Natural Aging of Non-Energized Aluminum Conductors
This paper reports the results of a photographic and electrical study of the mechanism by which a new aluminum conductor ages. A systematic approach of monitoring the aging process revealed the movement of water drop location from the top of a new conductor to the bottom of an aged conductor. Through photographic water drop analysis and electrical test results it has been determined that an aluminum conductor, even though not energized, is essentially aged in 4 to 7 months in the environment of northern Indiana, USA. A seasonal effect was found to add up to 5 months to this period.
Potential reduction of audible noise from new and aged overhead transmission line conductors by increasing their hydrophilicity
In the context of audible noise from high voltage overhead lines, an increase of hydrophilicity is frequently suggested in literature as a means to reduce A-weighted noise emissions. Laboratory tests with hydrophilic coatings of new conductors within the project CONOR (a consortium formed by utilities from Austria, Germany and Switzerland, a Swiss authority and further institutions) executed at the authors’ institute showed very promising results, especially concerning the reduction of the humming component of audible noise. Hence it was desirable to evaluate hydrophilic coatings as noise-reducing remedies on operational high voltage lines, especially with a view to clarifying the importance of conductor ageing, which was not tested in the previous laboratory experiments. Indeed, the beneficial effects of conductor surface ageing with respect to corona have been known for over half a century. But as the impact of conductor ageing compared to hydrophilic coatings on audible noise was unknown, field tests with the coatings have been initiated on overhead lines with well aged cables. A first opportunity to do this offered itself with a line crossing the Swiss Alps with conductors aged well over 50 years. The measurements of the field test revealed not only low noise levels for the coated span but also low levels of the uncoated section of the line. Temporary deenergisation of the line permitted one more access to the conductors themselves so that their hydrophilicity could be assessed: The wettability was found to be fairly good on the treated as well as on the untreated conductors. The increase of hydrophilicity of the conductor cables resulting from ageing proved to be high. A second field test in a rural environment of southern Germany on a line with conductor cables of about 20 years of age supports the findings of the first field test that the coating of aged cables does not noticeably reduce audible noise emissions. Even though artificial ageing of conductors at the manufacturing stage is suggested in literature, a viable method has not yet been given. But other methods to increase the hydrophilicity of new cables, such as sandblasting, are conceivable as well. This method was applied in connection with a refit of a line to different conductor bundles by one of the project partners. In the case of low surface gradients the results show a clear reduction of the audible noise emissions compared to reference lines with the same conductor bundles and new conductor cables which had not been sandblasted. The presented findings indicate that the hydrophilic coating of a well aged conductor will in general be superfluous, while the coating or other surface treatment of new conductors – for refit or a new line – can be recommended to bring about a noise performance comparable to that of aged conductors.
Prediction of net pressure on pressure equalized cavities
Abstract A numerical model has been developed for prediction of net pressure on pressure equalized cavities. The results based on this model show good agreement with those obtained from mock-up tests. Parametric studies verify that reductions in cladding load are possible, with proper design of curtain walls.