Response of electrical transmission line conductors to extreme wind using field data

Conductors are long, slender, flexible, and wind sensitive structures. In most cases of transmission lines, 60-80% of wind loads coming to the support structures are transferred from conductors. Thus, assessment of conductor response due to extreme wind is an important part of the overall prediction of wind loads on transmission structures, Extreme winds not only contain high wind speeds but also randomly fluctuating gusts. These gusts cause fluctuating dynamic responses of conductors. Since the responses fluctuate randomly, they need to be assessed in probabilistic terms.

An analytical model for estimating dynamic response of transmission line structures to wind loads is developed by Davenport. The model can be verified using field data to determine its effectiveness. Bonneville Power Administration (BPA) has conducted experimental studies in the field at the Moro site to collect wind and electric transmission structure response data. During 1981-1982 BPA collected 23 separate 12-minute duration records that included wind speed, wind direction and conductor response data. The conductor response records include load cell, transverse swing angle, and longitudinal swing angle recordings.

The BPA data of wind and conductor response are analyzed in detail to gain as much information as possible. The analysis of wind data include determination of wind characteristics of mean wind profile, turbulence intensities, and gust spectra. The conductor response in terms of peak responses, effective force coefficients, peak factors, and response spectra are obtained. The response spectra are further analyzed to obtain contributions of background response and resonant response. Comparison of the analytical model with field data reveals that the model underestimated background response and overestimated resonant response.

Results of these data analyses are used to improve the analytical model to predict conductor response in extreme wind. The significant improvement includes determination of peak factors from upcrossing rates, refinement in the expression for background response and determination of conductor aerodynamic damping ratios from field data.