--- title: "Components of a medium head high discharge plant" subject: "Power Plant Design" chapter: 3 key: "semester_8/power_plant_design:medium-head-high-discharge-components" source: https://www.bctengineer.com/q/semester_8/power_plant_design/medium-head-high-discharge-components site: BCT Engineering --- # Components of a medium head high discharge plant Power Plant Design · Chapter 3: Hydro Power Plant Design - Asked in: 2082 Shrawan, 8 marks; 2074 Magh, 3+5 marks (asked 2 times) - Video: [Types of hydro power plants, Classification of Hydro power plants, #HydroPlant](https://www.youtube.com/watch?v=2Ya1i7oQphg) — Mechanical Engineering Management - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/power_plant_design/medium-head-high-discharge-components - Whole chapter: https://www.bctengineer.com/md/semester_8/power_plant_design/chapter-3 ## Question List down the various components of a medium head relatively higher discharge hydropower plant and mention their functions. ## Short answer Components include diversion weir, intake with trash rack, desander, headrace tunnel, surge tank, penstock, powerhouse with Francis turbines, tailrace, and electrical systems. The weir diverts flow, desander removes sediment, surge tank controls water hammer, and Francis turbine converts energy. ## Answer A medium head (about 30–300 m), relatively high discharge plant is usually a **run-of-river or pondage run-of-river** scheme with a diversion weir/dam, a long large-diameter water conductor, a surge tank and a powerhouse with **Francis turbines**. #### Layout ```text Reservoir/headpond ____ Intake | |__[TR]___ Headrace tunnel _________ |Dam/| (gate) \ Surge |weir| \ tank |____|--> Spillway Desander [ST] | | +-> Riparian release Penstock | \______| \ [Powerhouse] Turbine+Gen | Tailrace -> River | Switchyard -> Grid ``` #### Components and functions **A. Civil components** 1. **Diversion weir / dam:** Raises the water level and diverts flow to the intake; may create a small pondage. 2. **Spillway and gates:** Pass flood water safely; undersluice gates flush sediment near the intake. 3. **Intake with trash rack:** Draws the design discharge into the conveyance; the trash rack stops floating debris; gates control flow. 4. **Gravel trap and settling basin (desander):** Remove sand and silt (particles above about 0.2 mm) to protect the turbines from abrasion — very important in Himalayan rivers. 5. **Headrace tunnel / canal:** Carries the large discharge at a mild slope to the forebay/surge tank with low head loss. 6. **Surge tank (or forebay):** Absorbs pressure rise (water hammer) during load rejection and supplies water during sudden load increase; protects the tunnel. 7. **Penstock / pressure shaft:** Carries water under pressure from the surge tank to the turbines; ends in a manifold for each unit, with a valve. 8. **Powerhouse:** Houses turbines, generators, control and auxiliary systems (surface or underground). 9. **Tailrace:** Returns water from the draft tube to the river. **B. Mechanical components** 10. **Main inlet valve (butterfly/spherical):** Isolates each turbine. 11. **Francis turbine** (suitable for medium head, high flow) with spiral casing, guide vanes and **draft tube** to recover kinetic energy. 12. **Governor:** Controls guide-vane opening to keep speed/frequency constant. 13. **Cooling water, drainage, dewatering and EOT crane.** **C. Electrical components** 14. **Synchronous generator** with **excitation system and AVR**. 15. **Generator circuit breaker, generator bus/leads**, CTs and PTs. 16. **Step-up (generator) transformer:** Raises voltage (e.g. 11 kV to 132 kV). 17. **Switchyard:** Breakers, isolators, busbars, lightning arresters for connection to the transmission line. 18. **Control, protection and SCADA; station auxiliary transformer; DC battery system; diesel generator** for black start; earthing system. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Why is a desander provided in a Himalayan hydropower scheme? A. To increase the head B. To settle sand and silt (above about 0.2 mm) and protect turbines from abrasion C. To store water for peaking D. To generate reactive power Answer: B. Heavy sediment erodes turbine runners, so particles are removed before the water reaches them. (Key point: Desander) 2. The surge tank: A. Absorbs water hammer pressure rise on load rejection and supplies water on sudden load increase B. Filters debris C. Steps up the voltage D. Measures discharge Answer: A. It protects the long tunnel from pressure changes and gives water during sudden load rise. (Key point: Surge tank) 3. Which turbine suits a medium head (30-300 m), high flow plant? A. Pelton B. Francis C. Turgo only D. Water wheel Answer: B. Francis turbines are used for medium head and high discharge. (Key point: Turbine choice) 4. What is the function of the governor and of the draft tube? A. Governor keeps speed constant by guide vane control; draft tube recovers kinetic energy B. Governor steps up voltage; draft tube holds sediment C. Governor stops debris; draft tube isolates the turbine D. Both control voltage Answer: A. The governor controls guide-vane opening for constant speed; the draft tube recovers energy at the runner exit. 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