Faults and defects in power transformers - a case study

Power transformers play a fundamental role in electrical power systems, in addition to representing significant investments involved in the implementation of these systems. To reduce the costs associated with a transformer´s life cycle and to guarantee its reliability and durability, it is essential to monitor its operating conditions, its insulation system, and the working conditions of its accessories and other components. Therefore, the aim of this work is to study the faults and defects that occurred in 34.5 kV, 69 kV, 138 kV, and 230 kV oil-immersed power transformers of the electrical system and the insulation system of CELG, a major electric energy concessionaire in the state of Goias, Brazil. The results of this study, i.e., the efficacy of the predictive technique for maintenance over the last 28 years (from 1979 to 2007), the characterization of faults and defects during this period, and the presentation of proposals for improvements in the predictive technique, aimed at reducing the number of stoppages in the electric power supply system, are expected to contribute to the body of knowledge in this field.