on-line motor monitoring - vibration geiman - baker instruments.pdf · on-line motor monitoring ......

On-line Motor Monitoring

Joe GeimanJoe GeimanBaker Instrument Co.Baker Instrument Co.

What are we really after?Induction motor and VFD applications

Reduce unscheduled downtimeReduce unscheduled downtime Indicates root cause analysisIndicates root cause analysis Save $ $ $Save $ $ $

Motor Failure Areas:IEEE Study EPRI Study

Motor Failure Areas:IEEE Study EPRI Study

Bearing44%

Rotor8%

Other22%

Stator26%

Bearing41%

Other14% Rotor

9%

Stator36%

Motor Failure Causes:IEEE Study

Motor Failure Causes:IEEE Study

0%

20%

40%

60%

80%

100%

Bearing Winding

Electrical FaultMechanical BreakageInsulation BreakdownOverheating

Safety and Connecting:Low Voltage (Less than 600V)

Motor

MCC

LoadBreaker

Step one: Running motorStep two: STOP motorStep three: Connect ExplorerStep four: Run and testStep five: STOP motorStep six: Disconnect Explorer

Explorer

Safety and Connecting:Medium and High Voltage (More

than 600V)

Motor

Load

CTs

Breaker

Step one: Motor is runningStep two: Connect Explorer CTsStep three: Connect Explorer PTs

Explorer

PTs

Motor

CTs

Breaker

PTs

EP

Explorer

First EnergyRC Pump

1 of 700+ EPs at one customer

Acquire Data:Safe, Fast & Easy W/ EP-1

Power Quality Analysis

PQ CapabilitiesPQ CapabilitiesVoltage and Current level, unbalanceVoltage and Current level, unbalance

distortionsdistortionsKvarsKvars, KVA, KW’s, Power factor, Crest, KVA, KW’s, Power factor, Crest

factor, Harmonic bar chartfactor, Harmonic bar chart ectect..

Motor Overheating

II22R LossesR Losses Motor CurrentsMotor Currents 100% rated Current100% rated Current 100% rated Temperature100% rated Temperature 110% rated Current110% rated Current 121% rated Temperature121% rated Temperature

Fan 1 hp 1740 rpm

Motor Condition: Broken Rotorbar

Rotorbar Frequency:

slip Synchronous rotor bar freq.% [RPM] [Hz]0.1 1798.2 59.880.2 1796.4 59.760.3 1794.6 59.640.4 1792.8 59.520.5 1791 59.40.6 1789.2 59.280.7 1787.4 59.160.8 1785.6 59.040.9 1783.8 58.921.0 1782 58.8

.

..

.

slip

21

synch

operatsynch

fundrotorbar

RPM

RPMRPMs

sff

Depends on SLIP!

•Harder to assess with lesser load

•Harder to assess with bigger motor

•Harder to assess with more efficient motor

Increasing Lines of Resolution:Increasing Lines of Resolution:

New Rotorbar y-axis Scale

AmA

dB

lfundamentasignal

dBres

30042

log105.38

log10].[down'dB'

Good Rotor Bar

Bad Rotor Bar

Case Study 1

2A High Pressure Pump2A High Pressure Pump ProblemProblem

Serious vibrationSerious vibration Vibration ReadingVibration Reading

•• High 7200High 7200•• Turn off motor 7200 peek disappearsTurn off motor 7200 peek disappears

Electricians do not believe it could be a rotor barElectricians do not believe it could be a rotor bar•• They have never seen a rotor problemThey have never seen a rotor problem•• Electricians have no way to confirm or deny theElectricians have no way to confirm or deny the

allegations of the mechanicsallegations of the mechanics

Show Data

2A high Pressure Pump2A high Pressure PumpBroken Rotor BarBroken Rotor Bar

1C high Pressure Pump1C high Pressure PumpGood Rotor BarGood Rotor Bar

2A High Pressure PumpBroken Rotor Bar

1C High Pressure PumpGood Rotor Bar (comparison)

Conclusion2A High Pressure Pump

Recommendation to customerRecommendation to customer It appeared to be a brokenIt appeared to be a brokenAll thought, only slightly into the cautionAll thought, only slightly into the caution

we questioned how saver the problemwe questioned how saver the problemwaswas

Results2A High Pressure Pump3 Broken Rotor Bars

Case Study 24a PA Fan

Problem Slight vibrationProblem Slight vibration

Broken Rotor Bar

Case Study 3

Rotor IssueRotor Issue Show need for higher acquisitionShow need for higher acquisition Show other places in spectrum toShow other places in spectrum to

represent or confirm rotor issuesrepresent or confirm rotor issues

Low Resolution DataNo Assessment Can Be Made

High Resolution DataAssessment Can Be Made

Results

Inspection found brazing issues at theInspection found brazing issues at theend ring causing high resistance joints.end ring causing high resistance joints.

