Turbine-Generator Lubrication Oil System Function

For large turbine-generators forced lubrication system and water cooling system should be continuously required during the operation of the turbine-generator and during coast down. The main function of lubrication system is to:

Function of Lubrication System:

• Lubrication system reduces the friction between the moving parts and static parts of the turbine generator which can occur at journal bearings and thrust bearings. Efficient lubrication system reduces the wear and tear; increases the efficiency. 
• Lubrication system acts as cooling medium and removes the heat generated at the moving parts due to friction.

Interruption to lubrication system supplying the turbine-generator damages the bearings and the rotating parts due to high friction. When the unit is under shut down condition, it must be continue to rotated (during shutdown condition turbine-generator set is rotated at 1 rpm speed by motor drive system) to assure uniform cooling in order to prevent thermal bowing (eccentricity) of the rotating element.

For a typical power plant Turbine-Generator unit, lubrication motors consists of the following:

1. Shaft-driven main bearing oil pump (MBOP)
2. AC motor-driven turbine bearing oil pump (TBOP)
3. DC emergency bearing oil pump (EBOP)

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Shaft driven main bearing oil pump is mounted on the turbine-generator shaft and delivers lubrication oil for cooling during normal operation of the plant. During plant start up or during plant shutdown condition, shaft driven main bearing oil pump cannot have sufficient pressure to deliver the lubrication oil to the system. Therefore AC motor-driven turbine oil pump provides lubrication oil during start up condition and also during hut down condition. These ac motors are backed with dc emergency bearing oil pump, which is supplied power by station battery and starts immediately when the oil pressure is low. A second backup dc pumps are sometimes provided.