Steam Turbine

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Steam Turbine AESK Specific

Leelanand Pilanawithana

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Turbine Design Data

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Turbine Design Data

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Steam Turbine – Construction Function

• Drive an AC generator at speed of 3000 rpm

Construction• Outer casing

consists of Front section – HP

Made of cast steel. Rear section – LP and Exhaust

Fabricated (exhaust)Bolted to front section.

Horizontally split Top part rest on front bearing pedestal. Bottom part is bolted to the top part.

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Steam Turbine – Construction Front Section

• Admission section consists of Four steam inlet connections assembled onto the outer casing. Inner casing Inlet insert assemble in outer casing, prevents inlet steam

come into direct contact with outer casing. Angel ring facilitate a flexible link between inlet inserts and

inner casing without steam leak.• Control valve chest ( 2 No)

• Placed beside the turbine and rest on separate foundation.• Consists of

Emergency Stop valve. Main shout off device between steam supply system and

turbine. Control valves (2 No)

Connecting lines were pre-stressed during installation to compensate for thermal stresses at operating temperature

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Front Section ….• Consists of

Bed Plate/Pedestal. Rigidly attached to turbine foundation. Lower part of the bearing housing and the front paw of the

upper part of the outer casings are rested on bearing pedestal independently.

Out casing and bearing housing are allowed to slide on pedestal with thermal expansion

Bearing Housing. This arrangement avoid any tilting of bearing housing as a

result of thermal movement of outer casing. Aligned to the turbine axis and there is a free movement along

axial direction. When thermal expansion occurs, the bearing housing follows the movement of outer casing.

Sliding surfaces are coated with special graphite substance.

Steam Turbine – Construction

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Steam Turbine – Construction

• Front bearing Main Oil Pump

Directly driven by turbine rotor through an oil lubricated flexible tooth coupling.

Pump is mounted on bearing shaft. Tooth coupling accommodates any displacement between

turbine rotor (expands with rising temperature) and the pump shaft (does not expand) due to the thermal expansion.

Tooth coupling

Rotor shaftPump shaft

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Turbine Cross section Front Bearing

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9

Turbine Cross section

First expansion StageOf HP Turbine

17A. Inner Balancing Piston (Area covered by dotted line)

17A

15A. Labyrinth seal

Labyrinth seal4 Nozzle groups

1ST Guide blade carrier fixed to inner casing

Steam flow is indicated by arrows

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Steam Flow The flow of steam is indicated by arrows. First steam flow through control valve, interconnection

piping and inlet insert to the middle of the turbine to the Inner Casing (Slide 18).

Four nozzle groups direct the steam to first wheel which is an Impulse Wheel. (together calls impulse turbine)

Steam escaped from the impulse stage inters into the Wheel Chamber from there steam enters to the reaction turbine stages.

(Wheel chamber pressure is a useful monitoring point for the turbine. By monitoring this pressure some important information such as blade fouling, inlet strainer (slide # 26) blocking and governor valve failure could be diagnosed.)

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Steam Flow

After steam emerges from reaction turbine and inner casing, its flow is reversed by the Ddummy Piston (slide # 9 & 12) and its Labyrinth Seal and passes through in between inner and outer casing toward to next expansion stages.

Steam has now lower temperature than inlet, cools the inner wall of casing admission section. While cooling, it absorb extra heat energy from the process.

Then steam flows to the middle section and then to the exhaust section.

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Balance Piston (Dummy Piston) Every reaction stage develops an axial thrust on

rotor by its rotating blades. This thrust acts in the direction of steam flow. In order to counteract this force and reduce the

load on the thrust bearing, a dummy piston is forged into the rotor

The balancing piston diameter is so calculated in such a way that the thrust force produce by it on the rotor is balanced out by the total thrust forces produce by rotating reaction blades.

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Balance Piston (Dummy Piston)

This condition must be maintained at all loads. Labyrinth sealing strips on rotor to prevent

steam leak also exerts little help toward balancing thrust on rotor.

Two dummy pistons are provided at position 17A (of slide # 9 and 14).

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Turbine Cross Section – 2, 3 & 4th expansion Stages

17A

14

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Turbine Cross Section – LP &Exhaust Top Half

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Turbine Cross Section – LP &Exhaust - Bottom Half

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Turbine Cross Section – Turning Gear and Rear Bearing

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Inner Casing And First Guide Blade Carrier

1. Steam ahead of the valve block.

2. Inlet Insert – Live steam inlet . Prevent direct contact of live steam with Outer Casing.

3. Upper section of the inner casing

4. Sealing rings5. Nozzle group – 2 in

each half6. Lower section of the

inner casing7. Supporting brackets –

rest in recesses in the lower section of the outer casing.

