32 Posts

IGBTs are the “Gatekeepers” of Current

(Case Study Electrical Defect detected thought CBM)

This is a case history brought to you with data from James Pearce – another great find! This shows how utilising multiple CBM technologies, with a certified and experience technician, can help prevent unplanned failure to assets.

 

Introduction:

Using vibration analysis and thermal imaging condition based monitoring techniques a change in condition was found and a diagnosis of electrical issue with the VFD was given. From this the variable speed drive history parameters were interrogated. This confirmed it was indeed an electrical issue. Further analysis carried out by the site electrical supervisor pinpointed the IVI card as the issue. The IVI card controls a lot of optic connections controlling the IGBT’s. This was replaced and the vibration, temperature and current reverted back to normal.

 

Background:

We have been monitoring assets at the production facility utilising vibration analysis and infrared thermography. On a routine survey a change in condition was noted and investigated.

The motor in this case study is a 4 Pole 50Hz AC motor on a Siemens Variable Speed Drive. This asset has 2 of the same motors both driving a roller each to crush and grind product.

 

On-Site CBM Recommendations:

Motor: It was reported on the day that the windings temperature has been higher in the warm weather and is 10oC warmer than the comparable motor. This survey there has been an increase in the electrical activity across the motor. Please note we can only detect indications of an electrical anomaly. Recommended actions to investigate the electrical drive.

 

Vibration Analysis Data:

The dominant change in condition in the vibration data was an appearance of running speed electrical frequency in the PeakVue data and the increase in the high frequency electrical data.

Figure 1 compares the last four PeakVue acceleration spectra taken from the motor non-drive end. This displays the normal 2xLF activity and then the appearance LF activity this survey.

Fig 1:

 

Figure 2 compares the last two Velocity spectra’s. This shows the increase in the high frequency electrical activity. The top plot is the normal activity and the bottom plot is with the defect.

Fig 2:

Normal data

Data with electrical defect

 

Thermal Imaging Data:

The thermal data below compares the suspect motor and the comparison motor. These motors are on the same asset performing the same duty at the same time.

This data confirms that the windings are indeed warmer on the suspect motor.

Normal Motor

Suspect Motor

 

Electrical Supervisors Investigation:

Below trace shows the current varying.

The below trace is the Phase 1 Current under load conditions, only reading positive part of cycle.

This compares Phases 1 and 3 motor current under load conditions.  Phase 1 only reading positive part of cycle.

On start-up temperatures all came back to normal.The IVI card in the inverter was replaced. The below plot is Phases 1 and 3 motor current equal after changing IVI card, under no load conditions.

 

NOTE:

An Insulated Gate Bipolar Transistor (IGBT) is a key component in what makes up a VFD (Variable Frequency Drive). An IGBT is the inverter element in a VFD, pulsing voltage.

IGBTs have become highly reliable devices that can handle high voltage devices and are able to switch in less than a nanosecond.

The IGBT acts as the switch used to create Pulse-Width Modulation (PWM). An IGBT will switch the current on and off so rapidly that less voltage will be channelled to the motor, helping to create the PWM wave. This PWM wave is key to a VFDs operation because it is the variable voltage and frequency created by the PWM wave that will allow a VFD to control the speed of the motor. Therefore, without the IGBT switching the current on and off so rapidly a PWM wave—and the speed control that comes with it— could not be created.

The IVI card in the drive controls a lot of optic connections controlling the IGBT’s

 

 

A reliable plant is a safe plant

…..an environmentally sound plant

….. a profitable plant

……a cost-effective plant


Failure mode ISO 15243: 5.4.2 Subsurface initiated fatigue

Is this normal Fatigue Failure, how many of you get to see a bearing actually fail from normal fatigue? Usually we come across bearing failures/damage due to secondary factors such as misalignment, over or under lubrication, imbalance, resonance and poor installation……

This is also a great example of how important knowing the asset you are monitoring is as to know when to remove the asset from service, ensuring that the client has got the maximum life out of the asset for the associated risks.

