--- title: "Components of a run-of-river plant" subject: "Power Plant Design" chapter: 3 key: "semester_8/power_plant_design:ror-components-functions" source: https://www.bctengineer.com/q/semester_8/power_plant_design/ror-components-functions site: BCT Engineering --- # Components of a run-of-river plant Power Plant Design · Chapter 3: Hydro Power Plant Design - Asked in: 2074 Bhadra, 8 marks; 2071 Magh, 3+5 marks (asked 2 times) - Video: [How Run of the River Hydroelectric Power Station Works](https://www.youtube.com/watch?v=rm9JqQGDwN0) — 3D-knowledge - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/power_plant_design/ror-components-functions - Whole chapter: https://www.bctengineer.com/md/semester_8/power_plant_design/chapter-3 ## Question Discuss the functions and importance of various components of hydropower plant with proper schematic diagram of ROR hydropower plant. ## Short answer A run-of-river plant diverts river flow without significant storage. Components: diversion weir, intake, gravel trap, desander (critical for sediment removal), headrace canal/tunnel, forebay or surge tank, penstock, turbine, generator, tailrace. Output varies with river flow. ## Answer A **run-of-river (ROR)** plant diverts part of the river flow through a waterway to a powerhouse without any significant storage, so its output follows the natural river flow. Each component has one job: take water in, clean it, carry it with little head loss, convert its energy, and return it to the river. #### Schematic of an ROR plant ```text River ==|== Diversion weir + intake (trash rack, gate) | [Gravel trap] -> [Desander / settling basin] | | Headrace canal / tunnel (low slope) v [Forebay] or [Surge tank] | | Penstock (steel pipe, steep) v [Valve]-[Turbine]-[Generator] POWERHOUSE | | Tailrace GSU transformer -> Switchyard | -> Transmission line v Back to river ``` #### Components, functions and importance | Component | Function | Importance | |---|---|---| | Diversion weir / barrage | Raises water level and diverts flow into intake | Gives a steady water level at intake | | Intake with trash rack and gate | Admits the design discharge, stops floating debris | Protects the waterway; gate closes for floods and maintenance | | Gravel trap | Removes coarse gravel just after intake | Prevents canal choking | | Desander (settling basin) | Settles fine sediment (usually particles above 0.2 mm) | Protects turbine runners from abrasion, very important in Himalayan rivers | | Headrace canal / tunnel | Carries water at low slope to the forebay or surge tank | Most of the head is gained here, so head loss must be small | | Forebay (canal system) | Small pond before the penstock; final settling and spill | Provides submergence and absorbs small load changes | | Surge tank (tunnel system) | Open shaft at end of pressure tunnel | Absorbs water hammer and supplies water on sudden load increase | | Penstock | Pressure pipe from forebay/surge tank to turbine | Converts elevation to pressure head; designed for water hammer | | Main inlet valve | Butterfly or spherical valve before turbine | Isolates the turbine for shutdown and emergency | | Turbine | Converts hydraulic energy to mechanical energy | Type chosen from head and discharge | | Generator | Converts mechanical energy to electrical energy | Usually a synchronous machine, run in step with the grid | | Governor and excitation | Control speed (frequency) and voltage | Keep the unit stable and in step with the grid | | Transformer and switchyard | Step up voltage, switching and protection | Connect plant to the grid | | Tailrace | Returns water to the river | Must avoid backwater that reduces net head | #### Key points - ROR plants are cheap and have small environmental impact, but output drops sharply in the dry season. - Because Nepalese rivers carry heavy sediment, the **desander** and good intake design decide the life of the turbines. - A **riparian release** (environmental flow) is always let past the weir for downstream life. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. In an ROR plant the output: A. Is independent of river flow B. Follows the natural river flow because there is no significant storage C. Is fixed by a large reservoir D. Is always at peak Answer: B. No storage means output drops sharply in the dry season. (Key point: ROR concept) 2. Which is correct? A. Gravel trap removes coarse gravel after the intake to prevent canal choking; desander settles fine sediment B. Gravel trap removes fine silt; desander removes boulders C. Both generate power D. Both control frequency Answer: A. The gravel trap removes coarse material; the desander removes fine particles above about 0.2 mm. (Key point: Gravel trap vs desander) 3. Which waterway uses a forebay and which a surge tank? A. Forebay at the canal system end; surge tank at the end of a pressure tunnel B. Surge tank for canal; forebay for tunnel C. Both only for tunnel D. Neither is needed ever Answer: A. A forebay ends a canal; a surge tank ends a pressure tunnel. (Key point: Forebay vs surge tank) 4. Why must tailrace avoid backwater, and why is a riparian release provided? A. Backwater reduces net head; release maintains environmental flow downstream B. Backwater increases head; release raises power C. Backwater cleans sediment; release fills the pondage D. Both reduce cost Answer: A. Backwater cuts net head; riparian release is the environmental flow for downstream life. (Key point: Tailrace and riparian release) ## Related in Power Plant Design - [Daily pondage run-of-river components](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Adaily-pondage-ror-components) — Power Plant Design, chapter 3 - [Hydropower plant components and functions](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Ahydropower-components-functions) — Power Plant Design, chapter 3, asked 2× - [Schematic of a PROR hydropower plant](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Apror-schematic-components) — Power Plant Design, chapter 3, asked 2× - [Reservoir type hydropower plant schematic](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Areservoir-plant-schematic) — Power Plant Design, chapter 3 - [ROR versus PROR hydropower plants](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Aror-vs-pror) — Power Plant Design, chapter 3 - [High dam hydropower project components](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Ahigh-dam-components) — Power Plant Design, chapter 3 ## Related in other subjects - [Combined plant components and T-s diagram](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Acombined-components-ts) — Power Plant Equipment, chapter 8, asked 4× - [RoR plant layouts; storage over RoR](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aror-layouts-storage-importance) — Hydropower Engineering, chapter 2 - [Intake site selection for RoR plant](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Aintake-site-selection-ror) — Hydro Power, chapter 5 - [Optimizing plant capacity of a RoR project](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aror-optimum-capacity-discussion) — Hydropower Engineering, chapter 3