Slip independent monitoring of wound-rotor induction machines

This paper deals with a time-scale method for stator and rotor incipient faults detection in wound-rotor induction machines. The initial study on the rotor incipient fault in induction machines consisted of the energy evaluation of a known low frequency bandwidth through time-scale analysis. It was shown that the stator current space vector magnitude (SCSVM) and the instantaneous magnitude of stator current (IMSC) are both good candidates to be used as an indicator for incipient rotor fault monitoring in the steady-state working condition of the induction machine. In this paper, it will be demonstrated that in the case of load fluctuation, there exists a time-varying dc component that may affect the energy criterion, resulting in a false alarm. Thus, a new technique based on a numerical phase lock loop (NPLL) is utilized to estimate and then remove this time-varying component before the SCSVM and IMSC energy calculations through time-scale analysis to handle this problem. Moreover, by definition of new frequency bandwidths associated with incipient stator fault in the rotor current signature, this technique can be extended to a more general slip independent incipient stator/rotor fault detection technique in wound-rotor induction machines. This proposal is validated through experimental tests based on a 10hp wound-rotor induction machine test-rig.