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8/3/2019 Study Motor Diagnosis

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Condition Monitoring and Fault Diagnosis of Induction Motors

Intelligent Mechanics Laboratory

School of Mec hanical Engineering

Pukyong National University

ConditionCondition Monitor ing and Fault DiagnosisMonitor ing and Fault Diagnosis

of Induction Motors using Vibration Signalof Induction Motors using Vibration Signal

Bo-Suk Yang*, Tien Han, Won-Woo Hwang and Kwang-Jin Kim


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ApplicationsApplications

Induction MotorsInduction Motors


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Why the condition monitoring/diagnosis is important?Why the condition monitoring/diagnosis is important?

Degradation of different parts

Although the motor cost, repair and refurbishment expense might not

be substantial but the cost associated with down time is enormous

Condition monitoring provides

Adequate warning of imminent failures

Diagnosing present maintenance needs Schedule future preventive maintenance and repair work

Minimum downtime and optimum maintenance schedules

Fault diagnosis

Allows the machine operator to have the necessary spare parts before

the machine is stripped down, thereby reducing outage times

Can be integrated into the maintenance policy, therefore the usual

maintenance at specified intervals can be replaced by a condition-based

maintenance


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Typical faults ofTypical faults ofInduction motorsInduction motors

Failure survey in induction motors

38%Stator

10%Rotor

40%Bearing

12%Others

FailureComponents

Ref. IEEE Motor Reliability Working Group


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Comparison of detection technologiesComparison of detection technologies

NoNoNoNoYesPartial discharge

NoNoYesYesYesCooling gaps

YesNoNoNoNoLubricating oil debris

NoYesYesYesNoAxial flux

YesYesYesYesNoMCSA

YesYesYesNoNoVibration

Bearing

damage

Rotor

barbroken

Air-gap

eccentricity

Stator

winding

Insulation

Faults it can detect

Method


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Why we choice the vibration method?Why we choice the vibration method?

Very popular, easy and accurate

Favored by mechanical engineers

Often a direct link with the problem

Piezo-electric vibration transducers are most popular

Axial, radial, and tangential where radial is used for mechanical

problems and tangential is used for detecting electrical problems

Exists a lot of skilled and experience

C di i M i i d F l Di i f I d i M


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Scheme diagram of condition monitoring and diagnostics system

What kind of system we use?What kind of system we use?

Data acquisitionMachinery

(Motor)

Pre-processingFeature

extraction

Fault

diagnosis

Vibration Signature

Wavelet transform Feature algorithm ART-KNN

C diti M it i d F lt Di i f I d ti M t


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What would this system do?What would this system do?

Alert the user of an impending mechanical or electrical faults

Provide early detection of machinery deterioration

Prevent costly damage failure and/or unsafe operation

C diti M it i d F lt Di i f I d ti M t


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Motor cross sectionMotor cross section



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ExperimentalExperimental apparatus designapparatus design

Pitch variable

(8) bladesBearing

Motor

Common bed

Full load

Over load



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Sensors positionsSensors positions

(Channel 5-8)

Channel 1-3: current signalChannel 4: run speedChannel 5-8: vibration signal

AC current probes

Speedometer

Accelerometers

(Channel 4)

(Channel 1-3)

AC current probes

Speedometer

Accelerometers

(Channel 4)

Control Panel



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4-channel Sony recorder

(Model: PCEO4AX)

8-channel Mobile FFT Analyzer

(ZONIC Model: 2300)

B & K Condition Amplifier

Measuring instrumentsMeasuring instruments



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Mechanical problemsMechanical problems

.

0.43-0.48x rpm pressure fed bearings onlyOil whirl & whip in sleeve bearings

0.5x, 1x, 1.5x, 2x, etc.Rotor rub

2x rpm

0.5x, 1.5x, 2.5x, 3.5x, etc.

Mechanical looseness

Tooth meshing frequencies (shaft rpm

teeth number) and harmonics

Damaged and worn gears

Impact rates for the individual bearing

components. Also vibrations at very highfrequencies.

