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SUMMER TRAINING UNDERGONE

AT NATHPA JHAKRI HYDRO

POWER PROJECT (250x6 MW)

NATIONAL INSTITUTE OF TECHNOLOGY

HAMIRPUR, (H.P.) 177005

(A Deemed University)

MAY-JUNE 2009

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ACKNOWLEDGEMENT

Foremost, I express my sincere thanks and gratitude to “Er. Harish

Sharma” and “Er. Jeeta Ukhal”, my Project Guides for their valuable

guidance and inspiration throughout the project. Their abundant enthusiasm

and zeal, with which they solved my difficulties whenever I approached

them.

I also express my heart-felt gratitude to “Er. Hans raj”, who cleared my

doubts regarding the operation of the Plant.

I would also like to commend the friendly support of the people at SJVNL.

As always and do shall remain, the moral encouragement and warm

affection from all the engineers and associates has helped me to come much

better with the successful completion of my project thereof.

AVINASH SINGH DOGRA B.TECH MECHANICAL ENGG. NIT-HAMIRPUR (06316)

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INTRODUCTION  TO  SJVNL The Satluj JaL Vidut Nigam Limited SJVNL (formally Nathpa

Jhakri power corporation limited - NJPC) was incorporated on

24th may 1988 as a joint venture of Govt. of India and Govt. of

Himachal Pradesh plan investigate , organize , execute , operate

and maintain Hydro Electric Power Project in the Satluj

River . Nathpa Jhakri ( 6x 250MW ) is the largest hydro -

electric project in India. A comparison with other

comparable projects ( single power station of 500MW and

above ) in India. Total capacity of this project is 1500 MW. It

is having 6 units of 250 MW capacity of each. The 1500MW

Nathpa Jhakri Hydro Project is the largest under ground hydro

project in the country and is the first project undertaken by SJVNL

for execution. Different states to which the balance power is

allocated are Himachal Pradesh , Haryana , Jammu & Kashmir,

Punjab, Rajsthan,Utter Pradesh, Chandigarh and Delhi.

The approved cost of the project was Rs. 7666.31 crores with

completion cost of 8058.34 crores. On completion the project had

cost Rs. 9083 crores.

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The main components of this project are: a) A 67.5 m high diversion dam on the Satluj River.

b) An underground desilting complex.

c) A 27.4 m long head race tunnel.

d) A 301 m deep surge shaft.

e) Steel lined pressure shaft.

f) Underground power house and transformer hall.

Nathpa  jhakri  project­a  brief  on  salient 

features It has a 62.50 m high concrete gravity dam at Nathpa village of

Kinnaur district of Himachal Pradesh and it divert 486 cumecs of

water through 4 Nos. power Intakes

Underground Desilting chamber 4 Nos. each of 525m long, 16.31 m

wide and 27.50 m deep which is the largest underground complex

for desiltation of water in the World.

A head race tunnel of 10.15 m dia. And 27.39km long which is the

longest power tunnel in the world and terminates to 21.6m/ 10.2m

diameter

It has the deepest surge shaft which is 301m deep.

There are three circular steel lined pressure shafts each of 4.9 m dia.

And 571 m to 622 m length which feed six generating units.

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The six generating units with Francis turbine of 250 MW and utilize a

design discharge of 405 cumecs and a design head of 428 m.

The discharge tubes to the collection gallery for discharging the water

back into the river through the 10.15 m dia and 982 m long tail race

tunnel.

The project has an underground Transformer hall and Power

house. There is a Surface Switch Yard for evacuation of power

through two no. of transmission lines.

The project also has an interesting feature of Sholding Works

Complex which enable diverting the water of Sholding Stream into

the HRT.

Annual energy generation of 6750.85 million units in a 90% (MU)

dependable year.

This project has also provided direct and indirect employment by

various national and international contract agencies working on the

project.

 

 

 

 

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Other main features of the project

Human resource development : The company is having well established strategy for imparting training to

the employees and involves other professional people to motivate the

employees for good working. The training imparted is two dimensional

i.e. in house training and through external professional institutions as

well.

Safety concern: SJVNL abides by its moral responsibility for maintaining a safer

environment for all its employee and also these of its contracting agencies

.Due attention is given to health and safety aspects in working areas. The

safety measures adopted encompass the best codes and practices, which

are disseminated to all the employees for ensuring compliance at all levels.

Future project: Agreement for the execution for the Rampur Hydro Electrical project

between SJVNL and govt. of Himachal Pradesh was signed on 20th October

2004 of 412 MW utilizing the tail race water of ongoing 1500MW Nathpa

Jhakri Hydro Electric Project is a run of the river scheme works for which

nave already been commenced by SJVNL and other project in the state

H.P.viz. Khab and Luhari projects and in Uttranchal and Sikkim shell be

taken for execution.

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Some Planning And Design Aspect :

Cable Anchors: It was found that a large number of cable anchors

of 200 tones capacity shall be needed in the dam complex. 285 cable

anchor have been provided for the excavation in the intake area. Another

185 have been installed in the left bank of dam and road to the top of

dam. 131 cable anchors are being installed for stabilization of both the

banks in the plunge pool area extending from 90 m downstream of dam

axis to 150 m downstream of dam axis.

Reservoir Flushing : Satluj river carries heavy sediment load during

snowmelt and monsoon season. Provision of low level sluices in the

dam ensures outflow of sediments from the reservoir whenever the water

availability is more that the design discharge. Further flushing of reservoir

behind Nathpa dam is also envisaged once or twice every year when the

discharge in the river exceed 1500 cumecs.

Desilting Cavern: The four desilting chambers are required to

function under adverse conditions of both external and internal water

pressure. Complete analysis both for the rock support during

excavation and long term stability during maintenance condition was

carried out through numerical modeling which involved through

investigation based on field and laboratory testing of rock mass properties

and geological details of joints, major shear planes etc.

