The Vibration of Transmission-Line Conductors

This paper is a continuation of a former one by the writer in May, 1926. Records are given of vibration in actual transmission lines under widely varying conditions and with various conductor materials. These observations indicate the limiting values of wavelength frequency and amplitude of such vibrations encountered in service. Laboratory experiments are described in which the observed conditions were artificially reproduced in a large conductor. The stresses adjacent to a point of support were studied with the aid of a microscope. The wave shape was plotted and the energy required to maintain vibration was recorded. All conductor vibration breaks observed in practise have occurred at supports or badly made joints. The conclusion is reached that if the radius of curvature at the support can be maintained at least equal to that at the center of a loop, no breakage wil occur. Mathematical expressions are given for determining the radius of curvature at the center of a loop, the bending moment at a support, and the necessary additional amount of conductor stiffness at the support to satisfy the desired condition. A simple form of stiffening device is described which even in a more crude form has been found effective in several cases of actual service.