Impulse turbine

Impulse reaction turbine

01. Steam expands completely in the nozzle.

01. Steam expands partially in the moving blades and partially in the fixed blades.

02. Pressure of steam remains constant during its flow through the blade passages.

02. Pressure of steam is not constant during its flow through moving and fixed blade passages.

03. Steam flow over the blades is uniform due to symmetrical blade profile.

03. Steam flow over the blades varies due to aerofoil section (unsymmetrical) blade profile.

04. Due to complete pressure drop in the nozzle, steam velocity and rotor speed are very high, resulting in centrifugal stresses acting on the blades. This may result in blade failure.

04. Since pressure drop occurs partially in the fixed blades, steam velocity and rotor speed are not high. Hence stresses developed are less.

05. The initial and final velocity of steam over the blades is constant or the final relative velocity can never be greater than the initial value, i.e. Vr₁ ≥ Vr₂

05. The initial and final relative velocities over the blades are not constant and the final relative velocity is always greater than the initial relative velocity.

06. As pressure drop in each stage is large, number of stages required is less. Hence turbine is compact.

06. Due to small pressure drop in each stage, it requires large number of stages. Hence size of turbine is bigger.

07. Part load efficiency of turbine is poor.

07. Part time efficiency of the turbine is good due to more efficient blades.

08. Speed of turbine is very high and hence requires compounding.

08. Speed of turbine is low and hence does not require compounding.

09. Turbine is compact and hence occupies less space.

09. Turbine is bigger and hence requires more space.

10. It is installed in small capacity power plants.

10. It is generally used in medium and large capacity power plants.