Condition Monitoring of Power Plant Equipment

8/8/2019 Condition Monitoring of Power Plant Equipment

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Condition Monitoring of Power

Plant Equipment

Presented by

S Bhattacharya, K R Bairwa,P Kukde

The Tata Power Co Ltd, Mumbai


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CONTENT

Concept of Condition Monitoring Condition Based Maintenance

Management System at Trombay

Case Studies


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Need of Condition Monitoring

Safety of Man and Machine

Plant availability Reliability

Operation at Best Efficiency

Minimization of Maintenance Cost

Health assessment & Minimizing the failures

Equipment Life Assessment

Input for developing Maintenance Strategy


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Safety of Man and Machine

Modern Power Plant Equipment are High Cost

Capital assets

Fire Hazards Fuel, Lubricating Oils, Electrical, etc


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Reliability

High reliability

Electricity is life line of the modern civilization Local

Trains, Hospitals, Industrial requirement, Domesticrequirements, sanitation, basic amenities, etc

Maximize reliability by performing plannedmaintenance based on condition monitoring.

Machinery in large power plant is desired to have high reliability.As maintenance has a large cost impact on the total operation, it

is however essential to only perform maintenance when it is

really required.


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Plant Availability

Shift form breakdown to condition based

maintenance

Machine health input for scheduling inspection &

maintenance

To guarantee the machine availability, avoid major breakdown &

to schedule inspection & maintenance, the condition of the

machines need to be monitored accurately, so that right

maintenance decisions can be taken


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Objectives of Condition Monitoring

Protect machines against major breakdowns

Machine health assessment.

Maximize operation efficiency.

Troubleshooting

Minimize maintenance cost

This is the basis for formulating maintenance strategy


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Machine Health Assessment

Parameter Identification

OEM guidelines

Operating Experience

Improved Diagnostic Analysis

Monitoring System

On line monitoring

Off line monitoring

Trends

Raw data monitoring

Data analysis and monitoring of derived parameters

Defined range of operation - Normal/Alarm/Trip value


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Machine Health Assessment

Feed back from Machine Operating History

Machine operating characteristics

History of past problems and its remedy

Residual Life Analysis

Comprehensive Equipment Health Survey

Pre-overhaul survey

Input from OEM and other plants

Residual life study


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Condition Based Maintenance Management

System at Trombay

Online monitoring of Critical Parameters

Periodic Data Collection and Trending Analysis

Inputs from equipment history, pre-overhaul survey

and past experiences

RLA


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Monitoring Parameters for Main Turbine

Mechanical Parameters

Vibration of Shaft and pedestal

Bearing metal temperature

Turbine Expansions

Axial shift,

Turbine metal temperature

Functional Parameters

Steam pressures and temperatures

Vacuum

Feed Water Parameters


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Limit Values of Operating Parameters

OEM recommendation

Steady state running parameters

Revise limit values based on condition monitoring

This forms the basis for deciding alarm & trip values


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Pre-overhaul survey of Main Turbine

Objective

Ascertain present running behavior Identify problem areas

Planning for high value insurance spares

Define scope of Quality overhaul Planned preparation

Focused approach to minimize outage duration

Decision making for future overhauls


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Studies to be conducted during Pre-Overhaul Survey

Running hours

Reports of all previous overhauls along with therepairs carried out and spares consumed

Discussions on Past / present problems

RLA reports Present vibration behavior/scan

Thermo-scan

Study of past and present operating data Heat balance diagram and reports of periodic

enthalpy drop tests


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Example:

High IP exhaust steam temperature in Unit 5

Possible causes: Steam leak through parting plane.

Inlet steam passing into exhaust directly through

angle seal rings Steam leakage through angle sealing rings of steam

extractions

Faulty RTD


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Analysis and Action Taken:

Machine EOH > 1.5 Lakh hours.

Parting plane fasteners replacement planned.

No history of steam leak through angle seal rings.

