Cacilda de Jesus Ribeiro

Power transformer disruptions- a case study

The article presents an analysis over an operational period of 33 years of 34.5-kV through 230-kV mineral-oil-filled power transformers that have been removed from service because of faults and defects.

Method for the evaluation and classification of power transformer insulating oil based on physicochemical analyses

Power transformers are strategically important assets in the electric power system, because they enable electricity to be transmitted over long distances, with low power losses and voltage drops. Failures of these devices can cause unscheduled interruptions in the supply of electricity, resulting in major disruptions, impaired image of the companies responsible, including penalties imposed by the regulatory agency, and in worst case scenarios, irreparable breakdown of these assets. In this context, the degradation of the insulation system in a power transformer is one of the main causes of problems, which if not properly investigated and/or monitored, can lead to its forced removal from operation [1].

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 transformers 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 Goiás, 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

Metrics for partial discharge detection by the acoustic emission technique to support decision-making

The identification of metrics or ranges of parameters for the detection of partial discharges by the acoustic emission method for the diagnosis and/or classification of power transformers according to their state is essential to support decisions about equipment stoppages at the proper time, i.e., before a failure occurs. This paper discusses these parameters based on the analyses of several field trials, using an algorithm to generate decision trees, as well as a case study to validate the methodology, which was successfully applied in preventive maintenance.

A mathematical contribution to the analysis of moisture migration in power transformer oil-paper insulation systems

This paper proposes mathematical models of moisture in paper-oil insulation systems for use in power transformers. This work is important because it helps shed light on the phenomenon of moisture migration in power transformer insulation systems, and also serves as a tool to underpin decisions by maintenance engineers in response to the occurrence of phenomena that may impair the performance of transformers. The methodology involves the use of computational intelligence tools and the finite difference method. The paper concludes with the description of a case study.

Rede Bayesiana Para Estimação De Falhas Incipientes Em Transformadores De Potência Utilizando Detecção De Descargas Parciais Por Emissão Acústica

De fundamental importância para a transmissão e distribuição de energia elétrica, os transformadores de potência são equipamentos de custo elevado. Durante sua operação, podem surgir defeitos em sua isolação, provocando uma diminuição de sua capacidade dielétrica. Segundo [1], a diminuição desta capacidade pode provocar o surgimento de descargas parciais (DPs) dentro do transformador de forma inesperada e de difícil detecção. Detectar defeitos incipientes de funcionamento nesses transformadores é de interesse econômico e operacional, uma vez que permite intervenções preventivas que evitem danos graves ao transformador o que, por conseqüência, garante maior continuidade e elevam a confiabilidade do fornecimento de energia elétrica aos – cada vez mais exigentes – consumidores.