2.2.1 Impulse-type turbine
Invented by Professor Rateau, an impulse turbine converts a proportion of the heat in the steam into velocity in the fixed blades. There is no heat drop and therefore no pressure drop across the moving blades. The mechanical work done in the moving blades is therefore solely due to the loss of a proportion of the velocity gained in the fixed blades.
Figure 1.9 shows a typical impulse-type stage velocity diagram. The relative velocity of the steam leaving the moving blades (W2) is less than the relative velocity of the steam entering the moving blades (W,). This emphasises the point stressed earlier that conversion of kinetic energy to mechanical energy takes place in the moving blades.