# You can’t analyse what you don’t know or understand #

 

This Case Study Application:

This is a DC motor that is direct coupled driving a gearbox.

 

 

Summary:

We have been monitoring this motor since 2006 and in May 2017 a subtle change in the PeakVue level was noticed, closer monitoring was initiated and a bearing inner raceway frequency was found. Next in June 2018 there was a further step change that prompted the decision to remove from service as we felt the risk of failure was too high.The motor was overhauled at the next opportunity, this was in July 2018.

 

 

Vibration Data:

Figure 1 is the Velocity spectrum, there are no indications of any defect in this data.

Fig 1:

 

Figure 2 is the Peak Acceleration 10 KHz FMax trend from October 2017 until change out in July 2018, this displays an increasing trend.

Fig 2:

 

Figure 3 is the PeakVue Max Peak Acceleration trend from October 2017 until change out, this also shows the increasing trend.

Fig 3:

 

Figure 4 is the PeakVue spectrum. This shows the running speed activity and a beautiful text book bearing ball pass inner raceway defect frequency with harmonics and sidebands at 1 Order.

Fig 4:

 

Figure 5 is the PeakVue time waveform, this shows a distinct periodic impactive activity.

Fig 5:

 

Figure 6 is the Auto correlation of the PeakVue time waveform. Auto correlation is great tool for distinguishing periodic activity within a time signal. This data shows us that there is a defect that is modulating by 1 Order. Therefore a component on the motor shaft, rotating with the motor shaft has a defect.

Fig 6:

 

Figure 7 is a zoom in on the Auto correlation of the PeakVue time waveform. From this we can see that the 1 Order activity is side banded by the inner raceway defect frequency.

Fig 7:

 

 

Images of the bearing defect

Image 1 is of the bearing inner raceway. This shows the track of the rolling element in the race way, due to the DC drive, also within the arrows there is the defect.

Image 1:

 

Image 2 is a microscopic image of the defect. Has anyone else pulled a bearing with this type of defect?

Image 2:

 

 

Failure Mode:

Suspected failure mode is ISO 15243: 5.4.2 Subsurface initiated fatigue,

The images show that this bearing had reached its end of life, the cyclic stress changes occurring beneath the contact surfaces had initiated subsurface micro cracks, and this would have been in part of the bearing at the maximum shear stress. We are at the point where the crack has propagated to the surface and spalling has started to occur.

 

 

Final Note:

A special thanks to James Pearce for the data and working with me on the analysis.

 

 

A reliable plant is a safe plant

…..an environmentally sound plant

….. a profitable plant

……a cost-effective plant

What’s the highest Acceleration levels on Gears you have recorded?

Apologies for the lack of posts over the month, it’s been a very busy time with the family.

This post is a short one just inquiring what levels of Acceleration impacting you have seen in the field from a gear set. This is one I came across a couple of months ago.

 

Summary:

  • Vibration data was collected with FMax of 10 KHz and Sample rate of 32,768.
  • The shaft rotates at 2990 RPM.
  • The gears are small and both have 65 teeth, their function is to transfer drive to an oil pump in a gearbox.
  • We recorded a Peak to Peak of 51.67 G’s compared to another identical asset running at 9.176 G’s.
  • Two weeks later the gears had a functional failure and stopped doing what they’re were designed to do.

 

 

Vibration Data:

This is the 1.3 Second Acceleration Time waveform comparing the suspect unit and an identical unit.

 

 

Images of Gears after Functional Failure:

Images of the gears on inspection.

 

 

A reliable plant is a safe plant

…..an environmentally sound plant

….. a profitable plant

……a cost-effective plant

Electrical defect found with Velocity data – Case Study

Has anyone found many electrical defects though vibration analysis? We know that VA will show the indications of electrical activity but not necessary the severity. This case study shows that the Velocity vibration data can indicate what the cause of the vibration problem is, this will enable the engineer to target the investigation.