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Head Race Tunnel :

    Tunnel Lining In Hot Water : Hot water has been encountered

in the HRT downstream of Wadhal Adit junction for a length of about 3

km. the chemical test of water has revealed that it can be aggressive to

normal concrete. Special precaution in concrete mix design with use of

pozzolana were taken to counteract the aggressiveness.

Steel Liner In HRT : Steel liner with length of 710 m and 375 m

respectively have been provided at Manglad and Daj creek of the head race

tunnel where rock covers are inadequate against maximum internal water

pressure which ranges from2.8 to3.1 MPa. With a view to avoid stress

relieving and limit the plate thickness to 40 mm the diameter of the

steel liner has been reduced to 8.5 m with transition both upstream and

downstream to 10.15 m diameter. In the absence of information of water

able in the hill full external pressure up to the natural surface has been

taken in the design of steel liner for the external water pressure.

Maintenance Access : Being a very long HRT it would be difficult to

inspect the same in case of emergency / shutdown. Keeping this point

in view intermediate vehicular accesses have been planned through Nathpa

and Wadhal construction adits here steel doors in an opening in the

concrete plugs has been provided.

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Power House Cavern : Only rock bolting and shotcreting has been adopted for the

excavation in the machine hall cavern. An integrated design approach

comprising empirical design through the NGI’s “Q” system, numerical

modeling and analysis of geological features were adopted for the

support system. A complete analysis of various stages of excavation

was carried out through numerical modeling and deformation was

monitored through multi - point borehole extensometers . The

deformation observed was within the predicted limits.  

DAM:  The function of the dam is not only to raise the water surface to

create artificial head but also to provide the poundage. Storage and facility

for diversion into conduit. The dam is straight gravity type dam having

the height 62.5 m on Satluj River at Nathpa to divert 405 cumecs of

water through four intakes. The dam is most important part of the

hydro electric project. It is built of concrete or stone masonry on a rock

hill.The length of the dam at the top is 170.2 m consisting of 63 m as non

over flow structure and 88.2 m as sluice block section with each having the

size 7 x 7.35 m With crest 1458.0 m.

Catchment area of the dam 49820 sq.km.

Design Flood 5660 cumecs.

Maximum water level 1495.50 m.

Minimum water level 1474.00 m.

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1) Selection Of Dam: Selection of dam to be constructed at a particular site depends upon

topography, Foundation survey , soil condition and other characteristic

of the location . The foundation of the dam must be sufficiently

strong to withstand the weight of the structure, water pressure etc.

without crushing , sliding or permitting movement of the structure .The

foundation of the dam should be sufficient impervious so that there will

be no objectionable passage of water.

2) Spill Way Gates: There are two spill way gates on the dam situated at Nathpa on Satluj

River. These act as a safety valve. It discharges the overflow water to

outside the dam when reservoir is full . This condition arises during

flood. These gates can be opened and shut automatically when water

overflows of the level and closes when water reaches in the level.

3) Radial Gates: There are five radial gates in the dam located in the lowest point of

the dam. Radial gates are always closed. They can be opened only in

condition when trees come in dam or reservoir due to flood. All these

things can be discharged through these gates. So radial gates can be opened

in these conditions.

4) Intake Gates: Intake structure comprises of four intakes of about 500 m long these

inlets of river has been designed to handle a discharge of 846 cumecs.

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Intake gates are trash racks type. The suitable opening of 19.26 m * 15.7 m

at the start of the base is reduced to 6m*5.2m through a suitable

transition. A continuous skimmer wall with top at EL. 1468.73 m is made

in front of all the four intake gates to restrict the entry of sediments into

the intakes. An opening provided in the skimmer at the downstream end

through which the bigger sediments are flushed out. Through four intake

gates the water goes to desilting chamber.

5) Desilting Chambers: An underground desilting arrangement comprising of four chambers is

made on the left bank of the river Satluj to exclude silt particles down to

0.2 mm size from water before it enter head race tunnel. Four intakes has

been made to feed four chambers through each tunnel respectively. The

flow to the chambers is regulated by the gates at the intake. There are four

desilting chambers each have a three meter wide collection trench in the

centre running along its length. The sediments from the collection trench

will fall down to the flushing tunnel 5m in diameter horse sluice. The

flushing gates will be provided at the junction of flushing conduits and main

flushing tunnel. Top of each chamber is connected to the head race tunnel

through link tunnel of diameter 5.02m. It reduces the flow of water and

also prevents the particle of 0.2 mm to the turbine. Here the water flows

with a velocity of 33.4 cm/sec.

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6) Silt Flushing Gates: There are four silt flushing gates they create a pressure in the

desilting chamber and Suck out salt and particles at the edge of the

desilting chamber.

7) HRT Intake Gates: After desilting chamber water goes through HRT intake gates. They

are also four in no. The water at the output of each HRT intake gates are

combined to main head race tunnel.

Head Race Tunnel The head race tunnel is 27.3 km long and have diameter 10.15m. it is

one of the largest Head Race Tunnels in he world. The tunnel diameter is

based on the techno economic studies for a discharge of 405 cumecs at

a flow velocity 5m/sec.The rock cover of head race tunnel vary from

about 90 m to about 1480 m along its length the head race tunnel is

provided with steel lining where the rock support is not expected.

There are six audits in the head race tunnel : a) Nathpa Adit EL. 1450.89m.

b) Sholding Adit EL. 876 m.

c) Nugalsari Adit EL 647 m.

d) Wadhal Adit EL. 842 m.

e) Manglad Adit EL.691 m.

f) Rattanpur Adit EL.1357 m

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Sholding Works: In order to augment the flow during the lean months of water

scarcity the water of the sholding khad one of the cribularies of Satluj river

is having a 26m long tunnel that divert a discharge of 8 cumecs through

a tunnel having a diameter of 2m. from here the water will enter the

hooper and desilting chamber.

