HELIX. Device formed by a series of elements called blades or paddles, which are mounted in a concentric from around an axis, rotating around this axis in the same plane.

HORSEPOWER (hp). Unit of power equal to 735.5 W.

HYDROELECTRIC POWER STATION. Centre for producing electricity by using energy from water power. Water is conducted through a discharge pipe to the station’s machine hall, where, through enormous hydraulic turbine-alternators , it generates electrical energy.