🔍 Key Concepts

• Purpose of turbine turning (jacking) gear in large propulsion steam turbines • How uneven heating or cooling can affect a long, heavy rotor (sagging/bowing) • When engineers typically engage the turning gear: during warm‑through, cool‑down, and/or lay‑up

💭 Think About

• Think about what happens to a long steel rotor if one side is hotter than the other while it is not rotating. How does slow rotation help? • Consider whether temperature differences can exist only when warming up, only when cooling down, or during both processes. • Ask yourself: besides starting or stopping, is there any other time the turning gear might be used, and is distortion prevention one of its main purposes?

✅ Before You Answer

• Verify whether thermal distortion (rotor bowing/sagging) can occur during both heating and cooling, not just one of them. • Check if standard engineering practice treats distortion prevention as a primary reason for using the turning gear, or if it is used only for periodic rotation with no concern for distortion. • Eliminate any choice that says the gear is "never used" during a phase where temperature gradients and rotor distortion are clearly possible.