What purpose do barring gears serve on a steam turbine?

Barring gears are crucial components in steam turbines, primarily serving the function of maintaining the rotation of the turbine shaft when it is not in operation, particularly during cool-down periods. When a steam turbine is taken off-line or is in cooling mode, barring gears allow for the slow, controlled rotation of the turbine shaft to prevent thermal shock and to evenly distribute temperature changes throughout the turbine. This gradual cooling helps to avoid unnecessary stress on the components, which could lead to structural damage or deformation.

Furthermore, continual movement of the shaft helps lubricate the bearings and other moving parts, ensuring that they remain in good working condition, thereby extending the life and reliability of the turbine. The operation of barring gears thus plays a vital role in maintaining the integrity of the turbine system as it transitions in temperature and operational states.