Transient-based rotor cage assessment in induction motors operating with soft-starters

The reliable assessment of the rotor condition in induction motors is a matter of increasing concern in industry. Though rotor damages are more likely in line-started motors operating under high inertias, some cases of broken rotor bars in motors supplied via soft-starters have been also reported in the industry. Motor Current Signature Analysis (MCSA) is the most widely spread approach to diagnose such failures. However, its serious drawbacks in many real industrial applications have encouraged the investigation on alternative methods enhancing the reliability of the diagnosis. This paper extends a recently introduced diagnosis methodology relying on the start-up current analysis to the case of soft-starter-operated motors. The approach has proven to provide very satisfactory results, even in cases where the classical MCSA does not lead to correct diagnosis conclusions. However, its extension to operation under soft-starters was still a pending issue. The experimental results shown in this paper ratify the validity of the proposed diagnosis approach in soft-starter-operated induction motors.