Epoxy Melting Off Rotor BarsRepresenting Excessive Heat

Cracked End Ring (Case Study 4)

Motor Current Signature AnalysisValues From Technical Associates.

54 – 60 dB Excellent54 – 60 dB Excellent 48 – 54 dB Good condition48 – 54 dB Good condition 42 – 48 dB Moderate condition42 – 48 dB Moderate condition 36 – 42 dB Rotor bar crack36 – 42 dB Rotor bar crack

developing ordeveloping or highhighresistance joints.resistance joints.

30 – 36 dB multiple cracked / broken30 – 36 dB multiple cracked / brokenbars or end – ringsbars or end – rings

indicatedindicated < 30 dB multiple cracked /< 30 dB multiple cracked /

broken bars orbroken bars orend-rings very likelyend-rings very likely

Current signature: FFT vs. DFLL

Amplitude: 20dB

Amplitude: 60dB

Resolution: 0.13Hz Resolution: 0.005Hz

FFT DFLL

Need: High Amplitude and Frequency Resolution

• Requires constant torque level• Torque ripple• Next one breaks sooner• Current increases• Temperature increases• Insulation life shortens• Typically non-immediate death

Motor Condition:Broken Rotorbar issues

Motor

MCC

Load1. frequency 2. speed

3. Torque4. Power

5. Voltage

6. Current

Chain of events:Cause and effect

N

SF

F

I

I

F : Force

I : Current

: Flux

Calculating Torque:

Flux: Generated by stator Voltage

Rotor Current: Monitored with Stator Current

TT(t) = f( V(t), I(t) )

According to Park’s theory, 1920.

RotorStator

Calculating Torque:

Explorer showed that not all motors run at constantExplorer showed that not all motors run at constantoperating condition. The 4 motors at the center displayoperating condition. The 4 motors at the center displaya larger variability to their operation. These are thea larger variability to their operation. These are thelocations which’ motors break with unusually highlocations which’ motors break with unusually highfrequency.frequency.

• The maintenance supervisor noted that some stirringpool motors (decontamination and recycling process)break with unusually high frequency.

Case study I: Hydro-mechanical resonance. Brewery.Case study I: Hydro-mechanical resonance. Brewery.

• The maintenance supervisor noted that some stirringpool motors (decontamination and recycling process)break with unusually high frequency.

• The Explorer showed that not all motors run atconstant operating condition. The 4 motors at thecenter display a larger variability to their operation.These are the locations which’ motors break withunusually high frequency.

• The Torque Ripple graphs clarified the source of theoperation’s variability.



Corrective action:

4160V submersible pump

Torque Signature:

Torque Ripple vs. Time

Hzssperiodtime

soccurrencefrequency 2.3

11.073.02

_#

Torque Ripple vs. TimeHz

ssperiodtimesoccurrence

frequency 2.311.073.0

2_

#

Torque vs. Frequency:Mechanical Imbalance

• Investigating vibration and torque forinaccessible loads:

Comparison of Duct-Mounted Vibration and InstantaneousAirgap Torque Signals for Predictive Maintenance of Vane Axial

Fans .

Comparison of Duct-Mounted Vibration and InstantaneousAirgap Torque Signals for Predictive Maintenance of Vane Axial

Fans .

Don DoanTexas Utilities

Ernesto WiedenbrugBaker Instrument Company

Don DoanDon DoanTexas UtilitiesTexas Utilities

Ernesto WiedenbrugErnesto WiedenbrugBaker Instrument CompanyBaker Instrument Company

Presented in IEEE CMD / 2005Ulsan, Korea

Presented in IEEE CMD / 2005Ulsan, Korea

Problem Application:Problem Application:

A Vane Axial Fan’s failure can result inunplanned outages, health and safety costs, andextensive damage to surrounding equipment.

A Vane Axial Fan’s failure can result inA Vane Axial Fan’s failure can result in

unplanned outages, health and safety costs, andunplanned outages, health and safety costs, and

extensive damage to surrounding equipment.extensive damage to surrounding equipment.

