Short Answer:

The types of steam turbines are mainly classified based on how steam expands and acts on the blades. The two main types are Impulse Turbine and Reaction Turbine. In an impulse turbine, steam expands completely in stationary nozzles before striking the blades, while in a reaction turbine, expansion occurs continuously in both stationary and moving blades.

Steam turbines can also be classified based on stages, steam pressure, direction of flow, and shaft arrangement. Each type is designed for specific applications, efficiency requirements, and power outputs. These classifications help in selecting suitable turbines for different power and industrial needs.

Detailed Explanation :

Types of Steam Turbines

A steam turbine can be classified into various types depending on the way steam energy is converted into mechanical energy, the number of stages used, the direction of steam flow, and the pressure conditions. Each type of steam turbine is designed to suit different operational conditions such as power output, speed, and efficiency. The most common and fundamental classification is based on the principle of operation, which includes Impulse Turbines and Reaction Turbines.

Classification Based on Principle of Operation

(a) Impulse Turbine:
In an impulse turbine, the entire pressure drop of steam occurs in the stationary nozzles before it strikes the moving blades. The nozzles convert the steam’s pressure energy into high-velocity kinetic energy jets. These high-speed jets hit the turbine blades, changing their direction and causing the rotor to spin.

Steam expands only in the nozzle.
The moving blades simply deflect the steam flow without any pressure change.
The work is done due to the change in momentum of the steam.

Examples:

De Laval turbine – A single-stage impulse turbine used for small power outputs.
Curtis turbine – A multi-stage impulse turbine that improves efficiency for larger systems.

Advantages of Impulse Turbine:

Simple design and construction.
Easy to maintain and operate.
Suitable for high-speed and high-temperature steam conditions.
Can be built for both small and large power outputs.

Disadvantages of Impulse Turbine:

Lower efficiency compared to reaction turbines for the same conditions.
Requires multiple stages for high power, increasing complexity.

(b) Reaction Turbine:
In a reaction turbine, steam expands both in stationary and moving blades. The pressure continuously decreases as the steam flows through each set of blades. The moving blades are designed like nozzles, and as steam passes through them, it produces both reaction and impulse forces that rotate the rotor.

Steam expands continuously during flow.
Both stationary and moving blades act as nozzles.
Work is done due to the combined effect of impulse and reaction forces.

Example:

Parsons turbine – A common reaction turbine used in modern power plants.

Advantages of Reaction Turbine:

Higher efficiency due to continuous expansion.
Suitable for large power generation and steady operation.
Operates smoothly and quietly.

Disadvantages of Reaction Turbine:

Complex design and higher manufacturing cost.
Requires precise blade alignment and sealing to avoid leakage.

Classification Based on Number of Stages

Single-Stage Turbine: Steam expands completely in one set of nozzles and blades. Used for small power applications like mechanical drives.
Multi-Stage Turbine: Steam expansion takes place in multiple stages to achieve higher efficiency and smoother operation. Used in large power stations.

Classification Based on Steam Pressure

High-Pressure Turbine: Operates at very high inlet pressure, generally above 40 bar. Used in modern power plants.
Medium-Pressure Turbine: Operates between 10 to 40 bar.
Low-Pressure Turbine: Operates below 10 bar, usually as the last stage in multi-stage systems to extract remaining steam energy.

Classification Based on Direction of Steam Flow

Axial Flow Turbine: Steam flows parallel to the turbine shaft. Most modern turbines use this type due to high efficiency and compact design.
Radial Flow Turbine: Steam flows perpendicular or radially toward or away from the turbine shaft. Used in small units and specific applications.

Classification Based on Shaft Arrangement

Single-Flow Turbine: Steam enters at one end and flows through to the other.
Double-Flow Turbine: Steam enters from the middle and flows in opposite directions to balance thrust and improve efficiency.

Classification Based on Exhaust Condition

Condensing Turbine: Steam exhausts into a condenser, where it is converted into water at very low pressure. Used for maximum efficiency in power plants.
Back-Pressure Turbine: Steam exhausts at higher pressure for process heating or industrial use. Common in cogeneration systems.

Conclusion

In conclusion, the types of steam turbines vary based on their design, working principle, and operational conditions. The two main types—Impulse and Reaction turbines—form the foundation for most designs. Impulse turbines are simple and rugged, while reaction turbines are efficient and suitable for high-power applications. Other classifications, such as number of stages, pressure, and flow direction, further define their use in power plants and industries. Understanding these types helps engineers select the right turbine for specific performance and energy requirements.