The Restoration of Main Turbine Barring Gear Stoppage Issue in Thermal Power Station

Barring gear (or "turning gear") is the mechanism providing to rotate the Turbine Generator shaft at a very low speed after unit stoppages. Once the unit is "tripped" (i.e., the steam inlet valve is closing), the turbine coasts down from 3000 rpm to Barring Gear speed of 75-80 rpm and runs at Barring Gear speed until next rolling or towards standstill after sufficient cooling of Turbine casing. There are two cases of particularly which this condition must be filled. However it is always true that turbine should be on barring gear. CASE 1: COLD START (TURBINE STARTING IN COLD CONDITION) Rotor is big enough in length and is supported at two bearings at extreme ends. It acts like simply supported beam. Rotor is bound to sag in this condition and if it is rolled at higher rpm in this condition, turbine will encounter with high vibration. To remove this sagging it is must that turbine must be on barring gear before rolling that too at least 8 hours.