Variation in distribution of wind pressure on overhead lines

Abstract

This report describes tests undertaken to ascertain to what extent lack of uniformity in the distribution of wind velocity along the front of a gust affects the total load on the towards of an overhead line. It is shown that on spans of length up to 300 ft. over level country, uniformity of distribution occurs. On larger span lengths uniformity is not maintained, measurements on a 600-ft. span showing a reduction of about 15 per cent per unit length of conductor as compared with the load on a 300-ft. span.Over level country the height of tower will increase with span length, since conductors are erected with a constant minimum ground clearance. In general, the wind speed increases with height above ground. If then the simultaneous wind-loads on a number of spans of different lengths are compared, there will be a tendency for the load on a long span to be greater than that on a short span, and it is inferred that this tendency to increase the load will very largely offset the reduction in load due to limitation in the extent of the wind gust.In the case of a long span over a valley, the measured wind load was found to be approximately equal to that calculated on the assumption of a uniform distribution of wind velocity as measured at the tower at conductor height.