9 HA GE Gas Turbine Lubrication Oil System
1.0 PURPOSE
The lubricating and hydraulic oil, seal oil , lift oil
requirement for gas turbine power plant are furnished by a separate, enclosed,
forced-feed lubrication module. This lubrication module, complete with tanks,
pumps, cooler, filters valves and various control and protection devices,
furnishes oil to the gas turbine bearing generator bearing (absorbing the heat
rejection load), starting means load gear and on dual fuel units the atomizing
air compressor. This module is also used to supply oil for the lift oil system
trip oil system and the hydrogen seals on the generator. Additionally, a
portion of the pressurized fluid is diverted and filtered again for use by
hydraulic control devices as control fluid.
The lubrication system is designed to supply filtered
lubricant at the proper temperature and pressure for the operation of the
turbine and its associated equipment.
1.1 Major System components include:
1.
Lubricant reservoir which serves as a base for
the accessory module.
2.
Two centrifugal pumps each driven by an AC
electrical motor. Each AC motor includes a motor space heater to prevent
condensation in the motor.
3.
Emergency oil pump with DC motor.
4.
Main seal oil pump driven by AC motor includes
motor space heater
5.
Emergency seal oil pump driven by DC motor.
Note, in most instances is ‘piggyback’ AC/DC motor driving one pump. If the
customer has opted to purchase separate AC and DC seal oil pump, then Two pumps
will be there.
6.
Dual lubricating oil heat exchangers in
parallel.
7.
Bearing header pressure regulator
8.
Mist Eliminator with redundant fan/motor and
motor space heaters.
9.
Pressure protection switches. On dual fuel
units, with single atomizing air compressors will have two pressure switches.
10.
Tank temperature thermocouples for pump start
permissive and immersion heater control.
11.
Lube Oil header thermocouples.
12.
Lube oil drain thermocouples.
Note: ‘A/B’ indicates dual element thermocouples.
The lube oil is circulated by a redundant set of AC pumps. A
DC pump is provided in case AC power to the site is interrupted. These pumps
are the first of the auxiliary equipment to be energizes during a startup sequence.
Following shutdown of the units, these pumps continue to ru throughout the
extensive cool down period and are the last of the auxiliary equipment to be
stopped. The lube oil system is self-contained. After lubricating and removing
het from the rotating equipment oil is returned to the lube oil tank. It is
cooled by oil to water heat exchangers as it is pumped from the tank and re
circulated. Various sensing devices are included in the design to ensure
adequate oil level in the tank oil pressure and oil temperature.
Oil tank is indicated by a thermocouples on the side of the
tank. Thermocouples connected to the control panel indicated lube oil
temperature in the bearing header.
Thermocouples in the bearing drains are also wired to the
turbine control panel for monitoring a bearing header oil sampling ports are
located upstream of bearing header pressure regulator VPR2-1
For turbine starting, a maximum oil viscosity of 800 SUS(173
centi stokes) is specified for reliable operation o the control system and for beating
lubricant. Thermocouples prevent turbine startup if the temperature of the
lubricant decrease to a point where oil viscosity exceeds 800 SUS(173 centi
stokes).
2.0 Functional Description
2.1 Lubricant Reservoir and Piping
The oil reservoir is integral with the module. The interior
of the tank is coated with an oil resistant protective coating. The top of the
tank is the base on which component s such as the pumps and heat exchangers are
mounted.
Under normal operating conditions oil is provided to the system
by one of two main ax motor driven centrifugal (PQ1-1 and PQ1-2). The selection
of lead and lag pimps is made by the operator through the turbine control,
system prior to startup. By alternating the lead/lag pump selection the
operating hours can be equalized .Each AC motor includes motor space heaters (23QA-1
and -2) to prevent condensation in the motor. All pumps have a check valve on
the discharge line so that oil does not flow into the tank through a pump,
which is not in service. Tow pressure switches (63QA-1 and -1B) are mounted in
the common header just downstream of the main pumps to ensure proper pump
operation. If either of these senses low pressure, an alarm is sounded and lag
pump is automatically started. If this occurs, the operator must manually shut
off one pump and check that system pressure is stable.
