Hydro turbines are classified into two types due to their operation.
1. Impulse type
2. Reaction type
1.1 Impulse Turbines
Prior to hitting the turbine blades, the water's potential energy is converted to kinetic energy by a nozzle and focused on the turbine. No pressure change occurs at the turbine blades.
Impulse turbines are most often used in very high head applications.
Ex: Pelton turbine
1.2 Reaction Turbines
Water flows through the runner converting its pressure to mechanical energy of the prime mover as it moves through the runner blades.
Reaction type turbines are use in low and medium head applications.
Ex: Francis, Kaplan