Energy losses in steam turbines
(i) Residual velocity loss- The steam leaves the turbine with a certain absolute velocity which results in loss of KE. This loss is about 10 to 12% .It can be reduced by multistaging.
(ii) Losses in regulating valves-Due to throttling action in valve , steam pressure drop occurs. Hence steam pressure at entry to turbine is less than the boiler pressure.
(iii) Losses due to friction in nozzle-Friction occurs both in nozzle and turbine blades. In nozzle, nozzle efficiency is considered, whereas in turbines, blade velocity coefficient is taken into account. This loss is about 10%
(iv) Loss due to leakage-The leakage occurs between the shaft, bearings and stationary diaphragms carrying the nozzles in case of impulse turbines. In reaction turbine the leakage occurs at blade tips. This is about 1-2%.
(v) Loss due to mechanical friction-This occurs in bearings and may be reduced by lubrication
(vi) Loss due to wetness of steam-In multistage turbine, condensation occurs at last stage ,so in dragging water particles with steam, some KE of stem is lost
(vii) Radiation loss-As turbines are heavily insulated to reduce the heat loss to surroundings by radiation and so these losses are negligible