A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into rotary motion. Because the turbine generates rotary motion, it is particularly suited to be used to drive an electrical generator about 80% of all electricity generation in the world is by use of steam turbines. Steam turbines are made in a variety of sizes ranging from small 1 hp (0.75 kW) units (rare) used as mechanical drives for pumps, compressors and other shaft driven equipment, to 2,000,000 hp (1,500,000 kW) turbines used to generate electricity.