Thanks to James Pearce for the data. linkedin.com/in/james-pearcevibrationanalysis

 

Background:

A routine client called after the operators noticed an increase in noise and vibration from a main plant drive motor. This is a DC motor and usually operates around 400-500 RPM. This is a rather old motor and drive system.

 

 

Initial Vibration Survey:

On attending site vibration data was collected, analysed and before leaving site recommendations were given.

Figure 1 is the Velocity Spectrum collected from the motor. This showed a 1 Order amplitude of 0.07mm/s RMS, with a dominant peak at 49.95Hz with an amplitude of 3.2 mm/s RMS with many harmonics. The motor was operating at 384 RPM during data collection.

Fig 1:

 

 

Figure 2 is the PeakVue Spectrum. This displayed a dominant peak at 149.86Hz, 3xLf. This was also sidebanded by running speed.

Fig 2:

 

The recommendations was to check all supply cable connections and inspect the variable speed drive components for condition.

 

 

Maintenance Inspection:

The site electrical engineer was dispatched to inspect the drive for this variable speed motor. Upon inspection 2 Thyristors were replaced and all electrical connections checked for security.

The operator then reported that the vibration magically disappeared.

 

 

Post Maintenance Vibration Survey:

Vibration data was then collected after maintenance. The motor was running at a higher speed of 456 RPM on the follow up survey.

Figure 3 is the Velocity overall trend from the initial survey and post maintenance survey. This trend shows the reduction on motion from 4.301 mm/s RMS to 1.162 mm/s RMS.

Fig 3:

 

 

Figure 4 compares the before and after maintenance Velocity Spectra’s. From this you can see the dominant 49.55Hz and harmonics have disappeared. The only activity left is a peak at 299.74Hz again sidebanded by 1 Order.

Fig 4:

 

 

 

Summary:

This again shows the benefits of sending a certified, experienced and correctly mentored Vibration Engineer and not a data dog to investigate vibration issues. James quickly pinpointed the cause of the excess vibration that enabled the client to efficiently target the area of concern and quickly rectify the issue saving time and money.

 

 

A reliable plant is a safe plant

…..an environmentally sound plant

….. a profitable plant

……a cost-effective plant

The Power of Water

This is a great example that shows how powerful water can be in destroying a bearing, after only 1 week, and also highlights that when you perform vibration analysis the normal Velocity data should never be forgotten about.

This case history comes from a great friend of mine Matthew Plant linkedin.com/in/mathew-plant-46000456 .

Matt collected the vibration data and performed the analysis and recommendations on his findings to his client.

 

Asset:

The asset is an Automotive Dynamometer test system in an altitude test facility, the bearing supports the dynamometer rolls. The unladen (no vehicle) rolls shaft weighs 3 tonnes and speed is variable from 0 to 720 rpm (0-250kmh). There is a SKF 22228CCKW33 installed at both shaft ends, the bearing in question however is location end, all radial loads are within spec.

 

Background:

This forms part of a routine maintenance condition based monitoring program. The client reported activation of the facility water sprinkler systems and a service inspection was scheduled to ensure no asset was damaged due to the water sprinkler activation.

 

Vibration Survey:

All the data is the survey before the incident and the survey after the incident. The data was collected one week after the incident due to de- contamination works.

On analysis of the vibration data the following points were noted;

Velocity Data:

Figure 1 is the overall Velocity trend. The overall Velocity increased from 0.137 mm/s RMS to 0.602 mm/s RMS. Even still low this was an increase of 440%

Fig 1:

 

Figure 2 compares the before and after incident Velocity spectra’s. This clearing indicates a change in the bearing condition after the incident. The top green plot is after the incident on site.

Fig 2:

 

Figure 3 is the Velocity spectrum and this show activity that is dominated by the bearing outer raceway defect frequency.

Fig 3:

 

PeakVue Data:

Figure 4 is the PeakVue Max Peak trend from before the incident at 2.019g’s and after the incident at 5.623 g’s

Fig 4:

 

Figure 5 compares the PeakVue spectra’s from before (Blue plot) and after the incident (Green plot).

