The turbine bearings must be lubricated to prevent damage that is caused by wear or increased temperatures.1 It is necessary to lift the turbine generator shaft before starting to turn the shaft. The jacking oil system is used to provide this function.
The purposes of bearing lubrication are as follows:
To provide a hydrodynamic oil wedge between the bearing and the shaft.
To provide an oil flow to maintain the white metal of the bearing below 110 C. The sources of heat inside the bearing include:
Thermal conduction
Friction between the oil film, the journal (portion of the shaft inside the bearing), and the white metal of the bearing
Turbulence within the oil itself
The oil temperature leaving the bearing is normally limited to 71 C. Older units used the same oil for lubrication and turbine control and protection (Fig. 8.1). Modern units use fire-resistant fluid (FRF) with a pressure of 7 to 17.5 Megapascals (MPa) for the turbine control system. Figure 8.2 illustrates the lubrication oil system of a modern unit. A directly driven centrifugal pump delivers oil at 1.1 MPa. The oil from this pump goes through an oil turbine. The oil pressure is reduced across the turbine to 0.3 MPa. The oil turbine drives a booster pump that supplies oil from the main tank to the suction of the centrifugal oil pump. The system is protected against overpressurization by a relief valve mounted on the oil tank. The relief...
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