I have four new 200 HP vertical pump motors on VFD. These readings are after one month run time. Is this carrier frequency or shock pulse?

Pumps_1-4.PDF (779 Kb, 116 downloads) Pump data

This is likely a carrier frequency at RBPF modulated by 2xLF, which, if is not trending up, does not present any danger.

Similar spectrums appearing on your pump?

The pump is sleeve bearings.

I have some similar to you. I don't worry about it 18 years its caused me no problem. It is probably the frequency the inverter uses to generate the variable frequency and voltage for the motor.I forgot what it is actually called.

Mike

Do yourself a favor and stop looking at spectra in g's. On VFD's, you should be primarily concerned with periodic spiking, not the constant broadband noise from the VFD that is in your time waveforms.

Robert I tend to agree with the other guys, if the trends are not rising don't worry about it. If the trends do rise check for bearing race fault frequency sidebands in that cluster of peaks, it could be electrical fluting of the bearings. You can find the line frequency in Hz somewhere on the VFD display see if the peaks line up close to 2X that (it will vary slightly with motor load)

Mike and Robert,

The frequency is called the "switching frequency". It is around 4KHz on alot of VFD's. Sometimes at 2 KHz. You can see it if you make your Fmax 360,000 cpm, use velocity. Or you may have one setup at 600,000 cpm, use acceleration. Hi Ron!

Lou Pag

Randle That's where I was headed with this. I have a major flutting issue with bearings here at our site. I have tried brushes and insulated bearings and am now in the process of trying the zero-ground conduit.

Robert,
There are many threads on this site that discuss VFD's and EDM (fluting) in bearings. Unfortunately, until the US falls in line with Europe and the electrical code calls for VFD shielded power leads, the market will remain confused and wallowing in brushes (including the AEGIS system!), insulated bearings, etc. etc. etc.
They are all band aids and ineffective at best. The reason for the shielding is to provide a low impedance path for the current to go from the motor winding back to the inverter. If the user does not provide that path, then the current will find it's own way, usually through the bearings, gearboxes, to plant ground.
The only other issue that can affect fluting is the old '12 inch rule', which states that if a motor has a dimension of 12 inches or greater between the shaft centerline and the motor foot, then that motor is large enough to have circulating currents between the ends of the motor, due to a potential difference between the ends of the windings. This type problem occurs in VFD application motors around the 444 frame size and higher. If you have a motor on a VFD with size or higher frame, then you need to do two things,
Insulate the bearings, AND use the inverter duty shielded cable.

Robert,
I am a vibration guy with a mechanical background and I also work at a plant with fluting issues. I have all kinds of problems getting electrical people and management to respond even when I show them the failed bearings. We have had limited sucess with shaft grounding brushes, but they have to be maintained, and our electrical staff is at skeleton force levels. We have just installed a new machine similar in size to a paper machine and it is full of VFD driven motors. I have already found signs of fluting in some of the bigger motors and have been trying to convince management that we should add some shaft grounding equipment. I have been looking at the Aegis system but I would be very interested to hear what you have tried and how it worked for you. I have read some of Ron's concerns in other posts on this subject and he is probably right about what the ideal solution is. The problem with that is the expense both on initial install and retrofit. The Aegis system gaurantees that a motor will not fail due to fluting if it properly installed, so I figure that I could at least try it out on a known bad actor. What I have a hard time grasping is why fluting affects some VFD driven motors and not others, even when the systems are similar or identical. I have heard that drive tuning can have an effect but we don't have anybody on staff that knows enough about it.
Good luck with your problem and please let me know how it is going.

