Final Training Report

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A Report on

6×250 MW NATHPA JHAKRI

HYDROELECTRIC PLANT

Prepared during the six week vocational training at Nathpa

Jhakri hydroelectric plant

Submitted to: Submitted by:

Antra Chowdhury

Anchal Sood

Kusal Chandel

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ACKNOWLEDGEMENT

We are thankful to our respective colleges for providing us an opportunity to

undertake six week vocational training at Nathpa Jhakri hydroelectric plant

and see in such detail the operation of the largest hydroelectric project in

India.

We express our sincere thanks to the GM/HOP Er. N.C. Bansal for

allowing us to undertake this vocational training. We want to thank our shift

in charge at the power house, Er. Shiv Prasad for ensuring that we make most

of our time at the power house in the operations department.

Also, we acknowledge the help extended by Er. Nishant Thakur, Er. Aman

Gupta, and Er. Rohit Verma whenever approached, in introducing, explaining

and clearing the concepts of the operation at the power house.

Yet again, the moral encouragement and cooperation from all the technicians,

foremen and associates has helped us to a successful completion of our training

thereof.

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PREFACE

The report attempts to provide an overview of the operation of the largest

hydroelectric project of the nation. It begins with an introduction of how the

project came into being. It then provides a sequential account of the course

that the river Satluj takes and how this water ultimately leads to a generation

of 1500MW. The report intends to provide a sufficiently detailed version of the

generation as well as transmission of hydroelectric power. Also, it presents the

various wisely applied mechanisms, auxiliaries and protection schemes etc.

that lead to the successful operation of the power house.

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INDEX

Title Page

Introduction 5-9

Project statistics 9-10

Overview of the Project 10-12

Nathpa Dam Site 12-17

Service Bay Floor 17-20

UAB Floor 21-30

Turbine Floor 31-41

MIV floor 42-45

Common Power plant auxiliaries 46-49

SILT Lab 49-50

Transformer Hall 50-54

Fire fighting system 54-55

GIS-1 55-58

POT Head Yard 58-62

Control Room 62-63

Unit Start/Stop Sequence 63-67

RSD1/RSD2/ESD 67-69

Future Projects 69-70

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Sjvn Limited- A Profile

SJVN Limited, a Mini Ratna & Schedule „A‟ CPSU under the Ministry of Power, Govt. of

India, is a joint venture between the Govt. of India & Govt. of Himachal Pradesh.

Incorporated in the year 1988, the Company is emerging as a major hydro power player in the

country.

SJVNL is presently operating the Country‟s largest 1500 MW Nathpa Jhakri Hydro Power

Station (NJHPS) in Himachal Pradesh which has been recognized as an engineering marvel

for its unique features.

Nathpa Jhakri Project- Salient Features

1) It has a 62.50 m high concrete gravity dam on Sutlej River at Nathpa village of Kinnaur

district of Himachal Pradesh.

2) World‟s largest underground Desilting Complex comprising of four chambers (each 525

m long, 16.31 m wide and 27.5 m deep).

3) One of the world‟s longest Head Race Tunnel of 27.39 km length and 10.15 m dia.

4) The HRT divides into 3 pressure shafts and they eventually divide into 6 penstocks.

5) It has the world‟s deepest Surge Shaft of 301 m depth.

6) Underground Power House with a cavern size of 222 m x 20 m x 49 m having six

Francis Turbine Units of 250 MW each.

7) The generated voltage of each unit is 15.75 KV and transmitted at 420 KV.

8) It is a run-off with small pondage type hydel project in which the river is diverted to the

dam which doesn‟t have a lot of capacity

9) There are three circular steel lined pressure shafts each of 4.9 m dia. and 571 m to 622 m

length which feed the six generating units.

10) 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.

11) The draft tubes to the collection gallery for discharging the water back into the river

through the 10.15 m diameter and 982 m long tail race tunnel.

12) The project has an underground Transformer hall which has 19 transformers to step up

the generated voltage of the 6 units before transmission. There is a Surface Switch Yard

for evacuation of power through two transmission lines.

13) The project also has an interesting feature of Sholding Works Complex which enables

the diversion of the water of Sholding Stream into the HRT, which is useful during the

lean season.

14) Annual energy generation is 6750.85 million units in a 90% (MU) dependable year.

15) A discharge of 1 cumec generates 4 MW power.

Location of the Project:

The 1500 MW Nathpa Jhakri Hydroelectric Project (NJHEP) is the first project undertaken

by SJVNL for execution. The generation component of the 6X250 MW Nathpa Jhakri Hydro-

Electric power project (NJHEP) in the Shimla and Kinnaur District of Himachal Pradesh

(H.P.) was sanctioned in April 1989 for execution by the Nathpa Jhakri Power Corporation

(NJPC) now known as Satluj Jal Vidyut Nigam Ltd. (SJVNL). NJPC effectively took over

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execution of NJHEP in August 1992. NJHEP envisages harnessing the Hydro power potential

in the upper reaches of river Satluj in the South West of Himalaya.

The Power House is 150 KM from the nearest Rail Head (narrow gauge) Shimla. The project

stretches over a length of about 50 KM from the dam site to the power house, on the

Hindustan Tibet Road (NH-22), which also connects the rail head to the project. The major

civil works of Nathpa Jhakri Hydro Electric Power Project were awarded during 1993 and the

construction commenced in 1994.

Expertise in Operation and Maintenance of Hydro Power Station:

The 1500 MW Nathpa Jhakri Hydro Power Station (NJHPS) has been running successfully

during the past eight years. The power station has generated over 38837 MU of electricity

during these years.

Serial No. Year Gross Energy Generation (in MU)

1 2003-04 1130.121

2 2004-05 5170.830

3 2005-06 4104.430

4 2006-07 6014.490

5 2007-08 6448.975

6 2008-09 6608.710

7 2009-10 7018.810

8 2010-11 7140.205

9 2011-12 2340.977 (till 22 June 2011)

Beneficiary States

The power generated is supplied to the following states:

Sr.

No.

State Allocation (In MW) Percentage of the

installed capacity

1 Haryana 64 4.27

2 Himachal Pradesh 547 36.47

3 Jammu & Kashmir 105 7.00

4 Punjab 114 7.60

5 Rajasthan 112 7.47

6 Uttar Pradesh 221 14.73

7 Uttaranchal 38 2.53

8 Chandigarh 08 0.53

9 Delhi 142 9.47

10 Unallocated quota at the disposal of the

Central Government

149 9.93

TOTAL 1500 100%

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Power Transmission:

In June 2009, SJVNL entered into a memorandum of agreement with IL&FS Limited, the

Power Grid Corporation of India Limited (PGCIL) and the PTC Financial Services Ltd. for

the establishment of a joint venture to construct and maintain the Indian part of a

transmission line connecting Nepal and India.

Grid Scheduling

As per the rule, any company selling electricity to PGCIL (Power Grid Corporation Of India

Limited) needs to declare its power schedule for the next day in terms of blocks of 15

minutes and the company is paid on the basis of that. If the generated electricity is less or

more than the schedule declared, penalty is imposed on the power selling company depending

on the grid frequency, i.e. only if the frequency is less than 50 Hz. Deviation from actual

energy generation is adjusted on the fourth day‟s generation. As per the bill board agreement

between SJVNL and NRLDC (Northern Region Load Dispatch Centre), SJVNL has to

declare MW exchanged (ceiling value for each 15 minute time block), MWH for the entire

day (ceiling value). In case of any revision in the generation schedule, the grid needs to be

informed minimum 6 hours before the change takes place.

The tariff plan, on the basis of which the grid pays to SJVNL, takes into consideration the

following:

a) ABT (Availability Based Tariff)

b) Energy Charge

c) UI charge (Unscheduled Interchange/ Injection)

The term Availability Tariff, particularly in the Indian context, stands for a rational tariff

structure for power supply from generating stations, on a contracted basis. The power plants

have fixed and variable costs. In the Availability Tariff mechanism, the fixed and variable

cost components are treated separately. The payment of fixed cost to the generating company

is linked to availability of the plant, that is, its capability to deliver MWs on a day-by-day

basis. The total amount payable to the generating company over a year towards the fixed cost

depends on the average availability (MW delivering capability) of the plant over the year. In

case the average actually achieved over the year is higher than the specified norm for plant

availability, the generating company gets a higher payment. In case the average availability

achieved is lower, the payment is also lower. Hence, the name „Availability based Tariff‟.

This is the first component of Availability Tariff, and is termed „capacity charge‟.

The second component of Availability Tariff is the „energy charge‟, which comprises of the

variable cost of the power plant for generating energy as per the given schedule for the day. It

may specifically be noted that energy charge (at the specified plant-specific rate) is not based

on actual generation and plant output, but on scheduled generation. In case there are

deviations from the schedule (e.g., if a power plant delivers 600 MW while it was scheduled

to supply only 500 MW), the energy charge payment would still be for the scheduled

generation (500 MW), and the excess generation (100 MW) would get paid for at a rate

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dependent on the system conditions prevailing at the time. If the grid has surplus power at the

time and frequency is above 50.0 cycles, the rate would be lower. If the excess generation

takes place at the time of generation shortage in the system (in which condition the frequency

would be below 50.0 cycles), the payment for extra generation would be at a higher rate.

Thus, the Indian version of Availability Tariff comprises of three components: (a) capacity

charge, towards reimbursement of the fixed cost of the plant, linked to the plant's declared

capacity to supply MWs, (b) energy charge, to reimburse the fuel cost for scheduled

generation, and (c) a payment for deviations from schedule, at a rate dependent on system

conditions. The last component would be negative (indicating a payment by the generator for

the deviation) in case the power plant is delivering less power than scheduled.

As mentioned earlier, the energy charge, at the specified energy charge rate of a generating

station, is payable for the scheduled energy quantum. The energy actually supplied by the

generating station may differ from what was scheduled. If actual energy supplied were higher

than scheduled, the generating station would be entitled to receive a payment for the excess

energy (the deviation from schedule, technically termed as Unscheduled Interchange (UI) in

Availability Tariff terminology) at a rate dependent on frequency at that time. If the energy

actually supplied is less than what is scheduled, the generating station shall have to pay back

for the energy shortfall, at the same frequency - linked rate.

UI rate:

Rs. 0 at 50.20 Hz to Rs. 8.75 at 49.50 Hz

Money is reimbursed based on two factors:

1) Plant availability factor

2) Energy generated

Plant availability factor: The NJHEP is a 1500 MW project and at the rated generation, the

ex- bus is 1482 MW. At 10 % overloading, it can generate 1650 MW. Suppose, for a day

maximum ex-bus declared by NJHEP is 1600 MW, then the PAF for that day is 107 %

(1600/1482) *100. Same is calculated for each day and average yearly PAF is calculated

by taking the average of all the daily PAFs. It has to maintain a minimum PAF of 84 %. The

total amount payable to NJHEP towards the fixed cost depends on the average PAF over the

year. In case, the average PAF actually achieved over the year is higher than the specified

norm, it gets a higher payment. For instance, suppose the fixed cost is 1200 crores and the

average PAF is 98 %, then the fixed cost paid by the grid will be 1400 crores

(98/84)*1200.

