Ac induction motor - vibration analysis

[shaiab]

Hello!

I want to ask about spectrum of ac induction motor, first of all, we measure points at non drive end + drive end - radial+axial direction.

At horizontal direction we measure not only velocity but also acceleration. Two questions:

1. I see a peak around 65000 rpm with sidebands at running speed (1500 rpm), I suspect it not a bearings failure but as electrical problem.


2. Here, too, I guess it electrical problem – suddenly the g' of the motor jumping and characterized by high peak around the 160000 – 200000 rpm, also with sidebands but at line frequency relative to motor running speed. For example, motor running speed is 1490 rpm the sidebands will be close to 6000 rpm. Even in case the motor has VFD (motor 3000 rpm 50-60Hz) and the running speed is close to 3600 so the sidebands will be 7200 rpm . Sometimes, it supported at the velocity spectrum by high harmonics at line frequency (6000 rpm).



I hope you're familiar to these problems and can tell me ''recommended action'' to prevent or reair it.

 

[itsmoked]

Is this motor unloaded?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[shaiab]

Hi,

The motor is under load, this is a routine vibration measurements.

 

[electricpete]

As long as you don't see pole pass sidebands (using high res spectrum) or high 2*LF, I don't think you're seeing any "electrical problem". The source of the vibration may well be a product of magnetic forces. There are sometimes complicated patterns generated by slot harmonics. Usually the 2*LF sideband you mention but sometimes for whatever reason it shows as 1x sidebands. I don't worry about it as long as I can confidently rule out mechanical problem or bearing defect pattern.

=====================================
(2B)+(2B)' ?

 

[shaiab]

Hello again!
thank you for the direct answer. i want you to know that sometimes the trend jumping twice or more. i just want to know when it severe(high value of g) and when the client have to know about it + what he have to do or check.Its Ok to recommend him to check consistency between the phase currents? or to take out the engine for inspection and repair?
thank's .