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A report on Prepared during the six week vocational training at SJVNL 1 NATHPA JHAKRI HYDROELECTRIC PROJECT

Hydroelectric Project

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Page 1: Hydroelectric Project

A report on Prepared during the six week vocational training at

SJVNL

Submitted to: Submitted by:

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NATHPA JHAKRI HYDROELECTRI

C PROJECT

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ujjwal

ACKNOWLEDGMENT

I am thankful to NIT Hamirpur for providing me an opportunity to undertake my six week vocational training at SJVNL Jhakri and see in such detail the operation of the largest hydroelectric project in India.

I express my sincere thanks to the HOP Er. N.C. Bansal for allowing me to undertake this vocational I want to thank our shift in charge at the power house, Er. A.K. Jindal for ensuring that we make most of our time at the power house in the operations department. I also take this opportunity to express my gratitude to Er. Roshan Kumar, whose guidance and encouragement made this training and report-making worthwhile.

Also, I acknowledge the help extended by Er. Sunil Prashar, Er. Deepankar Raitura, Er. Amardeep Daroch and Er. Rahul Tiwari 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 me come to a successful completion of my 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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INTRODUCTION TO HYDRO POWER

The theory of hydro power is to build a dam on a large river that has a large drop in elevation. The dam stores lots of water behind it in the reservoir. Near the bottom of the dam wall there is the water intake. Gravity causes it to fall through the penstock inside the dam. At the end of the penstock there is a turbine propeller, which is turned by the moving water. The shaft from the turbine goes up into the generator, which produces the power. The water continues past the propeller through the tailrace into the river past the dam.

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A hydraulic turbine converts the energy of flowing water into mechanical energy. A hydroelectric generator converts this mechanical energy into electricity. The operation of a generator is based on the principles discovered by Faraday. He found that when a magnet is moved past a conductor, it causes electricity to flow. In a large generator, electromagnets are made by circulating direct current through loops of wire wound around stacks of magnetic steel laminations. These are called field poles, and are mounted on the perimeter of the rotor. The rotor is attached to the turbine shaft, and rotates at a fixed speed. When the rotor turns, it causes the field poles (the electromagnets) to move past the conductors mounted in the stator. This, in turn, causes electricity to flow and a voltage to develop at the generator output terminals.

Hydro power has come into focus as a promising source of electricity to meet the growing demand in the country. India has an estimated hydro potential of about 150,000 MW, of which very little has been tapped. Keen to develop substantial hydel capacity, the government ,in 2003 , came out with a policy initiative to add 50,000MW of hydro capacity by 2017.

Growth in hydro power is essential as the country is heavily dependent on fossil fuel based generation. Though, on the face of it, thermal power projects seem more feasible, they come with their own set of problems. Volatile oil prices, dwindling fuel reserves and increasing concern for the environment implications of fossil fuel put a question mark on the long term sustainability of these projects

Besides, hydel projects are also economical in the long run. Once they are up and running, the variable cost is practically zero and is limited only to the O&M costs. The character of this cost is also non-inflationary, since it is not dependent on imported fuel. Hydro Power Projects are easy

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to back down or start up and so they can be used for peaking power, a flexibility not available with thermal projects.

However Hydro project has certain drawback as well. At the preliminary stage, projects get delayed indefinitely for want of clearance from various authorities. Then, these projects have long and uncertain gestation periods, which heighten the risk and prolong the payback period. Most projects often require large scale rehabilitation and resettlement of local population

Hydro projects have therefore been taken up mostly by central and stage agencies, and there has been very little private participation. The state utilities account for about 79 percent of the total capacity and central utilities account for about 18 percent. While in earlier years, the states, especially in the southern region, developed a number of hydro projects; their contribution in recent years has been limited.

Hydro Power is clearly an ideal solution to rising cost of power for the consumer. In recent survey, the central electricity authority identified 68 projects with a capacity of over 27000 MW that can be developed at tariffs of less than Rs2.50 per unit. This should attract both the government and private players. Greater activity can be expected in Hydro in the coming years.

HYDROPOWER SITUATION IN INDIA

India has one of the highest hydropower potentials in the world. There is potential for an installed capacity of over 150,000MW, and for an additional 90,000MW of pumped storage schemes. At a 55% load factor, the hydro schemes could produce some 82,5000MW of power. However, of the total hydro potential in India, only 15% has so far been utilised, with another 7% under various stages of development. Turning opportunities into business has proved very difficult in India and the share of hydroelectricity has gone down to 25% of the overall national power generation capacity.

INTRODUCTION TO SJVNL (Satluj Jal Vidyut Nigam Limited)

SJVNl houses six generating units each of rated capacity 250MW. All the six generating units have been successfully commissioned. Nathpa Jhakri boasts the largest and longest headrace tunnel, largest desilting chambers, deepest and largest surge shaft, and the largest underground power complex. The project has added 1500MW capacity to the Indian Northern Grid since the first unit was commissioned in October 2003.

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Project Commissioning Schedule

The commissioning schedule of NJHPP was as follows:

Unit MW Synchronization Commissioned

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

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

Unit-IV 250 Jan. 22nd –2004 30 March , 2004

Unit-III 250 Feb. 13th –2004 31 March , 2004

Unit-II 250 March 09th2004 06 May , 2004

Unit-I 250 March 31st2004 18 May ,2004

SJVNL was originally a joint venture between the central government, which provided most of the project funding, and the state of Himachal Pradesh. The present authorized share capital of SJVNL is Rs. 4500 crores. The debt equity ratio for the Nathpa Jhakri Hydro Electric Project (NJHEP), the first project executed by SJVNL is 1:1 and the equity sharing ration of Govt. of India and Govt. of HP is 3:1 respectively. The project includes a 62.5m-high dam and underground desilting complex and a 250MW Francis unit. It supplies Himachal Pradesh and the Northern Regional Grid States in India.

