The efficiency of the turbine stages, and cycle and unit heat rate, are influenced to a considerable degree by the efficiency with which the thermal potential energy of the steam is converted to kinetic energy and then power in the individual stages (blade rows) of the unit. It is known that the efficiency of the individual stages is a function of the efficiency of the rows comprising it, which are in turn influenced by the individual blade vanes and their arrangement within the unit. Arrangement is important in respect to the spacing of each vane relative to the elements within its own row and also from row to row. Typical stage arrangements for both impulse and reaction stages are shown in chapter 1. However, no detail was given in that chapter quantifying or even indicating their effect on efficiency.

In addition to their form and spatial relationships, the efficiency potential of the vane, which is a three dimensional body, is influenced by other considerations relating to geometric characteristics and the use of stage hardware. These also need to be considered.

The following sections will consider stage geometry and its effect on the efficiency of the rows and, where appropriate, the stage. It must also be recognized that the properties of the steam are fundamental to establishing the absolute efficiency of the stage and therefore the unit.

The various methods published for predicting the efficiency of the steam path rely upon the provision of a basic correction factor...