What can be seen is a 3.566 Order and harmonics. This 3.599 Order is the fundamental defect frequency for the SKF 22228CCKW33 installed. You can also note that 2XBSF is the highest frequency.

Fig 5:

 

Acceleration Data:

Figure 6 compares the before (Blue plot) and after (Green plot) of the raw Acceleration time waveform. This also indicated a high increase in the acceleration impactive data (note crest >5).

Fig 6:

 

Figure 7 compares the before (Blue plot) and after (Green plot) Acceleration spectra’s. This also shows an increase in the friction and impactive levels.

Fig 7:

Vibration Analysis Summary and Recommendations:

Due to the high increase in all vibration parameters and defect frequencies evident for the bearing outer raceway and rolling elements it was advised to replace the bearing.

What was the ‘Alarm bell’ for the analysts was the Velocity data.

 

Root Cause

Obviously water ingress was the instigator in the corrosion; however it was noted that the SKF SNL housings should withstand wash down. Further inspections pointed to the cap lifting eye being absent allowing water to enter the enclosure through the W33 lubrication groove.

 

Bearing Inspection:

On inspection the damage due to the bearing after running one week after the water incident was highly evident.

Outer Raceway.

Outer Raceway.

Inner Raceway.

 

Bearing Replacement:

The new bearing was then installed using the hydraulic nut drive up method.

 

A reliable plant is a safe plant

…..an environmentally sound plant

….. a profitable plant

……a cost-effective plant

Introduction:

Fluid film bearings are mainly monitored with proximity probes. It is often stated that “you can’t detect early defects in fluid film bearings with normal vibration techniques (Velocity, Acceleration or a bearing condition unit)”. But in fact you can detect the effects of a fluid film bearing deteriorating with a normal accelerometer.

Under abnormal circumstances metal to metal contact might occur, leading to occasional high-frequency noise that can be detected with normal vibration equipment. The following case study is a great example of this and also using lubrication analysis as part of a maintenance program.

This case history covers a Production facility Extraction Fan which has been monitored as part of a site wide Condition Based Monitoring program. The drive of this program is to integrate condition monitoring techniques and to drive the maintenance program.

This fan unit had a motor that is a direct drive to a fan shaft, the fan shaft has a white metal fluid film bearing. The fan is a standard overhung centrifugal of about 2.5 meters diameter.

This data was collected over an extended period by myself and Ian Graham.

 

Vibration Analysis:

Ian Graham flagged this reliability risk very early in the program for having a considerable 1 Order impact present in the PeakVue™ data (see Figure 1).

Figure 1 shows the initial Vibration data collected on the fan bearing with the 1 Order event present.

 

 

Vibration Trend Analysis:

Figure 2 is the PeakVue™ Trend of the bearing as it was nursed through until maintenance could be conducted.

This showed the initial level, reduction in levels after an oil flush, then a period of monitoring until another oil change and a bearing inspection.

 

 

Lubricant Analysis:

As the initial fan data had a dominant 1 order event and was being monitored on a monthly basis, we needed to determine whether the event was consistent or deteriorating, and what possible causes were.

Oil samples were then taken (see image 1), on visual inspection the oil was in a very poor contaminated condition. The lab report (see image 2) stated a serious concern with particulate matter contamination and high levels of Sodium, Iron, and Tin.

The indications of Tin suggested probable sleeve (Babbitt) wear of the bearing.

Image 1 is the Fan DE bearing oil sample:

Image 2 shows the initial oil sample report and diagnosis with emphasis on the high Tin levels:

 

Maintenance Actions:

This fan was a critical component of the facilities production process, however with a plant upgrade planned for the very near future, the decision was made to closely monitor the deterioration of the assembly rather than to rectify this potentially expensive piece of equipment.

The temporary measure of an oil flush and change was conducted immediately, with a visual inspection planned for the next shutdown.