8. Shims – for vertical alignment.

9. Lug for axial alignment.

10. Supporting brackets11. Eccentric bolt – for

radial alignment. 12. Sealing ring – Prevents

steam leak from 1st balancing piston.

13. First guide blade carrier

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14. Angle ring – connect Inlet Insert to nozzle passage

15. Outer casing

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Steam Turbine – Construction Inner Casing

Front section…• The admission section.

Inner casing Symmetrical in design and axially and horizontally split. Constitute fist expansion stage of the HP turbine. Live HP steam inlet Reduces and Protects outer casing from high inlet

pressure steam. Supported by outer casing and could be expand to all

directions. Consists of,

— Four Nozzle Groups, which admit steam to Control Stage (consisting one wheel of Impulse Turbine) and then to the Wheel Chamber (space between impulse turbine and reaction turbine?).

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Inner casing Consists of…

— Sealing rings, which mess up with sealing rings of the rotor to forms the labyrinth seal. ( Labyrinth seals arrest hot gas leak through two surfaces one of which moves relative to the other with has no physical contact. (See image in next slide.)

— Angle ring, which provide a flexible link between the Inlet Insert and inner casing Nozzle Passage without steam leak.

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─ Guide Blade Carrier # 1 – It fixed to the inner casing and carries first 16 fixed guide blades known as Diaphragms.


Labyrinth seal.

sealing ring Stationary Member

Rotor sealing strips

Guide Blade Carrier # 1

Rotating member

Guide Blades

Hole for Joint Assembly Bolts

Circumferential groove

Face for mounting Lugs for carrying adjusting Slims

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Casing Labyrinth Gland

Outer labyrinth gland

Rotor

Air

Air

Gland sealing steam supply

Gland Leak off steam

Inner labyrinth gland

Packing Gland

Passage #1 Passage #2

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Casing Labyrinth Gland Location

• Where the rotor shaft penetrates the turbine casing and exhaust hood, the internal steam space is sealed to the low pressure side or to the atmosphere by labyrinth glands.

Design • At casing ends on the periphery of the inner surface fixed in

sealing strips together with the corresponding sealing strips on rotor shaft are forming a seal without mechanical contact.

• Inside these sealing strips potential energy (pressure) of steam is converted to kinetic energy (velocity), subsequently dissipating kinetic energy by forming steam eddies between strips.

• Two passages are incorporated. Passage #1 for supply of gland sealing steam (for negative pressure

use) or to collect leaking high pressure steam (for positive pressure use)

Passage # 2 for to collect leak off steam by the gland steam condenser.

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Casing Labyrinth Gland

Purpose • Prevents the leaking of steam out of, or air into the turbine

casing where the turbine rotor shaft extends through the turbine

casing. Use

Sealing against Positive pressure for high pressure steam Sealing against negative pressure (vacuum) for exhaust. Has to

block penetration of air into the casing.

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Control valve Chest

Steam In Steam Out

Emergency Stop ValveControl Valves

Control Valve Actuators

ESV Actuator

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Emergency stop value

Connected to valve actuator

(Governor control)

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Control Valve

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Turbine Rotor

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Turbine Rotor

Forged from single blank, from thrust bearing collar (5) to the rear coupling flang(15).

It is supported by two pressure lubricated Journal bearings Pos(6 and 17).

Jacking Oil Journal bearings accommodate rotor shaft lift oil system,

(Jacking oil system). Which enables rotor to be raised form contact with the bearing

while rotor at slow rolling. Minimizes wear at start-up, warming-up and cool-down with a

shutting down.

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Turbine Rotor

Thrust Collar (Pos 5) • Rotor is located axially by a thrust bearing collar Relative to the

casing (front).• Absorb any residual steam thrust from rotor bladings. • It also forms the fix point of the rotor in the front bearing housing.• When the temperature of the turbine casing rises, rotor is carried

forward by forward bearing housing.• Since the rotor temperature rises at the same time, rotor expand

toward rear bearing of the turbine.• The overall rotor movement, with respect to the rear coupling

flange of the rotor is negligible and could be tolerated.

