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
- Double flow self balanced cylinder
- Mutually balanced individual cylinders
- By putting balancing drum in the HP Module
- Having holes in the Discs of the blading
- Reverse flow in individual cylinder after partial Expansion.
- Optimizing Steam Extraction Locations
- 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.