• Vane Axial Fans are commonin nuclear environments

• It is almost impossible topredict bearing faults for

Vane Axial Fans.

• Vane Axial Fans are commonin nuclear environments

• It is almost impossible topredict bearing faults for

Vane Axial Fans.Nuclear Comanche Peak Station

TXU Electric

HorizontalApplication

VerticalApplication

Vane-axial Fan Maintenance Challenge:Vane-axial Fan Maintenance Challenge:

Application frequently called: “Fan-in-a-can”

Impossible to monitor with preferred technology(vibration on bearing housing)

Cost prohibitive to issue a “change in design”for all Vane axial Fans for this Nuclear PowerPlant. (Nuclear Industry in U.S. average cost permeter of retrofitted wire > U$ 5,000)

Application frequently called: “Fan-in-a-can”Application frequently called: “Fan-in-a-can”

Impossible to monitor with preferred technologyImpossible to monitor with preferred technology

(vibration on bearing housing)(vibration on bearing housing)

Cost prohibitive to issue a “change in design”Cost prohibitive to issue a “change in design”

for all Vane axial Fans for this Nuclear Powerfor all Vane axial Fans for this Nuclear Power

Plant. (Nuclear Industry in U.S. average cost perPlant. (Nuclear Industry in U.S. average cost per

meter of retrofitted wire > U$ 5,000)meter of retrofitted wire > U$ 5,000)

Laboratory Investigation:Laboratory Investigation:

Set up a Vane Axial Fan in a Laboratory, and create:• Healthy operation (baseline data)• Advanced Bearing fault (Stage III)

Gathering Data:• Vibration data obtained from the bearing housing – preferred

diagnostic method – (used as benchmark of planted faults).• Accelerometers connected to the outside of the duct.• Calculated Instantaneous Airgap Torque using Park’s theory.

Statistical Data Analysis:• Statistical evaluation using “single sided experiment design”.• 9 samples needed for certainties exceeding 95% and 90% for

errors type I, and type II, respectively.

Set up a Vane Axial Fan in a Laboratory, and create:Set up a Vane Axial Fan in a Laboratory, and create:

•• Healthy operation (baseline data)Healthy operation (baseline data)

•• Advanced Bearing fault (Stage III)Advanced Bearing fault (Stage III)

Gathering Data:Gathering Data:

•• Vibration data obtained from the bearing housing – preferredVibration data obtained from the bearing housing – preferred

diagnostic method – (used as benchmark of planted faults).diagnostic method – (used as benchmark of planted faults).

•• Accelerometers connected to the outside of the duct.Accelerometers connected to the outside of the duct.

•• Calculated Instantaneous Airgap Torque using Park’s theory.Calculated Instantaneous Airgap Torque using Park’s theory.

Statistical Data Analysis:Statistical Data Analysis:

•• Statistical evaluation using “single sided experiment design”.Statistical evaluation using “single sided experiment design”.

•• 9 samples needed for certainties exceeding 95% and 90% for9 samples needed for certainties exceeding 95% and 90% for

errors type I, and type II, respectively.errors type I, and type II, respectively.

Chosen Fan / Motor:Chosen Fan / Motor:

Motor: Baldor 3.7kW (5hp),4-pole, 480V.

Fan: Aerovent 304 mm (24 in). System used in the Exhaust of

the Electrical Control Room.

Motor:Motor: BaldorBaldor 3.7kW (5hp),3.7kW (5hp),

4-pole, 480V.4-pole, 480V.

Fan:Fan: AeroventAerovent 304 mm (24 in).304 mm (24 in).

System used in the Exhaust ofSystem used in the Exhaust of

the Electrical Control Room.the Electrical Control Room.

Note: The support system of this motor/fan has along transmission path – which may dampenmechanical signals on their way to the duct.

Note: The support system of this motor/fan has along transmission path – which may dampenmechanical signals on their way to the duct.

The “known good” Signals:The “known good” Signals:

Redundant verification: Accelerometers: 100mV/g ICP Cognitive Systems CV395B Analyzer Bentley Nevada ADRE 208P SWANTECH stress wave analysis

Redundant verification:Redundant verification: Accelerometers: 100mV/g ICPAccelerometers: 100mV/g ICP

Cognitive Systems CV395B AnalyzerCognitive Systems CV395B Analyzer

Bentley Nevada ADRE 208PBentley Nevada ADRE 208P

SWANTECH stress wave analysisSWANTECH stress wave analysis

Additional Instrumentationensuring constant operating condition:

Airfolow Meters Humidity Meter ThermocouplesCurrent Meters Laser tachometers

Additional Instrumentationensuring constant operating condition:

Airfolow Meters Humidity Meter ThermocouplesCurrent Meters Laser tachometers

Field-friendly alternative #1:Duct-mounted Accelerometers

Field-friendly alternative #1:Duct-mounted Accelerometers

Vibration Transducers 100mV/g ICP.

