Identify the incorrect statement about turbines and installation Which of the following statements is wrong?

Introduction / Context:
Turbines are broadly categorized into impulse and reaction types. Installation details (e.g., use and geometry of the draft tube) and suitable head ranges differ between types. Correct classification is crucial for design and operation.

Given Data / Assumptions:

• Impulse turbines (e.g., Pelton) extract energy from jet momentum; reaction turbines (e.g., Francis, Kaplan) operate with pressure change across the runner.
• Draft tubes are associated with reaction turbines to recover kinetic head.

Concept / Approach:
Francis is the quintessential reaction turbine. Reaction turbines typically serve low to medium heads with higher discharges, while Pelton serves high heads with lower discharge. Draft tube diffuser angles are limited (≈5–8° half-angle) to maintain attached flow and good pressure recovery.

Step-by-Step Solution:
Classify Francis: reaction (not impulse).Head/discharge suitability: reaction ⇒ low/medium head, high flow (statement a is acceptable).Draft tube taper limitation: <≈ 8° is standard practice to avoid separation (statement b acceptable).Impulse installation: often above tail water; no draft tube required (statement c acceptable).Therefore statement d is the incorrect one.

Verification / Alternative check:
Standard classifications and manufacturer data sheets confirm Francis/Kaplan as reaction machines.

Why Other Options Are Wrong:
Options a, b, c, and e correctly describe widely accepted practice.

Common Pitfalls:
Assuming “reaction” means only Kaplan; forgetting that Francis spans a broad head range and is still reaction.

Final Answer:
A Francis turbine is an impulse turbine.