4 Prevost Oil Analysis

Oil Analysis – An Important Tool for Transformer Diagnosis

Conference on Electrical Power Equipment Diagnostics Bali, Indonesia Thomas Prevost

31 October 2013

Oil Analysis

Study and test the oil to determine the condition of overall insulation system 1. 2. 3. © OMICRON

Dissolved Gas Analysis DGA Oil Quality Furans Page 2

Oil Diagnostics

Oil Quality

DGA © OMICRON

3

Page 3

Source of Gas – Byproducts of Faults

• Oil • Hydrogen • Hydrocarbons

• Cellulose • Carbon Oxides • Water

© OMICRON

Page 4

Oil - Byproducts Methane

H Ethane

H C H Ethylene

H H

C C

H

H

H

H C

H

H

H C H H

Heating Heating

H HH H Heating C C C C C H H HH H H Arcing

Corona

H C C H

H H

Acetylene

Hydrogen

© OMICRON Page 5

Degradation of cellulose Carbon Monoxide

C

Carbon Dioxide

O

O

C

O

Heating

H

OH

CH2OH O

Section of Cellulose Molecule

H

OH

H H

O

O H H

O

OH

H H

H

O

O CH2O Heating

O H H Water

© OMICRON Page 6

DGA Analysis

1. Fault Gas Levels 2. Rate of Gas Generation (Trend) 3. Ratio of Gas Levels

© OMICRON

Page 7

Gases reported: Fault Gases • Methane • Ethane • Ethylene • Acetylene

Atmospheric Gases CH4 C2H6 C2H4 C2H2

• Nitrogen • Oxygen

N2 O2

• Carbon Monoxide CO • Carbon Dioxide CO2

© OMICRON Page 8

Sources of Fault Gases in Transformers Thermal Faults: Normal Operating Temperature: • Carbon Monoxide CO • Carbon Dioxide CO2 150 ºC – 500 ºC: 150-250 ºC : Relatively large quantities of low molecular weight hydrocarbons • Hydrogen H2 • Methane CH4 250-350 ºC : Increasing hydrogen relative to methane • Ethane C2H6 350-500 ºC : Still increasing hydrogen and ethylene • Ethylene C2H4 © OMICRON Page 9

Sources of Fault Gases in Transformers Electrical Faults: Partial Discharges: Oil: Cellulose:

Hydrogen Hydrogen, Carbon Monoxide

Oil:

Acetylene, Hydrogen

Arcing:

© OMICRON Page 10

Combustible Gas Generation vs. Approximate Oil Decomposition Temperature Partial Discharge (Not Temperature Dependent) Range of Normal Operation Hot Spots

Arcing Conditions

(Of increasing temperature)

200o

300o

Hydrogen (H2)

CH4>H2

Trace

C2H2>10% of C2H4

700o

C2H4>C2H6 150o

Acetylene (C2H2)

C2H6>CH4

500o

Ethylene (C2H4)

350o

250o

Ethane (C2H6)

800o

65o

Methane (CH4)

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. © OMICRON Page 11

DGA Diagnostic Methodology 1. Determine if DGA results are “Normal” 1. Single sample – compare results to C57.104-2008 – Table 1 2. If greater than condition 1 then retest sample within two months 1. 2.

Verifies results from first test Establishes gas generation rate

3. Greater than one sample 1. 2.

Calculate gas generation rate 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 to determine fault type and possible cause. 1. Key gas 2. Gas ratios

© OMICRON

Page 12

IEEE C57.104-2008 Table 1 Dissolved Key Gas Concentration Limits (μL/L (ppm)) H2 Hydrogen

CH4 Methane

C2H2 Acetylene

C2H4 Ethylene

C2H6 Ethane

CO Carbon Monoxide

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

400110000

19214630

Condition 4

>1800

>1000

>35

>200

>150

>1400

>10000

>4630

Status

CO2 Carbon Dioxide

TDCGb

© OMICRON Page 13

IEEE C57.104 2008 Table 3 Gas Generation Rates TDCG Levels (μL/L) Condition 4

Condition 3

Condition 2

Condition 1

>4630

1921–4630

721–1920

≤ 720

TDCG Rate (μL/L /day)

Sampling Intervals and Operating Procedures for Gas Generation Rates Sampling Interval

Operating Procedures

>30

Daily

Consider removal from service. Advise manufacturer

10-30

Daily

30

Weekly

10-30

Weekly

30

Monthly

10-30

Monthly

30

Monthly

10-30

Quarterly

700°C). -DT: mixtures of discharges and thermal faults. -S: stray gassing of oil (T < 200 °C), catalytic reactions (not related to faults).

