PrinciplePrinciple It changes thermal energy to mechanical energyIt changes thermal energy to mechanical energy..

Heat (thermal energy) produces steam pressure, and the steam pressure is converted to steam velocity by the nozzle. After steam strikes the buckets, Heat (thermal energy) produces steam pressure, and the steam pressure is converted to steam velocity by the nozzle. After steam strikes the buckets, steam velocity decrease.steam velocity decrease.

The rotor turns and produces mechanical work. Means Rotation of rotor.The rotor turns and produces mechanical work. Means Rotation of rotor.

Operation principleOperation principle

The flow of steam into the steam chest is controlled by the The flow of steam into the steam chest is controlled by the governor valve. By controlling the amount of steam, the governor valve. By controlling the amount of steam, the governor valve controls the output of mechanical energy.governor valve controls the output of mechanical energy.

For the steam to flow into the casing through the nozzle, the For the steam to flow into the casing through the nozzle, the steam pressure in the casing must be lower than the steam steam pressure in the casing must be lower than the steam pressure in the steam chest..pressure in the steam chest..

The high – velocity steam directed toward the buckets is an The high – velocity steam directed toward the buckets is an impelling force (impulse) which causes the rotor to turn. impelling force (impulse) which causes the rotor to turn.

The buckets are mounted on a wheel The buckets are mounted on a wheel rather than directly on the shaft and rather than directly on the shaft and the nozzle or nozzles are located in the nozzle or nozzles are located in

the wall of the steam chestthe wall of the steam chest..

Classification of Steam turbines:

Based on exhaust condition:CONDENSINGBACK- PRESSUREEXTRACTIONINDUCTIONBased on stage design:

ImpulseReactionBased on steam flow:

Axial flowRadial flowMixed flowBased on stages:

Single stageMulti stage

Condensing TurbinesCondensing Turbines

condenser at the exhaust condenser at the exhaust low pressure at the exhaust by low pressure at the exhaust by

heat removal heat removal Utilize all of the available Utilize all of the available

thermal energy present in the thermal energy present in the steam.steam.

Since large pressure drops are Since large pressure drops are common in condensing common in condensing turbines, the steam pressure is turbines, the steam pressure is usually reduced in steps. usually reduced in steps. Condensing turbines are Condensing turbines are usually multi-stage turbine.usually multi-stage turbine.

BACK- PRESSURE TURBINE

# #Back pressure turbine is operated in back Back pressure turbine is operated in back pressure which is higher pressure than pressure which is higher pressure than

atmospheric pressureatmospheric pressure..

# #The exhaust steam can be used effectively The exhaust steam can be used effectively in any other machine and finally steam in any other machine and finally steam

converted to condensed water which returns converted to condensed water which returns to boilerto boiler..

Extraction and InductionExtraction and Induction

Extraction:Extraction:Steam removed from a stageSteam removed from a stagecan be used for processes thatcan be used for processes thatneed steam at pressures andneed steam at pressures andtemperature above thetemperature above thepressure and temperature ofpressure and temperature ofthe exhaust.the exhaust.Removing steam at intermediateRemoving steam at intermediatestage is stage is ExtractionExtraction..

Induction:Induction:Some times excess steam isSome times excess steam isavailable in the plant, at theavailable in the plant, at thepressure of a turbinespressure of a turbinesintermediate stage.intermediate stage.This steam can be induced into theThis steam can be induced into theturbine at that stage.turbine at that stage.

Some steam may be removed fromSome steam may be removed from

or added to a stage before it reachesor added to a stage before it reaches

the exhaustthe exhaust..

ImpulseImpulse

The high – velocity steam The high – velocity steam directed toward the buckets directed toward the buckets is an impellingis an impelling

(impulse) force(impulse) force

which causes the rotor to turn.which causes the rotor to turn.

1.1. All the steam expansion All the steam expansion occurs through a stationary occurs through a stationary nozzle.nozzle.

2.2. Steam dose not expand to Steam dose not expand to a great extent in the bucket.a great extent in the bucket.

Reaction turbinesReaction turbines

Reaction turbine:Reaction turbine:The steam expands as it The steam expands as it

flows flows through the bucket.through the bucket.1.1. All expansion occurs All expansion occurs

in the in the buckets mounted on buckets mounted on the rotor.the rotor.