 

Maintenance Inspection:

During the shutdown the bearing housing was split and the bearing shells separated. The damage to the bearing was very extensive with ‘scalloping’ of the Babbitt material evident in the direction of rotation forming a build-up at the end of the lower shell. The cause of this is most likely the failure of the lubricants ability to sustain an adequate oil wedge between the shaft and the bearing.

Image 3 shows the Fan DE white metal bearing upon inspection:

Image 4 shows the Lower half shell of the white metal bearing with a piece of ‘free floating’ Babbitt that was found in the sump:

 

Conclusion:

In conclusion, with the company’s utilisation of all the available Condition Monitoring technologies and tools, they were able to monitor and be consistently and accurately informed of the state of deterioration of the bearing. This allowed them to implement a rolling program of temporary measures to stave off what was essentially an unserviceable critical machine until the Factory upgrade was conducted.

.

A reliable plant is a safe plant

…..an environmentally sound plant

….. a profitable plant

……a cost-effective plant

 

 

_________________________________________________________________________________________

7th August 2018: Additional data as requested by JUAN CARLOS URQUIOLA

Below is the Velocity data from September 2017 and June 2018, there is a difference in the number of an amplitude of the 1 order as associated harmonics.

 

Below is the Acceleration high frequency spectrum, this shows two mounds of activity that has side bands of 1 order and 2 orders.

 

What happens when recommendations are not followed – “when things are left to burn”.

How often have you performed a reliability survey and issued a report of findings and recommendations to reduce the risk of unplanned system failure… and the client does not follow the recommendations.

This is one example of an infrared thermal imaging survey that highlights the importance of following the recommendations and also that a thermal survey should be performed by an experienced/qualified reliability technician who does not just rely on the thermal camera to rush round the site but also uses the human senses and experienced to assess system condition.

 

 

Initial Survey:

One panel unfortunately had Perspex in the way of the cable terminations, so this could not be surveyed with thermal imaging. Through the perspex cover it was noticed that the cable sheath has split, probably due to excess heat and exposing the copper cable.

This was reported on the day to the site supervisor, and in writing in the report. Site confirmed that they were going to schedule in repair at the soonest opportunity due to the high unknown probable risk.

This is the thermal image of the panel, note no readings as infrared energy doesn’t pass through Perspex.

This is the digital image of the panel showing the Perspex cover and damaged cables.

 

 

Unplanned Failure:

This was not inspected/repaired and the panel caught on fire. This caused shutdown of the plant and a huge costs to the company in downtime and reputation due to unfilled orders to their customers.

Images of the failed component.

 

Repair:

Image of the repair. Here you can see the burn fire marks on the back panel.

 

 

Conclusion:

Sometimes we try our best to ensure our clients do the right thing for reliability on their plant. Unfortunately they don’t always action what we recommend, not matter how much we try to convince them. In this instance all we can do is keep spreading the word of how important it is to know the condition of your system and then to actually action any risks. This in turn will reduce the risk of unplanned failure.

A special thanks to James Pearce for sharing his experience.

 

Recently I saw a post from Terrence OHanlon of Reliabilityweb.com, that I feel summed up Reliability.

A RELIABLE plant is a SAFE plant

…..an ENVIRONMENTALLY SOUND plant

….. a PROFITABLE plant

……a COST-EFFECTIVE plant

This month’s blog is to promote the thinking that when drive trains are aligned they should be aligned to the bearing tolerances and not the coupling tolerances. In addition how many people receive an alignment report with a soft foot check? We have found that some companies allocate their employees a laser alignment kit tell them what buttons to press and send them in the field. Without proper training and mentoring how will these employees learn correct Precision Alignment? Without correct training they will not know how to fix problems if they don’t understand fully what they are doing.

This month’s blog shows the importance of Precision Alignment including soft foot check and that the users of laser alignment equipment should be properly trained and mentored in Precision Alignment.