Surge Shaft: The main surge shaft is located at the intake of the penstock at 27.3

km form head race tunnel. It is just like wall. Its function is to avoid the

water hummer effect. Three penstocks are taken from the surge shaft at the

bottom , two from side of surge shaft and one is taken from the centre of

the surge shaft. A 12 m dia Horse shoe shaped 185m long lower gallery

at EL 1370m has also been provided. The minimum water level in the

surge shaft is about 30 m. The surge shaft is concrete lined of adequate

thickness. It is the deepest surge shaft in the world.

Three drainage galleries at different elevations has been provided

around the surge Shaft to relieve the external water pressure on the lining.

Pressure Shaft: Three shafts of diameter 4.9m and length varying from 619m to 660m

take off from the surge to an angle of 45 degree to the horizontal. These

are lined with high tensile steel of thickness varying from 32mm to

60mm. Each pressure shaft is bifurcated into the branch tunnel of dia

3.45 m. Each pressure shaft is designed to carry a discharge of 315

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cumecs . Butterfly valve housed in valve chamber has been

constructed in the horizontal reach of pressure shaft for its repair and

maintenance. A spherical valve has been provided in each penstock branch

tunnel inside the machine hall cavern to enable closing of penstocks

whenever required.

Other features of surge shaft : a) pressure relief valves has been provided in the top 80 m of the

concrete lining to reduce the external pressure as an additional

margin.

b) A 25 cm deep sill beam has been provided on the collar of the

surge shaft to prevent any trash lying on the pond floor.

c) The slopes of the top pond are well drained. The drainage water is

disposed off very far away from the pond.

d) Due to very high head and difficulty in maintaining verticality of

guide rails, stop logs could not be provided in the surge shaft.

e) An inspection ladder has been provided in the connecting shaft

forming approach to the drainage galleries.

Valve Assembly: The valve assembly consists of a top and bottom valve body and a

double lattice valve disc assembly with all necessary seals, bearings and

seats. A valve chamber 79.52 m long 9.5 m wide and 22.34 m high has

been excavated 106 m downstream of the surge shaft essentially in quartz

mica schist.

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Valve Body : The valve body is manufactured in cast steel and are flanged on both

sides. The top and bottom sections are assembled with an ‘O’ ring seal

and locilite 574 between faces and located with stainless steel dowels.

The valve incorporate support feed fabricated with the valve body to

available the valve to secured to the foundation by the use of soleplates.

Valve Seat: Two valve seats are fitted within the valve body to form seal with each

disc seal on The lattice blade with valve in the closed position. During

normal operation the Downstream forms the water seal. The downstream

is machined with the ‘O’ ring seal located groove. A Nitrile rubber ’O’

ring seal is assembled in the groove and prevent leakage b/w the valve ring

and seat ring.

Maintenance Seal : The purpose of the guard wall maintenance seal is to provide a double

isolation when used in conjunction the service seal. The principle of

double isolation is essential whenever personnel are required to enter the

downstream – dewatered penstock. The upstream and downstream

chambers formed between the seat ring and the valve body are connected by

drilling to a penstock pressure water control system.

Air Release Valve:

Fitted on the top of the valve body is a orifice air release valve,

operated by a float. The valve release air to atmosphere during fitting of

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the valve body and when full of water seals the orifice to prevent

leakage. Most of the air trapped during penstock filling will be released

via the four anti vacuum valves. When all four anti vacuum valves are

closed all remaining trapped air is released via these valves operated by a

float.

Anti-Vacuum Valve Assembly: Four Anti-Vacuum valves are fitted and two on each side of the

downstream pipe works. The 500mm nominal diameter float operated

anti vacuum valves sense the pressure drop downstream of the penstock

guards valve and open and allow air into the penstock preventing the

formation of vacuum. When the chamber is filled with water the float

rises extending the springs and contacts the Nitrile rubber sealing ring

POWER HOUSE : Nathpa Jhakri project has an underground power house with

internal dimensions 222 m* 20 m and 29 m high located at 200 m

below the natural earth level . The main access tunnel to the power house

is 731.5 m long .The power house has an arched roof with concrete lining.

The main inlet valve has also been provided at an EL. 982.5

The power house has four floors .

The turbine floor is at an EL. 990 m . The main auxiliaries in this

floor are Governor , Oil cooler , Brake Dust Collector , Oil Vapour

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Collector , Secondary water pump and the turbine pit . The turbine

is coupled with Generator with the help of the shaft.

The generator floor is at an EL. Of 995 m here we also have Unit Auxiliary

Board, Temperature measuring gauges, the Excitation Transformer for

providing the Starting torque to start the generator and the 220 V battery

room.

Service Bay Floor at an EL. Of 1000.5m from here the functioning of

generating units is controlled with the help of operating system .

MIV Floor is the lowermost floor of the power house. It contain six

individual MIVs, each weighing 92 tonnes and being controlled by the

lifting of a counter weight 76 tonnes by means of a servomotor which is

operated hydraulically.

The construction cum downstream Surge gallery is provided to reach

the tail race and to facilitate the excavation of the machine hall , the tail

race and pressure shaft.

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Fig1: Block diagram of power station

 

TURBINE : The Turbine used here is the “ VERTICAL FRANCIS TURBINE ”

means the rotating parts of the unit have a vertical axis of rotation.

This turbine belongs to the reaction turbine family. The water is under

pressure as it enter the runner and completely fills all its channel as it

passes through . The head for the Francis turbine is usually between

that of Kaplan ( low head ) turbines and that of Pelton (high head)

turbines.

