15 May 2022

Steam Turbine Centering | Turbine Fundamentals and Basics | Basic Aspects of Steam Turbine Maintenance | Part#3 | Content-11 |

CENTERING

Steam Turbine Centering:-
Steam Turbine Centering for Turbine Fundamentals and Basics and Aspects of Steam Turbine Maintenance.
Next activity after the alignment is over, is Centering. Centering means all the Stationery components like Glands, Diaphragms etc. are positioned in such a fashion that any point on its ID is at equal distance from the rotating part that is SHAFT at all positions in their vertical Plane.
Centering is the Radial clearances between the Diaphragms/Casing blades with the Rotor.
Again due to Adjustment in the machine during hot condition and change of the Rotor position due to hydrodynamic Lubrication the stationery components are given some offset during the adjustment of centering in Cold Condition.
Centering readings is carried out on the bottom halves of the Diaphragms and Glands only.

 

Steam Turbine Centering Procedure :
  1. Centering is done by putting a Dummy shaft in place of actual Turbine Rotor. In some sets Piano wire is also used.
  2. The position of the Dummy shaft /Piano wire in the bearings is set such that the seal bore reading is same as with seal bore reading with the actual real rotor.
  3. Three reading are taken in each component at left horizontal , Right Horizontal and bottom Vertical by means of Inside micrometer.
  4. Correction is affected by means of Keys in the Diaphragms/casing.
  5. it is measured by actually lifting ,downing and moving left and right the inner casing w.r.t rotor which is  rotated in the bearings.It is also called as ROLL CHECK .At the moment where  touching/Resistance is   observed  gives  value of  the clearance between casing and rotor. Inner casing movement is affected by  means of  Hydraulic Jacks and Screws. It is a faster means of Centering check.
Steam Turbine Centering Correction : If the reading deviates from design value then the necessary correction is done in the keys as shown in the figure.
Steam Turbine Centering Check List:-

 

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