GE Power Systems
MS9001E LUBE OIL SYSTEM These switches are used for alarm and trip functions (header temperature) and a turbine start permissive (minimum tank temperature). To keep the oil above the minimum temperature, tank temperature switches will also cycle the lube oil heaters on and off.
General The lubricating requirements for the gas turbine power plant are furnished by a common forced–feed lubrication system. This lubrication system, complete with tank, pumps, coolers, filters, valves and various control and protection devices, furnishes normal lubrication and absorption of heat rejection load of the gas turbine and generator. Lubricating oil is circulated to the turbine bearings, generator bearings and the accessory gearbox. The lubricating oil is also supplied to the starting means torque converter for use as hydraulic fluid as well as for lubrication. This same fluid is also used as control or trip oil, high pressure hydraulic oil and generator seal oil.
To start the turbine, a maximum oil viscosity of 800 SSU is specified. To assure meeting that requirement, temperature switch 26QN prevents starting the unit unless the oil temperature in the tank is above 16 °C (60°F).
Functional Description
Major components of the lube oil system include:
Lubricant Reservoir and Piping
1. Lube Lube oil rese reservo rvoir ir in the the acces accessor sory y base base The reservoir and sump for the lubrication system is a 12,490 liter (3,300 gallon) tank which is i s fabricated as an integral part of the accessory base. Lubricating oil is pumped from the reservoir to the lube oil header by the accessory gear driven main pump, the ac– power auxiliary pump, or the dc–power emergency pump. Bearing header pressure is regulated to a pressure of 1.7 bar (25 psig) by pressure regulating valve VPR2–1. The header supplies lube oil to the turbine–generator bearings, the accessory gear, the torque convertor and the hydraulic supply system. The trip oil and seal oil systems get their oil supply from the pump discharge header before VPR2–1, but after the coolers and filters. After lubricating the bearings the lubricant flows back through various drain lines to the lube reservoir. reservoir.
2. Main lube lube oil pump pump (shaft (shaft driven driven from from the accesaccessory gear) 3. Auxi Auxilia liary ry lube lube oil oil pump pump 4. Emer Emerge genc ncy y lube lube oil oil pump pump 5. Auxilia Auxiliary ry and and emerg emergenc ency y seal seal oil pump pump 6. Lube Lube oil oil hea heatt exch exchan ange gers rs 7. Lube Lube oil oil filt filter erss 8. Pressu Pressure re relie relieff valve valve VR1–1 VR1–1 in in the main main pump pump discharge header 9. Bearin Bearing g header header pressu pressure re regula regulator tor VPR2– VPR2–1 1 10. Mist eliminator eliminator Refer to the Lube Oil Schematic Piping Diagram.
Whenever possible the lube oil feed piping is contained within the oil tank or the t he drain lines. The oil feed and drain lines to and from the number one bearing are directly connected between the accessory base and the turbine base. The feed and drain lines connecting the accessory base to the rest of the gas turbine–generator exit the reservoir on the aft left side and join the turbine base on the left side just aft of the turbine forward support. There is an oil drain
Assorted lube oil temperatures may be monitored at the primary operator interface of the SPEEDTRONSPE EDTRONIC™ Mark V control system. Thermocouples are mounted in the lube oil bearing header, the drain lines of all the journal bearings, the thrust bearing drain and are also embedded in the bearing metal. There are temperature switches monitoring lube oil header temperature and lube oil tank temperature. A00204
1
MS9001E LUBE OIL SYSTEM
GE Power Systems channel that is fabricated as part of the turbine base. This oil channel runs along the left inside of the turbine compartment and crosses the turbine base at the aft end. This channel serves as the drain line for the number two bearing and receives the drain oil from the number three turbine bearing and the generator bearings. This channel also contains the feed lines to the turbine number two and three bearings and the generator bearings.
motor 88QV and the body of the mist eliminator should be adjusted to maintain 0 to –2” water negative pressure on the lube oil tank with the unit at base load. A lube level gauge and alarm system is mounted on the side of the lube reservoir. This is a hermetically sealed, float–arm operated device. The float mechanism operates a Full/Empty dial gauge and two electric switches, 71QH and 71QL. The two switches activate annunciator circuits to alarm if the liquid level rises above or drops below predetermined levels. The oil level gauge indicates F (Full) or E (Empty) before the alarm is sounded. The “Lube Oil Level High” alarm sounds when the oil level is within 254 mm (10 in.) of the tank top. The “Lube Oil Level Low” alarm sounds when the oil level is less than 432 mm (17 in.) from the tank top.