CONSTRUCTION PERIOD

The original plan called for a five-year construction period, but a rockslide shortly after the civil contract was signed in 1993 required extensive stabilization work, and the project had to be redesigned. Main equipment orders were placed in March 1994, and substations and other electrical equipment were ordered in October 1996.The delay was aggravated by disagreements between the contractors and the sponsors. Further disruption came from labour troubles and alleged discrepancies between the bid documents' data and actual site conditions. In April 1999, the Union Cabinet approved the revised cost of Rs7,666 crore for Nathpa-Jhakri hydroelectric power project. The original cost estimate for the was Rs7,217 crore.

Flash floods in August 2000 led to extensive loss of time and money to the project, and caused so much destruction to the dam and power house that the World Bank almost wrote off the project. Soon after it was taken over by the National Hydroelectric Power Corporation, though, employees worked round the clock to complete all restoration works to the pre-flood level. At the October 2001 and March 2002 review missions, the World Bank commended the phenomenal progress of works at the project sites and expressed its full satisfaction.

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The Satluj Jal Vidyut Nigam Limited [SJVNL], formerly Nathpa Jhakri Power Corporation Limited [NJPC] was incorporated on May 24, 1988 as a joint venture of Govt. of India and Govt. Himachal Pradesh to plan, investigate, organize, execute, operate and maintain hydroelectric power projects.

Nathpa Jhakri HE Project (1500 MW), the country’s largest underground hydroelectric power project, was the first project undertaken by SJVNL for execution.

LOCATION

The generation component of the 6x250 MW Nathpa Jhakri Hydro-Electric power project (NJPC) in the Shimla and Kinnaur District of Himachal Pradesh (H.P.) was sanctioned in April 1989 for execution by the Nathpa Jhakri Power Project now known as Satluj Jal Vidyut Nigam Ltd. (SJVNL), NJPC effectively took over execution of NJHPP in August 1992.NJHPP envisages harnessing the Hydro power potential in the upper reaches of river Satluj in the South West of Himalaya.

This is located in the state of Himachal Pradesh, on the downstream of Wangtoo Bridge and derives its name from the names of two villages in the Project vicinity - Nathpa in district Kinnaur and Jhakri in district Shimla - in the interiors of Himachal Pradesh. The Project was conceived as a run-of-river type hydro power development, harnessing hydro-electric potential of the middle reaches of the river Sutlej, one of the principal tributaries of the river Indus, in the south west Himalayas. The Project's Dam has been constructed near village Nathpa and its Power House has been constructed on the left bank of the river Satluj at village Jhakri. The project stretches over a length of about 44 Km from the dam site to the power house, on the Hindustan Tibet Road (NH-22).

Prior to formation of SJVN (NJPC), NJHPS was being executed by Himachal Pradesh State Electricity Board (HPSEB). The generation component of 1500 MW NJHPS was sanctioned in April 1989 for execution by SJVN (NJPC). SJVN (NJPC) officially took over NJHPS on August 01, 1991, following an agreement between GOI and GOHP during July 1991. However, the effective takeover of the NJHPS could result only during February 1992, due to an agitation by the employees of HPSEB. The Major Civil Works of NJHPS were awarded during June – Sep. 1993 and the construction works commenced in early 1994.

OVERVIEW OF NATHPA JHAKRI HE PROJECT

NJHEP is run of the river type hydro power plant with small pondage. The water conductor system of NJHEP consists of Dam, Power intakes, Desilting chambers, HRT, Surge shaft, Pressure shaft and the Tail race.

NJHPP has several unique features and is totally underground except for its Dam and the Pot Head Yard. Besides providing 1500 MW of valuable peaking power to the Northern Grid, NJHPP will generate 6750.85 Million Units of electrical energy in a 90% dependable year.

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SAILENT FEATURES

1. It has a 62.5m high concrete gravity dam at Nathpa village of Kinnaur district of Himachal Pradesh and it diverts 405 cumecs of water through 4 power Intakes.

2. Underground Desilting chambers (4 in number) each of which is 525m long, 16.31m wide and 27.5m deep. It is the world’s largest underground complex for desiltation.

3. A head race tunnel of 10.15m dia. and 27.39km long is the longest power tunnel in the world and terminates into a surge shaft with a varying diameter of 21.6m (top)/ 10.2m (bottom).

4. It has the deepest surge shaft which is 301m deep.5. There are three circular steel lined pressure shafts each of 4.9 m dia which feed six

generating units.6. The six generating units utilize a design discharge of 405cumecs and a design head of 428m

(486m is the gross head).7. The discharge tubes to the collection gallery discharge the water back into the river

through the 10.15m dia and 982m long tail race tunnel.8. The project has an underground Transformer hall and Power house. There is a Surface

Switch Yard for evacuation of power through two transmission lines.9. There is a Sholding Works Complex which enables the diversion of water of Sholding

Stream into the HRT.10. Annual energy generation amounts to 6612million units in a 90% (MU) dependable year.

