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22.. SSwwaattii KKaannoojjiiaa

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AACCKKNNOOWWLLEEDDGGEEMMEENNTT

We would firstly like to thank

Mr..ASHOK KUMAR VERMA (H.R. - D.G.M.). for

allowing us to undergo summer training at NTPC

Koldam, all of the HR team of the Company for

their continued guidance. We would also wish to

convey our warm regards to

Mr. S.N. JHA (D.G.M. -ME)

Mr. ABHISHEK GAIROLA(ENGINEER ).for

enlightening us with all the knowledge database

that we needed for this report.

We would also like to thank

Mr. SANJAY BODH (ENGINEER-ME)

Mr SANDEEP SINGH (ENGINEER-ELECTRICAL)

TPO –…INSTITUTE OF TECHNOLOGY

(..BANARAS HINDU UNIVERSITY)… for providing us this wonderful opportunity to

work with the NTPC family.

CCOONNTTEENNTTSS

Overview of NTPC

Hydro Power Plants

Hydro Turbines

Power House

Hydro Generators

Design Study

Project Report on Study of different

parts of Francis turbine and Assembly of

Francis Turbine

About NTPC LIMITED

NTPC- National Thermal Power Corporation

It is the largest state-owned power generating company in India. Forbes

Global rank for 2009 ranked it 317th in the world. It is an Indian Public

Sector company listed on the Bombay Stock Exchange although at

present the Government of India holds 84.5%(after divestment the stake

by Indian government on 19 October 2009) of its equity. With a current

generating capacity of 34194 MW.

NTPC has been operating its plants at high efficiency levels. Although

the company has 18.79% of the total national capacity it contributes

28.60% of total power generation due to its focus on high efficiency.

NTPC’s share at 31 Mar 2001 of the total installed capacity of the

country was 24.51% and it generated 29.68% of the power of the

country in 2008–09. Every fourth home in India is lit by NTPC. As at 31

Mar 2011 NTPC's share of the country's total installed capacity is

17.75% and it generated 27.4% of the power generation of the country

in 2010–11. NTPC is lighting every third bulb in India. 170.88BU of

electricity was produced by its stations in the financial year

Future Goals

The company has also set a serious goal of having 50000 MW of

installed capacity by 2012 and 75000 MW by 2017. The company has

taken many steps like step-up its recruitment, reviewing feasibilities of

various sites for project implementations etc. and has been quite

successful till date.

NTPC will invest about Rs 20,000 crore to set up a 3,960-megawatt

(Mw) coal-based power project in Madhya Pradesh. Company will also

start coal production from its captive mine in Jharkhand in 2011–12, for

which the company will be investing about Rs 1,800 crore.

Power Burden

India, as a developing country is characterized by increase in demand

for electricity and as of moment the power plants are able to meet only

about 60–75% of this demand on an yearly average. The only way to

meet the requirement completely is to achieve a rate of power capacity

addition (implementing power projects) higher than the rate of demand

addition. NTPC strives to achieve this and undoubtedly leads in sharing

this burden on the country.

NTPC Headquarters

NTPC Headquarters is divided in 8 HQ.

S.No. Headquarter City 1 NCRHQ Delhi

2 ER-I, HQ Patna

3 ER-II, HQ Bhubaneshwar

4 NR Lucknow

5 SR HQ Hyderabad

6 WR-I HQ Mumbai

7 WR-II HQ Raipur

8 Hydro HQ Delhi

NTPC Plants

Thermal-Coal based

S.No. City State Installed Capacity(MW) 1 Singrauli Uttar Pradesh 2000

2 Korba Chhattisgarh 2600

3 Rmagundam Andhra Pradesh 2600

4 Farakka West Bengal 2100

5 Vindhyachal Uttar Pradesh 3260

6 Rihand Uttar Pradesh 2000

7 Kahalgaon Bihar 2340

8 Dadri Uttar Pradesh 2310

9 Talcher Orissa 3000

10 Unchahar Uttar Pradesh 1050

11 Talcher Orissa 460

12 Simhadri Andhra Pradesh 1500

13 Tanda Uttar Pradesh 440

14 Badarpur Delhi 705

15 Sipat Chhattisgarh 1000

16 Sipat Chhattisgarh 1980

17 Bongaigaon Assam 750

18 Mouda Maharashtra 1000

Total 25815

Coal Based (Owned by JVs)

