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Outdoor Investigation of the Corona Characteristics and Audible Noise of a Hybrid AC/DC Overhead Line

Electric utilities are looking for novel methods to increase the transmission capacity of existing transmission lines. The conversion of conventional AC towers to hybrid AC/DC lines allows for significantly more power and reduces the need for new rights of way. Still, due to the fixed geometry, there will be coupling effects between the AC and DC systems. Corona effects, such as audible noise, which are crucial for public acceptance, must be controlled to obtain crucial public acceptance. An outdoor test setup is used to investigate the corona audible noise and partial discharges of parallel AC and DC bundles. The effect of a DC bias on the AC corona as well as an AC ripple on DC corona are studied for varying surface gradients and weather conditions. The AC and DC audible noise clearly increased for most cases of a DC bias or AC ripple, respectively. The relative increase was found higher if the conductor was only slightly above corona as it happens in dry conditions with light pollution. Still, the highest level of AC audible noise was observed during wet weather and for DC during dry conditions.