Future Project

Agreement for the execution of the Rampur Hydro Electrical project between SJVNL and govt. of Himachal Pradesh was signed on 20th October 2004 of 412MW utilizing the tail race water of the ongoing 1500MW Nathpa Jhakri Hydro Electric Project. It is again, a run of the river scheme on which work has already commenced by SJVNL and other projects in the state of Himachal viz. Khab and Luhri projects and in Uttranchal and Sikkim shall be undertaken shortly.

SOME PLANNING AND DESIGN ASPECT

Reservoir Flushing

Satluj river carries heavy sediment load during snowmelt and during the monsoon season as well. Provision of low level sluices in the dam ensures outflow of sediments from the reservoir whenever the water availability is more than the designed discharge. Further flushing of reservoir behind Nathpa dam is also envisaged once or twice every year when the discharge in the river exceeds 1500 cumecs.

Desilting Cavern

There are four desilting chambers present which function under conditions of both external and internal water pressure. Complete analysis both for the rock support during excavation and long term stability during maintenance conditions was carried out through

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numerical modeling which involved through investigation based on field and laboratory testing of rock mass properties and geological details of joints, major shear planes etc.

HEAD RACE TUNNEL

Tunnel Lining In Hot Water

Hot water has been encountered in the HRT downstream of Wadhal Adit junction for a length of about 3 km, which has chemically proven to be aggressive to normal concrete. The addition of ‘pozzolana’ in the concrete mix design helped combat this problem.

Steel Liner In HRT

Steel liner with length of 710 m and 375 m respectively have been provided at Manglad and Daj creek of the head race tunnel where rock covers are inadequate against maximum internal water pressure which ranges from 2.8 to3.1 MPa. With a view to avoid stress relieving and limit the plate thickness to 40 mm the diameter of the steel liner has been reduced to 8.5 m with transition both upstream and downstream to 10.15 m diameter.

USE OF ADITS

Being a very long HRT, it would be difficult to inspect it in case of emergency/shutdown. Keeping this in view, intermediate vehicular accesses have been planned through Nathpa and Wadhal construction adits. Here, steel doors in an opening in the concrete plugs have been provided.

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

Project Cost

The project is estimated to cost RS 7,666.31crores at June, 1998 price level with completion cost of 8058.34crores, which had been approved by the Cabinet Committee on Economic Affairs (CCEA) in its meeting, held on April 28, 1999. However on completion, the project’s cost was Rs.9083crores.

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Sales

Besides providing 1500 MW of peaking power to the Northern Grid 12% of the power is to be supplied free of cost to the Himachal Pradesh and 25% of the remaining 88% of power generated, will be supplied to HP at the Bus Bar rates. The balance power available shall be distributed amongst the Northern Regional Grid States based on their actual energy consumption as well as the quantum of the central assistance to them.

To summarize the above:

Free power to HP : 12 percent Power to HP at Bus Bar rate : 22 percent

Balance power available for the Northern Grid: 66 percent.S. No. Year Actual Energy (Ex Bus)

in MUSaleable Scheduled Energy (Ex Bus) in MU

1. 2004-05 5108.77 4467.64

2. 2005-06 4055.16 3533.93

3. 2006-07 5942.30 5179.06

4. 2007-08 6385.33 5564.72

5. 2008-09 6547.78 5759.47

6. 2009-10 6956.70 6120.75

7. 2010-11 (up to September-10)

4988.86 4390.19

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ALLOCATION OF POWER BY NATHPA JHAKRI HEP

Balance power allocated to different status/UTS of Northern Region presently is as under: -

S.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

PROJECT STATISTICS

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DESCRIPTION AS PER REVISED COST EXTIMATE

a) Location

b) Diversion DamTypeMax. height above foundation level Full reservoir levelMin. draw down level

c) Disilting ArrangementTypeNumber & sizeFlow through velocityParticle size to be removed

d) Head Race TunnelShape & typeDiameterLength

e) Surge ShaftTypeDiameter

Total height

f) Pressure ShaftsType

g) Power HouseTypeSizeType of turbineGross headDesign headNumber and capacity of generating units

h) Tail Race Tunnel

State Himachal Pradesh District Kinnaur/Shimla Vicinity Dam downstream of Wangtoo bridge at Nathpa & power house near Jhakri village on left bank of river sutlej. Concrete gravity62.5m1492 m1474.00m

UndergroundFour parallel chambers each 525m x 16.31m x 27.5m33.0 cm/sec.Particle greater than 0.2 mm

Circular, concrete lined10.15m27.395km

Restricted office21.6m circular for height of about 210m & a connecting shaft of 10.5m diameter. And about 90.0m high.301.0m

Circular, steel lined with high tensile steel

Underground222m x 20m x49mVertical axis Francis turbine486m428m6 x 250 MW

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SizeLength

i) Power PotentialEnergy generation in a dependable year

10.15m, circular982m

6612MU in a 90% dependable year

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 27.395km long. The tunnel diameter is designed for a discharge of 405cumecs. The HRT 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 points 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. Its shape is circular and is concrete lined. The length of the tunnel is 27.394km and diameter equals 10.15m. The design discharge of HRT is 405 cumecs and the velocity of water in it is 5m/sec.

Spill Way Gates

There are two spill way gates on the dam situated at NATHPA. These act as a safety valve. They discharge the overflow water out of the dam when the reservoir gets full. This happens during flood and machine tripping. These gates can be opened and shut automatically when water overflows to the level and closed when water is sufficiently within limits. The spill way has two bays each of 7.5/2.5m inside it which are controlled by two counter weight balanced gates used for maintaining the level of the reservoir at EL-1490.50m.

