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Wind Turbines Technology

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  1. Wind Turbines Technology Cataldo Pignatale Product Support Manager Vestas Italia S.r.l. Desire-Net Project

  2. Session Contents • Aim: at the end of this session participants will have an overview of the wind turbine generators technologies developed over the years and implemented on the modern wind turbines • Duration: 35-40min

  3. Agenda • Wind turbines characteristics • Control of power • Type of generators • Connection to grid • Control systems • Grid integration of wind trubines • Construction technologies of a modern wind turbine

  4. Wind turbines characteristics

  5. Wind Turbine Generator Definition: Machine capable to convert the kinetic energy of a wind tube into electrical energy. “Betz' law’’’: less than 16/27 (or 59%) of the kinetic energy in the wind can be converted to mechanical energy using a wind turbine.(Betz' law was first formulated by the German Physicist Albert Betz in 1919)

  6. Main parts of a modern wind turbine Blade Hub Nacelle Tower Foundation

  7. Vertical axis rotor 3 blades Horizontal axis rotor Downwind turbine Active yaw mechanism Free yaw mechanism Upwind turbine Pitch control With gerabox Without gearbox 1 blade 2 blades Wind Turbines Characteristics • Rotor axis: horizontal, vertical; • Alignment to the wind: upwind, downwind; • Alignment to the wind: active (forced) or passive (free) yawing system; • Number of blades: even, odd; 3, 2, 1; • Control of power: pitch, stall, active stall, yaw; • Rotation transmission: with or without gearbox; • Type of generator: synchronous, asynchronous; • Grid connection: direct, indirect;

  8. Control of power

  9. Wind attack point Wind attack point Control of powerReducing the power at high windspeed At high wind the power is reduced by pitching the blades. This can be done in two ways. • Reducing the lift and over speeding called Pitch variable speed • Reducing the lift by generating stall Flow on upper and lower surface equal  no lift

  10. Control of powerPitching Low wind High wind Stop Pitch variable speed and optislip Passive stall Active stall

  11. Control of powerWind Power and Power Curves ‘A’ is area ‘v’ is velocity (wind speed) ‘’ is air density ‘Cp’ power coefficient Wind power Power Pitch variable speed Active stall Rated power Passive stall Max Power = ½ · A ·v3· · Cp m/s

  12. 25 2500 kW 2000 kW 20 1500 kW 1000 kW 500 kW 15 0 kW Wind speed m/s 10 5 -10 -20 0 +10 +20 +30 Pitch angle (deg) Control of powerIso-power map wind speed and pitch angle ―Stall control ― Pitch control 72 m rotor 2MW turbine

  13. Blade turning gear Pinion Battery bank Control of powerPitching mechanism Electrical Hydraulic

  14. Type of generators

  15. Type of generator Synchronous Asynchronous

  16. + kW (generator) 1000 rpm - kW (motor) 60 x frequency number of pole pairs rpm = Type of generatorFixed speed asynchronous generator 50 Hz 6-poled stator Rotational speed

  17. Stator field = 1000 rpm Rotor mechanically = 1100 rpm Type of generatorVariable speed asynchronous generators 50 Hz AC DC AC DC

  18. Connection to the grid

  19. Connection to grid Direct PCC Grid frequency AC Grid frequency AC

  20. Connection to gridIndirect Rectifier PCC Inverter Variable frequency AC (e.g. from synchronous generator) DC Irregular switched AC Grid frequency AC

  21. Control systems

  22. Generator switchgear AC f = constant n = costant Bypass contactor Parking brake Gearbox HV switchgear Rotor bearing Getriebe 1:50 Asynchronous generator Soft start equipment Step-up transformer 6 ... 33 kV, f = 50 Hz/ 6 ... 34,5 kV, f = 60 Hz WTG control Passive Stall ABB drawing Control systems Fixed speed

  23. Generator switchgear AC f = constant n = costant Bypass contactor Parking brake Gearbox HV switchgear Rotor bearing Getriebe 1:50 Asynchronous generator Soft start equipment Step-up transformer 6 ... 33 kV, f = 50 Hz/ 6 ... 34,5 kV, f = 60 Hz WTG control Pitch drive Active Stall, Pitch Control ABB drawing Control systems Fixed speed

  24. Generator switchgear AC f = constant n = semi-variable Bypass contactor Parking brake Gearbox HV switchgear Rotor bearing Getriebe 1:50 RCC unit Soft start equipment Asynchronous generator Step-up transformer HEAT 6 ... 33 kV, f = 50 Hz/ 6 ... 34,5 kV, f = 60 Hz RCC control Pitch drive WTG control Variable slip, pitch control ABB drawing Control systems Semi-variable speed

  25. Generator switchgear AC f = constant n = variable Parking brake Gearbox HV switchgear Rotor bearing Generator side converter Getriebe 1:50 Grid side converter Doubly-fed asynchronous generator Step-up transformer 6 ... 33 kV, f = 50 Hz/ 6 ... 34,5 kV, f = 60 Hz Pitch drive Converter control WTG control Variable speed control DFIG (doubly fed induction generator) ABB drawing Control systemVariable speed

  26. Generator switchgear AC f = variable n = variable Converter Parking brake Gearbox HV switchgear Converter control Rotor bearing Getriebe 1:50 Asynchronous or synchrounous generator Step-up transformer 6 ... 33 kV, f = 50 Hz/ 6 ... 34,5 kV, f = 60 Hz Pitch drive WTG control Variable speed control with full scale converter ABB drawing Control system Variable speed

