Fault Diagnosis of Rotating Machinery by Vibration Analysis

7/28/2019 Fault Diagnosis of Rotating Machinery by Vibration Analysis

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FAULT DIAGNOSIS OF ROTATINGMACHINERY BY VIBRATION

ANALYSIS

repare y:

ARINDAM MISRA

Under the guidance of

MR. SNEHASIS SAMADDAR

DGM, CESC LTD

UNMESH - 2012

Summer Internship Programme

CESC Ltd.



PROJECT CONTENTS

Theory of vibration and analysis techniques.

Application of vibration analysis techniques.

pp ca on o a anc ng ec n que o re uce

vibration.

Identification of problem in journal bearing.

Study of relation of temperature and pressure

with damping effect of oil wedge.



THEORY OF VIBRATION AND

ANALYSIS TECHNIQUES

Vibration is repeatable oscillatory motion.

It is manifestation of any of many defects

like unbalanced force or couple .

Vibration increases bearing loading anddecreases bearing life.

Regular vibration monitoring/analysis can

predict fault, shorten shutdown time and

decrease costs due to sudden failure.



THEORY OF VIBRATION AND ANALYSIS

TECHNIQUES

Normal, Alert or Alarm classification depends

upon amplitude of velocity, displacement or

acceleration.



THEORY OF VIBRATION AND ANALYSIS

TECHNIQUES

Frequency in

Terms Of RPM

Most Likely causes Other possible causes &

Remarks

1x RPM

Unbalance

1. Eccentric shaft

2. Misalignment

3. Bent shaft4. Looseness

5. Distortion—from soft foot or piping

strain conditions

6. Bad belts—if belt RPM

7. Resonance8.High clearance in journal bearing

9. Electrical problems

10.Reciprocating problems

2 x RPM Mechanical looseness 1)Misalignment if high axial vibration

2) Reciprocating forces

3) Resonance

4) bad belt if 2 x RPM of belt

3 x RPM

Misalignment Usually a combination of

misalignment and excessive axial

clearance (looseness).




ANALYSIS TECHNIQUESLess than 1x RPM Oil Whirl (Less than 1/2

x RPM) or Oil Whip

1) Bad drive belts

2) Background vibration

3)Sub-harmonic resonance

4) "Seat" Vibration

Synchronous(A.C line frequency) Electrical Problems Common electrical problems include broken rotor

bars, eccentric rotor, and unbalanced phases

in poly-phase systems, unequal air gap.

2xSynch. Torque Pulses Rare as a problem unless resonance is excited

Frequency Many TimesRPM (Harmonically Related Freq.)

Bad GearsAerodynamic Forces

Hydraulic forces

Mechanical

Looseness

Reciprocating Forces

Gear teeth times RPM of bad gear Number of fan blade times RPM

Number of impeller vane times RPM

May occur at 2, 3, 4 and sometimes

higher harmonics if severe looseness

High Frequency

(Not Harmonically Related)

Bad Anti-Friction

bearing

1) Bearing vibration may be unsteady amplitude

and frequency

2)Cavitations, recirculation and flow turbulence

causes random high frequency vibration

3)Improper lubrication of journal bearings

4)rubbing




ANALYSIS TECHNIQUES Various analysis techniques include FFT, TIME WAVE

FORM, RATIO of V/H/A, POLAR, ORBIT etc.

Any vibration contains large number of frequencies.

Need to find out the Fundamental Frequency.

Relation between Fundamental and other Predominant

frequencies important.

Many faults cause vibration at same frequency, need TIME

WAVE FORM, RELATIVE PHASE AND RELATIVE

VIBRATION in different directions for pinpointing the

problem.



APPLICATION OF VIBRATION

ANALYIS TECHNIQUE

As a part of the project, vibration

different machines of power plant at

CESC LTD. comprising of fans,pumps, turbo-generator sets.




ANALYIS TECHNIQUE

BOILER FEED PUMP 3A OF BBGS

High vibration at 1X at non-drive end of pump in vertical direction. Probable cause from analysis of relative vibration amplitude and

phase: Misalignment.




