Audible Noise and Corona Losses of DC Circuits on Hybrid Overhead Lines

Hybrid overhead lines (OHL) are a promising concept to increase transmission capacity without building new lines. Due to the small distance between the AC and DC circuits on a hybrid OHL, an AC ripple will be superimposed on the DC conductor surface gradients which influences audible noise (AN) and corona losses (CL). In this paper, calculations regarding capacitive and inductive coupling affecting the surface gradients of the DC circuit of a fictive Austrian 420 kV hybrid OHL are presented. Furthermore, AN measurements were carried out to investigate how an AC ripple affects AN of a DC circuit on hybrid OHL. The results show that the AC ripple increases AN, especially for positive DC polarities, and that the effectiveness of conductor surface treatments is reduced noticeably. Additionally, the gathered results were used to carry out AN and CL predictions for the analyzed Austrian OHL.