Meteorological conditions associated with the full-span galloping oscillations of overhead transmission lines

Abstract

The recorded phase-to-phase faults associated with the full-span galloping of CEGB overhead transmission lines over a 7-year period have been correlated in the form of histograms of number of faults as a function of wind speeds prevailing at the times of the faults. It is shown that, for bundled conductors, the results are in reasonable agreement with the theoretical predictions of Hunt and Richards for the minimum wind speeds necessary to cause phase-to-phase faults. 1 presented a theory for determining the maximum energy input from the wind into the full-span galloping oscillations of ice-accreted bundled overhead transmission lines. The main assumption made was that the galloping motion could be represented by a vertical oscillation which was sinusoidal in time. One of the conclusions of the paper was that, for any particular conductor and tower geometry, there is a critical wind speed below which oscillation amplitudes large enough to cause interphase clashing cannot be maintained. The critical wind speed is found to be a function of the maximum lift coefficient of an iced conductor or bundle of conductors,which can only be estimated using wind-tunnel models of ice-laden conductors. This is the biggest unknown in the theory, and should be borne in mind when applying the theory. At the time the paper was published, there was very little information available about the wind speeds prevailing at the times of full-span galloping of bundled conductors, and it was not possible to assess how close the critical wind speed was to the.actual lower-bound wind speed found in practice. This paper presents data collected from the CEGB transmission system over a 7-year period, and is a first attempt at examining the meteorological conditions under which largeamplitude full-span galloping occurs on bundled overhead transmission lines.