Energy based charges depends on the energy charges of the nearest thermal power plant.

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Project Commissioning Schedule

The commissioning schedule of NJHEP was as follows:

Unit MW Synchronization Commissioned

Unit-V 250 Sep. 29, 2003 06 Oct., 2003

Unit-VI 250 Nov.23, 2003 02 Jan., 2004

Unit-IV 250 Jan. 22, 2004 30 Mar, 2004

Unit-III 250 Feb. 13, 2004 31 Mar, 2004

Unit-II 250 Mar 09, 2004 06 May, 2004

Unit-I 250 Mar 31, 2004 18 May, 2004

Project Statistics

Description As Per Revised Cost Estimate

1. Location

State

District

Vicinity

2. Diversion Dam

Type

Max. height above foundation level

Full reservoir level

Min. draw down level

3. Desilting Arrangement

Type

Number & size

Flow through velocity

Particle size to be removed

4. Head Race Tunnel

Shape & type

Diameter

5. Surge Shaft Diameter

Total height

Himachal Pradesh

Kinnaur/Shimla

Dam downstream of Wangtoo bridge at Nathpa &

power house near Jhakri village on left bank of river

Sutlej.

Concrete gravity

62.5m

1495.5 m

1474.00m

Underground

Four parallel chambers each 525m x 16.31m x 27.5m

33.0 cm/sec.

Particle greater than 0.2 mm

Circular, concrete lined

10.15m

21.6m circular for height of about 210.0m & a

connecting shaft of 8.8 m diameter. And about 90.0m

high.

301.0m

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6. Pressure Shafts Type

7. Power House Type

Size

Type of turbine

Gross head

Design head

Number and capacity of generating

units

8. Tail Race Tunnel Size

Length

9. Power Potential Energy generation in a dependable

year

Circular, steel lined with high tensile steel

Underground

222m x 20m x 49m

Vertical axis Francis turbine

486m

428m

6 x 250 MW

10.15m, circular

982m

6750.85 MU in a 90% dependable year

Overview of the Project

The Nathpa Jhakri Hydro Electric Project is based on the discharge of river Satluj. The water

of the Satluj River is not stored in the Dam but some part of the water flowing in the river is

diverted into the Dam using radial gates and the rest of the water flows normally in the river.

As there is no storage, this project is a run off the river type project. To remove the extra

water from the reservoir, spillway gates have been provided.

The water enters the HRT from four intake gates, which are followed by four Desilting

chambers. The excessive silt needs to be removed from this water and this is made possible

due to the Desilting complex in the dam. This complex can be cleaned using the silt flushing

gates. The water finally flows into the Head Race Tunnel which is about 27.3 Km long. Its

construction is a tedious and time consuming process. Thus, for easy completion of this task,

the contract is given to various companies and they start digging from different regions of the

same tunnel at the same time. This speeds up the process and after the entire tunnel has been

made using the GPS navigation, the sites of digging are closed and then they are called

ADIT. The various ADIT employed in the construction of the HRT were:

Nathpa Adit

Sholding Adit

Nulgalsari Adit

Waldhal Adit

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Manglad Adit

Ratanpur Adit

The Sholding Complex is an important feature during the lean season. The water from this

khad goes into the head race tunnel to add to the discharge.

At the end of the HRT lies the Surge Shaft (at Ratanpur) to absorb the back hammering of

the water in the HRT and hence, avoid its damage from the huge force the water may exert in

case of closing of the pressure shafts. The surge shaft is followed by the valve house

containing three butterfly valves. The water from the HRT goes into three pressure shafts if

these valves are open. These pressure shafts further divide into 6 penstocks, which end in the

spiral casings of the 6 generating units. For the rotation of the runner of a particular unit, the

Main Inlet Valve after the penstock must be open. The water after passing through the turbine

flows through the draft tubes to get accumulated into the tail race tunnel, whose contents are

then thrown back into the river at the outfall.

The power house at Jhakri is an engineering marvel in itself. It consists of a huge

underground complex comprising a massive Machine Hall, which also houses the Control

Room, a fully equipped conference hall. The power house measures 222m x 20m x 49m. It

consists of a centralized control room, an exhibition room, a medical room, silt testing

laboratory and many rooms for the various concerned officials. The benefits of an

underground power house, as compared to the over ground one are as follows:

1. Being close to the border with China, an underground power house is comparatively safer

from sabotage.

2. An underground power house provides better safety against an earthquake.

3. An underground power house is secure from the danger posed by potential landslides,

which may otherwise wreck havoc.

The power house at Jhakri receives the water of the River Sutlej from the Dam site through a

network of underground tunnels that passes through the Surge Shaft and the Butterfly valve

House. Eventually the penstock empties into the MIV located in the lowermost floor of the

powerhouse. Before proceeding further, a note must be made of the vertical cross section of

this powerhouse. It consists of the following floors, enumerated from top to bottom:

Service Bay Floor (Elevation: 1000.5m above mean sea level): It is the topmost floor where

each of the six units of the power house are represented as a circular unit. Each unit has a pair

of green and red indicator. The red light goes on when unit is in the operating condition.

Generator Floor (Elevation: 995m above mean sea level): This floor is directly located

below the Unit Bay Floor. It houses the six generators of the power house, one for each one

of the six units of the power house. It also houses the bus duct and the various auxiliaries

associated with the working of the generator.

Turbine Floor (Elevation: 990m above mean sea level): This floor, which is directly below

the Generator Floor houses, the six vertical axis Francis turbines. Each one of the six turbines

receives water from the six MIV which are opened using hydraulic pressure created by the

governor system on this floor.

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MIV Floor (Elevation: 982.5m above mean sea level): This floor is the lowermost floor of

the power house. It contains six individual MIVs, each weighing 92 tonnes and being

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

operated hydraulically using oil.

There is an underground Transformer Hall at an EL. 1044 m and is 270 m long and 7 m D-

shaped. There are 19 single phase Transformers, one being a spare transformer. These are

used to step up the generated voltage for transmission.

Above the transformer hall is the GIS-I (Gas Insulated Switchyard), which is used to

synchronize the stepped up voltage to the bus voltage and also to couple the two buses

together. This uses the compressed SF6 (Sulphur Hexafluoride) gas for insulation and the

circuit breakers and isolators also use the same gas. This switch yard has been made possible

underground due to the use of this gas, which makes it safe for such an operation.

GIS-I is connected to GIS-II, which opens outside the power house and is also known as POT

HEAD YARD (Point Of Transmission Hydro-Electric Aerial Distribution Yard). This is

used to synchronize two incoming lines from BASPA-1 and BASPA-2 with the bus and then

transmit the same and the generated voltage to Abdullapur and Nalagarh.

Nathpa Dam Site

The dam site of Nathpa (Distt Kinnaur) is at distance of 48 Km from the power house at

Jhakri (Distt. - Shimla) by road. It is located on the Hindustan Tibet road, which traverses

steeps gorges & near vertical slopes as it winds its way along the river Sutlej.

The dam at Nathpa is a concrete gravity type diversion dam. As such, it is not a storage dam

& can only provide backup water supply for 4 hours during lean periods. The base of the dam

site is merely 8m wide. The function of dam is not only to raise the water surface to create

artificial head but also to provide the poundage. The height of dam 62.50m on Satluj River at

Nathpa to divert 405 cumecs of water through four intakes .The dam is most important part of

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

Following are the detailed statistics for the Nathpa dam:

Type Concrete gravity type diversion dam

Base of dam 1433.0m

Top of dam 1495.5m

Max. height of dam above foundation

level

62.5m

Length of dam at road level 170.2m

Full reservoir level 1495.5m

Max. water level 1495.5m

Min. draw down level 1474.0m

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Pondage available 441 hectare meter

Spillway type Overall spillway or solid gravity spillway

Number & type of gates 5 nos. radial gates

Selection of Dam

Selection of the dam to be constructed at a particular site depends upon topography,

foundation survey, soil condition and other characteristics 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.

Spill Way Gates

There are two spill way gates on the dam situated at NATHPA River SATLUJ. They acts as a

safety valve. It discharges the over flow water to outside the dam when reservoir is full. This

condition arises during flood and machine tripping. These gates can be opened and shut

automatically when water overflows to the level and closes when water reaches in the level.

Spillway gates can‟t be closed manually. The spill way has to bays each of 7.5/2.5m inside

and shall be controlled by two counter weight balanced gates used for maintaining level of

the reservoir at EL-1495.50m.

Crest level EL-1492.50m

Gates Two counter weight balanced gate each of size 2.5*7.5m

Radial Gates

There are five sluice radial gates in the dam. Radial gates are always closed. They can be

opened during the Dam flushing, at the time of high discharge and in the event of flood in

river. The hydraulic motors used open and close radial gates are interconnected through

bypass valves so each gate can be opened or closed by any one of hydraulic motor. The

opening speed of hydraulic motor is 0.5 meter per minute when opened electrically and half

of it when opened from petrol engine driven pumps. It takes 19 minute for full opening of a

radial gate when operated electrically.

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Intake Gates

There are four intake gates through which water goes to desilting chamber. Before Intake

gates, trash racks are provided to avoid entry of heavy material like boulders etc to enter in

the HRT. The Intake structure, comprising of four intake gates is about 500m long. This inlet

of river has been designed to handle a discharge of 486 cumecs. An inclined independent

trash rack, four vertical and one horizontal has been purpose in front of each intake with trash

racking machine located at the platform provided above following reservoir level to facilitate

cleaning of rocks. The rectangular opening of 19.26m*157m at the start of the base is

reduced to 6.0m*5.2m through a suitable transition.

Desilting Chambers

An underground desilting arrangement comprising of four chambers is made on the left bank

of the river Satluj to settle silt particles down to 0.2mm size from water before it enters the

head race tunnel. Four intake gates are made to feed the four chambers through each tunnel

respectively and independently. The flow into the chambers is regulated by gates at intakes. a

proper transition from 6.0m wide approach tunnel to 16.31m wide at the center and 27.5m

high, leaving semi circular roof and 5m deep continuous Hooper at the bottom. Each chamber

will have a 3m wild collection trench in the center running along its length. The Hooper

portion of the chamber slopes towards this trench. The sediments from the collection trench

flow down to the flushing tunnel 5m in diameter. The flushing gates will be provided at the

junction of flushing conduit and main flushing tunnels. It reduces the flow of water and also

prevents the particle of 0.2mm to the turbine. It is the underground complex for the

generation of Hydroelectric Power in the world.

Type Underground

No. & Size

Four parallel chambers each 525m long,

16.31m wide at center and 27.5m deep.

Flow through velocity particle size to be

removed

33.4cm/sec particle greater than 0.2mm.

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Silt Flushing Gates

Silt flushing gates are also four. They create a pressure in the desilting chamber and flush out

silts and particles at the edge of the desilting chamber.

