PSI - Issue 64

Jayathilake S. et al. / Procedia Structural Integrity 64 (2024) 137–144 Jayathilake S. et al. / Structural Integrity Procedia 00 (2024) 000–000

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vertical action and the sag controls the tension of the conductor. In the sense of controlling the sag in the conductor and providing proper clearance to the land, powerline installation is started with an initial tension force (Douglass & Thrash, 2018). The initial sag can alter with the probable environmental actions and forces induced within the conductor due to the variation in the electricity power. The wind is a significant weather factor with variations in speed and direction, particularly notable in Australia throughout the year. This impacts the design and performance of the conductors in the OPDN (Kiessling et al., 2014; Lee & Ham, 2021; Otero et al., 2012). The wind flowing over cylindrical objects, such as electric conductors, creates eddies or vortices, generating alternating pressure patterns causing a vibration, which is a phenomenon of periodic upward and downward forces on the conductor due to wind interaction (Du Plessis, 1994). A pressurised area around the conductor is developed due to the formed eddies with the wind action. This induces additional pressure on the surface of the conductor; therefore, the conductor is subjected to an increased tension force. AS/NZS1170.2 (2021) guides for understanding the probable wind actions in all regions in Australia. AS/NZS7000 (2016) has been developed for the requirement of the design of overhead powerlines in Australia and New Zealand. These two standards guide to calculation of the conductor forces due to the wind action. The design site wind velocity ( V sit,β ) is chosen based on the regional gust wind speed in the selected return period ( V R ). Further, it is modified by considering factors such as terrain category at average conductor height ( M z, cat ), wind direction ( M d ), shielding appliance ( M s ), and topography ( M t ) as shown in Eq. (1). Design wind pressure is calculated by Eq. (2). , = × ( , × × ) (1) =0.6 , 2 ×10 −3 (kPa) (2) As per AS/NZS7000 (2016), wind force perpendicular to the conductor ( F c ) is the function of wind velocity ( V sit,β ), the drag coefficient ( C d ), Conductor wind span ( L ), the diameter of the conductor ( d ), span reduction factor ( SRF ), and angle between wind direction ( α ) as given in Eq. (3). = × × × × × 2 (kN) (3) Similarly, temperature changes in the conductor and environment also influence the induction of power conductor thermal stress. The thermal stress in the conductor can vary due to several factors such as overloading current, failure of the operator, wildfire, short-circuit, and lightning (Zainuddin et al., 2020). Additionally, variations in topography and climatic conditions influence the changes in temperature throughout the year from extreme heat to snow conditions. Power conductors face significant challenges in specific environments with extreme heat and high temperatures due to the thermal expansion of their construction materials (Polevoy, 1998). This causes the conductor to sag by reducing the clearance to the ground. Therefore, provision for the conductor temperature variation is included for conductor tension calculation in Appendix R of AS/NZS7000 (2016) as described in Eq. (4). Where the a and b are as in Eqs. (5 & 6) respectively. 3 + 2 − =0 (4) = � 2 2 24 2 + � − � + ( − ) � − (5) = 2 2 24 (6) Here, the conductor is suspended between two supports and the geometry can be either an inclined span or a level span within ( L ) distance. Here, H i and H f are initially applied tension, and the final tension of the conductor respectively. The final tension in conductor is induced by uniformly distributed load ( W i ), temperature difference ( t f - t i ), and change in creep strain ( ε f – ε i ) of the conductor. The notation of subscript ‘ f ’ refers to controlling constraint while ‘ i ’ refers to the constraints while sagging. Notation ( E ) represents the Young’s modulus of the conductor while ( A ) represents the total cross-sectional area of the conductor. Continuous exposure to wind and thermal stresses affects the mechanical properties of the conductor and degrades its durability (Zainuddin et al., 2020). Tensile loss, fatigue, power leakages due to degrading, and reduced ground clearance severely affected the long term performance of the OPDN conductors. The deterioration process in the conductors happens over its service