Composite Materials for Electrical Transmission Mast Structures

The Large energy demand in the global market, a total estimate of 14050 million tons of oil equivalent in 2017 [1], and especially the electrical power consumption has increased the necessity of expanding power grids for transmission and distribution. Although underground transmission lines seem to be the primary choice with respect to the visual impacts, due to high costs and technical difficulties, overhead lines are still the preferred tools for this matter. However, mainly because of public resistance towards installation of overhead line structures and their negative impact on the landscape, designers have been motivated to come up with new concepts to overcome this issue. One of these concepts developed by BYSTRUP, an architecture company in Denmark, is known as ‘The Composite Pylon’. Using non-conductive materials for the structure of this pylon results in the omission of conventional insulators since the overhead transmission lines may be rigidly and directly mounted to the power pylon structure; this lowers the electrical clearances and the size of the power pylon structures may be reduced considerably. Other advantages of this concept are a lighter structure, broader public acceptance and simpler installations.
The overall framework of this thesis is focused on the multi-environment (mechanical and electrical) ageing of GFRP (Glass Fiber Reinforced Polymer) materials. The experiments have been carried out small-scale (coupon size) and large-scale (full-length arm) specimens, while subjected to fatigue mechanical and electrical loads simultaneously. The material selection is based on the conventional structural resins with continues glass fiber reinforcements.
The first part of the work in this thesis is related to the calculation of different types of loads, which are applied on the structure mainly by wind, ice or their combination. These calculations are based on the procedures suggested by Euro code standards for overhead line structure designs.
The second part is focuses on developing an experimental setup for fatigue testing of coupon specimens, capable of applying simultaneous mechanical and electrical loads. An S/N (stress/number of cycles to fail) curve diagram has been developed in order to compare the fatigue life of unidirectional GFRP specimens, while subjected to pure mechanical and combined mechanical-electrical loads.
The third part is related to investigating the effect of different layup configuration and manufacturing defects (pre-delamination and voids) within the material, on the fatigue resistance while subjected to mechanical and electrical stresses simultaneously.
In the final part of this thesis, an experimental setup has been developed for large scale testing of a full-length arm of the power pylon while subjected to combined mechanical and high voltage electrical loads. At the end, the results from the fatigue experiments were compared to the finite element simulations.