Tagged With "ANGLE"

Topic

Change in Vibration Levels between startup cycles

DuPlesis ·
We have a Gas Turbine Driven Compressor Train. Gas Turbine has dual shafts i.e. Gas Producer Rotor and Power Turbine Rotor. We are observing increase in vibration levels between startup cycles. APHT Plots indicate vibration levels of around 20 microns with phase angle of 150 Degrees for one start up cycle. After another startup, vibration levels increase to around 40 Microns with Phase angle of 220 Degrees. Phase angle changes from 150 deg to 220 deg and back. Orbit Plots are circular and...
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Re: Change in Vibration Levels between startup cycles

Shurafa ·
With the this limited data, people would guess. More details (vibration plots, repair records etc) should help reduce guessing. Will it be possible to tabulate the readings for the few starts to have a better understanding about any patterns? Maybe something like this: Date, time, speed, load, probe, overall, 1x amp and phase. It would also be interesting to see Bode plots for startup and shutdown. Regards- Ali M. Al-Shurafa
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Re: Change in Vibration Levels between startup cycles

Rotating Guy ·
Hi Duplesis, I agree what Mr. Ali said to see start-up and shutdown plot, if i were at your position, i would clear all the E&I problems were might occur in your trend, then prior to suspect mechanical problem, my assessment in your given trend plot, i would suspect the grounding or electrostatic discharge from cable which affect the probe, but it is just assumption then you must figure it out. if you could send the waterfall plot during the time of the incident will might help. regards,
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Re: Change in Vibration Levels between startup cycles

William_C._Foiles ·
Compare polar and/or Bode plots from some coastdowns after running to thermal equilibrium. Trend plots by time will not be that helpful. If something is changing permanently, you should see it.
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Re: Change in Vibration Levels between startup cycles

Ngo Dinh ·
Need more information but for me, I do not think this is a big thing due that: 1,The phase when operating is quite stable. 2. 1X is not much and the amplitude change increase, decrease, increase again through times of starting (not change increasing through time). I have ever seen the same case of changing vibration between both end of gas turbine after each time of starting. It could be change a little bit shaft position after shutdown. I suggest you check: 1. Polar or bode plot at starting...
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Re: Phase rule +/-30 degrees

Shurafa ·
Do you mean that, in practice, the phase angle is considered stable if its value does not change a lot? Your definition of a lot of change is greater than 30 dg plus or minus the center value of the phase? Regards- Ali M. Al-Shurafa
Topic

Phase rule +/-30 degrees

ConfMx ·
why phase rule +30/-30 degrees = same angle?
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Re: Phase rule +/-30 degrees

John from PA ·
Not certain what you mean; can you provide a source?
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Re: Phase rule +/-30 degrees

John from PA ·
https://www.reliableplant.com/...eld-balancing-rotors mentions a 30/30 rule as well as many other rules. Scroll down for the content titled “Selecting a proper trial weight”. After 40 years of doing field balancing, I’m sure glad that “rules are made to be broken.”
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Re: Phase rule +/-30 degrees

Walt Strong ·
" I’m sure glad that “rules are made to be broken.” " I agree. I have used the 30/30 Rule many times, but I have also departed in many directions and achieved a good balance result. We still don't know whether OP is referring to Balancing or something else. Walt
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Re: Phase rule +/-30 degrees

OLI ·
Indeed.
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Re: Phase rule +/-30 degrees

Walt Strong ·
" A ratio of this vector change to the average vector can be useful as can just the magnitude of the vector change. " I agree, but I have not seen a balance program display the Vector Ratio; perhaps it does calculate it; or not. I have seen the vector change guidelines described as indicated by either a sufficient phase change or an amplitude change. The underlying principle is that the Vector has a sufficient change. I have no idea what context the OP was questioning about. Walt
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Re: Phase rule +/-30 degrees

Walt Strong ·
The only "Rule" that mentions +/- 30-degrees is for Balancing, where this phase change amount is recommended for a good Trial Weight vibration response. I have never heard of it meaning the same angle. Can you clarify your question? Walt
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Re: Phase rule +/-30 degrees

