Tagged With "FFT"

Topic

bearings

AsadAli ·
how mush amplitude FFT Spectrum acceleration/velocity at bearing frequency fault we consider healthy bearing or faulty bearing??? guide me dear...
Topic

High Vib in STG GB

Akhil rathore ·
Dear all Due to some reasons the load over one of the STG increased from 15MW to 25MW, no major change observed in Generator & Turbine online & offline vibrations But the single stage reduction GB (6300 rpm to 3000 rpm) showed high increase in offline vibrations i.e from 8 mm/s rms to 13 mm/s rms, but the shaft vibrations were not having any change i.e 30 microns Data Turbine rpm:- 6300 Generator rpm:- 3000 No. of teeth on high speed shaft:- 37 No. of teeth...
Topic

Shovel system vibration measurements

Alvaro Loayza ·
Hi everybody, I've been working on vibration analysis at RCM department for a year. When I arrived I noticed that vibration analysis for shovel drive systems was made with standard FFT process but an experienced contract analyst suggested that we needed to use a kind of order track filter or a trigger on hoist systems because RPM was variable from 0 to 600 rpm on DC motor. I've been researching and find out lot of information about this but still not sure what would be the best way to...
Reply

Re: High Vib in STG GB

Akhil rathore ·
OOPS its John, I misspell let me try for time synchronous averaging..I'll get back on this..
Reply

Re: High Vib in STG GB

John from PA ·
Originally Posted by Akhil rathore: OOPS its John, I misspell let me try for time synchronous averaging..I'll get back on this.. If you have doubts on the tooth count see if you can get a good feel for turbine speed. I'm assuming you are connecting to the grid and it is reasonably stable and hence can trust the 3000 RPM. But with the tooth counts you provided the turbine speed would be about 6324. If I just use your 6300/3000 speeds and run that through my tooth count calculator there are...
Reply

Re: High Vib in STG GB

John from PA ·
In cases where there is an unidentifiable frequency in a gearbox used for power generation I'm always a bit suspicious of the machine being a double helical and the axial spacing being incorrect. Is the gearbox a single helical or double? Does this machine have a limited end float coupling between the steam turbine and gearbox that has a pre-stretch value? By limited end float I mean diaphragm or disk type. Can you supply a cross section drawing of the gearbox? Not that it is a major...
Reply

Re: High Vib in STG GB

Akhil rathore ·
tooth counts & shaft speeds have been verified from manual & operation panel also there is no peak at 233100 cpm or 234,000 cpm it is a double helical gearbox with flexible disc coupling
Reply

Re: High Vib in STG GB

Edwin de B ·
I think the origin of this vibration is not at 72242 but half of it. Place your harmonic cursor on 36121cpm and you will see. There is each time a higher and lower amplitude of the harmonics of this component. It then is a 5.7X running of turbine. It does not seem like it a lot, but the frequency can be of an inner race defect of a roller bearing. Probibly not present here but you could check it. (maybe not main bearing but something attached like an oilpum or so)
Reply

Re: High Vib in STG GB

Akhil rathore ·
@edwin the only thing that worries me is whenever I think of any solution I have to correlate it to all 3 STG gearboxes, because all 3 of them are giving same FFT spectrum.
Reply

Re: High Vib in STG GB

John from PA ·
Do you have the ability to accomplish a time synchronous average on the signal using both (separately of course) the pinion and gear speeds as the trigger? A good alternative would be increasing the resolution to better identify the frequency. I see that the 72242 is very close to a 24X of the gear. What would be of interest is if the frequency drops out with a pinion speed triggered TSA but remains with a gear triggered TSA. This would support that a potential error from the manufacturing...
Reply

Re: High Vib in STG GB

Akhil rathore ·
Any of you having SKF aptitude analyst. I can give you the mab (database) file
Reply

Re: High Vib in STG GB

Akhil rathore ·
Transducer is accelerometer with 100mv/g sensitivity using dual rail magnet mounting.
Reply

Re: High Vib in STG GB

John from PA ·
Originally Posted by Akhil rathore: Transducer is accelerometer with 100mv/g sensitivity using dual rail magnet mounting. Any chance you could stud mount one to see the effect on the 72K frequency?
Reply

