Tagged With "rotor"

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Balancing duel rotor variable pitch axial fans

John.OGE ·
We are a coal fired power plant and one of our units has large duel rotor variable pitch axial fans for Induced Draft made by Westinghouse. Does anybody know balancing experts (SME) that are familiar with these kind of units?
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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?
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Parameter identification of a rotor bearing system with floating ring bearing

PBCR ·
Hello everyone,   Introduction:  I've been reading the book by Mr. Donald Bently "Fundamentals of Rotating Machinery Diagnostics". Compared to other rotor models, Bently-Muszynska model looks easy to interpret.Especially with the...
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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.
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PdMA RIC Test Bad Rotor

Chris184 ·
How many have experience with the PdMA tester and would you suspect a motor with the attached test results to look like the photos. We performed a single phase rotor test and had almost 20% current swing while rotating the shaft, so the fact of a...
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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...
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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!
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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,
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Rotor winding insulation problem

Lampard Nguyen ·
Dear Experts, We have a MV wound rotor motor, 2900KW, 6600V stator winding, 2700 V rotor winding. This is a cement milling motor in cement plane. Last year, the corrected insulation resistance of Wound Rotor is high, 1000 Mega ohm. But recently, rotor...
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Storage of turbomachinery spare rotors

vikramdeeps ·
Hi Guys,   Usually the turbo machinery rotors are hang vertically for long term storage.I know some theories such as L3/D4 ratio,API 686 also has one clause says bearing span/Diameter ratio but no mentioned about any values for reference for...
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Definition of trim balancing?

abdulbasitb ·
What does the word "trim" imply when used in the term "trim balancing"?
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Re: Balancing duel rotor variable pitch axial fans

arie mol ·
Over the recent 25 years I have balanced many of these MWatt Industrial fans worldwide. Do you face a specific problem?
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Re: Balancing duel rotor variable pitch axial fans

John.OGE ·
This fan has proven difficult to balance. Not many plants use a two stage variable pitch axial fan. The specific fan is a Westinghouse Sturtevant Two-Stage Induced Draft Axial Fan (885 RPM, 7000 hp, hydraulically actuated blade pitch). Have you balanced similar types of fans?
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Re: Balancing duel rotor variable pitch axial fans

arie mol ·
John, Have you balanced similar types of fans? No for Westinghouse. Yes for Howden, fans were made in the Netherlands and Denmark. In coal fired plants. Problems encountered that will make balancing troublesome: * Loose parts in hollow impeller hub(s). Solid stuff like corrosive settlements of pitch control lub oil leakage into hub. A repeated initial run proves such unbalance instability: different amplitudes and/or phase angles for both runs. Clean hub first. * A resonant condition near...
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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.
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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...
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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?
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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...
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Re: Rotor broken bars problem, is it right?

Shurafa ·
Nice photos. I like these clear pictures. Regards-Ali M. Al-Shurafa
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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.
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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...
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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...
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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...
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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...
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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...
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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!
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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.
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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...
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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...
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Re: Rotor Bar Defect?

Lampard Nguyen ·
Vib_Guy, Please inquiry this link: http://www.utilityproducts.com...s-8220rotor8221.html Good luck!
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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.
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Re: Definition of trim balancing?

Walt Strong ·
I quickly scanned through ISO standard 1940-1 and found no mention of the word. I think it's safe to say it does not define a fundamental property associated with balance. I have seen the word "trim" used two ways. One description is used to describe an additional weight that is added during balancing when the correction weight is not adequate. Typically in this case you could installing new correction weight, or you could add a small trim weight to meet requirements. The second description...
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Re: Definition of trim balancing?

William_C._Foiles ·
1940 has been updated. The balancing standards have new numbers. The old 1940 was for low speed balancing. If you look at ISO 21940-2, the definitions, you will find a definition
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Re: Definition of trim balancing?

Shurafa ·
This term is a part of the vocabulary explained in ISO 1925:2001 - Mechanical Vibration -- Balancing -- Vocabulary. According to this standard, it is usually the small balance that one would perform in order to reach the final balance condition after the main balancing target has been achieved. Regards- Ali M. Al-Shurafa
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Re: Definition of trim balancing?

Walt Strong ·
"According to this standard, it is usually the small balance that one would perform in order to reach the final balance condition after the main balancing target has been achieved." Thanks for the update on the actual ISO definition that closely matches one of the ones that I gave earlier. Walt
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Re: Definition of trim balancing?

Shurafa ·
Just to avoid a possible misunderstanding, the statement above is not the actual verbag of the standard. It is rephrased. Regards- Ali M. Al-Shurafa
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Re: Definition of trim balancing?

William_C._Foiles ·
It could be that I have referenced a draft ISO standard planned to replace 1925. I didn't check our standards site for availability.
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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.
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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.
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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!
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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.
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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?
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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.
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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?
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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!
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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...
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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!
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