Steam turbine performance — definition of stage efficiency The “stage efficiency” of a steam turbine stage is defined as the ratio of the work done on the blades per kilogram of steam to the total energy supplied per stage per kilogram of steam. Identify this efficiency.

Introduction / Context:
Turbine performance is expressed through several efficiencies that isolate different loss mechanisms. “Stage efficiency” aggregates the quality of both stationary and moving elements in one stage and is frequently used for preliminary design and performance guarantees.

Given Data / Assumptions:

• Single turbine stage consisting of nozzles (fixed blades) and moving blades.
• Steady flow of steam with measurable inlet and exit states.
• Negligible shaft mechanical losses within the definition of stage efficiency.

Concept / Approach:
Stage efficiency η_stage compares the useful work actually obtained in the rotor (per kg of steam) to the total energy supplied to that stage (per kg). The “total energy supplied per stage” includes the isentropic heat drop available to the stage adjusted by nozzle performance, capturing how effectively the stage converts available enthalpy into rotor work.

Step-by-Step Solution:
Define: η_stage = (work on blades per kg) / (total energy supplied per stage per kg).Distinguish from blading (diagram) efficiency: η_diagram = (work on blades) / (kinetic energy supplied to blades).Distinguish from nozzle efficiency: η_nozzle = (actual KE at nozzle exit) / (ideal isentropic heat drop through nozzle).Mechanical efficiency covers shaft/gear losses and is separate from fluid-dynamic stage losses.

Verification / Alternative check:
When nozzle losses are small and velocity triangles are well-matched, stage and diagram efficiencies converge; significant nozzle losses make η_stage lower than η_diagram.

Why Other Options Are Wrong:
Option A divides by kinetic energy at blade inlet, not by total energy fed to the stage. Option B focuses only on fixed-blade performance. Option D concerns power transmission after fluid work is produced.

Common Pitfalls:
Using stage efficiency to represent the entire turbine including bearings and generator—those belong to mechanical and overall plant efficiencies.

Final Answer:
Stage efficiency