New Tools For Vibration Cm (Presentation) Rams 2011 Chris Engdahl

New Tools for Vibration Condition MonitoringChris EngdahlGE Energy, Measurement & Control

Solutions

5th Reliability, Asset Management & Safety (RAMS) Conference 2011

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April 13, 2023

Why do Predictive Maintenance?

Maintenance Planning

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The PdM/PM Advantage : PLANNING

F1

F0

Timeline Towards Failure

W-1

Work Execution

W-2W-4W-5W-6W-? W-3

Scheduling Process

Planning Process

Evaluation/Approval

P2 Advanced Vibration diagnostics - 5 months

P3 IR Thermography – 3 months

FunctionalFailure

Hard Failure

P0P1

Wear Debris - 6 months

P6 Hot to touch 3 days

P5 Audible noise - 2 weeks

P4 Overall Vibration Increase – 10 weeks

Better information, better planning

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Dynamic Energy Index (DEI)KurtosisSkewnessCumulative ImpulseAcceleration EnvelopingSideband Energy RatioHigh Pass Filtering

New Tools for Vibration Condition Monitoring

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• Sum energy in discrete bands• Bands correspond to component ranges• Normalize by Torque

Dynamic Energy Index (DEI)

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101

102

103

104

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

Frequency (Hz)

Am

plitu

de (

g)

Beari

ng

Pla

neta

ry S

tag

e

Inte

rmed

iate

Sta

ge

Hig

h S

peed

Sta

ge

Str

uctu

ral

DEI Frequency Bands

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Kurtosis

0 5 10 15 20 25-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

Time (ms)

Timebase Waveform, Healthy Signal

Tail

Kurtosis = 3.9

BroadCenter

0 5 10 15 20 25-8

-6

-4

-2

0

2

4

6

8

Time (ms)

Timebase Waveform, Failing Generator Bearing

WideTail

Kurtosis = 14

NarrowCenter

Variance (standard deviation squared) involves the square of differences between data and the meanVariance is the 2nd momentSkew is the 3rd moment

Kurtosis is the 4th moment. It puts more emphasis on the tails of the distribution

Spikier waveforms have higher Kurtosis

Normal vibration 3Sine wave 1.5

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Skewness Calculation

Timebase waveform is treated as a statistical set of data

Skewness = 3rd statistical moment of the set

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Generator Bearings: ESD Noise, High Skewness

0 50 100 150 200 250 300 350-5

-4

-3

-2

-1

0

1

2

3

4

5

Time (ms)

Acc

eler

atio

n (g

)

WTG128 Generator Outboard Timebase 5/20/2009 2:49:00 PM 1447 rpm; kurt = 9.87; skew = -1.95

Asymmetric noise, > 5 g (noise can be symmetric!)Kurtosis highDirect high

This noise happens only on some machines on particular bearings;probably associated with grounding brush problems

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• Passage of debris through gear mesh produces a detectable impulse.

• Use signal processing to automatically detect, measure, and accumulate a damage index.

Cumulative Impulse

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4.538 4.54 4.542 4.544 4.546 4.548 4.55 4.5520

1

2

3

4

5

6

7

8

Time (s)

g

SlavePlanetaryRotor16Apr10second1; corner = 0.1 Hz; order 2; 13 events for DI = 66 GE CONFIDENTIAL

Processing Example

AmplitudeResets

AdaptiveThreshold(12 x LP signal)

Low-pass filtered signal (red)

DecayEnvelope

Final Maximum For Event (red dot)

RectifiedSignal

EventTerminationEvent

Start

DefaultThreshold4 g

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Acceleration Enveloping Algorithm

• High pass filterExclude mechanical vibration contentInclude structural resonance frequency range

• Rectify• Envelope• FFT

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0 50 100 150 200 250 300-5

-4

-3

-2

-1

0

1

2

3

4

5

Time (msec)

Ac

ce

lera

tio

n (

g)

Amplitude modulationand envelope

Defect Repetition = IRBP

One revolution

DefectRepetitionFrequency

StructuralRinging

Impact-LikeEvent

Figure 6. Bearing elements generate a localized impact force and structural resonance response each time the damaged region is engaged.

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Sideband Energy Ratio

Frequency

Am

plitu

de

1XMesh

2XMesh

3XMesh

Healthy Gearmesh

Frequency

Am

plitu

de 1X

Mesh

2XMesh

3XMesh

Damaged Gearmesh

Low (or missing)Sidebands

Higher and/or moresidebands

Sideband Energy Ratio = S (sideband amplitudes)

Center mesh frequency amplitude

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Spectrum Data From Gearbox Test

Early In TestLittle Damage

Late In TestSignificant Damage

Very LowSidebands

HigherSidebands

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WTG 130 High Speed Gearbox

0 50 100 150 200 250 300 350-1.5

-1

-0.5

0

0.5

1

1.5

Time (ms)

Acc

eler

atio

n (g

)

WTG130 High Speed Timebase 4/27/2009 3:23:00 AM 1440 rpm; kurt = 2.99; skew = -0.14

Lots of stuff!

