LUBE AND JACKING OIL SYSTEM
Description And Function Of Components Of The Lubricating Oil System
‒ Main oil tank
The oil necessary for operation is stored in the main oil tank. The oil
pumps draw the turbine oil from the main oil tank and forward it to where it is
needed. Large solid contaminants in the returning oil are removed by the
strainers in the main oil tank before the oil reaches the suction section of
the main oil tank. Air and oil vapour are drawn out of the main oil tank by the
oil vapour extractor. The main oil tank level is monitored. The turbine oil can
be drained from the main oil tank.
‒ Full-load oil pumps
The full-load oil pumps are submersible pumps, which draw oil directly
from the main oil tank. One full-load oil pump must always be in operation to
supply the lubricating oil system with turbine oil.
‒ Emergency oil pump
The emergency oil pump is a submersible pump, which draws oil directly
from the main oil tank. The turbine oil is forwarded by the emergency oil pump
while bypassing the oil cooler and oil filter in the lubricating oil system
when the full-load oil pumps are unavailable for turbine oil supply due to a
fault in three-phase power supply.
‒ Main oil tank heating
The task of the main oil tank heating is to keep up a minimum oil
temperature while the turbine is at a standstill. This ensures that activation
of turbine oil supply is possible at all times. Otherwise there is the risk of
damages at the mechanical equipment due to excessive viscosity. During turbine
oil supply is in operation, the main oil tank heating is activated if oil
temperature falls below a minimum oil temperature. This assures an adequate
volumetric flow of oil for cooling of the bearings. The main oil tank heating
is manually activated and deactivated in the control room or as a function of
temperature by the Sub loop “Oil Tank Heating”. The Sub loop control “Oil Tank
Heating” is activated by the subgroup control “Turbine Oil Supply” or manually
activated and deactivated in the control room.
‒ Shaft Turning Gear for Gas Turbine.
After the gas turbine has been shut down, the power train (gas turbine
and generator) is rotated at a low speed (e.g., 120rpm) during turning gear
operation. This flow of air forced through the gas turbine by the blading
ensures uniform cooldown of the gas turbine. Distortion of the casing (arching:
caused by passive cooling without sufficient air flow through the engine,
involves more rapid cooling of the lower casing regions) and rotor is
prevented, shaft rotation remains unrestricted and the turbine-generator is
ready for the next start.
The gas turbine remains in turning gear mode until it is restarted.
‒ Lubricating oil throttle valve
The oil pressure in the pressure oil system is reduced by the adjustable
lubricating oil throttle valve to the desired lubricating oil pressure
downstream of the lubricating oil filter.
‒ Oil coolers
One oil cooler is always in operation to remove the heat generated by
the bearings from the turbine oil. The second oil cooler is on standby.
Changeover to the standby oil cooler must be made when the oil cooler in
operation clogs or leaks. The maximum flow rate of the cooling water through
the oil cooler in operation must be maintained for good heat transfer and
preventing deposits in the cooler tubes.
‒ Piping and valves
The turbine oil is supplied to where it is
needed through piping. The dimensions of the oil lines are a function of oil
velocity and the oil pressure during operation. Piping, oil coolers, and oil
filters are equipped with drain valves. Oil coolers and oil filters can be filled and vented. Air and oil vapour is extracted from the return
lines. Sampling valves are provided for taking oil samples.
‒ Lifting Oil System
‒ Process
engineering functions of the lifting oil system.
Supplying the bearings with pressurised lifting oil during shutdown of
the line of shafting or at low turbine generator speed during hydraulic turning
gear operation a hydrostatic lubricating film is built up by the running
lifting oil pump between every shaft
journal and bearing. This film protects against metal-to-metal contact between
the bearing and shaft journal and reduces friction until a hydrodynamic
lubricating film builds up itself at higher circumferential velocity of the
shaft journal and assumes this task. The lifting oil system is not longer in
operation at a speed above approx.(1560 rpm).
Components Of The Lifting Oil System
In addition to piping, valves, and monitoring equipment, the following
equipment, filters, and valves are necessary for operation of the lifting oil
system.
