Vibrations, currents and stray flux signals to asses induction motors rotor conditions

Rotor-Bar Breakage Mechanism and Prognosis in an Induction Motor

“…In this work, the state vector xk is composed by two variables, one discrete signaling the state of the bar and the other continuous evaluating a defect's indicator value (8). For the first one, four states are defined, according to [28]: healthy ("1"), which in this case also includes the compensation stage; hot spots ("2"), breaking ("3") and broken bar ("4").…”

“…The diagnosis of rotor asymmetries has been a subject of detailed study in the last years, applying, in order to detect it, a wide battery of signal processing methods to magnitudes such as vibrations [8], voltages [9], flux and currents [7]; prevailing the techniques belonging to this later group due to their effectiveness and easy application, especially the ones that use the decomposition in frequency of the current waveform, known as Motor Current Signature Analysis (MCSA), which are of widespread use in the industry.…”

Vibration Transient Detection of Broken Rotor Bars by PSH Sidebands

“…The negative sequence component of the magnetic flux wave caused by a rotor broken bar produces a torque ripple at frequency 2sf, which modulates the main harmonics existing in the vibration spectrum. Such modulation is a clear sign of the presence of this fault [4].…”

“…where p is the number of pole pairs, s is the slip, is the supply frequency in rad/s, n 3 -n 7 are integers denoting the different harmonic order and is the peak magnetomotive force for the harmonic of order n 3 , n 4 .…”

“…In general, during a direct startup several of these PSH can be detected. In addition, throughout such a direct startup, the currents in the induction motor can be multiplied six times from the usual levels for stationary full load operation, and the frequency swept of the components may cross mechanical resonant regions [4], enhancing the asymmetry effects and facilitating detection.…”