4_prevost_oil analysis.pdf

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31 October 2013

Oil Analysis An Important Tool for Transformer Diagnosis

Conference on Electrical Power Equipment Diagnostics

Bali, Indonesia

Thomas Prevost


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Oil Analysis

Study and test the oil to determine

the condition of overall insulation

system

1. Dissolved Gas Analysis DGA

2. Oil Quality

3. Furans

Page 2 OMICRON


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Page 33

Oil Diagnostics

DGA

Oil Quality


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Source of Gas Byproducts of Faults

Oil

Hydrogen

Hydrocarbons

Cellulose

Carbon Oxides

Water

Page 4 OMICRON


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Page 5

C CH

H

H

H

C

H

HH

H

C

H

H

H

C

H

H

H

C

C C

C

C

H HH H H

HH HH

H

C CH H H HAcetylene

Ethylene

Methane

Ethane

Hydrogen

Heating

Heating

Arcing Corona

Heating

Oil - Byproducts


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Page 6

Degradation of cellulose

O

H

O

HO

H

OH

OH

O

H H

CH2O

CH2OH

H

O

HH

O

OH

H

Heating

Heating

C O O C O

O

H H

Carbon Monoxide Carbon Dioxide

Water

Section of

Cellulose

Molecule


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DGA Analysis

1. Fault Gas Levels

2. Rate of Gas Generation (Trend)

3. Ratio of Gas Levels

Page 7 OMICRON


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OMICRON

Page 8

Gases reported:

Fault Gases

Methane CH4 Ethane C2H6

Ethylene C2H4Acetylene C2H2

Carbon Monoxide CO

Carbon Dioxide CO2

Atmospheric Gases

Nitrogen N2

Oxygen O2


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OMICRON

Page 9

Thermal Faults:

Normal Operating Temperature:

Carbon Monoxide CO

Carbon Dioxide CO2

150 C 500 C:

150-250 C : Relatively large quantities of low molecular

weight hydrocarbons

Hydrogen H2 Methane CH4

250-350 C : Increasing hydrogen relative to methane

Ethane C2H6

350-500 C : Still increasing hydrogen and ethylene

Ethylene C2H4

Sources of Fault Gases in Transformers


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OMICRON

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Electrical Faults:

Partial Discharges:

Oil: HydrogenCellulose: Hydrogen, Carbon Monoxide

Arcing:

Oil: Acetylene, Hydrogen

Sources of Fault Gases in Transformers


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OMICRON

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Gas Generation(Not to Scale)

Approximate Oil Decomposition

Temperature above 150oC

IEEE and IEC Codes to Interpret Incipient Faults in Transformers, Using Gas in Oil Analysis,

by R.R. Rogers C.E.G.B, Transmission Division, Guilford, England. Circa 1978.

Partial Discharge (Not TemperatureDependent)

Range of Normal OperationHot Spots

(Of increasingtemperature)

Arcing Conditions

65o

150

o

200o

300o

800o

700o

500o

350o

250o

Hydrogen (H2)

Methane

(CH4)

Ethane (C2H6)

Ethylene (C2H

4)

Acetylene (C2H2)

CH4>H2

C2H6>CH4

C2H4>C2H6

C2H2>10% of C2H4

Trace

Combustible Gas Generation vs.

Approximate Oil Decomposition Temperature


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DGA Diagnostic Methodology

1. Determine if DGA results are Normal1. Single sample compare results to C57.104-2008 Table 1

2. If greater than condition 1 then retest sample within two months1. Verifies results from first test

2. Establishes gas generation rate

3. Greater than one sample

1. Calculate gas generation rate2. Compare rate to values in C57.104-2008 Table 3

1. Sampling interval

2. Action

2. If DGA results are abnormal then follow various methodologies todetermine fault type and possible cause.1. Key gas

2. Gas ratios

Page 12 OMICRON


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OMICRON

Page 13

Dissolved Key Gas Concentration Limits (L/L

(ppm))

StatusH2

HydrogenCH4

MethaneC2H2

AcetyleneC2H4

EthyleneC2H6

Ethane

CO

CarbonMonoxide

CO2

CarbonDioxide TDCGb

Condition 1 100 120 1 50 65 350 2500 720

Condition 2 101-700 121-400 2-9 51-100 66-100 351-570 2500-4000 721-1920

Condition 3 701-1800 401-1000 10-35 101-200 101-150 571-1400 4001-10000

1921-4630

Condition 4 >1800 >1000 >35 >200 >150 >1400 >10000 >4630

IEEE C57.104-2008 Table 1


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OMICRON

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TDCG

Levels(L/L)

TDCG Rate

(L/L/day)

Sampling Intervals and Operating Procedures for Gas

Generation Rates

SamplingInterval Operating Procedures

Condition 4 >4630 >30 Daily Consider removal from service.

