1111Challenges for reliable offshore transformersTRANSFORMING YOUR NEEDS INTO SOLUTIONS Challenges for Reliable Offshore Transformers Dr. Jan Declercq, Raymond Van Schevensteen Pauwels International N.V. Belgium

2222Challenges for reliable offshore transformersTRANSFORMING YOUR NEEDS INTO SOLUTIONS Transformers as critical components  Wind turbines are electricity generator units; therefore all components are critical:  Mechanical: blades, gearbox, tower,…  Electrical: generator, converter, transformer, circuit breaker, control unit,…  Medium Voltage Transformer has to be designed as generator step-up transformer and fully integrated in wind turbine performance and specifications … and now Multi Megawatt Turbines for offshore installation

3333Challenges for reliable offshore transformersTRANSFORMING YOUR NEEDS INTO SOLUTIONS Operating conditions are different  Normal transformer in normal environment 1000 kVA in apartment

4444Challenges for reliable offshore transformersTRANSFORMING YOUR NEEDS INTO SOLUTIONS Operating conditions are different  Generator step-up transformer in WTG

5555Challenges for reliable offshore transformersTRANSFORMING YOUR NEEDS INTO SOLUTIONS Operating conditions are different  Generator step-up transformer in wind turbine Multi Mega Watt offshore

6666Challenges for reliable offshore transformersTRANSFORMING YOUR NEEDS INTO SOLUTIONS So MMW WTG needs GSU Transformer EHV transmission Generation 100 MW >220 kV Transmission Sub-transmission 110 – 70 kV Embedded generation Distribution MW 30 kV Overloading, power quality, economics, environment, maintenance, reliability

7777Challenges for reliable offshore transformersTRANSFORMING YOUR NEEDS INTO SOLUTIONS Types of medium voltage transformers  Mineral liquid-filled transformers  Cast resin transformers  SLIM ® and Bio-SLIM ® technology Fire & bio-degradable liquid and Nomex ® insulation Same operating range of voltages and power What about other specifications?

8888Challenges for reliable offshore transformersTRANSFORMING YOUR NEEDS INTO SOLUTIONS Functional Specifications of transformers  Power  Liquid-filled up to 10 MVA and high voltages 36 kV and above  No load losses  As low as possible, always energized  Liquid filled 50 % less losses compared to dry type  Ex. 2 kW * 8760 h/y * 0.05 EUR/kWh per turbine per year  Load losses at working temperature customized to needs  Medium voltage  12 kV, 24 kV, 36 kV insulation level up to BIL 200 kV  Low Voltage  400 V, 660 V, 690 V, 1000 V, 3000 V, 6000 V  Impedance  6 % up to 14 % for weak grids  Dimensions  Mass for nacelle, reduced dimensions, “fits the door“ These specifications are not sufficient to guarantee performance and reliability

9999Challenges for reliable offshore transformersTRANSFORMING YOUR NEEDS INTO SOLUTIONS Operating conditions Thermal Stresses  Average 60% loading but …  Full loading for several days Short term peak overloads Sharp load fluctuationsHarmonics Higher air temperature in turbine 1,000 1,500 2,

10 Challenges for reliable offshore transformersTRANSFORMING YOUR NEEDS INTO SOLUTIONS Operating conditions Thermal Stresses Load P Current I Losses RI 2 Temperature Lifetime T ins 98 C Thermal stresses give mechanical stresses and accelerated ageing So verify insulation materials, overload tests, higher MVA, cooling inside

11 Challenges for reliable offshore transformersTRANSFORMING YOUR NEEDS INTO SOLUTIONS Operating conditions Electrical Stresses  Different electrical environment  Switching surges from Circuit Breakers  Overfluxing from overvoltages  Lightning strikes  Frequency variations  Voltage dips Causing higher electrical stresses on electrical insulation system Increased risk for initiating Partial Discharges So verify electrical performance, specify extra testing Example PD tests, chopped wave

12 Challenges for reliable offshore transformersTRANSFORMING YOUR NEEDS INTO SOLUTIONS SWITCHING PRE-STRIKE OR RE-STRIKE SOURCE VICTIM RESONANCES IN TRANSFORMER WINDINGS VOLTAGE TRANSIENT THROUGH CABLE COUPLING Switching surges It is an EMC problem: breaker and transformer can be less compatible in the specific network arrangement

13 Challenges for reliable offshore transformersTRANSFORMING YOUR NEEDS INTO SOLUTIONS Operating conditions Mechanical Stresses  Mechanical environment  Compact design  Optimized dimensions for inside installation  Optimized connections  In case of nacelle design, vibration tests including connection of cables Verify mechanical design and test accordingly Verify sensitivity of mechanical stresses on electrical insulation system

14 Challenges for reliable offshore transformersTRANSFORMING YOUR NEEDS INTO SOLUTIONS Operating conditions Chemical Stresses  Environment  Cooling air  Humidity  Dust, salt  Aggressive environment  People Verify protection of electrical system Specify higher IP class, C5 offshore painting, air filters, extra housing Maintenance interventions for transformer or peripherial equipment

15 Challenges for reliable offshore transformersTRANSFORMING YOUR NEEDS INTO SOLUTIONS  Specify good protection and materials Cast resin F1 or class K3 liquid Cast resin transformer versus silicone liquid filled transformer tested according Cenelec Operating conditions Safety

16 Challenges for reliable offshore transformersTRANSFORMING YOUR NEEDS INTO SOLUTIONS Operating conditions Safety  Tests performed at Ineris France, February and April 2004

17 Challenges for reliable offshore transformersTRANSFORMING YOUR NEEDS INTO SOLUTIONS New challenges  Wind offshore:  WTG go to higher MVA ratings from 2 MW to 6 MW  Connection voltages mostly 33 kV  Extreme reliability (MTBF > 500 years)  Reduced maintenance So optimize transformer technology, design, manufacturing and testing to meet the wind turbine demands

18 Challenges for reliable offshore transformersTRANSFORMING YOUR NEEDS INTO SOLUTIONS New markets  Wind offshore:  >3 MVA transformers for offshore and nacelle  UK, 7 GW projects  Belgium, NL 300 MW  Spain, 2000 MW  Denmark, 400 MW  Germany, 68 GW

19 Challenges for reliable offshore transformersTRANSFORMING YOUR NEEDS INTO SOLUTIONS Conclusions for offshore transformers  Different transformer technologies are available for multi- megawatt turbines  Dimensions, losses, reliability (MTBF), protection, electrical environment are important because the operating conditions in a turbine are severe!  Fire behavior of dry type and high temperature liquid filled transformers are comparable  Good protection and prevention is always needed, independent of transformer technology  Verify compatibility for aggressive offshore environment  Improve specifications for WTG transformers  Improve testing specifications for WTG transformers  IEC TC14 Transformer Committee will write standards for wind turbine use (approved 2005, start 2006)