1) FIXED PIONTS (TURBINE EXPANSION)
The fixed points of the turbine are as follows:
a) All the bearing pedestal
b) Middle of the longitudinal girder of Lp turbine
c) The thrust bearing in HP-IP pedestal.
2) CASING EXPANSION
The HP & IP turbines both rest with its lateral on the bearing pedestals at the turbine center line level. The expansion of HP front pedestal and that of IP turbine from HP-IP pedestal towards IP-LP pedestal by casing guides.The casing of the Lp turbine is located axially in the center area of the longitudinal beam by fitted keys cast in the foundation. Free lateral expansion is allowed .The center guides for this casing are recessed in the foundation cross beams. There is no restriction on the axial movement of the casing. When there is a temp difference rise , the outer casing of LP turbine expands from its fixed point. Difference in expansion betn the outer casing and the fixed bearing pedestals are taken up by the bellow expansion joints.
3) ROTOR EXPANSION
Thrust bearing is incorporated in HP-IP pedestals. Seen from this point both the rotor and casing of turbine expands towards the front bearing housing of HP turbine. The rotor and casing of IP and lp turbines expands towards the generator
4 ) DIFFERENTIAL
Differential expansion between rotor and casing results from the difference between the casing expansion and rotor expansion. Maximum diff. expansion of HP-IP turbine occurs at the farthest from the thrust bearing.
Differential expansion between the rotor and casing of LP results from the difference betn the expansion of the shaft assembly (IP+LP rotor) originating from the thrust bearing and the casing expansion which originates from the fixed point on the LP turbine longitudinal beam.