Re: High Vib in STG GB

Akhil rathore ·
Jhon.. 2 things 1. what i can do is i can remove the magnet from accelerometer & use it as hand held..(if that helps) 2. To verify the frequencies, I used another make analyzer with separate sensor, however sensitivity & mounting method was same..similar frequencies were observed.. I personally doubt the teeth count..but i verified it twice from the name plate on the gearbox also from the data sheet provided from OEM. now If i go with what Edwin said that its not 72k but half of that...
Reply

Re: bearings

Imran@.. ·
please see attached file.
Reply

Re: bearings

John from PA ·
Check this resource as well. http://www.engr.uconn.edu/~aly...lling%20Bearings.pdf
Reply

Re: Shovel system vibration measurements

CETMA ·
Order tracking works well as long as you have a good speed input. The most common method for collecting vibration data on shovels is to put it in a test mode where data is collected under constant speed conditions. The down side to this method is that it is not under normal load conditions.
Reply

Re: Shovel system vibration measurements

Data Dog ·
Alvaro - Having many years experience performing shovel diagnostics on P&H shovels, you are most likely referencing the hoist system (0-600 RPM). The downside with Order Tracking is that you have only ~7 seconds to capture data. Not enough time to capture standard velocity readings on such slow speed machinery. I can only recommend what worked very well for us was utilizing PeakVue, CSI's patented technology. Works well on all the shovel systems. Hope this helps. -Mike
Reply

Re: High Vib in STG GB

Akhil rathore ·
Hi John The problem still persists in the herringbone Gearbox, & has got worse will need to start this thread again as i have some more inputs & some more question that can help us to come to a conclusion.
Reply

Re: High Vib in STG GB

John from PA ·
It has been a year...has the GB ever been shut down and examined inside through an inspection port? Can that be done now?
Reply

Re: Shovel system vibration measurements

BradGab ·
Hi Alvaro- I am currently performing vibration analysis on the hoist, crowd, and swings for a CAT shovel. We are using CSI equipment with order tracking and peakvue. Using the 2140 will take some time ~2hrs of downtime to perform the test since you test it away from the face. Emerson does have their 6500 online system specifically for monitoring shovels and is an option for PH shovels. We are looking at implementing it for the CAT since it cuts the time down to ~20mins. I agree with Mike and...
Reply

Re: Shovel system vibration measurements

Alvaro Loayza ·
I have suggested my supervisor to implement online systems. Order tracking is very difficult because we don't have access to motor shaft and it has been imposible for us to get it. Thank you very much for your response. Greetings
Reply

Re: High Vib in STG GB

Akhil rathore ·
Yes one Gas turbine GB was examined, & found "tiger stripes" on the gear, other than this nothing. Let me refresh the details & question 3 no.s of Steam turbines Gearboxes details teeth= 37/78, rpm =6300/300 2 no.s of Gas turbines Gearboxes details teeth= 43/74, rpm =5300/300 All the above mentioned 5 machines show similar spectrum in their Load gearboxes ( Herringbone gears) with harmonics of "72,000" as their problem causing frequency. Also this "72,000" is not constant, it varies...
Topic

High 1X motor vibration and baseplate stiffness

Unplugged.Charles ·
Dear, these days I'm facing on several motor vibration problem. This is one of them. I want to hear your opinions. [Problem] the motors vibration amplitude for multi stage pumps was raised up from 3 to 9 mm/sec RMS for this year. On the FFT, 1X horizontal vibration is dominant about 90% of overall value. And this motor vibration is transferred to motor base - foundation - concrete floor and near same machine motor that is still power off but vibration is about 1 ~ 1.5 mm/sec. Is it motor...
Reply

Re: High 1X motor vibration and baseplate stiffness

rgf12 ·
Generally speaking the box channels used like this are quite stiff as long as the underlying base is solid ( no grout issues or cracked welds). I would do a bump test on the base in 2 directions to see what the natural frequency is and isf it is close to the running speed of the motor. If that isn't the driver then you can move on to other possible causes. What does the pump vibration data look like? What type of coupling?
Reply

Re: High 1X motor vibration and baseplate stiffness

Ron Brook ·
If you still have vibration without power to the motor, then something running near this motor is causing that vibration. For a motor to change vibration over time, several things are possible: The motor base may have settling issues causing a rigid body mode to move closer to running speed. The motor could have thermal issues causing rotor bow. If there is vibration close by, check that out first
Reply

