The Altitude Effect and Correction of Audible Noise for HVdc Transmission Lines

Audible noise (AN) is very important for the construction of transmission lines for the sake of the environment. Especially, at high-altitude areas, it has become a key technical factor deciding conductor types and tower structures. In order to determine the altitude effect and the correction of AN for HVdc transmission lines, four reduced-scale test lines with the same parameters were built up at elevations of 50, 1700, 3400, and 4300 m in China, respectively. Simultaneously, two full-scale test lines were set up in Beijing and Tibet, whose altitudes were 50 m and 4300 m, respectively. Using the test facilities, the AN of HVdc transmission lines had been measured for a four-year period, from January 2010 to July 2014. Through a statistical analysis of a large amount of data, AN characteristics of HVdc transmission lines at different altitudes are obtained. By comparing the statistical results from different altitude areas, it is found that AN of HVdc transmission lines is nonlinearly dependent on altitude. Finally, an AN altitude correction formula of HVdc transmission lines is proposed. It shows that from 0 to 4300 m, the AN correction value of HVdc lines is far less than the predicted value by an HVac method.