The Influence of Altitude on A-Weighted Sound Level and Noise Spectrum for Unipolar HVDC Transmission Lines

The audible noise (AN) of HVDC transmission line at high altitude area is the key factor to determine the conductor type. However, the research on the AN of unipolar HVDC transmission lines is relatively lacking at present. In this paper, three DC test lines with an altitude of 1700 m – 4300 m were used to carry out AN tests of unipolar DC transmission lines under different conductor surface electric field strengths, and the influence of altitude on A-weighted sound level and noise spectral characteristics of unipolar DC transmission lines were obtained. The research results show that, the A-weighted sound level of unipolar DC transmission lines presents a nonlinear trend of change. When the conductor surface electric field strength is larger, the nonlinear law is more obvious. In addition, the frequency range of corona noise is mainly concentrated in the frequency band above 1000 Hz. With the increase of frequency, the corona noise shows a trend of gradually increasing first and then decreasing.