عملکرد فرسودگی رساناهای سربار
Abstract
1-Introduction
2-Bending stress and H/w parameter
3-Materials and experimental procedure
4-Results, analysis and discussions
5-Conclusions
Acknowledgements
References
Abstract
The objective of this work is to conduct an experimental campaign to evaluate the effects of the catenary parameter (H/w) on the fatigue life of overhead conductors, being H the horizontal tensile load of the power line and w the weight per unit length of the conductor. A battery of twenty seven (27) fatigue tests was carried out on three types of conductors, an AAAC 900 MCM, an AAC Orchid and an ACSR Tern. For this study, all tests were conducted using the value of H/w = ۲۱۴۴ m. Fatigue damage, one of the major problems affecting power line conductors around the world, is caused by Aeolian vibration, characterised by high frequency and low amplitude movements. Based on field observations, the H/w parameter has recently been proposed as a fatigue design criterion for different families of cables. However, there is little experimental data available in the literature to assess the impacts of this hypothesis. Comparison between the generated S-N curves proved that an ACSR Tern conductor could sustain a significantly higher number of cycles before fatigue failure than the AAAC 900 MCM for this level of H/w. Meanwhile, the AAC Orchid presents a fatigue life situated between the AAAC 900 MCM and the ACSR Tern conductors. Failure analysis of the broken samples revealed not only that cracks initiated in the fretted areas of the aluminium wires but also that their morphology presented clear evidence of fatigue failure, such as observable beach marks and secondary cracks. Additionally, a failure map has been raised to determine the precise layer and the position from the clamp mouth where the wires broke. Furthermore, the provided information could be helpful for planning the maintenance of power lines.
Introduction
The overhead conductor is the only part carrying electricity, so its contribution has been estimated as carrying up to 40% of all power line transmission costs. However, this transmission line is susceptible to wind, snow, earthquakes and other weather conditions [1]. Aeolian vibration is the main cause of conductor fatigue failure, especially at devices which restrain its movements [2-4]. Frequently, the observed fatigue failure on overhead conductors occurs near or inside the suspension clamp, or devices attached to the conductor. That fatigue is characterized as the fretting fatigue of conductor strand during its aeolian vibration due to the fixation torque of the device on the conductor and also due to the microslip motion between wires and between the conductor and the device. A suspension clamp is one of the critical devices in term of fretting fatigue of conductor strand as there are many loads acting on the assembly conductor/clamp [5,6]. Among the loads, there are the tensile load of the conductor, the bending displacement due to the Aeolian vibration and the clamping torque. The control of the stretching tension of conductors at the design stage has been a concern for many years [1]. One of the reasons is that the tension of conductors during the most severe climate period does not exceed the allowable tension of the conductor. On the other hand, the stretching tension must be controlled in order to restrict the violation of the line clearance and also to protect the conductor against the harmful Aeolian vibration. It is well-known that a conductor becomes more vulnerable to Aeolian vibration when its tensile tension increases.