His power plant engineers, how are you? I hope all is well. Today, we discussed a critical topic: “TOP 22 REASONS BEHIND STEAM TURBINE VIBRATION IN POWER PLANT, “w”ich is related to turbine operation. I suggest that every power plant engineer should know about this. In this topic, I covered all the conditions in turbine operation in which the turbine faces vibration problems.

In the power plant, a steam turbine is a prime mover, and blades and vanes are mounted on this prime mover, which helps expand steam. So, all these mountings have their center of mass now when this center of mass does not lie on the central axis of the shaft, they create an imbalance of centrifugal forces while rotating. This imbalance creates vibrations as the direction of this is unbalanced. Here, we discuss the different reasons for the steam turbine vibration.

TOP 22 REASONS BEHIND STEAM TURBINE VIBRATION IN POWER PLANT

1. Unbalance of the steam turbine rotor

2. Unbalanced steam turbine rotor parts.

3. Loss of parts of steam turbine cylinders

4. Deposited on steam turbine blades

5. Damage to journal bearings

6. Rotor shaft axial shift

7. Differential expansion

8. Excessive vibration due to piping strain

9. System operating parameters

10. Turbine actuator fluctuation

11. Turbine lubrication troubles

12. Turbine foundation troubles

13. Poor alignments of the turbine part

14. Worn/unbalanced coupling to the driven machine

15. Uneven cooling/warming of the steam turbine rotor

16. Poor connection between the turbine casing and the bearing pads on the foundation frame

17. Uneven of oil film

18. Improper installation of turbine blades

19. Casing temperature fluctuation

20. Water in the lube oil lubrication system

21. Lack of lubrication

22 . The improper axial and radial clearance

some of the main turbine vibrations are discussed below. I hope you understand and avoid such causes in the steam turbine and make the operation the best and most efficient. lelet’siscussed some point which causes steam turbine vibration

VIBRATION DUE TO TURBINE CASING TEMPERATURE FLUCTUATIONS:-

It is also an essential factor which causes turbine vibration. Temperature differences create many casing problems that directly impact turbine vibration. When the temperature difference during the cold startup of the sstartupbine varies up to a limit, the casing problem occurs and can cause misalignment in many different ways, primarily related to expansion and contraction due to temperature fluctuations.

Suppose the turbine cylinder has a temperature misbalance caused by insufficient thermal isolation from the casing and weak insulation in other areas of the steam turbine cylinder. Loss of thermal isolation at the connection between joints and pipes to the casing by poor isolation of steam turbine cylinder, usually at the bottom of the steam turbine cylinder.

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When the turbine starts quickly in hot conditions and returns to within curvature limits, the rotating blades and stationary diaphragm may rub, damaging seals and diaphragm glands. This rubbing creates a heavy vibration in the turbine cylinder.

The effect of a rotor’s thermal bending on the casing can also be determined. When the casing top is hotter than the bottom, the casing tends to bend down if the temperature gradient is constant from the top to the bottom and along its lengths. The maximum bending stress occurs mid-casing vertically and between the casing supports horizontally. Due to this effect, the turbine cylinder causes vibration.

VIBRATION DUE TO TURBINE SHAFT RUBBING:-

Insufficient clearance between labyrinths or diaphragms disturbs the end sealing of the rotor, causing rubbing in the labyrinths or diaphragms. This condition occurs when the high-speed/mass turbine is in use.

The rotor comes into contact with the stationary part or surface of the turbine due to a small clearance between the labyrinths or diaphragm glands seals and the rotor. There is a high chance metal temperature increases at the point of contact due to friction. The rubbing of moving parts of the rotor with the stationary part of the rotor impresses a layer of metal on the surface of the rotor. This rubbing can cause elastic deformation of the rotor at the point of impact and temporary rotor shaft bending. The shaft bending will usually cause increased vibration in the steam turbine.

VIBRATION DUE TO UNEVEN COOLING OF STEAM TURBINE ROTOR:-

Whenever we shut down the turbine, uneven cooling of the rotor may be one of the factors that cause vibration in the steam turbine. After unit shutdown, the high-temperature rotor may be bending solely due to the rotor’s mass and the distance between the bearing supports. If it is left in a stationary position to cool, the turbine shaft will get permanent bending in this condition. This effect of a permanent shaft bend caused by uneven cooling immediately appears as high rotor vibration in the next startup.