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TURBINE FUNCTION: The water from the penstock enter the spiral casing. In the spiral

casing , the water is spread around the whole circumference by stay

vanes , and is lead in towards the guide apparatus. The guide apparatus has

movable vanes , which are controlled by the governor and can be set

independent of output. After this impact the water continues in the Draft

Tube and out the tail race tunnel. The effect is transferred from the Runner

to the Generator, which is directly connected to the Turbine Shaft. The

turbine develops the power partly due to the velocity of the water and due

to difference in pressure acting on the front and back of Runner buckets

such a Turbine essentially consist of guide apparatus consisting of outer

ring of stationary guide blades fixed to the casing of turbine and an inner

ring consist of rotating blade forming a wheel or a Runner. As the water

passes over the rotating blades of the Runner both pressure and

velocity of the water reduced causing a reaction force on the turbine.The

guide blades of the turbine are pivoted about axis an parallel with turbine

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axis so that quantity of the water entering in the turbine may be

regulated by turning them simultaneously in one direction or the other,

their motion is automatically controlled by Governor. Francis type turbines

can be constructed in vertical or horizontally but horizontal construction

more accessible and have higher speed, but for large machine vertical

construction is preferred to effect higher speed. As compare to Pelton wheel

a Francis turbine offer advantage of high efficiency at full load and at 75%

of full load . This turbine can be designed fir higher speed than Pelton Wheel

.The gross head of the turbine is 488m and design head is 425m.

TURBINE COMPONENTS: 1) Rotating parts.

2) Turbine guide bearings.

3) Turbine upper and lower cover.

4) Guide vanes.

5) Governor (Regulating mechanism).

6) Spiral casing.

7) Draft tube.

8) Shaft seal.

9) Dewatering system.

1.) ROTATING PARTS : There are mainly three rotating parts:

a) Runner.

b) Turbine shaft.

c) Oil slinger.

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a) Runner:

The Runner has been welded up from crown and band of stainless

cast steel to Vanes from stainless steel plates. The vanes have been

machine worked. The crown band have “Roots” towards the vanes.

Air for stabilizing purpose is allowed through the Runner centre via the

shaft seal and drilled holes in the turbine shaft flange. The moment of

force on the runner is transferred to the turbine shaft through the

shear pin connection. The coupling bolts between the turbine shaft

flange and the Runner are tensioned by means of hydraulic

wrence.

b) Turbine Shaft:

The turbine shaft is made of SM steel with flanges hammered

out at both ends. The turbine shaft and generator shaft are connected

by flanges. The connection primarily transfer the moment of force

through the shear studs.

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Francis Turbine Runner

c) Oil Slinger:

The Oil slinger is located below the turbine bearing and

connected to the turbine shaft. Its purpose is to collect the oil from turbine

bearing and during operation bring the oil into rotation inside the slinger

cylinder from where it is catched by the oil scraper and led to the oil cooler

and the bearing oil reservoir.

2.) Turbine Bearing : Bearing Design:

The turbine bearing is radial vertical slide / guide bearing. The

bearing has a strong construction and a simple manner of operation, which

require a minimum of maintenance. The bearing house is split and attached

to the upper turbine cover. It has two manhole hatches for access and

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inspection of shaft seal and pipe connections. The bearing shell consist of

two segments, which are bolted together and attached to the upper side

of the bearing house. The shell has four oil pockets and four babbit metal

Surfaces with machined wedge shaped entrances , which ensure a stable

centering of The turbine shaft. The bearing has been fitted with an

inspection hatch ,dip stuck for oil slinger, Fluid level gauge for bearing

house, thermometers and level switches for surveillance. The bearing has

been fitted with external oil cooler. This is automatically put into

Operation when the cooling water system is started.

Bearing Function:

When the unit starts the oil slinger start rotating , oil is slung

up into the cylinder section and cover the vertical with a layer of oil. The

thickness of this layer will be determined by the position of the oil scraper.

The amount of the oil in the oil slinger is regulated by means of the oil

scraper, which is attached to the bearing shell When there is a sufficient

rotating speed , the damming up pressure become strong enough to

force the oil up through the ascending pipe through the oil cooler and out

into the bearing house. From there the oil flows down through the four

windows in the bearing house cover and is spread out to the four oil pockets

in the bearing shell. A film of oil follow with the shaft in the wedge shaped

entrance on the bearing shell and builds up the guiding oil layer.

3.)Turbine cover: The Turbine has two covers:

Upper cover and Lower cover

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Upper Cover: The upper cover is bolted to the spiral casing ring. It

serves as a bearing for the regulating ring and a support for the upper

stationary labyrinth seal, turbine inner cover with shaft seal as well for the

longest trunnion of the guide vanes. The interchangeable upper

stationary labyrinth seal is made of forged steel and is bolted to the

cover. The seal surface on the labyrinth seal faces the equivalent seal

surface on the upper rotating labyrinth seal bolted to the Runner.

Lower cover: The lower turbine cover is bolted to the spiral casing stay

ring. It serves as a support for the short trunnion of the guide vanes, the

lower stationary labyrinth seal and the draft tube cover. Supporting

sleeves of Aluminum Bronze for guide vane bearing have been installed.

Corrosion resistant austenite steel has been welded into the wearing

Psurface of the lower turbine cover between the wear ring and the lower

labyrinth seal.

4.) Governor: The Turbine has two servomotors. The connection between the

servomotor and the regulating ring consist of an adjustable connecting

rod and a spherical bearing. It sense the speed of the turbine

rotation and generate a signal proportional to the difference between

the turbine speed and the governor speed reference and therefore

develop a hydraulic control signal sufficient to control the turbine. The

adjustable rod is used for pre tensioning the guide apparatus.

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When pre tensioning the guide apparatus the guide vanes

are given a Moment which produces a force toward closed

position. This compensate for slackening and deformation in the lever

and link connection and provides a closing force greater than or

approximately equal to hydraulic opening force on the openings

force on the vanes with full pressure in the spiral casing.

5.) Spiral Casing: The spiral casing the waterway between the penstock and the guide

apparatus. It has been constructed to ensure constant water speed

around the whole Circumference of the guide apparatus. The spiral casing

is built from a stay ring and a plate shell to an all welded construction of

fine grained sheel steel .The spiral ring is consisting of an upper and lower

ring connected to each other by welded stay. The stays has been shaped

in a hydraulically favorable way in order to lead the water in towards

the guide apparatus with the least possible loss.

