4_Prevost_Oil Analysis.pdf
Transcript of 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
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Oil Diagnostics
DGA
Oil Quality
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Source of Gas Byproducts of Faults
Oil
Hydrogen
Hydrocarbons
Cellulose
Carbon Oxides
Water
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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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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
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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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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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Electrical Faults:
Partial Discharges:
Oil: HydrogenCellulose: Hydrogen, Carbon Monoxide
Arcing:
Oil: Acetylene, Hydrogen
Sources of Fault Gases in Transformers
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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
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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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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.
Analyze for individual gases.
Determine load dependence.10-30 Monthly
30 Monthly Exercise caution.
Analyze for individual gases.
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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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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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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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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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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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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Moisture Content
Karl Fisher Titration
Requires approximately 10 mL of oil.
Results are in ppm (mg/kg)
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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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Dielectric Strength
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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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CH2OH
O
H
H
H
OH
OHO
H
H O
Glucose Unit
Cellulose Degradation
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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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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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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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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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2- Furfural vs. DP Correlation Plots
Correlation of DP with 2-FAL
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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