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0 2000 4000 6000 8000 10000 12000 140000

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

X: 1247Y: 0.1732

Frequency (Hz)

Acc

eler

atio

n (g

)

WTG130 High Speed Spectrum of Timebase 4/27/2009 3:23:00 AM 1440 rpm

X: 625Y: 0.08677

X: 503.1Y: 0.1409

X: 334.4Y: 0.05194

X: 168.8Y: 0.02408

Where is the noise?

1X and 2X HS mesh lines are strong

1X, 2X, and 3X IS mesh lines are strong

Mesh frequencies obscure the interesting stuff

Envelopingbandpass region

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To filter or not to filter…

0 1 2 3 4 5 6 7 8-1

-0.5

0

0.5

1

Revolutions of HS Shaft

Acc

eler

atio

n (g

)

WTG130P High Speed Timebase 4/27/2009 3:23:00 AM 1440 rpm; kurt = 2.99; skew = -0.14

0 1 2 3 4 5 6 7 8-1

-0.5

0

0.5

1

Revolutions of HS Shaft

Am

plitu

de (

g)

WTG130P High Speed Timebase 4/27/2009 3:23:00 AM 1440 rpm; HP filtered at 5000 Hz; kurt = 16.943

Chaos

Clarity

Kurtosis = 3

Kurtosis = 17

Who would have thought this was hiding in that?

Raw

5 kHzHPfilter

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0 1 2 3 4 5 6 7 8-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Revolutions of HS Shaft

Am

plitu

de (

g)

WTG130P High Speed Timebase 4/27/2009 3:23:00 AM 1440 rpm; HP filtered at 5000 Hz; kurt = 16.943

High-Pass Filtered at 5 kHz

Repeating patterns of 3 impulses modulated at 1X HS rotor speed

Impulses are ringing the gearbox structure

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Bently Nevada 3701 ADAPT monitor.

Introducing new condition monitoring technologies….

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Case History 1:

Generator Bearing FaultDetection & Replacement

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Generator Inboard Bearing, WTG 128, Before Replacement

IRBP Fault0 5 10 15 20 25 30 35 40 45 50

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Frequency (Orders of HSS)

Acc

eler

atio

n (g

)

WTG128 Inboard Generator Enveloped Spectrum 1/16/2009 1:47:00 PM 1347.641 rpm

IRBP Frequency

Envelope SpectrumTimebase

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Generator Inboard Bearing, WTG 128, After Replacement

0 5 10 15 20 25 30 35 40 45 500

0.2

0.4

0.6

0.8

1

1.2

1.4

Frequency (Orders of Main Shaft))

Acc

eler

atio

n (g

)

WTG128 Generator Inboard Envelope Spectrum 4/27/2009 8:51:00 AM 1426 rpmEnvelope SpectrumTimebase

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Case History 2:

Cracked Race

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1.5 MW Wind Turbine Gearbox And Sensor

HSSAccelerometer

High-Speed Output Shaft (HSS)Downwind Bearing

2 stage gearboxPlanetary + Parallel

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137 137.5 138 138.5 139 139.5 140-3

-2

-1

0

1

2

3

Time (ms)

Am

plitu

de (

g)

WTG137 High Speed Timebase 5/11/2009 11:18:00 AM 1240 rpm; HP filtered at 5000 Hz; kurt = 149.484

Initial DetectionSeptember 2008

RepeatingImpulses

1 RevolutionRepeating sequences of impulses

Each sequence is one defect encounteringmultiple rolling elements in load zone

Impulses are separated by element passagefrequency

Single Impulse

HSS accel timebase waveformNear full speed~5 g peak

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Initial Detection, Envelope Spectrum

Split Lines1X HSSIRBP10.8 X

1X Sidebands

Strong 1X modulation 1X + harmonics 1X sidebands on IRBP

2 overlapping series 1X + harmonics IRBP +/– 1X, 2X, … Difference visible at split lines

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April 2010Same Machine

High-Low-High

1 Revolution

DoubleImpulse

Double impulse indicates newdamage. Not separated by IRBP.

New damage is smaller than older damage.

High-low-high pattern suggestsmultiple faults.

1X line higher because of denserpattern of impulses.

Average bearing fault impulseslower, so IRBP line lower.

IRBP Line Lower1X Line Higher

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Trend Data, August Through AprilDirect

IRBP

Kurtosis

Direct changes little

IRBP decreases

Kurtosis decreases

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Inspection And Crack

RollingElement

InnerRace

Surface

Crack does not extendacross race

This was largest of 4cracks found

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Diagnostic Sequence

A clear IRBP bearing defect frequency found in the envelope spectrum

Very narrow impulse/response signatures in the timebase waveform suggested a narrow defect

Clear 1X modulation of the impulse amplitude, consistent with inner race fault

Second turbine with similar symptoms suggesting multiple faults, inspected, and cracks found

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April 13, 2023

Questions?