Reporting false indications of startup analysis when diagnosing damper damages in synchronous motors

The analysis of the startup current has been recently revealed as an excellent informational source for the diagnosis of the rotor condition in electric motors. In induction machines, the analysis of such current may provide important advantages versus the classical method employed for rotor assessment (Motor Current Signature Analysis, MCSA), as the avoidance of eventual false indications obtained with the traditional approach or its suitability for any operating condition of the machine. In this context, the startup current analysis is increasingly employed to complement (or even to discard) the diagnostic conclusions obtained with MCSA. With regards to synchronous motors, the analysis of the startup current is also an interesting option to determine the condition of the damper cage. However, the investigation on this latter issue is still incipient and only circumscribed to particular geometries of the damper. The present paper analyses the suitability of the startup current analysis for assessing the condition of the damper cage in salient-pole synchronous motors. The interesting results show that, for these machines, due to the particular construction of the damper, false positive indications are obtained when relying on startup analysis. This important fact is of great interest to avoid false diagnostics in the field when assessing the condition of such elements.