This survey was conducted by a great friend of mine and recent VCAT 3 Certified Seasoned Analyst James Pearce. linkedin.com/in/james-pearcevibrationanalysis

 

Background:

We were called to investigate an apparent increase in vibration levels after a high pressure hot water pump was replaced with a new pump end and a reconditioned drive motor. The operator felt that it was not running as smooth as the old pump set.

 

Instrumentation:

For this survey James used the CSI 2140 Dual channel Machinery Health Analyser. Data analysis was carried out using the CSI AMS Machinery Health manager software V5.61.

 

Methodology:

Vibration data including Velocity, Acceleration and bearing condition unit PeakVue was collected from each bearing location as close as possible to the source. Where applicable additional data including high resolution vibration data was collected.

 

Executive summary:

There are elevated directional Velocity vibration levels when running at 2680 RPM (Low speed). This is due to a coincidence of a system natural frequency being excited by a motor Soft Foot condition.

 

Maintenance Recommendations:

  • Check/inspect condition of the foundation, looking for looseness and any deterioration in the base plate.
  • Perform precision alignment that must start with a soft food check and soft foot elimination. Followed by precision laser alignment.
  • If these actions do not resolve the issue then stiffening of the base may allow for improved precision alignment and may move the system resonance out of the running speed range.

 

Analysis Summary:

  • There are increased directional Velocity vibration levels at the motor when running at 2680 RPM.
  • After reviewing the vibration data it was decided to perform further checks and the motor holding down bolts was loosened one time when in operation, this is to check for distortion of the motor rotor to stator air gap. During this test it was and found that the Velocity amplitude reduced. The amplitude reduced to its lowest level when the motor non-drive end foot bolt (bolt closest to pump #1) was loosened (see figure 1&2). This indicates there is a soft foot issue.
  • In addition an overall vibration coast down test & resonance bump test was performed. This data confirmed a natural frequency at 2X 2680RPM (see figure 3).

 

HPHW Pump #2 Motor Non-Drive End

The motor has elevated directional Velocity vibration levels. By loosening one motor fixing foot bolt at a time, the Velocity amplitude reduced. The amplitude reduced to its lowest level when the motor non-drive end foot bolt (bolt closest to pump #1) was loosened.

Figure 1 compares the Velocity spectra when running at 2680RPM, for the one order levels, as found state (4.332mm/sec RMS) & where the amplitude decreased the most after the motor foot bolt was loosened (2.651mm/sec RMS).

Fig 1:

 

HPHW Pump #2 Motor Non-Drive End

Figure 2 is a photo of the motor indicating which foot bolt was loosened which resulted in the best decrease in amplitude.

Fig 2:

 

HPHW Pump #2 Motor Drive End

Figure 3 is the data from a resonance bump test & overall vibration coast down test, performed at the motor drive end (DE).

The top plot bump test result indicates a system natural frequency that will coincide with twice the running speed (when running at the low speed) and amplify the vibration levels.

The bottom plot amplitude peak from the coast down test also confirms this condition with a peak at 5336 RPM, twice the running speed at the low speed setting.

Fig 3:

Hello. This is a different avenue than my usual posts, this one is a link to a paper I have just written with the great knowledge and help from Dr K.

 

Briefly:

I was introduced to Dr Knezevic (Dr K) of the Micre Akademy though a great mentor in thermal imaging Austin Dunne of the Institute of Infrared Thermography.

Please click on this link to learn more about the great work of the Micre Akademy

Please click on this link to learn more about the Institute of Infrared Thermography

 

About this Paper:

MIRCE Science is a theory for predicting expected functionability performance for a functionable system type. Accuracy of the predictions is governed by the degree of the scientific understanding of the physical mechanisms, and human rules, that govern the motion of functionable system types though MIRCE Space. The main objective of this paper is to address vibration monitoring as one of the possible mechanisms that governs motion of a gearbox through functionability states, which are contained in MIRCE Space. In general, and to illustrate this process through a case study related to heavy gearbox used in Plastics Manufacturing industry, conducted by the author with vibration data collected on site by Ian Graham.

