Explaining the impact of conductor surface type on wet weather HVDC corona characteristics

• Root-cause analysis of wet weather HVDC corona characteristics is presented.
• Conductor surface structure influences size and distribution of water drops.
• Large water drops lead to surface instability corona mode (Taylor cone mode).
• Small water drops lead to pure corona mode.
• Mode type strongly affects loss current and audible noise of discharges.

Corona of HVDC overhead-lines is important in the planning of transmission corridors. Effects that need to be considered include corona losses (CL), audible-noise (AN), radio-interference (RI) and ground level ion currents. Water on conductor surfaces influences these quantities. It was previously shown that certain conductor surfaces lead to considerable reductions in wet weather CL. This publication studies the causes of these differences using optical methods. A key finding is that the size of water drops is decisive for differences in CL. Furthermore, different discharge mechanisms are shown to be the reason for differences in AN during and after rain showers.