Interaction of Surface Gradient, Precipitation Rate and Conductor Surface Treatment on Corona Induced Audible Noise of AC Overhead Transmission Lines

Overhead Transmission lines are prone to emit audible noises under foul weather conditions (e.g. rain or fog), which can be a significant source of annoyance for people living close to the line. Apart from mere fulfilment of emission limits given by legislature, transmission system operators nowadays often seek to reduce audible noise emissions as far as possible to minimize public opposition towards overhead lines. A very promising approach for the reduction of audible noise emissions are hydrophilic conductor surface treatments, which influence the way water drops form on the conductors. However, very little is known about the operating behavior and limitations of hydrophilic conductors. This contribution therefore strives to illustrate how the electric field intensity around the conductors (surface gradient) and the precipitation rate affect the effectiveness and the emission behavior of hydrophilic conductors compared to standard conductors. The presented results are derived from a newly developed prediction model, which is based on noise emission measurements performed on 25 different bundle conductor arrangements carried out in an acoustically optimized high voltage laboratory. The compiled results indicate that hydrophilic surfaces can provide significant noise reductions, which tend to diminish with increasing surface gradient. Above a certain point of intersection, hydrophilic conductors exhibit higher emission levels than standard conductors. Since this behavior has been observed to depend strongly on the bundle conductor geometry, results for various numbers of sub-conductors and sub-conductor diameters are presented. From a practical point of view, this contribution shall raise awareness regarding the optimal utilization of hydrophilic conductors by illustrating the principal correlations and by providing first guidelines.