INFLUENCE OF BUNDLE CONDUCTORS IN UHV AC TRANSMISSION LINESThis work presents research methodologies that enables to understand the influence of bundle sub conductors in ultra-high voltage (UHV) AC transmission lines upon electric fields. It has as main objectives the evaluation of sensitivity of surface gradient potential (SGP) of overhead line conductors, critical analysis of the main analytical and numerical existing methods to quantify SGP distribution, and the study of electromagnetic modeling of transmission lines, regarding power frequency, carried out using Maxwell's equations. Therefore, it is performed a large-scale simulation of a case study of a 1000 kV AC line, taking into account different bundle spacing and different bundle arrangements. To each one of these configurations, the average and maximum SGP of each conductor are calculated by Successive Images method. The simulations consider the simplified transmission line model, reducing the problem into two dimensions. It is observed that the maximum and average values increase when bundle spacing increases. Nevertheless, it is found that the percentage change in gradient is not as significant as compared to the spacing between sub conductors. In addition to that, it is seen that gradient distribution on sub conductors is non-uniform. It is noteworthy that only 8 and 10 sub conductor' arrangements meet the critical gradients for visual corona. The results of this research indicate that gradient distribution is sensitive to conductor spacing and to the geometry of the bundle arrangements. The latter being the more influential. The numerical method applied to the case study showed good accuracy for transmission lines with multiple bundle conductors. Finally, it is recommended to evaluate the influence of different conductors on UHV AC transmission lines performance and it is suggested the use of numerical methods based on lumped parameters (e.g. finite elements) to better evaluate critical parameters which are ignored by transmission line simplified model, like conductor sag and proximity to towers.