Tagged With "Barring"

Topic

Pole Pass Reading in Standard Route Readings

oju ·
Was wondering how many here take high res readings to monitor pole pass in their standard route readings? If so have you found issues?
Topic

number of rotor bar

aziz58 ·
dear all is any on know how can i find number of rotor bar with out disassemble the electric motor. i can,t find that information in motor document or name plat . best regards.
Topic

Rotor Bar Defect?

Vib_Guy#1 ·
I have a 630 kW 2 pole motor on a VSD driving a HP feed pump in a small power plant. I’ve only been taking readings monthly for about 5 months and it’s been trending at an average of 1.95 mm/s (0.077 in/s). The speed over these readings varied from 2385 to 2832 RPM. This month my horizontal readings have risen to 5.7 mm/s (0.22 in/s) accompanied with a growling noise. My horizontal spectrum has a large 1X with 4 decreasing harmonics and multiple sidebands which I think are PPF. A few...
Topic

Rotor broken bar problem or variable load or vibration issue cause sideband around line frequency on current FFT spectrum?

Lampard Nguyen ·
Hello, I am considering what the rotor broken bar problem proporly in 2 following case which you can get on attachment. Please tell me your opinion! Thank you!
Topic

Rotor broken bars problem, is it right?

Lampard Nguyen ·
Dear Experts, Could you please give me some advise about this photos, Is it rotor broken bars problem? I performed current signature analysis test for this motor. In my opinion, there is pole pass frequency peaks with low amplitude. Thank you so much! Regards,
Reply

Re: Rotor broken bars problem, is it right?

edisonindia ·
It's a aluminum die cast rotor. Not really sure what your third picture shows. If you have the test equipment, you could do a growler test.
Reply

Re: Rotor broken bars problem, is it right?

electricpete ·
First photo shows gouge in end ring. That could be the cause of the pole pass sidebands. Second photo shows gouge on od of bore. I look for something to judge the size of the gouge. I think the gouge shown in photo 2 is also shown in the third photo just above 26 (between 2 and 6). It doesn't appear to have penetrated to a bar. So I think it is confined to the bridge area above the bars. 3rd photo - I assume that white flash is just a reflection (maybe the photo is taken through a clear...
Reply

Re: Rotor broken bars problem, is it right?

electricpete ·
Now I'm seeing the sideband was around 53 db below the main peak? Normally I start getting really interested at 45db. What load was that? Was there any trend?
Reply

Re: Rotor broken bars problem, is it right?

Walt Strong ·
I am trying to understand the motor current spectrum. The dominant frequency is near 45 Hz which is not common 50 Hz or 60 Hz line frequency. So was the measurement made with the motor running with VFD at reduced speed and therefore at reduced load? Did you calculate the pole-pass sideband frequency and identify it on the plot? The interpretation of side-band amplitudes may be inconclusive, if the measurement was made at reduced speed and load. I had made a diagnosis of induced draft fan...
Reply

Re: Rotor broken bars problem, is it right?

Shurafa ·
Nice photos. I like these clear pictures. Regards-Ali M. Al-Shurafa
Reply

Re: Rotor broken bars problem, is it right?

edisonindia ·
If the motor was not having any issues like stalling, overcurrent, current oscillation or excessive temperatures, I would run it. pete It is not cost effective to repair die cast rotors. Best to replace them, if found defective. I had replaced a few die cast rotor windings with copper for a set of 6.6 KV motors about 2 decades back, but that was a special case since the OEM had gone bust and the client was desperate.
Reply

Re: Rotor broken bars problem, is it right?

Lampard Nguyen ·
Hello, Thank so much for all recommendation. Some information about this case: - Motor is driven by VSD with line frequency supplies to motor is 45.1 Hz. - Motor has been running with 67% FLA. - Rotor was fall when maintenance, It caused some incisions on rotor which you can see on my photos. We don't have any spare part to replace for motor. Therefore, motor must run with crashed rotor. So, we want to perform MCSA for diagnostic rotor condition. With this result, I think there is not bad...
Reply

Re: Rotor broken bars problem, is it right?

