---
title: "Hydropower generation with block diagram"
subject: "Power System Analysis I"
chapter: 1
key: "semester_4/power_system_analysis_i:hydropower-generation-block-diagram"
source: https://www.bctengineer.com/q/semester_4/power_system_analysis_i/hydropower-generation-block-diagram
site: BCT Engineering
---

# Hydropower generation with block diagram

Power System Analysis I · Chapter 1: General Background

- Asked in: 2075 Baisakh, 4 marks
- Video: [Hydro Electric Power Plant , Block Diagram , Working & Other](https://www.youtube.com/watch?v=1wn-pl6ckfQ) — PM Home Tuitions 
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/power_system_analysis_i/hydropower-generation-block-diagram
- Whole chapter: https://www.bctengineer.com/md/semester_4/power_system_analysis_i/chapter-1

## Question

Explain how electrical energy can be generated from a hydropower plant with basic block diagram.

## Short answer

Hydropower converts water's potential energy into kinetic energy, then mechanical shaft power in a turbine, then electrical power in a synchronous generator. Key blocks are reservoir, headrace, forebay/surge tank, penstock, turbine, generator, step-up transformer, switchyard, and tailrace; available power is P = eta rho g Q H.

## Answer

A hydropower plant converts the **potential energy of water** stored at a height into kinetic energy, then into mechanical energy in a turbine, and finally into electrical energy in a generator. Power available:
$$
P = \eta\rho g Q H\quad(\text{W})
$$
where $Q$ = discharge (m³/s), $H$ = net head (m), $\eta$ = overall efficiency.

#### Block diagram
```text
 [Reservoir/Intake/Dam]
          |
   [Headrace / tunnel]
          |
 [Forebay / surge tank]
          |
      [Penstock]
          |
   [Turbine] --shaft--> [Generator] -> [Step-up Tx]
          |                 |              |
     [Tailrace]       [Exciter, AVR]   [Switchyard]
          |                                |
        River                           Grid
```

#### Working
1. **Dam/intake:** Stores or diverts river water and creates head.
2. **Headrace and forebay/surge tank:** Carry water to the penstock; the surge tank absorbs pressure changes (water hammer).
3. **Penstock:** Pressure pipe that brings water down to the powerhouse, converting potential energy to pressure/kinetic energy.
4. **Turbine:** Pelton (high head), Francis (medium head) or Kaplan (low head) turns the water energy into shaft rotation; governor controls flow to keep speed constant.
5. **Generator:** Synchronous generator coupled to the turbine produces 3-phase AC at 11 kV.
6. **Transformer and switchyard:** Step up the voltage (e.g. 11/132 kV) and connect to the grid.
7. **Tailrace:** Returns water to the river.

Example: Kali Gandaki "A" (144 MW) in Nepal uses this arrangement with Francis turbines.

## Check yourself

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

1. Order of energy conversion in hydropower?
   A. Electrical - mechanical
   B. Potential - kinetic - mechanical - electrical
   C. Chemical - thermal
   D. Nuclear - thermal
   Answer: B. Water head turns turbine which turns generator. (Key point: Energy conversion)

2. Power available from water?
   A. P = rho Q / H
   B. P = eta Q / (g H)
   C. P = eta rho g Q H
   D. P = rho g H / Q
   Answer: C. Proportional to discharge Q and head H. (Key point: Power formula)

3. Purpose of surge tank?
   A. Store energy
   B. Raise voltage
   C. Control frequency
   D. Absorb pressure changes (water hammer)
   Answer: D. It protects the penstock from sudden pressure rise. (Key point: Surge tank)

4. Turbine for high head?
   A. Pelton
   B. Kaplan
   C. Francis
   D. Propeller
   Answer: A. Pelton high, Francis medium, Kaplan low head. (Key point: Turbine choice)

## Related in Power System Analysis I

- [Conventional vs renewable energy for generation](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Aconventional-vs-renewable-generation) — Power System Analysis I, chapter 1, asked 2×
- [Basic structure of power system](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Abasic-structure-power-system) — Power System Analysis I, chapter 1

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