The oil feed and drain lines to the number three bearing and the generator bearings exit the turbine base through the lateral drain channel on either the left or right side,depending on site layout, and run to a surge tank located midway between the turbine base and generator. The surge tank is the interconnection point between the number three bearing and the generator bearings and the rest of the lube oil system. The external piping is aligned and welded in the field and is supported by pipe stands
Dual parallel shell–and–tube lube oil coolers are used, oil on the shell side and cooling water flowing through a fin–tube U–bundle. There is a transfer valve installed between the two coolers to direct oil flow through either heat exchanger. Only one heat exchanger will be in service at a time; thus cleaning, inspection, and maintenance of the out–of–service heat exchanger can be performed without interrupting oil flow or shutting the gas turbine down. By means of the manually operated worm–driven transfer valve, one heat exchanger is put into service as the other is taken out, without interrupting the oil flow to the main lube oil header. The transfer of operation from one to the other should be accomplished as follows:
Mounted on or supported from the top of the lube oil tank are the ac– and dc–motor driven lube oil pumps, the ac– and dc–motor driven seal oil pump, and various control and protective devices. Extending into the tank from the side are the lube oil heat exchanger assembly and the lube oil filter assembly. Access to the tank for inspection is through various covers on the tank top. The pressure regulating and pressure relief valves are mounted external to the tank for easy access. Two reservoir drain connections are provided on the side near the tank bottom. All drain points are shown on the Package Connection Outline.
1. Open the fill & pressurizing valve and fill the standby heat exchanger until a solid flow of oil can be seen in the flow sight in the heat exchanger vent pipe; this indicates a “filled” condition
The lube oil piping consists mainly of welded fabrications of seamless steel pipe with gaskets used at bolted flanges. The feed lines are 304L stainless steel, while the drain lines are carbon steel. Visual oil flow checks can be made using the flow sights provided in the drain lines. This flow should be checked after each turbine teardown.
2. Operate the transfer valve with a wrench to bring the standby heat exchanger into service 3. Close the fill valve
The lube oil system is vented to atmosphere through a mist eliminator. The mist eliminator separates the oil from the “oil mist” and drains it back to the reservoir. This reduces the amount of oil released into the atmosphere. The throttling valve between suction MS9001E LUBE OIL SYSTEM
The water discharge line from the out–of–service cooler should be open and the water feed line to the out–of–service cooler should be closed; this allows thermal expansion and contraction without allowing flow. 2
A00204
GE Power Systems
Oil Filters
NOTE When servicing a heat exchanger, be sure the cooling water isolation valves to the in–service cooler are open and the water isolation valves for the to–be–serviced cooler are closed.
Main Oil Filters Filtration of the bearing header oil is accomplished by 5–micron, pleated–paper filter elements installed in the pump discharge header downstream of the lube oil heat exchangers. The filter assemblies are mounted in the lube oil tank. Dual parallel filters are used with a transfer valve installed between the fi lters to direct oil flow through either filter and into t he lube oil header. Only one filter will be in service at a time; thus cleaning, inspection, and maintenance of the out–of–service filter can be performed without interrupting oil flow or shutting down the gas turbine. By means of the manually–operated, worm– driven transfer valve, one filter is put into service as the second is taken out. Again, this is done without interrupting the oil flow to the main lube oil header. The transfer of operation from one filter to the other should be accomplished as follows:
Pressure Regulation Two regulating valves are used to control lube oil system pressure. A back–pressure relief valve, VR1, limits the positive displacement main pump discharge header pressure to 6.9 bar (100 psi) and relieves excess oil to the lube reservoir. The lube pressure in the bearing header is maintained at approximately 1.72 bar (25 psi) by the diaphragm– operated regulating valve VPR2–1. The diaphragm valve senses oil pressure in the bearing header and opens to allow more flow. Piped in parallel to VPR–2 is an orifice which permits approximately 85 percent of required system flow. VPR–2 opens as required to maintain header pressure.
1. Open the fill & pressurizing valve and fill the standby filter until a solid flow of oil can be seen in the flow sight in the filter vent pipe. This indicates a “filled” condition. 2. Operate the transfer valve to bring the standby filter into service 3. Close the filler valve
Mist Eliminator
A differential pressure gauge is connected across the filters to indicate when the filter elements need replacement. Filters should be changed annually or when the differential pressure gauge indicates a differential pressure of 1.03 bar (15 psi) or greater. Pressure switch 63QQ–1 is provided to alarm if the differential pressure exceeds 1.03 bar.
