A probabilistic based application design guide for the use of tubular conductors in the design of high voltage substations.
Groenewald, Abraham Johannes Smit.
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The requirement for new and existing outdoor air insulated substations to support larger blocks of power in restricted spaces requires an investigation into new bus conductor systems. This study has considered the use of supported, as opposed to suspended, round tubular conductors that have high current capacity necessary for this purpose. The advantages are associated with the fact that smaller clearances are attainable as a result of the restriction of horizontal deflection under fault conditions, and vertical deflection under own weight (sag) due to the rigidity of the tubular conductors as long as the bus tube is correctly sized for the application. Since the tubes are sized for mechanical strength, they are generally oversized electrically, allowing greater flexibility in busbar configuration. Forces due to gravity, wind vibration, fault current and tubular conductor thermal expansion, as well as the restrictions on electromagnetic fields have been considered. The design criteria for conductor and insulator strength calculations also formed part of the study. The study was carried out in a step-by-step analysis of the above considerations. An Excel based programme was developed to analyse the sensitivity of conductor and insulator strength calculations, due to errors in the estimation of various parameters that are required for these calculations. The tolerances in manufacturing and deviations in experimental data were determined and used to evaluate the results obtained and provide a level of confidence that any errors that may arise could be mitigated against by choosing the correct components. The result of the study is a design guide that allows substation designers to develop tubular busbar systems that will operate successfully in the conditions they were designed for. The guide provides an integrated design approach with methods for calculating the forces to which rigid bus structures are subjected.