How to detect rotor bar damage on HVAC motors? I use the prism 4 software and i'm new to this kind of problem. Maybe, someone is knowledgeable about this prob, i need help. What to watch out and the level of vibration or peak that is critical?

You might watch out for:
pole pass sidebands around 1x and around harmonics of 1x
time-dependent vibration, increase over a few hours after startup
growling noise
oscillating ammeter reading
perhaps increasing slip under constant load

But none of the above is particularly conclusive. Pole pass sidebands around line frequency in the current spectrum above a threshhold level (approx 45db down) is the most effective check. Needs to be checked above 50% load and preferably above 75%

Thank you electricpete. Hope you have something or illustration for this kind of problem. It would be of great help. Most of our HVAC motors fail because of rotor bar problem and stator problem. So how can i determine if it is on stator or rotor problem?

A current spectrum will evaluate the rotor bars. Stator winding condition is best determined through more traditional testing (in my opinion) like hi-pot, megger, PI, etc. Epete can probably give you more detail on stator testing. What kind of HVAC equipment are these motors driving? Chillers, air handlers, compressors, pumps? If you're having a lot of rotor bar issues I would be trying to find a root cause problem that is resulting in these failures. While rotor bar failures do definitely occur, I don't find them to be common unless something is wrong in design or operating parameters.

Hi,

Joe's a very valid question....you mentioned "most of the HVAC failures"...that's quite an open statement: how many motors, what are they driving, for how long, what's the operating context, ....what's the history???

cheers
Rennie

quote:

Originally posted by Depostmann:
Thank you electricpete. Hope you have something or illustration for this kind of problem......

See: http://maintenanceforums.com/eve/forums/a/tpc/f/3751089...701084213#6701084213

Hi,

The motors we are using drive the belt conveyors mostly 24 hours operation with fluid coupling. The ratings are: 300KW, 3.3KV (Pri), 63A (Pri), 1190RPM, 6 poles. Some of our belt conveyors is driven by 3 or 4 motors (300KW).
I think this is all.

D...

Thanks for the data ArildF. I really appreciate it. And to all experts who shared their knowledge. Thank you...

Hi all friends
i would like to share the following information :
- Cracked rotor bars:
cracked rotor bars will generate pole pass frequency sidebands around 1X and its harmonics(2X,3X, and so on)>
an induction motor defective rotor bars will produce a vibration signature that slowly varies up and down in the amplitude at twice the slip frequencyof the motor (Beating)

- loose rotor bars :
will be a peak at rotor bar pass frequency, with sidebands of twice line frequency.

best regards

thank you eng.ahmad for the information. the information you've shared will be of great help to me. thank a lot...

d...

i have had 3 1500 hp motors develope broken rotor bars. i caught all 3. approx 1/2 hz sidebands showed up around 1X also in each instance i noticed a distinct audable and physical beating of the motor.
maby a herz or so.
Mike