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- 2074 Asoj · 1+3 marks
- 2071 Shrawan · 1+2 marks
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Classification of water turbines
Short answer
Water turbines are classified by action, head, flow direction, specific speed, and shaft position. In impulse turbines all pressure energy becomes kinetic energy in the nozzle and the runner operates at atmospheric pressure without a draft tube. In reaction turbines pressure drops through the runner, the casing is full of water, and a draft tube is needed.
How do you classify the water turbines? Differentiate between impulse and reaction turbines.
A water turbine converts the kinetic and pressure energy of water into mechanical rotation of a shaft that drives a generator.
Classification of water turbines
- By action of water:
- Impulse turbines (Pelton, Turgo, Cross-flow/Banki)
- Reaction turbines (Francis, Kaplan, Propeller)
- By head: high head (above 250 m, Pelton), medium head (60–250 m, Francis), low head (below 60 m, Kaplan/propeller).
- By flow direction: tangential flow (Pelton), radial flow (Francis, older), mixed flow (modern Francis), axial flow (Kaplan, propeller).
- By specific speed: low (Pelton), medium (Francis), high (Kaplan).
- By shaft position: horizontal or vertical.
Impulse vs reaction turbine
| Point | Impulse turbine | Reaction turbine |
|---|---|---|
| Energy conversion | All pressure energy is converted to kinetic energy in the nozzle before the runner | Only part is converted before the runner; the rest changes as water flows through the runner |
| Pressure | Atmospheric pressure at the runner | Pressure above atmospheric at inlet, and below at outlet |
| Casing | Not full of water; casing just protects | Runner is completely enclosed and full of water |
| Head | High head, low flow | Low to medium head, high flow |
| Draft tube | Not needed | Needed |
| Flow regulation | Nozzle and spear valve | Guide vanes (wicket gates) |
| Examples | Pelton, Turgo, Cross-flow | Francis, Kaplan |
| Cavitation | Not a problem | A risk |
| Specific speed | Low | Medium to high |
In Nepal, Pelton and cross-flow turbines are used in micro/small hydro in the hills, while Francis is used in medium-head plants such as Kaligandaki A, and Pelton in high-head plants such as Khimti and Upper Tamakoshi.
✓ Answer checked by Claude Opus 5.5 (high effort)
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