Cognitive Systems Spectrum Analyzer

Accelerometers mounted directly at Mounting Rod on the Duct.

Vibration Transducers 100mV/g ICP.Vibration Transducers 100mV/g ICP.

Cognitive Systems Spectrum AnalyzerCognitive Systems Spectrum Analyzer

Accelerometers mounted directly at Mounting Rod on the Duct.Accelerometers mounted directly at Mounting Rod on the Duct.

Field-friendly alternative #2:Torque Signature Analyzer

Field-friendly alternative #2:Torque Signature Analyzer

Explorer II (Baker Instrument Company)

Measures 3 currents and 3 voltages at MCC.

Calculates airgap torque (Park 1929).

Obtains operating speed from current and torquesignatures.

Monitoring Imbalances: 1x mechanical frequencies inairgap torque spectrum.

Explorer II (Baker Instrument Company)Explorer II (Baker Instrument Company)

Measures 3 currents and 3 voltages at MCC.Measures 3 currents and 3 voltages at MCC.

Calculates airgap torqueCalculates airgap torque (Park 1929)(Park 1929)..

Obtains operating speed from current and torqueObtains operating speed from current and torquesignatures.signatures.

Monitoring Imbalances: 1x mechanical frequencies inMonitoring Imbalances: 1x mechanical frequencies inairgap torque spectrum.airgap torque spectrum.

• 7.6 grams create 0.39 gm (0.54 oz in) imbalance.

• Comparing amplitudes of 1 x mechanical frequenciesfor “unfaulted” vs. “faulted” data.

• 7.6 grams create 0.39 gm (0.54 oz in) imbalance.

• Comparing amplitudes of 1 x mechanical frequenciesfor “unfaulted” vs. “faulted” data.

• Start: Precision balancedfan (baseline).

• Planted Fault: 7.6 gramsimbalance.

• Start: Precision balancedfan (baseline).

• Planted Fault: 7.6 gramsimbalance.

Fault 1: Mechanical ImbalanceFault 1: Mechanical Imbalance

Comparison of the amplitudes of 29.9Hz (1x mechanical)frequencies for 1 set of balanced data, with one set ofimbalanced operation:

Comparison of the amplitudes of 29.9Hz (1x mechanical)Comparison of the amplitudes of 29.9Hz (1x mechanical)frequencies for 1 set of balanced data, with one set offrequencies for 1 set of balanced data, with one set ofimbalanced operation:imbalanced operation:

Fault 1: Mechanical ImbalanceFault 1: Mechanical ImbalanceResults:

Duct Accelerometer:Duct Accelerometer:-- 99% certain that imbalanced data has higher99% certain that imbalanced data has higher

amplitude.amplitude.-- Amplitude is only 6.7% higher.Amplitude is only 6.7% higher.

Conclusion:Conclusion:This methodThis method “could”“could” be used, but the very low amplitudebe used, but the very low amplitudegain renders it unfeasible for maintenance.gain renders it unfeasible for maintenance.

Airgap Torque Method:Airgap Torque Method:

99% certain that imbalanced data has higher amplitude.99% certain that imbalanced data has higher amplitude.

Amplitude is 150 times higher ( >40dB ).Amplitude is 150 times higher ( >40dB ).

Conclusion:Conclusion:According to this experiment, this methodAccording to this experiment, this method CANCAN bebeused for maintenance.used for maintenance.The large amplitude gain makes it very robust andThe large amplitude gain makes it very robust andeasy to interpret.easy to interpret.

