TURBINE OILING SYSTEM

1.  OIL SUPPLY

A single oil supply line lubricates and cools the bearing, governs the m/c and operates the hydraulic actuators and safety and protective devices.

During start-up & shut-down, aux oil pump supplies the control oil. Once the turbine speed is more than 2850 rpm, the main oil pump (M.O.P) takes over. It draws oil from main tank .The lubricating oil passes through oil cooler, before can be supplied to the bearing (Under emergency, lube oil can be supplied by a DC oil pump).Before the turbine is turned or barred, Jacking oil pump  (2 nos.) supplies high pressure oil to the jack up the TG shaft to prevent boundary lubrication and also supplies high pressure oil to drive the hydraulic motor(turning gear)

2)Turbine lubricating oil system

•  Function:

          1. Provides a supply of oil to journal bearings to give an oil wedge as the shaft rotates.
          2. Maintains the temperature of turbine bearings constant at the required level.
         3. Provides a medium for hydraulically operating the governor gear and controlling the steam 

             admission valves.               
         4. Provides for hydrogen cooled generators a sealing medium to
             prevent hydrogen leaking out along the shaft.   

3)Main components

     1) Main Oil Pump

     2)Auxiliary Oil Pump

     3) Emergency Oil Pump

     4) Jacking Oil Pump

     5) Main Oil Tank (MOT)

     6) Centrifugal

3.1) Main Oil Pump

•  This pump is located at the front bearing pedestal of the HP turbine.
• It is coupled to the turbine rotor through a gear coupling.
• When the turbine is running at a normal speed of 3000rpm, then the desired quantity of oil to the governing systems and the lubrication systems is supplied by this pump.

3.2)Auxiliary Oil Pump

•  Auxiliary Oil Pump can meet the requirements of lubrication system under emergency conditions

• One stage vertical centrifugal pump driven by an A.C. electric
  motor.
• It has radial impeller and volute casing.
•  The pump automatically takes over under interlock action
  whenever the oil pressure in the lubrication system fails below
  certain desired level. 

3.3) Emergency Oil Pump

•  Emergency oil pump has been foreseen by as a back-up
  protection to AC driven standby oil pump.
•  This is a centrifugal pump, driven by DC electric motor.
•  This automatically cuts in whenever there is a failure of AC
  supply at power station

3.4)Jacking Oil Pump:

•  JOP ensures that there is no metal contact between a journal
  and the bearing.
•  Positive displacement pumps that provide high pressure supply
  of oil under strategic journals of the turbo generator and oil lifts
  the shaft slightly.
•  This greatly reduces the static friction and bearing wear.
• The JOP can be stopped after the lubricating oil film is
  established between the shaft and bearings.
•  Pressure produced is 120 bars

3.5) Main oil tank

•  The oil used for lubrication is stored in the Mai Oil Tank.
•  Capacity -20/32 m3.
•  The Main Oil Tank holds the oil inside the tank for a period long
  enough to ensure liberation of air from the oil.
•  Filters are located inside the tank to filter the oil during its
  normal course.
•  The oil tank is supported on a framed structure just below the
  turbine floor at the left hand side of the turbine.

 

CONSTRUCTION OF BEARING NO.1

1) BEARING

The TG unit is mounted on 1 bearing.HPT rotor is mounted on two bearings, a double wedged journal bearing at the front and combined/journal bearing adjacent to front IP rotor coupling. The IP & LP rotors have a journal bearing each at the end of the shaft. The journal bearing of IP & LP rotors are self adjusting tragspiegal bearings. The bearing pedestals are anchored to the foundation and are fixed in position. The HP & IP cylinder rest through their support palms on bearing pedestals’. The axial position of HP cylinder is fixed at the casing guide on the front end of HP-IP pedestal .The expansion of IP cylinder takes from hp-ip pedestal towards generator. The fixed point for the LP outer casing is at the center of the longitudinal girder.

Turbine Bearing Arrangement

1) FIXED PIONTS (TURBINE EXPANSION)

      The fixed points of the turbine are as follows:

      a) All the bearing pedestal

      b) Middle of the longitudinal girder of Lp turbine

      c) The thrust bearing in HP-IP pedestal.

2) CASING EXPANSION

The HP & IP turbines both rest with its lateral on the bearing pedestals at the turbine center line level. The expansion of HP front pedestal and that of IP turbine from HP-IP pedestal towards IP-LP pedestal by casing guides.

The casing of the Lp turbine is located axially in the center area of the longitudinal beam by fitted keys cast in the foundation. Free lateral expansion is allowed .The center guides for this casing are recessed in the foundation cross beams. There is no restriction on the axial movement of the casing. When there is a temp difference rise , the outer casing of LP turbine expands from its fixed point. Difference in expansion betn the outer casing and the fixed bearing pedestals are taken up by the bellow expansion joints.

3)  ROTOR EXPANSION

Thrust bearing is incorporated in HP-IP pedestals. Seen from this point both the rotor and casing of turbine expands towards the front bearing housing of HP turbine. The rotor and casing  of IP and lp turbines expands towards the generator 

4 ) DIFFERENTIAL EXPANSION

Differential expansion between rotor and casing results from the difference between the casing expansion and rotor expansion. Maximum diff. expansion of HP-IP turbine occurs at the farthest from the thrust bearing.

Differential expansion between the rotor and casing of LP results from the difference betn the expansion of the shaft assembly (IP+LP rotor) originating from the thrust bearing and the casing expansion which originates from the fixed point on the LP turbine longitudinal beam.