A turbine is any motor in which a shaft is steadily rotated by the impact of a current of steam, air, water or other fluid directed from jets or nozzles onto the blades of a wheel. A turbine generally consists of a series of curved blades or vanes on a central spindle arranged to rotate. The whole of it is enclosed by a casing fitted with passageways that let the fluid in and out as necessary.
Turbines are primarily classified according to the fluid employed in: water or hydraulic turbines, steam turbines, gas turbines, mercury-vapour turbines and others. According to the principal direction of fluid flow, they are classified into parallel-flow turbines or axial-flow turbines, radial-flow turbines (including the outward and inward-flow types), mixed-flow turbines, and so forth.
If we compare turbines with other prime movers we can see that they require less floor space, lighter foundation, less attention, lower consumption of oil and maintenance cost and excellent regulation. They have extreme overload capacity and great reliability because of their simplicity of construction.