Metodologia e análise de desempenho na tecnologia de coleta de corrente em máquinas elétricas : estudo de caso em um acionamento ferroviário

Abstract

Within the scope of rotating electrical machines, even today, the current collection, whether in commutators or slip rings, is very common. The conditions for the application of this technique, presumably expensive, laborious and therefore obsolete, dictate the performance, lifespan, occurrence of failures, the amount and cost of maintenance of the various equipment that use this technology. Due to the bad reputation and, especially, because of its interdisciplinary, current collection technical specificities were, in a way, relegated to oblivion, resulting in a knowledge gap. This work investigates the interaction among and not between dimensional geometry, environmental conditions and physical-chemical properties, which, under the influence of electrical, magnetic, mechanical, chemical and thermal aspects, determine the behavior of the brushes contact with the track in the process of collecting current from brushed rotating electrical machines. Initially, we present a literature review focused on the macroscopic aspects of the phenomenon, explaining the empirical recommendations that contribute to the proper functioning of the equipment. Next, from a micro perspective, a brief investigation of wear mechanisms is developed, relating them to the recommendations presented above. The work also presents a case study of a direct current (dc) railway machine, that had been operating with abnormal wear on the commutator. The tribological performance of the dry contact was investigated as a function of the brush material, the implemented spring pressure, the operating current and other relevant variables. The problem was mitigated by changing the material of the brushes and the stiffness of the springs. However, in order to avoid failures in operation, an experimental bench test with the measurement of force and temperature in the contact. At the end, using several techniques, including scanning electron microscopy, the contact face of the brushes submitted to the test was inspected, concluding about the copper deposition to the face.