Isentropic efficiency of the steam turbine: The isentropic efficiency of an optimized steam turbine is 90% for an advanced power plant. But, at 2,000 psia the turbine exit steam quality is only 77 percent. Stea… For this example, qb = (1,474.1 – 69.7) + (1,526.5 – 1,248.1) = 1,682.8 Btu/lbm. Thermal Efficiency of Steam Turbine. Such high moisture content can damage low-pressure turbine blades. The reason lies in relatively low steam temperature (6 MPa; 275.6°C). // -->