In order to build UHV AC transmission lines at high altitudes, it is
necessary to analyze the audible noise characteristics of the existing
EHV transmission lines at high altitude areas to guide the design. The
typical test data of audible noise for 750 kV single circuit
transmission lines measured at the Guanting long-term observation
station, located at an altitude of 1854 m, were collected. Two methods
of sorting the test data of audible noise and extracting valid data were
given. Then the levels of audible noise under different weather
conditions were analyzed, which showed that audible noise was raised
with the increase of instantaneous rainfall and snowfall. Typical
frequency spectrums of audible noise under different weather were also
obtained, the pure tone at 100 Hz was more prominent under rainy and
snowy weather, and the pure tone oscillation attenuated at different
positions. Audible noise at different locations presented the better
attenuation characteristics with the increase of distance during rainy
days. The statistical results and calculated difference of audible noise
over 5.5 hours with continuous rainfall were obtained. For the quiet
plateau areas, the calculated difference between audible noise during
rainy days and fair weather can be taken as 25 dB.