The working principle of steam turbine is very important to be known in the power plant system. Steam turbine is the engine, where the energy of working fluid is used directly to rotate the turbine blades. In the turbine, the working fluid undergoing a process of expansion, namely the pressure drop and flow continuously. The working fluid of steam turbine is steam. Steam turbine classification can be categorized based on steam flow direction, working principle, exit steam and steam pressure.
In general, the steam turbine system consists of several components, such as: compressors, pumps, boilers, combustion chamber, condenser and turbine. Turbine is much in use for power generation, aircraft, in the industry, and others.
Steam turbine is one of machine types that use a method of external combustion engine. The heating of working fluid (steam) is done outside the system. In brief the working principle of steam turbine as follows:
- Steam enters into the turbine through a nozzle. In the nozzle, heat energy from steam is converted into kinetic energy and the steam is expanding. Steam pressure at the exit of nozzle is smaller when compared with at the time of enter into nozzle, but otherwise the velocity of steam out from nozzle is greater than at the time of enter into the nozzle.
- The steam gushing out of the nozzle is directed to the turbine blades with arches shaped and fitted around the wheel turbines. Steam flowing through gaps between the turbine blades is deflected towards following the curve of the turbine blades. The changes in steam velocity raise the force that encourages and then rotate the turbine wheel and shaft.
- If the steam still has velocity when it leaves the turbine blades means that only some of the kinetic energy of steam is taken by the turbine blades which are running. More than one line of blade motion is installed to utilize the remaining kinetic energy when steam leaves the turbine blades.
- Before entering the second line of blade motion, so between the first row and second row blades motion is mounted one line fixed blade (blade guide) that allows you to change the direction of the steam velocity, so steam can enter the second line of blade motion in the right direction.
- The velocity of steam when it leaves the last blade motion should be made as small as possible, so that the available kinetic energy can be utilized as much as possible. Thus the steam turbine efficiency is higher because of energy loss is relatively small.
Therefore the working principle of steam turbine should be well designed to perform highest efficiency and produce small turbine heat rate.