Which component provides mounting for the 2nd, 3rd, and 4th stage in the turbine section?

Which component provides mounting for the 2nd, 3rd, and 4th stage in the turbine section?

• A. Turbine main casing
• B. Exhaust frame
• C. Inlet plenum
• D. Bearing housing

Answer: (A)

In a multi‑stage turbine, the stages are mounted to a rigid structure that provides alignment and support for the rotor disks and the stator vanes. The turbine main casing serves this role, acting as the primary mounting frame for the later stages (2nd, 3rd, and 4th). It encloses the turbine, provides the bolt patterns and interfaces to secure each stage assembly, and helps keep axial and radial alignment correct as steam or gas flows through the successive stages. The other components have different functions: the exhaust frame relates to the exit path, the inlet plenum handles upstream air delivery, and the bearing housing contains the bearings supporting the rotor rather than mounting the turbine stages themselves.

In a multi‑stage turbine, the stages are mounted to a rigid structure that provides alignment and support for the rotor disks and the stator vanes. The turbine main casing serves this role, acting as the primary mounting frame for the later stages (2nd, 3rd, and 4th). It encloses the turbine, provides the bolt patterns and interfaces to secure each stage assembly, and helps keep axial and radial alignment correct as steam or gas flows through the successive stages. The other components have different functions: the exhaust frame relates to the exit path, the inlet plenum handles upstream air delivery, and the bearing housing contains the bearings supporting the rotor rather than mounting the turbine stages themselves.