8.5 Turning gear
The turbine rotors must be turned continuously throughout the process of warming-through the unit prior to start-up and, in addition, during the cooling process following a shutdown. Rotor and cylinder distortion could occur as a result of uneven heating or cooling if the facility for turning the rotors were not available to provide circulation within the cylinders. Cylinder metal temperatures, specified by the manufacturer, are the normal criteria for allowing a warm turbine to cease barring.
Two independent turning gear facilities are usually provided:
- Hand barring arrangement.
- Electrical turning gear (ETC).