Steam Turbine Lube Oil System in Thermal Power Plant

Function of Steam Turbine Lube Oil System in Thermal Power Plant

Lubrication and Cooling of turbine and generator bearings.
Metallic debris flush out from bearings.
Jacking up the shaft and provide hydrostatic lubrication during low speed operation (viz. Turning Gear Operation, Start Up and Shut down)
Supply of Control Oil to Governing and Protection System
Supply of Control Oil to LP Bypass Governing.

Steam Turbine Lube Oil System is equipped with:

AC motor driven Turbine Oil Pump (TOP) or Auxiliary oil Pump
AC motor driven Main Stating oil Pump (MSP)
DC motor driven Emergency Oil Pump (EOP)
AC motor driven Jack Oil Pump (JOP)
DC motor driven Jack Oil Pump (JOP)
Shaft Driven Main Oil Pump (MOP)
Booster Oil Pump (BOP)
Turbine Oil Cooler
Main oil Tank (MOT)
Oil Purification Unit
Overhead oil tank

Start-up Checks

Adequate Lube oil tank level.
Oil temperature in the tank is as per requirement.
Check and confirm that the vacuum of the main oil tank is satisfactory.
Electrical Power supply of all electrical accessories is correct.
Supply air pressure to the instrument and control system is normal.
The entire local indication instrument is calibrated and functioning properly.
Confirm that the turbine oil lube system does not leak oil.
Valve checks
Oil cooler changeover checks

Start-up Procedure

Before Start-up, all the system startup checks are completed.
Start the main oil tank fume extractor and exhaust fan.
When the oil temperature in the oil tank is lower than 20°C, turn off the cooling water of oil cooler and heat the oil to 35°C by electric heater in MOT. When the oil temperature is 35°C then start TOP and operate the oil system for circulation. Due to oil circulation in the pipe line temperature of the oil will increase upto 38°C, then put the oil cooler in service.
When the suction pressure of JOP is adequate then start the JOP and observe the discharge pressure. When the discharge of JOP is adequate then pressurized oil will lift up the journals of each bearing to the design height at each bearing.
Now the turning gear can be operated and unit oil system is ready for start.

Note: The turning gear motor is not allowed to start until the bearing oil supply pressure exceeds the required pressure, JOP oil pressure exceeds the required pressure and overhead tank is filled to required level.

Start the MSP, when the impulse stating speed of the unit is 2000 rpm (May vary as per design) stop the JOP. During the unit speed up, MSP and TOP should operate normally to supply lubricating oil to the unit.
When the turbine speed is 2850 rpm (may vary as per design) then MOP will be in operation. With the rising of turbine main shaft speed MOP starts to deliver oil. The oil supply pump will operate according to the oil flow of MOP so that output oil pressure is low. This low pressure will last till the BOP supplies oil together with the oil supply pump and finally take the place of it.
The operation of the pumps should be monitored during the turbine main shaft rotating speed rises to the rated speed till the final adjustment of the system is completed.
When the unit speed is 3000 rpm (may vary as per design) the system oil pressure is stabilized. Then first stop the MSP and after that stop the TOP.
When the MOP is in service and turbine lube oil system pressure is stabilized then put the system in AUTO MODE (i.e. turn control switch to AUTO for TOP, EOP and MSP).

Turbine Lube Oil System Shutdown Condition

In case of emergency shutdown, the TOP and MSP must start automatically before the turbine decelerates to 2850 rpm (may vary as per design).
JOP starts when turbine decelerates to 2000 rpm (may vary as per design).
In case TOP failure, EOP should be interlocked to ensure safe shutdown.
Stop the JOP and TOP only after the turning gear stops.
After check, stop the turning gear and then stop the JOP and finally stop the TOP.
Confirm that emergency oil pump can start automatically.
STOP the EOP.
Close the oil cooler cooling water inlet and outlet valve.
Stop turbine oil purifier.
If necessary, stop the tank fume extractor.

Overhead Oil Tank

This tank is placed at a height and oil is always filled in this tank. Overhead tank capacity is so designed that during all pump failure it can supply oil to the bearing for 20 to 30 minutes.