. It is sometimes observed in structures with aerodynamically bluff cross-sections such as towers, cranes and ice-covered cables, and was so named because of its violent feature. Conductor gallop is the high-amplitude, low-frequency oscillation of overhead power line due to the wind. The natural frequency mode range from 0.1 to 1Hz, the oscillations can exhibit amplitudes well in excess of a meter or 0.1 to 1 times the sag of the span. The displacement is sometimes sufficient for the phase conductors to infringe operating clearances, and causing flash over. The forceful motion also adds significantly to the loading stress on insulators and electricity pylons, raising the risk of mechanical failure of either. A well-known criterion for instability, introduced by Den Hartog (1933), states that the instability exists when the sum of the lift slope and drag is negative, or 4 Reported incidents in the world : Reported incidents in the world 5 Reported incidents in the world(contd..) : Reported incidents in the world(contd..) O = No activity to report, X = Activity to report, - = No report 6 Factors influencing galloping : Factors influencing galloping Ice accretion type and shape (eccentricity, weight, aerodynamic properties) wind velocity Conductor self-damping (vertical, torsion) in the low frequency range Span lengths (including all spans of a section) and section length longitudinal stiffness at attachment point on tension tower Number of sub conductors and their arrangement Spacers (kind of spacer, location, eccentric weight effect) Angular orientation of ice in the presence of wind Ratio vertical/torsional frequency for each mode, in the presence of wind 7 Protection methods : 8 Protection methods There are three main classes of countermeasure employed against galloping: 1. Removal, or preventing formation, of ice on conductors. 2. Interfering with the galloping mechanisms to prevent galloping from building up or from attaining high amplitude. 3. Making lines tolerant of galloping through ruggedness in design, provision of increased phase clearances, or controlling the mode of galloping with interphase ties. Slide 9: 9 DAMPERS: Energy dissipation devices(EDD) are used to dissipate energy imparted to a structure during a dynamic excitation 1. Friction damper 2. Viscous damper 3. Visco elastic dampers 4. Metallic dampers Passive Dampers No external power source is required Utilizes motion of the structure Active Dampers A large power source is required for operation of electromechanical or electro hydraulic actuators Uses feedback system Semi-Active Dampers Small external power is required to produce adjustable control forces Utilizes motion of the structure also Literature Review : Literature Review Pierre McComber,Alain Paradis.A cable galloping model for thin ice accretions. Atmospheric Research,1998. It was verified by measuring the wind forces coefficients that galloping can not be predicted by the DenHartog criterion for thin ice accretions. A two-degree-of-freedom numerical simulation model with rotational lift included was shown to develop galloping vibrations in a numerical simulation. The necessary resonance of the natural frequencies permitting galloping was explained by the vortex shedding lock-in effect. This indicates that the lock-in effect must be a key factor in the development of galloping for thin ice accretions. Since galloping for thin ice accretions resulting from freezing rain accounts for a good percentage of the galloping cases, this model should be of some help to researchers working on preventing transmission line damage due to galloping. 10 Literature Review : Literature Review Y. M. Desai, P. YU, N. Popple Well and A. H. Shah, Finite element modeling of transmission line galloping. Computers and Structures 57 (1995). A computationally efficient finite element model has been developed to analyze the galloping of a multi-span transmission line. An expedient time marching scheme is presented to compute the envelope of motion. This scheme, unlike conventional time integration methods, can be used advantageously in situations involving nonlinear damping. Computational effort has been minimized by performing the time integration in the sub-space. Good correlations are obtained with field data. 11 Literature Review : Literature Review Muhammad Bilal Waris et. al ,” Galloping response prediction of ice-accreted transmission lines” An aero-elastic experiment has been performed on a four-conductor cable model. The results indicate that galloping amplitude is higher in system with synchronized frequencies. The critical velocity may also be overestimated using Don-Hartog’s principal. Further, the efficiency of aerodynamic models has been investigated using nonlinear 3D-FEM simulations. Comparison of quasi-steady and unsteady aerodynamic force model is provided considering the aero-elastice xperiment. Unsteady model is found to provide better results as compared to quasi-steady model. 12 Objective : Objective To develop algorithm for controlling galloping response using passive control device (linear analysis). To develop algorithm for controlling galloping response using semi active devices (linear analysis). To develop algorithm for controlling galloping response using Semi active control considering as non linear analysis. 13 Numerical Example : Numerical Example 14 Equation of motion: Numerical Example : Numerical Example 15 Numerical Example : Numerical Example 16 Numerical Example : Numerical Example 17 The value of damping is given by approximately by Tentative Schedule : Tentative Schedule 18 References : References J. P. Den Hartog, “Transmission Line Vibration Due to Sleet,” AIEE Transactions, Vol.51, 1932, pp. 1074-6. G. V. Parkinson and T. V. Santosham, “Cylinders of Rectangular Section as Aero elastic Nonlinear Oscillators,” ASME Paper No. 67-VlBR-50, 1967. A. S. Richardson, J. R. Martuccelli and W. S. Price, “An Investigation of Galloping Transmission Line Conductors,” IEEE Transactions Paper, Vol.82, 1963, pp. 4 1 1-3 1 C. O. Harris, “Galloping Conductors,” Second report on a Utilities Research Commission Project at University of Notre Dame, 1949. D. C. Stewart, “Experimental Study of Dancing Cables,” AIEE North Eastern District Meeting, May 1937, Buffalo, NY A. T. Edwards, “Current Status-Galloping Problem,” CIGRB Report 22-76 (WG 0 15P) 0 1. 19 Slide 20: O. Nigol and D. G. Havard, “Control of Torsionally-Induced Conductor Galloping with Detuning Pendulums,” IEEE Paper A78 125-7, January 1978. W. N. McDaniel, “An Analysis of Galloping Electric Transmission Lines,” AIEE Transactions, Vol. PAS-79, 1960, pp. 406- 12. M. Novak and H. Tanaka, “Effect of Turbulence on Galloping Instability,” ASCE Journal of Engineering and Mechanical Division, Vol. 100, No. EM1, February 1974, pp. 27- 47. F. Cheers, “A Note on Galloping Conductors,” NRC (Canada) Laboratory Technical Report MT- 14, June 1950. 20 THANK YOU : THANK YOU 21

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