Gentlemen,

I have a 2000HP, 700 Volt, 2245 AMP DC Motor w/ FAG 6236 bearings. I am seeing harmonics of Line Frequency surrounded by what I believe are sidebands of cage frequency. I am also seeing harmonics of cage frequency. The commutator has a ridge, and the brushes can be seen jumping. The brushes themselves are in good shape. The amplitudes are in excess of .7 in/sec on the outboard motor bearing in the vertical direction. 80 G's pk-pk in the waveform. This motor is extremely critical, and no down is scheduled until July. Can this be a cage problem coupled with a drive problem, or are the cage frequencies a non-issue. Any information you can offer would be greatly appreciated.

Thanks.

2000_HP_Banbury.pdf (44 Kb, 70 downloads)

The last 2 or 3 plots sure look like flutting pattern to me. Are you sure the spacing isn't BPFO or BPFI

Roy,

The sidebands are of 326 cpm which is within a cycle or two of cage frequency. BPFO is however very near 3600 cpm, 3556 cpm to be exact. Sidebands of cage frequency surrounding BPFO frequencies? hmmm.... Thanks for the input. We installed grounding brushes on the other two motors, but this one is a new install and we do not believe there is one on the motor. Thanks for you input. This will definately help in my decision making.

Looks like fluting to me too. Is it really loud sometimes?

Good Luck,

Its loud all the time as far as I know, and is getting worse. I recalculated the BPFO frequencies using an SKF 6236, and they are dead nuts on. Right at 3600 cpm.

Here are some photos from the bearing we removed from the motor. Sure enough, fluting. Thanks for all of you input.

That's the stuff allright. I'm not sure if it's me or what but I have seen this more on Banbury mill motors than anywhere else.

Good Luck,