Re: High 1X motor vibration and baseplate stiffness

nishanthreddy33 ·
settling issues causing a rigid body mode to move closer to running speed.what does it mean?@ron brook
Reply

Re: High 1X motor vibration and baseplate stiffness

Walt Strong ·
Vibration looks higher after shaft alignment. Looks like a lot more shims under one end (NDE?). Are you really sure that alignment is good? Walt
Reply

Re: High 1X motor vibration and baseplate stiffness

Ron Brook ·
Walt, The height of the shims looks OK but they don't cover the entire foot of the motor. That can cause a stiffness issue. Of course, a bad alignment will also cause higher vibration.
Reply

Re: High 1X motor vibration and baseplate stiffness

Unplugged.Charles ·
Yes, motor NDE foot was not supported with wider shims. I agree with you Mr.Brook. to RGF12 Pump vibration is maximum 1.0 mm/sec RMS. It's very stable. And coupling is flexible disc type. to all At first, we added beams for increasing horizontal stiffness as like pictures. And motor - pump was re-aligned by laser tool again. Vibration amplitude was reduced. Now it shows about 5mm/sec RMS. But motor still has strong 1X vibration. And motor terminal box, cable, paved floor and the others still...
Reply

Re: High 1X motor vibration and baseplate stiffness

Ron Brook ·
If you have a beat frequency, that is proof that there is something else running near the same speed that is added and subtracting to the vibration at 1x. Check all equipment neat this motor. Have you checked the alignment yet? Have you soloed the motor?
Reply

Re: Induction motor's vibration problem

ivibr8 ·
If this seems to be an issue that is getting worse (at least audibly), then can you quantify with past data? or is what you provided the only data you have? Harmonics could be the result of several things; misalignment is just one of the possibilities. I'm having a hard time reasoning how that could result in the noise getting worse with time (unless its causing increased clearances). IMO, the level of 2X and 3X (in relation to 1X) just doesn't bother me at this time (i.e. with no previous...
Reply

Re: Induction motor's vibration problem

ivibr8 ·
AI 1. What is history with this pump? Has this noise suddenly appeared or was it simply noted by data taker? What have operators noted? Audible noise from a motor is not that unusual and doesn't necessarily mean its a problem. (The resolution around the 640 hz and 2280 hz peaks seems low). 2. When the pump is shutoff, does the noise SUDDENLY disappear? Watch a "live display" of the spectrum during a shutoff if you can; suggest you watch 0-2KHz as a minimum. 3. Read thru this post...
Reply

Re: Induction motor's vibration problem

ai.engineer ·
IVIBR8 . Thanks for the reply, in fact the noise was appeared since major inspection of the motor (this motor has been operating since 2011 but the noise increase day after day). during the shutoff, I can take the measuring vibration because I'm not always available. but if you see the spectrum, there are peaks in the 1X, 2X & 3X. it seems misalignment no? As well, there are slide bands around 2280 Hz +- 60Hz. what do you think about this spectrum, is it normal?
Topic

Induction motor's vibration problem

ai.engineer ·
We have vertical multistage pump driven by electric motor on the combined cycle power plant. Motor details are: 4 poles, 1482 rpm, 300 KW, 50 Hz AC motor. During our routine condition monitoring, we are detected sound coming from the motor. We are taken vibration measuring, the amplitude at the motor 1.58 mm/s rms 1RH. I 'm truly need someone who help me to explain well this issue. you find attached some spectrum FFT's velocity and acceleration, knowing that I don’t know the number of rotor...
Reply

Re: Induction motor's vibration problem

ai.engineer ·
I wanna thank you a lot JP . in the past, we were inspected by external company which follow our machines, each 3 months, they gave us only the result without spectrum (mean ok or not ok), therefore, we decide to make our technical office. it has to be said, we are beginner but we make many training courses about in. If I understand well, that we cannot consider this spectrum as a problem even if there is a noise come from the motor, in fact, I should follow it during shutdown of the pump or...
Reply