S.No. Name of the

JV

City State Installed

Capacity(MW) 1 NSPCL Durgapur West Bengal 120

2 NSPCL Rourkela Orissa 120

3 NSPCL Bhilai Chhattisgarh 574

4 - Nabinagar Bihar 1980

5 - Kanti Bihar 110

Total 2904

GAS based

S.No. City State Installed Capacity(MW) 1 Anta Rajasthan 413

2 Auraiya Uttar Pradesh 652

3 Kawas Gujarat 645

4 Dadri Uttar Pradesh 817

5 Jhanor Gujarat 648

6 Kayamkulam Kerala 350

7 Faridabad Haryana 430

Total 3995

NTPC HYDEL

The company has also stepped up its hydroelectric power (hydel)

projects implementation. Currently the company is mainly interested in

the North-east India wherein the Ministry of Power in India has

projected a hydel power feasibility of 3000 MW.

There are few run of the river hydro projects are under construction on

tributory of the Ganges. In which three are being made by NTPC

Limited. These are:

Loharinag Pala Hydro Power Project by NTPC Ltd:

In Loharinag Pala Hydro Power Project with a capacity of 600 MW

(150 MW x 4 Units). The main package has been awarded. The present

executives' strength is 100+. The project is located on river Bhagirathi (a

tributory of the Ganges) in Uttarkashi district of Uttarakhand state. This

is the first project downstream from the origin of the Ganges at Gangotri(Project

stopped by GoI).

Tapovan Vishnugad 520MW Hydro Power Project by NTPC Ltd:

In Joshimath city

Lata Tapovan 130MW Hydro Power Project by NTPC Ltd: Also in

Joshimath (under environmental revision)

Koldam Hydro Power Project 800 MW in Himachal Pradesh

(130 km from Chandigarh)

Amochu in Bhutan

Rupasiyabagar Khasiabara HPP, 261 MW in Pithoragarh, near

China Border.

Hydro Power Plants

Reservoir : Holds the water from the river

Dam : Civil construction

Penstock : Large pipes through which water flows from the

reservoir to the turbine

Turbine :Turned by the force of water on their blades

Power Plant : Power generation and transmission

Generator : Converts mechanical energy of turbine into electrical

energy

Control Gates : Control the flow of water

Types of Hydro Power Plant

Storage Plants

Pumped Storage Plants

Run-off River Plants

Storage Plants

Impound and store water in a reservoir formed behind a dam. During

peak demands, enough water can be released to meet the additional

demand. Water flow rate may change greatly May involve dramatic

environmental consequences including soil erosion, degrading

shorelines, crop damage, disrupting fisheries and other wildlife, and

even flooding .

Pumped Storage Plants

Reuse water after it is initially used to generate electricity. Water is

pumped back to the reservoir during peak-off hours During peak hours

this water is used again for generating electricity.

Run-of-River Plants

Amount of water running through the turbine varies with the flow rate

of water in the river .Amount of electricity generated changes with

seasons and weather conditions .Since these plants do not block water in

reservoir, their environmental impact is minimal.

Hydro Turbines Hydro turbines can be classified on the basis of force exerted by water

on the turbine.

Reaction Turbines

Francis

Kaplan

Propeller

Bulb

Impulse Turbines

Pelton

Type of turbine to be used in a plant is decided on the basis of

available head

Head Range

Kaplan- 2m to 70 m

Francis-30m to 450

Pelton-above 300

Also a turbine is characterized by its specific speed.

FRANCIS TURBINE Reaction Turbine: The principal feature of a reaction turbine that distinguishes it from an impulse

turbine is t that only a part of the total head available at the inlet to the turbine

is converted to velocity head, before the runner is reached. Also in the reaction turbines the working fluid, instead of engaging only one or two blades,

completely fills the passages in the runner. The pressure or static head of the fluid

changes gradually as it passes through the runner along with the change in its kinetic energy based on absolute velocity due to the impulse action between the

fluid and the runner. Therefore the cross-sectional area of flow through the

passages of the fluid. A reaction turbine is usually well suited for low heads. A radial flow hydraulic turbine of reaction type was first developed by an American

Engineer, James B. Francis (1815-92) and is named after him as the Francis

turbine.