Damaged rolling element bearing

(ball, races, etc.)

1x rpm usually, 2x rpm often,

3x & 4x rpm sometimes

Misalignment & bent shaft

1x rpm ( temperature & lad dependent)Unbalance

Dominant Vibration FrequencyFault



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Electrical problemsElectrical problems

1x supply frequencyUnbalanced supply inputs

6x supply and harmonicsAdjustable speed drives

Double supply

Double slip frequencyEccentricity (static/dynamic)

Double slip frequency

1x-slip frequency

Rotor asymmetry

(broken rotor bar, broken end ring)

Double supply frequencyStator asymmetry

(unbalanced supply, inter turn short)

Dominant Vibration FrequencyFault



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1. Bearing fault causes1. Bearing fault causes

Improper lubrication

Contamination

Corrosion

Improper installation/misalignment



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Fault frequency of bearing elementsFault frequency of bearing elements



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Bearing fault (Bearing fault (outer race)outer race)

NSK

Mfg.

2.034.9323.0660.38351.3190.312586203

BSFBPFIBPFOFTFPitch

Dia.

R.E

Dia.

Ball

No.

Brg.

No.

172.95 Hz

178.59 Hz

3X

57.65 Hz

59.53 Hz

Running speed

174.375 Hz176.7549 HzFull-load

181.4067 Hz182.5190 HzNo-load

Test valueTheoretical valueCondition

0.00 0.01 0.02 0.03 0.04 0.05 0.06

-0.10

-0.08

-0.06

-0.04

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

Amp

litude

Time (s)

Normal condition

Bearing fault

0.00 0.01 0.02 0.03 0.04 0.05 0.06

-0.10

-0.08

-0.06

-0.04

-0.02

0.00

0.02

0.04

0.06

0.08

0.10 Normal condition

Bearing fault

Amplitude

Time (s)

No-load conditionFull-load condition



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g g

0 20 40 60 80 100 120 140 160 180 2000.000

0.005

0.010

0.015

0.020

3x2x

Amplitude

Frequency (Hz)

horizental

axial

vertical (output)

vertical (rear)

1x fo

0 20 40 60 80 100 120 140 160 180 200.000

0.005

0.010

0.015

0.020

horizental

axial

vertical (output)

vertical (rear)

Amplitu

de

Frequency (Hz)

1x

2x 3x

fo

No-load condition Full-load condition

Characteristic frequency components: 1x, 2x, 3x and fo



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g g


Wavelet transformWavelet transform



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Damage condit ion

Depth : 15.0 mm

Diameter: 5.0 mm

2. Rotor bar damage2. Rotor bar damage

Rotor bar damage

Total rotor bar : 34Broken bar : 12



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Main reasons for the rotor bar and end ring breakage are:Main reasons for the rotor bar and end ring breakage are:

Thermal stress due to thermal overload and unbalance, hot-spots, sparking

or excessive losses

Magnetic stress caused by electromagnetic forces, unbalance magnetic pull

electromagnetic noise and vibration

Residual stresses due to manufacturing problems

Dynamic stresses arising from shaft torque, centrifugal forces and cyclic stress

Environment stresses caused by contamination or abrasion of the rotormaterials due to chemical or moisture

Mechanical stress due to loose laminations, fatigued parts or bearing failure



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Detection of broken rotor barDetection of broken rotor bar

Frequency components in axial vibration signal due to axial force

f = {(- qa + qb) + (qa - qb) s}fs , f = {(2 - qa - qb) + (qa + qb) s}fs

Wherefs is the supply frequency in hertz, s is the slip, qa, qb = 1, 2, 3



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0 20 40 60 80 100 120 140 160 180 2000.0000

0.0002

0.0004

0.0006

0.0008

0.0010

A

mplitude

Frequency (Hz)

0 20 40 60 80 100 120 140 160 180 2000.0000

0.0002

0.0004

0.0006

0.0008

0.0010

Am

plitude

Frequency (Hz)