The spairal casing has been fitted with outlets for index

measurements and a manhole for inspection. The outlets for pressure

measurements , dewatering and air escape are positioned on the expansion

box at the inlet of the spiral casing . The main part of the spiral casing has

been concreted in a solid slab being supported against the downstream

rock wall. The hydraulic force acting on the spiral casing inlet is thereby

balanced against the rock.

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Spiral casing 6.) Draft Tube: The outlet consist of a draft tube and a draft tube steel lining

continuing with a concrete lined tunnel and forms the water way from

the runner to the race Channel. The draft tube cone is welded and

consist of two parts. The upper part is bolted to the lower fixed

labyrinth seal. It is made from stainless steel. The lower part is attached

to the draft tube steel lining with a flexible flange connection. It has one

manhole for access to the draft tube and it is fitted with four stub pipes

with cover for installation of an inspection platform. The draft tube

steel liner is completely set in concrete. It has been welded and fitted

with a flange toward the draft tube cone. The draft tube can be

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emptied into the dewatering pit by slight extension of the cross section in

the direction of the flow from the runner outlet to the end of the plate

covering. The draft tube have 10 segments with a plate thickness of 30

mm and total wt.34000kg.

7.) Shaft Seal : Shaft seal is attached to the inner cover , which again is attached

to the upper turbine cover. Due to the rotation of the water in the gap

between the runner and the upper turbine cover the gaps in the shaft seal

will be water free when the turbine is in operation. In order to prevent

the contaminated water downstream of the turbine to enter past the

upper labyrinth seals and up through the shaft seal during start and stop

of the unit. When the shaft has come to a complete standstill the service

seal will be closed , valves in drainage and overflow pipes will be

automatically closed and flushing water pump stopped. At certain output

the turbine may need air to the outlet section of the runner. This

ventilation take place through a separate air pipe, which is connected to the

shaft seal support ring. The air pipe is fitted with a check value preventing

the tail water from leaking out during standstill.

8.) Shaft Seal Flushing Water: In order to prevent the contaminated water from entering into the

shaft seal during start and stop sequence of the unit and when rotating

speed is too low to keep the shaft seal dry , the shaft seal flushing

water system will provide filtered water at sufficient water. The intake is

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from the pressure equalizing piping between upper turbine cover and draft

tube. A centrifugal pump is increasing the pressure and flushing strainer

particles above 200 micron is removed. The system will

automatically be put into operation during start and stop of the unit.

9.) Penstock Dewatering System: The dewatering system consists of one high pressure drainpipe for

each unit. The inlet is upstream the MIV and the system consist of a gate

valve and a hand manufactured needle valve. Dewatering is made from

the penstock to the draft tube down to the tail water level. After setting the

draft tube gate the remaining water is drained through the draft tube to the

dewatering pit from where it is pumped to discharge outside the draft

tube gate by dewatering system.

The movement of MIV is shown in the fig. below:

MIV in Closed Position

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MIV fully Opened

10.) Guide Apparatus : The Governors action on the two main servomotors is

transferred via rod connections to the regulating ring . The actual

guide apparatus consists of 23 guide vanes, check plates on upper and

lower turbine cover as well as guide vane lever and links.

The guide vanes are made of forged stainless steel and had

been shaped to provide the best possible hydraulic conditions. The guide

vanes have bearings on upper and lower turbine covers . These are self

lubricating slide bearings with Teflon covering. The coupling between

guide vane and guide vane lever is a pure friction coupling, thus

allowing the guide vane to slide away in case of foreign object is

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preventing the guide vane from being closed. An alarm in that case

will be activated. The guide vane lever and regulating ring is connected by

links. The links are joined by self - lubricating bushing on stainless steel

pins attached to the regulating ring and the guide vane lever respectively.

The guide vane movement is shown in the fig.

a)

0% OPEN

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                         100% OPEN

 

GENERATOR:  The vertically mounted synchronous generator converts the

hydraulic energy of water into electrical energy. The generator will be

vertical shaft type having salient poles with closed air circuit ventilation

and suitable for coupling to a machine turbine.

It will have static excitation system energizing the field coils. The

slip rings, Permanent magnet generator and mechanical over speed

device will be located suitably on a fabricated shaft, which in turn will be

fitted to a rotor spider. The speed of the turbine wheel must therefore

match the synchronous speed of the generator.

The generator will have a combined thrust and guide bearing below

the rotor. The generator will have the rating and characteristic as the

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components will be designed to withstand seismic forces as applicable.

Generator Components : The generator consist of following components-

1. Foundation

2. Stator

3. Rotor

4. Air water cooling system

5. Slip ring system

6. Excitation

7. Bearing

8. Braking and lifting equipment

1) Stator : The rotor winding is excited by a direct current

and induces a voltage in the stator winding. This is taken by Bus

bar to the main current lines. The stator consist of the Frame ,

Laminated stator core and the stator winding embedded in the

slots of the laminated core.

HOUSING – Depending upon the operating condition of the

machine, the generator housing absorb the generated mechanical

loading and transfer these to the foundations.

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Generator components

STATOR FRAME – The stator frame will be build up of weld able steel

plates and will have adequate depth to prevent distortion during transport or

under any operating condition.

STATOR CORE -- The stator core will be built of stamping of high

grade , non aging cold rolled silicon alloy with varnished insulation on both

sides. The segments will be secured to the frame by dovetail notches

engaging with corresponding dovetail key bars welded to stator frame.

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ANTI CONDENSATION HEATERS – Low temperature to prevent,

condensation on the winding during period of shut down will be

mounted below the winding located below lower air guide. They are of

tubular or box type construction consisting of a coiled resistant wire

embedded in an electrically insulting and heat conducting compound and

protected with a metal sheath.

Air-Water Cooling:

The mechanical and electrical losses arising in the course of

operation of the and the temperature rise of the components this cause

must be reduced by cooling. generator rotor and stator are air cooled ,

while the bearings are water cooled.