HRT Intake Gate

After desalting chamber water goes through HRT intake gates. Like desilting chamber, HRT

intake gates are also four. The water at the output of the every HRT intake gates are

combined at main Head Race tunnel.

Head Race Tunnel

The 10.15m diameter circular Head Race Tunnel from the junction point at the link tunnels

from desilting chambers to the surge shaft is 27.3 km long. The tunnel diameter is based on

techno economic studies for a discharge of 405 cumecs. The rock cover of HRT varies from

about 90m to about 1480m along its length. The Head Race Tunnel is provided with steel

lining in the Manglat and Daj creek area where rock support is not expected.

There are six adits in HRT which were used during the erection work as the access approach

to the HRT.

1. Nathpa Adit EL-1450.89m, length 1062.50m.

2. Sholding Adit 876m

3. Nugalsari Adit 647m

4. Badhal Adit 842m

5. Manglat Adit 691m

6. Ratanpur Adit 1357m

It is longest tunnel in the world.

Shape circular, concrete lined

Length 27394.59m

Diameter 10.15m

Design discharge 405 cumecs

Velocity 5.0m/sec

Sholding Works

In order to augment flow during the lean months, the water at Sholding khad is diverted to

HRT. It has a 26m long tunnel that will divert a discharge of 8 cumecs through a 2m diameter

D-shaped inlet tunnel in the underground desilting chamber. The inlet tunnel will terminate in

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23m long where after water will enter depris choking of 12.5m into 10.15m size and desilting

chamber of 56m into 1d0.15m size.

Location ------ Across Sholding Khad at EL-1544.53m

Type ------ Trench weir

Design discharge ------ 8 cumeces

Flushing water ------ 2 cumeces

Length ------ 26m

Width ------ Varies from 4.625m to 2m

Depth ------ 0.82m to 3.92m

Surge Shaft

The main surge shaft is located at the intake of the penstock at 27.3 km form head race

tunnel. It is 301 m deep. 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 diameter 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 have been provided around the surge

Shaft to relieve the external water pressure on the lining.

Fig 3. Surge Shaft Representation

PRESSURE SHAFT

Three shafts of diameter 4.9m and length varying from 619m to 660m take off from the surge

to an angle of 56 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

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

.A spherical valve has been provided in each penstock branch tunnel inside the machine

hall cavern to enable closing of penstocks whenever required.

BUTTERFLY VALVE

The butterfly valve is of spherical type, has a diameter of 4.9 m and can be opened only when

the counter weights on both sides of valve are lifted upwards. It is called butterfly valve as it

is operated by using 2 servo motors .This valve is either open or close. It is located between

the surge shaft and penstock. Its purpose is to allow or restrict completely the water supply

from the HRT to the penstock. If in any case butterfly valve closed due to any failure ESD

occur of both units.

The self-closing of the valve is ensured by a counter weight. It is a steel body provided with

integrally cast supporting feet, lifting lugs and heads for locking the valve rotor in closed and

opened position.

The counter weight is lifted by a servomechanism. This is taken care of by nitrogen cylinders

maintained at a pressure of 100bar. Whenever due to any leakage pressure goes below 94 bar

oil pressure unit starts and maintains its pressure.

The counter weight is lifted and only then is the butterfly valve opened. Hence, a constant

pressure is to be maintained. It could have been engineered in a way that counterweight

would have to be lifted only when butterfly valve was meant to be closed. This meant not

having to supply power to keep it lifted till the time the unit was to be functional. However, it

has been designed the way it is because if ever there is a power failure and the units cannot

run, the BFV shuts down and hence no damage is caused to the rest of the structure and

machinery. Had it been designed otherwise, in case of power failure the water would have

kept rushing into the whole machinery and destroyed all of it.

Service Bay Floor

There are three modes for machine operation:

Local mode (Unit Control Board manual)

Auto mode (UCB auto)

Central control room mode

The start/ stop, control and operation of machines as well as their auxiliaries rest in the

cubicles placed on this floor. Two panels for each unit are present on this floor: Excitation

panel and Control Panel. The UCB auto mode is operated from the Service

Continuous excitation is demanded by the rotor as it‟s an electromagnet and hence the

excitation cannot be removed if the unit is to be kept running. The excitation panel broadly

consists of the following cubicles:

Measuring cubicle

Interfacing cubicle

PCC cubicle

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Generator control cubicle

Governor electronic cubicle

Protection A cubicle

Protection B cubicle

The measuring cubicle contains the measurements of current, voltage, temperature, moisture

content (of the transformer oil) and all other relevant measurements of the unit it is attached

to. Two synchrotacts are present on this cubicle that compare the voltage, frequency and

phase sequence of the generator side and of the line side. After 90% of the rated voltage and

97% of rated speed has been achieved, command for synchronization reaches the machine.

The interface cubicle is the one through which the information from the measuring cubicle is

communicated to the rest of the cubicles.

PCC (Programmed/ Process Control Cubicle) is the brain of the UCB panel. All the

commands and the processing come from the PCC cubicle.

Generator cubicle: This acts as a back-up for the generator if the PCC cubicle fails to

perform its required actions on the generator.

Governor control cubicle: The governor cubicle consists of a DTL (digital turbine logic),

BU-DTL (back up DTL) and Speed Monitor and Alarm Unit.

Protection A cubicle: this cubicle is responsible for the protection scheme employed for a

given unit and its excitation panel.

Protection B cubicle: This serves as a backup to the whole protection scheme provided in

the Protection A cubicle.

The service bay floor also houses a mini control room in which there is kept an operating

system same as that in the main control room. All the ongoing activities in the power house

related to any cubicle and any machine can be looked for, and controlled from this mini

control room too.

Actually all the remote terminal units (RTU) for turbine, generator, transformer, 415V supply

and CFA01 are connected to the main chip i.e. AC410 (Motorola) through optical fibre cable

known as AF100 bus. As the CFA01 panel is near the chip it is connected to the main chip

via coaxial cable. They are connected to the chip via modem.

Now all the ongoing activities in any RTU are received by a chip and this chip is connected

to the central control room (CCR, housing OS-1) and mini control room (housing OS-2). It is

due to this unique feature installed in the UCB (unit control board), we can control any

activity in the power house from the control room itself.

19 | P a g e

Flood Control Panel: This panel operates the flood controlling pumps in case of flooding of

the power house. They are installed at different elevations levels so that each floor can be

recovered back during flooding, discharge of these pumps go back outside through MAT.

There are 12 pumps each of a capacity of 120 lps.

D/W control cubicle: The dewatering pumps are used to dewater the penstocks, spiral

casings and the draft tubes. The D/W control cubicle panel holds the control of starting and

stopping these dewatering pumps. These pumps are four in number and each has a capacity of

120lps.

EOT (Electric Overhead Travelling) Cranes 250 Tonnes: There are two Electrical

Overhead Travelling cranes which are used when maintenance of machine parts like runners,

turbines, generator parts and lifting of other such heavy machinery is required to be done.

The cranes have the following specifications:

Span: 20m

Main Hoist: 250T

Auxiliary Hoist: 50 T

Auxiliary Hoist: 10 T

Main Voltage: 415V, 50Hz

Control Voltage: 230V, 50 Hz/ 24V dc

Service Bay: It refers to the portion of the service bay floor where the various equipments

such as runner are serviced and maintained.

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Air Conditioner Room:

The central air conditioning plants or the systems are used when large buildings are to be air

conditioned completely. The window and split air conditioners are used for single rooms or

small office spaces. If the whole building is to be cooled it is not economically viable to put

window or split air conditioner in each and every room. Further, these small units cannot

satisfactorily cool the large halls, auditoriums, receptions areas etc.

In the central air conditioning systems there is a plant room where large compressor,

condenser, thermostatic expansion valve and the evaporator are kept in the large plant room.

They perform all the functions as usual similar to a typical refrigeration system. However, all

these parts are larger in size and have higher capacities. The compressor is of open

reciprocating type with multiple cylinders and is cooled by the water just like the automobile

engine. The compressor and the condenser are of shell and tube type. While in the small air

conditioning system capillary is used as the expansion valve, in the central air conditioning

systems thermostatic expansion valve is used.

The chilled is passed via the ducts to all the rooms, halls and other spaces that are to be air

conditioned. Thus in all the rooms there is only the duct passing the chilled air and there are

no individual cooling coils, and other parts of the refrigeration system in the rooms. What is

we get in each room is the completely silent and highly effective air conditions system in the

room. Further, the amount of chilled air that is needed in the room can be controlled by the

openings depending on the total heat load inside the room.

There are two types of central air conditioning plants or systems: direct expansion air

conditioning plant and chilled water central air conditioning plant. SJVNL power house uses

the latter.

Chilled water central air conditioning plant: This type of system is more useful for large

buildings comprising of a number of floors. It has the plant room where all the important

units like the compressor, condenser, throttling valve and the evaporator are housed. Earlier,

water in the condenser used to be taken from the POT HEAD yard located away from the

power house. But later on, it was provided with a separate water supply. The evaporator is a

shell and tube. On the tube side, the Freon fluid (F22) passes at extremely low temperature,

while on the shell side the brine solution is passed. After passing through the evaporator, the

brine solution gets chilled and is pumped to the various air handling units installed at

different floors of the building. The air handling units comprise the cooling coil through

which the chilled brine flows, and the blower. The blower sucks hot return air from the room

via ducts and blows it over the cooling coil. The cool air is then supplied to the space to be

cooled through the ducts. The brine solution which has absorbed the room heat comes back to

the evaporator, gets chilled and is again pumped back to the air handling unit.

The central air conditioner also needs a blower motor – which is usually part of the furnace –

to blow the cool air through the duct system.

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UAB Floor (EL. 995.0 m)

Various DTTS:

A Remote Terminal Unit (RTU) is a microprocessor-controlled electronic device that

interfaces objects in the physical world to a distributed control system (DCS) by

transmitting telemetry data to the system and/or altering the state of connected objects based

on control messages received from the system.

Marshalling box is a of panel which is situated next to transformer, it contains OTI or oil

temperature indicator, WTI or winding temperature indicator, heater switch, pump control

switch, fan control switch, MCB and contractors.

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GENERATOR:

The synchronous generator in the power house is vertically mounted and converts the

hydraulic energy of water into electrical energy. It has salient poles with closed air circuit

ventilation and coupled to a machine turbine. The field coils are energized by a static

excitation system. The slip rings, permanent magnet generator and mechanical over speed

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

synchronous speed of the generator. A combined thrust and guide bearings are located below

the rotor.

Rated power 278MVA

Maximum power 305MVA

Voltage generated 15.75 ± 5% kV

Current 10190 A

Power factor 0.9

Poles 20

Rpm 300

Runaway 545

Insulation (Both stator and rotor) Type F

Air gap 30mm

Excitation current 2400A

Rated excitation voltage 249V

Stator winding resistance 1.22m ohm

Rotor winding resistance 119m ohm

Efficiency 98.65%

Stator: Stator is double layered with 252 slots, 504 bars and laminated core

Rotor: Rotor has20 poles, 300rpm speed and Runaway speed 545rpm.

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BRAKING AND LIFTING:

Operated at 20% of rated speed, air pressure is 6-8 bars. There are 16 brake pads and 8 dust

collectors.

Excitation Transformer(EX):

It is Dry type transformer which utilizes some of the generated power for self-excitation. It

steps down the generated voltage at 15.75kV to 100-150V which is then converted to D.C.

with the help of thyristors (3 bridge 6 thyristors)

The specifications are:

Rated Capacity 1780kVA

Conn. 5-6 16538V

Conn. 4-6 16144V

Rated Voltage Conn. 4-7 15750V

Conn. 3-7 15356V

Conn. 3-8 14963V

Rated Current 65.2A

Um 24/1.1kV

Imped. Volt 5.9%

Rated Frequency 50Hz

Vect group Yd5

Type of Cooling ANAN

Trans Weight 4.15t

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Auxiliary Transformer (T1):

The generated voltage is 15.75kV. It steps down the 15.75kV to 440 V to run the auxiliaries.

The specifications are:

Rated Capacity 630kVA

Phases HV Three Delta

LV Three Star

Insulation class F

Winding material Copper

Vector grp Dyn11

Type of cooling ANAN

Total Weight 3400kg

Rated Voltage and Current Conn. 6-5 HV-16537.50V,21.99A

Conn. 5-7 HV-16143.75V,22.53A

Conn. 7-4 HV-15750.00V,23.09A

Conn. 4-8 HV-15356.25V,23.69A

Conn. 8-3 HV-14962.50V,24.31A

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Various Panels and their significance:

Below is the outline of UAB (Unit Auxiliary Board) panel:

NGT & NGR and their significance:

If the system has a neutral which is available, a single phase distribution transformer can be

used in conjunction with a loading resistor to provide high resistance grounding. This is

particularly well suited for grounding of generators, in that it allows the system to operate

like an ungrounded system under normal conditions, while still retaining the ability to limit

ground fault current. Such a Transformer is called Neutral Grounding Transformer (NGT).

NGR is employed in AC distribution networks to limit the fault current which would flow

from the transformer or generator neutral star point in the event of an earth fault in the

systems. It is used when the neutral of supply transformer is accessible and its own

impedance is not enough to limit fault current. Specifications of NGT are:

KVA Rating 200kVA

Voltage Rating (HV side) kV 20kV

Voltage Rating (LV side)kV 0.22kV

Resistance R‟ps(N-N‟)milli-ohm 16mΩ

Resistance R‟es(N-G‟)milli-ohm 90mΩ

N-G(Total) milli-ohm 106mΩ

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Bus Duct:

Bus ways, or bus ducts, are long bus bars with a protective cover. Rather than branching the

main supply at one location, they allow new circuits to branch off anywhere along the route

of the bus way. 400 kV transmission lines are connected to GIS through SF6 to air filled

bushings through 400 kV bus ducts.

Turbine Floor (Governor): EL. 990 m

FRANCIS VERTICAL SHAFT REACTION TURBINE:

The reaction turbine, as the name implies, is turned by reactive force rather than by a direct

push or impulse. Francis Turbine is an inward-flow reaction turbine that combines radial and

axial flow concepts.

Francis turbines are the most common water turbine in use today. They operate in a head

range of ten meters to six hundred and fifty meters and are primarily used for electrical power

production. The power output ranges from 10 to 750MW, mini-hydro excluded. Runner

diameters are between 1 and 10 meters. The speed range of the turbine is from 83 to 1000

rpm. Medium size and larger Francis turbines are most often arranged with a vertical shaft.

Vertical shaft may also be used for small size turbines, but normally they have horizontal

shaft.

The working fluid changes pressure as it moves through the turbine, giving up its energy. A

casement is needed to contain the water flow. The turbine is located between the high-

pressure water source and the low-pressure water exit. The inlet is spiral shaped. Guide vanes

direct the water tangentially to the turbine wheel, known as a runner. This radial flow acts on

the runner's vanes, causing the runner to spin. The guide vanes (or wicket gate) may be

adjustable to allow efficient turbine operation for a range of water flow conditions.

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As the water moves through the runner, it‟s spinning radius decreases, further acting on the

runner. At the exit, water acts on cup-shaped runner features, leaving with no swirl and very

little kinetic or potential energy. The turbine's exit tube is shaped to help decelerate the water

flow and recover the pressure.

Francis type turbines can be constructed in vertical or horizontally. Horizontal construction is

more accessible and has higher speed, but for large machines, vertical construction is

preferred to affect the higher speed.

As compare to Pelton wheel, a Francis turbine offers advantage of high efficiency at full load

and at 75% of full load; this turbine can be designed for higher speed than Pelton Wheel.

For this project, the gross head of the turbine is 486m and design head is 428m.

TURBINE:

The water from the penstock enters the spiral casing on the opening of the Main Inlet Valve.

In the spiral casing, the water is spread all round the circumference through stay vanes. The

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

passes through .

Block Diagram of Turbine Function

The guide vanes are responsible for controlling the amount of water that comes out of the

spiral casing onto the runner. These vanes are controlled by the governor via two servomotors

on either side of the turbine pit. These servomotors control the guide vanes by performing an

action similar to that for a steering on a ring that rests on these guide vanes.

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The guide apparatus has movable vanes, which are controlled by the governor and can be set

independent of output.

The effect of water hitting the runner is transferred to the Generator, which is connected to

the Turbine Shaft. The turbine develops the power partly due to the velocity of the water and

partly due to difference in pressure acting on the front and back of Runner buckets. Such a

turbine essentially consists of guide apparatus consisting of an outer ring comprising of

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

rotating blade forming a wheel or a Runner. The guide blades of the turbine are pivoted

about an axis parallel to the turbine 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 the governor.

Turbine Components:

1. Rotating Parts : There are mainly three rotating parts:

a) Runner

The runner has been formed by welding crown and band of stainless cast steel and the vanes

of stainless steel plates. The vanes have been machine worked and the crown band has

“Roots” towards the vanes. Air used for stabilizing purpose is allowed through the Runner‟s

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 wrench.

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 is done primarily to

transfer the moment of force through the shear studs.

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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 the

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

bearing oil reservoir.

2. Turbine Guide 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 requires minimum maintenance. The

bearing house is split and attached to the upper turbine cover. It has two manhole hatches for

access and inspection of shaft seal and pipe connections. The bearing shell consists 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 Babbitt 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 starts 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

sufficient rotating speed , the damming up pressure becomes 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:

i) 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

ii) 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 made of aluminum and bronze guide vane bearing

30 | P a g e

have been installed. Corrosion resistant austenite steel has been welded into the wearing

surface of the lower turbine cover between the wear ring and the lower labyrinth seal.

Governor and its auxiliaries:

Governor

Governor is the brain of the machine and it uses hydraulic oil to generate pressure of 100 bar.

It is an arrangement consisting of hydraulic system, electrical/ electronic hardware

components and of the software program which is used to regulate the turbine operation

under all circumstances.

The jacking system to open the M.I.V. (Main Inlet Valve) is controlled by the governor.

The governor uses centrifugal pump to create a pressure of 100 bar used for:

1. Controlling guide vane opening using servo motor

2. Opening of the bypass valve

3. Opening of the M.I.V.

Specifications: Governor (Capacity Wicket Gate, E= 336 KNm

Max. Working Pressure: 100 bar)

Hydraulic pump trip setting (MCB setting): 157A

Guide vane opening time: 23.4 sec

Guide vane closing time: 13.2 sec

The counter weight of the MIV is lifted by a servomechanism. This is taken care of by a

green cylinder filled with oil and maintained at a pressure of 100bar. It is connected to the

nitrogen cylinders kept on the turbine floor which help maintain this pressure by

compensating for any change, both increase and decrease, in this value of pressure. The sole

control of this maintenance of pressure lies with the governor.

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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

senses the speed of the turbine rotation and generates a signal proportional to the

difference between the turbine speed and the governor speed reference and therefore

develops a hydraulic control signal sufficient to control the turbine. The adjustable rod is

used for pre tensioning the guide apparatus. When pre tensioning the guide apparatus the

guide vanes are given a moment which produces a force toward closed position. This

compensates 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

vanes with full pressure in the spiral casing.

The governor‟s action on the two main servomotors is transferred via the regulating ring.

The actual guide apparatus consists of 23 guide 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 have 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 preventing the guide vane from being closed. An alarm in that case will be

activated. The guide vane lever and regulating ring are connected by links. The links are

32 | P a g e

joined by self - lubricating bushing on stainless steel pins attached to the regulating

ring and the guide vane lever respectively

Guide Vane In Closed Position

Guide Vane In Open Position

Components of Governor:

OPU tank: Oil Pressurizing Unit tank

OPU pump: Oil Pressurizing Unit pump (96 KW, 415 V, 1485 rpm, 3 ph IM)

Hydraulic oil cooler: This is used to cool the oil in the tank of the governor when its

temperature is about 50°C.

Guide

Vanes

Axis

Of Guide Vane

Links

Regulating

Ring

OPENING AND CLOSING OF GUIDE VANES

0o

15o

OPENING AND CLOSING OF GUIDE VANES

Water

0o

0 %

Guide

Vanes

Axis

Of Guide Vane

Links

Regulating

Ring

OPENING AND CLOSING OF GUIDE VANES

0o

15o

OPENING AND CLOSING OF GUIDE VANES

Water

100 %

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Hydraulic safety valves

Hydraulic control valve (solenoid operated)

Main control valve (distributor valve)

Guide vane servomotor: Servomotor moves the guide vanes by applying pressure

(piston attached to the lever).

Piston accumulator system: Piston Accumulator: 16 cylinder filled with nitrogen are

used to produce a pressure of about 100 bar, so that it can be used in an emergency

such as power failure, to stop the machine and avoiding it to over speed.

Hydraulic oil filter elements

MIV hydraulic control valve (solenoid operated)

MIV control valve (hydraulics operated)

Protection: To avoid overheating of the oil, temperature sensors like R.T.D. and

thermistors are used along with thermo-switch.

DV Pos. Transmitter

Main Control Valve (DV)

Accumulator Shut off valve

Hydraulic Oil Filter

Hydraulic E.S.D. (Emergency Shut Down) valve: In this the brakes are applied

without unloading the machine.

Start Stop Valve

Change over valve: To switch on one of the pumps and closing the other.

Servo Valve (DTL): Digital Turbine Logic

Servo Valve (BUDTL): Back up Turbine Logic

M.I.V. E.S.D. valve ( air bleed)

M.I.V. Control valve (hyd. op.)

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Brake Dust Collector:

Ratings:

Capacity: 1200 cubic metre per hour

H.P.: 5, Type: C/Fan, Rating: Cont., KW: 3.7, Volts: 415, Ph: 3, Amp: 7, RPM: 2830.

The brake dust collector consists of an extraction unit, hoppers around brake assembly around

brake assembly for trapping the brake dust and flexible hoses for connecting hoppers to the

extraction unit. The extraction unit will have a 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.

