Download - Final Project
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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