CONSTRUCTION OF MULTISTAGE TURBINE

Basically there are 3 types of turbines:

1)High pressure turbine

2)Intermediate turbine

3)Low pressure turbine

1) High pressure turbine

  HPT outer casing is a barrel without any axial /radial flanges. This kind of design prevents any mass accumulation and thermal stress.  Also perfect rotational symmetry permits moderate wall thickness of nearly equal strength at all sections. The inner casing is axially split and kinematically supported by outer casing. Because of low differential pressure flanges and connecting bolts are smaller in size. Barrel design facilities flexibility of operation in the form of short start up times and higher rate of load changes even at initial steam conditions.

2) Intermediate turbine

It is of single flow construction .Attached to axially split casing is an inner casing axially split, kinematically supported and carrying the guide blades .The hot reheat steam enters the inner casing through top and bottom of the casing. Arrangement of inner casing confines high inlet steam condition to admission branch of the casing. The joints of the outer casing are subjected to lower pressure/temperature at the exhaust of the inner casing.

3) Low pressure turbine

Double flow LP turbine is of .All shell are axially split and are of rigid welded construction. The inner shell taking the guide blades is attached kinematically in the middle shell. Independent of outer shell, middle shell is supported at four points on longitudinal beams. Three rings carrying the last guide blade rows are also attached to the middle shell.