Two units of brake dust collector are used which work alternately and are used to collect the

dust due to the application of the brakes.

O.V.E. (Oil Vapour Extractor): This is used to absorb the oil vapour produced due to the

heat generated in the U.G.B (Upper Guide Bearing) and L.G.B. (Lower Guide Bearing)

where oil is used as a coolant.

The oil vapour extraction system sucks off the vapour of the generator bearing. This oil

vapour is generated during operation and led to the filters outside in the generator room, the

pollution of the machine is this way avoided.

As soon as the generator starts running with the operating temperature, the oily fog is

developed in the bearing oil container by very finely distributed oil drops. “breathing” the oil

in bearing or pressure differences inside and outside the bearing cause the oil vapour, 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 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, the generator is equipped with a special oil vapour

suction system.

Heat Exchangers:

RATINGS OF WATER HEAT EXCHANGER:

Nominal capacity: 43,00,000 kcal/hr

Heat transfer surface=435.1 m2

Working pressure = 10 bar

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Testing pressure =13 bar

Working temperature: 95 degrees (max)

0 degrees (min)

The water enters the turbine through a spiral casing. There are 23 guide vanes surrounding it.

The pressure of water in the draft tube is 2bar and that in the spiral casing is more or less 45

bar.

The basement of the power house is the dewatering gallery or drainage water gallery. Leaked

water from all the machines goes to this gallery. It‟s 7m below the MIV floor.

Oil circulating pumps:

Two controlled oil pumps of the „axial piston pump‟ type. Their size is identical, which

makes them redundant. Under normal circumstances, one pump is sufficient for all operation

conditions. Nevertheless, if the oil pressure should ever fall below the required pressure

value, the second pump will automatically switch in. The oils pumps extract the oil from the

control oil tank through a suction strainer, and direct it through non-return valve and a shut

off valve into the collector. The non-return valve is intended to prevent the oil from flowing

back through a stationary pump, which would be otherwise rotate backwards.

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Secondary Cooling water pumps:

COOLING SYSTEMS

Secondary Cooling Pump rating:

3 Phase Motor, 75 KW, 1480 rpm, 415 V, 50 Hz, cos ø: 0.86

C/W Pump Control Cubicle has controls for:

a) Primary circuits (Raw water)

b) Secondary Circuits (Treated water)

The primary pump cools the water that goes into the water heat exchanger via the secondary

cooling pump placed at the Turbine floor. The secondary pump further cools the oil-water

heat exchanger. While the primary pump is an open loop system, the secondary water pump

and the oil-water heat exchanger are closed loop systems.

Both oil and water are used as coolants in the machines. The number of primary pumps with

each unit is two. However, only one of them is functional at a time. The pump priority is

changed every few hours so that a pump doesn‟t wear out way before the other one.

Primary: present on the MIV FLOOR. Its rating is 37kW. The water enters the pump at a

pressure of 2.5bar. They are two in number for each unit but only one is used at a time. These

pumps are switched from time to time so that either of the two doesn‟t get excessively used

and hence worn out way sooner than the other. The pumps are three phase squirrel cage

induction motor. Rating: 50hp, 37kW, 985rpm, 50Hz, 66A, 415+-10%,delta connected,

power factor =0.83.

Secondary: present on the Turbine floor. Its rating is double that of the primary one. Its rating

is 75 kW. Again they are two in number just like the primary cooling pumps. The water

pressure is 5bar. The cool water is taken from the draft tube.

The water enters the turbine through a spiral case. There are 23 guide vanes surrounding it.

The pressure of water in the draft tube is 2bar.

The basement of the power house is the dewatering gallery or drainage water gallery. Leaked

water from all the machines goes to this gallery. It‟s 7m below the MIV floor.

HP oil Pump or H.S. Pump (Hydraulic System Pump):

There are two such pumps present together, one operated from A.C. and other using D.C. The

D.C. operated pump is required in case of A.C. power failure. It is used for jacking the

machine by injecting a line layer of oil below it. This is used while stating and shutting down

the machine, as there will be a lot of friction and the machine needs to be lifted a bit to avoid

damage to it.

37 | P a g e

Servomotor:

This is not actually a motor, but it is a hydraulic system used to open the MIV. The pressure

created by the OPU (Oil Pressurizing Unit) is transferred hydraulically to lift the counter

weight and this pressure acts due the green coloured cylinder and piston pair and this is called

the servomotor.

Shaft seal system:

Shaft seal is a rubber seal to stop the back water flow from the tail race tunnel to the runner.

This seal is opened when the machine is to be switched on. The shaft seal in the runner is air

operated and the air compressor needs to maintain a pressure of 6.8 bar.

Shaft seal flushing system: During the start and stop of a machine and during low rotational

speed of the turbine, the flushing water system is functional. It prevents the contaminated (silt

containing) water from affecting the shaft seal (which is made of rubber and hence is prone to

damage by silt particles and other contamination at such high speed). Hence at such times,

the flushing water system provides filtered water at sufficient pressure. The intake is from the

pressure equalizing piping between the upper turbine cover and the DT. A centrifugal pump

increases the pressure by 15mWC and in automatic back flushing strainer, the particles above

200microns get removed.

Turbine Shaft Seal Cubicle

1) Shaft seal System Control

2) Head cover pump

Head cover pump: It is used to remove the water leakage around the shaft service seal.

MIV Service Seal system:

The service seal in M.I.V. is applied by water pressure and it is to be removed before the unit

needs to be started.

MIV Maintenance Seal System: This is to be applied when the unit needs to be opened for

maintenance.

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Various panels and their significance:

Governor Control Panels:

MIV control panel

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Governor hydraulic control panel

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Governor accumulator panel: It shows the pressure of both the hydraulic oil in the

governor and the nitrogen gas accumulator.

Governor motor control panel

Governor hydraulic terminal

MIV terminal box

MIV seal control cubicle

Governor electronic cubicle

Hydraulic Pump Setting

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Turbine Shaft Seal Cubicle

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MIV FLOOR(El 982.00 m):

This floor is the lowermost floor of the power house. It contains six individual MIVs, each

weighing 92 tonnes and being controlled by the lifting of a counter weight 79.33 tonnes by

means of a servomotor which is operated hydraulically.

Cooling System:

Generator and Turbine have bearings (Upper guide bearing, lower guide bearing, thrust

bearing). Cooling system is required for dissipating the head generated in these bearings.

There are two cooling systems: Primary Cooling System and Secondary cooling system.

Primary cooling Water System:

For Primary cooling raw water from tailrace is used. It consists of a 3 phase induction motor

(415V, 50 Hz, 37kW) and a pump. Primary Cooling Pump cools the water that goes into the

water heat exchanger via the secondary cooling pump placed at the Turbine floor. The

secondary pump further cools the oil-water heat exchanger. While the primary pump is an

open loop system, the secondary water pump and the oil-water heat exchanger are closed

loop systems.

Both oil and water are used as coolants in the machines.

There are primary pumps for each unit. However, only one of them is functional at a time.

The pump priority is changed every 8 hours so that a pump doesn‟t wear out way before the

other one.

The sump area has 3 types of pumps: Flood control pumps, dewatering pumps and drainage

pumps. (DW and DR pumps are almost at 6 bar pressure)

Drainage pumps:

MIV floor is characterized by a sump area which is further categorized as drainage sump and

dewatering sump. The drainage sump is for all the leakage (water). For the maintenance

purposes when the machines are supposed to be dewatered, the water is thrown into the

dewatering sump.

The drainage sump is concrete lined.

43 | P a g e

The leakage flows through the drain to the sump. The submersible pumps (which remain

submersed in water) pump the water from sump to the MAT (Main Access Tunnel). Float

switches are present which act as water level sensors, depending on the level of water, pumps

are switched ON.

Number of Pumps switched ON Water Level.

MAT is 800mm tunnel. Water is then thrown into the tail race. There are 4 drainage pumps.

Dewatering pumps:

There are 6 gates for 6 tailraces. The river level is 1008m and Draft tube level is 985m which

leads to a 30m head, means a pressure of 2 Bar. Water is filled till runner, gate is closed then

the valve is opened for dewatering by D/W pumps, then the machine can be opened.

Dewatering pumps are used to empty the Draft Tube. There are 4 dewatering pumps.

Total capacity (DR and DW) is 2200lbs. The dewatering sump is steel lined.

Flood control pumps:

There are 12 flood control pumps. In case of a flood, these pumps operate at the rate of 120

litre/sec.

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Main Inlet Valve (MIV) :

MIV floor houses 6 MIV‟s, one each for the six units. MIV are of spherical type with a

diameter of 2.3m. It is located between the spiral casing and the penstock. It allows the water

to flow from penstock to spiral casing in open condition and blocks the flow of water when it

is closed. MIV can be either fully open or fully close. MIV is bolted between the conical pipe

on the upstream side and dismantling pipe on the downstream side. It can be opened only

when counter weight is lifted upwards. Counter weight of 79.993t ensures self-closing of

valve. It is a steel body provided with integrally cast supporting feet, lifting lugs and heads

for locking the valve rotor in closed and opened position. The hydraulically pre-stressed

foundation bolts prevent the body from lifting.

Pressure required to open MIV is 100 bar. This applied by governor using hydraulic oil

pressure. By pass valves are required on both the sides of MIV to avoid damage to MIV.

There are two seals viz. Service seal and Maintenance seal on the sides of MIV. When

maintenance work is to be done both Maintenance seal and service seals are used for extra

security. There are two by pass valves as shown in the diagram which equalize the pressure

on either sides of MIV, before the MIV is opened.

The counter weight is lifted by a servomechanism. This is taken care of by a green cylinder

filled with oil and maintained at a pressure of 100bar.Nitrogen cylinders are kept as a back-

up. The sole control of this maintenance of pressure lies with the governor.

The counter weight is lifted and only then is the MIV opened. Hence, a constant pressure is to

be maintained. It could have been engineered in a way that counterweight would have to be

lifted only when MIV was meant to be closed. This meant not having to supply power to keep

it lifted till the time the unit was to be functional. However, it has been designed the way it is

because if ever there is a power failure and the units cannot run, the MIV shuts down and

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hence no damage is caused to the rest of the structure and machinery. Had it been designed

otherwise, in case of power failure the water would have kept rushing into the whole

machinery and destroyed all of it.

Spiral Casing :

The Francis turbine is essentially a modified form of propeller turbine in which water flows

radially inwards into the runner and is turned to emerge axially. The runner is mounted in a

spiral casing with internal adjustable guide vanes. The water enters from the penstock to the

spiral casing which completely surrounds the runner. The cross-sectional area of this casing

decreases uniformly along the circumference to keep the water velocity constant in

magnitude along its path towards the guide vane.