1. Lifting Oil
Pump1
2. lifting oil
pump 2
3. Pressure Relief
Valve Of Lifting Oil Pump
4. Pressure Relief
Valve Of Lifting Oil Pump
5. Filling Valve
For Lifting Oil Pump
6. Filling Valve
For Lifting Oil Pump
7. Isolating Check
Valve
8. Isolating Check
Valve 1
9. Lifting Oil
Filter 1
10. Lifting Oil
Filter 2
11. Double
Multiport Butterfly valve
12. Pressure Relief
Valve
13. Lifting oil
throttle valve upstream of bearing
The Components Of The Lifting Oil System And Their Function Are Described Below:
- Lifting oil pumps
The lifting oil pumps are positive displacement pumps. The pumps draw
turbine oil directly from the main oil tank and forwards it through an oil
filter to the bearings as long as turbine generator speed is less than approx
(1560 rpm). One pump is used as the duty pump, while the other one is in
standby.
-Pressure relief valves
This pressure relief valve is a safety valve which opens when the set
allowable pressure is exceeded (e.g. if the lines downstream of the lifting oil
pump are blocked). With the pressure relief valve open the pump discharges
directly back to the tank which prevents pipe bursts. During initial plant
start up the pressure relief valve is set to the maximum system pressure and
does not therefore open under normal operating conditions.
-Filling valves
The filling valve is arranged downstream of the lube oil filter together
with the filling line and provides a connection to the lifting oil pump to
supply this pump with oil so that it is not started up dry even after extended
downtimes. The filling valve must therefore be opened with the lube oil pumps
running before starting up the lifting oil pumps.
-Duplex lifting oil filter
One filter element of the switchable duplex lifting oil filter is always
in operation for protecting the turbine and generator bearings against solid
contaminants. The differential pressure on the lifting oil filter in operation
is a measure of the filter clogging.
Oil Vapour Extraction System
-Process engineering function of the oil vapour extraction system.
Oil vapour forming, for example, due to turbulent flow of turbine oil in
the bearing pedestals and due to release of entrained air in the oil return
lines and main oil tank is removed by one of the two oil vapour extractors of
the oil vapour extraction system.
The negative pressures above the oil surface in the bearing pedestals,
oil return lines, and main oil tank prevent turbine oil or oil vapour from
escaping into the atmosphere. Accumulation of hydrogen gas in the bearings and
in the main oil tank is also prevented. Accumulation of hydrogen gas cannot
occur with the oil supply deactivated - no oil flows from the generator
bearings through the generator seal oil supply tank to the main oil tank - as
the generator seal oil supply tank and the main oil tank are hydraulically
isolated by a loop. Turbine oil and oil vapour are separated in the oil
separator of the oil vapour extractors so that the air released into the
atmosphere is virtually free of oil. The separated oil is returned to the main
oil tank.
-Major Components of the oil vapour extraction system.
2. Oil vapour
extractor 1
3. Oil vapour
extractor 2
4. Oil separator
5. Make-up air
flap with filter
6. Piping and
valves for the vapour extraction system.
The Components Of The Oil Vapour Extraction
System And Their Function Are Described Below:
-Oil vapour extractors
2x100 %-capacity oil vapour exhausters are provided, of which one runs
as the duty exhauster and the other serves as the standby exhauster. The oil
vapour exhausters are located on the main oil tank. One of the two single-stage
oil vapour extractors, whose characteristic is matched to volumetric flow of
oil-enriched air, must be in operation as long as the generator is filled with
hydrogen. The check valves downstream of the oil vapour extractors prevent the
extractor in operation from drawing in air through the standby extractor.
-Oil separator
Virtually all of the turbine oil in the vapour phase is removed by the
oil separator. Inadequate oil separation is usually caused by excessive
volumetric flow of oil vapour. Consequently, the throttle valves in the oil
vapour extraction lines must not be opened too far and the lid of the main oil
tank must be airtight.
-Make-up air flap with filter
The make-up air flap is used during commissioning to set the required
negative pressure and required volumetric flow for the oil separator. A filter
is arranged ahead of the make-up air flap to prevent any contamination in the
ambient air from ingression the oil separator.
-Safety valves
The safety valves for the oil separator and the main oil tank protect
against excessive negative pressure and open upon violation of the maximum
value stipulated for negative pressure, as set using the make-up air flap.
These safety valves do not open under normal operating conditions.
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