Fault 1: Mechanical ImbalanceFault 1: Mechanical ImbalanceResults:

Bearing Signature Analysis

•• Mechanical world:Mechanical world: Stage II:Stage II:

nnmm = Mechanical (shaft) speed= Mechanical (shaft) speed i,ki,k = 1,2,3,…= 1,2,3,…

•• Electrical world:Electrical world: Stage II:Stage II:

nnfundfund = fundamental electrical frequency= fundamental electrical frequency i,ki,k= 1,2,3,…= 1,2,3,…

mn2kBPFOisFrequencieFault

fund.n2kBPFOisFrequencieFault

Motor Failure Areas:Bearings

Motor Failure Areas:Bearings

harm. * BPFO 2 * RPM

Known Good Bearing Known Outer Race Defect

Torque SpectraBPFO Controlled Lab Test… how it works

Electrical Frequencies Removed Electrical Frequencies RemovedMarking 1 * BPFOAdding Electrical Harmonic Sidebands

Signal Quality:Signal Quality:

harm. * BPFO 2 * RPM Torque (Nm) Current (A)RMS 0.5 5

Signal 0.025 0.0022Noise 0.0012 0.0005

Torque S/N = 4.8 * betterTorque S/RMS = 125 * better

“It can be found”“It is in your face”

4 pole 5hp

Eccentricity in Spectrum:

•• Location:Location:

•• “1x” types:“1x” types:•• Current signals:Current signals: fffund.fund. ±± ffmech.mech.

•• Torque signals:Torque signals: ffmech.mech.

•• - “Bar-pass” types:- “Bar-pass” types:•• Current signals:Current signals: nn ·· ffmech.mech. ±± 11 ·· fffund.fund. (hopefully there)(hopefully there)•• Torque signals:Torque signals: nn ·· ffmech.mech. (many times not(many times not

there)there)

• 4-pole motor.

• 1x = just below 30Hz.

rpmHz s 8.17686048.29 min

Eccentricity, Torque Signature:“1 x” location

Eccentricity, Current Signature:Eccentricity, Current Signature:“1 x” location“1 x” location

rpmHz s 2.17656058.3060 min

• 4-pole motor.

• 1x = just above 30Hz.

Eccentricity, Torque Signature:Eccentricity, Torque Signature:“Rotorbar Pass Frequency” location“Rotorbar Pass Frequency” location

• 2-pole motor. 2nd peak @ freq. just below Harmonic.

• 1920Hz / 60Hz = 32bars (1920Hz is synchronous rotorbar pass frequency)

rpmHz

fHzbars

Hz

s

mech

5.35936089.59

89.5932

56.1916

min

.

Eccentricity, Current Signature:“Rotorbar Pass Frequency” location

• 2-pole motor.

•1860Hz / 60Hz + 1 = 32bars

rpmHz

fHzbars

HzHz

s

mech

5.35936089.59

89.5932

6051.1856

min

.

“1x” locations

# of Poles Synchronous 1% slip "1x" Torque "1x" Current[RPM] [RPM] [Hz] [Hz]

2 3600 3564 59.4 0.64 1800 1782 29.7 30.36 1200 1188 19.8 40.28 900 891 14.85 45.1510 720 712.8 11.88 48.1212 600 594 9.9 50.1

.elec.1 mechfundx fff .trq.1 mechx ff

Comparing Ieccent. with Teccent.

•• TTeccent.eccent. at “expected” frequencyat “expected” frequency•• IIeccent.eccent. at “expected” frequency – 60Hz.at “expected” frequency – 60Hz.•• TTeccent.eccent. -28.43 dB relative amplitude.-28.43 dB relative amplitude.•• IIeccent.eccent. -34.9 dB relative amplitude.-34.9 dB relative amplitude.

Teccent. is at the understandable location.

Teccent. has a 4.5 times larger signal.

Demodulated Signals:Torque vs. Current

Demodulated Signals:Torque vs. Current

Demodulated Torque Demodulated Current1* RPM 2* RPM 1* RPM 2* RPM

Bad Motor #1Bad Motor #2Good Motor #1Good Motor #2

3.47E-05 7.94E-05 0.00324 0.031504.26E-05 7.96E-05 0.00398 0.030912.96E-05 1.35E-05 0.00245 0.031093.46E-05 1.42E-05 0.00308 0.03057

Factor 1.20 5.90 1.31 1.01

Conclusions:• Demodulated Current method does not agree with vibration’s methods.

• Demodulated Torque reacts like vibration’s methods.

• This method is independent of Motor design.

• This method does not disagree with IEEE motor scientist’s research.

Case study II: Cooling tower fan and gear signatures.Coal-fired power plant.


Input Shaft Freq.Intermediate Shaft Freq.Output Shaft Freq.

Blade Pass Freq.



1st Mesh Frequency2nd Mesh Frequency



BPFO

BPFI + - 2 x Electrical

+ - 2 x Electrical



SKF 22310c

on-line motor monitoring - vibration geiman - baker instruments.pdf · on-line motor monitoring ......

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