The objective of this work is to demonstrate the benefits of predictive maintenance, in particular the analysis of insulating oil of power transformers, to prevent material losses and damages in a steel industry. For its development, initially, a bibliographic review was carried out on the types of transformers, maintenance and, more specifically, the methods for interpreting insulating oil analysis (DGA – dissolved gases analysus). Based on this, two case studies were presented. Real cases of transformer failure were addressed, in which they used oil analysis, more precisely, the concentration of dissolved gases, to determine the diagnosis, as well as an analysis of costs and production losses related to each case. The first case concerns a 6MVA transformer that was replaced due to internal deterioration caused by the accumulation of gases, which generated overheating of the active part of the transformer and damaged it, leaving the equipment inoperative. In the second case, the study presents a 75MVA transformer that unexpectedly failed with a high acetylene level. In this scenario, it was not turned on again before carrying out diagnostics to identify the possible defect, which revealed the loss of the equipment. For each case, the results of oil analyzes were used, that is, the concentration of combustible gases, to determine the cause of the failure, with the aid of the most used methods in the industry. Furthermore, for each situation, the cost involved was estimated, considering
material damage and loss of production, highlighting the benefit of good planning and execution of maintenance on transformers.
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