The optimization of mechanical dampers to control self-excited galloping oscillations

The use of mechanical dampers for the control of the self-excited galloping of transmission lines is considered. Two particular dampers, an in-span damper and a resilient mounting, are studied, two mass representations being used. For both dampers it is possible to produce an optimum damper either by maximizing the negative damping excitation that the damped system can withstand, or by choosing the smaller logarithmic decrement of oscillation of the system to be as large as possible in the absence of excitation. These two procedures do not produce the same damper parameters. Simple analytical expressions are produced for the optimum parameters, and these are shown to agree well with numerically optimized parameters. For the in-span damper, either method of optimization gives a damper for a much wider range of ratios of the damper to conductor masses than is predicted by earlier work. For the resilient mounting the optimization based on damping gives very similar behaviour to that of the in-span damper. When aerodynamic excitation is considered for the resilient mounting, a clear optimum exists only for a small range of mass ratios. Results from a representation of the conductor by a stretched string are used to define the range of mass ratios over which the two-mass damper idealizations may be used to define damper properties.