The mist eliminator consists of a vessel containing three coalescing filters (“candles”), a motor–driven fan and a bypass valve. Oil is separated from the airstream by the coalescing filters and returned to the main lube oil tank. The fan overcomes the pressure differential caused by the flow through the coalescing filters and maintains a slight negative pressure on the lube oil reservoir. The bypass valve opens to bypass the mist eliminator should the motor or fan fail; this prevents the tank from being pressurized in the event of such a failure. The fan should be throttled to provide zero to –2 inches of water pressure in the tank. A00204
Lubricating Oil Pumps Lubrication to the bearing header is supplied by three lube pumps: 1. The main lube oil pump is a positive displacement pump mounted on and driven by the accessory gear. It is a “piggy–back” design, two 3
MS9001E LUBE OIL SYSTEM
GE Power Systems pumps using the same drive shaft. It is rated at 2725 lpm (720 gpm), 7.0 kg/cm 2 (100 psig).
ter the unit is shutdown until the cooldown cycle has been switched off. The cooldown cycle cannot be switched off until fourteen hours after shutdown.
2. The auxiliary lube oil pump is a submerged centrifugal pump driven by an ac motor and rated at 3218 lpm (850 gpm), 7.9 kg/cm 2 (112 psig). The auxiliary pump has a higher rating than the main pump to accommodate the needs of the torque converter during slow–roll and start–up operation.
The orificed check valve between the auxiliary pump discharge and the main pump discharge provides oil flow from the motor operated pumps to the main gear pump to lubricate and prime the main pump at start–up.
Emergency Lube Pump
3. The emergency lube oil pump is a submerged centrifugal pump driven by a dc motor and is rated at 1590 lpm (420 gpm), 1.4 kg/cm 2 (20 psig).
The emergency lube pump is a submerged centrifugal pump driven by a dc motor. This pump is the back–up to the auxiliary pump. If pressure switches 63QT–2A and 2B sense a drop in lube oil header pressure below 0.55 bar (8 psi), the emergency lube oil pump will be started and the unit will trip on low lube oil pressure. Pressure switch 63QL–1 acts as a back–up to 63QT–2A and 2B, activating the emergency lube oil pump if header pressure drops below 0.41 bar (6 psi). The contacts of switches 63QT–2A and –2B are hard–wired to both the turbine control panel and the emergency lube oil pump motor–starter circuitry and will alarm and start the pump if activated. The contacts of pressure switch 63QL–1 are hard–wired in the motor–starter circuitry for the emergency lube oil pump and have no alarm capability. 63QL–1 should start the pump on low lube oil pressure if for some reason 63QT–2A and –2B do not. Switches 63QT–2A and 2B are located at the aft end of the generator and switch 63QL is located at the gauge cabinet in the accessory compartment.
Main Lube Pump The main lube pump is mounted on the aft side of the lower casing of the accessory gear. It is driven by a splined quill shaft from the lower drive gear and provides lube oil during turbine full speed operation.
Auxiliary Lube Pump The auxiliary lube pump is a submerged centrifugal pump driven by an ac motor. It provides lube oil during startup and shutdown of the gas turbine, periods when the main pump cannot supply sufficient pressure for safe operation. When the turbine attains 95% rated speed during start–up, the auxiliary pump is stopped. Similarly, the auxiliary pump starts when unit speed drops below 14HS during shutdown. It also provides back–up to the main lube oil pump; if pressure switch 63QA–1 senses a drop in pump discharge header pressure to below 4.83 bar (70 psi) when the unit is above 95% rated speed, the auxiliary lube oil pump is activated.
Should the auxiliary pump fail during a normal shutdown sequence, the emergency lube pump will be started automatically by the action of low lube oil pressure switch 63QL–1 and continue to run until the turbine shaft comes to rest.
The auxiliary lube oil pump also supplies the oil pressure that drives the torque convertor during turbine cooldown. To prevent rotor bow after a hot shutdown, the torque converter maintains the rotor at a slow roll speed of approximately 3.0% of rated speed. During this time the auxiliary pump supplies oil to the bearings of the turbine–generator and drives, lubricates and cools the torque converter. The auxiliary lube oil pump will continue to run afMS9001E LUBE OIL SYSTEM
Seal Oil Pump The seal oil to the generator bearings is normally supplied by the main lubricating system through a separate line directly to the seal oil control unit of the generator. This line is plumbed into the system upstream of pressure regulating valve VPR2–1. The seal oil control unit will regulate the seal oil pressure 4
A00204
GE Power Systems to maintain it a nominal 0.32 kg/cm 2 (4.5 psi) above the hydrogen gas pressure. There are two seal oil pumps backing up the main lubricating system, one ac–powered and one dc–powered. In the event of low lube system pressure or lube system shutdown for service, the seal oil pump supplies the pressure required to seal in the generator hydrogen. Check valves prevent oil supplied to the generator bearing seal line by one source from feeding back into the inactive source.