Advise manufacturer10-30 Daily

30 Weekly Exercise extreme caution.

Analyze for individual gases.

Plan outage.

Advise manufacturer.

10-30 Weekly

30 Monthly Exercise caution.


Determine load dependence.10-30 Monthly

30 Monthly Exercise caution.


Determine load dependence.

10-30 Quarterly Continue normal operation.


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Factors influencing the interpretation of results:

Type of faults:

-PD: partial discharges of the corona-type.

-D1: discharges of low energy.

-D2: discharges of high energy.

-T1: thermal fault (T < 300C).

-T2: thermal fault (300 C < T < 700C).

-T3: thermal fault (T > 700C).

-DT: mixtures of discharges and thermal faults.

-S: stray gassing of oil (T < 200 C), catalytic reactions (notrelated to faults).


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Typical faults in the equipment:

-PD: corona partial discharges in voids or gas bubbles(poor drying, impregnation).

-D1: partial discharges of the sparking type, tracking in

paper, small arcing, arc breaking in LTC oil.

-D2: short circuits with power follow-through, flashovers,

tripping, gas alarms; extensive damage, metal fusion.


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Typical faults in the equipment:

-T3: large circulating currents, shorts in laminations,carbon particles in oil.

-T2: circulating currents, defective contacts,

carbonization of paper.

-T1: overloading, insufficient cooling.

-S: stray gassing , catalytic reactions on wet metal

surfaces.


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Mixtures of faults

-mixtures of faults sometimes occur rather than pure faults and may be more difficult to identify with certainty.

-for instance, mixtures of faults D1 and T3 may appear

as faults D2 in terms of gas formation.


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Energy/ temperature required to produce gases:

-Low energy/temperature: H2, CH4, C2H6, CO, CO2.

-High temperature: C2H4.

-Very high temperature/energy: C2H2.

-In practice, always mixtures of gases are formed.


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Fault identification methods

-Key gas

-Rogers

-Duval Triangle

-CO and CO2(paper involvement in faults)

-O2/N2 (hot spots, membrane leaks)

-C2H2/H2(OLTC leaks)


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OMICRON

Page 21

Oil

Cellulose

Hydrogen

Carbon Monoxide, Carbon Dioxide

Partial Discharge

Oil Low Temperature Hydrogen, Methane, Ethane

High Temperature Hydrogen, Ethylene, Methane, Ethane

Cellulose Low Temperature Carbon Dioxide

High Temperature Carbon Monoxide, Carbon Dioxide

Pyrolysis

(Acetylene is most significant)

Hydrogen, Acetylene, Methane, Ethane, Ethane, Ethylene

Arcing

IEEE C57.104-2008 Key Fault Gases


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Possible Faults


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Possible Reasons


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Rogers Ratio


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DGA Diagnosis (Duval)


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OMICRON

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Oil Quality Tests

Tests the condition of the insulating fluid.

Use results for maintenance action No action

Recondition

Reclaim

Replace Use the results to access the condition of the

Insulation System

Dielectric Strength

Power Factor

Moisture Acid

Furans


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OMICRON

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Oil Quality Tests

Several standards are referenced for oil quality testsand result interpretation:

IEC 60422 Mineral Insulating Oil in Electrical Equipment

Supervision and Maintenance Guide

IEEE Guides

C57.106-2006 Guide for Acceptance and Maintenance of

Insulating Oil in Equipment

C57.152 IEEE Guide for Diagnostic Field Testing of FluidFilled Power Transformers, Regulators, and Reactors


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Dielectric, Physical and

Chemical Analysis

Dielectric measurementsBreak down voltage ASTM D 877

Break down voltage ASTM D 1816 IEC 60156Power factor ASTM D 924 IEC 60247 Physical propertiesInterfacial tension ASTM D 971 EN 14210

