Single-stage turbines and speed reduction A single-stage steam turbine is rarely used for large pressure drops because the required wheel speed becomes extremely high, necessitating large reduction gearing. Do you agree with this statement?

Introduction / Context:Large pressure drops create very high nozzle exit velocities. To extract work efficiently in a single stage, blade peripheral speed must be a significant fraction of jet speed, pushing rotor r.p.m. to impractical values and demanding heavy speed-reduction gear trains. Multi-stage compounding resolves this issue.

Given Data / Assumptions:

• High overall pressure ratio across the turbine.
• Single impulse stage with one nozzle row and one moving row.
• Generator speed and mechanical stresses impose limits on allowable rotor speed.

Concept / Approach:For high-efficiency impulse operation, blade speed ratio φ = U/V1 is typically around 0.4–0.5. If V1 is several hundred m/s to over 1000 m/s for large drops, U must also be very large, yielding r.p.m. values incompatible with direct coupling to standard generators. Staging distributes the enthalpy drop, lowering per-stage velocities and enabling practical shaft speeds with better efficiency and reduced exit losses.

Step-by-Step Solution:Relate nozzle speed to required blade speed via φ ≈ 0.4–0.5.Note that single-stage U then implies excessive r.p.m. for typical diameters.Conclude that reduction gearing would need to be large and inefficient; multi-stage designs avoid this.

Verification / Alternative check:Historical Curtis wheels were used to reduce speed but still required multiple velocity steps; modern turbines universally use multistage arrangements for utility service.

Why Other Options Are Wrong:“Disagree” ignores well-established design practice and speed limitations of rotors and generators.

Common Pitfalls:Assuming only electrical frequency drives the choice; mechanical stress and tip-speed limits are equally important.

Final Answer:Agree