Desgaste prematuro e falhas recorrentes em rolamentos de motores de indução alimentados por inversores: análise e proposta de solução

Abstract

This paper presents an assessment of the possible causes to premature faults in three-phase induction motors bearings when fed by inverters, based on a real study case. The preliminarily determined potential fault causes have been initially discussed on a theoretical basis and, subsequently, experimentally evaluated by means of collection and analysis of vibration data, stator current and common mode current/voltage. As a result of the investigation it was concluded that the presence of common mode currents in the levels verified may lead motor roller bearings to faults. Such diagnosis was confirmed during a shutdown of the machine caused by a new fault in its bearings. Afterwards, a comprehensive assessment was carried out comparing the different types of filters to minimize those currents, based on which the best alternative to implement a prototype was chosen. All simulationsand procedures for specifying filter size and constructive features are presented. Finally, after installing the filter to the referred to equipment, common mode measurements were carried out again and compared directly to those previously taken, thus showing that the filter used, characterized by a common mode transformer is enough to reduce both the peak value and the efficient value of the common mode current and, consequently, the undesirable related phenomena. The results from simulations and trials show that the common mode transformer represents a valuable alternative as compared to the conventional RL and RLC filters since, in addition to minimize the common mode phenomena, it dissipates a negligible amount of power.