ANALYIS TECHNIQUE

SEAL AIR FAN 2B OF BBGS

MACHINE POSITION DIRECTION VALUE(OVERALL)(mm/s)

(RMS)

FAN NON DRIVE END AXIAL 2.069

HORIZONTAL 2.118

VERTICAL 1.06

CONCLUSION: IN GOOD CONDITION

.

HORIZONTAL 2.638

VERTICAL 1.318

MOTOR DRIVE END AXIAL 1.336

HORIZONTAL 2.297

VERTICAL 1.877 NON DRIVE END AXIAL 1.591

HORIZONTAL 2.613

VERTICAL 1.804



APPLICATION OF BALANCING

TECHNIQUE SEAL AIR FAN 2A OF SGS

History of high vibration

Overall vibration of 14.47 mm/s (R.M.S. VELOCITY)

93% of overall vibration at 1x

PRIMARY CAUSE OF VIBRATION : UNBALANCE



APPLICATION OF BALANCING

TECHNIQUE

FINAL MEASUREMENT : 5.61 mm/s , BELOW THE ALARM LEVEL



IDENTIFICATION OF PROBLEM IN

JOURNAL BEARING

In general it is very complex

Requires FFT, POLAR AND ORBIT analysis

Analysed bearing 2 of BBGS unit 3

It is a combined radial and thrust journal bearing

Overall high vibration only in X direction for long time

Continuous change of phase of the vibration over the same time

period

FFT OF SHAFT VIBRATION




JOURNAL BEARING

PHASE HISTORY

BEARING 2




JOURNAL BEARING

High vibration only at 1X

In the direction of high pressure

High pressure direction has high stiffness, low amplitude

Pressure fluctuation inside the bearing decreases stiffnessand damping, causing high vibration

Most probable reason high clearance

However, AMPLITUDE IS STILL WELL BELOW THE ALARM LEVEL



STUDY OF DAMPING EFFECT OF LUBRICATION OIL

Above analysis created interest in me to study the effect of

temperature and pressure on journal bearing damping in details

Ocvirk solution P =

From Ockvirk’s solution P is inversely proportional to

decreases as the clearance increases, hence to decrease

be increased

µ decreases with increasing temperature, pressure decreases

with µ, so shaft vibration may be reduced by increasing

temperature

Temperature, flow, viscosity, pressure inter-related. Hence

influencing the final effects, which is complex and needs further

study



This was an extended part of my project. The

intention was to see if any vibration of journal

bearing can be reduced by adjusting the properties of

hydrodynamic lubrication.

Since outage of TG sets are very costly it would

provide a temporary alternate solution to shut-down.

This extended part of the work could not be completed

due to lack of in depth theoretical information and

time.

All the gathered information on this has been

provided in the project report towards the end, so that

further work can be done later



HOW THE PROJECT WAS USEFUL

Obtained enough knowledge on an unknown and

complicated topic of vibration analysis

Gathered practical knowledge and hands on

experience on vibration analysis techniques.

My project report is a small and handy guidebook

for vibration theory, defects of rotating machines,

vibration analysis techniques which can be used by

e prac oners o v ra on ana ys s.

Vibration Analysis on various running equipment

helped to identify the root causes of the problems.

By critical analysis, possibility of high clearance

could be detected in one of the turbine bearings

Study of damping effect of oil wedge will provide

food-for-thought for future practical applications



ACKNOWLEDGEMENT

THANKS TO CESC LTD. FOR PROVIDING ME THIS

OPPORTUNITY

I AM INDEBTED TO MR. SNEHASIS SAMADDAR FOR

CONSTANT GUIDANCE, SUPERVISION AND

ENCOURAGEMENT THROUGHOUT THIS PROJECT

I AM ALSO GRATEFUL TO MR. CHANDRACHUR BISWAS,

MR. SUBHAMAY DAS, MR. ASIM ROY, MR. SANJOY

ADHIKARY, MR. RANAJIT KUMAR DAS

MY SPECIAL GRATITUDE TO MY MOM, DAD AND

TEACHERS

Fault Diagnosis of Rotating Machinery by Vibration Analysis

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