LOSSES IN STEAM TURBINES

The various losses in steam turbines and their causes are as follows:

1. Residual Velocity Loss: This loss occurs due to the absolute exit velocity of steam and is equivalent to  where v_a2 is the absolute exit velocity of steam. In a single stage turbine, it may be about 10−12% and can be reduced by using multi-stages.
2. Frictional and Turbulence Loss: Friction loss mainly occurs in nozzles and turbine blades. The nozzle efficiency is used to account the friction loss. The loss due to friction and turbulence is about 10%.
3. Leakage Loss: It occurs at the following points:
   1. Between the turbine shaft and bearings
   2. Between the shaft and stationary diaphragms carrying nozzles, and blade tips
   3. Through the labyrinth glands
   The total leakage loss is about 1−2%.
4. Mechanical Friction Loss: Friction between shaft, bearing, and regulating valves accounts for this loss. It can be reduced by proper lubrication.
5. Wet Steam Loss: The velocity of water particles is less than that of steam; therefore, water particles have to be dragged with the steam causing loss of kinetic energy.
6. Radiation Loss: This is due to much higher temperature of turbine as compared to the surroundings. This loss can be reduced by proper insulation.