Steam turbines are the most common and versatile prime movers used today. The capabilities and flexibility of operation, as well as the range of power provided is unparalleled in today's power generation and process markets. The components of Steam Turbine are:

• Blades
• Rotors
• Casings
• Seals
• Nozzles.

Steam turbines consist of circularly distributed stationary blades called nozzles which direct steam on to rotating blades or buckets mounted radially on a rotating wheel. In a steam turbine nozzles apply supersonic steam to a curved blade. The blade whips the steam back in the opposite direction, simultaneously allowing the steam to expand a bit. A stationary blade then redirects the steam towards the next blade. The process repeats until the steam is completely expanded. The moving blades are mounted radially on the rotor. The stationary blades are mounted to the case of the turbine. Typically, the blades are short in proportion to the radius of the wheel, and the nozzles are approximately rectangular in cross section.

Several stages of expansions are obtained by using a series of nozzles and buckets, with the exhaust from the buckets of one stage flowing directly into the nozzles of the following stage.

A compact machine can be built economically with ten or more stages for optimum use of high pressure steam and vacuum exhaust by mounting the wheels of a number of stages on a single shaft, and supporting the nozzles of all stages from a continuous housing. Large axial turbines must be operated under such conditions that the exhaust steam does not contain more than 10 to 13% of liquid since condensate droplets could seriously erode the high velocity nozzles and blades. The moisture content of the exhaust is dependent upon the inlet steam pressure/temperature combination. Special moisture removal stages may be incorporated in the design when the steam superheat temperature is limited.