The generator has a closed cooling circuit and is therefore sealed off on

all sides against the surrounding surface. The foundation walls from the

enclosure from the machine house, and the outer cover separates the

generator from the turbine room. The enclosure at the circumference is

provided by the generator pit. The cooling air enters tangentially through

the rotor and enters the stator through the gaps. The air water coolers

arranged after the stator removes the heat that the air has absorbed.

2) Rotor :

The rotor and rotor winding are excited with the direct current,

and generate a constant magnetic field. The rotational movement at the

specified synchronous speed induces a sinusoidal alternating current

voltage in all phases of the stator winding. The rotor will be designed to

safety withstand all mechanical stresses imposed by the maximum runway

speed. The static and dynamic balancing of the rotor will be carried

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out , as a part of precommissioning test at site and values of rotor

vibrations will be kept with in allowable limits according to satnderds.

The rotor consist of following components;

1) Shaft NDE

2) Pole wheel

3) Slip ring

4) Hub

5) Yoke ring

6) Long pole

7) Brake ring

8) Current feed

9) Pole body

10) Pole and plate

11) Pole winding

12) Damper winding

13) Pole body insulator

14) Shaft DE

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4) Slip Ring And Brush Gear :

The collector will be of mild steel and mounted on the top of

the generator tube shaft. The brush gear for the collector will be

mounted on insulated studs supported on the top bracket and will be

arranged to permit convenient access for maintenance and inspection.

The insulation for slip rings and their connections will be non-

hygroscopic and oil resistant. The slip ring system transfer the direct

current necessary for excitation of the rotor from the fixed brushes to the

slip ring and thus to the rotor poles.

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5) Bearings :

The two different bearings are attached to the rotor i.e. Guide

bearing and Thrust bearing. The thrust bearing must take up the entire

weight of the rotating components of the machine set (rotor and turbine)

and axial thrust of the hydraulic machine. Both journal bearing

together with turbine journal bearing ensure a centered machine run

from the standstill up to the runway speed of the turbine.

Thrust Bearing : Thrust bearing is of pivoted segmental pad type in

which the stationary parts consist of a set of Babbit segmental pad

supported on circular pad supports made of alloy steel forgings. The

bearing is self lubricated and immersed in oil bath in which plugged n type

of water cooled oil coolers are placed to remove the bearing losses. Radial

and circumferential movement of the pads is prevented by means of

stoppers.

Thrust bearing

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Guide Bearing : The guide bearing will be of the pivoted pad type

consists of arrow of white metal pads arranged in a support ring to bear

on a journal surface. A pivot bar will be bolted to the back of each guide

pad to enable the pad to rock slightly to take up a suitable position and

facilitate formation of oil film when running. The air surface above the

oil surface will be vented to the atmosphere by vapor pipes and air

pressurized oil vapor seal will be fitted to prevent the escape of oil vapor

into the generator air circuit.

 MAIN ELECTRICAL EQUIPMENTS :

1) Synchronous Machine (Generator) : It is a three phase double excited machine because its field winding

is energized form a dc source and its armature winding is connected to an

ac source. Its working as a generator delivers or exports ac power. A

synchronous generator is universally employed for the generation of three-

phase power at all generating stations. Most of the synchronous motors are

of silent pole type as it is most suitable for the slow speed water turbine

generators and are called Hydrogenates. There are six generators in the

power house each having 250 MW capacity and driven by speed of 300

rpm. Each generator is having 96 brushes in which 48 are positive and 48 are

negative. There are two slip rings one is positive and other is negative.

The slip ring give excitation Current to rotor through brushes according to

load.

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Generator specification:

Rated speed 300 rpm

Turbine Rated Head 428 m

Rated output 250 MW

Rated Output (Generator) 278 MVA

Power Factor 0.9

Terminal Voltage 15.75 KV

Manufactured By ALSTOM / GERMANY

2) Excitation System: In large synchronous machine the field winding is always provided on the

rotor. Some important excitation systems are :

DC Exciters : This is an old conventional method of exciting the

field winding of synchronous generator. Here three machines pilot exciter,

main exciter and three phase alternator are mechanically coupled and

therefore driven by the same shaft. The pilot exciter feed the field winding

of the main exciter. The dc output from the main exciter is given to the

field winding of the main alternator through brushes and slip rings. The

conventional method of excitation suffers from cooling and

maintenance problem as associated with the slip ring, brushes and

commutators as the alternator rating rise. This trend led to the

development of the static excitation and brushes excitation system.

Static Excitation : Here the excitation voltage for the main

alternator field is drawn from output terminal of the main 3- phase

alternator. For this purpose a three phase transformer TR step down the

alternator voltage to the desired value. This three phase voltage is fed to the

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3-phase full converter bridge using thyristors. The power output from the

thyristor is delivered to the field winding of the main alternator through

brushes and slip rings. For initiating the process of static excitation first of

all field winding is switched on to the station battery bank to establish

the field current in alternator. The alternator aped is adjusted to the rated

speed.

3) Braking and Jacking System : The generator brakes will consist of a number of steel shoes

mounted on a vertical piston moving in cylinder and will operate against

a polished circular steel brake track located on underside of rotor. Brakes

will be automatically applied when the speed of the rotor reduce to a

preset value and will remain applied continuously so that the unit stops

completely.

The brakes will also serve as a convenient means for jacking the

rotor for maintenance purpose for this a complete hydraulic rotor jacking

unit will be provided. Limit switch is provided which shows the

indication that the rotor is raised to maximum permissible limit. The

arrangement of piping will be such that after jacking system has been in use

air under pressure can be applied to the system to clear the pipes of oil.

4) Brake Dust Collector : The brake dust collector consists of an extraction unit, hoppers

around brake assembly for trapping the brake dust and flexible hoses for

connecting hoppers to the extraction unit. The extraction unit will have a

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motor driven exhaust fan and will be fitted with an easily removable

sheet steel bin for collecting heavy dust. The lighter air born particles will

be collected by a suitable fabric based filter. The starter panel for motor

having provision for automatic start and stop of the motor will also be

provided.

