Buffeting and Self-Excited Load Measurements to Evaluate Ice and Dry Galloping of Yawed Power Transmission Lines

Abstract

Dry and ice galloping of power transmission lines (conductors) that occur at moderate to large wind speeds cause large-amplitude motion in these long-suspended cables. This phenomenon can cause catastrophic damages such as flashover, wire burning, tripping, transmission line tower collapse, accident, interphase short circuit, and structural or fatigue failure of transmission towers or conductors. Wind-induced cable vibration, which has been extensively studied, can be classified based on its sources, such as rain-wind-induced vibration (RWIV), vortex-induced vibration (VIV), wake galloping, and dry/ice galloping. This study primarily focuses on the predictions of time-domain response and onset of dry- and ice-conductor galloping by measuring the self-excited and buffeting load parameters of the bare conductors and conductors with ice formation in normal and yawed wind. In this regard, a series of static and dynamic wind tunnel experiments were performed to fundamentally study the conductor vibration in dry and ice conditions. Surface pressure distribution and aerodynamic forces were measured for stationary section models of nonyawed and yawed dry conductors in a smooth flow. Additionally, the dynamic response of dry and iced conductors using a one-degree-of-freedom system was recorded by employing a free vibration setup to extract self-excited load parameters. Buffeting load parameters were measured by generating a sinusoidal-oscillating wind upstream of dry and iced conductors for different yaw angles. The experiments resulted in the identification of the Strouhal number (St), aerodynamic load coefficients (CD and CL), buffeting indicial derivative functions, aerodynamic stiffness, and aerodynamic damping of a conductor for yaw angles (β) ranging from 0° to 45°. Dynamic tests led to the proposing of several empirical equations to determine the critical reduced velocity (RVcr) or critical wind speed for dry and ice galloping of conductors at a given Scruton number (Sch) and yaw angle. Finally, a procedure was proposed to calculate the least damping required to suppress the conductor galloping under dry or iced conditions up to the design wind speed. The wind load parameters identified in this study can be used to numerically simulate the dynamic load and response in the time domain of dry and iced conductors in turbulent wind.