Unsteady aerodynamic force modelling for 3-DoF-galloping of four-bundled conductors

Abstract

Galloping of overhead transmission lines is characterised by large-amplitude, low-frequency, vertical–horizontal–torsional three degree-of-freedom (DoF) oscillations, which can potentially induce interphase short circuits and fatigue in the conductors and support structures. Numerical analyses are useful for estimating the galloping response of transmission lines, and unsteady aerodynamic forces should be evaluated for accurate simulation. In this study, the unsteady aerodynamic force modelling of four-bundled conductors is investigated based on aerodynamic force measurement test results. Three types of unsteady aerodynamic force measurement tests were performed: under constant torsional angular velocity and under torsional and vertical 1-DoF sinusoidal oscillations. Evaluating the dependence of the aerodynamic forces on the various motions enabled an improved unsteady aerodynamic force model to be developed, considering the effect of angular velocity. First, two-variable aerodynamic coefficients were proposed as a function of the angle of attack and non-dimensional angular velocity. These coefficients were determined via tests performed at constant torsional angular velocities; results with different combinations of wind speed and angular velocity confirmed that the non-dimensional angular velocity can be used to define the unsteady aerodynamic forces. Then, the validity of the two-variable aerodynamic force formulation was confirmed for predicting torsional or vertical 1-DoF oscillations, by comparing the unsteady aerodynamic force obtained via the sinusoidal forced-vibration tests and via the constant angular-velocity tests. Finally, results of the time-history​ analyses using the two-variable aerodynamic coefficients were compared with those of previous wind-response measurement tests to obtain the best unsteady aerodynamic force model for simulating large-amplitude 3-DoF galloping. These results indicate that the unsteady aerodynamic forces for 3-DoF-galloping of four-bundled conductors can be evaluated using the relative angle of attack, the rate of change of the relative angle of attack, and the relative wind speed, using two-variable aerodynamic coefficients measured under constant angular velocity conditions.