STEAM TURBINE

Presentation Outline

• Theory of Turbine

• Turbine casing

• Rotor & Blades

• Sealing system & barring gear

• ESV’s, IV’s and CV’s

• Coupling and Bearing

Steam Turbine• A steam turbine is a mechanical device that

extracts thermal energy from pressurized steam, and converts it into useful mechanical work.

Classification

Impulse turbine

Reaction turbine

Pressure compounded

Velocity compounded

Impulse Turbines• An impulse turbine uses the impact force of the

steam jet on the blades to turn the shaft. Steam expands as it passes through the nozzles, where its pressure drops and its velocity increases. As the steam flows through the moving blades, its pressure remains the same, but its velocity decreases. The steam does not expand as it flows through the moving blades.

Impulse Turbine

Velocity compounded impulse turbine

Pressure compounded

Reaction Turbines

• In the reaction turbine, the rotor blades themselves are arranged to form convergent nozzles. This type of turbine makes use of the reaction force produced as the steam accelerates through the nozzles formed by the rotor.

Reaction turbine

RANKINE CYCLE

GENERATOREXCITER

1 2 34 5 6

ESV1

CV1

CRH

IPSV1IPCV 1

CONDEN

FROM RH

LPBYPASS

TO LP HEATERS

HPT 1X17IPT 2X12

LPT 2X6

TURBINE LAYOUT

TURBINE COMPONENTS

• CASING• ROTOR• BLADES• SEALING SYSTEM• STOP & CONTROL VALVES• COUPLINGS & BEARINGS• BARRING GEAR

Turbine CasingsHP Turbine Casing outer casing: a barrel-type without axial or

radial flange. Barrel-type casing suitable for quick startup

and loading. The inner casing--- cylindrical , axially split. The inner casing is attached in the horizontal

and vertical planes in the barrel casing so that it can freely expand radially in all directions and axially from a fixed point (HP-inlet side).

HP Turbine Casing

IP Turbine Casing

The casing of the IP turbine is split horizontally and is of double-shell construction.

Both are axially split and A double flow inner casing is supported in the outer casing and carries the guide blades.

Provides opposed double flow in the two blade sections and compensates axial thrust.

• Steam after reheating enters the inner casing from Top & Bottom.

LP Turbine Casing

The LP turbine casing consists of a double flow unit and has a triple shell welded casing.

The shells are axially split and of rigid welded construction.

The inner shell taking the first rows of guide blades, is attached kinematically in the middle shell.

Independent of the outer shell, the middle shell, is supported at four points on longitudinal beams.

Steam admitted to the LP turbine from the IP turbine flows into the inner casing from both sides.

LP Turbine Casing

Anchor Point of Turbine Purpose: Taking care of thermal expansions

and contractions of the machine during thermal cycling.

The fixed points of the turbine are as follows:• The bearing housing between the IP and LP

turbines.• The rear bearing housing of the IP turbine.• The longitudinal beam of the I.P turbine.• The thrust bearing in rear bearing casing of

H.P turbine.

RotorsHP Rotor:

The HP rotor is machined from a single Cr-Mo-V steel forging with integral discs.

In all the moving wheels, balancing holes are machined to reduce the pressure difference across them, which results in reduction of axial thrust.

First stage has integral shrouds while other rows have shroudings, rivetted to the blades are periphery.

IP Rotor• The IP rotor has seven discs integrally forged

with rotor while last four discs are shrunk fit. • The shaft is made of high creep resisting Cr-Mo-

V steel forging while the shrunk fit disc are machined from high strength nickel steel forgings.

• Except the last two wheels, all other wheels have shrouding riveted at the tip of the blades. To adjust the frequency of the moving blades, lashing wires have been provided in some stages.

LP Rotor• The LP rotor consists of shrunk fit discs a shaft.• The shaft is a forging of Cr-Mo-V steel while the discs

are of high strength nickel steel forgings.• Blades are secured to the respective discs by riveted

fork root fastening. • In all the stages lashing wires are providing to adjust

the frequency of blades. In the last two rows satellite strips are provided at the leading edges of the blades to protect them against wet steam erosion.

BLADES most costly element of turbine blades fixed in stationary part are called guide

blades/nozzles and those fitted in moving part are called rotating/working blades.

blades have three main partsAerofoil: working part

RootShrouds

• shroud are used to prevent steam leakage & to guide steam to next set of moving blades.

BLADES Three types of root arrangements are commonly used.

They are (1) T-roots: for small blades; (2) Fir Tree or serrated roots - for longer blades; (3) Fork and Pin root: for longer blades shrunk on disc type rotors.

Integral shroud for are used for shorter blades and shrunk fitting for larger blades.

Lacing wires are also used to dampen the vibration and to match frequencies in the longer blades.

