Critérios de projeto de estruturas de linhas aéreas de transmissão em Minas Gerais

Abstract

This work presents a study of wind climatology in the state of Minas Gerais and the evaluation of the nonlinear geometric behavior of structures often used in overhead transmission lines (OHLs). For this purpose, a database was built with the wind speeds of the main national meteorological networks (INMET, ICEA, and INPE), which was treated to obtain consistent series of annual maximum speeds. This database is much broader than the one used in the elaboration of ABNT NBR 6123:1988 and ABNT NBR 5422:1985 standards. As recommended by IEC 60826:2017, the Generalized Extreme Values (GEV) distribution and the Inverse Distance Weight (IDW) interpolation method were used in the determination of extreme wind speed values and the mapping of isopleths for Minas Gerais, respectively. Besides the isopleths, a heat map was proposed, which allows a more precise determination of the basic wind speed value to be adopted as reference. The use of these maps is crucial in the development of structure designs and the speeds obtained from them were employed in the evaluation of the nonlinear geometric behavior of a typical suspension structure used in OHLs, when subjected to wind action. Numerical models contemplating the geometric nonlinearities present in the structural system (tower, insulators, and cables) were developed and allowed, after their processing, to evaluate the influence of these nonlinearities on the forces acting on the supporting structure. The results of the proposed complete model were compared with the results obtained through the analysis of an isolated tower, with external forces applied to the suspension point of the cables, a model frequently used in OHL design and recommended by the American standard ASCE 10-15. To quantify the influence of geometric nonlinearities on the system, different cable lengths, average wind speeds and unevenness between adjacent towers were evaluated. The understanding of the nonlinear behavior of the structural system allowed the identification of some standards and verification of the limits for which the simplifications proposed by the reference standards are acceptable. In other words, given the results obtained in this work, it was possible to establish practical criteria to be used by designers in the design of OHL structures.