---
title: "Francis turbine in pumped storage plant"
subject: "Power Plant Equipment"
chapter: 1
key: "semester_7/power_plant_equipment:francis-turbine-pumped-storage"
source: https://www.bctengineer.com/q/semester_7/power_plant_equipment/francis-turbine-pumped-storage
site: BCT Engineering
---

# Francis turbine in pumped storage plant

Power Plant Equipment · Chapter 1: Hydro Power Plant

- Asked in: 2075 Chaitra, 8 marks
- Video: [How Francis Turbines Work (Hydropower)](https://www.youtube.com/watch?v=skQNf5_61Ps) — saVRee
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/power_plant_equipment/francis-turbine-pumped-storage
- Whole chapter: https://www.bctengineer.com/md/semester_7/power_plant_equipment/chapter-1

## Question

Explain the use of Francis turbine in pumped storage plant. Is this type of power plant feasible to install in Nepal's power system? Give reasons.

## Short answer

A Francis turbine is used as a reversible pump-turbine: one machine operates as a turbine for generation and as a centrifugal pump in reverse for pumping. It is feasible in Nepal due to high-head sites, run-of-river surplus, evening peak demand, and potential cheap import, though high cost and dry-season energy deficit are obstacles.

## Answer

In a pumped storage plant the **Francis turbine is used as a reversible pump-turbine**. One machine works as a turbine when water flows down and as a centrifugal pump when it is rotated in the opposite direction. It is coupled to a reversible synchronous machine that works as a generator or as a motor.

```text
 Upper reservoir
   |   generating: water down
   v ^ pumping: water up
 +-----------------+   +------------------+
 | Francis pump-   |===| motor-generator  |== grid
 | turbine (spiral |   | (reverses for    |
 | casing, runner, |   |  pumping)        |
 | wicket gates)   |   +------------------+
 +-----------------+
   | ^ draft tube
 Lower reservoir
```

#### Why a Francis machine is used
- The Francis runner is a mixed/radial flow reaction runner, so its shape is very close to that of a centrifugal pump impeller. When driven backwards it pumps water efficiently.
- It covers the head range of most pumped storage sites (about 30 m to 700 m).
- One machine replaces a separate pump and turbine, so the power house, valves and civil works are smaller and cheaper.
- Wicket gates control flow in turbine mode and are set for best efficiency in pump mode.
- Mode change is quick (a few minutes), so it gives fast peaking and spinning reserve.

#### Operation
1. **Turbine mode (peak hours):** Water from the upper reservoir enters the spiral casing, passes through the wicket gates and runner, and leaves through the draft tube. The machine generates power.
2. **Pump mode (off-peak):** The machine is started as a motor (by a starting motor, back-to-back start or static frequency converter) in the reverse direction with the runner dewatered by compressed air, then water is admitted and pumped up.
3. Efficiency is slightly less than a separate pump and turbine (about 90 % in each mode, 70–80 % for the cycle).

#### Feasibility in Nepal
It is **feasible in Nepal**, mainly for the reasons below, though high cost and dry-season energy deficit are the main obstacles.
- **For:** high heads in hilly terrain; run-of-river plants give night and monsoon surplus that can be stored; time-of-day peak in the evening; possibility of cheap off-peak import from India and solar surplus; better frequency and reserve support for the grid; sites near existing reservoirs like Kulekhani have been studied.
- **Against:** large investment and long construction; in winter there is little surplus to pump with; 20–30 % energy loss; heavy sediment in rivers wears Francis runners; reservoir projects may be a higher priority.

Overall, with time-of-day tariffs and power trade, a pumped storage plant using Francis pump-turbines is a sound option for meeting Nepal's peak demand.

## Check yourself

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

1. Why can a Francis runner also serve as a pump?
   A. It is an axial-flow propeller
   B. It is an impulse wheel with buckets
   C. It has no wicket gates
   D. It is a mixed/radial flow reaction runner, shaped much like a centrifugal pump impeller
   Answer: D. When driven in reverse, its radial-flow shape pumps water efficiently. (Key point: Reversible pump-turbine)

2. What is an advantage of using one Francis pump-turbine rather than separate machines?
   A. Higher cycle efficiency than separate machines
   B. Smaller, cheaper power house, valves and civil works
   C. No need for a motor-generator
   D. No starting arrangement is needed
   Answer: B. One machine replaces separate pump and turbine; efficiency is actually slightly lower. (Key point: Advantage of one machine)

3. How is the machine started in pump mode?
   A. Water is simply allowed in with the runner full
   B. Using the penstock pressure
   C. As a motor in reverse with runner dewatered by compressed air, using a starting motor, back-to-back start or static converter
   D. By closing the draft tube
   Answer: C. Dewatering reduces starting torque; a separate starting method brings the motor to speed. (Key point: Starting in pump mode)

4. Which is a main obstacle to pumped storage in Nepal?
   A. Lack of any high head sites
   B. No run-of-river surplus at any time
   C. Large investment and winter energy deficit, plus sediment wearing runners
   D. Francis turbines cannot be built
   Answer: C. High heads and ROR surplus favour it, but cost, dry-season deficit and sediment are the obstacles. (Key point: Feasibility in Nepal)

## Related in Power Plant Equipment

- [Pumped storage plant and feasibility in Nepal](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Apump-storage-nepal-feasibility) — Power Plant Equipment, chapter 1, asked 5×
- [When pumped storage is economically feasible](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Apumped-storage-economic-feasibility) — Power Plant Equipment, chapter 1
- [Operation of pumped storage hydro plant](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Apump-storage-operation) — Power Plant Equipment, chapter 1, asked 2×
- [Reheat gas turbine power plant](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Agt-reheat-plant) — Power Plant Equipment, chapter 6
- [Pumped storage to reduce peak generation loss](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Apump-storage-peak-loss) — Power Plant Equipment, chapter 1, asked 3×

## Related in other subjects

- [Pumped storage plant: power, turbine, setting, surge](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Apumped-storage-turbine-surge-numerical) — Hydropower Engineering, chapter 7
- [Pumped storage plant and benefit to Nepal](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Apumped-storage-benefit-nepal) — Hydropower Engineering, chapter 2
- [Francis turbine velocity triangles and power](https://www.bctengineer.com/question.md?key=semester_5%2Ffluid_machines%3Afrancis-turbine-numerical) — Fluid Machines, chapter 3
- [Short note: Pumped storage hydropower](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Apumped-storage-hydropower) — Energy Environment and Society, chapter 5