5) Oil Vapor System: The oil vapor extraction system sucks of the vapor of generator

bearing. This oil vapor is generated during operation and led to the filters

outside the generator room. The pollution of the machine is this way

avoided.

General:

As soon as the generator starts running with the operating

temperature , the oily fog Is developed in the bearing oil container by

very finally distributed oil drops . “Breathing” the oil in bearing or

pressure differences inside and outside the bearing cause the oil vapor, a

mixture of air and oil that produces a different wetting of the parts and

surfaces at the outside. These damp places result in providing an ideal

background for dirt beginnings . During high speed of rotor or high

load the differential pressure increases also between the bearing

chambers and the environment. In this case the bearing seal and shaft oil

separators cannot hold back the oil mist any longer. To prevent this then

generator was equipped with a special oil vapor suction system.

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Design And Function: Two pipelines are attached parallel above at the upper and

lower bearing chamber. The two pipes are led outward to the two

suction filters. The particles separated by the filter run off on the inside of

the separation pipe. The ventilator for the production of suction flow is

inserted above the separation pipe within the clean air side. An activated

Carbon filter is mounted behind the electrostatic unit to absorb smells and

gases. Cleaned air is blown by the activated carbon filter into the open air.

 

TRANSFORMERS The Transformers used are manufactured by BHEL.The various

specifications of the transformers are given below:

 

TRANSFORMER SPECIFICATIONS

Make Bharat Heavy Electrical Limited

Types of cooling ODWF(oil drift water force)

Rating HV & IV (MVA) 102

Rating LV (MVA) 102

No load voltage HV (KV) 420/√3

No load voltage LV (KV) 15.75

Line current HV (AMPS) 421

Line current LV (AMPS) 6476

Temperature Rise oil (OC) 55(deg)

Temperature Rise windings 65(deg)

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Phase 1(single)

Frequency HZ 50 Hz

Connection Symbol YNd 11

PARTS OF TRANSFORMER:

1) CONSERVATOR

It is used generally to conserve the insulating property of the oil from

deterioration and protect the transformer against failure on account of bad

quality of oil. It is a small tank mounted on main tank and the two are

connected by a pipe. The main tank is completely filled with oil but

conservator tank is partially filled with oil. Its function is to allow space for

expansion of oil due to heating and contraction due to cooling of oil

2) SILICA GEL DEHYDERATING BREATHER

The breather is used to prevent entry of moisture inside the

transformer tank. The breather consists of silicagel. When air is taken in or

out of the transformer due to contraction or expansion of oil in the tank,the

silicagel absorbs moisture and allows the air free from moisture and allows

the air free from moisture to enter the transformer.

3) BUCHHOLZ RELAY

It is a gas-actuated relay used for protecting oil immersed transformers

against all types of faults. It indicates presence of gases in case of some

minor fault and takes out the transformer out of circuit in case of serious

fault.

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4) BUSHINGS

Bushings are made from highly insulating material to insulate and to

bringout the terminals of the transformer from the container.

5) OIL GAUGE

Every transformer is provided with an oil gauge to indicate the oil

level.

6) TAPPINGS

The transformers are usually provided with few tapings on secondary

side so that output voltage can be varied for constant input voltage.

7) RADIATORS

The radiators increase the surface area of the tank and more heat is

thus radiated in less time. It is generally used in large capacity transformers

50 KVA and above.

8) NON RETURNING VALVE (NRV)

It is used where air is produced and is stored in compressor. It is

between compressor and air producer. It means that air is not returned back

when it reaches in the NVR.

9) OLTC

It is known as On Load Tap Changer. If the supply from the previous

sub-station is coming according to the requirement and less than the required

supply OLTC is used to increase the supply to level of load.

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10) WINDING TEMPERATURE INDICATOR:

It is a device which indicate the temperature of winding of

transformer and possible damage to the transformer due to overload can be

prevented. The sensing bulb of dial thermometer is inserted inside the

heating coil The terminal of heating coil are connected to temperature

gauge.

Gas insulated switch yard  The increased demand for electrical energy in big cities and

industrial areas has made it necessary to bring high voltage systems to the

load centers. It is very difficult and sometime impossible to find a suitable

place for installation of the air insulated switch gears. The SF6 GIS

guarantees out standing advantages for the planning and operation of high

voltage supply networks.The space requirement can be less than 10% of the

space taken up by air insulated switchgear ,as all the live parts are metal

enclosed and sealed the SF6 GIS is completely immune to atm. conditions.

With SF6 GIS all foreign bodies are prevented from coming into contact

with live parts this ensure maximum safety.

GENERAL RATINGS RATED VOLTAGE - 420KV

RATED NORMAL CURRENT- 4000A

RATED FREQUENCY – 50Hz

RATED LIGHTNING IMPULSE WITHSTAND VOLTAGE – 1425KV

RATED SWITCHING IMPULSE WITHSTAND VOLTAGE – 1050KV

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RATED SHORT TIME WITHSTAND CURRENT – 50KA

RATED DURATION OF SHORT CIRCUIT – 1s

RATED POWER FREQUENCY WITHSTAND VOLTAGE – 520KV

RATED PEAK WITHSTAND CUERRENT – 125KA

SF6 DENSITY NORMAL FILLING – 48.1Kg/m3

MINIMUM – 42.7Kg/m3.

SF6 GAUGE PRESSURE – (1013mbar) AT 20°C

NORMAL FILLING – 6.3 bar

MININMUM – 5.55bar

AMBIENT TEMPERATURE MAXIMIUM INDOOR – 30°C

MINIMUM OUTDOOR -20°C

DISCONNECTOR TYPE - SF16

EARTHIONG SWITCH TYPE - MR16-ML16

OPERATING DISONNECTOR AND EARTHING SWITCH DEVICE

TYPE - BET-CLT

 

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CURRENT BREAKER RATINGS TYPE - FB16

RATED S.C. BREAKING CURRENT SYMMETRICAL – 50KA

RATED S.C. MAKING CURRENT – 125 KA

OPERATING SEQUENCE : TRANSFORMER 0-3min-CO-3min-CO.

