The fretting fatigue analysis between strands of ACSR
In this paper, self-made fretting fatigue wear test bed was used to investigate fretting fatigue and wear properties of overhead transmission line between the strands, and then the fretting fatigue fracture life and the fracture surface microscopic morphology of ACSR in different testing conditions was analysed. The results show that under larger included angle, larger ACSR tensile force and larger fretting amplitude, the fretting fatigue life of the wire was reduced. The crack initiation and propagation occurs in the contact edge, and the angle is 45° between fracture surface and the wire axis. Fretting fatigue fracture can be divided into three areas: micro-crack nucleation area, fatigue crack propagation area, crack area, and the three regions have different fatigue properties.
Failure analysis of aluminum cable steel reinforced (ACSR) conductor of the transmission line crossing the Paraná River
The failure of the conductor of the 460 kV overhead transmission line located along the crossing of the ParanaRiver was investigated. As a result of this failure,a blackout took place in the southern states of Brazil in January of 2002, reaching approximately 67 million inhabitants. Investigation of the external aluminium layer of the ACSR conductor near the fracture showed typical static deformation marks and dynamic fretting wear tangential marks,both associated with the presence of Al2O3 debris. Additionally,encrusted silicon particles were observed on the external surface of the strands. The internal Al layer showed elliptical deformation marks also associated with Al2O3 debris. Both Al2O3 and Si particles are efficient abrasive material,which associated with slight relative motion of metallic surfaces (clamp/ strand and strand/strand) can promote fretting wear. Two types of fracture surface of the Al strands were identified: 45 and quasi-normal surfaces,the former being the predominant type. Delamination and particle detachment were the mechanisms of superficial degradation observed on the Al strands,indicating that the rupture of the strands occurred under a gross slip fretting regime induced by sub-conductor oscillation. Inspection of the internal surface of as-cast Al-10%Si spacer clamps revealed different stages of intense circumferential wear caused by the preferential cracking and particle detachment of the eutectic constituent of the as-cast microstructure. This intense wear reduces the clamp- ing contact pressure,which allows higher displacement amplitude and leads to the critical fretting regime. Finally,a few suggestions are discussed to minimise the occurrence of future failures. # 2002 Elsevier Science Ltd. All rights reserved.
Effect of lubricant in electrical conductor fretting fatigue
Bending fatigue tests have been performed on the lubricated electrical conductor ZEBRA held with two different spacer clamps. A constant axial load of 25% RTS (rated tensile strength) was imposed on all specimens. After each test, fretting patterns have been studied for each aluminium layer. OM and SEM metallographic examinations have been carried out to study fretting cracking behaviour. Compared with a similar unlubricated conductor, results show that the lubricant plays an important role in preventing contact wear and in retarding fretting cracking. Further tests on single lubricated and unlubricated aluminium wires show that influence of lubricant on fretting fatigue strongly depends upon the contact conditions (normal load and slip amplitude).