Crest level EL-1488.00mGates Two counter weight balanced gates each of size 2.5*7.5m

NATHPA DAM SITE

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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 sufficiently impervious so that there will be no objectionable passage of water.

The dam site of Nathpa (Distt.Kinnaur) is at distance of 48km from the power house at Jhakri by road. The dam at Nathpa is a concrete gravity type diversion dam. It is not a storage dam but can provide a backup water supply for 4 hours during lean periods. The base of the dam site is merely 8m wide. The function of the dam is not only to raise the water level to create an artificial head but also to provide pondage. The height of dam is 62.5m on Satluj River at Nathpa to divert 405 cumecs of water through four intake gates .

Following are the detailed statistics of the Nathpa dam:

Type Concrete gravity type diversion dam

Base of dam 1433.0m

Top of dam 1493.5m

Max. height of dam above foundation level

62.5m

Length of dam at road level 170.2m

Full reservoir level 1488.5m

Max. water level 1488.65m

Min. draw down level 1474.0m

Pondage available 441 hectare meter

Spillway type Overall spillway or solid gravity spillway

Number & type of gates 5 radial gates

Radial Gates

There are five radial gates in the dam located in the lowest point of the dam. Radial gates are always closed. They can be opened only in condition when trees come in dam or reservoir due to flood. All these things can be discharged through these gates. So, radial gates can be opened during the Dam flushing, high discharge in the river and in the event of flood in river.

Intake Gates

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Intake structure comprising of four intake gates of about 500m length are provided through which water enters the desilting chamber. It is designed to handle a discharge of 486cumecs. Trash racks are provided before these intake gates to avoid entry of heavy material like bolders etc. in the Head Race Tunnel. An inclined independent trash rack, four vertical and one horizontal have been placed in front of each intake with trash racking machine located at the platform provided above the 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 arrangement consisting of four desilting chambers is made on the left bank of the river to settle the silt particles down to 0.2mm size from water before it enters the HRT. Four intake gates are made to feed these four chambers through each tunnel respectively and independently. The flow into the chambers is regulated by gates at intake. A proper transition from 6m wide approach tunnel to 16.31m wide at the center and 27.5m high leaves semicircular roof and 5m deep continuous hopper at the bottom. Each chamber has a 3m wide collection trench in the center running along its length. The hopper portion of the chamber slopes towards this trench. The sediments from the collection trench flow down to the flushing tunnel, 5m in diameter. Flushing gates are provided at the junction of flushing conduit and main flushing tunnels. It reduces the flow of water and also prevents the particles of size 0.2mm to the turbine.

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.

SILT FLUSHING GATES

The four flushing gates create a pressure in the desilting chambers and flush out silt particles at the edge of the chambers.

HRT INTAKE GATE

After desilting chamber, water passes through HRT intake gates. They are four in number. The water coming out of each HRT intake gate joins to enter the main Head Race tunnel.

SURGE SHAFT

The deepest surge shaft in the world belongs to the NJHPP. It is located at the intake of the penstock at 27.3km from the HRT. Its role is to prevent the back hammering by water in the HRT. Three penstocks are taken from the surge shaft at the bottom, two from its sides and one from its centre. A Horse-shoe shaped 185m long lower gallery of 12m diameter at an elevation of 1370m has also been provided. To relieve the external water pressure on the lining, three

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drainage galleries at different elevations are provided around the surge Shaft. As an additional margin, pressure relief valves have been provided in the top 80m of the concrete lining to reduce the external pressure.

The minimum water level in the surge shaft is about 30 m. it is adequately lined with concrete. Of course, the water present in the surge shaft is more or less the same quantity present at the head of the dam.

A 25cm deep spill beam has been provided on the collar of the surge shaft to remove any trash lying on the pond floor. The slopes of the top pond are well drained. The drainage water is disposed off very far away from the pond. Stop logs have not been used for the same due to very high head and difficulty in maintenance of verticality of guide rails. To reach the drainage galleries, an inspection ladder has been provided in the connecting shaft.

PRESSURE SHAFT

Three pressure shafts of diameter 4.9m and length varying from 619m to 660m take off from the surge shaft at an angle of 45 degree to the horizontal. These are lined with high tensile steel of thickness 32mm to 60mm. Each of these shafts is bifurcated into the branch tunnel of diameter 3.45 m and is designed to carry a discharge of 315cumecs. A spherical valve has been provided in each penstock branch tunnel inside the machine hall cavern to enable closing of penstocks whenever required.

MAINTENANCE SEAL

The purpose of the guard wall maintenance seal is to provide a double isolation when used in conjunction with the service seal. The principle of double isolation is essential whenever it is required to enter the downstream–dewatered penstock.

AIR RELEASE VALVE

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Fitted on the top of the valve body is an orifice air release valve, operated by a float. The valve releases air to atmosphere during fitting of the valve body and when full of water, seals the orifice to prevent leakage. Most of the air trapped during penstock filling will be released via the four anti vacuum valves. When all four anti vacuum valves are closed all remaining trapped air is released via these valves operated by a float.

ANTI-VACUUM VALVE ASSEMBLY

Four Anti-Vacuum valves are fitted, two on each side of the downstream pipe works. The 500mm nominal diameter float operated anti vacuum valves sense the pressure drop downstream of the penstock guards valve and open and allow air into the penstock preventing the formation of vacuum. When the chamber is filled with water the float rises extending the springs and contacts the Nitrile rubber sealing ring.

POWER HOUSE

The power house at Jhakri consists of a huge underground complex comprising of a massive Machine Hall, which also houses the Control Room and 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) An underground power house provides better safety against an earthquake.

