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Thesis Format

Integrated Article

Degree

Master of Engineering Science

Program

Civil and Environmental Engineering

Supervisor

Hangan, Horia M.

Abstract

Atmospheric icing on mountainous terrain can produce catastrophic damages to transmission lines when incoming particles impinge and accrete on the cable surface of the system. The first challenge in wind-ice loading is determining joint statistics of wind and ice accretion on transmission lines. This study analyzes the weather characteristics for a specific site of study using 15 years of historical data to use as inputs for ice accretion modeling. The joint wind and ice hazard is characterized by simulating 500 years of icing events from the fitted probability distributions of ice accretion and wind on ice velocities. The second challenge of wind and ice loading is to deal with the wind induced vibrations when the iced conductors present complex asymmetrical shapes. The vertical galloping, characterized by high amplitude and low frequency motions, produce extra tension to the transmission towers which is not considered in the Canadian standard (CSA-C22.3) for the design of wind and ice loads for overhead transmission lines. For the dynamic analysis, the Den Hartog’s principle is applied to identify potential instabilities and the linear theory of free vibrations of a suspended cable is performed for the estimation of the extra tension produced by the free stream velocity acting on the one-degree-of-freedom iced conductor. The static and dynamic loading resulting from the present study are compared with the wind and ice design cases based on the Canadian standard (CSA-C22.3).

Summary for Lay Audience

When transmission lines are exposed to harsh weather conditions, such as strong winds and intense ice storms, the system may experience serious damage if it is not previously design to withstand these conditions. The ice may accrete on the cable surface of the system giving place to undesired behavior of the wire, potentially creating overloading which may lead to transmission line failures. Failures may produce economic losses, long blackouts, and unfortunately human deaths in the worst scenario. There is thus a need to conduct research of the wind and ice effects on transmission lines located in mountainous terrain. Although the effects of wind speed and atmospheric icing have been widely studied separately, little attention has been given to both acting simultaneously. For this reason, the present work attempts to reduce uncertainties when dealing with the joint wind and ice hazard, by quantifying its contribution to the total tension transmitted to the transmission towers. The resulting effects from the present study are compared with existing guidelines for the design of wind and ice loading on overhead transmission lines (The Canadian standard CSA-C22.3).

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

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