This type of startup nation is caused by insufficient clearance between stationary and rotating parts and the shaft offset located in the bearing. When the clearance is minimum between stationary or rotating parts of the steam turbine, there is a high chance of rubbing along the rotor and causing damage.

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When the stationary and rotating parts come in contact, localized heating of the rotor metal occurs at the contact point and causes shaft bending. To avoid rotor bending during cooling, the turbine should remain on the barring gear until the cylinder temperature is below 150 c and the oil temperature below 75 deg. Celsius

VIBRATION DUE TO UNEVEN WARMING OF TURBINE ROTOR:-

Proper heating of the turbine casing and rotor is necessary during a steam turbine’s cold startup. We put the turbine in rolling mode and observed that the turbine shaft rotated at a fixed r.p.m. for a couple of minutes. This time is called hold time. During this time, the turbine’s stationary and rotating parts were thermally expanded, and proper warming up of the steam turbine rotor or turbine cylinder took place.

In many conditions when their automatic turbine rolling function is not available in that conditions proper heating of the internal parts of the steam turbine does not take place, so there is a high chance of uneven shaft warming caused by rubbing between stationary and rotating parts, which can cause further bending of the shaft in the same direction of the existing bow and causes additional contact with stationary parts increasing temperatures and therefore causes more bending.

The allowed bending in a 3000 rpm turbine is up to 0.02 – 0.03 mm in each section. When the turbine is barring gear, its limit is slightly exceeding up to 0.05mm.

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VIBRATION DUE TO MISALIGNMENT OF COUPLING:-

Misalignment of coupling is also an essential factor that causes vibration inside the steam turbine. The system may bend whenever the coupling between two shafts or between a shaft and bearing is misaligned. Misalignment between two shafts of an integrated rotor can cause an eccentricity of the mass centre of the rotor. This eccentricity creates a centrifugal force in the radial direction at high rotational speed, bending the rotor.

VIBRATION DUE TO IMPROPER OIL FILM:-

When the turbine shaft rotates inside the journal bearing, the shaft pushes oil from the bottom, causing the oil film thickness to change. In these conditions, the centerline of the shaft moves up and to one side. Regarding shaft movement, the segmented bearing should automatically adjust, and the contact surface of the journal bearing should remain in a good position. If there is too much contact surface, friction will increase on the bearing surface, causing increased rubbing and corrosion of the bearing surface and increased vibration and eccentricity.

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WATCH THIS VIDEO IN HINID ( TOP 22 REASONS BEHIND STEAM TURBINE VIBRATION IN THERMAL POWER PLANT )

VIBRATION DUE TO RUBBING OF BLADES TIPS TO TURBINE CYLINDER WALL:-

This cause is one of the major causes which produces vibration inside the turbine whenever the internal parts of the steam turbine are not properly thermally expanded, so there is a high chance of contact with the rubbing of blade tips on the cylinder walls in reactive stages. Rubbing blade tips to the cylinder wall causes increased vibration to blade bending, usually at the turbine blade root. So whenever we start the turbine during hot conditions, pay close attention. If the turbine vibration exceeds the limit, the turbine should be stopped immediately.

VIBRATION DUE TO BLADE PROFILE CHANGE:-

During the running of the steam turbine, a centrifugal force is applied to the turbine blades to cause a tensile force in the blade cross-section. If the centre of mass is not on, the radial line of turbine blades bending stress also occurs. This bending stress is created in blade joints under the pressure effect in the high-pressure steam flowing through the turbine cylinder. The magnitude of these stresses depends upon the steam flow rate; the temperature drops across the blade stages, the rotating speed of blades, and blade weight.

In those conditions, superheated steam entering the first stage and saturated steam entering the final stage also affect the mechanical properties and corrosion of the blade materials. A small change in blade weight or centre of gravity can cause a rotor imbalance and vibration.

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joginder chauhan

Hi, all power engineers. I am Joginder Chauhan. I am the founder of the website www.askpowerplant.com. I am also a power plant engineer with over ten years of experience in the power sector. During this period, I learned about different power technologies like AFBC, CFBC, TRAVELLING GRATE, PULSATING GREAT, PF BOILER, WHRS, and many more. My motive for this site is to share my power sector knowledge with every person who belongs to this field; on this website, I share information related to boiler operation, boiler maintenance, turbine operation & maintenance, boiler & turbine question answers, D.M plant, and all topic related to power plant sector please join this website for latest updation regarding power plant ………..thanks ( JOGINDER CHAUHAN )

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