---
title: "Components of a hydroelectric power plant"
subject: "Fluid Machines"
chapter: 2
key: "semester_5/fluid_machines:hydroelectric-plant-components"
source: https://www.bctengineer.com/q/semester_5/fluid_machines/hydroelectric-plant-components
site: BCT Engineering
---

# Components of a hydroelectric power plant

Fluid Machines · Chapter 2: Hydroelectric Plant

- Asked in: year not given, 6 marks
- Video: [Components of Hydroelectric Power Plant | Hydroelectric Power Plant | Power Pant | Fluid Mechanics](https://www.youtube.com/watch?v=MSR7Acw_Q6U) — Professor Nidhi Trivedi
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/fluid_machines/hydroelectric-plant-components
- Whole chapter: https://www.bctengineer.com/md/semester_5/fluid_machines/chapter-2

## Question

With the help of a neat layout, describe the essential components of a hydroelectric power plant and state the function of each.

## Short answer

A hydroelectric plant uses a reservoir and dam for storage and head; intake with trash rack and gates; penstock to deliver water under pressure; a turbine (impulse or reaction) converting water energy to mechanical; a generator; a draft tube for reaction turbines recovering kinetic energy and allowing placement above tailrace; and a tailrace channel.

## Answer

A hydroelectric plant converts the potential energy of water stored at a height into electricity. Power available is $P=\rho g Q H\eta$.

```text
  Reservoir
  ~~~~~~~~~~~|  Dam            Surge tank
  ~~~~~~~~~~~|====+             |
  ~~~~~~~~~~~|    Intake  ______|_____
  ~~~~~~[Trash   rack]--/ Penstock    \
         [Gate]                        \
                                       [Turbine]=[Gen]
                                        |
                              Draft tube|  Tailrace -->
                                       ~~~~~~~~~~~~~~
```

#### Essential components

1. **Catchment area and reservoir:** collects and stores rainfall and river water. Its storage gives the control of flow through the year.
2. **Dam:** raises the water level to create head and storage. Types: gravity, arch, buttress, earth or rockfill. It has a spillway for passing flood water safely.
3. **Intake structure with trash rack and gates:** takes water into the waterway. The trash rack keeps out logs and debris; gates control and stop the flow. A silt-settling basin (desilter) is also used on rivers carrying silt.
4. **Headrace (canal or tunnel):** carries water from the intake to the forebay or surge tank.
5. **Forebay or surge tank:** the surge tank is a vertical open chamber near the penstock. It absorbs pressure rise (water hammer) when the turbine gates close suddenly and supplies water when load increases.
6. **Penstock:** a steel or reinforced concrete pipe taking water at high pressure from the forebay to the turbine.
7. **Powerhouse:** contains the turbines, generators, governors, control panel, and cranes.
8. **Water turbine:** converts water energy to mechanical energy (Pelton for high head, Francis for medium, Kaplan for low head).
9. **Generator:** coupled to the turbine to produce electricity.
10. **Draft tube (reaction turbines):** a diverging pipe below the runner which allows the turbine to be set above the tailwater level and recovers the kinetic energy of the exit water.
11. **Tailrace:** channel carrying the used water back to the river.
12. **Switchyard and transformer:** step up voltage for transmission.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. The surge tank is provided to:
   A. Step up voltage
   B. Hold the generator
   C. Absorb pressure rise (water hammer) and supply water on load increase
   D. Remove silt
   Answer: C. The surge tank absorbs water hammer when gates close and supplies water when load rises. (Key point: Surge tank)

2. The trash rack at the intake:
   A. Recovers kinetic energy
   B. Controls flow
   C. Generates power
   D. Keeps out logs and debris
   Answer: D. Trash racks stop debris; gates control and stop flow. (Key point: Trash rack)

3. Draft tube in a reaction turbine allows:
   A. Silt removal
   B. Runner above tailwater level and recovery of exit kinetic energy
   C. Higher voltage
   D. Flood spilling
   Answer: B. A diverging draft tube lets the turbine be set above tailwater and recovers exit kinetic energy. (Key point: Draft tube)

4. Which turbine suits high, medium and low head respectively?
   A. Kaplan, Francis, Pelton
   B. Francis, Pelton, Kaplan
   C. Pelton, Francis, Kaplan
   D. Pelton, Kaplan, Francis
   Answer: C. Pelton for high head, Francis for medium, Kaplan for low head. (Key point: Turbine selection)

## Related in Fluid Machines

- [Classification of hydroelectric plants](https://www.bctengineer.com/question.md?key=semester_5%2Ffluid_machines%3Ahydroelectric-plant-classification) — Fluid Machines, chapter 2

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