15

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.

16

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.

17

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.

18

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.

19

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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IEEE C57.104-2008 Key Fault Gases Partial Discharge Oil Cellulose

Hydrogen Carbon Monoxide, Carbon Dioxide

Pyrolysis Oil

Low Temperature Hydrogen, Methane, Ethane High Temperature Hydrogen, Ethylene, Methane, Ethane Cellulose Low Temperature Carbon Dioxide High Temperature Carbon Monoxide, Carbon Dioxide

Arcing Hydrogen, Acetylene, Methane, Ethane, Ethane, Ethylene (Acetylene is most significant) © OMICRON Page 21

Possible Faults

Possible Reasons

Rogers Ratio

DGA Diagnosis (Duval)

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 © OMICRON Page 26

Oil Quality Tests Several standards are referenced for oil quality tests and 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 Fluid Filled Power Transformers, Regulators, and Reactors”

© OMICRON Page 27

Dielectric, Physical and Chemical Analysis Dielectric measurements Break down voltage

ASTM D 877

Break down voltage

ASTM D 1816

IEC 60156

Power factor

ASTM D 924

IEC 60247

Interfacial tension

ASTM D 971

EN 14210

Particle Count

ASTM D 6786

Sludge

ASTM D 1698

Water content

ASTM D 1533

IEC 60814

Visual

ASTM D 1500

ISO 2049

Specific gravity

ASTM D 1298

ISO 3675

Color (lab)

ASTM D 1500

ISO 2049

Color (field)

ASTM D 1524

Physical properties

IEC 60970

Chemical properties Polychlorinated biphenyl

ASTM D 4059

IEC 61619

Acidity

ASTM D 974

IEC 62021

Dissolved gas

ASTM D 3612

IEC 60599

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 and should be reconditioned by filter pressing or vacuum dehydration. • Class III This group contains oils in poor condition that should be reclaimed using Fuller’s 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.

© OMICRON Page 29

IEEE C57.106-2006 Suggested Limits

If limits for: • IFT • Dissipation Factor • Acidity are exceeded the oil should be reclaimed otherwise the oil can be reconditioned if the limits are exceeded.

© OMICRON Page 30

Moisture Content

Karl Fisher Titration

Requires approximately 10 mL of oil.

Results are in ppm (mg/kg)

© OMICRON Page 31

Interfacial Tension (IFT) Measures the strength of the interface between the oil under test and water. Indicator of the presence of polar contaminents.

© OMICRON Page 32

Dielectric Strength

© OMICRON Page 33

Aging process : Cellulose depolymerization

CH2OH OH

O OH O

OH

O

O

O

CH2OH

OH

OH

OH

CH2OH

CH2OH H

OH

O OH O

OH

CH2OH

O

OH

O

O

CH2OH

OH

OH

OH

© OMICRON Page 34

Cellulose Degradation

CH2OH H O

O

H OH H

O H

H

OH

Glucose Unit

© OMICRON Page 35

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

© OMICRON Page 36

Degree of Polymerization Paper Insulation Aging in Mineral Oil

DP

DP

DP

DP

DP

1000

733

549

405

309

Progressive aging with time

End of mech str.

DP 181

Brittle & dark

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.

IEEE Transformer Committee Panel Session – October 25, 2005

© OMICRON Page 37

Degradation of Cellulose

CO

HOH

CH2OH

CARBON MONOXIDE

O H H H C OH H O

O

H

H

H

WATER CHO

O

H

OH

HOH

FURAN HOH WATER WATER © OMICRON Page 38

Furans

Most labs determine the concentration of five furanic compounds: 1. 2. 3. 4. 5.

2-furaldehyde 5-methyl-2-furaldehyde 5-hydroxylmethyl-2-furaldehyde 2-acetyl furan 2-furfuryl alcohol

(2FAL) (5M2F) (5H2F) (2ACF) (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.

© OMICRON Page 39

Correlation of DP with 2-FAL

2- Furfural vs. DP Correlation Plots © OMICRON Page 40

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

© OMICRON Page 41

Questions

31 October 2013