Damping of Composite Mast Structures

The required expansion of the European electrical grid by 50.000 km within the next 10 years provides the opportunity to install visually innovative and beautified power pylons, generating a broad public acceptance. The use of non-conductive composite materials for the novel power pylon will enable the direct attachment of the conductor lines without classic insulators and, consequently, a reduction in its size.

The use of a direct cable-pylon connection will increase in the dynamic interaction, so that wind-induced vibrations like the severe galloping phenomenon, may lead to structural damage due to excessive vibration amplitudes. The necessary measure to mitigate conductor line galloping is assumed to be achieved by introducing damping into the directly linked composite cross arm.

In order to design the power pylon for potential galloping events, the fibre direction dependent damping properties of the non-conductive composite materials is thoroughly investigated for environmental conditions typical for galloping. Additional damping may be achieved by the application or implementation of several damping enhanced treatments.

In the thesis, potential damping treatments for an application in high-voltage environment are evaluated with regard to the damping behaviour at low temperatures and frequencies, typical for galloping conditions. The damping behaviour of composite coupon specimens and sub-structures is therefore numerically and experimentally investigated.

The present thesis is organized in four parts, all concerning the mitigation of conductor-line galloping by the damping enhancement in composite materials and (sub-)structures. The first part presents a selection of promising damping treatments for composite materials and structures, suitable in high-voltage applications and effective at environmental conditions typical for conductor-line galloping.

The manufacturing feasibility and potential side effects of the treatments are assessed using examples. In the second part the dynamic-mechanical characterisation is described for damping-modified composite materials and mast sub-structures at temperatures and frequencies typical for galloping, focusing on treatments at micro-scale, meso-scale and macro-scale level.

The third part presents a numerical damping simulation approach using the modal strain energy method. The numerical results are thereby compared with experimental results of coupon specimens and structural tests. In the final part of the thesis a numerical galloping analysis is conducted to evaluate the effect of damping and different cable support conditions for a potential mitigation of conductor-line galloping.