Steam Turbine: Operation, Working Principle, and Advantages

Steam Turbine

Turbines are used to generate electricity all over the world. The use of turbines is growing by the day. Various types of turbines are used depending on the application requirements. A steam turbine is the most common type of turbine and is used to generate cheap electricity all over the world.

What is a Steam Turbine?

A steam turbine is a mechanical device that converts steam’s thermal energy into mechanical work in the form of rotational energy. Because it uses steam as a working fluid, this turbine is known as a steam turbine. Sir Charles A. Parsons invented the first steam turbine in 1884.

Mechanical work is generated in this turbine by the turbine shaft. This shaft is connected to the steam generator, which converts the mechanical power of the shaft into electrical power.

Steam has an advantage over water in that it expands very quickly. The output power is directly proportional to the speed of the steam turbine. As a result, in order to achieve the highest output, the steam turbines must operate at maximum speed. Wheel turbines, unlike steam turbines, cannot rotate at high speeds.

It can maximize efficiency by utilizing the kinetic energy of the steam. These turbines have several advantages over other types of turbines, including the fact that they produce inexpensive electricity and do not pollute the environment. Because of these factors, turbines have supplanted reciprocating engines as prime movers in large power plants. Steam turbines operate on the thermodynamic principle. That is, as the steam expands, the temperature decreases.

Steam Turbine Working Principle

The working principle of a steam turbine is very simple. The Rankine cycle underpins the operation of a steam turbine.

During the operation of a steam turbine, water from an external source (such as a river, sea, or canal) is first transferred into the boiler section via a pump. The water in the bowler is then heated to a very high temperature, allowing it to convert to supersaturated steam.

The boiler’s steam generation varies depending on the combustion heat, flow rate, and heat transfer surface area. The steam produced by the boiler is directed into the turbine area. Actually, after passing the steam through a nozzle, the pressure energy of the steam is converted into K.E in these turbines.

As the steam collides with the rotor blades, dynamic pressure is created on the shaft and rotor blades. As a result, both the shaft and the blade begin to rotate in the same direction. The thermal energy of the steam is converted into rotational energy of the rotor blade as a result of this process, and the rotor begins to rotate. The turbine rotor is connected by a shaft. The shaft begins to rotate after receiving rotational energy from the rotor.

A coil connects a generator known as a steam generator to the shaft. In a magnetic field, the shaft rotates the generator coil. The electricity generates and flows inside the wires as the coil rotates in a magnetic field. The vibration is much lower than with other engines of the same speed due to the simple structure of these turbines.

Components of a Steam Turbine

The steam turbine has the following major parts:

  • Housing
  • Rotor blades
  • Rotor
  • Governer
  • Turning Gears
  • Sentinel Valve
  • Nozzle ring and reversing blade assembly
  • Labyrinth Seal

Housing

All low and high-weight operating loads are supported by the housing. The housing is equipped with a rotor, blades, a governor, and numerous other internal components.It is designed in such a way that the thermal load is minimized. It protects all of the steam turbine’s internal components.

Rotor

The rotor has multiple buckets that rotate in tandem with the rotor. There is a shaft in it. The driven pump is connected to one side of the shaft, and the speed controller and quick speed trip system are connected to the other end of the shaft.It is an important component of a steam turbine because it converts the thermal energy of the steam into mechanical power.

Blades

These blades are used to transfer energy from the rotor to the high-velocity steam. The effectiveness of the turbine is significantly influenced by the design of these blades.

Governor

A steam turbine installs a governor system, a speed-dependent control system. It also goes by the name “Controller.” It employs to regulate the turbine’s speed.By adjusting the steam flow through the turbine, a governor valve is installed to regulate the turbine speed. It is equipped with a steam valve, a counterweight with a spring return, and a servo motor system.This turbine part uses a direct assembly or a magnetic pulse from the gear to record the speed of the turbine shaft.

The steam turbine’s outlet and inlet conditions can change, and the amount of power needed from the pump can alter the turbine’s speed. The governor weights and governor valves are rearranged as a result of the speed variation.

Labyrinth seal

By allowing a small leak, the labyrinth seal can reduce leaks from the high-pressure side to the low-pressure side. The smallest possible distance must exist between the shaft and the labyrinth.

Nozzle ring and reversing blade assembly

The lower inner half of the steam end casing is where the nozzle ring is mounted. Inside the nozzle ring, the nozzle is installed. It directs the steam from the steam chamber to the Curtis stage’s first row of blades. There are two rows of blades on the Curtis stage.

The reversing blade assembly is typically installed between the rows of Curtis stage blades. This unit is connected to the nozzle ring. The primary purpose of the reverse blade assembly is to direct steam away from the Curtis stage’s first row of blades and toward the stage’s second row of blades.

Sentinel Valve

The sentinel valve serves as an alert mechanism. It mounts on top of the turbine outlet end casing, demonstrating an excessively high pressure inside the end case. The sentinel valve releases a small amount of steam into the environment if the casing pressure rises above a specific operating pressure threshold. This valve makes an audible noise while it is leaking. This valve cannot be used as a safety valve.

Turning Gears

Large turbines frequently employ these gears. Throughout the heating and cooling process, this gear gradually rotates the rotor. This is done to maintain the rotor or shaft’s balance and straightness by maintaining a nearly uniform temperature all around it.

Efficiency of Steam Turbines

The size and type of the steam turbine, as well as the temperature and pressure of the steam entering and leaving the steam turbine, all have an impact on its efficiency. Additionally, the steam flow rate affects it. Large thermal power plants are the best candidates for steam turbines. For the purpose of producing electricity, steam turbines of various sizes up to 1.5 GW are available.

How to Enhance the Effectiveness of Steam Turbines

There are many ways to increase the steam turbine’s effectiveness, some of which are listed below:

  • You can also use spill bands to reduce throttling loss.
  • Use of highly effective blades and nozzles can reduce friction losses.
  • The pressure in the exhaust housing can be decreased by using an exhaust air baffle.
  • A trade-off between capital expenditure and the cost of generating steam over the turbine’s lifetime typically determines the specific properties that are used in a given application. So, this is a technique for optimization.
  • Under certain circumstances, the expanded steam is extracted by the turbine in a water heater. Before being transferred to the turbine, this steam is used for water heating after extraction. Compared to a simple Rankine cycle, the loss from the cold source is significantly lower in a water pre-heater system because the energy from the extracted steam is fed back into the system. Additionally, this extraction procedure is completed in stages. According to theory, the quantity of steam extraction stages directly relates to the efficiency of the power plant. The efficiency of the power plant will increase with more steam extraction stages.

Advantages of Steam Turbines

  • A particular type of rotating heat engine that works well for powering generators is this one.
  • Comparing reciprocating engines to a steam power generator, reciprocating engines have a low thermal efficiency.
  • Compared to reciprocating piston engines, the power to weight ratio is extremely high.
  • Contrary to a reciprocating engine, these turbines have low rotating parts.
  • Large thermal power plants are the ideal applications for these turbines. For the purpose of producing electricity, turbines of various sizes up to 1.5 GW are available.
  • Typically, steam has a high enthalpy content. This indicates that steam has a lower mass flow than gas turbines.
  • In particular, steam turbines are more dependable in applications that call for constant high performance.
  • A steam turbine generates electricity at a relatively low cost.

Disadvantages of Steam turbines

  • Its initial cost is high.
  • The efficiency of this turbine is inferior to the reciprocating engine when operating at partial load.
  • It is longer than a reciprocating engine and takes longer to start up than a gas turbine.
  • It responds to changes in energy demand less quickly than the reciprocating engine and gas turbine.

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