TABLE OF CONTENTS At the inception of an overhead line project, as part of the feasibility study, the location of the load centres both present and projected, together with present and future generation sources, will be established. The required transfer capacity of the line will then be known and the type of construction fixed. The economic study of the line design will have established the optimum span length and tower heights to provide proper ground clearance from the line conductor to satisfy the local ground clearance requirements. In most parts of the world the electricity supply authority or utility will have a schedule of mandatory ground clearances for the range of transmission voltage in use.
Initially, the available maps covering the line route are obtained and a straight line between the line terminals drawn on the overall planning map. A convenient scale for use for a line 200 km or more in length is 1:250 000. The major topographical features of the regions crossed by the route should then be considered; for example, areas with major access problems or regions with known areas of bad or poor quality ground should not be crossed if excessive foundation prices are to be avoided. Areas of outstanding natural beauty should also be considered. It may be necessary to avoid crossing areas with particular types of vegetation.
Other features crossed by the route must be considered, for example airports, major highways, pipelines, the lines of sight between microwave aerials...