Since in the reaction type machine the pressure drop also occurs across the moving blades it is necessary to provide effective sealing at the blade tips.

SEALING GLANDS

• Steam is supplied to the sealing chamber at 1.03 to 1.05 Kg/sq.cm abs and at temperature 130 deg.C To 150 deg.C from the header.

• Air steam mixture from the last sealing chamber is sucked out with the help of a special steam ejector to gland steam cooler.

• Provision has been made to supply live steam at the front sealing of H.P. and I.P. rotor to control the differential expansion, when rotor goes under contraction during a trip or sharp load reduction.

Labyrinth seal

BEARINGS:

General bearing---6no.s Thrust bearing ---1no.Bearings are usually forced lubricated and have provision for admission of jacking oil

Front Bearing Pedestal• The Front Bearing Pedestal is located at the turbine

side end of the turbine generator unit.• Its function is to support the turbine casing and bear

the turbine rotor.• It houses the following componentsa. Journal bearingb. Hydraulic turning gearc. Main oil pump with hydraulic speed transducerd. Electric speed transducere. Over speed tripf. Shaft vibration pick-upg. Bearing pedestal vibration pick-up

• The bearing pedestal is aligned to the foundation by means of hexagon head screws that are screwed in to it at several points.

• The space beneath the bearing pedestal is filled with non shrinking grout.

• The bearing pedestal is anchored at to the foundation by means of anchor bolts.

• The anchor bolt holes are filled with gravel,it gives a vibration damping effect.

Front Bearing Pedestal

Front Bearing Pedestal

Bearing Pedestal(HP Rear)

• The Bearing pedestal(2) is located between the HP and IP turbine.

• Its function is to support the turbine casing and bear the HP IP rotor.

• It houses the following components

1. Combine Journal and Thrust bearing

2. Shaft vibration pick-up

3. Bearing pedestal vibration pick-up

4. Thrust Bearing trip(electrical)

Combined Journal and Thrust Brg.

• The magnitude and direction of axial thrust of the turbine depends on the load condition

• The Journal bearing is elliptical sleeve bearing.• The bearing liners are provided with a machined babbit

face.• Located at each end of bearing shell, babbitted thrust

bad forms 2 annular surfaces.• These collars and thrust pads permit equal loading of

thrust bearing.• Thrust pads are of tilting type.• Metal temperature of the journal bearing and thrust

pads is monitored by the thermocouples.

JOURNAL BEARING

JOURNAL BEARING

IP Rear Bearing PedestalArrangement:The bearing pedestal is located between the HP and IP

turbines. Its function is to support the turbine casing and bear the HP and IP turbine rotors. The bearing pedestal houses the following turbine components:

Journal bearing Shaft vibration pick-up Bearing pedestal vibration pick-up Hand barring arrangement  Differential expansion measurement device

Journal BearingThe function of the journal brg.is to support the

turbine rotor.• The journal brg. Consists of the upper & lower

shells,bearing cap,Spherical block, spherical support and key.

• The brg shell are provided with a babbit face.• Brg is pivot mounted on the spherical support to

prevent the bending movement on the rotor.• A cap which fits in to the corresponding groove in

the brg shell prevents vertical movement of the brg shell.

• The brg shells are fixed laterally by key.• Each key is held in position in the brg pedestal by

2 lateral collar.

• The Temperature of the brg bodies is monitored by thermocouple.

• Upper and lower shell can be removed without the removal of Rotor.

• To do this shaft is lifted slightly by means of jacking device but within the clearance of shaft seal.

• The lower bearing shell can be turned upward to the top position and removed.

LP TURBINERear Bearing Pedestal: The bearing pedestal is situated between the

LP turbine and generator. Its function is to bear the LP rotor. The bearing pedestal contains the following turbine components: Journal bearing Shaft vibration pick-up Bearing pedestal vibration pick-up

BARRING GEARThe primary function of barring gear is rotate the turbo generator rotors slowly and continuously During startup and shutdown periods when changes in rotor temperature occurs > Shaft system is rotated by double row blade wheel which is driven by oil provided by AOPA manual barring gear is also provided with hydraulic gearBarring speed 210/240 rpm

ESV & CV2 main stop valves and 2 control valves located symmetrically

The main steam is admitted through the main steam inlet passing first the main stop valves and then the control valves. From the control valves the steam passes to the turbine casing.

Turbine is equipped with emergency stop valve to cut of steam supply with control valves regulating steam supply Emergency stop valve are actuated by servo motor controlled by protection system Control valves are actuated by governing system through servo motors to regulate steam supply

CouplingsShaft is made in small parts due to forging limitation and other technological and economic reason,so coupling is required between any two rotors

Here using rigid couplingDue to high torque flexible coupling can’t be usedCoupling between HP&IP IP&LP LP&generator GEN&exciter MOP&HP

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