Evaluation of the detectability of rotor faults and eccentricities in induction motors via transient analysis of the stray flux

The stray flux that is present in the vicinity of an induction motor is a very interesting information source to detect several types of failures in these machines. The analysis of this quantity can be employed, in some cases, as a supportive tool to complement the diagnosis provided by other quantities. In other cases, when no other motor quantities are available, stray flux analysis can become one of the few alternatives to evaluate the motor condition. Its non-invasive nature, low cost and easy implementation makes it a very interesting option that requires further investigation. On the other hand, the analysis of transient quantities has been proven to be very useful for overcoming certain deficiencies of the classical steady-state-based methods while providing a reliable diagnosis of some failures. The basic idea of the transient analysis is to detect `patterns' or `signatures' caused by the transient evolutions of fault components by means of applying sophisticated signal processing tools. The aim of this work is to evaluate the suitability of the stray flux analysis during the startup transient as a way to detect certain faults in induction motors (broken rotor bars and eccentricities), even when these faults coexist in the motor. To this end, advanced signal processing tools will be applied. Several positions of the flux sensors are considered in this study. Also, for the first time, a fault indicator based on startup stray flux analysis is introduced and its sensitivity is compared versus other indicators relying on other quantities. It must be emphasized that, since the capture of the transient and steady-state flux signals can be carried out in the same measurement, the application of the approach presented in this work is straightforward and its derived information may become crucial for the diagnosis of some faults.