What is the primary function of steam in power generation?

The primary function of steam in power generation is to drive turbines for additional power generation. In steam power plants, water is heated to produce steam, which then expands and moves through turbines. The kinetic energy from this expanding steam is converted into mechanical energy as it moves the turbine blades. This mechanical energy is subsequently transformed into electrical energy by a generator connected to the turbine.

This process is fundamental to the operation of thermal power plants, where the steam's pressure and temperature can be finely controlled to maximize efficiency and output. The other choices do not encapsulate the primary role steam plays: it is not used for cooling the turbines, it serves more as a medium rather than a direct fuel source, and while it does contribute to generating electrical energy, its main purpose is to drive the turbines that ultimately lead to that energy production.