Overhead electric lines. An account of the work of the British Electrical and Allied Industries Research Association

The British Electrical and Allied Industries Research Association have undertaken a comprehensive research into the problems arising in the construction and uses of overhead electric lines. The research has been productive of valuable results. The present paper deals with two sections of the work: (1) as to the strength of wooden poles, single and compound, and (2) as to the intensity of wind pressures on wires and cables such as are used for overhead power lines and on the poles and lattice structures for supporting them. The tests on wooden poles disclosed a fundamental weakness in the usual design of compound poles and led ultimately to the development of a much improved design. Accurate figures were also obtained of the rupturing strength of red fir poles. The improved design of compound pole is described and the weakness of existing designs is pointed out. The wooden poles were tested under practical conditions. The information gained was supplemented by a series of tests on small-scale models, which confirmed the claims made for the greatly increased strength of the new designs of compound poles. The tests of wind pressures were made on wires of various sizes, on cylindrical sections corresponding to those of wooden poles and on angle bars and a lattice framework. Definite values of the coefficient relating wind pressure with velocity have been recorded by these tests, the figures being of considerable value to designers. Sufficient data have been obtained to enable, for the first time, a proper allowance to be made by the designer for wind pressures on wires and cylindrical poles of the sizes commonly used for electric power lines. A series of experiments to determine the wind pressure on angle bars is described. The results indicate that the wind pressure on a fabricated frame may be estimated from the data obtained by tests on standard sections. The work of the Association described has produced valuable results and the researches are being continued.