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Condition Monitoring of Power Condition Monitoring of Power Transformers using Dissolved Gas Transformers using Dissolved Gas
( G )( G )Analysis (DGA)Analysis (DGA)
Ahmad Shahsiah Ph D P EAhmad Shahsiah, Ph.D., P.E.Exponent Failure Analysis Associates
March 16, 2009
00M23SF.000 0000 0309 AS00
OverviewOverview
n DGA - Why Do We Care?n DGA Why Do We Care?n DGA Background n Potential Source of Errorn Potential Source of Error n Previous Works
Thn Theoryn Simulations and Resultsn Experimentsn Summary and Conclusions
2
DGA DGA -- Why Do We Care?Why Do We Care?
n Incipient faults could exist in power transformerstransformers
n Early detection of the faults could significantly reduce the cost of repair and loss of servicep
n Industry standards do not always give the right answer
n Understanding the dynamic nature of evolution and migration of characteristic gases improves our interpretation of DGA analysis
3
DGA BackgroundDGA Background-- History History fn Breife History
0Late nineteenth century: Mineral oils have been used for electrical insulation and cooling purposes01928: Attempts to diagnose the type of failure from
l d f il i dgases evolved from oil-immersed power transformers started by Buchholtz1970: Dorneneburg differentiated faults of thermal01970: Dorneneburg differentiated faults of thermal or electrical origin (Brown-Boveri Review publication)publication)01973: Halstead made a thermodynamic
assessment the formation of gaseous hydrocarbonsassessment the formation of gaseous hydrocarbons in Mineral Oil
4
DGA BackgroundDGA Background-- History History
n Briefe History- continued 1975: Rogers suggested the ratio method01975: Rogers suggested the ratio method along with a coding system to recognize the type of the faultthe type of the fault 01977: Modified Rogers method also
included in IEC document 10A 5301980’s and early 1990’s: attempts to
incorporate expert systems in fault p p ydiagnosis based on DGA01999-03: IEC 60599 latest edition.
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DGA BackgroundDGA Background-- Chemical ReactionsChemical Reactionsn Decomposition of Oil0Hydrogen, Methane, Ethane, Ethylene, Acetylene0Mechanism of formation:
Scission of C-H bonds: low energy faults such as partial di h f ld l (C )discharge of cold plasma (Corona)Scission of C-C, C=C and C≡C bonds and recombination: more and more energy or higherrecombination: more and more energy or higher temperature needed.
0Hydrogen can be generated as a result of variety of reactions
Large quantities of hydrogen have been reported in t f th t h d b i dsome transformers that had never been energized
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DGA BackgroundDGA Background-- Chemical ReactionsChemical Reactions
n Decomposition of Cellulose Insulation Mostly Carbon Monoxide and Carbon Dioxide0Mostly Carbon Monoxide and Carbon Dioxide
0Minor amounts of hydrocarbons and Furanic compoundscompounds0Mechanism of formation:
C-O bonds in Cellulose polymer chains are thermallyC-O bonds in Cellulose polymer chains are thermally less stable than hydrocarbon bonds in oilScission of cellulose polymer chains higher than 105°C Complete decomposition and carbonization above 300°C300 C
7
DGA BackgroundDGA Background-- IEC 60599IEC 60599n Electrical discharge - visually detectable faults
defined by IEC 605990Partial discharge (PD): Possible X-wax deposition,
pin holes or carbonized perforation in paper0Discharge of low energy (D1): Large carbonized
perforation through paper, carbonization of paper f b ti l i ilsurface, or carbon particles in oil
0Discharge of high energy (D2): Extensive destruction and carbonization of paper metaldestruction and carbonization of paper, metal fusion at the discharge location, extensive carbonization in oil in some cases tripping ofcarbonization in oil, in some cases tripping of equipment
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DGA BackgroundDGA Background-- IEC 60599IEC 60599n Thermal faults - visually detectable faults
defined by IEC 60599y0Thermal faults, in oil or/and in paper, below 300°C
if the paper has turned brownish (T1) and above 300°C if the paper has carbonized (T2)0Thermal faults of temperature above 700°C (T3) if
there is strong evidence of carbonization of the oil, metal coloration(800°C) or metal fusion (>1000°C)
n Suggested ratios: 0C2H2/C2H4, CH4/H2, C2H4/C2H6
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DGA BackgroundDGA Background-- IEC 60599IEC 60599
Range of 90% typical concentration values observed in power transformers (all types) (ppm in volume)
TX type H2 CO CO2 CH4 C2H6 C2H4 C2H2ypNo LTC 60-150 540-900 5 100-13 000 40-110 50-90 60-280 3-50
Communicating LTC
75-150 400-850 5 300-12 000 35-130 50-70 110-250 80-270
Incremental ratios of CO2/CO less than 3 are generally considered as an indication of probable paper involvement in a fault
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Potential Source of ErrorPotential Source of Error
n Gases Fluctuate in Healthy Transformers.n Gases Migrate Between the Oil and Paper.n This Could Cause Problems when Interpreting
DGA R ltDGA Results.n No Published Information about the Phenomenon
T D tTo Date.n A Physical Model can Help with Interpretation of
DGA Analysis Data Especially in the Case of CODGA Analysis Data Especially in the Case of CO2and CO.
11
Review of Previous WorksReview of Previous Works
n IEC 60599 and ANSI/IEEE C57.104.n Detroit Edison Company Studied the Gasn Detroit Edison Company Studied the Gas
Migration in HPFF Cables.Kh d Mi t St di d th Mi tin Khan and Miyamoto Studied the Migration of CO2 and CO.
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Literature DataLiterature Data
n Diffusivity Data by Detroit Edison Co.n ASTM D2779 - Gas Solubility in the Oil.yn CO2 in Paper Pulp.n Oommen’s Methodn Oommen s Method.
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D i M d lD i M d lDynamic ModelDynamic Model)ln(2 TDccvcD
tc
∇∇+∇⋅−∇=∂∂ αDiffusion Equation:
Z
Vz
Oil Semi
Approximations:• Soret Effect is Ignored.
t∂
X
Oil Semi infinite paper
• Diffusion in the x Direction.
• Velocity in the z Direction.
I i l Oil D t
zcv
xcD
tc
z ∂∂
−∂∂
=∂∂
2
2
In a single Oil Duct:
Transport in Oil is Faster than Diffusion:
2cDc ∂=
∂2x
Dt ∂=
∂
SimulationSimulation ResultsResultsSimulation Simulation Results Results (animation)(animation)
COCO22 Equilibrium CurvesEquilibrium Curves
n ASTM D2779 - Gas Solubility in the Oil.yn CO2 in Paper Pulp by D.J. Salley.n Oommen’s Methodn Oommen s Method.
ASTM D2779 ASTM D2779 –– Solubility of Solubility of Selected GasesSelected Gases inin the Oilthe OilSelected Gases Selected Gases in in the Oilthe Oil
1000000
1200000
1400000
1600000
vol.
200000
400000
600000
800000
ppm
by
v
CO2
180000
0273 288 311 339 355
T (K)
80000100000120000140000160000
by v
ol. Hydrogen
NitrogenCO
020000400006000080000
ppm
COOxygen
0273 288 311 339 355
T (K)
COCO22 Equilibrium CurvesEquilibrium Curves
40000
50000
m b
y vo
l.)
20000
30000
on in
pap
er (p
pm 0 C15 C27 C38 C56 C
0
10000
Con
cent
ratio
56 C80 C
00 50000 100000 150000 200000 250000
Concentration in oil (ppm by vol.)
COCO22 Equilibrium Curves at Lower Equilibrium Curves at Lower ConcentrationsConcentrationsConcentrationsConcentrations
Model ParametersModel Parameters
Headspace sampling
Reservoirs
1000 ml 1000 ml
ports
Inert gas
2000 ml 2000 ml
Relaxation chambers
Oil sampling ports
Precision pump
PressboardMain container
1000 ml Heater tape
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Model ValidationModel Validation
1000 l
Headspace sampling port
Reservoir
Inert
ml
Relaxation chamber
Pressboard
gas2000 ml
chamber
Oil flow
Oil sampling port
Precision pump
1000 ml
Heater tape
Main container
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Main container
Experimental DataExperimental Data
1000
10000
m b
y vo
l.)
CO CO2
100
Con
cent
ratio
n (p
pm
Introducing gas and temp. step up (25-70C)
Temp. step down (70C to 25C)
Temp. step up (25C to 70C)
Temp. step down (70C to 25C)
Temp. step up (25C to 70C)
100.0 200.0 400.0 600.0 800.0 1000.0 1200.0 1400.0 1600.0
Time (hours)
10000 C2H4 C2H6 C2H2
1000
ation (p
pm by vo
l.)
Introducing gas and temp. step up (25-70C)
Temp. step down (70C to 25C)
Temp. step up (25C to 70C)
Temp. step down (70C - 25C) Temp. step up
(25C to 70C)
1000.0 200.0 400.0 600.0 800.0 1000.0 1200.0 1400.0 1600.0
Con
centra
22
0.0 200.0 400.0 600.0 800.0 1000.0 1200.0 1400.0 1600.0
Time (hours)
Experimental Comparison Experimental Comparison –– COCO22
23
Summary and ConclusionsSummary and Conclusionsn Concentrations of CO and CO in Transformer Oil cann Concentrations of CO2 and CO in Transformer Oil can
Change Considerably due to a Temperature Change Because of the Migration Process.
Thi L d t Si ifi t E h I t ti DGA0This can Lead to Significant Errors when Interpreting DGA Analysis Data
n Migration Phenomenon of Characteristic Gases can be E l i d b Diff i PExplained by Diffusion Process.
n Application of the Model Works Best in the Case of Carbon Dioxide and Carbon Monoxide.
n Diffusion Time Constant and Steady-State Ratio of Gases in an Oil-Paper System have been determined.
n Steady state Ratio of CO in Oil / Paper System wasn Steady-state Ratio of CO2 in Oil / Paper System was obtained using Oommen’s Method Similar to the Case of Moisture.
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nThis Project Received the Endorsement of DEIS Liquids Technical Committee in 2004.
nThis Project Received the DEIS Fellowship jAward in 2005.
nSix Technical Papers, a Thesis and a BookSix Technical Papers, a Thesis and a Book have been Published based on the Methodology and Results of this ResearchMethodology and Results of this Research
Questions?Questions?
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