Fault Diagnosis of Rotating Machinery by Vibration Analysis

FAULT DIAGNOSIS OF ROTATING MACHINERY BY VIBRATION ANALYSIS

Prepared by: 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.




Application of balancing technique to reduce 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 and decreases 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 1x RPM

Most Likely causes

Unbalance

2 x RPM

Mechanical looseness

Misalignment 3 x RPM

Other possible causes & Remarks 1. Eccentric shaft 2. Misalignment 3. Bent shaft 4. Looseness 5. Distortion—from soft foot or piping strain conditions 6. Bad belts—if belt RPM 7. Resonance 8.High clearance in journal bearing 9. Electrical problems 10.Reciprocating problems 1)Misalignment if high axial vibration 2) Reciprocating forces 3) Resonance 4) bad belt if 2 x RPM of belt Usually a combination of misalignment and excessive axial clearance (looseness).

THEORY OF VIBRATION AND ANALYSIS TECHNIQUES Less than 1x RPM

Synchronous(A.C line frequency)

Oil Whirl (Less than 1/2 1) Bad drive belts x RPM) or Oil Whip 2) Background vibration 3)Sub-harmonic resonance 4) "Seat" Vibration 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 Times RPM (Harmonically Related Freq.)

Bad Gears Aerodynamic Forces Hydraulic forces Mechanical Looseness Reciprocating Forces Bad Anti-Friction bearing

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 higher harmonics if severe looseness

High Frequency (Not Harmonically Related)

sometimes

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

THEORY OF VIBRATION AND 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 analysis has been carried out on 14 different machines of power plant at CESC LTD. comprising of fans, pumps, turbo-generator sets.

APPLICATION OF VIBRATION 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.

APPLICATION OF VIBRATION ANALYIS TECHNIQUE


SEAL AIR FAN 2B OF BBGS

MACHINE

POSITION

FAN

NON DRIVE END AXIAL HORIZONTAL VERTICAL DRIVE END AXIAL HORIZONTAL VERTICAL

2.069 2.118 1.06 3.264 2.638 1.318

MOTOR

DRIVE END

1.336 2.297 1.877 1.591 2.613 1.804




DIRECTION

AXIAL HORIZONTAL VERTICAL NON DRIVE END AXIAL HORIZONTAL VERTICAL

CONCLUSION:

VALUE(OVERALL)(mm/s) (RMS)

IN GOOD CONDITION

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

IDENTIFICATION OF PROBLEM IN JOURNAL BEARING PHASE HISTORY

COMPARISON OF ORBITS OF BEARING 6 AND BEARING 2

IDENTIFICATION OF PROBLEM IN 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 stiffness and 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 vibration PMAX needs to be increased or the supply pressure is to 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 the practioners of vibration analysis. 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