RUNNER

Manufacture is always making best efforts to design and manufacture highly efficient runners to meet all requirements or Specifications.

The runner is designed in consideration of various parameters for computation by

both theoretical analysis of internal flow and experimental investigation by model tests. The runner is usually made of carbon steel castings and overlay

coating of stainless steel welding will be made on critical areas of cavitations if

necessary. For higher head machines, the runner is made of stainless steel castings. Especially 13%a Chrome steel with enriched Nickel content becomes

widely used for its excellent anticavitation corrosion characteristics and

mechanical strength.

HEAD COVER AND BOTTOM RING The head cover and the bottom ring are so designed as to avoid causing excessive

deformation which may lead to seizure of wicket gate movement. Particular care is taken to ensure that the positioning of bores to receive the wicket gate stems

which should be matched between the head cover and bottom ring. For a larger

diameter of bore size, these bores are accurately positioned and machined by using numerical controlled machines.

Upon special request, seal packing of the trapezoidal section will be located in

grooves machined in the distributor faces of the head cover and bottom rings to minimize water leakage through the wicket gates fully closed.

MAIN SHAFT

The main shaft for the turbine is made of high-grade forged carbon steel. When

the size of the main shaft exceeds the limitation of forging capacity or

transportation or it is economical, the main shaft is formed by welding steel plates or a combination of forged steel and steel plates.

The main shaft is connected to the generator shaft or the intermediate shaft by a

flange coupling. The shaft surface passing through the shaft seal is protected with a stainless steel shaft sleeve to prevent the main shaft from wearing.

HYDRO GENERATORS Hydro Generators are low speed salient pole type machines. Rotor is

characterized by large diameter and short axial length. Capacity of such generator varies from 500 KW to 700 MW. Power factor are usually 0.90 to 0.95 lagging.

Available head is a limitation in the choice of speed of hydro generator.

Standard generation voltage in our country is 3.3KV, 6.6KV, 11 KV ,13.8 KV, &

16KV at 50 Hz. Short Circuit Ratio varies from 1 to 1.4.

A TYPICAL HYDRO GENERATOR

CLASSIFICATION

Classification of Hydro Generators can be done with respect to the position of rotor

Horizontal

Vertical (two types)

Suspension Type

Umbrella Type

Components of Generator STATOR

Stator Sole Plates

Stator Frame Stator Magnetic Core

Stator Windings

ROTOR Rotor Shaft

Rotor Spider

Rotor Rim Rotor Poles

Ring Collectors

BRACKETS Upper Bracket Lower Bracket

GENERATOR AUXILIARIES

Excitation System Air Cooling System

Braking And Jacking System

Bearings Fire Protection

Heaters

SALIENT FEATURE OF NTPC , KOLDAM

HYDROELECTRIC POWER PROJECT BILASPUR , HIMACHAL PRADESH

1. Location

State :Himachal Pradesh

District :Bilaspur

Dam :On Sutlej River about 6 kms upstream of Dehar Power Plant of BSL Project

2. Hydrology

Catchment (Sq Kms) :53770

Maximum annual rainfall (mm) :2450

Minimum annual rainfall (mm) :570

Design flood for Spillway Probable Maximum Flood (m

3/s) :16500

Design Flood for river diversion during Construction (1 in 200 years return period) (m

3/s) :6500

Standard Project Flood (m3/s) : 11400

90% available discharge (without storage) (m3/s) :102

3. Dam

Type : Rock and gravel fill with impervious central clay core

Crest of dam(m) : 648

Height of dam above deepest foundation(m) : 163

Crest length(m) : 500

Crest width(m) :14

Upstream slope : 2.25 H to 1.0 V

Downstream slope : 2.0 H to 1.0 V

4. Spillway

Type : Chute

Crest of spillway : Gated

Crest level(m) : 625

Total width of crest(m) : 108.5

No. of gate bays : 6 each of 15.5 clear span

Length of chute(m) : 420

Type of gates : Radial

Size of gates (m x m) : 15.5 x 17.3

5. Diversion structure

Numbers : 2

Type : Horse shoe

Finished diameter(m) : 14

Length of tunnels(m) : T-1=870m T-2=910m

Maximum velocity(m/s) : 20

Design capacity(cumecs) : 650

6. Coffer dams

Upstream coffer dam ( Included in main dam)

Type : Gravel with impervious core

Height(m) : 25

Crest level(m) : 515

Slope upstream : 2.25 H to 1.0 V

Slope downstream : 1.5 H to 1.0 V Downstream coffer dam

Type : Gravel fill with impervious core

Height(m) : 60

Crest level(m) : 558

Slope upstream : 1.5H to 1.0 V

Slope downstream : 1.5 H to 1.0 V

7. De-silting arrangement

Type : Submerged in body of reservoir, underneath approach channel to spillway

Particle size removal : 0.25 mm size and above

Size : 14 chambers each of 18 m width

8. Reservoir

Top EL of dam(m) : 648

Maximum water level corresponding to PMF(M) : 646

Full reservoir level (m) : 642

Minimum draw down level(m) : 636

Gross capacity at FRL(mcm) : 57.6

Dead storage capacity at MDDL(mcm) : 48.6

Maximum reservoir depth(m) : 142

9. Power intake

No. of intake bays : 4

Size of each slide gates(m x m) : 6.45 x 6.45

10. Penstock tunnels

Type : Circular steel lined

No. of penstock tunnels : 4

Maximum discharge through each penstock(m3/

s) : 196

Diameter of penstock tunnels(m) : 6.45

Maximum velocity through penstock(m/s) : 6

Total length of penstock tunnel(m) : 1600

11. Power plant

Type : Surface

Power house size(m x m x m) : 107 x 42 x 48

No. of units : 4

Type of turbines : Francis, Vertical shaft

Installed capacity(MW) : 800 (4 x 200)

Minimum gross head(m) : 127

Maximum gross head(m) : 140

12. Tailrace channel

Type : Open channel

Length(m) : 100

Minimum tail water level(m) : 502

Maximum tail water level(m) : 525

13. Power benefits at 100% load factor (MW)

Installed capacity : 800

Firm in 90% dependable year : 101.9

Firm in 50% dependable year : 137

14. Energy generation (GWh)

90% dependable year : 3054

50% dependable year : 3369

Design annual energy : 2990.34

PPRROOJJEECCTT RREEPPOORRTT

OONN

TTUURRBBIINNEE AASSSSEEMMBBLLYY

Francs turbines are most widely used among water turbines and the development of the Francis turbines in the last decade has opened up a large range of new application possibilities for this type. These advances, motivated by a search for maximum profitability, have become possible as the result of improved knowledge of the water flows in turbines and other hydraulic phenomena.

Francis Turbine has a circular plate fixed to the rotating shaft perpendicular to its

surface and passing through its center. This circular plate has curved channels on

it; the plate with channels is collectively called as runner. The runner is encircled by a ring of stationary channels called as guide vanes. Guide vanes are housed in

a spiral casing called as volute. The exit of the Francis turbine is at the center of

the runner plate. There is a draft tube attached to the central exit of the runner. The design parameters such as, radius of the runner, curvature of channel, angle

of vanes and the size of the turbine as whole depend on the available head and

type of application altogether.

A complete investigation and intensive research are carried out and efforts are put

forth in the improvement of turbine performance, the selection of suitable materials, and the construction design in consideration of difficulties imposed by

mechanical, manufacturing, and maintenance factors at the design stage.

Working of Francis Turbine

Francis Turbines are generally installed with their axis vertical. Water with high

head (pressure) enters the turbine through the spiral casing surrounding the guide vanes. The water looses a part of its pressure in the volute (spiral casing) to

maintain its speed. Then water passes through guide vanes where it is directed to

strike the blades on the runner at optimum angles. As the water flows through the runner its pressure and angular momentum reduces. This reduction imparts

reaction on the runner and power is transferred to the turbine shaft. If the turbine

is operating at the design conditions the water leaves the runner in axial direction. Water exits the turbine through the draft tube, which acts as a diffuser

and reduces the exit velocity of the flow to recover maximum energy from the

flowing water.