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Main Lube oil Pump

Baffle

Shaft Nut

Impeller

Discharge Compartment Bar

Cover

Combine Radial and Thrust bearing

Lube oil

Lube oil Drain

Suction

Sealing Ring

Feather Key

Radial Bearing

Pump tooth coupling

Rotor Shaft

Bearing Housing

Pump Discharge

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Hydraulic Turbine (Turning Gear Pos # 14 ) Drives the rotor when machine is being warmed-up or cooled-down. Use lube oil as its motive fluid. Motive force is developed by the Aux Lube Oil Pump discharge

pressure. Its operation is controlled by a

motorize valve. Use to prevent rotor warping. Manual Baring Wheel

(Pos #16) is used when above is not available.

Turbine Shaft

Blade wheel

Segment Shape Nozzle Housing

Lube Oil In

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Turbine Blades Type of Blade Used

• Impulse for control stage• Reaction type for drum blading• Tapered and Twisted blade for low-pressure

condensing turbine Converts thermal energy into mechanical energy. Efficiency of the turbine depends on the blading. All fixed and moving reaction blades has same

profile and same angle of incident. Made out of rust resistance steel.

Typical Impulse blade Typical reaction bladeTapered and Twisted

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Blades – Impulse Stage

Moving blade

Blade

Nozzle or blade

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Blades – Reaction Stage

Drum blading – Moving blades with shroudingFig 1

Low-pressure blading with damping wireFig 2

DAMPING WIREShrouding

Shroud - An extended metal rim enclosing the ends of the tips of blades

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Turbine Blades – Fixed Blade

Segment of fix blade – Low Pressure stage

Reverted ShroudingRevertBlade Pitch could be adjusted at installation time using spacers which are screwed and also braced.

Blade Foot

Spacer

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Rotor Drum Blading

Root – Inverted T

Several blades are assembled together

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LP Condensing Turbine Blading

Tapered and Twisted Blades – (Slide 28, Fig 2)

• Twisted form is to accommodate the substantial circumferential velocity difference between at the hub and at the blade tip.

─ This allows uniform distribution of steam across the blade.

─ At this stage possibility to form water droplets are very high, twisted form prevents this action.

─ Due to the twisted form water droplets if any, travel toward the tip of the blade and tends to atomize due the high circumferential velocity.

─ Twisted form ensure the steam enters at the correct angel.

• Tapered form is to accommodate the centrifugal force, that could be produce by the water drop lets.

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Blade Tip Sealing

There is no steam pressure drop across, fix or moving blades in an impulse stages.

Therefore no blade tip sealing is required in impulse stages. But in reaction stages, there is a pressure drop across fix and

moving blades. To prevent any leakage of steam between the clearance of the

moving blades and blade carrier, as well as fix blades and the rotor, blade tip sealing has been introduced in all medium and low pressure reaction turbines.

Blade tip sealing is accomplished by shrouding the blade and caulking labyrinth seals at blade clearances of guide blade carriers and rotor.

Shrouded Turbine BladesRotor

Rotor Blade

Blade Shroud

Stator

Blade tip seal

Seal Groove Caulk material to fix the seal strip

Note; -Similar arrangement with fix blade and rotor

Blade Tip sealing arrangement for moving blade

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Journal Bearings

1. Bearing Shell Upper half

2. Oil Pockets for bearing oil.

3. Tapered Dowel Pin used to secure the two half relative positions.

4. Bearing Shell Lower half.

5. Jacking Oil passage for rotor lifting. Reduces dry friction.

6. Oil Pocket for Jacking oil

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2

1

3

4

5

7

6

910

5

6

8

8

1112

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Bearings - Journal

7. Fillister head screw Assembles the two half together.

8. Annular Channel Pressure oil flows intothis form external pipe connection.

9. Bearing Oil Passage (A hole drilled through the bearing up to the annal oil channel) Lube oil flows through this to the bearing oil pockets and to the rotor and the

bearing babbit contact surface. It receives lobe oil from Annular Channel (Pos # 9).

10. Bearing Babbit Surface. Rotor and bearing contact ` area on the bearing surface, where the

bearing metal is coated.

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Steam Turbine Bearings – Journal

11. Jacking oil connection.12. Embedded Thermocouple

To monitor bearing metal temperature ( both half). Note: - 1. A cylindrical pin is inserted at the parting line of the bearing

shell and the lower part of the bearing housing. It prevents axial or radial displacement of bearing shell.

2. The cross section area of the bearing inside is slightly elliptical in shape.Larger diameter between two oil pockets (Pos # 2). This ensures uniform oil flow and allows to form a thing oil film between the entire contact surface.

3. Oil quantity could be throttled by a adjustable orifice 4. When the rotor is lifted, still it could shifts to a one side.5. To prevent this, in front bearing two jacking oil ports are provided at equiv-

distance from the vertical center line in either side of the bearing. 5. For jacking oil, to adjust the pressure a variable orifice is provided.