Walt Strong ·
Cando, This is a very interesting case history, but I would like to understand the sequence of events. Did you remove the motor rotor after conducting the motor current spectrum analysis? If not, what was the reason for removing it? Did the motor current spectrum reveal eccentricity after the motor was reassembled with the damaged rotor or before it was removed? During the installation of the damaged rotor to put it back into service, I would assume that the following would have been...
Reply

Re: Rotor broken bars problem, is it right?

electricpete ·
I agree, based on: 1 - Apparently you have run the motor since the damage to take the current signature. 2 - You have a vsd, so the rotor doesn't see the severe duty of direct on line start. 3 - you are planning to continue monitoring. If you see an increasing trend in sideband under similar conditions that might be a time to be concerned. If damage occurred while stationary, I'm curious what created the mark around the circumfence of rotor at that location. Maybe the od got dinged and...
Reply

Re: Rotor broken bars problem, is it right?

Lampard Nguyen ·
Hello, Rotor was fall when we disassembled motor for replacing bearings and visual inspection of rotor also. It is only time based maitenance for this motor. But, unlucky, rotor was crasked. Current Signature analysis (both of rotor broekn bars FFT and eccentricity FFT which I attached above) is performed after maitenace to ensure motor can run with this rotor for ordering new rotor delay. Of course, we will monitor this motor operation by MCSA and vibration analyis. Firstly, we will do...
Reply

Re: Rotor broken bars problem, is it right?

Howard Penrose ·
Cando Had you performed MCSA prior to this condition being found? It is often the case in cast aluminum rotors that casting voids exist that would cause the low level rotor bar (PPF) frequency that you are seeing. Some manufacturers have more prevalent cast rotor voids than others based upon their casting process. If that is the case and you are not seeing torsional issues, then you are probably OK. The notching in the rotor in this size machine most likely is not an issue as you have a...
Reply

Re: Rotor Bar Defect?

Lampard Nguyen ·
Hi Vib_Guy, Did you have perform MCSA or Rotor influence check for this motor? In order to ensure that is rotor broken bars problem, MCSA and RIC test can help you do that. In my opinion, high 1X and harmonics was caused by structural looseness, misalignment. Side-band was caused by variable Load of Pump (it also causes motor's speed changed during operation). Good luck!
Reply

Re: Rotor Bar Defect?

Chris184 ·
Im not sure id jump on the rotor looking at what I see. I'll attach some data I collected on a 2pole 700hp with a rotor defect. I do not see a elevated 2xlf or, as you pointed out, rotor bar pass frequencies. I would post the MCSA, however I cant remove the identifying text or logos off of that report...however it did show sidebands Fp side bands of Lf at 36dB, and the presence of "Swirl Effect" at the 5th harmonic of line frequency.
Reply

Re: Rotor Bar Defect?

Ron Brook ·
Once you a have a VFD in the picture, all bets are off. The fluctuations you are seeing could be an issue with the VFD controls. Is there a tach involved or are you running volts/Hz? Either way, there are also other issues with VFD control that can cause modulation. The Vibration is your best bet for calculating the running speed of the motor. Compare this against the VFD output to calculate your slip frequency. Multiply this by two to get the PP sideband frequency. You are probably correct...
Reply

Re: Rotor Bar Defect?

Vib_Guy#1 ·
Hi Ron, No tach involved, just a VFD working off a set-point so speed constantly varies by small amounts. Like I said, because my time record is 50 seconds, I have a feeling some side bands are getting swallowed up by smearing. Also, I'm getting the speed from the time stamp on their control system. Is their time the same as mine? Who knows?. I try to set my data collector to universal time and hope that it doesn't lose seconds/minutes over time. Rotor bars sprang to my mind because I've...
Reply

Re: Rotor Bar Defect?

Lampard Nguyen ·
Vib_Guy, Please inquiry this link: http://www.utilityproducts.com...s-8220rotor8221.html Good luck!
Reply

Re: Rotor Bar Defect?

Chris184 ·
Vibe_Guy The attached has data showing the swirl effect. The link posted by Cando explains it well as there is not much to it. Would it be possible to arrange that the VFD be temporarily locked into a single frequency and not change and keep the load as steady as possible during your next visit for data collection? Just curious, what analyzer are you using.
Reply

Re: Rotor broken bar problem or variable load or vibration issue cause sideband around line frequency on current FFT spectrum?

edisonindia ·
Stator current will be swinging if you have broken rotor bars.
Reply

Re: Rotor Bar Defect?

Vib_Guy#1 ·
Thanks Chris, Interesting stuff. I'm using a VibXpert II, but I would expect the results to be pretty much the same from any other half decent data collector. It's just a 0.5 - 200 Hz velocity reading with 12800 LOR. The speed variation is process related, so I would imagine trying to get it fixed for my data collection would be a big fat no. Thanks for the help.
Reply

Re: Rotor broken bar problem or variable load or vibration issue cause sideband around line frequency on current FFT spectrum?

