What is the use of turning gear main motor and piggy motor in steam turbine?

The turning gear main motor and piggy motor in a steam turbine are used for maintaining the turbine's rotation during startup and shutdown phases. The turning gear main motor provides slow rotation of the turbine shaft to ensure proper lubrication and prevent thermal stress on the components. The piggy motor, often a smaller auxiliary motor, assists in this process by allowing for fine adjustments or providing additional support during low-speed operations. Together, they help maintain the integrity and longevity of the turbine system.