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Section III Wind Turbines

Section III Wind Turbines. Types of turbines Relative merits of each type General structure of turbines. Big Wind/Small Wind Definition. By common practice, small wind is defined as nameplate power rating of 100 kW or less.

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Section III Wind Turbines

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  1. Section IIIWind Turbines • Types of turbines • Relative merits of each type • General structure of turbines

  2. Big Wind/Small Wind Definition • By common practice, small wind is defined as nameplate power rating of 100 kW or less. • Large wind is considered to be for turbines with a nameplate rating greater than 100 kW. • Sometimes a further refinement of turbine classifications occurs into small, intermediate, and large.

  3. Sizes and Applications • Small (10 kW) • Homes • Farms • Remote Application • Intermediate • (10-250 kW) • Village Power • Hybrid Systems • Distributed Power • Large (660 kW - 2+MW) • Central Station Wind Farms • Distributed Power • Community Wind

  4. Wind Turbines • Horizontal Axis, HAWT (all large power turbines are this type) • Upwind • Downwind Wind Direction Wind Direction

  5. Turbine Types • Vertical Axis, VAWT • Good for low wind and turbulent wind (near ground) Wind Direction

  6. World’s Largest Turbines • Enercon E-126 • Rotor diameter of 126 m (413 ft) • Rated at 6 MW, but produces 7+ MW • Clipper (off-shore) • Rotor diameter of 150 m (492 ft) • Hub Height is 328 ft • Rated at 7.5 MW

  7. Typical Utility Scale Turbine in 2011 • Clipper 2.5 MW • Hub height 80 m (262 ft) • Rotor diameter 99 m (295 ft) • 4 PM generators in one nacelle 3.28 ft/m

  8. Vestas 1.65 MW turbines at NPPD’s Ainsworth wind farm • Class 5 wind site (average wind speed is 19.5 mph) • 36 turbines in farm • Hub height is 230 feet • Rotor diameter is 269 feet • Project cost was about $1,355/kW ($1.36/W)

  9. Small Wind Turbine • Bergey Excel 10 kW • Hub height 18-43 m (59-140 ft) • Rotor diameter 7 m (23 ft)

  10. 2.4 kW Skystream bySouthwest Wind Power • Hub height is 45-60 ft. • Rotor diameter is 12 ft. • Installation cost is about $7 to $8.50 per Watt

  11. Major types of VAWT

  12. VAWT • 30 m Darrieus • Helical Twist VAWT are designed to operate near the ground where the wind power is lower and produce drag on the trailing blades as they rotate through the wind.

  13. Vertical axis turbines • PacWind Seahawk, 500 W - Drag type • PacWind Delta I, 2 kW • Lift type • Darius turbine, few 10’s kW • Lift type

  14. Lift and Drag • Lift turbines are those that have the blades designed as air foils similar to aircraft wings. The apparent wind creates lift from a pressure differential between the upper and lower air surfaces. • Lift turbines are much more efficient that drag type turbines • Drag turbines operate purely by the force of the wind pushing the blade.

  15. Lift and Drag • All utility-scale wind turbines are lift devices. • All small turbines (HAWT or VAWT) that produce power efficiently are lift devices. • Drag-type devices are “Yard-Art” • In Drag-type turbines, Power transfer from the wind maximizes at about 8.1 % • Compare to the Betz Limit of 59% for Lift devices

  16. HAWT* • We will focus on HAWT because these designs generally give better performance than VAWT *All further discussion relates to lift turbines

  17. Nacelle The nacelle houses the generator, sometimes a gearbox, and often power electronics converters and control electronics. Electrical Disconnect Switch Tower Foundation

  18. Typical foundation for turbines rated 1 to 5 kW mounted on monopole towers. Bolt set being placed into foundation pit prior to concrete pour. Conduit for electrical connection between turbine and disconnect switchgear.

  19. Tower section (base) for large HAWT Note the large number of bolt holes as compared to the small turbine on the previous slides

  20. W is the angular velocity of the rotor tip in units of radians/second R is the blade length plus the rotor radius Wind Direction with velocity, v

  21. Exercise 6 1). The two major types of turbines as designated by the orientation of their axis of rotation of the blades are • 2-bladed or 3-bladed • Upwind and Downwind • Vertical and Horizontal • Lift and Drag

  22. Exercise 6 2). A Drag-type turbine can capture more of the available power in the wind than a Lift-type. • True • False

  23. Exercise 6 3). Which of the following statements are true. • Horizontal-axis turbines are generally used for large wind farms instead of Vertical-axis turbines. • Lift-type turbines are always Horizontal-axis types. • Wind turbines can be designed to face up into the wind or point downwind. • B. and C. • A. and C. • A., B., and C.