Labyrinth Seal :

A labyrinth seal provides a tortuous path to help prevent leakage. A labyrinth seal may be

composed of many grooves that press tightly inside another axle, or inside a hole, so that the

fluid has to pass through a long and difficult path to escape. Sometimes screw threads exist

on the outer and inner portion. These interlock, to produce the long characteristic path which

slows leakage. For labyrinth seals on a rotating shaft, a very small clearance must exist

between the tips of the labyrinth threads and the running surface.

Draft Tube :

The outlet consists of a draft tube and draft tube steel lining continuing with a concrete lined

tunnel and forms the water way from the runner to the tail race channel. The draft tube cone

is welded and consists of two parts. The upper part is bolted to the lower fixed labyrinth seal.

It is made of 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 fit with

four stub pipes with cover for installation of an inspection platform. The draft tube steel liner

is completely set in concrete. The draft tube cone can be emptied into the dewatering pit by

slight extension of the cross section in the direction of flow from the runner outlet to the end

of the plate covering. The draft tube has 10 segments with a plate thickness of 30mm and

total weight 34,000kg.

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COMMON POWER PLANT AUXILLARIES

There are certain auxiliaries in the power plant that are used for the proper functioning and

operation of the entire power plant in itself. Some of the more important such auxiliaries are

enlisted below:

1) HT-LT System It is the lifetime of the entire power plant as it manages the external electricity supply to the

power plant and it is constitute system. This system is placed inside a separate room and

receives external supplies from two sources, so that if one of the two fails the other can

always work. The two sources of supply are:

22KV O/H line Jeori substation

22KV local feeder

DG 1

DG 2

The HT feeder is rated for 33kv but we are feeding only 22kv through HT feeder. The supply

of the two 22kv feeder is step down by the step down transformer into 415 volts, which is

given to LT side. In LT side, there are three service station board SSB#1, SSB#2 and SSB#3.

Service Station Board # 1

It gives supply voltage in the followings:

1. 220 V battery charger-1 2. Cabling.

3. Lift-1 4. T/F cover EDT

5. PCC station control. 6. Bus duct lighting.

7. Air supply system. 8. Ventilation-1

9. Lift-2 10. Air compressor-1

11. 48 V battery charger-1

Service Station Board #2

It is very important service station board because it gives supply voltage for UAB (Unit

Auxiliary Board) during the starting of unit which is very important for every unit.

1. GIS – 1 S 2. 420 bus duct tunnel light

3. Unit auxiliary board – 6 4. UAB – 2

5. Light and heating for floor 1000.5m 6. GIS – 2 (Pot head yard)

7. Drainage Gallery. 8. UAB – 3

9. Dewatering pumps. 10. UAB – 4

11. Ventilation 12. DG incomer

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13. Jacking oil pumps 14. UAB – 5

15. UAB – 1 16. UAB - 6

Service Station Board # 3

It gives supply voltage to the followings:

1. Inter connected tunnel light. 2. Dewatering pump control.

3. Air condition – 2 4. Operation Station.

5. Powerhouse ventilation motors. 6. Ventilation – 2

7. Dewatering pump – 3. 8. GIS – 2 (Pot head yard).

9. Lightening & heating control room. 10. 420 bus duct tunnel light.

22KV/415V

2.5 MVA

Bus Coupler

22 KV line 22 KV line

22KV/415V

2.5 MVA T1T2

DG1 DG2

415 V

750 KVA

415 V

750 KVA

SSB 3 SSB1SSB2

C.B C.B

C.B C.B

C.B

C.BC.B

Single line diagram of HT/LT Room incomers and outgoing

3 3

UAB 6 UAB 5 UAB 4 UAB 3 UAB 2 UAB 1

From

UAT 6

From

UAT 5

From

UAT 4

From

UAT 3

From

UAT 2From

UAT 1

Red : closed

Green: open

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2) Backup Generators (DG 1 And DG 2) In case the HT-LT System fails due to the some or the other reason, the power plant gets

backup power supply from the two DG sets. In case the HT-LT System fails due to the

some or the other reason, the power plant gets backup power supply from the two DG

sets. These DG sets are located adjacent to the POT HEAD Yard.

Rating of the DG:

3 phase, 415 V, 1043 A, 750 KVA, Excitation: 36 V, RPM: 1500

Each Diesel generator is provided with two oil tanks of 1000 litre capacity each and the

DG consumes about 150 litre oil in one hour.

Self charging battery of 48 V DC is used to kick start the machine. It moves the pinion which

is attached to the rack and which is further attached to the generator shaft and thus in turn it

moves the shaft of the generator and hence, 3 phase A.C. power is generated.

Priming motor is a low rating motor used to liquefy the jammed oil, which can then be

circulated all over the machine. It also has a suction device to suck the clean air from outside

for the combustion of the fuel. Radiator is a water tank used for the cooling of the machine

and the cooler starts when the temperature of the machine goes above 80°C. The water filter

uses magnets to remove iron particles from the water and hence, circulate clean and particle

free water for cooling purpose.

The D.G. Set is equipped with 4 water tanks of 1.5 lakh litre capacity each. The three tanks

are used for fire fighting and one tank is used for the supply of the secondary cooling system

at the power house.

The air in the power house is circulated mainly because of the 3 blower present near the DG

set. The rating of the blowers is as follows:

No. of blowers installed 3 Nos.

Drive/Motor Star/Delta Sq. Cage Induction Motor

Pulley OD blower side (mm) 940 mm

Pulley OD motor side (mm) 230 mm

Groove (mm) 28 mmX10 mm (deep)

Shaft to shaft centre distance (mm) 2100 mm

Cycle 50 Hz

Motor KW 90

Motor RPM 1475

Blower Shaft Diameter (mm) 110

No. of grooves 8

Capacity 2,81,250 m3/hr

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3) Battery Bank This is the last and final backup provision to keep the power supply afloat. A temporary

backup power supply in the form of chemical batteries is available for emergency usage.

4) Dewatering System Due to unavoidable reasons there is always some amount of water leakage from and

around the turbine. This leakage water accumulates in a leakage sump. Thus a

dewatering system is in place to periodically empty the leakage sump.

5) Drainage System As the power house is underground structure, there is some amount of seepage from the

walls of tunnels. This seepage water is taken out of the powerhouse building by means of

a well-designed drainage system.

6) Air compressor It is used for the proper functioning and working of power plant system such as the shaft

seal and bus duct.

SILT LAB:

The silt particles can be differentiated on the basis of their size as follows:

Coarse particles: size> 0.2 mm

Medium particles: size> 0.075 mm and size < 0.2 mm

Fine particles: size < 0.075 mm.

The process used in the silt lab for determination of the concentration of the silt is known as

gravimetric method of determination of silt. The steps involved in the separation of the silt

are:

1. Coarse silt content

1000 ml of sample water is passed through 200µ sieve the coarse particles collected in the

sieve are dried and weighted

Coarse silt (in ppm) = (wt. in gm of coarse particles) * 106/(1.4*1000)

= 714.285* (wt. in gm of coarse particles)

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2. Medium silt content

1000 ml of silt sample after passing through 200µ sieve is collected in beaker. Stir the

sample and wait for 30-40 seconds for the medium particles to settle down. Gently pour

the sample from this beaker to other beaker. The settled particles are dried and weighted.

Medium silt (in ppm) = (wt. in gm of coarse particles) * 106/(1.4*1000)

= 714.285* (wt. in gm of coarse particles)

3. Fine silt content

Stir the 1000 ml of sample in beaker and suck 25 ml of sample through pipette. Heat this

25 ml sample in china dish till all the water gets evaporated. Dry fine silt content gets

deposited in the china dish. Place this china dish on moisture extractor and weight it after

it reaches the room temperature. Original weight of the china dish is taken before the

sucked sample is taken in it for our calculations.

Fine silt (in ppm) = (weight of the china dish with deposited fine silt – original weight

of the china dish-0.0035)*106/(1.4*25)

Where 0.0035gm is the weight of soluble content

In addition to this silt reading are also taken at Powari and Wangtoo after every 4 hours. The

maximum permissible level for silt at Wangtoo is 4000 ppm and that for the draft tube sample

is 2000 ppm. If the concentration of the coarse silt particle is more than 75 ppm, then also the

plant is shut down.

TRANSFORMER HALL

There is an underground Transformer Hall at an EL. Of 1044 m and is 270 m long and 7 m

D-shaped.

GENERATOR TRANSFORMER

In a power plant generator transformers are used to step up the voltage level suitable for the

transmission. The main purpose of stepping up the voltage level is to reduce the current level

and hence to minimize the transmission loss.. In our power plant there are 19 single phase

transformers each of 102MVA capacity (3Phase transformer bank).Three for each unit

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and one in spare (standby unit). The main logic behind using single phase nested of three

phase transformers is to remove the problem of transportation due to heavy weight and size

and the space limitation in the underground complex. Also the main advantage of single

phase transformers is that in case any fault occurs in any phase the faulty transformer can be

replaced by the spare one and hence complete shutdown of the unit is not required. In this

way the flexibility and reliability of the system is improved.

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)

Phase - 1(single) Frequency HZ - 50 Hz

Connection Symbol - YNd 11 Type - shell type T/F

Weight of core and winding - 55095kg Weight of oil - 18165kg

Total weight - 9275kg

PARTS OF TRANSFORMER

(i) Secondary winding (ii) Primary winding

(iii) Oil level (iv) Conservator

(v) Breather (vi) Drain Coke

(vii) Tubes for cooling (viii) Transformer Oil

(ix) Earth Point (x) Explosion vent

(xi) Temperature gauge (xii) Buchholz Relay

(xiii) Secondary terminal (xiv) Primary Terminal

(xv) Winding temperature indicator (xvi) Non Returning valve

(xvii) On Load Tape Changer

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

52 | P a g e

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

Buchholz Relay

Buchholz relay is a gas actuated relay used for protecting oil immersed transformer. The

beauty of this relay lies in the fact that unlike any other relay it gives indication that the

system is unhealthy and thus prevents the transformer from severity of fault. The relay

operates on the well known fact that almost every type of electrical fault in a liquid immersed

transformer gives rise to gas. This gas is collected in the body of relay. If the quantity of gas

collected is more than the set value, this relay gives alarm or trip command which ever case

may be. The device provides protection against a no. of internal faults, but it also indicates in

several cases, the type of fault. This is possible because the gas is collected in relay and from

its odour, color and composition, it can indicate what the fault may be and about its nature.

Gas Collecting Device

The gas collecting device is used to collect the gas is formed as a result of any fault inside the

transformer. The device is connected to the Buchholz relay by means of pipe. Whenever an

analysis of the gas is to be done, the gas is first made to collect in this, and then it is sent for

analysis. The main advantage of this device is that the gas can be obtained for analysis

without taking shut down. Hence the operation of transformer is not disturbed.

Silica Gel Dehydrating Breather

Breather is used to prevent the moisture coming in the transformer oil when the volume of the

oil decreases due to fault in temperature. The level of oil in the conservator tank decreases.

To compensate this decrease in level, conservator tank takes atmospheric air from the

atmosphere through this breather and oil expands, oil level inside conservator increases and

air is pushed out through the breather.