OPERATING SEQYENCE : BUS COUPLER 0-0.3s-CO-3min-CO.

SF6 DENSITY

FILLING – 48.1kg/m3

MINIMUM – 42.7kg/m3.

SF6 GAUGE PRESSURE(1013mbar) AT 20°C

FILLING – 6.3 bar

MINIMUM – 5.55bar

CIRCUIT BREAKER OPERATING MECHANISM TYPES CIF 70-40-240

TRIP COIL DC 220 V

OTHER EQUIPMENTS LBB PTOTECTION AND TRIP CIRCUITS – SUPVN

GIS – A SAFETY ASPECT GIS has considerably lower risk of injury to personnel due to enclosed

live parts. 

Electric fields are shielded by grounded GIS enclosures. 

Magnetic fields due to conductor current are reduced by GIS

enclosure current. 

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Worker exposure to electric and magnetic field in GIS  is generally

limited to vicinity of GIS interfaces. 

 

ADVANTAGES OF GIS GIS is compact in size .

Insulation not exposed to environment.

High reliability

Reduced static and dynamic operating load.  

DISADVANTAGES OF GIS High cost .

Long outage period as repair of damage part at site is difficult.

Requirement of cleanliness are very stringent.

Dust and moisture inside the compartment can cause flashover.

 

VARIOUS COMPONENTS OF GIS Circuit Breakers  

Isolators and earth switches. 

Bus bar 

Current and voltage transformer 

Surge arrestor 

Bushings 

Metallic bellows 

Local control cubicles 

Monitoring device 

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DESIGN ASPECTS OF DAM 

1) RADIAL GATES: These are manufactured by GE(UK) Ltd. These are 5 in number and their

purpose is to prevent the overtopping of dam and flooding. During the

period of high water level the gates are opened to release water in a

controlled and safe manner. Depending upon the water level and rate of

water rise one or more gates can be opened. The gates are basically used to

regulate the water level with in the water level and for flushing put sediment

upstream of dam.

Each radial gate is operated by the two double acting hydraulic

cylinder retract to open and lower the gate. Five units are installed for each

gate and all are interconnected so that one unit can be used for any of the

gate in case the unit corresponding to particular gate fails.

Five petrol driven emergency pumps units are also been installed

enabling a further method of gate operation in case of emergency.

A local control house located between gate 1&2, houses the power unit and

controls for gate 1,2&3 and another local control house is located between

gate 4&5, houses the power unit and controls for gate 4&5.

The complete hydraulic system is manufactured by Dennley Hydraulics

(dennley engg. Co. heckmondwike ltd.) .

The radial gate assembly comprises of following subassemblies:

1) Gate leaf fabrication

2) Cross bracing Structures

3) Radial arm assemblies

4) Pivot hubs and bearings

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5) Guide roller assemblies

6) Sill Seals

7) Side Seals

8) Lintel Seals

9) Dogging Arrangement

2) TECHNICAL DATA:

RADIAL SLUICE GATES

Quantity 5

Clear Span of Opening 7.5m

Clear Depth of Opening 9.13m

Sill Level 1457.37m

Lintel Level 15466.50m

Gate Lip Fully Open Level 1467.20m

Skin Radius (inside) 12m

Pivot Trunnion axis level 1467.00m

Full Reservoir Level (FRL) 1495.50m

Max Reservoir Level (MRL) 1498.5m

Silt Depth 9.13m

Seismic Coefficient Horizontal 0.28g

Seismic Coefficient Vertical 0.14g

Design Code IS4623:1984

Permissible Stresses

Gate 0.55ys

Skin Plate 0.45ys

Embedded Parts 0.4ys

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Occasional Loads 133% (normal Stress)

Hoist Type Double Acting Servo

Gate Speed Operation 0.6m/min ± 10%

Hoist Design Code IS10210:1993

Material

Skin Plate Stainless BS1501 gr304 S61

Gate Structure BS EN 10025 gr275

Seal Faces Stainless Grade 304L

Anchor Girder BS EN 10025 gr275

Anchor Ties BS EN 10025 gr355

GATE OPERATING CYLINDERS

Quantity 10 (2 per radial gate)

Cylinder Bore 420mm

Cylinder Rod diameter 200mm

Total Stroke 7808mm

Working Stroke 7742mm

Seismic Design Coefficient 0.28g

Max push per cylinder (extended) 332KN (at servo after losses)

Max pull per cylinder 1800KN (at servo after losses)

Working Pressure (annulus) 200 bar

Working Pressure (full bore) 40 bar

Test Pressure 300 bar

Cylinder Operating speed 0.475m/min ± 10%

Design Code IS10210 (1993)

Mounting Gimbel Barrel Mounting

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Full bore Pressure relief valve 28bar

Cylinder Piston Transducer 24V dc supply

4-20 mA output

4 mA extended

20 mA retracted

Proximity Switches

Quantity 2 (per cylinder)

Supply 24V dc

Type Inductive Wire Type

Setting 55mm from end of retracted stroke

70mm from end of extended stroke

HYDRAULLIC POWER UNIT

Quantity 5

Operation Normally each unit is dedicated to its

respective gate.

Emergency Reservoir All 5 units are interconnected so that

each unit can be used to operate any

gate.

Hydraulic Reservoir 2000 liters capacity

Hydraulic Oil Mineral ISO VG15

Hydraulic pump Tandem Type

Hydraulic Pump Motor 415V, 3Phase, 50 Hz, 55kW

Working Pressure Up to 200bar (gauge)

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PETROL ENGINE DRIVEN EMERGENCY PUMP UNIT

Quantity 5

Power Source Petrol Engine

Starter HandPump/Accumulator

Engine Power 60W (80 BHP) approx

Cooling Water Cooled and Cooling fans

Hydraulic Pump

Speed approx 2000rpm

Output Min of 80 liters per minute at 200bar

gauge.

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