Conductor optimisation for overhead transmission lines

Continuous changes in the cost of suitable (conductive) material for bare overhead conductors, changes in electrical and mechanical requirements, and improvements in manufacturing technology, have resulted in the development of a variety of possible applications or options for overhead transmission lines. In the early days, simple copper wire or copper based bare conductors were used but nowadays, more cost effective solutions, such as aluminium and variations of aluminium alloy conductors are used extensively in the power system. The conductor of an overhead power line is considered as the most important component of the overhead line since its function is to transfer electric power, and its contribution towards the total cost of the line is significant. The conductor costs (material and installation costs) associated with the capital investment of a new overhead power line can contribute up to 40% of the total capital costs of the line. Furthermore, power losses in the lines account for the bulk of the transmission system losses, which in South Africa is about 1200 MW at peak load. These are critical economic factors which need careful analysis when selecting a conductor for a new overhead line, which will be in operation for an excess of 25 years. Choosing a larger conductor configuration will have higher up front capital costs, but this may lead to lower overall life cycle cost. Consequently, much attention has to be given to the careful selection of a conductor configuration to meet the present and predicted future load requirements. A process needs to be followed to optimally choose a conductor and tower configuration. This paper presents a procedure which has been formulated and tested to optimise the selection of the conductor and tower configuration from an overall system point of view. The paper also highlights the significance of incorporating planning and load forecast considerations, power quality constraints, voltage collapse studies, corona and audib- e noise, induction and transposition studies, line performance studies, and life cycle cost of maintenance for the different options, in the optimisation algorithm. The methodology and results of an actual case study are presented to demonstrate the effectiveness of the proposed procedure. The paper provides a valuable guide to assist with the selection of conductor and tower configurations for new overhead transmission lines