Field determination of conductor drag coefficients

Abstract

Electrical conductor drag coefficients are normally determined by wind tunnel tests. The effective conductor drag coefficients derived from measuring actual conductor wind loads experienced in operating transmission line structures do not correlate well with the wind tunnel results. Most of these full-scale wind loading experiments measure swing angles and insulator forces on long conductor spans in the open air while wind tunnel tests measure drag force directly on short conductor segments under laboratory conditions. Difficulties arise when attempting to identify the causes of discrepancies in drag coefficients derived from these two different types of testing. To identify the causes of these discrepancies, an experiment was conducted to directly determine the conductor drag coefficients in the open air using a tunnel-like test setup. This field experiment was intended to determine whether the conductor drag coefficients obtained in wind tunnels match those determined in the open air. Three conductor models, 3.66 meters long and of similar surface roughness, were used for testing. A test frame with necessary instrumentation attached was installed on a platform 20 meters above the ground. The results of this study show that the conductor drag coefficients obtained in open air are in agreement with wind tunnel drag data in the wind velocity range for which field data were recorded.