1. 1 Part B2: Hydropower B2.2 Hydropower system design

2. 2 B2.2 Hydropower system design Topics: System design Entry arrangements –Forbays, penstock inlets Penstocks and surge control –Size of the penstock, pressure forces, anchoring the penstock, water hammer and its control Exit arrangements –draft tubes Turbine selection –Force triangles, Turbine types, specific speed, cavitation and its prevention Electronics and control –Types of generator, Turbine control, transmission

3. 3 B2.2.1 Hydropower system design Entry arrangements: Anatomy of a forebay

4. 4

5. 5 B2.2.1 Hydropower system design Entry arrangements: Trash rack losses Values for K t

6. 6 B2.2.1 Hydropower system design Entry arrangements: trash racks

7. 7 B2.2.1 Hydropower system design Entry arrangements: Alternatives to trash racks

8. 8 B2.2.1 Hydropower system design Entry arrangements: Velocity into the penstock v1v1 v3v3 p1p1 p3p3 Energy line v2v2 p2p2 htht Typical values for penstock velocities 2-5 m/s

9. 9 B2.2.1 Hydropower system design Entry arrangements: Entry losses into the penstock

10. 10 TypeKeKe Hooded1.0 Projecting0.8 Sharp corner0.5 Slightly rounded0.2 Bell mouth (r>0.14D)0 B2.2.1 Hydropower system design Entry arrangements: Entry losses into the penstock

11. 11 B2.2.2 Hydropower system design Penstocks: Comparison of penstock materials MaterialFriction loss WeightCorrosion resistance CostEase of Jointing Pressure resist Ductile iron Asbestos cement Concrete Wood staves GRP uPVC Mild steel HDPE MDPE PoorExcellent

12. 12 B2.2.2 Hydropower system design Penstocks: Installation

13. 13 B2.2.2 Hydropower system design Penstocks: Friction losses in penstocks Darcy’s formula See B2.1.1 Typical penstock losses are 5-10%

14. 14 B2.2.2 Hydropower system design Penstocks: Multiple penstocks

15. 15 B2.2.2 Hydropower system design Penstocks: Losses in bends

16. 16 B2.2.2 Hydropower system design Penstocks: Losses in bends r/DKbKb 10.6 20.5 30.4 40.3 For 45º use K x 0.75 For 2 use K x 0.5 r D

17. 17 B2.2.2 Hydropower system design Penstocks: Other Losses Contractions Valves D 1 /d 2 KcKc 1.50.25 20.35 2.50.40 50.50 TypeKvKv Spherical0 Gate0.1 Butterfly0.3

18. 18 B2.2.2 Hydropower system design Penstocks: Energy lines

19. 19 B2.2.2 Hydropower system design Penstocks: Anatomy of a penstock

20. 20 B2.2.2 Hydropower system design Penstocks: Slide blocks

21. 21 F e = Force due to extension C e = Coefficient of extension = Change in temperature E = Young’s modulus D = Penstock diameter t = Wall thickness B2.2.2 Hydropower system design Penstocks: Thermal expansion FeFe FeFe

22. 22 B2.2.2 Hydropower system design Penstocks: Expansion joints

23. 23 B2.2.2 Hydropower system design Penstocks: Forces on bends Hydrostatic Velocity F = fluid density g = gravity h = total head A = penstock area Q = discharge v = velocity

24. 24 B2.2.2 Hydropower system design Penstocks: Bends

25. 25 B2.2.2 Hydropower system design Penstocks: Forces on bends: Thrust blocks

26. 26 B2.2.2 Hydropower system design Penstocks: Anatomy of a penstock

27. 27 B2.2.2 Hydropower system design Penstocks: Water hammer

28. 28 T c =critical time (s) L =pipe length (m) C p =speed of sound in the pipe C w = speed of sound in water (1420m s -1 ) G = bulk density of water (2GPa) E =Young’s modulus D =diameter of the pipe (m) t =wall thickness (m)  h =additional pressure due to water hammer (m of water) g = gravity  v =Change in flow velocity (m s -1 ) B2.2.3 Hydropower system design Penstocks: Water hammer

29. 29 B2.2.2 Hydropower system design Penstocks: Water hammer: Dealing with it

30. 30 B2.2.2 Hydropower system design Penstocks: Water hammer: Dealing with it: Surge tanks

31. 31 B2.2.2 Hydropower system design Penstocks: Getting it wrong…

32. 32 B2.2.3 Hydropower system design Draft tubes Parallel sidedTapered Allows turbine to be set above water level but uses vacuum pressure on underside to increase effective head Recovers part of the velocity head by diffusion action Limited by the vapour pressure of water

33. 33 B2.2.3 Hydropower system design Draft tubes: Exercise Using Bernoulli's equation and mass continuity, show how a tapered turbine regains velocity head and converts it to pressure reduction at the turbine p 2 v 2 p 1 v 1

34. 34 B2.2.3 Hydropower system design Draft tubes: configurations

35. 35 B2.2.3 Hydropower system design Draft tubes

36. 36 B2.2.3 Hydropower system design Draft tubes

37. 37 Next…turbines