Rotor Bar Crack in Cooler Fan
Vibration analysis indicated a rotor bar crack, confirmed by MCSA and inspection. The motor was replaced, reducing vibrations from 2.6 to 1.4 mm/s (RMS).
Observation: Vibrations readings found normal, but vibration spectrum and time
waveform is indicating 1X harmonics with PPF sidebands and beatings in timewavform
with PPF.
As per above spectrum and TWF suspected rotor bar crack. For confirmation
conducted MCSA.
MCSA Severity chart: dB difference: > 60: Excellent, 54-60: Good, < 48-54: Moderate,
42-48: Cracked bars, 36-42, broken rotor bar, 30-36: Multiple cracks, <30: severe rotor faults.
Observation:
Difference in dB level is 23 in MCSA, which is indicating severe rotor bar crack.
Recommendation: In view of the above diagnosis, it is recommended to replace the motor and check the
Motor for rotor bars defect.
Findings after inspection: Inspected motor on 2.2.23 and observed Cracks on Rotor.
Observations: dB difference is 54, indicating heathy rotor condition.
Conclusion:
1. Spectrum and TWF indicating 1X harmonics with PPF sidebands, suspected rotor defect.
2. MCSA done found 23 dB difference, confirmed rotor defects.
3. Inspected Motor rotor found rotor crack.
4. Replaced the motor.
5. Motor vibrations reduced from 2.6 to 1.4 mm/s (RMS).
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