In a steam turbine, a balance piston is not a dummy piston but rather a real and essential component designed to improve the efficiency and performance of the turbine. A balance piston is used in certain types of steam turbines, particularly in reaction turbines, to help maintain axial balance and reduce the axial thrust force on the rotor.
A steam turbine consists of a rotor with blades attached to it. Steam is directed onto these blades, causing them to spin. As the blades turn, they exert a force on the rotor in the axial direction, along the length of the rotor.
Here's how a balance piston works in a steam turbine
Role of Balance Piston:
Steam turbines are designed to convert the energy of high-pressure steam into mechanical rotational energy, which is then used to generate electricity or perform other mechanical work.
During the operation of a steam turbine, steam enters the turbine blades or buckets and expands, creating a force that drives the rotor in a rotary motion.
However, this expansion of steam also generates an axial thrust force along the length of the rotor. This axial thrust force can be significant, especially in larger turbines.
Purpose of balance piston
To counteract the axial thrust force and prevent excessive axial movement of the rotor, a balance piston is often used.
The balance piston is typically located at the opposite end of the rotor from the steam inlet. It is exposed to the same steam pressure as the turbine's inlet.
The balance piston is attached to the rotor, and its movement is opposed by a set of springs or hydraulic systems.
How balance piston Works:
When high-pressure steam enters the turbine and imparts a force on the rotor blades, it also exerts an equal and opposite force on the balance piston.
This opposing force on the balance piston helps to balance out the axial thrust force generated by the steam expansion on the other side of the rotor.
The balance piston essentially acts as a hydraulic or mechanical counterbalance, minimizing the net axial thrust force on the rotor.
The pressure acting on the dummy piston generates an equal and opposite axial force. This force counterbalances the axial thrust generated by the turbine blades. By adjusting the pressure on the dummy piston, operators can control and balance the axial forces within the turbine.
Why balance piston is required:
By reducing the axial thrust force, the balance piston helps to maintain the stability and longevity of the turbine.
It also reduces the wear and tear on the thrust bearings, which are responsible for supporting the axial load of the rotor.
Overall, the use of a balance piston contributes to the efficient and reliable operation of the steam turbine.
It's important to note that the design and location of balance pistons can vary among different types and manufacturers of steam turbines. While balance pistons are common in reaction turbines, they may not be present in all steam turbine designs.