lubricant to the bearings exceed 79.4 °C (175°F). Temperature switch 26QA–1, also located in the bearing header, will cause an alarm before this limit is reached. Switch 26QA–1 is set at 73.9 °C (165°F). Differential pressure switch 63QQ–1 will cause an alarm at a differential pressure across the oil filters of 1.03 bar (15 psi). The SPEEDTRONIC Mark V Control System requires that before the unit is tripped on low lube oil pressure, both trip switches 63QT–2A and 63QT–2B must indicate low pressure or either of the trip switches and low pressure alarm switch 63QA–1 must indicate low pressure. Similarly, before the unit is tripped on high lube oil header temperature, both trip temperature switches 26QT–1A and 26QT–1B must indicate high temperature, or either of the trip switches and temperature alarm switch 26QA–1 must indicate high temperature. This ‘voting logic’ prevents a trip due to a malfunctioning sensor.
The seal oil pump is driven by two motors (one ac and one dc) mounted in tandem. If ac power is available, the pump is driven by the ac motor, 88QS–1. If ac power is unavailable, the pump is driven by the dc motor 88ES–1. If the auxiliary lube oil pump is on or if the unit is above 50% rated speed, and pressure switch 63SA–1 senses low seal oil differential pressure, the ac motor will start. The dc motor is activated by either a low lube oil pressure signal from the bearing header (63QA–1) or by the undervoltage relay (27MC–2) in the Motor Control Center.
Test Valve – Low Lube Oil Pressure Auxiliary Pump Start
Pressure and Temperature Protective Devices
A test valve mounted on the gauge cabinet provides the means of checking automatic startup of the auxiliary lube pump and pressure switch 63QA–1 while the unit is operating normally on the main lube pump.
The condition of dangerously low lubricating oil pressure is detected by pressure switches that close after header pressure decreases to a specified value; this condition trips the unit. Pressure switches 63QT–2A and –2B in the lube oil feed piping to the generator bearings trip the turbine if the lubricant pressure drops to 0.55 bar (8.0 psi). Pressure switch 63QA–1 should sense a drop in pump discharge header pressure, turn on the auxiliary lube oil pump and sound an alarm before 63QT–2A and 2B trip the unit. Pressure switch 63QA–1 is set at 4.83 bar (70 psi). Pressure switch 63QL–1 acts as a back–up to 63QT–2A and 2B, activating the emergency lube oil pump if header pressure drops below 0.41 bar (6 psi).
A spring–loaded normally–open isolation valve is used to isolate the test valve and switch. The test valve is installed in the piping parallel to the switch and is normally closed, holding lube system pressure on the switch. When performing a test, the isolation valve should be held closed and the test valve should be opened gradually to lower the lube oil pressure in the switch piping. When the oil pressure falls to the setting of switch 63QA–1, the auxiliary pump should start. Upon closing the test valve and opening the isolation valve, lube pressure is returned to normal and the pump should stop as a result of the restoration of pressure on the 63QA–1 switch.
Likewise, temperature switches 26QT–1A and 1B are installed in the lubricating oil header piping and cause the unit to trip should the temperature of the A00204
5
MS9001E LUBE OIL SYSTEM
GE Power Systems and is normally closed, maintaining lubricating system pressure on the switch. When performing a test, the isolation valve should be held closed and the test valve should be opened gradually to lower lubricating system pressure in the piping in which the switch is mounted. When the oil pressure falls to the setting of switch 63QL–1, the emergency pump should start.
Test Valve – Low Lube Oil Pressure Emergency Pump Start A test valve is also used to provide the means of checking the automatic operation of the emergency lube oil pump and pressure switch 63QL–1. This can also be done while the unit is operating normally on the main lube pump.
Upon closing the test valve and opening the isolation valve, lube pressure is returned to normal and the pump should stop as a result of the restoration of pressure on the 63QL–1 switch.
A spring–loaded normally–open isolation valve is used to isolate the test valve and switch. The test valve is installed in the piping parallel to the switch
GE Power Systems Training MS9001E LUBE OIL SYSTEM
6
A00204
