Kaplan turbine selection by specific speed (metric system) A Kaplan (axial-flow reaction) turbine is generally preferred for installations having a specific speed in the range of approximately 300 to 1000 r.p.m. (metric specific speed scale). State whether this statement is correct.

Introduction:
Specific speed is a widely used index to match hydraulic turbines to site conditions of head and discharge. Kaplan turbines are axial-flow reaction machines suited to low heads and high discharges, which correspond to higher specific speed values. This question checks recognition of the typical specific speed band for Kaplan selection in the metric system.

Given Data / Assumptions:

• Specific speed in metric form, customarily expressed in r.p.m. with power in kW and head in metres.
• Standard turbine families: Pelton (impulse, high head, low specific speed), Francis (mixed flow, medium specific speed), Kaplan/propeller (axial flow, high specific speed).
• Typical guideline ranges are approximate and may vary slightly by source and manufacturer.

Concept / Approach:
Metric specific speed for turbines is commonly defined as N_s = N*sqrt(P) / H^(5/4). For lower heads H with comparable power P, N_s rises; thus axial-flow turbines occupy the high N_s region. Practical design charts place Kaplan around N_s ≈ 300 to 1000, Francis around ≈ 60 to 300 (overlapping), and Pelton typically ≈ 10 to 60 (single-jet lower, multi-jet higher but still well below Kaplan).

Step-by-Step Solution:

Verification / Alternative check:
Manufacturer catalogues and classic charts consistently show Kaplan at high N_s due to the axial-flow geometry and blade pitch control designed for low-head sites with large discharges. While exact cutoffs differ slightly by text, the band 300–1000 is a standard teaching guideline.

Why Other Options Are Wrong:

• No / below 200 / above 1000: Do not match accepted ranges for Kaplan; below 200 is closer to Francis, and above 1000 is beyond common Kaplan guidelines.
• Applicable to Pelton: Pelton is a low N_s impulse turbine, not axial-flow.

Common Pitfalls:
Confusing specific speed (selection index) with unit speed; mixing metric with imperial definitions; assuming the ranges are exact rather than practical guidelines with overlap between families.

Final Answer: