Computational handbook for power line engineers

Abstract: The high voltage power network in Sweden consists mainly of overhead power lines, that is conductors suspended in the air by supports. Ideally when projecting a power line, all supports should be placed equidistantly and the conductors should be suspended at equal height. When this is not applied, the support placement may have consequences, such as uplifting forces in a support, which should be avoided. The objective of this thesis was to investigate both what in　uences the support placement, and what consequences that may come out of it. This was investigated using mainly analytical calculations on poles and conductors, but was also implemented on a specic case. When solving the case, support placement and FEM software were also used and compared with the analytical calculations. It was found that the support placement is in　uenced by both environmental factors; such as terrain, obstacles and solidity of the ground, as well as how long spans that are possible to construct. The span length is the distance between two nearby supports and is limited by sag, that is the de　ection of the conductors, and the strength of the supports. The sag is dependent on the tension in the conductor, which is dependent on wind and ice loads, temperature and creep; a permanent elongation that for certain materials occur over time even if the load is constant. Since the sag will increase over time, and especially at high temperatures, the distance between the conductors and the ground will decrease. This extra de　ection must be accounted for when designing the power line and determining the span length. When it comes to support designing, both bending and buckling should be accounted for. The greatest loads the supports are in　uenced by are transferred from the conductors, and therefore are dependent of the span length. An analysis of buckling and bending as function of span length was therefore conducted on non-guyed timber pole supports. It was concluded that bending stresses; due to wind loads on the support and especially on the conductors, are usually the critical aspect when designing standard power line supports.