  27. Stator Rotor Stator Rotor Grid Grid IGBT Capacitor battery Grid Stator Rotor DC Ac dc Grid Ac dc DC Stator Rotor DC Ac dc Grid Ac dc DC Control system Generator layout Pitch/Stall/Active stall Semi-variable speed 1-10 % slip 1-2% slip Variable speed, full scale converter Variable speed (DFIG)

  28. Grid integration of wind turbines

  29. Grid integration of wind turbines Electric power path to consumers Power station 400,000V 20,000V Transformer station Consumer 400/ 230 V 150,000V Transformer station 20,000V Transformerstation

  30. Grid integration of wind turbines Medium and high voltage components G Generator Main contactors Transformer Switchgear Grid

  31. Grid integration of wind turbines Step-up transformer location Nacelle housing Inside tower housing External housing

  32. Grid integration of wind turbines Connection of wind turbines

  33. Grid integration of wind turbines The wind turbines operate as a part of an integrated power system with other production sources and consumers. Therefore there is a mutual influence between the wind turbines and the grid. The following issues have to be considered: • Layout of grid-connecting infrastructure • Power quality assessment • Electrical system stability issues

  34. Grid integration of wind turbines Power quality assessment • Operation of wind turbine can be disturbed if following grid parameter are not within defined limits: • Voltage • Frequency • Voltage unbalance • Harmonics level • Wind turbine connection shall not reduce existing power quality on the grid

  35. Grid integration of wind turbines Parameters relevant for correct operation of wind turbines • Voltage limits: • Regime limits • Slow transient limits • Frequency limits: • Normal operation limits • Admitted transient limits • Voltage unbalance: • Admitted operational limits • Harmonics level: • Recommended maximum value: As defined in EN 50160

  36. Grid integration of wind turbines Possible negative impacts of WT to the power quality on electrical grid Wind turbines can cause the following negative impact on the grid: • Stationary voltage increase • High in-rush current • Flicker • Harmonics and inter-harmonics Generally, the wind turbines´ impact on the grid depends on: • Wind turbines characteristics • The gridcharacteristics at the connection point (PCC) Strong grids can accept more wind turbine without negative consequences on power quality. Weak grids can accept limited number of wind turbines, or the grid has to be reinforced.

  37. Grid integration of wind turbines Flicker Flicker describes the effects of rapid voltage variations on electrical light. The flicker level can be measured with an instrument called flicker-meter. • Flicker during continuous operation • Flicker due to generator switching Limits are defined at PCC and global effect has to be calculated as aggregated contribution of all the installed wind turbines. Wind turbine´s performances concerning flicker emission are characterised by: • flicker coeficient cf • flicker step factor kf

  38. Grid integration of wind turbines Harmonics and inter-harmonics Voltage deviations from the perfect sinus shaped 50 Hz curve result in harmonics. Harmonics are not wanted on the grid because they cause increased losses and in serious cases it may lead to an overloading of the capacitors, trans-formers and electrical appliances as well as disturbances of communication systems and control equipment. It is differed between: • Even harmonics e.g. 100, 200, 300… Hz • Odd harmonics e.g. 150, 250, 350,550 … Hz • Inter-armonics (50 multiplied with decimal numbers)e.g. 165 Hz, 2525 Hz etc.

  39. Grid integration of wind turbines Standards and recommendations All units that deliver electrical power to electrical system shall respect relevant power quality standards. The most relevant documents for wind turbines are: • IEC 61400-21 standard: • “Power quality requirements for grid connected wind turbines” • IEC 61400-3 standard: • “ EMC limits. Limitation of emissions of harmonic currents for equipment connected to medium and high voltage power supply systems” • Local requirements

  40. Grid integration of wind turbines System stability issue Large wind farms can influence not only locally grid but also a large part of whole power supply system • Dynamic grid stability may be a limiting factor to the grid connection of large wind farms • Grid stability analyses are needed • Data for modeling or models of Wind Turbines may be requested Each country can issue local grid code requirements that have to be duly considered in designing wind parks. Fulfilment of grid code requirements might require installation of additional equipments (capacitor banks, static VAR compensators, dynamic VAR compensators).

  41. Coonstruction tecnologies of a modern wind turbine

  42. Main parts of a modern wind turbine Blade Hub Nacelle Tower Foundation

  43. Onshore foundation • Gravity concrete foundation • Rock anchor foundation

  44. Offshore foundation • Monopile • Tripod • Gravity • Floating

  45. The tower Tubular • Steel plates are rolled and welded • Flanges at each section • Shot blasted and coated with paint • Lattice • Bars are prepared in factory and assembled on site • Bolted junctions • Hot galvanized steel

  46. Blade concepts • Supporting carbon spar and glass fiber airfoil shells • Wood carbon strong shell technology

  47. Supporting carbon spar concept • The supporting spar with a rectangular section • The airfoil shells with sandwich construction at the rear

  48. Wood carbon concept • Plywood and carbon rods are used where high strength is needed • Balsa or foam is used where only stiffness is needed

  49. Main components in the nacelle Main bearings/Main shaft Hub Anemometer Pitch system Gearbox Hydraulic station Yaw system Generator Disc brake Coupling

  50. Questions?