Audible noise of hybrid AC/DC overhead lines: Comparison of different prediction methods and conductor arrangements

The concept of partial conversion of existing tower phase arrangements to hybrid HVAC/HVDC overhead lines has become an attractive solution to meet the demand for higher power transmission capacity. Due to mutual AC/DC coupling effects, corona phenomena such as audible noise can be affected and have thus to be predicted accurately. In this paper, existing empirical equations are used to predict corona audible noise for several hybrid AC/DC tower geometries and conductor arrangement scenarios. For some of the examined conductor arrangements, the surface gradient on the AC conductor is significantly affected by a DC bias from an adjacent pole, leading to a possible increase in audible noise. Furthermore, for some of the investigated scenarios, very high surface gradients on the DC conductors occur, resulting in remarkable DC fair and even foul weather audible noise levels. Large deviations between different prediction methods are observed and discussed. Depending on the conductor arrangement, the foul weather DC audible cannot be neglected for hybrid towers and contributes to the AC noise.