Fretting fatigue in electrical transmission lines

Abstract

One of the worst problems in overhead electrical transmission line fatigue is fretting, which can lead to wire failure or even conductor breakage at suspension clamps. However, fretting behaviour is extremely complicated owing to its synthetic geometry and loading condition. The tests concern bending fatigue on the overhead electrical conductor DRAKE. The imposed amplitude ranges from 0.60 to 0.80 mm. The static axial load was set at 25% RTS (Rated Tensile Strength). The tests were performed (including the static test) with a frequency of 10 Hz for any number of cycles. Post-test studies of the fretting scars were carried out by OM and SEM. Plastic flow, local wear and fretting cracking were observed at different conductor locations. Fretting cracking depends strongly on fretting regime, and the later propagation on the external load. Fretting regime and external load are determined by numerous factors such as contact type and position. Through metallographic examinations, it has been demonstrated that fretting is most likely to lead to cracks in the vicinity of the keeper contact edges, and probable propagation occurs at the upper half-section for the outer contact. The wire failure is found precisely in this zone and it fits our analysis well.