Breather generally consists of oil sealing arrangement and a reseal containing silica gel

crystal. These crystal have a properly of absorbing moisture from air which passed through it.

The color of dry silica is blue. After a cycle of operation it changes into faint pink color. The

pink color indicates that the crystals are saturated. In this condition these crystal are activated

by heating it at a temperature of 150-200degree C for two or three hours when the crystals

regain their original color.

Pressure Relief Valve

This is protective device which is installed on the tank transformer when pressure inside the

tank is more than the pre-set value due to any internal fault; this device operates and gives a

tripping command to the circuit breaker. It allows the pressure to drop by instantaneously

opening a port, gives visual indication of valve operation by raising a flag, and operates a

micro switch which has a 1NC & 1 no. contacts which are used in control circuit.

Oil Gauge

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

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Oil Temperature Indicator

The function this device is to measure the temperature of oil. This device is set for alarm and

trip. When the temperature of the transformer oil rises above the pre-set value, the alarm or

trip is given as the case may be.

Winding Temperature Indicator

This is a precision instrument designed for the protection of transformer. One no. of

instrument with three contacts can be provided to indicate the temperature of hottest part of

winding. This device performs the fallowing action. It indicates the maximum winding

temperature irrespective of the condition of loading temperature of the cooling medium and

attitude. Thus the load on the transformer can be kept within the limit.

It gives the alarm when the temperature rises above the set value.

It gives the trip command to the breaker when the temperature is above the set level.

Bushings

Bushings are made from highly insulating material to insulate and to bring out the terminals

of the transformer from the container.

420KV oil-SF6 bushing

LV bushing

Tapping

The transformers are usually provided with few tapings on secondary side so that output

voltage can be varied for constant input voltage.

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.

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.

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.

Oil Flow Indicator

This device indicates the flow of oil in cooler when the transformer is in operation. It

indicates the specified rate of flow of liquid in the direction in specified pipe, and operates

mercury switches for indicating alarm when the flow drops.

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Water Flow Indicator

This device indicates the flow of water through the cooler when the transformer is in

operation. The application of this device is same as that of above device.

Transformer Oil Pumps

Pumps have been used to circulate the oil through the cooler. The oil is cooled by water

circulating in the cooler the power rating of this pump is 5.5 KW and the speed is 2660 rpm.

Sudden Pressure Relay

This is a protection device when the rate of rise of pressure is more than the specified value

these devices operates and give the tripping command to the breaker.

FIRE FIGHTING SYSTEM

General

Arrangement of fire protection in SJVN power station is normally divided into following

three groups.

i) Fire protection for generators

ii) Fire protection for generator transformers

iii) Fire protection of area and equipment and power house not covered under above two

groups.

Generators

a. General: Generators are with closed air-circulation systems and are provided with

automatic CO2 extinguishing systems.

b. System design:

(1) General design considerations are as follows:

(i) CO2 concentration of 30 percent should be maintained within the generator housing for a

minimum period of 20 min without the use of an extended discharge.

(ii) CO2 release should be actuated by the following:

• Generator differential auxiliary relay

• Thermo-switches in the hot air ducts of each air cooler.

• Manual operation at the cylinders.

• Remote manual electrical control.

The CO2 fire extinguishing system normally consists of a sufficient amount of CO2 to

maintain an inert atmosphere during the deceleration of the machine. Two rates of discharge

of CO2 are provided by two groups of CO2 cylinders one group of cylinders, providing the

initial discharge, to ensure a rapid build-up of CO2 concentration, to put out fire and other

group of cylinders, providing the delayed discharge to ensure concentration of CO2

maintained for an extended period. Capacity of the bank is sized for protection of only one

individual generator and CO2 cylinders is arranged for the discharge to any one of the main

units. The amount of CO2, for initial and delayed discharge, should be determined by the

55 | P a g e

manufacturer, taking into account the volume of the air spaces in the generator enclosure and

the deceleration time of the machine. Size and the number of cylinders required in each bank

are accordingly determined.

Transformers

Fire protection at a transformer is provided to limit damage to other nearby transformers,

equipment, and structure. It is assumed that a transformer fire will result in loss of the

transformer. Water sprinkler systems are provided for single phase step up oil-filled

transformers and CO2 systems for other transformers like excitation transformer and

auxiliary transformer.

Gas Insulated Switchyard - I:

A high voltage substation in which all or most of the insulation is provided by a gas (SF6)

operating above atmospheric pressure within earthed metal enclosure. GIS is compact in size

and insulation is not exposed to environment. Furthermore, it has high reliability with an

Availability Factor of 99.57%. In NJHP B142 type GIS is used, which is light in weight due

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to compactness. It entails lesser cost in civil work and building due to reduction in size and

volume of switchgear.

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 currents are

reduced by GIS enclosure current. Leakage rate is very less- less than 1% per year. SF6 can

break 4 Million Amps without deteriorating its quality. Gas is divided into different

compartments, so that if a fault occurs in one part , it does not affect the operation of other

compartments

LCC panels:

Local Control cubicles are user for control of bay and SF6 density inside the compartment. It

also controls electrical interlocking between various components viz. C.B., Isolators, Earth

switches. It also acts as an interface between GIS and central Control Room.

Circuit Breaker:

Three phase metal enclosed, SF6 gas insulated hydraulically operated Circuit Breaker is used.

Interrupting current level for B is 50 kA with an opening time of 28ms, closing time of 60ms

and arc time of 16ms. Pressure inside the breaker is 360 bar. It is like a long instrument that

fits into a space when closed. When the pressure falls below 340 bar, the motor (415V)

operates. Line breakers are provided with closing resistor (220V) to limit heavy line charging

currents.

Rated current Line CB 2000A

Rated current Bus coupler 4000A

No. of poles. 3

Rated SC current (rms value of ac

component)

50kA(1sec.)

Rated short circuit making current 125kA

Operating mechanism Hydraulic

No. of trip coils 2 per pole

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Isolator:

The isolator is used to insulate the various parts of electrical circuits. It is able to make or

break loop currents and capacitive load current during energizing or d-energizing the

substation. Each isolator is equipped with a moving contact located in the isolator enclosure.

The fixed contact is located in the equipped insulator. The visual indicator mechanically

linked to the transmission shaft allows verification of the isolator‟s open or closed position.

Impulse withstand voltage across open gap 1665 KVp

Switching impulse withstand voltage 1245 KVp

Rated normal current 4000 A

Earth Switches:

There are two kinds of earth switches. High speed earth switch and low speed earth switch.

High Speed Earth Switch:

This earth switch is capable of closing on a short-circuiting current.

High-speed earth switches are capable of interrupting the inductive and capacitive currents.

These switches are fitted with a stored energy closing

system to provide fault-making capability. Short Circuit making capacity rating = 125 KA

Low Speed Earth Switch:

It serves to earth the part of the GIS where it is installed. This is used for providing safety

during maintenance work. The live part of Earthing switch can be electrically insulated from

the enclosure to facilitate input of signal for certain settings and tests.

Bus bar:

It is an element in the main current circuit and is made of Al tubing. It can be called a bar fit

together in silver-plated multi-finger contacts.

Current Transformers:

Current Transformers are used for protective and metering functions. They have effective

magnetic shield to protect against high frequency transients. CT used is 5 core-type.

Rated Voltage 420/630/425kVA

500/1A 5VA

500/1A 5VA

500/1A 30 VA

500/1A Rot 75<10Ω, Io<30mA

500/1A Rot 75 d5E

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Voltage Transformers:

The Voltage transformers are of inductive type. VTs are located inside the independent gas

compartment. They are used for protective, metering of synchronization of machines with

Grid. They have effective magnetic shield to protect against high frequency transients.

Surge Arrester:

Surge arrestor is Valve type, made of non-linear resistor discs. Surge arrester is made up of

stack of zinc oxide disks. One end of stack connected to live part and the other end of stack is

connected to earth. Under normal operation, the discs are resistive and no current circulate

between phase & earth. In the event of lightening impulse (rise in voltage in the bar), the

disks allow current through, which is evacuated through earth.

Rated voltage of arrestor 336kV(rms)

Max. continuous Voltage capability 265kV(rms)

Max. discharge current 10kA

Energy level 10kJ/kV

Bushings:

Oil to SF6 Bushing:

The transformer bushings comprise of oil insulation on the transformer end and enclosed by

an SF6 gas filled compartment on GIS side.

SF6 to Air Bushing:

400 kV transmission lines are connected to GIS through SF6 to air filled bushings through

400 kV bus ducts.

Metallic Bellows:

These bellows are provided to prevent the expansion in the metal due to overheating (or

heating).

Monitorinig Devices:

Density Switches:

Density switches are fitted to all compartments and are used for monitoring quantity of SF6

gas filled in each compartment.

G9 Of GIS-II Circuit Breaker

Rated Pressure 5.3 bars 6.3 bar

Alarm 4.8 bars 5.8 bar

Trip 4.5 bars 5.5 bar

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Rupture Disc:

The rupture disc / safety diaphragm is a disc made of varnish coated carbon. It is designed to

give away in the event of SF6 gas over pressure within the compartment.

POT HEAD Yard

The POT HEAD YARD (Point Of Transmission Hydro Electric Aerial Distribution Yard)

420 KV GIS switchyard is located in such a way that the complete GIS is placed within a

building at an elevation of approximately 1173m. GIS-2 switch gear comprises of bus bars,

bus isolators, circuit breakers, current transformers, Potential transformers, disconnect

switches, high speed make proofing grounding switches, Transition bus, SF6/Air bushing.

There are 6 outgoing bays and 2 more bays for future extensions: 2 bays for inter connection

to Baspa stage-2 HEP, 2 bays for inter connection to Kol Dam, 2 bays for inter connection to

Abdullahpur, 2 bays for future extension. The rating of each bay is 2000A, 50 kA short

circuit rating. The rating of Bus bar is 4000A. GIS-1 switch gear at elevation 1051.5 meter is

connected to GIS-2 by 420KV, 4000Amps, and Sf6 CGI double bus system. The length of

this double bus system is approximately 250m.

Incoming and outgoing feeders:

There are 2 incoming feeders from Baspa (54km line) and 4 outgoing feeders (2 to

Abdullapur (180km line) and 2 to Nalagarh (145km line).

Wave trap:

It is connected in series with the power (transmission) line. It blocks the high frequency

carrier waves (24 kHz to 500 kHz) and let power waves (50 Hz - 60 Hz) to pass through. It is

basically an inductor of rating in Milli henry (approx 1 milli Henry for 220 KV 1250 Amp.).

Line Trap has three main components: Main coil, Tuning Device, Lightning Arrestor.

Capacitor Voltage Transfomer:

A capacitor voltage transformer (CVT), or capacitance coupled voltage transformer (CCVT)

is a transformer used in power systems to step down extra high voltage signals and provide

a low voltage signal, for measurement or to operate a protective relay.