The oil is first pumped through one of the two parallel
exchangers. Each is designed to maintain the oil at the proper bearing
temperature. The maximum allowable bearing header temperature under normal
operating conditions is 160F (71.1C). The oil then flows through one of the two
full flow parallel filters. A three way transfer valve controls selection of
which set of heat exchangers/filter is in use. The lubricant oil filters have
removable filter elements. A differential pressure gauge provides visual
indication of the Differential pressure over the filter. Pressure switches
provide a high differential pressure alarm signal across each filter .Filter element
should be replaced near or at the alarm set point.
Three Taps which are located downstream of the filters,
supply lube oil to the generator bearing seals. Hydraulic/lift oil system and trip
oil system respectively. Pressure regulating valve then controls the oil
pressure to the turbine and generator bearing and the turning gear.
The system is ventilated through a mist eliminator mounted
on top of the lube oil reservoir. A slight negative pressure is maintained in
the system by redundant motor driven fans pulling air through eliminator. This
negative pressure draws sealing air through the gas turbine bearing seals. Each
C motor includes a motor space heater to prevent condensation in the motor. The
motor driven fans have no DC backup motors and are not required to run in the emergency
situation, when the DC pumps has taken over. The fans are set up to run in a
lead/lag configuration and are designed to run one at a time. The selection of
lead and lag fans is made by the operator through the turbine control system
prior to startup. The lag fan takes over whenever the lead fan has failed to
run has been overloaded or if there is insufficient vacuum in the lube oil
reservoir. If the lag fan is started automatically by the control system due to
insufficient tank vacuum level, the lead fan will be automatically shut off.
Pressure switch provides a low differential pressure alarm
signal when there is insufficient vacuum in the lube oil reservoir. A
regulating valve is downstream of each fan and is adjusted to regulated tank
vacuum level.
A level alarm device (float operated) is mounted on the top
or side of the reservoir. The float mechanism operates level switches. The
switches are connected into the alarm circuit of the turbine control panel to
initiate an alarm if the liquid level rises above or falls below the levels
shown on the schematic piping diagram the oil level is visually indicated by a gauge
mounted on the top or side of the tank an oil drain connection is located on
the side of accessory module to drain the reservoir.
2.2 Standby Immersion Heaters
During standby periods, the oil is maintained at a viscosity
proper for turbine start-ip by immersion heaters installed din the oil
reservoir thermocouples control the heaters and maintain fluid temperature to
achieve allowable viscosity if the heaters fail to function and oil reservoir
temperature drops below the pout where oil viscosity exceeds 800SUS,
thermocouples will initiate a low oil temperature alarm and will prevent a
turbine startup while running lube oil header thermocouples constantly monitor
the header oil temperature these thermocouples are hardware voted to the median
temperature and are wired back to control panel and compared to alarm and trip
settings.
2.3 Pressure Protection Devices
Two pressure switches mounted on the main pump discharge
header sense lube oil pressure. If either of these senses low lubricant oil
pressure an alarm is sounded and the lag pump is automatically started pressure
switches in combination with alarm switches, Trip the unit and start the
emergency DC motor-driven pump when they sense low pressure. This will occur if
AC power is lost. For a trip, one of the two switches and one of the two switches
must signal. This voting logic prevents a trip due to a false signal.
The DC emergency pump is designed to provide adequate lube
oil circulation for coast down following a trip once the unit is at rest the dc
pump should only operate a few minutes per hour, in order to remove het but
conserve battery life. If the bearing metal temperature is above 250 F, the DC
pump is run continuously. The emergency pump is sized to clear the trip pressure
switches but will not clear the alarm pressure level. On the dual fuel units
with a single atomizing air compressor a pressure switch is provided at the oil
supply to the air compressor gearbox. Two pressure switches on dual fuel units
with two atomizing air compressor. These pressure switches will alarm if low
pressure is sensed at those points but they will not start the lag pump.
