Modelagem matemática aplicada ao diagnóstico de falha de componentes elétricos de subestação

Abstract

Electrical components maintenance in power substations is a fundamental part in the search for greater efficiency within the national electric power system. As the wear of electrical equipment is normally followed by changes in its operating temperature, infrared thermography is currently the most used technique for monitoring assets condition in substations. However, the lack of knowledge of physical principles involved and interferences associated with measurement process often leads to the misuse of thermography and the non-use of its potential. In this work, mathematical models were developed in order to describe the heating and cooling process of electrical connectors and switchgears under typical operating conditions of these components in an unsheltered power substations environment. The validation of these models was performed from a battery of laboratory tests, wind tunnel and outdoor environment, including, in the latter case, solar radiation effects on test samples. Theoretical results of the models were used to evaluate influence factors on measurements, and also the best moment to perform thermographic inspections in order to minimize such interferences. Furthermore, a theoretical thermal response of electrical connectors and switchgears was investigated after implementing an annual historical load, obtained from an operational database of a substation CEMIG. These simulations in transient regime allowed the evaluation of mechanical resistance loss mechanism in conductors within electrical connections over several years of operation; and to switchgears, the formation process and growth of oxide layer on metal interfaces in touch. The results showed that conductors strength loss on a new connection is not significant in the first year of operation, but can be significant in following years, requiring a continuous monitoring. The growth of the oxide layer on the contacts in switchgears is not a critical mechanism that increases electrical resistance under normal operating conditions, however for currents close to nominal value, the phenomenon significantly influences electrical contact failure.