All India Civil Engineering (CE) Group

Degree of Reaction
The degree of reaction (R) of a turbine is a measure of how much of the energy conversion occurs in the rotor compared to the stator. A 50 percent degree of reaction indicates that half of the pressure drop occurs in the rotor (moving part) and half in the stationary part of the turbine.
Classification of Turbines by Degree of Reaction
- Pelton Tu... morerbine: R = 0% (Impulse turbine)
- Francis Turbine: R = 45% to 65% (Mixed turbine)
- Kaplan Turbine: R = 70% to 100% (Reaction turbine)
Specific Speed and Degree of Reaction
As the degree of reaction increases, the specific speed of hydraulic turbines tends to decrease. This is because higher degrees of reaction correlate with lower flow velocities in the turbine, influencing the specific speed, which is a function of flow rate and rotational speed.
Specific Speed Calculation
Given Data:
- Velocity at entrance (V) = 10 m/s
- Pressure head (H) = 240 m
- Elevation above tail race (z) = 5 m
- Discharge (Q) = 15 m³/s
- Diameter (D) = 2 m
- Width (b) = 0.28 m
- RPM = 450
- Hydraulic Efficiency (η_h) = 94%
- Overall Efficiency (η_o) = 92%
(i) Specific Speed (Ns):
To calculate specific speed, we use the formula:
Ns = (N * Q^0.5) / H^0.75
Substituting values and solving gives us a specific speed of approximately 83.25.
(ii) Degree of Reaction (R):
Using the formula R = (H_static - H_dynamic) / H_static, we find that the degree of reaction is around 48.71%.
Final Results
- Specific Speed: 83.25
- Degree of Reaction: 48.71%
Thus, the correct option is C: 83.25 and 48%.