During turbine fact finding inspection no sign of

leakage observed. Also clearances were within

design limits.

RTD

Problem identified with data acquisition and transfer.


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Strategic decision based on past experience:

HP front shaft high vibration problem persisted for 4years.

Problem resolved by carrying out slow speed dynamic

balancing at site.

This practice is being followed for all rigid rotors at

Trombay. All rotors balanced till date have hadsubstantial mass imbalance.


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Vibration analysis

Vibration is one of the most significant parameter for

interpreting machine-health and indication for problems

at incipient stage.

For machine health monitoring, the simplest method of

detecting any abnormality with the machine is to look for

the change in vibration pattern and level.


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Guidelines for Vibration Analysis

Gradual rise in vibration are due to:

Bearing deterioration/ wearDeterioration of base frame/ grouting

Wear, corrosion, deposition on rotating

componentsSettling of foundations

Deterioration in alignment


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Abrupt change in vibration could be due to:

Change in operating parameters like flow,

pressure, temperature, etcModification / maintenance deficiency ( e,g

bearing misalignment) if it increases just after

maintenance.Operating shocks resulting in machine

deterioration / damage

Hot misalignmentBearing lubrication problem


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Very high vibrations can be attributed to:

Resonance

Imbalance of rotating parts

Expansion restrictions/ Piping strains

Foundation problem/ Foundation loading

Loading of bearings

Lubrication problems

Improper dimensional tolerances

Machine performance does not meet withrequired performance, hydraulic forces,aerodynamic forces-design problem.

Equipment damage e.g rubbing, rotor bent,

gear mismatch, etc


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Vibration spectrums analysis indicative of thefollowing problems:

Unbalance

Bent shaftMisalignment of couplings, bearings and gears

Looseness

RubbingEccentricity of rotating components

Resonance

Journal bearing problems oil whip, oil whirl


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Guidelines for Vibration AnalysisSalient Points for vibration analysis:

Shaft is the source of energy in rotating machinery.

Shaft could get its energy from: process medium, imbalance, restrictions,variation of design settings, expansion problem, rubbing, electrical problem,inconsistency of oil film, etc

Energy of shaft shows through bearing, casing, foundation, pipe, etc Acceptable energy/ vibration of shaft may show unacceptable vibration in

bearing due to problem in bearing, foundation, casing , pipe pulls, etc

Latent design defects/deficiencies surfacing at a later date can be source of

vibrations. e.g foundation, pipe pull, resonance, etc. Recognize the focal point of vibrations

Look for temperature effect on vibrations

Look for effect on vibration behavior due to loading of machine

Study the recent maintenance carried out if any. Look for change in operating parameters if any

Look into the history of vibrations of the machine

Look for abrupt change/ trend of vibration

Look for change in running parameters of the machine like bearingtemperatures, etc.

Look for change in lubrication, oil quality, etc


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Main Turbine Unit # 5 LP free

standing blade failure.

Case Study 1


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Main Turbine Unit # 5 LP free standing blade failure.

Background

LP turbine free standing blade failure occured on running machine,which lead to catastrophic failure of the machine. Being the first incident

of this nature and our unit being the oldest 500MW unit in India, the

study of blade failure detection was undertaken in collaboration with

BARC, Mumbai.


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Observations and analysis:

Blade vibrations were recorded twice, before & after shutdown.

1. During vacuum drop many peaks of vibration corresponding to

natural frequency of LP II & LP III observed. These were

not seen during normal steady state operation.


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2. Drastic variation in amplitude is seen in BPF component of LP

II & LP III during excitation. Normally, the amplitude are

steady unless the blades are disturbed and set into vibration.


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3. Side band harmonics are seen on both sides of the BPF. The

harmonics are 20 Hz on either side of the BPF. The presence of

the side bands indicates problem with the blades. Theseharmonics vanished after replacement of the cracked blades.


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4. The Amplitude of the BPF have drastically reduced after

replacement of the cracked blades.

