1.6.0 GT 9HA Bearings

General

The 9HA.01 gas turbine unit has two double tilting pad journal bearings which support the gas turbine rotor and two self-equalizing tilting pad thrust bearings to maintain the rotor-to-stator axial position. These bearings are incorporated in the inlet casing and exhaust frame which are supplied oil from the main lubricating oil system.

Lubrication

The main turbine bearings are pressure-lubricated with oil supplied, from the oil reservoir. Oil feed piping where practical, is run within the lube oil drain lines, or drain channels, as a protective measure. In the event of a supply line leak, oil will not be sprayed on nearby equipment, thus eliminating a potential safety hazard.

The oil flows through branch lines to an inlet in each bearing housing. When the oil enters the housing inlet, flows into an annulus around the bearing. From the annulus, the oil flows through machined holes or slots to the bearing rotor interface.

Lubricant Sealing

Oil on the surface of the turbine shaft is prevented from being spun along the shaft by oil seals in each of the bearing housings. These labyrinth seals are assembled at the extremities of the bearing assemblies where oil control is required. A smooth surface is machined on the shaft and the seals are assembled so that only a small clearance exists between the oil seals and the shaft. The oil seals are designed with tandem rows of teeth and an annular space between them. Pressurized sealing air is admitted into this space to prevent lubrication oil reservoir is vented to atmosphere after passing through an oil vapor extractor.

Load Coupling

A rigid, hollow coupling connects the forward compressor rotor shaft to the generator. A bolted flange connection forms the joint at each end of the coupling.

1.5.0 Turbine Section (GE 9HA Details)

Turbine

5.1 Turbine Section

The turbine section is the area in which energy in the form of high temperature pressurized gas, produced by the compressor and combustion sections, is converted to mechanical energy. The 4^th stage axial flow turbine consist of the rotor, casing, exhaust frame, exhaust diffuser, buckets, nozzles and shrouds.

5.2 Turbine Rotor

A) Structure

The turbine rotor assembly consists of the aft turbine shaft, the first-, second-, third-, and fourth-stage turbine wheel assemblies with spacers and turbine buckets.

Concentricity control is achieved with mating rabbets on the turbine wheels, wheel shaft, and spacers. The wheels, spacers and aft shaft are held together with 5 sets of bolts that pass through each of the wheels and mating up with bolting flanges on the shafts and spacers. Selective positioning of rotor members is performed to improve balance the assembly.

B) Wheel Shafts

The aft shaft of the turbine rotor includes the NO.2 bearing journal.

C) Wheel assemblies

Spacers between the first and second, the second and third and between the third and fourth-stage turbine wheels determine the axial position of the individual wheels. These spacers carry the flow path seals. Near flow path seals are attached to the spacers using circumferential dovetails and serve to protect the rotor surface from hot gas path temperatures. The 1-2 spacers forward and aft faces include radial slots for cooling air passages.

Turbine buckets are assembled in the wheels with fir-tree-shaped dovetails that fit into matching cut-outs in the turbine wheel rims. All three turbine stage buckets are precision investment-cast. The shank on these buckets effectively shields the wheel rims and bucket dovetails from the hot gas path temperatures while mechanically damping bucket vibrations. Stage three and four buckets are further aided in damping vibration with interlocking shrouds at the buckets tips. These shrouds increase the turbine efficiency by minimizing tip leakage. Radial teeth located on the bucket shrouds mate with stepped surfaces on the stator hardware create labyrinth seals against gas path leakage around the bucket tips.

The increase in size of the buckets from the first to the fourth stage is necessitated by the pressure reduction resulting from energy conversion in each stage, requiring an increased annulus area to accommodate the gas flow.

D) Cooling

The turbine rotor is cooled to maintain reasonable operating temperatures and, therefore, assure a longer turbine service life. Cooling is accomplished by means of a positive flow of cool air extracted from the compressor and discharged radially outward through a space between turbine wheel and the stator, into the main gas stream. This area is called wheelspace.

E) Wheel space

Each turbine wheel has a forward and aft wheelspace that needs to be purged to prevent the hot gas air path from permeating these cavities. By maintaining these cavities purged, the integrity of the turbine structure will be maintained.

The first-stage forward wheelspace is cooled by compressor discharge air. An inducer at the inner flowpath efficiently pre-swirls the extraction air, which is then passed through holes in the midshaft and 0-stage spacer. Inducer air then flows through the first-stage forward wheelspace and is routed through the first stage bucket, is discharged into the main gas stream aft of the first-stage nozzle.

All other wheelspaces are purges with 10^th stage compressor extraction air (taken form the inner diameter flowpath at stage10), which flows through the rotor bore, up through passages in the turbine wheels, and into the turbine flow path.

5.3 Buckets

Air is introduced into each first-stage and second-stage bucket through a plenum at the base of the bucket dovetail. it flow through precision cast serpentine passages and is introduced into the flow path through a series of cooling holes on the airfoil surface, tip and trailing edge.

Unlike the first-stage buckets, the third-stage buckets are cooled with machined internal air passages that travel the entire length of the foil. This cooling air enters cavity in tip shroud before exiting into the main gas stream. Air is introduced, like the first and second-stage, with a plenum at the base of the bucket dovetail.

The holes in the first, second, and third stage buckets are spaced and sized to obtain optimum bucket cooling while minimizing the compressor extraction air.

The Fourth-stage buckets are not internally air cooled. The tips of these buckets, like third stage buckets, are enclosed with interlocking by tip shrouds that are designed to minimize tip leakage and dampen the mechanical vibration of these long arifoils.

5.4 Near Flow path seals

a. Near flow path seals are installed using dovetail mounting in the 1-2, 2-3, and 3-4 spacer. These replaceable seals provide protect the turbine rotor wheelspaces from hot gas path temperature. Sealing teeth on this part mate with honeycomb attached to the power nozzles to isolate turbine stages.

5.5 Structure

The casing area of the turbine section is composed of six major elements. These are the:

a.       Inner turbine shell

b.      Outer turbine shell

c.       Nozzles

d.      Diaphragms

e.      Shrouds

f.        Exhaust Frame

The Inner turbine shell makes up a portion of the gas path annulus and supports the power nozzle assemblies and shrouds. The inner turbine shell is encased and supported by the outer turbine shell. The outer turbine shell also provides a pressure barrier structural strength to the gas turbine. Cooling air extracted from the compressor flows to static hot gas path components though the outer turbine shell. The inner turbine shell is allowed to ‘float ‘slightly within outer turbine shell for improved performance from bucket tip clearance control. The inner and outer turbine shells are split horizontally to provide access for servicing internal components

The exhaust frame supports the rotor at the aft bearing, makes up the outer wall of the gas-path annulus, and supports the exhaust diffuser. It is split horizontally to facilitate servicing.

           

      Inner Turbine Shell

The inner turbine shell controls the axial and radial positions of the shrouds and nozzles. It determines turbine clearances and the relative positions of the nozzles to the turbine buckets. This positioning is critical to gas turbine performance.

The inner turbine shell is cooled during operation by air flowing from the 8^th and 11^th stage compressor extraction air. After cooling the inner turbine shell, 8^th and 11^th stage air is directed to the third and second-stage nozzles respectively for cooling.

The center-line of the inner turbine shell is aligned to the rotor center-line during assembly and is supported by ledges in the outer turbine shell.

   

       Outer Turbine Shell

The outer turbine shell is bolted to and aft end of the compressor discharge casing. It supports the inner turbine shell, provides structural strength to the gas turbine, makes up the outer pressure boundary, and provides a connection point for compressor extraction piping.

 Nozzles

In the turbine section there are four stages of stationary nozzles which direct the high-velocity flow of the expanded hot combustion gas against the turbine buckets causing the turbine rotor to rotate. Because of the high pressure drop across these nozzles, there are seals at both the inside and the outside diameters to prevent loss of system energy by leakages. Since these nozzles operate in the hot combustion gas flow, they are subjected to thermal stresses in addition to gas pressure loading.

       First-Stage Nozzle

    The first-nozzle receives the hot combustion gases from the combustion system via the transition pieces. The transition pieces are sealed to both the outer and inner sidewalls on the entrance side of the nozzle.

      The 9HA.01 gas turbine first-stage nozzle contains a forward and aft cavity in the vane and is cooled by a combination of film, impingement and convection techinques in both the vane and sidewall regions.

      The nozzle segments, each with a single airfoil, are supported at the inner diameter by a horizontally split retaining ring which is supported by the aft end of the compressor discharge casing. They are supported at the outer diameter by the first stage shroud.

    Second-Stage Nozzle

    Air exiting from the first stage buckets is again expanded and redirected against the second-stage turbine buckets by the second-stage nozzle. This nozzle is made of cast segments, each with two airfoil. The male hooks on the entrance and exit sides of the outer sidewall fit into female grooves on the aft side of the first-stage shrouds and on the forward side of the second-stage shrouds to maintain the nozzle concentric with the turbine shell and rotor. This close fitting tongue-and-groove fit between nozzle and shrouds acts as an outside diameter air seal. The second-stage nozzle is cooled with 11^th stage extraction air.

        Third-Stage Nozzle

     The third-stage nozzle receives the hot gases as it leaves the second-stage buckets, increase its velocity by pressure drop, and directs this flow against the third-stage buckets. The nozzle consists of cast segments, each with one airfoil. It is held at the outer sidewall forward and aft sides in grooves in the turbine shrouds in a manner similar to that used on the second-stage nozzle. The third stage nozzle is cooled by 8^th stage compressor extraction air.

       Fourth-Stage Nozzle

      The fourth-stage nozzle receives the hot gas as it leaves the third-stage buckets, increases its velocity by pressure drop, direct this flow against the fourth-stage buckets. The nozzle consists of cast segments, each with three airfoils. It is held at the outer sidewall forward and aft sides in grooves in the turbine shrouds in a manner similar to that used on the second-stage nozzle. The fourth-stage nozzle is uncooled.

    Diaphragm

Attached to the inside diameter of the second third, and fourth –stage nozzle segments are the nozzle diaphragms. These diaphragms deter air leakage past the inner sideall of the nozzles and the turbine rotor The high/low, labyrinth seal teeth are machined into the inside diameter of the diaphragm. They mate with opposing sealing lands on the turbine rotor. Minimal radial clearances between stationary parts (diaphragms and nozzles) and the moving rotor are essential for maintaining low inter-stage leakage, this result in higher turbine efficiency.

   Shrouds

Unlike the compressor blading, the turbine buckets tips do not run directly against an integral machined surface of the casing but against thin walled segments mounted female grooves located in the turbine shell. The shrouds primary function is to provide a cylindrical surface to minimize bucket tip clearance leakage.

The turbine shrouds’ secondary function is to provide a high thermal resistance between the hot gases and the comparatively cool turbine casing. By accomplishing this function, the turbine casing cooling load is drastically reduced, the turbine casing diameter is controlled, the turbine casing roundness is maintained, and important turbine clearances are assured.

The first stage stationary shroud segments are in low pieces. The gas-side inner shrouds is separated from the supporting outer shroud to allow for expansion and contraction and thereby improve low-cycle fatigue life. The inner shroud is cooled b impingement, film, and convection.

He shroud segment are maintained in the circumferential position by radial pins from the inner turbine shell. Joints between shroud segments are sealed by fixable metal seals.

  Exhaust Frame

Gases exhausted from the fourth turbine stage enter the diffuser where velocity is reduced by diffusion and pressure is recovered. The exhaust frame is bolted to the aft end of the turbine casing. Structurally, the frame consists of an outer cylinder and an inner cylinder interconnected by the radial struts. The No. 2 bearing is supported from the inner cylinder.

Exhaust frame radial struts cross the exhaust gas stream. These Struts position the inner cylinder and No. 2 bearing in relation to the outer casing of the gas turbine. The struts must be maintained at a constant temperature in order to control the center position of the rotor in relation to the stator. This temperature stabilization is accomplished by protecting the struts from exhaust gas with an airfoil shaped metal firing that forms an air space around each strut. Off-base blowers provide cooling air flow through the No. 2 bearing tunnel and then to the fourth-stage aft wheelspace and air space of the struts.

Removable trunnions on the sides of the exhaust frame are used with similar trunnions on the inlet casing to lift the gas turbine when it is separated from its base.

The exhaust diffuser located at the aft end of the turbine is bolted to the exhaust frame. At the exit of the diffuser, the gases are directed into the exhaust plenum.

 .

1.3.2-GE 9 HA Compressor and Turbine Design

3.3 Casings of Compressor

The casing area of the compressor section is composed of three major sections. These are the:

·         Inlet casing

·         Compressor casing

·         Compressor discharge casing

These casings, in conjunction with the turbine casing, form the primary structure of the gas turbine. they support the rotor at the bearing points and constitute the outer wall of the gas path annulus. All of these casings are split horizontally to facilitate servicing.

3.3.1 Inlet Casing

The inlet casing is located at the forward end of the gas turbine. its primary function is to uniformly direct air into the compressor. the inlet casing also support the No.1 bearing assembly. The No.1 bearing assembly housing is a separate component assembled into the inner bellmouth. The upper half bearing housing is flanged and bolted to the lower half bearing housing. The inner bellmouth is positioned to the outer bellmouth by nine air foil-shaped radial struts. The struts are cast into the support which is bolted and doweled to this inlet casing.

The inlet casing lower half is equipped with two large integrally cast trunnions which are used to lift the gas turbine.

Variable inlet guide vanes (VIGV) are located at the aft end of the inlet casing and are mechanically positioned, by a control ring and vane arm arrangement connected to an actuator drive and linkage arm assembly. The position of these vanes has a effect on the quantity of compressor inlet air flow.

3.3.2 Compressor Casing

The compressor casing contains the variable stator vane stage 1 through stage 3 and the fixed stator stage 4 through stage 8. Each stage of variable stator vanes is mechanically positioned, by a control ring and vane arm arrangement connected to an actuator drive through a torque tube and linkage arm assembly. The positioned of these vanes has an effect on the quantity and efficiency of the compressor air flow.

The aft end of the compressor casing contains extraction ports to permit removal of 8^th stage compressor air. This bleed air is used for turbine static hardware cooling functions and is also used for pulsation control during start up and shutdown.

3.3.3 Compressor Discharge Casing

The compressor discharge casing (CDC) is the final portion of the compressor section and is the longest single casting. The CDC is situated at the gas turbine midpoint, between the forward and aft supports, and is, in fact, is the keystone of the gas turbine structure. the CDC contains the final compressor stages 9-14, and contains extraction ports to permit removal of 11^th stage compressor air used for turbine static hardware cooling functions.

The CDC and its components form the flow path surfaces of the compressor diffuser, and join the compressor and turbine casings. The CDC also provides support for the combustion casings, transition piece support bracket and the inner support of the first stage turbine nozzle.

The compressor discharge casing consists of two cylinders, one being a continuation of the compressor and the being an inner cylinder that surrounds the compressor rotor. The two cylinders are concentrically positioned by twelve radial struts.

A dual-path diffuser is formed by the tapered annulus between the outer cylinder and inner cylinder of the discharge casing and a third member which splits the compressor flow into two steams. The diffuser converts some of the compressor exit velocity into added static pressure for the combustion air supply.

3.3.4 Blading

The compressor rotor and stator blades are air foil shaped and designed to compress air efficiently at the high blade tip velocities. The blades are attached to the compressor wheels by dovetail arrangements. The dovetails are very precise in size and position to maintain each blade in the desired position and location on the wheel.
The compressor stator blades are air foil shaped and are mounted by similar dovetails into ring segments stage 4 through stage 14 stage 14 and exit guided vane. The ring segments are inserted into circumferential grooves in the casing and are held in place with locking keys. The variable inlet guide vane and variable stator vanes stage 1 through stage 3 are mounted through Trunnion holes in the casing walls and secured with a vane arm and nut assembly.

1.3.1-GE 9 HA Compressor and Turbine Design

Oo

GE 9 HA Compressor and Turbine Design

1.0  Introduction

1.1 General

The 9HA is a single-shaft gas turbine designed for operation as simple cycle unit or in a combined steam and gas turbine cycle. The gas turbine assembly contains six major section or groups

1. Air Inlet
2. Compressor
3. Combustion system
4. Turbine
5.  Exhaust gas system
6.   Support systems

This section briefly describes how the gas turbine operates and the interrelationship of the major components.

1.2 Gas Path Description

The gas path is the path by which gases flow through the gas turbine from the air inlet through the compressor, combustion section and turbine, to the turbine exhaust.

When the turbine starting system is actuated, ambient air is drawn through the air inlet plenum assembly, filtered and compressed in the multi-stage, axial-flow compressor. For pulsation protection during startup, compressor bleed valves are open and the variable inlet guide vanes (VIGV) and variable stator vanes (VSV) are in the closed position. When the high-speed relay actuates, the bleed valves begin operation automatically and VIGV and VSV actuators energize to position the VIGV and VSV for normal Turbine operation. Compressed air from the compressor flows into the e spaces between the outer combustion casing and the combustion liners and enters the combustion zone through metering holes in each of the combustion liners.

Fuel from an off-base source is provided to flow lines each terminating at the primary and secondary fuel nozzles in the end cover of the separate combustion chambers.

Options:

On liquid fuel machines, the fuel s controlled prior to being distributed to the nozzles to provide an equal flow into each liquid fuel distributor valve mounted on each end cover and each liquid fuel line on each secondary nozzle assembly.

On gas-fuel machines the fuel nozzles are the metering orifices which provide the proper flow into the combustion zones in the chambers.

The nozzles introduce the fuel into the combustion zone within each chamber where it mixes with the combustion air and is ignited by one or more of the spark plugs. At the instant when fuel is ignited in the one combustion chamber flame is propagated, through connecting crossfire tubes, to all other combustion chambers where it is detected by four primary flame detectors, each mounted on a flange provided on the combustion casings.

The combustion hot gases flow through the flow sleeves and transition pieces and into the four-stage turbine section. Each stage consists of a row of fixed nozzles and a row of turbine buckets.

In each nozzle row, the kinetic energy of the jet is increased, with an associated pressure drop, which is absorbed as useful work by the turbine rotor buckets, resulting in shaft rotation used to turn the compressor and generator rotor to generate electrical power.

After passing through the fourth-stage buckets, the gases are directed into the exhaust diffuser. The gases then pass into the exhaust plenum and are introduced to atmosphere through the exhaust stack or go to HRSG in combined cycle mode.

2.0 Base and Supports

2.1   Turbine Base

The base that support the gas turbine is a structural steel fabrication of welded steel beams and plate. Its prime function is to provide a support upon which to mount the gas turbine.

Lifting trunnions and support are provided, two on each side of the base in line with the two structural cross members of the base frame. Machines pads on each side on the bottom of the base facilitate its mounting to the site foundation. Two machines pads, atop the base frame are provided for mounting the aft supports

2.2   Turbine Supports

 The 9HA.01 has rigid leg-type supports at the compressor end and supports with top and bottom pivots at the turbine end. The support legs maintain the axial and vertical positions of the turbine, whole two gib keys coupled with the turbine supports legs maintain its lateral position. One gib key is machined o the lower half of with exhaust frame. The other gib key is machined on the lower half of the compressor inlet casing. The key fit into guide block which are welded to the cross beams of the turbine base. The keys are held securely in place in the guide blocks with bolts that bear against the keys on each side. The key-and-block arrangement prevents lateral or rotational movements of the turbine while permitting axial and radial movement resulting from thermal expansion.

3.0 Compressor Section

3.1 General

The axial-flow compressor section consists of the compressor rotor and the compressor casing. Within the compressor casing are the variable inlet guide vanes, the variable stator vanes, the various stages of rotor and stator blading, the exit guide vanes and the compressor exit diffuser.

In the compressor, air is confined to the space between the rotor and stator where it is compressed in stages by a series of alternate rotating (rotor) and stationary (stator) air-foil-shaped blades. The rotor blades supply the force needed to compress the air in each stage and the stator blades guide the air so that it enters the following rotor stage at the proper angle. The compressed air exits through the compressor discharge casing to the combustion chambers. Air is extracted from the compressor for turbine cooling and for pulsation control during startup.

3.2 Rotor

The compressor portion of the gas turbine is an assembly of wheels, a speed ring, a forward stub shaft (FSS), Tie bolts, the compressor rotor blades, and a mid-shaft.

The first three wheels have slots broached around their periphery. The rotor blades and spacers are inserted into these slots and held in axial position by a ring on the forward side of each wheel. Wheels stages 4 through stage 14 have a circumferential position using blade-locks positioned at several circumferential locations on each wheel. The wheels are assembled to each other with mating rabbets for concentricity control and are held together with tie bolts. Selective positioning of the wheels is made during assembly to reduce balance correction. After assembly, the rotor is dynamically balanced.

