Abstract
Corona induced audible noise emitted by overhead lines is known to be a serious environmental issue, which also influences public acceptance of overhead line projects. In the case of AC overhead lines, this phenomenon mostly occurs during foul weather (e.g., rain, snow, fog). To be able to estimate the corona noise emitted by a planned overhead line, empirical prediction models were already developed in the 1970s. These models are based on measurement results of several outdoor test lines, which were then extrapolated to different conductor bundle geometries. The developed prediction formulas have proven their validity many times in the past and are still widely used today. More recently, however, several weaknesses have become apparent, most notably in accounting for the influence of the rain rate and for hydrophilic conductor surface treatments, which are now increasingly used to reduce corona noise. Additionally, precipitation events with very low rain rates (such as fog and mist) are covered poorly by existing formulas. While the quality of the existing models is certainly impressive, particularly given their age and breadth of parameters covered, it is questionable whether their accuracy is sufficient in light of increasingly stringent noise limits and the changing climate. These shortcomings were recently observed in a newly installed overhead line. Noise predictions had indicated that no issues were to be expected for this line. In reality, however, a number of complaints were led shortly after the first energization, particularly at very low rainfall rates. This contribution discusses how this particular problem was analysed and subsequently solved. To gain a deeper insight into the noise emission behaviour of conductor (bundles) with treated as well as untreated conductors at different rain rates, two different experimental approaches were pursued. On the one hand, the overhead line in question was equipped with sensors for long-term measurement of the climatic conditions and the occurring noise levels. In particular, a disdrometer was used, which allowed a detailed characterization of the precipitation. On the other hand, tests were carried out in an acoustically optimized high-voltage laboratory under controlled conditions. The aim of the tests was to check the validity of existing audible noise prediction models under different climatic conditions. Due to the observed phenomena, very low precipitation rates were the focus of the investigations. Additionally, the tests should also help to gain a better understanding of the operating behaviour of hydrophilic conductors. Hereby, the aim is to ensure the optimisation of noise reduction as far as reasonably practical to mitigate future third-party disturbance. The measurements carried out on the overhead line as well as the laboratory tests clearly indicate that the noise levels occurring at very low rain rates can be higher than those occurring at medium rain rates. Additionally, the results collected conclusively show that surface treatments can indeed provide significant noise reduction. However, it was found that the noise reduction potential decreases with increasing conductor surface gradient. Regarding the validity of existing prediction models, it was observed that although they provide a consistent trend regarding the expected noise level, their results mostly lie between the measurement results for untreated and treated conductors. The noise levels occurring at very low rainfall rates are consistently underestimated in existing models and thus insufficiently covered in the prediction. The experience shared in this contribution is intended to show how various measurements can help to improve prediction accuracy. From a theoretical point of view, the shortcomings of existing models are addressed. From a practical point of view, this contribution shall raise awareness regarding corona induced audible noise at very low rain rates as well as the optimal utilization of hydrophilic conductors.
Original language | English |
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Pages (from-to) | 1-16 |
Number of pages | 16 |
Journal | CIGRE Science and Engineering |
Volume | 35 |
Publication status | Published - Dec 2024 |
Keywords
- Audible Noise
- Conductor Audible Noise
- Corona
- Disdrometer
- Hydrophilic
- overhead Lines
- Rain Rate
- Surface Treatment
ASJC Scopus subject areas
- Control and Systems Engineering
- Renewable Energy, Sustainability and the Environment
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering