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4th UPDEA SCIENTIFIC COMMITTEE March 12, 2008
Transformer Operations & Failure Avoidance
Rui Da Silva, SERGI FRANCE
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Introduced Power Factor Testing 1929
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What We Are Trying To Avoid
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Number of Transformer Events/Yr
0
5
10
15
20
'91 '92 '93 '94 '95 '96 '97 '98 '99 '00 '01
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Data Sources (1)Insurance - Carrier & Industry Sources
AllianzMunich ReSwiss ReLloyds SyndicatesFactory Mutual Research & EngineeringFM Global, previouslyAllendale MutualArkwright MutualProtection MutualAIG / Hartford Steam Boiler Inspection and InsuranceRoyal InsuranceIndustrial Risk InsurersAmerican Insurance Association
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Data Sources (2)Power Industry Sources
Edison Electric Institute McCoy Power Reports INPO Operational Reliability Program IEEE RAM Comm (Reliability Availability & Maintainability Utility Data Institute Electric Power Reserch Institute American Power Conference, extracts 1990 to 2001 Intl. Joint Power Conference, extracts 1989 to 2001 MFR’s : GE, Alstom, ABB, Siemens, Westinghouse
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0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
2 8 14 20 26 32 38 44 50 56 62 68 74
Age
Haz
ard
Fu
nct
ion
Aging Forecast
latest forecast model ….. ff(t) (t) = = A + A + e e tt
1 + µ1 + µ e e t t
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Insurer’s Exposure to Losses
Civil
63%18% 8%4%<2%
SYSTEMS &COMPONENTSSTART
5%
10%
32%
18%
15%
MechanicalCompletion
Testing OperationalPerformanceErection
10% Rise
= 15 Year History
= 2002/2006
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Forced Outage (Unplanned Maintenance/Repair Times)
Time-to-Repair Distributions for Minor, Major and Catastrophic Events
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.10
1 10 100 1,000
Time to Repair, Hours
Pro
ba
bil
ity MINOR
(5 hr/ event)MAJOR
(55 hr / event)
Catastrophic(230 hr/event)
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US Power Plant Fatalities
0
2
4
6
8
10
12
14
1971 1976 1977 1989 1992 1993 1994 1995 1999 2000
Fatalities due toExplosions and Fires
Total: 35 people
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Transformer Failure Modes
Thermally induced Electrically Induced Mechanically Induced
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Transformer Failure Modes
ElectricallyInduced
• Over Voltage• Surges• Partial
Discharge• Static
Electrification
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Transformer Failure ModesMechanically Induced
Conductor Tipping
Conductor Telescoping
Hoop Buckling
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Mechanical Failure
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Transformer Failure Modes
Thermally Induced Overloading Failure of cooling system Blockage of axial spaces Over-excitation (over-voltage or
under-frequency)
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Cause of Failures
20 years of claims
Insulation issues 18%
Electrical Disturbances
29%
Maintenance issues13%
Lightning16%
Loose Connection
13%
Moisture7%
Overload2%
Other2%
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Types of Transformers
Distribution, for residential serviceGenerator Step-up TransformersAutotransformersMulti-winding transformers(> 2 windings)Rectifier Transformers--SmeltersFurnace Transformers--Steel MillsInverter Transformers-DCConverter Transformers-DCRegulating Transformers--Voltage, Current Phase, AngleInstrument Transformers--Voltage/CurrentOther
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Generator Step-Up Transformers(GSU’S)
Usually (90%+) two-winding transformersLarge KVA (50000kVA and higher, up to 1,300,000 kVA)Used at Power Plants
Fossil-Coal/Oil/GasNuclearHydro
Raises the voltage from the generator voltage (12-26 kV)to the Transmission System Voltage (69-765kV)to allow efficient transmission of power from the energy source to the load.
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Autotransformers•Primary use is to connect two transmission systems of different voltages•The two systems must by Y-connected and of the same phasing and polarity•“Short-ended” autos (re 200/190 kV) or “long-ended” (200/20 kV) are not practical.•Autotransformers can step voltage up or down.
Typical voltage ratings of Autotransformers in NA
138/69 kV230/115 kV345/138 kV345/230kV500/230kV500/345kV
765/345 kV765/500 kV765/138 kV500/161 kV
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►How to protect your investment?
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TRANSFORMER PROTECTORTransformer Specification
Evaluate system requirements Evaluate transformer requirements Evaluate client standards Review or create entire specification Design Review – At Factory Drawing & Materials Review Scheduling Coordination Core & Coil – Pretank Inspection Factory Test
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Core Form vs Shell Form Transformers
Core FormRound Coils( Cylinder)Coils Wrapped on a tube then
loaded on coreCore stacked in legs and then
windings are placed over them
Vertical Core LegsWindings Concentric around
each otherMajority of Transformers in the
world
Shell FormFlat Coils in rectangular shapeCoils stacked into groupsInterleaved windingsCore stacked around the coilsCore is HorizontalStronger under short circuitGenerally more expensiveMajor advantages in GSU’sABB (Cordoba), IEM (Mexico), Schneider (France), Mitsubishi(Japan), Hyosung (Korea),GE (UNITED STATES!)
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Basic ConstructionBasic Construction
CORE FORMSHELL FORM
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Core Form Construction
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Shell Form Construction
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Single Phase vs Three Phase Units
Three Phase Most Economical Smallest footprint Simplifies station design Most Common
Single Phase- Min of 3 units- Easier to spare (4th Tx)- Greater
Reliability/Availability- 3-Phase too large to ship- Larger footprint- More Expensive
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TRANSFORMER PROTECTORField Testing - Oil Diagnostics
OIL Dissolved Gas Analysis (DGA) Profile (Main Tank, OLTC) Furan Analysis Moisture Content Dielectric Strength Oil Condition Inhibitor Content Metals Corrosive Sulfur Acidity Degree of Polymerization
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TRANSFORMER PROTECTORThe different components of the protection
1. Depressurization Set
2. OLTC Depressurization Set
3. Oil-Gas Separation Tank
4. Explosive Gas Elimination Pipe
5. Cabinet
6. Explosive Gases Evacuation
7. Conservator Shutter
To create an evacuation opening before the dynamic pressure becomes uniform static pressure
5
62
4
7
31
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1/ The dynamic pressure peak travels at the speed of sound inside oil
2/ Rupture of the disk, depressurisation, evacuation of the oil-gases mixture
4/ Nitrogen injectionN2
3/ Opening of the air isolation shutter5/ Explosive gases production is stopped after 45 min
THE TRANSFORMER PROTECTION : OPERATION
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TRANSFORMER PROTECTORCOMPUTATIONAL INVESTIGATIONS
Pressure Wave Propagation
Gas and Oil Behaviours
Complex Geometry
Compressible Two-Phase Flow Model
EM, thermal, viscosity, gravity
Numerical Tool Finite Volume Method on Unstructured mesh
Numerical Tool Validation
2002 and 2004 Tests on Transformers
Extrapolation to Transformers
>100MVA
Protection Validation
High Fault Currents
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Energy Transfer
Modelling
Gravity Effect
Modelling
Hydro Effect
Modelling
Viscous Effect
Modelling
PeP 1Equation of state :
Physical Modeling
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TRANSFORMER PROTECTORAny Questions?