The FSS is machined to provide the thrust collar, which carries the forward and aft thrust loads. The FSS also provide the journal for the NO. 1 Bearing, the sealing surface for the No.1 bearing Oil seals and the compressor low pressure air seal.

The Mid shaft provides the sealing surface for several high-pressure air seals, locations of balance weight grooves the compressor-to-turbine marriage flange. Axial holes pass through the aft end of the Mid Shaft to supply the first stage bucket cooling air compressor 14^th stage.

1.2.2- 9HA GE Gas Turbine Lubrication Oil System

9 HA GE Gas Turbine Lubrication Oil System

2.4 Heat Exchanger and Filters:

The lubricant oil heat exchangers(LOHX-1 and LOHX-2) connect o the parallel lubricant filters(LF3-1 and LF3-2) This design is provided so that filters not in service can be changed without taking the turbine out of service.

Filter housings and heat exchangers are self-venting. A sight glass is located in the vent line from e filter and heat exchanger. When the heat exhanger and filter housing are full, oil will be visible in this sight glass.

By means of the manually-operated three-way transfer valve, one filter can be put into service as the second is taken out, 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:

1.           Close the drain valve of the filter. Open the filter valve and fill the standby filter until a solid oil flow can be seen in the flow sight in filter vent pipe. This will indicate a “filled” condition.
2.            Operate the transfer valve to bring the standby filter into service.
3.          Close the filler valve.                                                                                                                   

This procedure simultaneously brings the reserve heat exchanger into service.

Note

Only one heat exchanger is intended to be in service at one time. After transfer, the operator must verify that the cooling water isolation butterfly valves to/from the heat exchanger not in service are closed. Do not leave all four cooling water isolation valves open.

2.5 Seal Oil

The seal oil to the generator bearing is normally supplied by the lubricating system by the lubricating system through a separate line directly to the generator in the event of low lube system pressure or lube system shutdown for service one of two seal oil pumps supply the oil required to seal in the generator hydrogen. Under normal circumstances the AC motor driven pump would serve this function however if this AC motor should fail or if AC power is lost the emergency DC motor is activated and drives the seal oil pump in piggyback AC/DC motor configuration separated AC and DC pumps). The AC motor includes a heater to prevent condensation in the motor. The seal oil pumps circulate oil through filter. Differential pressure switch provides a high differential pressure alarm signal across the filter. The filter element should be replaced near or at the alarm set point.

2.6 Optional Devices

Pressure transmitters

The lubrication module may include the following additional pressure transmitters (indication only) when selected by a customer as an option;

1.      Differential pressure transmitters which provide remote monitoring capability of differential pressure across oil filters.

2.       Pressure transmitter which provides remote monitoring capability of bearing header pressure.

3.       Pressure which provides remote monitoring capability of tank oil level.

These transmitters are indication only devices. They do not alarm or trio the machine in case of failure, low pressure, level etc.

Lube Oil Conditioner

The lube oil system may also include a lube oil conditioner when selected by a customer as an option. The lube oil conditioner is a stand-alone, kidney-loop lube oil conditioning skid designed specifically to remove particulate contamination (from 0.2 to 2 microns in size). Particulate contamination in this size range is the precursor to varnish formation and accumulation. The implementation of lube oil condition together with monitoring and maintenance of the lubrication oil additive package will help prevent the formation and accumulation of varnish and therefore varnish related turbine trips due to sticking hydraulic servo valves etc.) The lube oil condition skid is a standalone customer located skid with all function controlled by an onboard PLC there is no interface to MK VI control system.

Oil entering the Lube oil conditioner skid is monitored for temperature via thermocouple LT-LC. The oil then passes through the pump and into the pre-filter which is monitored for pressure by transducer. The oil then passes into the charging/mixing vessel, which is monitored for pressure by a transducer. Next, the oil moves to the final canister, containing the post-filter which is monitored for pressure by transducer. Finally, oil exiting the skid is monitored for pressure by transducer. All of these devices communicate solely with the PLC onboard the Lube Oil Conditioner Skid.

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.