Salam and hello everybody,
We are facing a problem in majority of our motors, where Rotor Bar Pass frequency appears in vibration spectra. In some cases, RBP Frequency has harmonics and sidebands as well which are spaced either at 1x line frequency or running speed. Moreover Line Frequency is also present in such cases. Amongst these motors some of them were running at high vibration i.e. 10 -15 mm/sec and main contributing peaks were Line frequency and RBP frequency. Upon our recommendations, the said motors were inspected thoroughly for rotor runout, gap b/w rotor and stator, winding condition, condition of rotor bars, unbalance of rotor etc. and no abnormality was found. In the end, the motors were installed back and are showing same vibration behavior as past. Moreover, current, voltage, line to line current and line to line voltage were also checked at rated load but all the readings were found within specified range. The electrical guys say that the motors are quite fine. But I am convinced that the problem is electrical related. But on the other hand, thorough inspection could not reveal any abnormality.
We have motor overhauling facility at our plant which was established one and a half year ago. I suspect that there is some common mistake that is occurring during overhaul of all motors. Because the history data of same motors does not show any indication of such electrical peaks and these peaks have started to appear after since the motors were overhauled at our plant site facility.
Can anybody suggest further checks?
Regards,
Yaser
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