What is a Turbine ?

-A Turbine is a device which converts the heat energy of steam into the kinetic energy & then to rotational energy.

-The Motive Power in a steam turbine is obtained by the rate of change in momentum of a high velocity jet of steam impinging on a curved blade which is free to rotate.

-The basic cycle for the steam turbine power plant is the Rankine cycle. The modern Power plant uses the rankine cycle modified to include superheating, regenerative feed water heating & reheating.

RANKINE CYCLE

Impulse & Reaction Turbine

1. Based on Blading Design

a) Impulse turbine

There is no pressure drop across moving blades. Steam energy is transferred to the rotor entirely by the steam jets striking the moving blades. Since there is no pressure drop, negligible thrust is produced.

b. Reaction turbine

Steam expands in both the stationary & moving blades. Moving blades also act as nozzles. High axial thrust is produced.

c) Combination of Impulse & Reaction turbine

IMPULSE TURBINE

a

IMPULSE REACTION TURBINE

DIFFERENCES

Impulse & Reaction Turbine

Impulse Reaction-Pressure drops in nozzles and not in moving blade -Pressure drops in fixed blade as

well as in moving blades-Constant blade channel area -Varying blade channel area-Profile type blades -Aerofoil type blades-Restricted round or incomplete admission of steam -All round or complete admission-Diaphragm contains nozzles -Fixed blades similar to moving blades attached to

casing serve as nozzles and guide the steam

-Occupies less space for same power -Occupies more space for same power-Higher efficiency in initial stage - higher efficiency in final stages.-Suitable for small power requirements -Suitable for medium or high power requirements.-Blade manufacturing is not difficult -Blade manufacturing process is difficult.-Velocity of steam is high -Velocity of steam is less.

On the Principle of working

1. Impulse Turbine

2. Reaction Turbine

Turbines Classification

Based on Inlet & Outlet Steam Condition

• Back pressure turbines – The Exhaust steam from the turbine flows out of the steam piping at medium or low pressure. Basically, the exhaust steam can be used effectively in any other machines or equipment in the plant.

• Condensing turbines – Full steam quantities entering into the turbine are exhausted, and converted to condensate in a condenser. The exhaust steam pressure is lower than the atmospheric pressure.

• Extraction turbines – Medium or low pressure steam required by the process plant is extracted from the intermediate stage of a condensing or back pressure turbine.

CONSTRUCTIONAL FEATURES• CASING : MADE OF CAST STEEL EXCEPT CONDENSING STAGE

WHICH IS MADE OF CAST IRON. IT IS MOUNTED ON THE FRONT-END BEARING PEDESTAL. EXPANSION OF CASING IS TOWARDS FRONT END.

• ROTOR : MACHINED FROM A FORGED BLANK OF ALLOY STEEL. ROTOR IS A SINGLE FORGING INCORPORATING THE THRUST BEARING COLLARS. IT IS SUPPORTED ON TWO PRESSURE LUBRICATED JOURNAL BEARINGS. EXPANSION OF ROTOR IS TOWARDS REAR END.

• CONTROL STAGE : CONSISTS OF MOVING BLADES & NOZZLES. NOZZLES ARE MACHINED FROM SOLID BLANKS. THE MOVING BLADES ARE MACHINED FROM SOLID BAR STOCK & HAVE INVERTED TEE ROOTS. TEE ROOTS ARE INSERTED INTO GROVES IN THE TURBINE ROTOR & CAULKED WITH BRASS STRIP.

1. External Losses

- ESV & strainer losses

- Governing losses (throttling losses)

- Leaving Energy Losses (Latent heat of exhaust steam in condenser)

- Radiation Loss to the surroundings

2. Internal Losses

a) Blade losses

i) Primary Losses:

Friction loss due to profile surface finish

ii) Secondary Losses:

- Impingement loss

LOSSES

Losses in Turbine (contd.)b) Inter stage Tip Leakages:

Steam throttles in the inter stage seals without doing work

c) Residual velocity Losses:

Kinetic energy of the leaving steam of one stage will be carried over to the next stage. As the axial clearances increase between the stages (or stage groups) part of the kinetic energy will be lost.

CROSS-SECTIONAL DRAWING OF BLADED ROTOR

CO

UPLI

NG

TH

RU

ST

CO

LLA

R

H.P.BLADES

L.P B

LAD

ES

HA

ND

BA

RR

ING

WH

EEL

MO

VIN

G W

HEEL

FO

R O

IL T

UR

BIN

E

DIS

CO

NN

EC

TC

OU

PLI

NG

Blade Profiles

• Impulse

• Reaction

• Twisted Blade

DEFINITION OF GOVERNING SYSTEM

“A SYSTEM WHOSE PURPOSE IS TO CONTROL A PRIME MOVER”

The function of governor is to control the speed of the turbine.It does this by controlling the flow of steam to the nozzles.When the governor reacts to speed, it controls the steam flow and steam flow by defination is power. Therefore, through speed governing shaft output speed is governed with variable power output.

Types of Governor

1. Mechanical Governor2. Hydraulic Governor3. Combination of mechanical & Hydraulic4. Pneumatic Governor5. Electronic Governor

Protection Requirements• Over speed

• Low Lube oil pressure

• Low vacuum

• Axial shift

• High Vibration

• Bearing temperature

• High/low extraction pressure

• Exhaust temperature

• Generator / Compressor protections

• Manual / Remote trip

EMERGENCY STOP VALVE

CYLINDER WITH TEST PISTON

STOP VALVE

HP GOVERNING VALVE ASSEMBLY

YOKE ASSEMBLY

SERVOMOTOR

PILOT VALVE

MECHANICAL TRIPPING DEVICE

(VERTICAL MOUNTING)

MECHANICAL OVER SPEED GOVERNOR