Axial Shift of Steam Turbine | Turbine Fundamentals and Basics | Basic Aspects of Steam Turbine Maintenance Part#3 | Content-21

Axial Shift of Steam Turbine

• Axial shift on the Rotors comes due to two components
• Direct Pressure Thrust: It is the axial thrust due the diff of the pressure X Area component across the moving stage blading and Discs
• Velocity Component: It is due to diff. of the velocity X Mass component across the moving stage blading.
• Total summation of all the above components leads to the Axial Thrust.

• Axial Thrust is +ve if it is towards generator
• Axial Thrust is -ve if it is towards HPT front
• There are many ways of balancing axial thrust

1. Double flow self balanced cylinder
2. Mutually balanced individual cylinders
3. By putting balancing drum in the HP Module
4. Having holes in the Discs of the blading
5. Reverse flow in individual cylinder after partial Expansion.
6. Optimizing Steam Extraction Locations
7. Sealing fins are also important component of balancing axial thrustThe Residual thrust  is taken care by the Thrust pads.Tripping Limits of Axial shift
   • The Max. + ve axial shift tripping value is just less than the minimum axial gap in the HP Casing which is in its first stage.
   • The Max. – ve axial shift tripping value is just less than the minimum axial gap in the IP Casing which is in its first stage.