INFLUENCE OF WETNESS ON EFFICIENCY OF THE FULL SCALE SIZE LOW PRESSURE TURBINES

ABSTRACT Efficiencies of 60Hz full size test turbines were measured in various wet steam conditions to reveal the wetness impact on the performance. We changed the wetness and stage load conditions independently under the condition of constant steam mass flow rate in the low pressure turbine. The test results told that the stage efficiency decreases with the increasing of wetness as many studies showed, furthermore, the stage efficiency decreases more in smaller load conditions than in the design point. In addition, blade length effects were examined by comparing two types of LP turbine to be found that the longer case got more deficits at the same wetness. Some theoretical evaluations were tried and a combination of some simple loss models explained the tendencies above, qualitatively. The evaluation showed that absolute value of mechanical wet loss such as braking loss remained unchanged regardless of load conditions, so in low load condition, ratio of mechanical loss to stage load increased, resulting decrease of stage efficiency. It also showed that increasing wet loss at the longer blade was mainly because higher circumferential velocity caused larger mechanical wet loss such as braking loss. INTRODUCTION The steam in low pressure steam turbines operating in thermal power plants is generally expanded to a vacuum, and the turbine exit operates in wet-steam conditions. In geothermal and nuclear power plants, almost all the turbine stages operate in wet steam because the inlet steam temperature is lower than that of thermal power plants. The wet steam includes variou

Influence of Wetness on Efficiency of the Full Scale Size Low Pressure Turbines

Efficiencies of 60Hz full size test turbines were measured in various wet steam conditions to reveal the wetness impact on the performance. We changed the wetness and stage load conditions independently under the condition of constant steam mass flow rate in the low pressure turbine. The test results told that the stage efficiency decreases with the increasing of wetness as many studies showed, furthermore, the stage efficiency decreases more in smaller load conditions than in the design point. In addition, blade length effects were examined by comparing two types of LP turbine to be found that the longer case got more deficits at the same wetness. Some theoretical evaluations were tried and a combination of some simple loss models explained the tendencies above, qualitatively. The evaluation showed that absolute value of mechanical wet loss such as braking loss remained unchanged regardless of load conditions, so in low load condition, ratio of mechanical loss to stage load increased, resulting decrease of stage efficiency. It also showed that increasing wet loss at the longer blade was mainly because higher circumferential velocity caused larger mechanical wet loss such as braking loss.</jats:p

An Experimental Flow Investigation of Low Pressure Turbine Stages With Various Wet Conditions

Detail flow characteristics of an actual size low pressure steam turbine stages under real operating conditions were examined in this paper. The main purpose of the experimental work was to obtain the radial distribution of the velocity triangles in the wet flow of the large size turbine, so that a series of tests were carried out with various wet conditions. Some particular changes of the flow pattern were observed at the exit of both the stator and the blade rows which would not predicted by steam turbine design tools. A kind of flow coefficient was defined and investigated as well as the steam velocities. With an assumption of the steam wetness distribution along the blade span, a tendency of the flow coefficient was appeared which was similar to previous work [7]. The wetness assumption was qualitatively verified by bore-scope observation of the water concentration on the stator surface and the fog condition of the steam path.</jats:p