Particle Count ASTM D 6786 IEC 60970Sludge ASTM D 1698

Water content ASTM D 1533 IEC 60814Visual ASTM D 1500 ISO 2049

Specific gravity ASTM D 1298 ISO 3675Color (lab) ASTM D 1500 ISO 2049Color (field) ASTM D 1524Chemical propertiesPolychlorinated biphenyl ASTM D 4059 IEC 61619Acidity ASTM D 974 IEC 62021

Dissolved gas ASTM D 3612 IEC 60599


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OMICRON

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IEEE Oil Classifications

Class I This group contains oils that are in satisfactory

condition for continued use.

Class II This group contains oils that do not meet the

dielectric strength and/or water content requirement of Table 5 andshould be reconditioned by filter pressing or vacuum dehydration.

Class III This group contains oils in poor condition that should

be reclaimed using Fullers earth or an equivelent method. Oils that

do not meet the interfacial tension (IFT), dissipation factor, and

neutralization number limits provided in table 5 should be reclaimed.


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OMICRON

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IEEE C57.106-2006 Suggested Limits

If limits for:

IFT

Dissipation Factor

Acidity

are exceeded theoil should be

reclaimed

otherwise the oil

can be

reconditioned if the

limits areexceeded.


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OMICRON

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Moisture Content

Karl Fisher Titration

Requires approximately 10 mL of oil.

Results are in ppm (mg/kg)


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OMICRON

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Interfacial Tension (IFT)

Measures the strength of the interface between the oil

under test and water.

Indicator of the presence of polar contaminents.


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OMICRON

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Dielectric Strength


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OMICRON

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Aging process : Cellulose depolymerization

CH2OH

O

OH

OH

O

CH2OH

OH

OH

O

O

CH2OH

OH

OH

O

CH2OH

O

OH

OH

OH

CH2OH

OH

OH

O

O

CH2OH

OH

OH

O

OH


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OMICRON

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CH2OH

O

H

H

H

OH

OHO

H

H O

Glucose Unit

Cellulose Degradation


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OMICRON

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Degree of Polymerization

Measurement of intrinsic viscosity after dissolving the cellulose

in a specific solvent.

Gives an average measurement of the number of glucose units

per molecular chain.

DP of Insulation Components prior to processing ~1200

DP of Insulation Components following processing ~1000

DP level considered as over-processed ~800

DP level considered end of life ~200


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OMICRON

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Degree of Polymerization

Effects of aging:

- darkening of color

-loss of electrical and mechanical strength; trans. failure

-shortening of cellulose chains DP lowered

-paper becomes wetter, and acidic

-by-products contaminate the oil

Source ABB Power Technologies, Inc.

Progressive aging with time

Paper Insulation Aging in Mineral Oil

DP DP DP DP DP

1000 733 549 405 309

DP

181

Brittle & darkEnd of

mech str.

IEEE Transformer Committee Panel Session October 25, 2005


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OMICRON

Page 38

HOH

CO HOH

HOH

CH2OH

OH

O

O H

H

H H OC

OH

H

OCHO

H

H

H

WATER

WATER

WATER

FURAN

CARBON

MONOXIDE

Degradation of Cellulose


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OMICRON

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Most labs determine the concentration of five furanic compounds:

1. 2-furaldehyde (2FAL)

2. 5-methyl-2-furaldehyde (5M2F)

3. 5-hydroxylmethyl-2-furaldehyde (5H2F)

4. 2-acetyl furan (2ACF)5. 2-furfuryl alcohol (2FOL)

Note: 2FAL is stable for years while all other furanic compounds are less

stable. They tend to form and then degrade to 2FAL over a time period of

months.

Furans


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OMICRON

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2- Furfural vs. DP Correlation Plots

Correlation of DP with 2-FAL


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OMICRON

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Summary & Conclusions

DGA is a valuable tool to detect transformer problems

Sample can be taken while transformer is in service

Can trend fault gases

Industry Acceptance

Oil Quality Testing can detect transformer problems as well as

indicate maintenance actions

Oil can be reconditioned or reclaimed

Inceases life of insulation system

Remove moisture, acids, particles etc.

The remaining life of the insulation can be estimated with Furan

analysis


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Questions

4_prevost_oil analysis.pdf

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