Estudo de identificação e análise de superação de transformadores de corrente

Abstract

In Brazil, the quick evolution of the Electrical Power System (EPS), especially of the National Interconnected System (SIN), has caused a significant increase in electrical demands on the equipment of the facilities. In particular, the current transformer’s (CTs) are sensitive equipment and such changes should not lead to the transformer core saturation under high currents, such as those that develop during the occurrence of a fault in the system. This work aims to present, from a predefined procedure, the criteria for analysis of CTs overcoming and to develop an application to facilitate the evaluation’s process of these equipment. The effects of the CT core saturation were widely analyzed with the help of ATP (Alternative Transient Program), characterizing the impacts on the waveform of the current in the secondary. The identification techniques and analysis of overcoming of CTs according to the methodology indicated by the Nation Electric System Operator (ONS) are shown. These techniques are able to report the degree of compliance of the equipment to the point of installation, and support the theoretical basis for a possible decision-making. It is proposed a computational tool in Java programming language, called PROSUPER (Overcoming Analysis Program), in order to simplify the quantitative treatment of magnitudes analyzed by the system agents. This tool makes possible the evaluation of CT under aspects of supportability of symmetrical and asymmetrical current and performance verification. A case study was developed considering the electrical system of the Energy Company of Ceará (Coelce) to demonstrate the analysis. This study was presented in two approaches: first, the evaluation of overcoming was performed with the exposure of equations established in theory, in the second, the analysis was performed from PROSUPER, and the results were compared to validate the developed application. It was verified that the fault current asymmetry is a decisive factor in the analysis of CTs overcoming and that, depending on the X/R ratio at the point of fault, the CT may enter into saturation for short-circuit currents under 20 times the nominal current.