Análise da medição de resistência de aterramento da malha de terra de uma subestação 69 - 13,8 kV energizada

Abstract

Effective grounding systems are vital to ensure the safety, reliability, and quality of electrical systems. In the context of substations, the ground grid is fundamental for protecting people from fatal accidents and preventing equipment damage during system faults. For this reason, the periodic measurement of grounding resistance is essential for the safety of people and the reliability of the electrical system, as it allows for the identification of system degradation before it compromises safety during a fault. However, the need to de-energize the installation to perform conventional tests generates high costs and operational impacts, which justifies the search for alternative methods applicable to systems in operation. The challenge intensifies in substations with restricted physical space, where the application of traditional techniques is impractical. The objective of this work is, therefore, to analyze the critical points of methodology and safety when applying the low-current, high-frequency injection technique to measure the grounding resistance of an energized 69 - 13.8 kV substation owned by a power utility company, under energized and restricted space conditions. The methodology consisted of a review of the technical literature and standards ABNT NBR 15749 and NBR 15751, in addition to a practical and quantitative case study at the subject electrical substation. The low-current, high-frequency injection method was applied with the positioning of the electrodes according to the physical limitations of the site. The results demonstrated the technical effectiveness of the method, obtaining consistent and non-discrepant grounding resistance values. It is concluded that the method is a viable and safe alternative, provided that its application is conditioned on two main factors: the adaptation of the field methodology to the site constraints and the rigorous implementation of safety protocols, such as a Preliminary Risk Analysis (PRA) and the proper use of personal protective equipment (PPE) and collective protective equipment (CPE).