Power Generation using Francis Turbine For power generation using Francis Turbine the turbine is supplied with high

pressure water which enters the turbine with radial inflow and leaves the turbine axially through the draft tube. The energy from water flow is transferred to the

shaft of the turbine in form of torque and rotation. The turbine shaft is coupled

with dynamos or alternators for power generation. For quality power generation speed of turbine should be maintained constant despite the changing loads. To

maintain the runner speed constant even in reduced load condition the water flow rate is reduced by changing the guide vanes angle. TThhee mmaajjoorr ccoommppoonneennttss iinnvvoollvveedd iinn ttuurrbbiinnee eerreeccttiioonn 1. Draft Tube Liner 2. Pivot Rings 3. Runner 4. Guide Mechanism a) Guide Vanes

b) Servomotors c) Links /lever d) Regulating Rings

5.Top Cover and bottom Ring 6. Turbo shaft and its bearing 7.Spiral Casing and Stray rings 8.Shaft Seal

9.Wicket Gates and Operating Mechanism

The turbine at NTPC Koldam is Francis Turbine.

Type : Francis with vertical shaft

Numbers : 4

Synchronous speed : 166.66

Rated net head(m) : 131.2

Generator rated output(MVA) : 222

TThhee ddeettaaiilleedd ssttuuddyy ooff ppaarrttss ooff FFrraanncciiss

TTuurrbbiinnee

DRAFT TUBE LINER

The most commonly employed draft tube is of elbow type, in a concrete structure, fixed with anchoring materials. Overall configuration of the draft tube is thoroughly checked at TOSHIBA Research Laboratory to ensure effective use of the head energy. The draft tube liner, of welded construction, is made of steel plate for general structure. With a larger draft tube, the horizontal section of the draft tube liner outlet is constructed with one or two center piers.

The draft tube liner is normally shipped or supplied to the site in several split pieces due to transportation limitation. These pieces are usually welded together during the field assembly. If necessary due to theoretical and practical reasons, a special air admission system is provided with a draft tube liner to reduce water-pressure pulsations in the draft tube.

Upper draft tube liner

Draft tube liner

The draft tube is a conduit which connects the runner exit to the tail race where

the water is being finally discharged from the turbine. The primary function of

the draft tube is to reduce the velocity of the discharged water to minimize the loss of kinetic energy at the outlet. This permits the turbine to be set above the

tail water without any appreciable drop of available head. A clear understanding

of the function of the draft tube in any reaction turbine, in fact, is very important for the purpose of its design. The purpose of providing a draft tube will be better

understood if we carefully study the net available head across a reaction turbine. The purpose to providing a draft tube The effective head across any turbine is the difference between the head at inlet to the machine and the head at outlet from it. A reaction turbine always runs

completely filled with the working fluid. The tube that connects the end of the

runner to the tail race is known as a draft tube and should completely to filled

with the working fluid flowing through it. The kinetic energy of the fluid finally discharged into the tail race is wasted. A draft tube is made divergent so as to

reduce the velocity at outlet to a minimum. Therefore a draft tube is basically a

diffuser and should be designed properly with the angle between the walls of the tube to be limited to about 8 degree so as to prevent the flow separation from the

wall and to reduce accordingly the loss of energy in the tube.

SPIRAL CASE AND STAY RING

The hydraulic research of the water passage through the spiral case to stay vanes becomes very important

in diminishing the losses of the flow and the angle

and the shape of stay vane cascades are carefully designed.

A new type of construction (parallel type)

advantageous in structural design is applied to all the stay rings.

The spiral case is made of steel plates for welded

structures or high tensile strength steel plates. This is provided in Reaction Turbine to distribute water uniformly through gates

into the runner & to give tangential whirl component of velocity to the runner.

This is normally weld fabricated of plate steel. While designing care is taken to achieve the uniform flow by gradually

reducing the sections. Spiral Casing is made in parts to suit transport

limitations. Smaller Spiral Casing cross sections have been achieved by increasing the flow velocities at spiral intake. The velocity coefficients are

normally kept between 0.14 (for low Ns) & 0.20 (for high Ns). However the

velocity should not exceed 9 to 10 m/sec (at max. flow).

With the event of more advanced methods of stress analysis & computer

technology considerable improvements have been achieved in plate thickness. For low head applications, customer some time prefer to go for concrete spiral

which work out cheaper compared to steel spiral.

During concreting the steel spiral, a reasonable gap is kept on top of spiral from

centre line by laying a wool felt of required thickness. This gap will allow

expansion of spiral during pressurizing & at the same time relives it from external loading due to concrete.

