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Condition Monitoring

Most failures give some warning of that fact that theyare about to occur.

This warning is called a potential failure An identifiable condition which indicates that a

functional failure is either about to occur or is in theprocess.

Techniques to detect potential failures are known as oncondition maintenance taskscondition monitoringtechniques

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THE P-F CURVE

TIME

FAILURE STARTS TO OCCUR

PWHERE WE CAN FIND OUT

THAT IT IS FAILING

(POTENTIAL FAILURE)

F

WHERE IT HAS FAILED

(FUNCTIONAL FAILURE)

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Condition Monitoring and Predictive Maintenance

Condition monitoring is carried out for two mainreasons:

To detect changes in condition that could lead to

catastrophic failure, particularly for machinery thatcould represent a threat to the health and safety ofpeople, or cause an environment incident. This is knownas Machinery Protection or ProtectiveMonitoring.

To identify the early onset of incipient failures so that aprediction can be made about their most likely progressand suitable actions can be planned. This is known as Predictive Maintenance and is often abbreviated toPdM.

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What does condition monitoring do for the user?

Condition monitoring provides users with a unique setof deliverable that allows them to organize maintenance

activities more effectively than is possible using simpletime or usage based scheduling:

It clearly identifies machines that have potentialproblems.

For a maintenance manager responsible for thousandsof machines an important output of the system is areliable exception report, which focuses attention eachday on a small number of machines for which a possibleearly fault has been detected.

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The system achieves this by testing measurementsagainst a set of alarm thresholds.

It identifies the nature of each problem.

Continuing the medical analogy, this is known as the diagnosis stage.

Since diagnosis often requires the comparison of resultsfrom several different types of measurement, thesystem allows the presentation of composite displays

combining vibration, oil analysis, pressure changes, andthermo-graphy readings.

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What does condition Monitoring do for the user?

Condition monitoring provides users with a unique set

of deliverables that allows them to organize

maintenance activities more effectively than is possible

using simple time or usage based scheduling: It clearly identifies machines that have problems

( Exception Report )

It Identifies the nature of each problem.

( Fault Diagnosis )

It predicts the most likely outcome of each problem.

(Fault prognosis )

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Condition Monitoring Techniques

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Infrared Thermography

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Infrared thermography is the science of

acquisition and analysis of thermal

information by using non contact thermalimaging devices.

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featuresIt is non-contactuses remote sensing

-Keeps the user out of danger

-Does not intrude upon or affect the target at all2.It is two dimensional

-Comparison between areas of the target is possible

-The image allows for excellent overview of the target

-Thermal patterns can be visualized for analysis

3.It is real time

-Enables very fast scanning of stationary targets

-Enables capture of fast moving targets

-Enables capture of fast changing thermal patterns

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applications Electrical Maintenance

Buildings

Furnaces and boilers

Mechanical, friction

Fluid flow problems

Tanks and vessels

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Infrared ThermographyElectrical HT Substation

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Infrared ThermographyElectrical Motor Winding

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Loose or tight belt heats up abnormally

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Blocked Heat Exchanger

I f d Th h

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Infrared Thermographyprinciple

VisibleSpectrum

An object when heated radiates electromagnetic energy. The amount of energy isrelated to the objects temperature. The Thermal Imager can determine the temperatureof the object without physical contact by measuring the emitted energy.

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principle The human eye responds to visible light in the

range 0.4 to 0.75 microns.

Infrared temperature measurement is made in the

range 0.2 to 20 microns. Thermal Imager can focus this energy via an

optical system on to a detector in a similar way tovisible light.

The detector converts infrared energy into anelectrical voltage which after amplification andcomplex signal processing is used to build thethermal picture in the operators viewfinder onboard the Thermal Imager.

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principle The amount of energy radiated from an object is dependanton its temperature and its emissivity.

An object which has the ability to radiate the maximumpossible energy for its temperature is known as a Black

Body. In practice there are no perfect emitters and surfacestend to radiate somewhat less energy than a Black Body.

As energy moves towards the surface a certain amount isreflected back inside and never escapes by radiative means.

60% of the available energy is actually emitted. The

emissivity of an object is the ratio of the energy radiated tothat which the object would emit if it were a Black Body.

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application

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applicationMeasuring the average temperature withinseveral rectangles in the scene

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electrical circuit Joints & connections have contact resistance.

Temp rises when current flows (Ohmic heat).

Looseness (constriction resistance) & oxidation (filmresistance) create HOT SPOT & resistive imbalance.

Cause open circuit, energy loss & fire hazards.

