TOP 22 REASONS BEHIND STEAM TURBINE VIBRATION IN POWER PLANT - ASKPOWERPLANT
TOP 22 REASONS BEHIND TURBINE VIBRATION IN POWER PLANT
TURBINE OPERATION

Heiii power plant engineers how are you I hope all is well today we discussed a very important topic “TOP 22 REASON’S BEHIND STEAM TURBINE VIBRATION IN POWER PLANT “which is related to turbine operation. I suggest that every power plant engineers should know about this. In this topic, I covered all the condition in turbine operation in which the turbine faces the vibration problems.

In the power plant steam turbine is a prime mover and on this prime mover blades and vanes are mounted which help in expansion of steam. So, all these mountings have their individual 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. And this imbalance creates vibrations as the direction of this unbalanced. Here we discussed different reasons which cause the steam turbine vibration.

TOP 22 REASON’S BEHIND STEAM TURBINE VIBRATION IN POWER PLANT

1.Unbalance of the steam turbine rotor

2.Unbalanced of steam turbine rotor parts.

3.Loss parts of steam turbine cylinders

4.Deposited on steam turbine blades

5.Damage of 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 vibration reasons discussed below I hope you understand about it and avoiding such causes in the steam turbine and make steam turbine operation best and efficient. let’s discussed some point which causes the steam turbine vibration

 

VIBRATION DUE TO TURBINE CASING TEMPERATURE FLUCTUATIONS:-

it’s also an important factor which causes turbine vibration. Temperature differences create many casing problems which are direct falls impact on turbine vibration. When the temperature difference during the cold start-up of the steam turbine varies up to a limit casing problem occurred and can causes misalignment in many different ways, mostly related to expansion and contraction due to temperature fluctuations.

If the turbine cylinder has 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 the hot condition it has returned to within curvature limits then rotating blades and stationary diaphragm may rub and causes damage to seals and diaphragm glands due to this rubbing a heavy vibration created in turbine cylinder.

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

VIBRATION DUE TO TURBINE SHAFT RUBBING:-

Due to insufficient clearance between labyrinths or diaphragm disturb the end sealing of the rotor so that rubbing in the labyrinths or diaphragm. This type of conditions comes when the high speed/mass turbine

Rotor comes into the contact of stationary part or surface of the turbine due to a small clearance between the labyrinths or diaphragm glands seals and rotor it’s a high chance metal temperature increased at the point of contact due to friction. Due to rubbing of moving parts of the rotor with the stationary part of the rotor an impress 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 into the steam turbine.

VIBRATION DUE TO UNEVEN COOLING OF STEAM TURBINE ROTOR:-

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

This type of vibration is caused by the insufficient clearance between stationary and rotating parts as well as shaft offset located in its bearing. When the clearance is minimum between stationary or rotating parts of the steam turbine there are very high chances of rubbing along the rotor to cause damage.

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When the stationary and rotating parts come in contact with each other localized heating of the rotor metal take place at the contact point and cause shaft bending. To avoided rotor bending during cooling, the turbine should be remaining on barring gear until the turbine cylinder temperature is below 150 c and the oil temperature is below 75 deg. Celsius

VIBRATION DUE TO UNEVEN WARMING OF TURBINE ROTOR:-

During cold startup of steam turbine it necessary that proper heating of turbine casing, as well as turbine rotor, take place where we put the turbine in rolling mode then we observed that turbine shaft rotating at fixed r.p.m for a couple of minutes that’s time is called hold time during this time turbine stationary and rotating parts are thermally expands and proper warming up of steam turbine rotor or turbine cylinder take place .

In many conditions when their automatically turbine rolling function is not available in that conditions proper heating of internal parts of steam turbine not take place so in that conditions it is high chances of uneven shaft warming caused by rubbing between stationary and rotating parts can causes 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 3000 rpm turbine is up to 0.02 – 0.03 mm in each section. When the turbine of barring gear then it’s a limit is a little bit exceeding up to 0.05mm.

READ MORE ARTICLE RELATED TO TURBINE OPERATION HERE :-

VIBRATION DUE TO MISALIGNMENT OF COUPLING:-

Misalignment of coupling is also an important factor which causes the vibration inside the steam turbine. Whenever the coupling between two shafts or between a shaft and bearing may cause bending in the system. Misalignment between two shafts of an integrated rotor can cause an eccentricity of the mass center of the rotor. This eccentricity created a centrifugal force in the radial direction at high rotational speed causes bending of the rotor.

VIBRATION DUE TO IMPROPER OIL FILM:-

When the turbine shaft rotating inside the journal bearing, the shaft pushed oil from the bottom of the bearing causing the oil films thickness to change. In this conditions, the centerline of the shaft moves up and to one side in the account of shaft movement, the segmented bearing should automatically adjust and the contact surface of the journal bearing remaining 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.

(YOU ARE READING ARTICLE ” TOP 22 REASON’S BEHIND STEAM TURBINE VIBRATION IN POWER PLANT ”  ON OUR WEBSITE WWW.ASKPOWERPLANT.COM)

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 produced vibration inside the turbine whenever out internal parts of steam turbine no proper thermally expanded so that it is high chances of contact rubbing of blade tips on the cylinder walls in reactive stages. Rubbing of blades tips to cylinder wall causes increased vibration to blade bending, usually at the turbine blade root. So whenever we started the turbine during hot conditions play close attention if turbine vibration goes above the limit immediately stop the turbine.

VIBRATION DUE TO BLADE PROFILE CHANGED:-

During the running of the steam turbine, a centrifugal force is applied of the turbine blades so in that cause a tensile force in the blade cross section if the center of mass is not one the radial line of turbine blades bending stress also occurred. 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 is depending upon the steam flow rate, the temperature drops across the blade stages, rotating speed of blades and also blade weight.

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

 

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