Lampard Nguyen ·
Hello Edsisonia, Two above cases also have swinging current. But, in my opinion, the first case is not rotor bar problem, because of no Swirl effect. Thank you!
Reply

Re: Rotor broken bar problem or variable load or vibration issue cause sideband around line frequency on current FFT spectrum?

Gary Stacey ·
Need to look for pole pass frequency side-bands around the line frequency. Relative height between SB and LF to confirm rotor bar issue and severity. Similar PPF SB around 1x in vibration spectra.
Reply

Re: Rotor broken bar problem or variable load or vibration issue cause sideband around line frequency on current FFT spectrum?

edisonindia ·
cando If the stator current is swinging, it's almost certain there is a rotor bar problem. Have you pulled out the rotor to physically check it?
Reply

Re: Rotor broken bar problem or variable load or vibration issue cause sideband around line frequency on current FFT spectrum?

Lampard Nguyen ·
Edisonindia, We have not ever pulled out rotor for visual inspection. I think swinging current also can be caused by mechanical vibration or variable load... Swirl effect is very useful for double check the rotor broken bar issue in current's FFT waveform.
Reply

Re: Rotor broken bar problem or variable load or vibration issue cause sideband around line frequency on current FFT spectrum?

edisonindia ·
I don't see how the vibration causes stator current swing. Yes, a variable load will. Is yours one?
Reply

Re: Rotor broken bar problem or variable load or vibration issue cause sideband around line frequency on current FFT spectrum?

Lampard Nguyen ·
Edisonindia, Low frequency vibration can cause swinging current. Because equation of stator current is: I(stator)=I(50 or 60 Hz) + I (50 +/- f_vibration). with low frequency vibration (from 0 to 5 Hz), you can see the sideband around line frequency likes as Pole pass frequency which can cause fault analysis. Thank you!
Reply

Re: Rotor broken bar problem or variable load or vibration issue cause sideband around line frequency on current FFT spectrum?

electricpete ·
I agree with op, it's always nice to have things to help confirm before you make the call to pull a motor. Would be awfully embarassing to send a motor out only to find it's there's nothing wrong with it. What kinds of things other than actual rotor problem can cause apparent elevated pole pass sideband around FL in the current spectrum: varying load which happens to vary at a frequency near pole pass frequency. Check frequency as preciselyy as you can.... the closer the match to exactly...
Reply

Re: Rotor broken bar problem or variable load or vibration issue cause sideband around line frequency on current FFT spectrum?

Lampard Nguyen ·
Hello Gary Stacey, http://www.reliableplant.com/R...ct-broken-rotor-bars Please got this link!
Reply

Re: Rotor broken bar problem or variable load or vibration issue cause sideband around line frequency on current FFT spectrum?

electricpete ·
Here's a previous topic about swirl frequency: https://www.maintenance.org/top...idebands-around-5-lf I think Cando has posted a few examples before this thread also. Now, a different subject. I notice the second case study has lower sideband much higher than upper sideband around line frequency. As far as I can tell that is often associated with a motor that drives a high inertia load (and of course high inertia loads also tend to make each start harder on the rotor bars). I'll bet this...
Reply

Re: number of rotor bar

Rotate ·
enjoy
Reply

Re: number of rotor bar

aziz58 ·
thanks dear do u have any formula to calculate number of rotor bar . i cant see some brand of electric motor in your attached file. best regards
Reply

Re: number of rotor bar

electricpete ·
There is no formula...it's a decision made by the oem. A motor with same speed, hp, voltage and dimensions from different oems can have different number if rotor bars.. You can attempt to determine it from the rbpf pattern in vibration: Rbpf with multiple 2LF sidebands. Sometimes it's a challenge to figure which are the sidebands and which is rbpf...the rbpf is the only one an exact multiple of running speed (if you have enough resolution to distinguish..also a challenge). In the end you...
Reply

Re: Rotor broken bar problem or variable load or vibration issue cause sideband around line frequency on current FFT spectrum?