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Steam Turbine Bearings – Thrust

Pivot Edge

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Steam Turbine Bearings – Thrust1.Bearing Housing2. Liner ring

Provides precise axial position for thrust bearing with respect to bearing housing 3. Top half of the Thrust-Bearing Casing4. Radial Oil Hole

From Outer Oil Channel (14) oil passes through toward rotor.5. Cylindrical Pin

Segments are retain radially by them and are thus secured against displacement.

6. And # 13, Segment Ring ( 2 No. Identical) Several pivotal segments (contact surfaces are Babbit Lined) form segment ring. Takes axial thrust from rotor collar and transmits it via thrust casing (3 & 9) and

Liner ring (2) to front bearing housing (1). 7. Thrust Collar

Forged and machined with rotor. 8. Inner Oil Channel

Receives oil flowing through as a thing oil film between the thrust pads and collar due to the centrifugal force acquired with the rotation.

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9. Bottom half – Thrust Bearing Casing10.Sealing Strips

Prevent aspiration of air along the shaft into the thrust bearing.11.Axial Oil Drain

Provides several oil drain passages only on top half connected to inner oil channel.

12.Thermometer Discharge oil temperature measurement. There are thermocouple embedded in the thrust pads to monitor metal

temperature of the thrust pads. 14.Outer Oil Channel

Between the bearing housing and thrust bearing casing Facilitates Lube oil flow to thrust bearing

15.Pivoting Edge. Provides required tilt depend on load.

Steam Turbine Bearings – Thrust

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Rear bearing Housing Assembly

Oil entry for Turning Gear

Oil Gland

Oil Drain

Hydraulic TurbineRear Journal Bearing

Oil Gland

Lube Oil Entry for Journal Bearing

Labyrinth Gland Rear

Exhaust Hood

Nozzle

Moving Blade

Nuzzle Segment

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Front Supporting System

Fig 1 Front Support

Fig 2 – Adjusting Element

Fig 3

Fig 4

CasingMoves with temperature

5A

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1. Turbine Casing2. Turbine Supporting Brackets

The hole diameter of the supporting bracket where the screw bolt # 4 is passed is larger than the bolt diameter. This is to facilitate the moment of the casing in horizontal direction which takes place with the rising temperature of the turbine casing and it is free to expand.

3. Casing Support Anchored in the turbine foundation.

4. Screw bolts Fix the turbine to the front support and in tern to foundation

(Prevents turbine lifting off).5. Shaft bearing housing – 5A. # 5 Support

Free to move with casing Carries Front bearing and Thrust bearing.

6. Adjusting Element Bearing housing # 5 and it supports # 5A rest freely on this. Aligns Bearing Housing # 5 vertically (See fig 4)

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7. Adjusting element Turbine Casing/Bearing housing, Horizontal.

8. Bolt9. Screw Bolts

Fix bearing hosing to front support These bolts allow few hundredth of a millimeter free play

between shaft bearing housing and casing support so that bearing housing can glide free

10. Screw In Adjusting Element Upon which supporting brackets # 2 of the turbine casing is

rest and align Turbine Casing # 1 Vertically (See Fig 2, slide 47)

11. Cup Springs Load the screw bolt # 4 to prevent any loosing due to vibration.

12. Center Rail


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Protective Equipments

Trip Bolt – Emergency Governor (Primary)• Auto stop the turbine immediately in the event of rotor speed is

being exceeded by 10 to 12%. Over speed primary trip.

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1. Socket-Head Cap ScrewLock in position Threaded Cap # 4 to the shaft.

2. Socket-Head Cap ScrewLock in position Screw Plug # 3

3. Screw Plug with a drilled hole in the centerHole gives access to the Adjusting Screw # 7. for Over speed

trip setting 4. Threaded Cap

Plugs the opening of radial bore in the shaft5. Guide Ring

Guide the movement Eccentric Bolt # 6 and Compression Spring # 8.

6. Eccentric BoltA bolt under the strong influence of the compression spring # 8

which can move few millimeters outward direction of the rotor shaft.

Trip Bolt….

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Trip Bolt…7. Adjusting Screw

Sets over speed trip setting. Sets the Eccentric bolt position in such a way that its center of

gravity is shifted off from the center of the turbine shaft by an amount which ensures that up to the rated speed the eccentric bolt will remain in it normal position inside the shaft.

Above the rated speed bolt protrudes from the shaft surface. At set speed it will hit the emergency governor lever and de-

activates the governor trip oil system tripping the turbine. 8. Compression Spring

Tries to keep the eccentric bolt in position by counteracting the centrifugal force produce by the bolt.

