---
title: "Powerhouse layout with Francis turbine"
subject: "Hydro Power"
chapter: 5
key: "semester_6/hydro_power:powerhouse-layout-francis"
source: https://www.bctengineer.com/q/semester_6/hydro_power/powerhouse-layout-francis
site: BCT Engineering
---

# Powerhouse layout with Francis turbine

Hydro Power · Chapter 5: Components of Hydropower System

- Asked in: 2071 Bhadra, 2+3 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/hydro_power/powerhouse-layout-francis
- Whole chapter: https://www.bctengineer.com/md/semester_6/hydro_power/chapter-5

## Question

Draw a typical layout of powerhouse with Francis turbine. How would you fix the appropriate dimension of the powerhouse?

## Short answer

A Francis turbine powerhouse has three levels: substructure (draft tube, spiral casing), intermediate (turbine/generator floor), and superstructure (machine hall with crane). Units are arranged in a row with an erection bay. Dimensions are based on runner diameter D: length = n × unit spacing + erection bay; width ≈ 4–5D; height includes draft tube depth (2.5–3D) and crane clearance (10–15 m above generator floor). Crane capacity set by heaviest lift.

## Answer

A powerhouse with Francis turbines has three main levels: the **substructure** (draft tube and spiral casing in mass concrete), the **intermediate structure** (turbine and generator floor) and the **superstructure** (machine hall with overhead crane).

#### Typical layout (cross-section)
```text
     ______________________________________
    |  roof truss / EOT crane rail         |
    |      [=== crane ===]                 |
    |                                      |
    |          _______                     |
    |         | GEN   |   generator floor  |
    |_________|_______|____________________|
    |          |shaft|    turbine floor    |
 penstock==>( spiral casing )  MIV         |
    |          \runner/                    |
    |           |    |  draft tube         |
    |__________/      \____________________|__ TWL
                \______\________~~~~~~~~~~~ tailrace
```
**Plan:** units in a row in the machine hall, with an **erection (service) bay** at one end at road level; control room, switchgear and transformer yard alongside.

#### Fixing the dimensions of the powerhouse
1. **Length** $= n \times$ unit spacing $+$ erection bay length $+$ end clearances.
   - Unit spacing is governed by the largest of: spiral casing width, draft tube outlet width, or generator barrel diameter, plus about 1.5–2 m for walkways and walls. Roughly 4–5 times the runner diameter $D$ for Francis units.
   - Erection bay ≈ 1 to 1.5 times the unit spacing, enough to assemble a rotor and runner.
2. **Width** is fixed by the spiral casing / generator size in the transverse direction (≈ 4–5 $D$) plus space for the main inlet valve (MIV) on the upstream side and governors, panels and walkways; draft tube length (≈ 4–5 $D$) fixes the substructure width.
3. **Height:**
   - **Below the turbine centre line:** draft tube depth (≈ 2.5–3 $D$) and the turbine setting $H_s$ below or above tailwater, fixed by the cavitation (Thoma) criterion.
   - **Above the generator floor:** height of the generator and exciter, plus the height needed for the crane to lift the rotor over other units, crane girder and roof (often 10–15 m above the generator floor).
4. **Crane capacity** is fixed by the heaviest part to be lifted (generator rotor or transformer).
5. **Other:** space for control room, auxiliaries, access, ventilation, and future units.

These empirical ratios (based on runner diameter $D$) are used at the feasibility stage; final dimensions come from manufacturer's drawings.

## Check yourself

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

1. The three main levels of a Francis powerhouse are
   A. substructure, intermediate structure and superstructure
   B. intake, canal and tailrace
   C. forebay, penstock and turbine
   D. dam, spillway and switchyard
   Answer: A. Substructure holds draft tube and spiral casing; superstructure is the machine hall. (Key point: Levels)

2. What governs the spacing between units?
   A. The length of the penstock
   B. The largest of spiral casing width, draft tube outlet width or generator barrel diameter, plus clearance
   C. The tailwater level only
   D. The crane rail gauge only
   Answer: B. Spacing is set by the largest of those widths plus 1.5-2 m. (Key point: Unit spacing)

3. Why is an erection bay provided?
   A. To store the penstock
   B. To dissipate energy
   C. To assemble and service the rotor and runner, at road level
   D. To house the surge tank
   Answer: C. It is about 1-1.5 times unit spacing at one end. (Key point: Erection bay)

4. Crane capacity is fixed by
   A. the number of units only
   B. the draft tube depth
   C. the tailrace width
   D. the heaviest part to be lifted, such as the generator rotor or transformer
   Answer: D. The crane must lift the heaviest piece. (Key point: Crane capacity)

## Related in Hydro Power

- [Why draft tube is used in Francis turbine](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Adraft-tube-francis) — Hydro Power, chapter 7
- [Purpose of governor and governing of Francis turbine](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Agoverning-francis-turbine) — Hydro Power, chapter 7
- [Francis turbine design (55 m³/s, 25 m)](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Afrancis-design-55) — Hydro Power, chapter 7
- [Francis turbine design (45 m³/s, 150 m)](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Afrancis-design-45) — Hydro Power, chapter 7
- [Francis turbine design (140 m³/s, 120 m)](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Afrancis-design-140) — Hydro Power, chapter 7
- [Pelton versus Francis performance characteristics](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Apelton-vs-francis-performance) — Hydro Power, chapter 7

## Related in other subjects

- [Powerhouse layout with vertical axis Francis turbine](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Apowerhouse-layout-vertical-axis-francis) — Hydropower Engineering, chapter 8, asked 3×
- [Powerhouse plan and sections (Francis, 10 MW)](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Apowerhouse-plan-section-francis-10mw) — Hydropower Engineering, chapter 8
- [Layout of a medium head Francis station](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Afrancis-medium-head-layout) — Power Plant Design, chapter 3, asked 2×
- [Powerhouse general arrangement and dimensions](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Apowerhouse-arrangement-and-dimensions) — Hydropower Engineering, chapter 8, asked 3×