 

Click here for the paper Vibration Monitoring Mechanism Of Motion

 

Acknowledgement:

The author wishes to acknowledge the support received from Dr Knezevic, MIRCE Akademy, Exeter, UK, while preparing this paper. As the “father” of MIRCE Science, Dr Knezevic, has inspired me to view how every day Condition Based Monitoring can have a significant impact on functionability performance of the whole system.  Consequently, I can now understand how many companies are performing Condition Based Monitoring but are not linking this to the business performance of the whole organisation/company. MIRCE Science is the body of knowledge that bring together these two very different but related disciplines, for the ultimate benefit of the user.

This is one I recently finished and thought it would be a great one to share so people know what can be achieved.

 

Background:

We had three pump sets suffering from elevated vibration levels when operated in different combinations. Conventional vibration analysis was performed and this indicated a structural resonant condition.

The pump motors are mounted on a false floor:

and the pump barrels are below the floor:

The pump with the worst motion was on pump 3, the one far away from the edge of the drop. Also this pump has the least structural support under the floor. When ran in certain combinations pump 3 would be excited very badly.

 

The cost effective solution.

I designed a vibration dynamic absorber.

Dynamic Absorbers are often overlooked and not used, they can be seen as a band aid or a last option for some vibration problems. Whereas in some cases they can be the only cost efficient option, and they are very effective.

The Vibration Dynamic Absorber is a unique bespoke item, maintenance free, that is designed to absorb unwanted energy. It is tuned to have the same resonant frequency as the structure to set up an out of phase signal reducing the signal generated by the structure.

 

How did I design these?

For this one it was more of a ‘gut feel’. I looked at the motor and then drew out a design that wouldn’t look out of place when mounted, and that had some adjustment to it when fitted as theory doesn’t always pan out in real life. Then from this I worked backwards to get the correct material dimensions/configuration so it was resonant at the target frequency. I also made some weight configurations so I could cover my target range.

I will be going back in 6 months to see how it fairs. I did consider a round bar and weight but thought that with the rectangular bar you have more control on what way it will be resonant. As once you have performed phase analysis on the motor you then know what way it is moving and can mount the absorber accordingly.

Image of Pump 2 Vibration Dynamic Absorber:

Image of Pump 3 Vibration Dynamic Absorber:

Pump 2 Live Motion Video

 

Pump 3 Live Motion Video

 

Pump 3 Slow Motion Video

 

What am I covering?

On pump 3 I am covering the one problem frequency, 1 Order, but the two arms are of different lengths in terms of the length from the point of pivot (clamping) to the mass. Also the arms are of different dimensions with different mass at the end so they could be tuned to the same frequency.

I also did find that the sweet spot was not necessary the point of higher deflection of the absorber and that the three motors all reacted differently.

 

Final Review of actual vs theory:

I have had time to review the final theoretical tuning of the three pumps to actual results. They are all different and no one motor is the same, they all have their own personalities dynamically wise.

Pump 3 had the highest overall vibration, one dominant frequency at 1 Order on pump 3 and this was successfully reduced.

Pump 1 and pump 2 had two frequencies in the data. And both of the vibration dynamic absorbers were tuned to the lower frequency not the one order.

 

Table of final overall levels:

Before After % reduction
Pump 1 Motor NDE (Top) 4.314 2.854 33.84%
Motor DE (Coupling end) 2.092 1.617 22.71%
Pump 2 Motor NDE (Top) 9.95 6.959 30.06%
Motor DE (Coupling end) 4.05 3.012 25.63%
Pump 3 Motor NDE (Top) 27.02 7.59 71.91%
Motor DE (Coupling end) 10.73 5.113 52.35%

 

Pump 1:

Pump 1 actually showed the text book results. The theoretical calculations for the tuned damper was for the lower frequency not the running speed (1520 CPM yes they are on soft start VFD). It actually split the frequency – text book……….beauty!!

 

I have more questions and theories now, this is pretty exciting stuff. Hopefully I can keep this going on other pumps.

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