To minimize damage from foreign matter and to be less sensitive to performance reduction due to increased leakage caused by packing rubs during operation.

To permit ease of maintenance, all parts are mounted on the high-pressure casing and require no special space around high-pressure turbine.

To reduce distortion and thermal stresses in the first stage region.

To prevent distortion and misalignment and to maintain proper packing clearance.

To maintain proper clearance at the shaft packing.

To handle low pressure steam and large volume flow.

To ensure even material properties and provide for excellent performance of the rotor during starting and loading ramp up/ramp down.

To maintain excellent stability to the low load bearings.

To simplify construction, occupy little space, and offer high load carrying capacity.

To sustain high maintainability.

To ensure high reliability.