  24. Physics Continued • Tip Speed Ratio, l, is the ratio of the blade-tip speed (linear velocity) to wind speed. l = WR/v • W is the angular velocity of the rotor • R is the radius of the rotor • v is the wind velocity

  25. Power Coupled to Turbine from the Wind • The Power Coefficient, Cp, is the percentage of the available power in the wind coupled into the turbine. Therefore, the Turbine Power, P, is: P = Cp Pw = Cp (½ rAv3) • The Power Coefficient, Cp, is a maximum (approaches Betz Limit) when the Tip Speed Ratio is in the range of 7.5 to 10. • l is actively controlled in large turbines • l is passively controlled in small turbines often through blade flexure

  26. Power Coefficient • In modern turbines, the power coefficient Cp is around 40% (0.40). • Remember the Betz Limit is about 59%.

  27. Pitch and Yaw • Pitch refers to the relative angle of the turbine blades to the incoming wind direction. Apparent Wind Direction Yaw is the direction of rotation of the turbine nacelle and rotor assembly as it pivots around the tower to move into or out of the wind.

  28. Turbine Output • Modern turbines are around 90% or more efficient once the power is coupled to the rotor shaft. • Reputable manufacturers will provide output power data at various wind speeds. Often these are provided as graphical plots.

  29. Turbine Power Curve • The output power flattens out to a relatively constant value that the power electronics converter system, generator, and mechanical systems are designed to handle.

  30. Why does the Power Curve Peak and then Lay Over? Ideally, Power goes as v3

  31. Blade positioning is actively or passively controlled to limit the power output from the turbine. • Power curve can be made smooth by active control (active stall or pitch for large turbines) • Passive Stall control has an overshoot depending on blade design (small turbines)

  32. Turbine Speed Specifications • Cut-in Wind Speed is the wind velocity at which the turbine will begin to generate electrical power. (3 to 4 m/s are typical) • Rated Wind Speed is the wind velocity at which the turbine will generate its nameplate electrical power. (12 to 15 m/s are typical) • Cut-Out Wind Speed is the wind velocity at which the turbine will shut itself down to keep the electrical and mechanical systems safe. (25 m/s or 60 mph is typical) • Survival Wind Speed is the wind velocity maximum at which the turbine can mechanically survive intact. (60 to 65 m/s is typical; 140 mph)

  33. Cut-in Wind Speed

  34. Rated Wind Speed

  35. Cut-out Wind Speed

  36. Real Turbines with Measured Performance

  37. Exercise 7 1). A cut-in wind speed is likely to be about • 12.5 m/s • 30 m/s • 42.5 m/s • 3.5 m/s

  38. Exercise 7 2). Using the power curve from the Skystream 3.7 above, what is the expected power production at a wind speed of 7.5 m/s?

  39. Exercise 7 3). Pitch refers to the orientation with respect to the apparent wind of what? • The Blades • The Nacelle • The Rotor • The Tower

  40. Exercise 7 4). Yaw refers to the orientation of what? • The Blades • The Nacelle • The Rotor • The Tower

  41. Exercise 7 5). The turbine does the best job of capturing the available wind power when the tip speed ratio is: • 2.3 kW • 8 • 14 m/s • 2

  42. Exercise 7 6). A turbine’s output power is controlled in high winds by • Lift or Drag Control • Upwind or Downwind Control • Pitch or Stall Control • Rotor or Yaw Control

  43. Operations and Maintenance Costs

  44. O & M • O&M costs constitute a sizeable share of the total annual costs of a large wind turbine. For a new turbine, O&M costs may easily make up 20-25% of the total normalized cost per kWh produced over the lifetime of the turbine. If the turbine is fairly new, the share may only be 10-15%, but this may increase to at least 20-35% by the end of the turbine’s lifetime. As a result, O&M costs are attracting greater attention, as manufacturers attempt to lower these costs significantly by developing new turbine designs that require fewer regular service visits and less turbine downtime. • O&M costs are related to a limited number of cost components, including: • Insurance; • Regular maintenance; • Repair; • Spare parts, and • Administration. Some of these cost components can be estimated relatively easily. For insurance and regular maintenance, it is possible to obtain standard contracts covering a considerable share of the wind turbine’s total lifetime. Conversely, costs for repair and related spare parts are much more difficult to predict. Although all cost components tend to increase as the turbine gets older, costs for repair and spare parts are particularly influenced by turbine age; starting low and increasing over time.

  45. Small Turbine Maintenance • Identify maintenance needs and implement service procedures for the tower, fasteners, guy cables, wind turbine, wiring, grounding system, lightning protection, batteries, power conditioning equipment, safety systems, and balance of system equipment. • Measure system output and operating parameters, compare with specifications and expectations, and assess the operating condition of the system and components. • If appropriate perform mechanical and electrical diagnostic procedures and interpret results.

  46. Example: Skystream Turbine Maintenance • From the ground, listen for abnormal sounds when the turbine is operating in moderate winds. • Perform visual inspection from the ground at least once per year with turbine off. • Check ground wire connection at tower and at grounding stake if possible • Check for blade cracks or breaks (use binoculars) • Check visually for damage to nacelle, nose, etc.

  47. Example of small business expenses from Ontario, NY

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