In the realm of steam turbine operations, maintaining smooth, efficient performance is crucial for reliability and productivity. However, one of the key challenges that engineers constantly contend with is vibrations. These subtle yet significant movements can impact everything from performance efficiency to maintenance costs. In this blog, we’ll unravel the primary causes behind steam turbine vibrations. By understanding these factors, we aim to shed light on how engineers mitigate risks and optimize turbine operations in the face of dynamic mechanical forces.
What are steam turbines? How Do They Work?
The most common method of power generation used to generate electricity is the steam turbine. A steam turbine is a machine that uses the pressure of steam to power a moving part inside a machine. The moving part, or blades, spin around a stationary shaft. The moving parts inside the steam turbine turn the shaft, which drives the machine and causes it to generate electricity.
As steam turbines run on steam, the first step is to heat water to a very high temperature. The water is usually heated using fossil fuel, solar heat, or another renewable energy source. The steam from the boiler is then pushed into the steam turbine, which quickly turns the turbine blades, producing mechanical or rotational energy. The steam is then transferred through a cooling tower or through natural cooling in a water source. To restart the process, some steam will be turned back into the water.
Steam turbines have a wide range of applications, although they’re most commonly used to power pumps, compressors, and generators. The rotors of a turbine are driven by the heat generated by boiling water (occasionally with the addition of a solvent), which eventually causes the linked shaft to rotate. A generator is linked to the shaft, which transforms the rotating motion into power.
The Most Common Causes of Steam Turbine Vibrations
A steam turbine is a complicated assembly with many fragile components; any uncontrolled vibration caused by a component might result in system failure and, as a result, a major calamity. As a result, determining the cause and severity of vibrations is critical for ensuring optimal operations and safety. The following are the most likely significant causes of vibrations in any thermal power plant’s steam turbine:
Rotor Unbalance in a Steam Turbine
The unbalance of a turbine rotor can be caused by a variety of factors. Uneven mounting, misalignment, or structural inaccuracies could be one of them. The production of local heating zones by friction is another reason for an unbalanced rotor, which might be a likely cause of vibrations in a steam turbine. When the rotor of the turbine touches/strikes the stator, a local hot area is created, causing shaft deformation. It can cause serious damage if left unresolved.
Wearing of Rotating Element
The rotating components of a working steam turbine are subjected to constant static and dynamic loading conditions. Wear, unbalance, and dislocation of the spinning parts might result in unwanted vibrations as a result of this continual loading and high pressure. The quick impact of steam on the turbine rotor can also cause parts to wear out. This effect occurs when the steam turbine is tripped suddenly and without warning. Component wear can result in small amplitude vibrations at first, but this does not always mean that the component will fail. However, if it is not amended for a long time, it will make the situation worse.
Deposition on Blades of the Steam Turbine Rotor
Deposit formation on turbine rotor blades and other components can be influenced by a number of factors. The deformation of turbine blades caused by these adhering deposits causes the blade surface to become rough and uneven. This phenomenon makes it more difficult for steam to flow and causes unwanted vibrations. It is critical to understand that deposits can form when steam is generated using contaminated or impure water. In a fouled condition, a 30MW steam turbine can lose up to 5% of its generating power.
Damage to the journal bearing
Various wear, fatigue, or crushing mechanisms can destroy one of the most sensitive elements of a steam turbine – the journal bearing – during service circumstances. The rotor shaft will be unstable as a result of this damage, which will cause uncontrolled and high amplitude vibrations. The failure of a journal bearing causes the turbine to shut down completely, resulting in a significant loss of power generation. The issue can be prevented by conducting timely investigations into the emergence of cracks in the bearing elements and treating them while they are still in the early stages of development.
Rotor Expansion and Differential Expansion
Differential expansion is the technical name for the measurement of the rotor’s axial thermal growth in relation to the casing. The rotor expansion, on the other hand, is an absolute measurement of the axial thermal development of the rotor in relation to the turbine’s foundation. The vibrations of a thermal power plant’s steam turbine are caused by uneven thermal expansions when the turbine is in the heating zone.
Fluctuations in the Actuator
An actuator and a regulating system are used to keep a turbine shaft rotating at a consistent speed in order to create constant electricity. However, due to a variety of operational difficulties, the steam intake may not always match the load requirements. It creates abrupt jerks and, eventually, turbine vibrations, which must be avoided.
Improper Lubrication
A turbine is made up of several rotating elements. Allowable operations are ensured by proper lubricating oil circulation among turbine components. A lack of lubricating oil can produce friction between components, resulting in unavoidable vibrations and serious damage. It’s important to remember that the International Association of Engineering Insurers reports that oil loss is the leading cause of steam turbine failures around the world.
The steam turbine control system
The steam turbine control system monitors and protects against hazardous situations in the power plant. The system is designed to operate automatically and limit damage in the event of a malfunction. Power plants that use steam turbines are typically much larger than power plants that use other types of engines. The steam turbine control system helps to ensure that the power plant remains operational even if a malfunction occurs. GE and Woodward provide gas and Steam turbine control systems. The GE series includes items like IS200DSPXH2BEB, IS200TRTDH1CCC, IS200VRTDH1DAB etc.
Conclusion
Vibrations are periodic to-and-fro motions of an object around a fixed point. Normal vibrations are present in any component that is subjected to a continual impact. However, when these vibrations begin to build and reach an unfavorable level, they result in permanent failure and, as a result, considerable system damage occur. Multiple reasons might cause needless vibrations in a thermal power plant’s steam turbine. They can be caused by a lack of lubrication, component wear, or dreadful service conditions. The importance of immediately diagnosing and treating such vibrations cannot be overstated. Any carelessness in this area can result in serious consequences and damage.