Re: Induction motor's vibration problem

ai.engineer ·
thanks guys for your reply. about bearing defect, I don't think that there is a problem come from bearing: BPFI = 13.15*25 = 328.75 Hz BPFO=10. 85*25 = 271.25 Hz BSF= 5.16*25= 129 Hz --> no one coincide with our peaks. Concerning the 1/2 x is 12.5 Hz, there are harmonics around the 1/2x wherein attached be low resolution about in. About 235 Hz, you have a reason, there are sidebands 1/2x, you find attached the resolution around it. if you pick up something useful, don't hesiate to clarify...
Reply

Re: Induction motor's vibration problem

Ralph Stewart ·
Thanks for the info. Can you take data again with more lines of resolution?
Reply

Re: Induction motor's vibration problem

Ralph Stewart ·
Can you get more data with more resolution? After a quick look, I see what appears to be 1/2x with at least 5 harmonics following the fundamental of 1/2x. Can you confirm if this is or is not 1/2x The 235 Hz peak appears to be modulated by 1/2x also. Confirm this? There are several peaks scattered in the plot that need to be identified also. Can you give us a little more info? Thanks and Have a Great Day, Ralph
Reply

Re: Induction motor's vibration problem

electricpete ·
I realize these are low level, but I'd try to identify patterns of the peaks to satisfy myself on whether or not you are seeing bearing defect.
Reply

Re: Induction motor's vibration problem

Ralph Stewart ·
Quote: "i can't take more than this resolution around 1/2x. what about 235Hz ?? " Does you analyzer not have 6400 lines or 12800 line ability? Thanks and Have a Great Day, Ralph
Reply

Re: Induction motor's vibration problem

Xracer ·
Then drop your Fmax to compensate for limited lines.
Reply

Re: Induction motor's vibration problem

ai.engineer ·
i can't take more than this resolution around 1/2x. what about 235Hz ??
Reply

Re: Induction motor's vibration problem

ai.engineer ·
Unfortunitely our analyzer have 800 lines of resolution.
Reply

Re: Induction motor's vibration problem

Ralph Stewart ·
Do you have an acceleration Waveform for the spectrum?
Reply

Re: Induction motor's vibration problem

Chris S. ·
I must say I was kind of leaning the same way as Ralph. With a 50hz line frequency, looking at the multiple half orders and busy noise floor and low amplitude indications of a bell curve I was considering this is indicative of a rub. Although the frequency identifiers are not identified in the spectral data you indicated a bearing issue is not suspected however this may be attenuating from the pump. I would perform a visual inspection with a strobe, check the bearing temperatures and review...
Reply

Re: Induction motor's vibration problem

Xracer ·
What parameter settings are you using? As Ralph mentioned, a higher res recording will show a better picture. Based off of your first posted pictures, It looks like your using a Fmax of 3000 Hz with Lines of resolution of 400 or maybe 800. Are you saying that with your data collector, you are unable to increase your lines of resolution to 1600, 3200, 6400, 128,000? An Fmax of 3000 hz with 400 lines of res, would give you a 22.5 hz separating freq. At 800 lines of res would be 11.25 Hz and...
Reply

Re: Induction motor's vibration problem

ai.engineer ·
you find attached an acceleration Waveform for the spectrum. The bearing temperatures beteween 40 - 50 °C, or the trip alarm in 85°C, therefore our parameters are OK. Concerning The resolution , i'm trying to increase it into software when i did the diagnostic. Knowning that i 'm begineer in vibration analysis, does he anyone explain to me, how can i use the right resolution ?? you can see in the picture below. THANKS
Reply

Re: Induction motor's vibration problem

ivibr8 ·
Resolution = (F.S. X WNF X2)/# Lines F.S. = Frequency Span; WNF = Window Noise Factor (Uniform=1.0; Hanning=1.5; Flat Top=3.8); Because of the "muddy" spectral data you've provided, the forum members are asking to improve the resolution (make it smaller) by reducing F.S. or increasing # Lines. Your analyzer seems old or limited if it can only provide 800 lines max. Can it do a zoom analysis? JP
Reply

Re: Induction motor's vibration problem

Ralph Stewart ·
The "new" data posted looks sort of like the old data, a wide bandwidth. I am sure you know already, that changing a setup will not have any effect on data which is already stored. It only has an effect on the data collected after the setup is changed. If this is new data, did you reload the route before taking the data?. Thanks and Have a Great Day, Ralph
×
×
×
×