Overhead-line oscillations and the effect of aerodynamic dampers

The paper is an attempt to further the understanding of aerodynamic effects in the large-scale vertical oscillations of overhead lines, usually known as `galloping¿. The energy per cycle dissipated by the aerodynamic drag is calculated, and then, assuming the lift coefficient of the cable to be less than some measured maximum value, the maximum possible amplitude of oscillation for a given windspeed is found. The theory gives a plausible value of the minimum windspeed at which the `clashing¿ of conductors can occur, and also a physical explanation for the given amplitude reached. The theory is then applied to the problem of estimating the effect of aerodynamic dampers in reducing the amplitude of galloping. Such dampers have been used in Canada, but the theory justifying their use appears, to the authors, inadequate. The method of calculation leads to an estimate of the minimum effect such dampers can have, and, as an example, the authors have examined the performance of some cylindrical dampers proposed for use on twin lines where pairs of cables are suspended about 0.3 m apart.