Assessment of overvoltages on medium voltage circuits of hybrid overhead lines due to direct lightning strikes

• Autor(a) principal: Moraes, Luana Batista
• Data de Publicação: 2024
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Biblioteca Digital de Teses e Dissertações da USP
• Texto Completo: https://www.teses.usp.br/teses/disponiveis/106/106134/tde-24062024-174839/
• topic: descargas atmosféricas diretas; desempenho frente a descargas atmosféricas; direct strokes; distribution lines; electromagnetic transients; hybrid overhead lines; lightning overvoltages; lightning performance; linhas aéreas híbridas; linhas de distribuição; measurements; medições; modelo reduzido; scale models; sobretensões atmosféricas; transitórios eletromagnéticos

The continuous population growth in large cities has become an obstacle in constructing new distribution lines due to the limitations of available space. To address this concern, the construction of hybrid overhead lines, which are overhead lines composed of sub-transmission and distribution circuits, has been seen as a viable solution. However, despite the advantages, few studies have been devoted to the lightning performance analysis of this type of line. This Ph.D. Dissertation analyzes surges caused by direct lightning strokes to a hybrid overhead line composed of 138 kV, 13.8 kV, and 220 V circuits, primarily focusing on the medium voltage (MV) line overvoltages. Specific models for the transmission towers and high-voltage (HV) insulators were validated through tests and simulations. A reduced-scale model of a section of four spans of an actual hybrid overhead line was developed and deployed. Currents were injected at the top of the central tower, and voltages were measured at different points along the tower and on the HV and MV circuits. Comparisons between measured and calculated (using the EMTP) results were performed on this line type for the first time. The deviations between the peak voltages measured and calculated absolute values varied from 1.2% to 16%. The results indicated the adequacy of the models used in the EMTP simulations and in the reduced-scale system. In addition to analyzing the overvoltages on the MV circuit and their dependence on the main parameters, critical currents were also calculated for different combinations of soil resistivity and ground impulse impedance. The analysis confirms the excellent lightning performance of the hybrid overhead line, even for the most challenging conditions considered in the study.