For Parson’s reaction steam turbine, degree of reaction is

Concept:

Degree of reaction 

• The Degree of reaction of a hydraulic turbine is defined as the ratio of change in pressure energy inside the runner per unit weight to the change of total energy inside the runner per unit weight. OR

• Degree of reaction or reaction ratio (R) is defined as the ratio of the static pressure drop/increase in the rotor (moving blade) to the static pressure drop/increase in the stage (both fixed blade and moving blade) or as the ratio of static enthalpy drop in the rotor to the static enthalpy drop in the stage.
• \(Degree\;of\;reaction = \frac{{Enthalpy\;drop\;in\;Rotor}}{{Enthalpy\;drop\;in\;Stage}}\)
• Degree of reaction may also be defined as the ratio of enthalpy drop in the rotor to the enthalpy drop in a stage.
•  i.e. \({\rm{R}} = \frac{{{\rm{Static\;enthalpy\;drop\;or\;rise\;in\;rotor}}}}{{{\rm{Stagnation~enthalpy\;drop\;or\;rise\;in\;stage}}}}\)
• Or, \(\rm R = \frac{{static\;pressure\;drop\;or\;rise\;in\;rotor}}{{stagnation\;pressure\;drop\;or\;rise\;in\;stage}}\)
• In the case of an impulse turbine, there is no change in the enthalpy in the rotor, so the degree of reaction is zero. R = 0.
• And for Parson’s turbine or 50% reaction turbine R = 0.5 and for Hero’s turbine R = 1.