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In its most basic form the device consists of three parts: two capacitors across which the

transmission line signal is split, an inductive element to tune the device to the line frequency,

and a transformer to isolate and further step down the voltage for the instrumentation or

protective relay. The device has at least four terminals: a terminal for connection to the high

voltage signal, a ground terminal, and two secondary terminals which connect to the

instrumentation or protective relay. CVTs are typically single-phase devices used for

measuring voltages in excess of one hundred kilovolts where the use of voltage transformers

would be uneconomical. In practice, capacitor C1 is often constructed as a stack of smaller

capacitors connected in series. This provides a large voltage drop across C1 and a relatively

small voltage drop across C2. CVTs in combination with wave traps are used for filtering

high frequency communication signals from power frequency. This forms a carrier

communication network throughout the transmission network.

Power line carrier communication (PLCC):

Power line carrier communication (PLCC) is mainly used for telecommunication, tele-

protection and tele-monitoring between electrical substations through power lines at high

voltages, such as 110 kV, 220 kV, 400 kV. PLCC integrates the transmission of

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communication signal and 50/60 Hz power signal through the same electric power cable. The

major benefit is the union of two important applications in a single system.

In a PLCC system the communication is established through the power line. The audio

frequency is carried by a carrier frequency and the range of carrier frequency is from 50 kHz

to 500 kHz. The modulation generally used in these systems is amplitude modulation. The

carrier frequency range is allocated to include the audio signal, protection and the pilot

frequency. The pilot frequency is a signal in the audio range that is transmitted continuously

for failure detection.

The voice signal is converted/compressed into the 300 Hz to 4000 Hz range, and this audio

frequency is mixed with the carrier frequency. The carrier frequency is again filtered,

amplified and transmitted. The transmission of these HF carrier frequencies will be in the

range of 0 to +32db. This range is set according to the distance between substations.

Battery Bank:

There are 2 battery banks. Ni-Cd rechargeable batteries of 48V (645Ah) and 220V (1500Ah)

are used for supply to relays and control panels. There are 4 battery chargers.

Synchronizing trolley:

Synchronization is a process of matching the voltage, frequency and phase angle of the bus

bar with the grid. It is done before transmitting the power to the grid. Synchronizing trolley is

used for matching the voltage.

Relays:

A protective relay is a device that detects the fault and initiates the operation of circuit

breaker to isolate the defective element from the rest of the system.

The relays detect the abnormal conditions in the electrical circuits by constantly measuring

the electrical quantities such as voltage, current, phase angle etc. which are different under

normal and faulty conditions. Through the changes in any quantity, the fault signals its

presence, location and type to the relays and the relay operates to close the trip circuit of the

breaker.

The different types of relays used are as follows:

1. Time delay relay

2. Impedance relay (distance relay)

3. Synchro-check relay

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4. Under voltage protection

5. Over load relay

6. Instantaneous over current relay

7. Instantaneous earth fault relay

8. IDMT over current relay

9. IDMT earth fault relay

10. Voltage control over current relay

11. Over voltage relay

12. Voltage balance relay

13. Buchholz relay

14. Restricted earth fault relay

15. Stator earth fault relay

16. Rotor earth fault relay

17. Auto recloser relay

18. Under frequency relay

19. Trip circuit supervision relay

20. Combined motor protection relay

CONTROL ROOM:

The major feature of the control room is its OS (operating system). This system is so

designed that each event whether minor or major, can be viewed and controlled. Each of the

six units can be closely monitored.

This operating system is connected to the Unit Control Board. The control room consists of 2

screens. On one of them, the time and the location of a particular event are clearly displayed

so that the human operators are well aware of the proper/improper functioning of the

generating units. The other screen provides for viewing of pictorial representation of

individual units, their specific parts and all the related measurements (frequency, rated

voltage, set value, discharge, pressure, temperature, labyrinth leakage, active power, reactive

power, their set points etc.).

The start/stop command of each unit is given from the control room. The command can either

be direct or step by step. In case of the direct command the steps of the specified sequence

are carried out automatically. In case of step by step command, each step of the specified

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sequence is carried out separately. This is done when a particular step in the sequence refuses

to run by direct command. If the step fails to be completed even by step by step command,

that step is completed either by local auto mode or manually.

The various set points for generation (active power and reactive power) are fed into the OS

and hence the operation of the generating units is controlled.

The minimum set point (active power) is 25 MW. When the active power falls below 80MW

a trip command is sent to the given unit. This is done because if the active power falls below

the 25MW mark the machine starts drawing power from the grid itself and hence the power

house gets penalized.

Unit Start Sequence

This is a step by step process involving 6 steps to start a particular generating unit. The next

step can only be started if all the conditions specified are fulfilled.

1) Firstly, all the auxiliaries need to be switched on.

Shaft seal flushing water is turned on. This is used to remove any undesired particles

that may damage the shaft seal.

Cooling water system is turned on for effective heat removal from the machines.

H.P. oil pump is switched on for jacking and lubrication.

Oil vapour extractor is turned on for removal of oil vapours formed due to the heat

generated.

Generator space heater is turned off. When the machine is at standstill the heater is

used to remove the moisture that might be present in the stator of the machine. But

while starting it is switched off, as enough heat will be generated as it is.

Transformer oil pumps are switched on to circulate oil for insulation as well as

cooling and lubrication.

The governor‟s hydraulic auxiliaries are switched on for the operation of the

governor.

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2) Now, when all the above steps have been completed, the generator brakes and the shaft

seal as well as the M.I.V. service seal need to be removed. Hence, the main inlet valve is

opened.

3) Once, the above tasks are completed, the digital turbine logic is started to operate.

4) When the speed switch indicates greater than 90% on, the excitation is switched on and

the H.P. oil pump is turned off. Also the shaft seal flushing water is switched off.

5) Now, when the speed switch is greater than 97% on and the generated voltage becomes

greater than 90%, the auto synchronizer is switched on.

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6) Once, the 420 KV generator circuit breaker is closed and the power controller and the

M.I.V are open, the change over takes place from the H.P.S.E.B. supply to the supply

from the auxiliary transformer, i.e. from 415 V UA (circuit breaker for the H.P.S.E.B.)

open to 415 V UT (circuit breaker for supply from auxiliary transformer) closed.

Unit Stop Sequence

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RAPID SHUT DOWN-1:

Genr upper guide bearing temp.

Genr lower guide bearing temp.

Genr thrust bearing temp.

Turbine guide bearing temp.

Genr stator temp.

Genr air cooler temp.

Genr turbine temp.

Bearing vibration

Turbine guide bearing RSD.

Gen lower guide bearing RSD.

Thrust bearing temp.

Genr upper guide bearing RSD.

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Genr air cooler temp.

GE(governer) common RSD.

Guide vane position high 85%.

Rapid shut down PB(push button).

Electrical rapid shut down.

SM AU watchdog fault.

SM 595 fault.

Pickup speed signal failure.

Excitation transformer high temp.

Penstock pressure low.

Cooling water system circuit fail.

MIVC common RSD.

MIV ESD valve position failure.

MIV 48V DC supply failure.

MIV 220V DC supply failure.

GHC(govr. Hydraulic control) common RSD.

Accumulator shutoff valve position failure.

GMC common RSD.

Piston accumulator level low.

Hydraulic pump 1 & 2 fault.

Accumulator manual valve close.

Nitrogen shut off valve close.

Accumulator pressure low.

Nitrogen pressure too low.

Oil system failure.

Bearing insulation failure.

Auxillary transformer temp. high

Transformer R phase oil temp. high.

Transformer R phase winding temp high.

Transformer Y phase oil temp high.

Transformer Y phase winding temp high.

Transformer B phase oil temp high.

Transformer B phase winding temp high.

RAPID SHUT DOWN -2:

EL rapid shut down 2A.

El rapid shut down 2B.

Genr. CO2 system operated.

Transformer R on fire.

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Transformer R buchholz operated.

Transformer R PR reliev der. Operated.

Transformer R emulsify system ON.

Transformer Y on fire.

Transformer Y buchholz operated.

Transformer Y PR reliev der. Operated.

Transformer Y emulsify system ON.

Transformer B on fire.

Transformer B buchholz operated.

Transformer B PR reliev der. Operated

Transformer B emulsify system ON.

Excitation trip.

SF6 too low on genr CB.

Auto trip 1 pressure.

Auto trip 2 pressure.

EMERGENCY SHUT DOWN

Emergency shutdown PB.

Butterfly valve ESD PB>

GE 220V dc supply failure.

GE 24V dc supply failure.

GE 48V dc supply failure.

Change over position failure.

DTL and BU DTL failure.

GE common ESD.

Speed switch 140%.

BFV 1 trip via RTU.

BFV 1 trip via hardware.

Mech over speed.

GHC common ESD.

GHC 220V dc supply failure.

GHC 24V dc supply failure.

GHC 48V dc supply failure.

Future Projects

Since the commissioning of the largest underground 1500 MW Nathpa Jhakri Hydro Power

Station, the Corporation has expanded its base from a single project to a Multi Project and

thereafter from a single state to an international Corporation. The Corporation is executing

the following Projects which are under various stages of construction/ investigation:

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S. No. Name of Project Capacity in MW Location

1 Rampur HE Project 412 Himachal Pradesh

2 Luhri HE Project 775 Himachal Pradesh

3 Dhaulasidh HE Project 66 Himachal Pradesh

4 Devsari HE Project 252 Uttarakhand

5 Naitwar Mori HE Project 60 Uttarakhand

6 Jakhol Sankri HE Project 51 Uttarakhand

7 Arun-III HEP 900 Nepal

8 Kholongchu HE Project 650 Bhutan

9 Wangchu HE Project 600 Bhutan

10 Tipaimukh HE Project

(in JV with NHPC)

1500 Manipur

In pursuit of expansion of the Corporation in the neighboring countries, a MoU was signed

with the Govt. of Nepal on March 02, 2008 for the development of 900 MW Arun-III Hydro

Electric Project which was bagged by SJVN in open global competition.

SJVN has been allocated two Hydro Electric Projects in Bhutan for the preparation of DPR

by the Ministry of Power. These are 650 MW Kholongchu HE Project and 900 MW

Wangchu HE Project.

The water that exits from the tail race tunnel is free from silt and has the required pressure

and hence can be used to operate another set of turbine and generator without having to invest

in the construction of the dam and the desilting chamber and e.t.c. Such plants are said to be

in tandem operation. An example of such a plant is the upcoming plant at Rampur (412 MW).

The Rampur Project has its intake structure at the outfall of the NJHEP and it also has 4

intake gates and a surge shaft of 38 m diameter and 140 m deep.

Initially it was proposed that a HRT of 13 m diameter be made for this project. However,

after reconsideration as the size of this diameter is unstable, it was decided that instead of a

single huge HRT, two smaller HRT of 9 m diameter each be constructed. The advantages of

this project are that it saves a lot of construction cost which is the area in which majority of

the capital is invested and also, a new project can be completed in a very less time and also,

there is no need for any desilting complex as the water is already free from it. However, it has

a drawback that if any unit of the NJHEP trips then, it will mean that the corresponding unit

of the RHEP will also not work as they are in Tandem operation.