1.2.1- 9HA GE Gas Turbine Lubrication Oil System

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.