OVERHEAD POWER LINE EQUIPMENT SELECTION

Published: 25th March 2009
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Before any overhead power line can be implemented a thorough investigation and study must be carried out to ensure that the most practical route is selected. The overhead line equipment plays a vital part in the selection of route, both pole mounted transformers and high voltage insulators are all determining factors. Maps are developed in order to identify the avoidance and exclusion areas and other requirements before the project can begin. Once final route selection has been agreed the utility poles have to be selected. The determining factor for wooden pole choice comes down to weight. The wooden poles are either free standing or furnished with pole mounted power transformers and hardware including an overhead line clamp.



Line hardware is seen as the most complex part of any design. Pole line hardware for overhead lines can be separated into conductor related hardware and structure related hardware. For the majority of overhead lines the conductor may form the most expensive single component of investment but at the same time the most exposed, dangerous and easily damaged. To ensure that the installation of the overhead line is proper and secure overhead line clamps are essential.



One of the key parts in any line is the tension clamp. The tension clamp essentially carries out what its name suggests and draws the overhead line conductor until there is sufficient tension and sag (height from ground to conductor). There are numerous different types of overhead line equipment from compression to automatic all of which will be chosen by engineers and project managers.



Once hardware has been chosen it is necessary to examine the insulation and insulator options.



There are two main types of high voltage insulators used on overhead power lines, suspension insulators and post insulators. Typically porcelain insulators are used for both a post insulator and a suspension insulator; there is also the option for glass insulators. Contamination considerations must be examined prior to installation. If an overhead power line is built near a coast, industrial area, desert, or at any other locales where airborne contaminants may build up on insulators, the problem of contamination induced flashovers must be considered. A layer of contaminants such as snow, rain, sand or fog can make the insulator more conductive and the creepage current along the surface of insulators will greatly increase. The orientation of the porcelain insulators has an effect on contamination performance. Suspension insulators or post insulators do not wash well in the rain due to the sheltering effects of the insulator skirts and contaminants will tend to stick and remain on the underside of the insulators. One way to compensate for this contamination which is inevitable is to increase the creep age or leakage distance of insulators. The creepage distance is the distance along the surface of the insulators from the top to the energised hardware, not including any metal such as insulator caps and pins.



Wooden utility poles, line hardware and porcelain insulators are the three main parts of any overhead power line and must be considered prior to project installation.



By Baron Turner of TurnerDow Website Optimisation on behalf of OTDS Power transformers, High Voltage Insulators and Pole Line Hardware. OTDS were established in 1978. Over the 30 years of business OTDS has specialized in the design, routing and supply of overhead line equipment.



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