Wednesday, February 2, 2011

On Extra High Voltage Overhead Power Transmission Lines


Extra High Voltage(EHV) power transmission lines have to be overhead on considerations of economy and available technology. A lot of research and development has gone into the design of EHV line components; but a lot more need to be done to improve the reliability and reduce maintenance expenditure. Remember, the overhead lines, being aerial lines, are subject to the vagaries of weather like changing wind action, temperature variation, rain, snow, lightning etc. Also a transmission line is composed of heterogeneous materials of varying characteristics which respond differently to the forces of nature. All these make the field behavior of overhead lines complex.
We need to remember that whenever there is high wind the early structures to succumb to the fury of nature and become dysfunctional are the overhead power transmission lines, reminding us the need to carry out more R&D into the design and performance of EHV supports.
The EHV conductors are normally stranded for improved fatigue performance under vibratory forces of atmospheric origin. But they still require external damping devices. Research into conductor damping is relevant in this context since an ideal overhead conductor should be such as to kill vibration at the point of origin; evolving a conductor that has distributed damping to combat vibratory forces has to be given adequate consideration in EHV lines design.
Insulators which are interfaced between the earthed supports and live conductors are  not only subject to transmitted forces but are exposed to huge direct forces due to  lightning. About 30% of line failures are known to be due to insulator failures of lightning origin. The difficulty to provide continuity to the earth for the line supports contribute to the majority of lightning failures of insulators. Earthing of EHV lines also constitutes an important topic of R & D in EHV line practice.
An overhead line system with supports, insulators, conductors and accessories comes in the way of scenic beauty and is often an eyesore to the viewing public. Therefore, developing aesthetic design is a subject in itself. The best an overhead line designer can do is to make his line merge into the nature say, design supports which look like tall trees, avoid sky-lining of conductors and take the lines away from populated areas. Considerable R&D needs to be done in developing aesthetic EHV   line design. It may be desirable to have a multidisciplinary approach in design of aesthetic EHV overhead power lines.
The requisite data for a comprehensive line design is available in relevant technical literature. But I hasten to add that the ancient works like Rigveda also contain a lot of information which will supplement the data. It may be interesting to note that even the temple architecture in India are educative in this respect. I hope to add more in subsequent  articles.

1 comment:

  1. Increasingly, transmission lines with overhead line materials are routed through areas of poor ground conditions, often for reasons of amenity. This results in the need for the use of special, generally larger, foundations.

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