Theoretical Analysis and Experimental Validation on Galloping of Iced Transmission Lines in a Moderating Airflow

Bing Huo,Fujiang Cui,Shuo Yang,Xuliang Li,Roberto Nascimbene

doi:10.1155/2021/9969435

Bing Huo, Fujiang Cui + Show 3 more

Open Access

https://doi.org/10.1155/2021/9969435

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Abstract

Galloping of an iced transmission line subjected to a moderating airflow has been analysed in this study, and a new form of galloping is discovered both theoretically and experimentally. The partial differential equations of the iced transmission line are established based on the Hamilton theory. The Galerkin method is then applied on the continuous model, and a discrete model is derived along with its first two in-plane and torsional modes. A trapezoidal wind field model is built through the superposition of simple harmonic waves. The vibrational amplitude is generally observed to be more violent when the wind velocity decreases, except in the 2nd in-plane mode. Furthermore, the influence of the declining wind velocity rates on galloping is analysed using different postdecline wind velocities and the duration of the decline in wind velocities. Subsequently, an experiment has been carried out on a continuous model of an iced conductor in the wind tunnel dedicated for galloping. The first two in-plane modal profiles are observed, along with their response to the moderating airflow. Different declining rates of the wind velocity are also verified in the wind tunnel, which show good agreement with the results simulated by the mathematical model. The sudden increase in the galloping amplitude poses a significant threat to the transmission system, which also improves the damage mechanism associated with the galloping of a slender, a long structure with a noncircular cross-section.

Highlights

Long, slender structures are widely employed in engineering applications wherein the external environment plays a major role, including high-voltage transmission lines, suspended cables, inclined cables, and deep-sea mooring
It can be determined that the increased amplitude is elicited by the decline in wind velocity. e amplitude of the in-plane mode increases from 0.215 m to 0.271 m, which is 1.3 times the value in the mean wind velocity. e amplitudes of the first two torsional modes are 32.7 and 4.92 times the previous values before the decline in wind velocity, respectively, which are of greater influences
The torsional modes are yet to be measured, the galloping is found to be unstable beyond the in-plane vibration during the decline in wind velocity. e phenomenon observed in the wind tunnel test is consistent with that obtained via theoretical analysis

Summary

Introduction

Slender structures are widely employed in engineering applications wherein the external environment plays a major role, including high-voltage transmission lines, suspended cables, inclined cables, and deep-sea mooring. Under adverse weather conditions such as rainfall or snowfall, the cross-section of these structures becomes noncircular, which causes instable aerodynamic forces in the airflow and leads to galloping. Wind tunnel test is a reliable method to analyse the impacts of the wind loads acting on the conductor On one hand, these tests mainly focused on the aerodynamic coefficients with different cross-sectional shapes [17, 18], ice thicknesses [19], wind attack angles [20, 21], and crosssection areas [22]. Erefore, galloping of the iced transmission line subjected to a moderating wind field is analysed, and a wind tunnel test is performed on a continuous conductor model in this study.

Theoretical Model

Experimental Validation

Conclusions