| Induction motors are the most wide spread prime mover in industry. All condition monitoring is well managed by vibration signatures alone, including faulty bearings, electrical problems and faults like unbalance, misalignment etc. Nearly all the fault symptoms can be identified using a vibration spectrum in the low frequency range. The dominant electrical fault symptoms show up in the line frequency, 2 times the line frequency and as slip modulation around the rotational speed and the line frequency. The slot frequency and its harmonics and modulation are the only symptoms to be diagnosed from a vibration spectrum taken in the higher frequency range, but the same information can be measured from the supply current. Frequency analysis of the stator current is an easy way to detect broken rotor bars, since the current with the sideband modulation is the only major signal present in the spectrum. Moreover, unlike the vibration signal with a comparison to a reference signal, the current sideband modulation amplitude level is a direct indicator. ADVISOR is capable of combining both methods in a motor fault diagnosis. | | |
