Galloping of electrical lines in wind tunnel facilities

Galloping is a large amplitude, low frequency, wind-induced oscillation of overhead electrical lines. In the vast majority of cases, an ice accretion is present on the conductor: this has the effect of modifying the conductor's cross-sectional shape such that it becomes aerodynamically and/or aeroelastically unstable. This paper deals with galloping generated during wind tunnel testing. A typical eccentric ice shape has been reproduced on a classical stranded overhead line conductor. In the first part, the quasi-static aerodynamic coefficients have been measured for different wind speeds in the range of galloping observations. In the second part the same sample has been suspended in the wind tunnel by springs in order to obtain a system as close as possible to an overhead line (vertical, horizontal and rotational movements are allowed). For appropriate angles of attack, galloping has been obtained. For an electrical engineer, there are two kinds of galloping: Den-Hartog galloping and flutter galloping. The first one is an aerodynamic instability because the main factor at the origin of this problem is the aerodynamic properties of the ice deposit. The flutter galloping is an aeroelastic problem. For this type of instability, the structural properties of the line are also important and there is a coupling between at least two degrees of freedom. Both of them were recorded. These tests make available a full set of data and recordings of limit cycles during galloping events. Such measurements can be used for numerical model validation and for efficiency evaluation of some anti-galloping means (detuning, increase of damping in vertical, torsion, modification of rotational inertia, etc.). (C) 1998 Elsevier Science Ltd. All rights reserved.