9. Tight Fitting Bolt Assembled into this and fixed to the turbine shaft by Threaded

Cap Note:- There is a facility to test this system while turbine on load

without affecting the operation.

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Atmospheric relief Diaphragm – Rupture DiskWhen there is low vacuum trip,

excessive presser builds-up in the turbine exhaust.

This condition rupture the diaphragm there by protecting any damage to the turbine internals.

At normal operation with vacuum atmospheric presses forces the diaphragm and rupture disk against the flange.

1.Rupturing Disk2.Breakable Diaphragm3.Supporting Flange4.Gasket5.Cylindrical Cage

1 2 3 4 5

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Monitoring Device

Speed Monitoring• Feed Back for turbine operation.• Secondary over speed trip – Electrical.• Consists of

Steel disk which carries in it periphery equally space axial identical holes.

Electromagnetic pickups screwed into the cover in front of the rotating disk. When disk holes move in front of the pickups, the

produce a AC voltage, frequency of which is proportionate to the rotor speed.

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Speed Monitoring…

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Casing Expansion Measurement

• Measurement of absolute displacement of the bearing pedestal as the result of the thermal expansion.

• This device should be observed all the time especially, during load changes, startup and shutdown.

• This and rotor position indicator permits conclusions to be made with regard to the axial position of the rotor.

1.ScaleVenire scale attached to

bedplate.2.Slider

Attached to bearing pedestal.

3.Bedplate

12

3

4

3

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Measurement of Rotor Axial Position• Axial displacement beyond specified

limit can have serious consequences such as clearance between stator and rotor blades, bearing clearance.

• Frequent checks permits early recognition and detection of rotor displacement.

Arrangement Thrust bearing forms the fix point of

turbine rotor. Located in front bearing housing

immediate vicinity of thrust bearing. Instrument operates on eddy current

principal.

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1. Proximitor Generates a high frequency (HF) signal

and fed to the coil in the transducer # 1. Measures and reports the HF signal

strength continuously. 2. Transducer

Produce a magnetic field in the vicinity.

1

5

3

3. Conductive Measuring Surface An eddy current is produce on the

measuring surface. Strength of the eddy current is depend

on the distance of the gap between the transducer and the measuring surface.

This eddy current in tern reduce the HF signal strength.

4. Gap5. Rotor

4

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Vibration Measurement

Vibration originates from the rotor. Transmits to external bearing housing surface through the

bearing oil film which has the damping effect and reduce the magnitude of the actual rotor vibration.

Bearing Housing Surface vibration (Secondary vibration)• Gives general indication vibration behavior of the turbine.

• Uses for vibration alarms and tripping of turbine at an abnormality.

Direct Rotor Vibration (Bentley Nevada Proximity Sensors)• Sensors operate on same principal describe as before on slide 57

for Measurement of Rotor Axial Position.

• Two sensors are arranged as shown.

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Vibration Measurement

450450

Rotor ShaftGaps

Proximity Sensor

Vibration Sensor

900

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Outer Casing Differential Temperature• This measurement help avoiding distortion to outer casing.• Separate limits of outer casing differential temperature are specified for startup

and steady state operation.

• Arrangement A hole is drilled up to the 50% of the body of the outer casing on each half of

casing. Thermocouples are installed in this holes. These thermocouples are pressed down against the bottom of the holes by a

compression spring. These thermocouples measure metal temperature of the each half and direct

Differential Temperature measurement is obtained.

Monitoring Device

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Turbine Stress Evaluation Measurements

Rotor Simulation• Using this measurement, an estimation of rotor temperature after

the impulse stage is made.• This estimate is also used for turbine stress evaluation. • Arrangement

Thermocouples are mounted into the inner casing to measure the temperature just after the impulse stage.

Leads of them are routed through inner casing to outer casing and terminated to a junction box.

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Turbine Stress Evaluation Measurement

Valve block Wall Temperature• Measure valve block body casing metal temperature.• Uses two thermocouples. • The difference of thermocouple measurements also are used for

stress evaluation.• Arrangement

Thermocouples are installed just after the right side emergence stop valve.

Two holes, one 50% of the valve wall body and the other 100 of the wall body are drilled to install these thermocouples.

Which are pressed down against the bottom of holes by a compression spring

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Turbine Stress Evaluation Measurement

These measurements are fed to the “Turbine Stress Evaluator” (TSE – Procontrol System) which regulate the startup and loading of the turbine.

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End

Steam Turbine

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