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2) An underground power house is secure from the danger posed by potential landslides, which may otherwise wreck havoc.

3) Being close to the border with China, an underground power house is comparatively safer from sabotage.

The power house receives 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. In all, there are four floors in the power house namely the following, enumerated from top to bottom:

Service Bay Floor (Elevation: 1000.5m above sea level): It is the topmost floor where each of the six units of the power house are seen as a circular unit. Each unit has a pair of green and red indicators. The red light is ON when the unit is running.

Generator Floor (Elevation: 995m above sea level): This floor is also called the UAB floor. It houses the six generators of the power house. It also houses various auxiliaries associated with the working of generator.

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Turbine Floor (Elevation: 990m above 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 MIVs.

MIV Floor (Elevation: 982.5m above sea level): This floor is the lowermost floor of the power house. It contains six individual MIVs, each weighing 92 tones and being controlled by the lifting of a counter weight 79.33 tones by means of a servomotor which is operated hydraulically.

There is an underground Transformer Hall at an EL. Of 1044 m and is 270m long and 7 m D-shaped. There are 19 single phase Transformers housed in this hall.

MIV FLOOR

The MIV floor is at an elevation of 982.5m from the sea level.

The Main Inlet valve is of spherical type, has a diameter of 2.3m and can be opened only when the counter weight is lifted upwards. This valve is either open or close. There are no degrees to which it can be opened. It is located between the spiral case and penstock. Its purpose is to allow or restrict completely the water supply from the penstock to the spiral casing. The main inlet valve is capable of closing under full flow conditions. The valve is bolted to the conical inlet pipe on the upstream side and to the dismantling pipe on the downstream side. The valve body is designated to transmit all axial forces to the penstock through the upstream flange connection.

The self-closing of the valve is ensured by a counter weight of 79.993 tons. 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.

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The counter weight is lifted by a servomechanism. This is done hydraulically with 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.

The servomotors are designed for opening under balanced pressure conditions and are operated hydraulically by pressure oil at 100 bars. The MIV is devised with two locking plugs, on the left and right side of the valve that withstand the servomotor forces in case of false opening control command. The position “MIV lock engaged” is monitored by a limit switch. The locking bolts are designed to withstand the servomotor opening forces only when the counter weight is installed. The counter weight must not be dismantled unless the penstock is empty.

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 during the time the unit was 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 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.

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The MIV floor also has the primary cooling pump whose rating is:

This 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.

Also, the MIV floor is characterized by a sump area which is further categorized as drainage sump and dewatering sump. While 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 sump area has 3 types of pumps: flood drainage pumps, dewatering pumps and drainage pumps. (DW and DR pumps are almost at 6 bar pressure). There are 4 drainage pumps and 3 dewatering pumps in all. This floor also has submersible pumps that come to use during the times of flood.

The drainage sump is concrete lined while the dewatering sump is steel lined.

DRAFT GALLERY: All the water that leaks out of any machine or equipment trickles down to the draft gallery which is 7metre under the MIV floor.

SPIRAL CASING: The spiral casing is the waterway between the penstock and the guide apparatus. It ensures constant water speed around the whole circumference of the guide apparatus.

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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.

PENSTOCK DEWATERING SYSTEM: The dewatering system consists of one high pressure drainpipe for each unit. The inlet is upstream the MIV and the system consists of a gate valve and a hand manufactured needle valve. Dewatering starts from the penstock to the draft tube down to the tailrace water level. After setting the draft tube gate, the remaining water is drained through the draft tube to the dewatering pit from where it is pumped to discharge outside the draft tube gate by the dewatering system.

TURBINE FLOOR (990m)

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. In reaction turbines, there are no nozzles as such. Instead, the blades that project radially from the periphery of the runner are formed and mounted so that the spaces between the blades have, in cross section, the shape of nozzles. Since these blades are mounted on the revolving runner, they are called moving blades. Fixed or stationary blades of the same shape as the moving blades are fastened to the casing in which the runner revolves. The fixed blades guide the gas into the moving blade system and, since they are also shaped and mounted to provide nozzle-shaped spaces between the blades, the freed blades also act as nozzles. A reaction turbine is moved by three main forces:

(1) The reactive force produced on the moving blades as the fluid increases in velocity as it expands through the nozzle-shaped spaces between the blades;

(2) the reactive force produced on the moving blades when the fluid changes direction; and

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(3) The push or impulse of the fluid impinging upon the blades. Thus, as previously noted, a reaction turbine is moved primarily by reactive force but also to some extent by direct impulse.

Francis type turbines can be constructed vertically or horizontally. Horizontal construction is more accessible and has higher speed, but for large machines, vertical construction is preferred due to the space constraints.

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.

The gross head of the turbine is 486m and design head is 428m.

TURBINE: The water from the penstock enters the spiral casing. In the spiral casing, the water is spread all round the circumference through stay vanes. The water is under pressure as it enters the runner and completely fills all its channel as it passes through . 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 regulating ring that rests on these guide vanes.

Block Diagram of Turbine Function

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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 the runner buckets. Such a turbine essentially consists of guide apparatus consisting of an outer ring comprises 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 such 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 welded up from crown and band of stainless cast steel to Vanes from stainless steel plates. The vanes have been machine worked. The crown band has “Roots” towards the vanes. Air for stabilizing purpose is allowed through the Runner centre via the shaft seal and drilled holes in the turbine shaft flange.

