---
title: "Characteristics of hydro turbines"
subject: "Power Plant Design"
chapter: 3
key: "semester_8/power_plant_design:turbine-types-characteristics"
source: https://www.bctengineer.com/q/semester_8/power_plant_design/turbine-types-characteristics
site: BCT Engineering
---

# Characteristics of hydro turbines

Power Plant Design · Chapter 3: Hydro Power Plant Design

- Asked in: 2079 Jestha, 8 marks
- Video: [Different Types of Water Turbines (Impulse, Reaction, Pelton, Cross-flow, Kaplan & Francis Turbine)](https://www.youtube.com/watch?v=Ac4E0n3knio) — Academic Gain Tutorials
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_8/power_plant_design/turbine-types-characteristics
- Whole chapter: https://www.bctengineer.com/md/semester_8/power_plant_design/chapter-3

## Question

Describe the characteristics of various types of turbines used in hydro electric power stations.

## Short answer

Impulse turbines (Pelton, Turgo, crossflow) convert head to a jet before the runner; reaction turbines (Francis, Kaplan, propeller) run full of water. Pelton suits high heads, has flat efficiency from 20–100% and no draft tube. Francis suits medium heads with high peak efficiency but poor part load. Kaplan suits low heads, has adjustable blades, good part load but high cavitation risk.

## Answer

Hydraulic turbines are of two main kinds: **impulse turbines**, in which the whole pressure head is turned into a free jet before it strikes the runner (Pelton, Turgo, crossflow), and **reaction turbines**, in which the runner is full of water under pressure and both pressure and kinetic energy act on it (Francis, Kaplan, propeller).

#### Pelton turbine (impulse, tangential flow)
- Head: high, about 50–1300 m; small discharge.
- Specific speed: about 10–35 per jet (up to ~60 with multiple jets).
- Water from one or more nozzles strikes double-cup buckets at atmospheric pressure; flow controlled by a spear (needle); a deflector cuts the jet on load rejection.
- Flat efficiency curve: high efficiency from about 20% to 100% load. Maximum efficiency about 90–92%.
- No draft tube; no cavitation in the runner; easy to inspect and repair, tolerant of sediment.

#### Francis turbine (reaction, mixed flow)
- Head: medium, about 10–350 m (most common 30–300 m); medium discharge.
- Specific speed: about 60–300.
- Spiral casing, stay vanes, adjustable guide vanes, runner (radial inflow, axial outflow) and draft tube.
- Highest peak efficiency (about 93–95%) but falls at part load below about 40–50%; vibration and draft tube surges at low load.
- Sensitive to cavitation and sediment erosion; runner setting fixed by Thoma's $\sigma$.

#### Kaplan turbine (reaction, axial flow)
- Head: low, about 2–40 m; large discharge.
- Specific speed: about 300–1000.
- Adjustable runner blades and guide vanes (double regulation) keep efficiency high over a wide load and head range.
- Large size, high speed relative to head; high cavitation risk, so deep setting.
- **Propeller turbine:** same with fixed blades; cheap but poor part-load efficiency.

#### Small-hydro turbines
- **Crossflow (Michell–Banki):** head 3–250 m, simple, cheap, flat efficiency (about 75–85%); used in Nepalese micro-hydro.
- **Turgo:** impulse, head 50–250 m, higher speed than Pelton for the same head.

#### Summary

| Feature | Pelton | Francis | Kaplan |
|---|---|---|---|
| Type | Impulse | Reaction | Reaction |
| Flow direction | Tangential | Radial in, axial out | Axial |
| Head | High | Medium | Low |
| Discharge | Low | Medium | High |
| $N_s$ (kW) | 10–35 | 60–300 | 300–1000 |
| Part-load efficiency | Very good | Poor | Very good |
| Draft tube | No | Yes | Yes |
| Cavitation risk | Low | Medium | High |

## Check yourself

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

1. How does an impulse turbine differ from a reaction turbine?
   A. Impulse has a draft tube; reaction does not
   B. Impulse converts the whole head to a free jet first; reaction runner is full of pressurised water
   C. Impulse is used only at low head
   D. Reaction turbines use a jet at atmospheric pressure
   Answer: B. Pelton, Turgo and crossflow are impulse; Francis, Kaplan and propeller are reaction. (Key point: Impulse vs reaction)

2. Which describes the Pelton turbine?
   A. Low head, high discharge, axial flow
   B. Medium head with adjustable runner blades
   C. High head, low discharge, flat efficiency, no draft tube
   D. Needs deep setting due to cavitation
   Answer: C. Pelton works at 50-1300 m and is tolerant of sediment. (Key point: Pelton)

3. What gives the Kaplan turbine high efficiency over a wide range?
   A. Fixed blades
   B. A spear valve
   C. Tangential flow
   D. Adjustable runner blades and guide vanes (double regulation)
   Answer: D. Double regulation maintains efficiency across load and head. (Key point: Kaplan)

4. Which is true of a Francis turbine?
   A. Highest peak efficiency but poor below 40-50% load
   B. Best at part load
   C. Needs no draft tube
   D. Works at 2-40 m head
   Answer: A. Francis has about 93-95% peak but falls at low load. (Key point: Francis)

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