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
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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
<10
Weekly
Exercise extreme caution. Analyze for individual gases. Plan outage. Advise Manufacturer
>30
Weekly
10-30
Weekly
<10
Monthly
Exercise extreme caution. Analyze for individual gases. Plan outage. Advise manufacturer.
>30
Monthly
10-30
Monthly
<10
Quarterly
>30
Monthly
10-30
Quarterly
<10
Annual
Exercise caution. Analyze for individual gases. Determine load dependence.
Exercise caution. Analyze for individual gases. Determine load dependence. Continue normal operation.
© OMICRON Page 14
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 < 300°C). -T2: thermal fault (300 °C < T < 700°C). -T3: thermal fault (T > 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)
20
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