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b) Turbine Shaft

The turbine shaft is made of steel with flanges hammered out at both ends. The turbine shaft and generator shaft are connected by flanges. The connection primarily transfers the moment of force through the shear studs.

c) Oil Slinger

The Oil slinger is located below the turbine bearing and connected to the turbine shaft. Its purpose is to collect the oil from turbine bearing and during operation bring the oil into rotation inside the slinger cylinder from where it is 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 and 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 (An alloy of tin with some copper and antimony; a lining for bearings that reduces friction) 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 have been provided. 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 a 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.

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

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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 of Aluminum Bronze for guide vane bearings 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.

BRAKE DUST COLLECTOR: The brake dust collector consists of an extraction unit, hoppers around brake assembly for trapping the brake dust and flexible hoses for connecting hoppers to the extraction unit. The extraction unit has a motor driven exhaust fan and is fitted with an easily removable sheet steel bin for collecting heavy dust. The lighter air borne particles get collected by a suitable fabric based filter. The starter panel for motor having provision for automatic start and stop of the motor is also be provided.

OIL VAPOUR EXTRACTER: 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 deposition. 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.

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.

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GOVERNOR

The turbine has two servomotors. The connection between the servomotor and the regulating ring consists 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 speed of 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

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moment which produces a force towards the 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 the hydraulic opening force on the vanes with full pressure in the spiral casing.

The governor is designed to regulate speed of the unit within a desired range also to maintain balance between power set point given and the power supply by changing the position of guide vanes. It works as a speed controller before unit is synchronized and afterwards it works as a power controller. In other words, it works as a speed controller before the circuit breaker is closed and as a power controller after it is closed.

Governing systems are designed are designed to regulate the speed of the unit within a desired range by increasing or decreasing the amount of water supplied to the turbine runner in order to maintain a balance between power supply and demand.

Governor 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.

Thus, the governor uses hydraulic system for producing actuating force which is required for turbine regulation and electrical/ electronic components and software program for controlling the actuation force as per the requirement as well as for the implementation of other functions of the governor system.

Power, P = 9.81 QHη kW

Speed = 120f/P rpm

The basic function of governor is to regulate the turbine operation during starting of the unit speed control as well as during running of the unit after synchronization.

COMPONENTS OF GOVERNOR HYDRAULICS:

OPU tank

OPU pump

Hydraulic oil cooler

Hydraulic safety valves

Hydraulic control valve (solenoid operated)

Main control valve (distributor valve)

Guide vane servomotor

Piston accumulator system

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Hydraulic oil filter elements

MIV hydraulic control valve (solenoid operated)

MIV control valve (hydraulics operated)

GOVERNOR CONTROL PANELS

MIV control panel

Governor hydraulic control panel

Governor motor control panel

Governor accumulator panel

Governor hydraulic terminal

MIV terminal box

MIV seal control cubicle

Governor electronic cubicle

Hydraulic Pump Setting

Hydraulic pump trip setting (MCB setting): 157A

Guide vane opening time: 23.4 sec

Guide vane closing time: 13.2 sec

COOLING SYSTEMS (two in number)

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 single 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.

Rating: 75kW, 415V, 50Hz, 126A, power factor = 0.86, speed = 1475rpm.

RATINGS OF WATER HEAT EXCHANGER:

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Nominal capacity: 43,00,000kcal/hr

Heat transfer surface=435.1m2

Working pressure = 10bar

Testing pressure =13bar

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.

GENERATOR FLOOR (UAB Floor)

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

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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 278MVAMaximum power 305MVAVoltage generated 15.75 +- 5% kVCurrent 10190 APower factor 0.9Poles 20 Rpm 300Runaway 545Insulation (Both stator and rotor) Type FAir gap 30mmExcitation current 2400ARated excitation voltage 249VStator winding resistance 1.22m ohmRotor winding resistance 119m ohmEfficiency 98.65%

Stator: static part specifications are as under:

Double layer

252 slots

504 bars

Core laminated

Rotor: rotating part specifications are as under:

20 poles

300rpm speed

Runaway speed 545rpm

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BRAKING AND LIFTING:

Operated at 20% of rated speed

Air pressure 6-8 bars

Brake pads are 16 in number

Extraction drive-op: 2 in number

Dust collectors are 8 in number

GENERATOR PROTECTION: Type REG 216, A.B.B

EXCITATION SYSTEM

Dry type transformer

Ratings: 1780kVA, 440V, ANAN type cooling, nominal field current: 2400A, nominal field voltage 249V.

3 bridge 6 thyristor of dc output

GENERATOR COMPONENTS

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The generator consists of following components-

1) Stator

The dc excited rotor winding induces a voltage in the stator winding. This is taken by a Bus bar to the main current lines. There is a stator frame and a laminated core. The stator windings are embedded in the slots of the laminated core.

2) Rotor

Direct current excites the rotor and the rotor windings. This excitation generates a constant magnetic field. The movement of the rotor at synchronous speed induces an ac voltage in all phases of the stator winding. The rotor is made strong enough to withstand the maximum runway speed. Also the rotor vibrations are also taken into account while ensuring the safety of the rotor.

3) HousingThe generator housing absorbs the generated mechanical loading and transfer these to the foundations.

STATOR:

Stator frame: The stator frame is made of weld able steel plates and has adequate depth to prevent distortion during transport and any operating condition.

Stator core: The stator core is made of high grade, non-aging cold rolled silicon alloy. A varnished insulation is provided on both sides of the core. Dovetail notches with corresponding dovetail key bars are welded to stator frame.