Most of these machines have vertical shafts although some smaller machines of

this type have horizontal shaft. The fluid enters from the penstock (pipeline leading to the turbine from the reservoir at high altitude) to a spiral casing which

completely surrounds the runner. This casing is known as scroll casing or volute.

The cross-sectional area of this casing decreases uniformly along the circumference to keep the fluid velocity constant in magnitude along its path

towards the guide vane.

Spiral case for 266MW turbine with 411m head Stay ring for 730MW turbine with 146m head

Shop assembly of spiral case and stayring for 730MW turbine with 146m head

SPEED RING

To resist the bursting forces due to pressure inside the spiral, the throat of the spiral outside the guide vanes is bridged by the ring of fixed stay vanes which

resist the axial loads on the spiral. The ring is sectionalized as necessary to meet

the shipping requirements. Weld fabricated & cast stay ring facilitate easier & better shop site erection in view of their inherent rigid construction & provides

for better alignment. Well designed construction provides greater resistance

against distortion during shop manufacture & at site against concrete working. To avoid distortion and to maintain dimensional stability, weld fabricated and cast

stay rings are stress relieved to relieve the residual internal stresses of forming,

welding & casting. Stay Ring made in parts is joined by studs which are slogged or heat tightened to achieve the required elongation. The inside profile of the

contour is seal welded to prevent leakage of water during testing & normal

working of Turbine. One or two stay vanes are made hollow to facilitate drainage of water from shaft seal by gravity in addition to the ejector. The ejector will

come into operation as soon as the level in top cover reaches the predetermined

level.

GUIDE APPARATUS Guide Vanes regulates the quantity and direction of the water to the Runner.

Smaller and medium sized vanes are cast in mild steel or stainless steel or

bronze. Relatively larger gates are of fabricated plate steel welded construction or dowelled to the vane trunnions. Longitudinal sealing edges, pivot ring & top

cover adjoining faces are mild steel guide vanes may be protected with stainless

steel against corrosion and abrasion. Pitting and wear on these faces is made good by weld overlay. Rubber sealing strips along the length of the vane and on

the top cover and pivot ring faces may be provided to reduce water leakage

during Shutdown or Synchronous Condenser Operation. The ring of vanes are swiveled for regulation by lever & link arrangement from

the regulating ring. The connecting link between lever and regulating ring is

provided with a safety device braking link or shear pin to break in the event of obstruction between guide vanes preventing the gate closure. The regulating ring

mounted on the top cover is rotated by one or two or more hydraulic Servomotors, through the connecting rods. The ring which is of cast iron, cast

steel or plate fabricated according to sizes and loads to be carried, has pins bolted

to the lower flange to which the guide vane links are attached. Turn buckles are used for adjustment of

bedding clearances which is simple in design compared to eccentric pin and can

cater for wider adjustments. HEAD COVER AND BOTTOM RING The head cover and the bottom ring are so designed as to avoid causing excessive deformation which may lead to seizure of wicket gate movement. Particular care is taken to ensure that the positioning of bores to receive the wicket gate stems which should be matched between the head cover and bottom ring. For a larger diameter of bore size, these bores are accurately positioned and machined by using numerical controlled machines. Upon special request, seal packings of the trapezoidal section will be located in grooves machined in the distributor faces of the head cover and bottom rings to minimize water leakage through the wicket gates fully closed. Top cover is the part of guide apparatus and the bearing required for guide vanes.

It is bolted on speed ring & covers the top of Guide Vanes and Runner. Top labyrinth is also housed in top cover which reduces the leakage and thus saves

the water which otherwise have gone to waste without producing the energy.

Loading on top cover is also reduced by introducing the runner labyrinth and relieving holes. Top Cover design depends on the turbine size, head and erection

method. Weld fabrication is widely adopted for large sized covers. The structure

is designed to provide adequate rigidity against cover deflection and slope at guide vane due to water load, servo reaction loading G.V. reaction and bearing

loads. Generator stator bore diameter shall be kept slightly bigger clearing the

O.D. top cover for taking out the top cover on house supports for guide bearing, shaft gland, regulating ring, air valve & piping. In the region adjoining the guide

vanes in the closed position the top cover surface is provided with stainless steel

linear plates. These linear plates can be of welded type or screwed type. Screwed type of linear plates are adopted in case customer wants it replaceable and spare

linear plates are supplied for this purpose.