William_C._Foiles ·
Phase alone lacks the amplitude; phase plus amplitude will give the vector. Look at how the vector changes. A ratio of this vector change to the average vector can be useful as can just the magnitude of the vector change.
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Re: Phase rule +/-30 degrees

Jason Tranter ·
I am going to guess that the OP is referring to the various training courses, pocket guides, and wall charts that may state, for example, "for unbalance, the phase difference between vertical and horizontal will be 90 degrees +/- 30 degrees" - and all of the similar rules for unbalance, misalignment, etc. The OP may wonder why there is a tolerance of 30 degrees. On the assumption I am right, the reason for the tolerance is because those rules (90 or 180 degrees phase difference) assume ideal...
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Re: Phase rule +/-30 degrees

Jason Tranter ·
Ah yes, quite correct. I answered too hastily. The graphic (from one of our simulators) illustrates John's correction.
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Re: Phase rule +/-30 degrees

John from PA ·
The relative phase between two transducers is also 90 deg when the major axis of the filtered orbit is directly in line with one of the probes.
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Re: Phase rule +/-30 degrees

William_C._Foiles ·
Interesting article, but I do not believe it is great nor the 30/30 rule. When you place a trial weight in the right location, you expect no phase change unless the weight is a little large in which case you get a 180 degree change. Either result can be excellent. Either result can produce valid (excellent) balance data if a trim is required. It is the vector change that is important.
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Re: Phase rule +/-30 degrees

ConfMx ·
Hola a todos. I thank you for your kind comments. I was out of reach web, reason why I had not provided more information. The exact point of the discussion or doubt is based on the following: An automotive manufacturer asks to perform some tests of residual imbalance in their balancing machines, asks that the resulting phases are NOT different in more than 10 degrees between each start of the balancing machine, without making any change in weights, speeds, sensor position, etc. In the...
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Re: Phase rule +/-30 degrees

Walt Strong ·
Imagine several "vibration experts sitting" on a park bench talking about baseball, or what ever. A small gust of wind blows a tiny piece of paper, similar to size contained in a Fortune Cookie, that reads " why phase rule +30/-30 degrees = same angle? "! The conversation shifts around to this paper phrase (not phase) as a topic. Unfortunately a real discussion cannot occur, because the author (OP) is not participating! Nice illustrations, as always, Jason. Walt
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Re: Phase rule +/-30 degrees

Akhil Rathore ·
please elaborate
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Re: Phase rule +/-30 degrees

ConfMx ·
Re: Phase rule +/-30 degrees
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Re: Phase rule +/-30 degrees

William_C._Foiles ·
To amplify what JohnPa said, with circular motion any orthogonal probes will have a 90 degree relation, and any probe location would be at a principal axis. Likewise, having equal amplitude does not mean that there is a 90 degree phase difference. If the motion is such that x = -y ( with probes at x and y), then the motion is equal but the phase difference between the probes is 180 degrees - a 0 degree phase difference with equal amplitudes is created by x=y. In fact, equal amplitudes at the...
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Re: Phase rule +/-30 degrees

OLI ·
What is the weight of a rotor? What is the weight of a peso?
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Re: Phase rule +/-30 degrees

Rohit02 ·
I think that the manufacturer is asking for the repeat-ability of the balancing machine. That too is considered important. For higher residual unbalances this is quite stable and you may not get more variation in phase. Also for shop balancing machines since there is less possibility of other problems such as alignment and rigidity phase angle is generally stable with less variation. However, if the residual unbalance is near the tolerance limit of the balancing machine then there might be...
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Re: Phase rule +/-30 degrees

Walt Strong ·
I agree with Rohit about the balance machine qualification. It was a nice focused discussion by John and Bill about proximity probes! Walt
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Re: Phase rule +/-30 degrees

John from PA ·
3 Mexican peso's = 0.12 Pound sterling
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