Electrification
Steam turbines

The efficiency of steam prime movers in converting the heat energy of fuel into mechanical work was a critical factor in the economic operation of steam central generating stations. Early projects used reciprocating steam engines, operating at relatively low speeds. The introduction of the steam turbine fundamentally changed the economics of central station operations. Steam turbines could be made in larger ratings than reciprocating engines, and generally had higher efficiency. The speed of steam turbines did not fluctuate cyclically during each revolution. This made parallel operation of AC generators feasible, and improved the stability of rotary converters for production of direct current for traction and industrial uses. Steam turbines ran at higher speed than reciprocating engines, not being limited by the allowable speed of a piston in a cylinder. This made them more compatible with AC generators with only two or four poles; no gearbox or belted speed increaser was needed between the engine and the generator. It was costly and ultimately impossible to provide a belt-drive between a low-speed engine and a high-speed generator in the very large ratings required for central station service.
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