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4 th UPDEA SCIENTIFIC COMMITTEE March 12, 2008 Transformer Operations & Failure Avoidance Rui Da Silva , SERGI FRANCE. Introduced Power Factor Testing 1929. What We Are Trying To Avoid. Data Sources (1). Insurance - Carrier & Industry Sources Allianz Munich Re Swiss Re
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4th UPDEA SCIENTIFIC COMMITTEE March 12, 2008Transformer Operations & Failure AvoidanceRui Da Silva, SERGI FRANCE
Data Sources (1) Insurance - Carrier & Industry Sources Allianz Munich Re Swiss Re Lloyds Syndicates Factory Mutual Research & Engineering FM Global, previously Allendale Mutual Arkwright Mutual Protection Mutual AIG / Hartford Steam Boiler Inspection and Insurance Royal Insurance Industrial Risk Insurers American Insurance Association
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
Aging Forecast latest forecast model ….. f(t) = A + a e b t 1 + µe b t
= 15 Year History = 2002/2006 Insurer’s Exposure to Losses 10% Rise 32% SYSTEMS & 18% COMPONENTS START 15% 10% 18% 4% 8% 5% <2% 63% Testing Operational Civil Erection Mechanical Completion Performance
Forced Outage (Unplanned Maintenance/Repair Times) Time-to-Repair Distributions for Minor, Major and Catastrophic Events 0.10 Catastrophic (230 hr/event) 0.09 MINOR (5 hr/ event) MAJOR (55 hr / event) 0.08 0.07 0.06 Probability 0.05 0.04 0.03 0.02 0.01 0.00 1 10 100 1,000 Time to Repair, Hours
US Power Plant Fatalities Total: 35 people
Transformer Failure Modes • Thermally induced • Electrically Induced • Mechanically Induced
Transformer Failure Modes Electrically Induced • Over Voltage • Surges • Partial Discharge • Static Electrification
Transformer Failure ModesMechanically Induced Conductor Tipping Conductor Telescoping Hoop Buckling
Transformer Failure Modes Thermally Induced • Overloading • Failure of cooling system • Blockage of axial spaces • Over-excitation (over-voltage or under-frequency)
Types of Transformers Distribution, for residential service Generator Step-up Transformers Autotransformers Multi-winding transformers(> 2 windings) Rectifier Transformers--Smelters Furnace Transformers--Steel Mills Inverter Transformers-DC Converter Transformers-DC Regulating Transformers--Voltage, Current Phase, Angle Instrument Transformers--Voltage/Current Other
Generator Step-Up Transformers(GSU’S) Usually (90%+) two-winding transformers Large KVA (50000kVA and higher, up to 1,300,000 kVA) Used at Power Plants Fossil-Coal/Oil/Gas Nuclear Hydro 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.
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 kV 230/115 kV 345/138 kV 345/230kV 500/230kV 500/345kV 765/345 kV 765/500 kV 765/138 kV 500/161 kV
Transformer 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
Core Form Round Coils( Cylinder) Coils Wrapped on a tube then loaded on core Core stacked in legs and then windings are placed over them Vertical Core Legs Windings Concentric around each other Majority of Transformers in the world Shell Form Flat Coils in rectangular shape Coils stacked into groups Interleaved windings Core stacked around the coils Core is Horizontal Stronger under short circuit Generally more expensive Major advantages in GSU’s ABB (Cordoba), IEM (Mexico), Schneider (France), Mitsubishi (Japan), Hyosung (Korea), GE (UNITED STATES!) Core Form vs Shell Form Transformers
Basic Construction SHELL FORM CORE FORM
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 Single Phase vs Three Phase Units
Field 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
7 2 6 1 3 5 4 The different components of the protection 4. Explosive Gas Elimination Pipe Cabinet Explosive Gases Evacuation Conservator Shutter Depressurization Set OLTC Depressurization Set Oil-Gas Separation Tank To create an evacuation opening before the dynamic pressure becomes uniform static pressure
THE TRANSFORMER PROTECTION : OPERATION 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 3/ Opening of the air isolation shutter 4/ Nitrogen injection 5/ Explosive gases production is stopped after 45 min N2
COMPUTATIONAL 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 2002 and 2004 Tests on Transformers Numerical Tool Validation Extrapolation to Transformers >100MVA High Fault Currents Protection Validation
Hydro Effect Modelling Gravity Effect Modelling Physical Modeling Energy Transfer Modelling Viscous Effect Modelling Equation of state :