Head cover Bottom ring

PIVOT RING

Pivot Ring or bottom cover houses the lower bearing of the guide vane and is

usually welded plate or cast steel construction. It is made in single piece or in

parts to suit transportation. It is provided with linear plates in similar way as adopted for top cover.

MAIN SHAFT

The main shaft for the turbine is made of high-grade forged carbon steel. When the size of the main shaft

exceeds the limitation of forging capacity or transportation or it is echonomical,

the main shaft is formed by welding steel plates or a combination of forged steel and steel plates.

The main shaft is connected to the generator shaft or

the intermediate shaft by a flange coupling. The shaft surface passing through the shaft seal is protected with a stainless steel shaft

sleeve to prevent the main shaft from wearing. Forged steel shaft, with working stress of approximately 350 to 500 kg/cm

2 at

rated output having UTS of having 5200 kg/cm2 are quite conservative and

assume reliable service. The shaft is coupled to the Runner through keys or fitted bolts at the lower end and through fitted bolts to the generator shaft at the

coupling end.

Forged shaft Fabricated shaft

SHAFT SEAL The gland has a function that is it prevents leakage of water up the shaft by providing a positive seal and the entry of air into the turbine at low pressure. There are various design having two rubber flaps which are cooled and lubricating by clean water is how being adopted generally. TOSHIBA adopts two types shaft sealing systems;

Labyrinth sealing system and Carbon ring sealing system. The labyrinth sealing system is made of bronze metal and its sealing part is provided with several circumferential grooves on its inner surface. Clean water under appropriate pressure is supplied to the middle of the sealing part so as to prevent river water from coming up. This system features extremely simple maintenance because of no shaft-contacting part. The carbon ring sealing system is of special construction, using two different ring materials. Since the bottom layer is exposed to river water, a synthetic resin ring with high wear-resistant is used, while the other layers are provided with extremely reliable carbon ring. These rings are arranged for depression against the shaft surface by springs and attachments. Clean water is also supplied to this system to cool the seals and to lubricate these seal surfaces which contact the main shaft. TOSHIBA has a shaft seal test facility that provides high design reliability through a series of investigations

Typical structure of shaft seals

GUIDE BEARING

It is highly desirable that the bearing is of high rigidity capable of

accommodating large load bearing capacity. In this regard segment-type bearings have been widely used for many years with self lubrication method

which permits simplified construction. Lubricating oil in the oil reservoir is

cooled by cooling water passing through a built-in cooling coil. The bearing segment itself is of steel plate with babbit lined and the adhesiveness of the liner

is thoroughly

checked by nondestructive examination at the works. On the other hand, cylindrical bearings are used occasionally, considering their

rigid, compact design. Depending on requirements, forced circulated

lubrication may be used for the main bearings of small capacity turbines. Turbine Bearing can be lubricated by water, grease or oil. In small size machine

rubber pads with water lubrication can be provided. Forced grease lubricated white metal lined bearings can be used for the smallest to largest sized shafts. But

these have not met such favour because of the disadvantage or continuous

wastage of grease. This has led the preference oil lubricated bearing of forced circulating type or oil

immersed self pumping type. Self oil lubricating white metal bearings generally

used for large size turbines, can be of shall or type with stationary or rotating sump. Titleling pad which have got advanced of achieving desired clearance at

site by simply rotating the studs and locking it in desired position.

The gland has a function that is it prevents leakage of water up the shaft by providing a positive seal and the entry of air into the turbine at low pressure.

There are various design having two rubber flaps which are cooled and

lubricating by clean water is how being adopted generally.

Typical structure of main guide bearings WICKET GATES AND OPERATING MECHANISM Design of the wicket gates must meet the requirements of both hydraulic and structural

strength. The wicket gates are usually made of carbon steel castings for the low head,

while stainless steel castings are adopted for the high head. Welded construction

wicket gates may be used for a low head or a large turbine, if required.

A wicket gate is usually manufactured in one piece together with its upper and lower

stems, with one or two upper bearings and one lower bearing all of which are

grease-lubricated or self-lubricated (oil-less) type.

The self-lubricated (oil-less) bearing has a base metal of aluminum manganese bronze

with a PTFE-type solid lubricating agent, offering excellent sliding characteristics

and mechanical strength and it is also used for the link mechanism.