4) Anti-condensation heaters

Low temperature to prevent condensation on the winding during period of shut down is mounted below the winding located below lower air guide. They are of tubular or box type construction consisting of a coiled resistant wire embedded in an electrically insulating and heat conducting compound and protected with a metal sheath.

5) Air-Water Cooling

The generator rotor and stator are air cooled, while the bearings are water cooled. The generator’s cooling circuit is sealed off on all sides from the surrounding surface. The cooling air enters tangentially through the rotor and enters the stator through the gaps. The air water coolers arranged after the stator cools off the air that has been heated in the course of cooling the generator rotor and stator.

6) Slip ring and brush gear

The slip ring system transfers the direct current necessary for excitation of the rotor from the fixed brushes to the slip ring and thus to the rotor poles.

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The brush gear is mounted on insulated studs supported on the top bracket of the collector and is provided to permit convenient access for maintenance and inspection.

7) Bearings

The rotor is provided with two types of bearings: Guide bearing and Thrust bearing.

The thrust bearing must take up the entire weight of the rotating components of the machine set (rotor and turbine) and axial thrust of the hydraulic machine. The runner is suspended from the thrust bearings. The runner doesn’t rest on the draft cone.

Guide Bearings: the upper and lower guide bearings are located on the top and bottom of the generator. These have a Teflon coated mirror finish.

EXCITATION SYSTEM:

The type of excitation system used is static excitation. In this method, the excitation for the main alternator field is drawn from output terminal of the main 3-phase alternator. For this purpose a 3-phase transformer steps down the alternator voltage to the desire value. This 3-phase voltage is fed to the 3-phase full convertor bridge using thyristors. The controlled power output from thyristor unit is delivered to the field winding of main alternator through brushes and slip rings. For initiating the process of static excitation, first of all, the magnetic field in the rotor is set up by an external supply (H.P.S.E.B.), to establish the field current in alternator. After the output voltage from alternator has built up sufficiently, the alternator is disconnected from outer supply and is switched on to the thyristor bridge output.

AUXILIARY TRANSFORMER: It is a step down transformer 15.7KV/433V. It is used for all the

auxiliary supplies in the power plant.

Auxiliaries for hydro power plant include:

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Governor oil system, lubricating oil pumps, coolant pumps, drainage pumps, fans, cooling oil

pumps, air compressors, cranes, batteries, battery charging unit, relay and associated protective

equipment, exciter etc.

The ratings of the auxiliary transformer are as below:

Rated power : 630 KVA

Secondary voltage : 433 V

Frequency : 50 Hz

Vector group : Dyn11

Type of cooling : ANAN

Insulation class : F

Winding material : Copper

Weight : 3400 kg

BUS DUCT:

Excitation transformer: It converts the ac supply to dc and then provides supply to the rotor. This is where the rotor gets its constant excitation from. It is essential that the supply is continuous as the rotor is an electromagnet and in absence of the supply, would lose its magnetism and hence the whole unit would be shut down.

Ratings: 1780kVA, 440V, ANAN type cooling, rated amperes: 2336A, rated voltage: 440V.

Tapping transformer: the tapping transformer steps down the 15.75kV supply to 440V. The 15.75kV is the supply coming from the generator (15.75kV is the generated output of each unit). After stepping it down to 440V, this is sent to the excitation transformer which in turn excites the rotor. Hence, the unit uses a part of its generated output to run itself. The supply from HPSEB has now been cut off and the machine is on its own.

Ratings: 630KVA, 433V, ANAN type cooling, insulation F type.

Measurement and protection transformer: There are 9 potential transformers in total for each generating unit, 3 PTs per phase. These are used for protection and measurement purposes. These PTs step down high voltages to values that meters can handle. These transformers work for single and three phase systems, and are attached at a point where it is convenient to measure the voltage.

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Earthing transformer: these transformers add to the protection scheme of each generating unit. They earth the dangerous voltages and keep the equipment as well as human operators safe (20kV/220V).

AUTOMATIC VOLTAGE REGULATOR

The voltage across the generator can easily be controlled as well as varied when required by using a reference setter, which compares the generator voltage actual value with the reference value (voltage set point) adjusted by the power plant operator, reference value is easily be varied within a specified value. It works on the principle of error detection. The alternator three phase output voltage obtained through a potential transformer is rectified, filtered and compared with a reference. The difference between actual and reference voltage is the voltage error. The voltage error is amplified through an amplifier and fed to the field circuit. Hence the voltage remains constant.

NEUTRAL GROUNDING RESISTOR (0.016 ohm and 0.09 ohm)

The purpose of a neutral grounding resistor is to limit the ground fault current to a safe level so that all the electrical equipment in the power system is protected. The resistor should be the only current path between the neutral of power transformers or power generators and ground. When the neutral of a system is not grounded it is possible for destructive transient over voltages to appear from line to ground during normal switching of a circuit having a line to-ground fault. Experience has proved that these over voltages cause aging and failure of

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insulation at locations on the system other than at the point of fault. In this way, a relatively unimportant line-to ground fault on one circuit may result in considerable damage to equipment and interruption of service on other circuits, not to mention the increased difficulty in finding the original location of the problem.

A neutral grounding resistor is designed to limit the ground fault current to a safe value while at the same time letting enough current to flow to operate the protective relays that will clear the fault. While the disturbance lasts the resistor must be capable of absorbing and dissipating the energy generated without exceeding the temperature limits. In this way the fault is safely limited, isolated, and the power system is protected against over voltages.