Randle,
Reliance Electric extensively tested the Aegis brushes. They worked for a while (3 months) and then the bristles took a set (they called it the brush effect), where just like an old paint brush, the bristles all curled to one side. The brush was then no longer effective. They rotated the brush axially and it worked for another 3 months then the same thing happened. Permanent fix? I think not.
Also, brushes on the shafts, as you have said are a band aid waiting to have a problem. If you and your maintenance staff miss a failed brush connection for just a few days, the bearing is on the slippery slope.
I agree that proper cable isn't cheap, but then again, what is the cost of the paper machine coming down in the middle of a run?
I have been chasing these issues for Reliance, Rockwell, Baldor, etc. for over 11 years and in every case it's the same issue.
1. The ticked off customer - "Why the heck didn't the sales engineer tell me I needed to install that inverter duty shielded cable?" The simple and sad answer? He would have lost the sale because the competition would have not demanded the cable.
2. The motor factory pulling their hair out because it is their product that is failing through no fault of their own. Think about it. What motor do you know that generates current spikes in the 5 kHz to 10 MHz region all on it's own? And there is the inverter manufacturer standing on the sidelines not even involved in the fight!
3. The customer trying all sorts of 'after the fact' fixes that are not permanent.
4. I tested several motors that had fluting and the customer wanted to know why the same drive affected one manufacturers motors but not the other? I asked if the drives were identical and he said absolutely. I measured the common mode current on both drives and found a 400% increase on one of the drives. The customer then informed me that the higher current was on the drive manufacturers NEW style drive! So, the inverter manufacturers, knowing they aren't even being dragged into these issues are designing, manufacturing, and installing even cheaper, electrically noisier drives!
The reason you can have one motor out of ten with the problem is the reason EDM currents and voltages are so hard to characterize in the first place. The grounding system of a VFD/Motor and cable system is highly complex, due to the fact that there are multiple system capacitances and impedances. Remember, these currents are looking for the lowest impedance path back to the drive ground. A round copper wire had high skin loses at higher frequencies, so as a result, it won't carry high frequency currents back to the drive. Now they are left to find their own path back. Ever notice that the worse cases reported are on belt drives? That's because in most direct driven systems, with conducting couplings, the current is disappated over more contact areas and therefore the amount of current carried through any one point is below a damaging level.
My advise to a user that is already in the 'installed and failing' mode, bite the bullet, first have someone who knows what they are doing measure the current to characterize it's magnitude and frequency. If it is indeed higher frequency, install the proper cable on your 'bad eggs'. Also, for those motors with a 444 frame or higher, insulate the bearings in the bracket.
Coming from the motor manufacturer side of this problem, I can only tell you how frustrating it is to see the totally inept NEC and NEMA ignore this issue and not DEMAND that VFD driven motors MUST be installed with the proper cable and insulated bearings. Then, the playing field would be even and the problem gone.
You can't tell me that the intial cost of the cable is more money than the maintenance headaches you are currently in the middle of.
Oh, and by the way, one of the highest currents I EVER measured on a motor with a grounding brush (not Aegis, just a plain carbon brush) was 6 amps! The bearings failed 8 times in one year! Changed the power cable, insulated the bearing brackets, motor has been on line continuously now for over 16 months.

I agree with Ron Insulated NDE bearings, brushes common mode chokes etc are all band aids. See attached file explaining about symmetrically earth foil screened cables and proper installation of AC frequency drive cabling.

ABB_Technical_Guide_5.pdf (1,427 Kb, 56 downloads)

Bruce,
You have presented the 'bible' on eliminating EDM due to VFD applications. I have used Links original paper to solve these issues for over 8 years.
Ron

Bruce, thanks for the ABB pdf. I am running the proper cabling issue past our electrical engineers. The article mentions a 360 deg. European cabling practice, is there some sort of standard for this?

Robert,
The ABB article explains in detail why it is important to have a 360 degree shield. It's not necessarily just a European practice, it's the solution to a serious problem. Again, if the US would adopt the standard, there would be peace in the valley! No more stones being thrown at motor manufacturers.
As far as retrofitting the proper cable, remember that these EDM issues don't always affect every motor. It is a real subtle difference from motor to motor as impedence. I would attack your 'worst actors' with the proper cable and if the motors are greater than a 444 frame, bearing insulation.
Ron