HVDC Corona Current Characteristics and Audible Noise During Wet Weather Transitions

For the connection of remote energy sources, HVDC offers higher efficiency and flexibility compared to conventional HVAC. As the acceptance for overhead lines in Europe is often low, the detailed understanding of its environmental effects, such as audible noise is of crucial importance. Still, only few experimental studies have investigated HVDC corona. Recent publications have demonstrated, that existing prediction models for DC audible noise show strong deviations when extrapolated for higher surface gradients. While audible noise is considered negligible in rain, research has shown that the discharge amplitudes increase significantly during transitions from dry to wet weather and vice-versa. In this study, the corona current and audible noise are investigated for a large range of surface gradients and rain rates. A special focus is set on the behavior during rain onset and dry-off. While the corona current increased during rain, the measured audible noise was significantly higher during the transitions before and after the steady state. The duration of these transition periods varied with rain rate and surface gradient. The observed effects are explained using corona pulse patterns and UV data. Compared to these measurements, existing audible noise prediction models were found to overestimate the sensitivity regarding the electric field.