Long-term evaluation of HVDC transmission line audible noise and its correlation with background noise

The audible noise (AN) generated by corona discharge from a full-scale, high-voltage direct-current (HVDC) transmission line was evaluated over a one-year period from December 2017 to November 2018. The double bipolar HVDC transmission line using a metallic return conductor was demonstrated using a full-scale tower having a height of 21 m in Gochang, Korea. The measured AN in an outdoor environment was statistically evaluated and compared in different seasons and weather conditions. The A-weighted spectrum of the HVDC corona noise exhibited a greater distribution than the background noise above 1.0 kHz in the frequency domain. Various background noises were considered and eliminated to improve the measurement accuracy. The highest AN levels were exhibited during the spring season. Individuals in the age range of 18-60 years were randomly selected to conduct a human-perception test. The results indicated that 15% of the participants became aware of the AN from the corona discharge when it was >5 dBA greater than the background noise. The AN was <36 dBA when the conductor surface gradient was <18 kV/cm with a six-bundle sub-conductor.