--- title: "Structural components and the surge tank" subject: "Power Plant Design" chapter: 3 key: "semester_8/power_plant_design:structural-components-surge-tank" source: https://www.bctengineer.com/q/semester_8/power_plant_design/structural-components-surge-tank site: BCT Engineering --- # Structural components and the surge tank Power Plant Design · Chapter 3: Hydro Power Plant Design - Asked in: 2072 Magh, 8 marks - Video: [What Is Surge Tank and Its Types](https://www.youtube.com/watch?v=T3W7AmTZoUY) — Amazing Engineering | ACES - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/power_plant_design/structural-components-surge-tank - Whole chapter: https://www.bctengineer.com/md/semester_8/power_plant_design/chapter-3 ## Question Draw the schematic diagram of hydropower plant showing different structural components. State the role of surge tank in hydropower plant construction. ## Short answer Structural components: dam/weir, intake, desander, headrace, forebay/surge tank, penstock, powerhouse, tailrace. Surge tank at junction of tunnel and penstock limits water hammer on load rejection, supplies water on load increase, reduces penstock thickness and improves governing. ## Answer The structural (mainly civil) components of a hydropower plant collect, store, clean and carry water to the turbine and return it to the river. #### Schematic ```text Reservoir/River ==|== Dam/weir + spillway | Intake (trash rack, gates) | Desander | Headrace tunnel ================\ | [SURGE TANK] | Penstock | [POWERHOUSE: turbine, generator] | Tailrace -> River ``` #### Structural components 1. **Dam or weir** with spillway: creates head/storage and passes floods. 2. **Intake:** admits water; trash rack keeps out debris. 3. **Gravel trap and desander:** remove sediment. 4. **Headrace canal or tunnel:** carries water at a gentle slope. 5. **Forebay or surge tank:** free water surface at the head of the penstock. 6. **Penstock** with anchor blocks and saddle supports. 7. **Powerhouse:** foundation, superstructure, crane beams. 8. **Tailrace channel.** #### Role of surge tank A surge tank is an open vertical shaft or chamber placed at the junction of the long low-pressure headrace tunnel and the steep penstock. - **Protects against water hammer:** when load is rejected, the governor closes the gates quickly. The moving water column cannot stop instantly; without a surge tank the pressure rise would travel through the whole tunnel. The surge tank lets the water rise in it, so the high pressure is limited to the short penstock. - **Supplies water on load increase:** when gates open suddenly, water is drawn from the tank until the slow tunnel flow speeds up, avoiding a drop in pressure (and vacuum) in the penstock. - **Reduces penstock and tunnel thickness:** lower design pressure means cheaper tunnel lining. - **Improves governing:** reduces the effective water inertia time constant $T_w = \dfrac{LV}{gH}$, since only the penstock length counts, making speed regulation stable. - **Types:** simple, restricted orifice, differential and chamber types. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Where is the surge tank placed? A. At the intake B. At the junction of the long headrace tunnel and the penstock C. At the tailrace outlet D. Inside the powerhouse Answer: B. It is an open shaft between the low-pressure tunnel and steep penstock. (Key point: Location) 2. How does a surge tank help when load is rejected? A. It stops the water instantly B. It opens the turbine gates C. Water rises in the tank, limiting high pressure to the short penstock D. It sends pressure through the whole tunnel Answer: C. The water column cannot stop instantly; the tank takes the rise so the tunnel is protected. (Key point: Load rejection) 3. What does the surge tank do when gates open suddenly? A. Closes the penstock valve B. Stores sediment C. Increases generator voltage D. Supplies water until tunnel flow speeds up, avoiding pressure drop Answer: D. Water drawn from the tank covers demand while the slow tunnel flow accelerates. (Key point: Load increase) 4. How does a surge tank improve speed regulation? A. Only penstock length counts in Tw = LV/gH, reducing water inertia time B. It increases tunnel length in Tw C. It raises the head D. It reduces turbine speed Answer: A. The shorter effective conduit reduces the time constant, giving stable governing. 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