Effect of Coatings on the Audible Noise of DC Corona Discharge and Its Mechanism

The rapid development of ultra-high voltage (UHV) transmission technology is playing key role in achieving China's goal of 'carbon neutrality'. Audible noise (AN) from transmission lines is gradually becoming one of the key concerns for OHL design. This article investigates AN emission under rainy and fogy conditions, when water droplets form on the surface of the overhead line (OHL) conductors which maximises the corona discharges. The experimental results have shown that the sound pressure level (SPL) varies significantly between positive and negative polarity. For the tested conductor sample, both hydrophilic and hydrophobic coatings suppress its corona discharge and AN level, in which the superhydrophilic coating achieved the best SPL reduction compared to the superhydrophobic coating and hydrophobic coating. The relationship between corona current and AN is further studied from the cage experiment. A model is proposed to estimate the SPL using corona current values. The calculation results show that the SPL of AN is approximately logarithmic function of corona current, and the verification test results show that the calculation error of the model in this paper is between 2-3%, which verifies the accuracy of the proposed method.