1x 2f- sf

2x

2f + sf

3 3f sf

3 10f sf


1x

2xf sf +

3x

Motor axial direction

Characteristic frequency components: sfsideband on the supply frequency



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3. Rotor unbalance3. Rotor unbalance

Adding unbalance mass

at an end of end ring

Experimental conditions

Experimental objective

Unbalance conditionMass : 8.4 g

Distance: 40.2 mm

Position: 0 , 36 , 72

Mechanical unbalance effect tovibration signal

Unbalance

mass



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53 54 55 56 57 58 59 60 61 62 630.0000

0.0002

0.0004

0.0006

0.00080.0010

0.0012

0.0014

0.0016

0.0018

0.0020

Amp

litude

Time (s)

Noraml

Unbalance

53 54 55 56 57 58 59 60 61 62 630.0000

0.0002

0.0004

0.0006

0.00080.0010

0.0012

0.0014

0.0016

0.0018

0.0020

Unbalance

Noraml

Amp

litude

Time (s)


1x

1x

Characteristic frequency components: 1x

Rotating frequency (Hz) Rotating frequency (Hz)



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4. Bowed rotor shaft4. Bowed rotor shaft

Experimental conditionsAir-gap: 0.25 mm

Deflection in mid-span: 0.075 mm



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0 20 40 60 80 100 120 140 160

0.000

0.002

0.004

0.006

0.008

0.010

mp

u

e

Frequency (Hz)

Normal

Bend shaft

0 20 40 60 80 100 120 140 160

0.000

0.002

0.004

0.006

0.008

0.010

Amplitude

Normal

Bend shaft

Frequency (Hz)

No-load condit ion Full-load condit ion

1x2x

1x

2x

Characteristic frequency components: 1x, 2x



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5. Rotor misalignment (qualitative tests)5. Rotor misalignment (qualitative tests)

Experimental conditions

Bearing diameter: 40 mm

Housing maximum diameter: 40.7mm

Parallel misalignment

Angular misalignment

Geometrical center

Rotor shaft



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Characterist ic frequency components: double supply frequency, slip frequency

Normal condition Parallel eccentricity Angular eccentricity

No-load condition



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Full-load condition

Normal condition Parallel eccentr ici ty Angle eccentricity



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Feature extractionFeature extraction

Upper-bound & Entropy error Kurtosis & skewness

Feature parameters: Mean, RMS, Shape factor, Skewness, Kurtosis, Crest factorRMSF, FC, RVF, Entropy Estimations, Entropy error,

Histogram (upper-bound and lower-bound)

Full-load condition



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Training results of ARTTraining results of ART--KNN algorithmKNN algorithm

0.800 0.825 0.850 0.875 0.900 0.925 0.950 0.975 1.0000

20

40

60

80

100

120

140

160

Numbe

rofneurons

Similarity coefficient

No-load

Full-load

0.800 0.825 0.850 0.875 0.900 0.925 0.950 0.975 1.00065

70

75

80

85

90

95

100

No-load

Full-load

Successrate(100%)

Similarity coefficient



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SummarySummary

Various motor conditions are tested under no-load, full-load conditions

Faulty bearing (outer race)

Rotor bar broken Rotor unbalance

Bowed rotor shaft

Rotor misalignment (parallel and angular)

The vibration analysis for motor faults is efficient tool

The features of signals can be extracted through vibration signatures

Classification algorithm, ART-KNN, are carried out to learn and

classify the conditions. The results can reach 100% success rate.



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Faulty stator

12

11Diagnosis system

Efficiency

10

9Feature selection

8

6 Diagnosis system test

Dealing with problem

Faulty bearing5

4

3

2Vibration signal and

stator current signal

Data diagnosis

(vibration & current)

Feature extraction

Unbalance Rotor,

Bowed Rotor

1

Diagnosis (ART-KNN)Signal acquisit ion and

Feature extractionExperiments

Rotor Eccentricity7

Others

Content

Month

Time ScheduleTime Schedule



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CBM information flowCBM information flow

Modeling & PrognosticsModeling & Prognostics

SensingFeatureExtraction

.. ..

Classification

DataFusion

Reasoning

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