The wicket gate operating mechanism is installed with eccentric pins between the gate

operating ring and each wicket gate to allow individual adjustment of wicket gate

openings. Shear pins with carefully calculated size are provided with an operating

mechanism. A pin will shear, should a wicket gate become blocked, and the remaining

gates can be operated as required. In some stations, a friction device is installed, which

prevents a free wicket gate from flutter or erratic movement without restricting

normal operation of the remaining gates when a shear pin break.

Wicket gates for a low head turbine Wicket gates of welded structure

Wicket gates for a high head turbine

Wicket gates servomotor Wicket gates operating linkage Self-lubricated bearing for wicket gate stem

Wicket gates operating mechanism

AIR VALVE

The tendency towards lower pressure in the draft tube during sudden load rejection results in rough and noisy running of the machine. This condition is

alleviated by vacuum is achieved due to sudden load rejection. In addition to

these valves one valve is provided which is directly connected to atmosphere and admits air as soon as it is required in the draft tube through the spider.

RUNNER The runner is designed in consideration of various parameters for computation by both

theoretical analysis of internal flow and experimental investigation by model tests.

The runner is usually made of carbon steel castings and overlay coating of

stainless steel welding will be made on critical areas of cavitation if necessary. For

higher head machines, the runner is made of stainless steel castings.

Especially 13%a Chrome steel with enriched Nickel content becomes widely used for

its excellent anti-cavitation-corrosion characteristics and mechanical strength.

If a welded runner is required for large capacity turbines, the vanes, crown and band may sometimes manufactured separately and subsequently welded together into one

runner. When a single piece runner is impossible due to transportation, the runner is

split into two or more sections.

The edges of runner blades are finished by numerical cantrolled machine to obtain

accurate curvatures of the edges which contribute for high performance.

The shape of the blades of a Francis runner is complex. The exact shape depends on its specific speed. It is obvious from the equation of specific speed. that higher

specific speed means lower head. This requires that the runner should admit a

comparatively large quantity of water for a given power output and at the same time the velocity of discharge at runner outlet should be small to avoid cavitation.

In a purely radial flow runner, as developed by James B. Francis, the bulk flow is

in the radial direction. To be more clear, the flow is tangential and radial at the inlet but is entirely radial with a negligible tangential component at the outlet.

The flow, under the situation, has to make a 900 turn after passing through the

rotor for its inlet to the draft tube. Since the flow area (area perpendicular to the radial direction) is small, there is a limit to the capacity of this type of runner in

keeping a low exit velocity. This leads to the design of a mixed flow runner

where water is turned from a radial to an axial direction in the rotor itself. At the outlet of this type of runner, the flow is mostly axial with negligible radial and

tangential components. Because of a large discharge area (area perpendicular to

the axial direction), this type of runner can pass a large amount of water with a

low exit velocity from the runner. The blades for a reaction turbine are always so

shaped that the tangential or whirling component of velocity at the outlet becomes zero. This is made to keep the kinetic energy at outlet a minimum.

Three Gorges Dam Francis Turbine Runner

Runner for 266MW turbine with 411m head

Servo motors

When the turbine load changes during generating operation, the servo motor shall operate the guide vane smoothly coordinating with the speed governor. The

operation shall be performed by oil pressure supplied from the pressure supplied

from the pressure oil supply system .the servomotors shall be capable to close the guide vane from the fully opened position to the fully closed ones against

maximum hydraulic pressure of 600m in water column due to water hammer

after load rejection.

Guide mechanism There are two main functions of the guide mechanism (a)To regulate the quantity of water supplied to the runner and (b)To adjust the direction of flow so that there is minimum shock at the entrance to runner blades. It consists of series of guide vanes of aerofoil section fixed between two rings, in the form of wheel known as guide wheel, Each guide vane can be rotated about the pivot centre ,which is connected to a regulating ring by means of a link and lever. By operating the regulating ring the vane can be rotated, varying the width of the flow passage between adjacent vanes, thus altering both the flow angle as well as quantity of flow.

AASSSSEEMMBBLLYY OOFF FFRRAANNCCIISS TTUURRBBIINNEE

325MW turbine with 116.2m head for Wivenhoe power station

266MW turbine with 411m head for Arimine No.1 power station