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Foul weather conditions can lead to corona discharges on high voltage overhead transmission lines which are perceivable as an audible broadband crackling and hissing noise. In such situations this noise is often accompanied by a humming noise at twice the mains frequency (2f).While the crackling and hissing noise component was widely investigated in the past, the 2f-component went largely uncommented. Only a scant amount of literature suggests mechanisms explaining the occurrence of this emission, but these suggestions are either vague or controversial.In this paper a mechanism analogous to that of ion loudspeakers is presented, which describes the sound levels of audible 2f-emissions from high voltage model lines quantitatively in a satisfactory manner. While the broadband component of corona noise emissions has its immediate origin in the discharges themselves, the 2f-emissions arise from the drift of ions left behind by the discharges. Due to collisions with gas molecules, these ions cause in the sum a rise of heat in and a force applying on the neutral gas, thus producing the 2f-emissions. Depending on the situation, both can give rise to contributions of similar magnitude. [ABSTRACT FROM AUTHOR]

In the case of ac high voltage overhead transmission lines, corona discharges may result in a broadband crackling and a humming noise at twice the mains frequency (2f). The computation of the emitted 2f-levels presupposes the knowledge of the apparent power and force passed by the ions to the gas in the surroundings of the conductors. In this paper a simulation determining these magnitudes used in a previous publication is presented. For that purpose the ideas of earlier publications by other authors to compute corona losses are followed. Their central idea is to define an onset field strength on the surface of the conductor which is not exceeded by injecting the right amount of charges in the vicinity of the conductor. This injection together with the recombination determines the amount of drifting ions. The novelty of the method applied in this work is the consideration of different onset field strengths over the conductor surface in dependence of the polar angle. Further 2f-force and 2f-power acting on the gas in the vicinity of the conductor are determined out of the resulting ion drift. The corona currents thus computed coincide fairly well with measured results. [ABSTRACT FROM AUTHOR]