This technique of detecting cracks in freestanding blades may be very

useful for monitoring the health of the machine and thereby detecting

blade cracks at the incipient stage.


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Control Fluid Pump CurrentHunting

Case Study 2


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Pump Specification

Make : KSB, Germany

Type : WKVM 100/2+3

LP Discharge : From 2nd Stage

HP Discharge : From 5

th

stage Rated Pressure : LP - 13.6 Bar

HP - 40 Bar


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Pump Layout

Pump 1Pump 2

LP Circuit

HP CircuitNRV


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Problem

Motor Current of CF Pump 2 hunting from 152 192

Amps.

No pressure hunting in LP Circuit.

HP circuit pressure hunting around 1 bar

(CF system is provided with accumulators to take

care of pressure fluctuations)


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Cause Effect DiagramOperational Hydraulic

Pump flow variation Loss of suction

System fluctuations Obstruction at suction

Load / Freq variation Blockage

Accumulators Detached suction pipe

Bladder failure Fluid foaming

Isolation from circuit change in air release property

Control system contaminationGovernor hunting air ingress

Fluid properties

Viscosity / Temperature

Contamination

Internal clearances

Increase in clearances beyond limits Damage to internals

Wear Impeller / Diffuser

Rubbing

Axial float setting

Setting during assembly

Pump operating in unstable zone Rotor faultInterstage leakages Design

Gasket failure Change due to internal damage Measurement error

Looseness

Mechanical Electrical

Pump charecteristics


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Possible Causes

Electrical fault

Rotor fault Motor of pump #2 swapped with motor of pump #1

Measurement error

RPM measurements carried out Power measurements carried out


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Possible Causes

Hydraulic problems

Obstruction in pump suction

During unit outage the Control Fluid was transferred

to another tank for tank inspection and no

abnormality found

Fluid foaming

No foaming observed and CF sample tested OK

Change in fluid viscosity

Operating temperature normal and no contaminationof fluid


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Possible Causes

Operational Problem

- Pump flow variation

No System fluctuation , accumulators found

healthy, and no hunting in governing system.


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Possible Causes

Mechanical Problems

- Increase in internal clearances

- Problem with Axial float setting- Damage to internals

Pump overhauled and performance tested at OEM

facility (partial test with LP stage blocked).No damage observed on internals, gasket failure or

looseness in the pump


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Possible Causes

Mechanical Problems

- Pump characteristics

In-situ pump flow measurements carried out. Flowhunting observed in HP circuit.

2

1

Pump

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41

LP Flow(m3/hr)

10 15

24.5 25

HP Flow(m3/hr)

152-192

167 -172

Current(Amp)

P Ch t i ti


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0

50

100

150

200

250

300

350

400

0 20 40 60 80 100 120 140

Flow

Head(m)

Unit 6 CF Pump 2 Char Modified hyd char

Pump Characteristics


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Corrective action

HP Impeller modification

It was observed that the pump operating point is in

unstable zone

Diameter increased by 10 mm to change the pump

hydraulics


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Pump behavior after modification

174170Current

(Amps)

40.539.6HP Pressure

(Bar)

13.513.6LP Pressure

(Bar)

21Pump


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Operational Hydraulic

Pump flow variation Loss of suction

System fluctuations Obstruction at suction

Load / Freq variation Blockage

Accumulators Detached suction pipe

Bladder failure Fluid foaming

Isolation from circuit change in air release property

Control system contaminationGovernor hunting air ingress

Fluid properties

Viscosity / Temperature

Contamination

Internal clearancesIncrease in clearances beyond limits Damage to internals

Wear Impeller / Diffuser

Rubbing

Axial float setting

Setting during assembly

Pump operating in unstable zone Rotor fault

Interstage leakages Design

Gasket failure Change due to internal damage Measurement error

Looseness

Mechanical Electrical

Pump charecteristics


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THANK YOU

Documents

Condition Monitoring of Power Plant Equipment