Why LP turbine rotor expansion is more than casing?

In a low-pressure (LP) turbine, the rotor expansion is greater than the casing due to the design and operational conditions of the turbine. The rotor experiences a significant drop in pressure and temperature as steam expands through the turbine stages, resulting in a larger volumetric increase compared to the casing, which is designed to contain the steam flow with minimal expansion. This difference allows for efficient energy extraction from the steam, optimizing the turbine's performance while maintaining structural integrity in the casing. Overall, the rotor's greater expansion accommodates the dynamic changes in steam properties as it moves through the turbine system.