--- title: "Daily pondage ROR with 150 m head" subject: "Power Plant Design" chapter: 3 key: "semester_8/power_plant_design:daily-pondage-150m-head" source: https://www.bctengineer.com/q/semester_8/power_plant_design/daily-pondage-150m-head site: BCT Engineering --- # Daily pondage ROR with 150 m head Power Plant Design · Chapter 3: Hydro Power Plant Design - Asked in: 2078 Chaitra, 8 marks - Video: [Component of ROR and PROR Hydropower Projects #hydropower #dam#engineering#powerhouse #energy](https://www.youtube.com/watch?v=xwlWEVewQKU) — Hydropower - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/power_plant_design/daily-pondage-150m-head - Whole chapter: https://www.bctengineer.com/md/semester_8/power_plant_design/chapter-3 ## Question Discuss major components of a Daily Pondage Run off the River type hydropower project with tentative head 150 m and discharge 10 m³/s per unit. Illustrate with suitable schematic diagram. ## Short answer For 150 m head and 10 m³/s per unit, shaft power is about 13.2 MW (Ns≈132), suited for Francis turbine. Components: diversion weir, intake, gravel trap, desander, daily pondage (~90,000 m³ storage), headrace tunnel, surge tank, penstock, butterfly valve, Francis turbine-generator, tailrace, switchyard. ## Answer For a **head of about 150 m** and **10 m³/s per unit**, the unit output is roughly $$ P \approx 9.81 \times 10 \times 150 \times 0.9 \approx 13.2\ \text{MW (shaft)} $$ and the specific speed at 600 rpm is $N_s = 600\sqrt{13244}/150^{5/4} \approx 132$, which lies well inside the **Francis** range (60–300). So the project is a medium-head **daily pondage run-of-river (PROR)** scheme with vertical Francis units of roughly 12–13 MW each. #### Schematic ```text River ==|== Diversion weir + gated spillway | Intake (trash rack, gates) | Gravel trap -> Desander (2 or more bays) | [ DAILY PONDAGE ] -- spillway/flushing | Headrace tunnel (pressurised) | Surge tank | Penstock (steel, ~150 m head) | Butterfly valve | Francis turbine + Generator (~13 MW) | | Draft tube Unit transformer | | Tailrace -> River Switchyard -> Grid ``` #### Major components 1. **Diversion weir and spillway:** raise water level and pass monsoon floods; undersluice keeps the intake free of sediment. 2. **Intake:** sized for total design discharge (10 m³/s × number of units) plus flushing water; trash rack and gates. 3. **Gravel trap and desander:** remove particles larger than about 0.2 mm, as sediment at 150 m head quickly erodes Francis runners and guide vanes. 4. **Daily pondage:** stores off-peak inflow; for example, to run a 10 m³/s unit for 5 peak hours when the dry-season inflow is only 5 m³/s, storage $= (10-5)\times 5 \times 3600 = 90{,}000$ m³ is needed. 5. **Headrace tunnel:** carries water under low pressure to the surge tank. 6. **Surge tank:** absorbs water hammer when governor closes the wicket gates and supplies water on load increase. 7. **Penstock:** about 150 m static head plus water hammer allowance (typically 20–30%), with anchor blocks and expansion joints. 8. **Main inlet valve:** butterfly valve, suitable for medium head. 9. **Francis turbine:** spiral casing, stay vanes, wicket gates, runner and draft tube; vertical shaft; runner set below tailwater as required by cavitation. 10. **Generator:** vertical synchronous generator at 11 kV, e.g. about 15 MVA at 0.85 pf, with excitation system and governor. 11. **Tailrace:** returns water to the river below the powerhouse. 12. **Electrical system:** unit step-up transformer (11/132 kV), switchyard, station supply and diesel generator for black start. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. For H = 150 m and Q = 10 m3/s per unit, with efficiency 0.9, what is the approximate shaft output? A. About 1.3 MW B. About 13.2 MW C. About 14.7 MW D. About 132 MW Answer: B. P = 9.81 x 10 x 150 x 0.9 = 13,244 kW, about 13.2 MW. (Key point: Unit output) 2. Why is a Francis turbine chosen here? A. Ns is about 20, within the Pelton range B. Ns is about 500, within the Kaplan range C. Ns of about 132 at 600 rpm lies within the Francis range of 60-300 D. Head of 150 m is too low for any reaction turbine Answer: C. Specific speed from head, power and speed fixes the runner type; 132 is well inside the Francis range. (Key point: Turbine type) 3. A 10 m3/s unit runs for 5 peak hours when dry-season inflow is 5 m3/s. What storage is needed? A. 180,000 m3 B. 45,000 m3 C. 9,000 m3 D. 90,000 m3 Answer: D. (10 - 5) x 5 x 3600 = 90,000 m3. (Key point: Pondage volume) 4. Why must the desander remove particles larger than about 0.2 mm at this head? A. Sediment quickly erodes Francis runners and guide vanes B. It would block the trash rack C. It increases the penstock thickness D. It lowers the generator voltage Answer: A. At 150 m head the high velocities make sediment very abrasive to runner and guide vanes. 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