Aditya ·
May too late to be relevant, but I don't think either of those two are broken bar cases. The first spectrum has just too many sidebands to be a rotor problem. My guess would be mechanical modulation. The second spectrum has only the lower PPF sideband, a true case would give you both the peaks. EPete - I do have some case studies of dynamic eccentricity causing PPF sidebands, but this doesn't always happen. Just saw a case last week where a 790 kW motor with sleeve bearings had excessive...
Reply

Re: Rotor broken bar problem or variable load or vibration issue cause sideband around line frequency on current FFT spectrum?

Lampard Nguyen ·
Hi Aditya, Thanks so much for your comment, could you please give me your case-study?
Reply

Re: Rotor broken bar problem or variable load or vibration issue cause sideband around line frequency on current FFT spectrum?

electricpete ·
I would respectfully disagree about significance of high LSB without much USB. To my mind it indicates high inertia of driven load. We have a series of motors with flywheels (high inertia) and they all have a pattern of LSB much higher than USB (they are also all healthy but I this represents small asymmetry in rotor and large asymmetry would increase both sidebands but keep the LSB higher than USB... ... ok that's just an assumption on my part). Example attached. The theoretical reasons for...
Reply

Re: Rotor broken bar problem or variable load or vibration issue cause sideband around line frequency on current FFT spectrum?

Gary Stacey ·
James I Taylor speaks a lot in his book regarding the relative heights of the upper and lower sidebands but this is a bit mystical to me also! I have always looked for both but am willing to be convinced otherwise. I have always understood the modulation to be as a result of a momentary torque reduction as the broken bar(s) pass by a pole as a result of the higher resistance nature of the broken bar circuit. This torque reduction is seen, due to conservation of energy principles, as a...
Reply

Re: Rotor broken bar problem or variable load or vibration issue cause sideband around line frequency on current FFT spectrum?

electricpete ·
[quote]I have always understood the modulation to be as a result of a momentary torque reduction as the broken bar(s) pass by a pole as a result of the higher resistance nature of the broken bar circuit. This torque reduction is seen, due to conservation of energy principles, as a momentary reduction in supply current hence the modulation at PP. So I tend to look for the classic upper and lower SB's. [/quote] Your explanation makes perfect sense to me on an intuitive level. And I would be...
Reply

Re: Pole Pass Reading in Standard Route Readings

Walt Strong ·
I usually make two measurements on the motor case near the terminal box. The first measurement is a high-resolution low frequency velocity spectrum for confirming motor speed and to detect rotor pole-pass sidebands. The second measurement is high-frequency acceleration to detect rotor bar and stator slot passing frequencies along with modulation sidebands. I have detected both electrical and mechanical faults with these type of measurements. There may be other ways to accomplish the...
Reply

Re: Pole Pass Reading in Standard Route Readings

Gary Stacey ·
I do not generally take a high res reading to look specifically for PP symptoms. I will if other issues such as audible modulation make me suspect there may be a developing rotor bar issue or if rotor dynamic eccentricity is suspected. Be interested to know what problems you have detected with the high frequency acceleration reading Walt? I don't doubt you have! Textbook states that RBF with 2x line frequency sidebands = rotor bar issues but I have not had much success with it. I quite often...
Reply

Re: Pole Pass Reading in Standard Route Readings

Dave Reynolds ·
Agree with Gary, we have low frequency hi resolution reading on ALL of our machines, only take it when we have driver and driven speeds that are 100 rpm or less speed difference, hear an audible noise or higher than usual vibration values. Keep in mind, IF you have broken/loose rotor bars, the motor will have poor performance, lose HP, draw higher than normal amps, have a modulating noise coming from the motor, will run hotter than a normal motor, time waveform will have modulation and will...
Reply

Re: Pole Pass Reading in Standard Route Readings

Walt Strong ·
"I will if other issues such as audible modulation make me suspect there may be a developing rotor bar issue or if rotor dynamic eccentricity is suspected." Gary, if you want to rely upon your hearing and some other means of detecting rotor dynamic eccentricity that is fine. If it is convenient for you to go back to the machine and make additional measurements that is fine. If you're making a decision not to take certain data because some faults are very unlikely that is fine. Most of the...
Reply

Re: Pole Pass Reading in Standard Route Readings

Gary Stacey ·
Sorry should have added that I do take high res readings if there has been any change in the routine data such as harmonics, increasing overall etc. With my standard data set we will see 'skirts' around 1x 2x etc which would also prompt investigation. As with Dave I have seen very little by way of rotor bar problems in my 20 years of collecting data. I am just traking one now on a smallish motor - previously we had only ever seen the issue on large FD/ID fan motors and we collected routine...
×
×
×
×