2.2. Require more stages Require more stages than impulse turbinethan impulse turbine

Single-stageSingle-stage

Single stageSingle stage

1.1. One wheel.One wheel.

2.2. Pressure is reduced Pressure is reduced in one stagein one stage

Multi -stageMulti -stage

Multi stageMulti stage1.1. More than one wheel.More than one wheel.2.2. Pressure is reduced Pressure is reduced

in stages in stages (Turbine having large (Turbine having large

pressure drops pressure drops between inlet and between inlet and exhaust are usually exhaust are usually multi-stage turbines)multi-stage turbines)

Look at the drawingLook at the drawing::

All the wheels are mounted All the wheels are mounted on one shaft.on one shaft.

Each stage is isolated by a Each stage is isolated by a diaphragm which holds the diaphragm which holds the nozzles. nozzles.

Instead of one large nozzle, Instead of one large nozzle, a row of smaller nozzles a row of smaller nozzles can be used.can be used.

There is row of nozzles per There is row of nozzles per stage.stage.

GovernorsGovernors

The governor valve:The governor valve:

1.1. Regulates the amount of steam AS REQUIRED into the Regulates the amount of steam AS REQUIRED into the turbine. turbine.

2.2. It is used to control turbine speed.It is used to control turbine speed.

LET US SEE---- LET US SEE----

HOWHOW

FirstFirst … … What is the governorWhat is the governor??It is a mechanism which opens and closes the governor valve. For It is a mechanism which opens and closes the governor valve. For

example, fly ball governor.example, fly ball governor.The drawing shows a fly ball governor:The drawing shows a fly ball governor:

As the governor turns, the centrifugal force moves the fly As the governor turns, the centrifugal force moves the fly balls further apart.balls further apart.

At low speed, the force of the spring keeps the fly balls At low speed, the force of the spring keeps the fly balls together.together.

At higher speeds, the fly balls move further apart. The At higher speeds, the fly balls move further apart. The faster the governor turns, the fly balls moves further away faster the governor turns, the fly balls moves further away from the center.from the center.

SecondSecond … … Operation of the governor Operation of the governor

valvevalve

1- 1- When the turbine is notWhen the turbine is not

operating, the spring holdsoperating, the spring holds

the fly balls close to thethe fly balls close to the

shaft. Before the turbine isshaft. Before the turbine is

started, the governorstarted, the governor

valve is wide open. valve is wide open.

2-2- As the shaft approaches As the shaft approachesoperating speed, springoperating speed, springtension is overcome by thetension is overcome by thecentrifugal force,centrifugal force,and the balls move away fromand the balls move away fromeach other, the governor valve iseach other, the governor valve isPushed to closed.Pushed to closed.When the turbine reaches When the turbine reaches operating speed, the governoroperating speed, the governorvalve allows less steam in thanvalve allows less steam in thanat startup, and turbine stopsat startup, and turbine stops accelerating.accelerating.

3-3- If the turbine speed is If the turbine speed is too fast, the governor too fast, the governor valve will be closed.valve will be closed.

Over speeds TripOver speeds Trip

If all loads are suddenly removed from a fully-loaded turbine, If all loads are suddenly removed from a fully-loaded turbine, the turbine may over speed.the turbine may over speed.

Some times the governor reacts too slowly or fails to respond at Some times the governor reacts too slowly or fails to respond at all.all.

If the steam is not shut off promptly, the turbine over speeds If the steam is not shut off promptly, the turbine over speeds until it flies apart.until it flies apart.

A trip pin in the turbine shaft is used to shut off the steam flow in A trip pin in the turbine shaft is used to shut off the steam flow in the shaft.the shaft.

1.1. At normal speeds the At normal speeds the trip pin remains inside trip pin remains inside the shaft by a spring.the shaft by a spring.

2.2. If the turbine over If the turbine over speeds, the pin is speeds, the pin is ejected from the shaft ejected from the shaft by centrifugal force.by centrifugal force.

The drawing shows a trip pin in the shaft.The drawing shows a trip pin in the shaft.

Look at the drawingLook at the drawing

1.1. When the turbine over speeds, the extended pin strikes When the turbine over speeds, the extended pin strikes the over speed trip.the over speed trip.

2.2. The trigger releases a latch holding the trip lever, which The trigger releases a latch holding the trip lever, which is then pulled down by a spring. The force of the spring is then pulled down by a spring. The force of the spring closes the trip valve which closes and cuts off the steam closes the trip valve which closes and cuts off the steam flow to the steam chest. flow to the steam chest.

3.3. The turbine stops.The turbine stops.

Main Parts of steam turbineMain Parts of steam turbine

RotorRotor

Steam chestSteam chest

CasingCasing

Over speed trip systemOver speed trip system

Governor systemGovernor system