Implementation of a PdM programme based on IRTcan certainly minimize sudden failures, energy loss& prevent fire hazards.

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Case Study-1: Switchyard-Isolator

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Case Study-2: Switchyard-Isolator

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Case Study-3: Switchyard-CT

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Case Study-4: Switchyard-Jumper

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Case Study-5: Switchyard-Conductor

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Case Study-6: Switchyard- Breaker

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Case Study-7: Switchyard- Breaker

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Case Study-8: Switchyard- Transformer

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Case Study-9: Switchyard- Transformer

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Case Study-10: Switchyard

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Case Study-11: Electrical Panel

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Case Study-16: HT Panel

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Case Study-17: HT panels

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C S d HT l

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Case Study 21: Motors

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Case Study-21: Motors


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Higher temp towards motor bearing

Higher temp towards coupling

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SEE THE HEAT.

Rise in temperature w.r.t ambient temperature.

Rise in temperature w.r.t. that of similarcomponent under similar operating conditions.

Absolute temp w.r.t. load ( % of full load ).

Available standards & OEMs data sheet.

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MOTOR MONITORING

53Condition Monitoring

C diti M it i d P di ti M i t

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For Electrical Equipments

Insulation Resistance / PI Surge Comparison

Motor Current Signature Analysis Broken Rotor bars, High resistance between bars & rings,

Shorted stator / rotor laminations

Power Signature analysis All the above + resistive & inductive unbalance, torque

variations

Hi Voltage Testing

Partial Discharge

In all these cases the PF interval is from several weeksto months

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MOTOR MONITORING55

Diagnostic testing to evaluate/ troubleshoot

circuit faults

Trending through periodic testing of motor

condition

Quality Assurance testing on new or

reworked motors (Baseline Test)

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Fault Zones56

Power Quality

Power Circuit

StatorRotor

Air Gap

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Summary of Motor Failures57

C t A l i F lt Z

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Current Analysis Fault Zones58

Rotor

In-Rush/Start-Up (peak in-rush current and time to

start motor)

Low and High Resolution (CSA) (pole pass

Frequency [FP] sideband amplitude)

Air Gap

Eccentricity (eccentricity peaks)

In-Rush/Start-UpBroken Bars

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Broken Bars59

Rotor Evaluation

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Evaluating the FFT Spectrum60

(From the previouslid )

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slide)

Diagram on the leftindicates a motor(rotor) in good health

This can be determined

by the difference inamplitude between theline frequency and thepole pass frequencysideband immediatelyto its left (>60 dB)

Diagram on the right61

Low/High Resolution TestBroken Bars

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Broken Bars62

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Power Analysis63

Power QualityVoltage and Current Waveforms

Voltage and Current Total Harmonic Distortion

Harmonic Voltage Factor (for motor derating)

Power CircuitVoltage and Current Imbalances

NEMA derating, based on voltage imbalanceStator Condition

Impedance Imbalance

Effects of Imbalanced

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Voltages and Currents64

Imbalanced voltages seen by the motor are

equivalent to introducing negative sequence

currents having a rotation opposite to that of

the positive sequence currents

Negative sequence currents reduce motor

torque

Effects of Imbalanced

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Voltages and Currents65

A small voltage imbalance produces a much

larger current imbalance

Increases the temperature of an operating motor at a

given load (compared to that of a motor operating

with balanced voltages)

Do not operate a motor with voltage

imbalance greater than 5% (per NEMA)

Voltage ImbalanceDerating Curve

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Derating Curve

With imbalanced voltages, ratedhorsepower of an induction motor shouldbe multiplied by the derating factor.

66

Consequences of Harmonics

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Consequences of Harmonics67

Harmonic currents tend to travel upstream, awayfrom the nonlinear loads that produced them and

towards the utility source. Adverse affects can be

Voltage distortion within facilities

Excessive neutral return currents

High levels of neutral-to-ground voltage

Overheated transformers

Large magnetic fields emanating from transformers

Decreased distribution capacity

Power factor rate penalties

Consequences of Harmonics

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68

Harmonics also interfere with vital electrical

processes

Programmable microprocessor controls and

monitoring devices

Variable speed drives for motorized equipment on the

assembly line are, like all electric equipment, sources

and victims of voltage harmonics

D i

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Derating69

Harmonic currents increase the temperature of

an operating motor at any given load

[compared to a motor operating with only fundamental

voltage (50 Hz signal)]


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Category Nos of available

techqs

1

1Dynamic Monitoring 17

Particle Monitoring 15

Chemical Monitoring 15

Physical Effect 24Temperature 4

Electrical Effect 15

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