Startup current analysis of incipient broken rotor bar in induction motors using high-resolution spectral analysis

This paper presents an experimental study of one broken-rotor-bar time-frequency evolution effects, when the bar is partially broken in an induction motor by gradually drilling one hole, each three millimeters, from healthy until the rotor bar is broken. The one phase current startup transient at each of three partially-broken conditions (0 mm, 3 mm, 6 mm and 10 mm) are analyzed, using the short-time multiple signal classification (MUSIC) method that provides a high-resolution and a time-frequency pseudo-representation of the signals, where fault-related frequencies and how they evolve in the time-frequency spectrum are obtained. Results show how the gradual drilling of one rotor bar produces a shifting in the fault frequencies as the defect increases. The sideband components around the supply frequency are shifted with respect to those from a healthy rotor bar condition obtaining a regular fault evolution from a healthy rotor bar until the bar is completely broken.