NEUTRAL GROUNDING TRANSFORMER (20kV/220V)

For delta-connected 3-wire electrical systems with no star point, one solution to the absence of a neutral for connection to the earth or ground connection is to create an artificial neutral by using a zigzag or delta-star earthing transformer with a low voltage secondary winding. This can be connected to a suitably rated resistor of which the other terminal is earthed.

The best way to ground a power system is to obtain the system neutral through a generator or transformer with a wye-connected winding. However, a system neutral may not be available, particularly in many older low voltage systems and a significant number of existing medium voltage systems. To avoid a high cost of replacing a source transformer, an existing delta-connected system can be grounded using a star/ open delta or star/ delta transformer.

During a line-to-ground fault condition, the zero sequence currents can flow into the ground at the point of the fault, and back through the neutral of the grounding transformer, hence providing facility to monitor & limit ground fault current. However Neutral Grounding Resistors are used for system grounding through Neutral Grounding Transformer & generators. A neutral grounding resistor limits the fault current, which is sufficient enough to operate protective relays, yet prevent unwanted fault damage.

The NGT is used not just for protection but also as a reference for voltage measurement.

SERVICE BAY FLOOR

There are three modes for machine operation:

Local mode (Unit Control Board manual) Auto mode (UCB auto) Central control room mode

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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 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

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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.

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.

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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 Tones: 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.

TRANSFORMER HALL

There is an underground Transformer Hall at an elevation of 1044 m (270m long and 7m D-shaped).

GENERATOR TRANSFORMER

In the power house, generator transformers are used to step up the voltage to a level suitable for transmission. The main purpose of stepping up of voltage is to reduce the current level and hence to minimize transmission losses.

In SJVNL power house, there are 19 single phase transformers in all, each of 102MVA capacity (3phase transformer bank) for each unit (6 units x 3 phases) and one in spare (the standby unit).

The main logic behind using single phase transformers instead of three phase transformers is due to the problem of transportation of heavy weight and size of –phase transformers and the large space these would have otherwise occupied 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.

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The various specifications of the transformers are given below:

TRANSFORMER SPECIFICATIONS

Make - Bharat Heavy Electrical Limited Types of cooling - ODWF(oil dripped water force)

Rating HV & IV (MVA) - 102 Rating LV (MVA) - 102No load voltage HV (KV) - 420/√3 No load voltage LV (KV) - 15.75Line current HV (AMPS) - 421 Line current LV (AMPS) - 6476Temperature Rise oil (OC) - 55(deg) Temperature Rise windings - 65(deg)Phase - 1(single) Frequency HZ - 50 HzConnection Symbol - YNd 11 Type - shell type T/FWeight of core and winding - 55095kg Weight of oil - 18165kgTotal weight - 9275kg

GENERATION TRANSFORMER

Oil immersed type transformer

RATINGS: 102MVA, 420 /√3 kV (high voltage side), 15.75kV (low voltage side)

Ynd11

ODWF cooling system (oil dipped water force)

Efficiency: 99.76%

PARTS OF TRANSFORMER

Secondary winding Primary winding Oil level Conservator Breather Tubes for cooling Transformer Oil Earth Point Temperature gauge Buchholz Relay Secondary terminal Primary Terminal Winding temperature indicator Non Returning valve On Load Tap Changer

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Conservator: It is used generally to conserve the insulating property of the oil from deteriorating and to protect the transformer against failure on account of bad quality of oil. It is a small tank mounted on main tank and the two are connected by a pipe. The main tank is completely filled with oil but conservator tank is partially filled with oil. Its function is to allow space for expansion of oil due to heating and contraction due to cooling.

Buchholz Relay: Buchholz relay is a gas actuated relay used for protecting oil immersed transformer. Its main advantage over other relays is that it gives indication that the system is unhealthy, thus preventing the transformer from severity of fault. The relay operates on the well-known fact that in case of most electrical faults in a liquid immersed transformer, a gas is formed. This gas is collected in the body of relay. If the quantity of gas collected surpasses the set value, this relay gives an alarm or trip command depending upon the case. The device provides protection against a no. of internal faults, but in several cases, it also indicates the type of fault. This is possible because the gas collected in relay can form its odor, colour and composition indicating both the fault and location of the fault.

Oil Gauge: It indicates the oil level in the transformer.

Oil Temperature Indicator: It measures the temperature of the transformer oil. It’s set for alarm and trip. When the temperature of the transformer oil rises above the preset value, the alarm or trip command is given as the case may be.

Gas Collecting Device: The gas collecting device is used to collect the gas formed as a result of any fault inside the transformer. A pipe connects this device to the Buchholz relay. For analyzing the gas formed, it is first collected in this device and then it is sent for analysis. The main advantage of this device is that the gas can be obtained for analysis without an actual shut down. Hence the operation of transformer is not disturbed.

Pressure Relief Valve: This is protective device which is installed on the tank transformer when pressure inside the tank is more than the preset 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 & one contact which are used in control circuit.

Winding Temperature Indicator: This is a precision instrument designed for the protection of transformer. This instrument with three contacts indicates the temperature of the hottest part of winding. It indicates the maximum winding temperature irrespective of the condition of loading temperature of the cooling medium. Thus the load on the transformer can be kept within a 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.

Silica Gel Dehydrating Breather: Breather is used to prevent the moisture getting into the transformer oil when the volume of the oil decreases due to change in temperature. The level of oil in the conservator tank decreases. The conservator tank takes in air from the surroundings (i.e. the atmosphere) to compensate for this decrease in level, through this

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breather and the oil expands. The oil level inside conservator hence, 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.

Bushings: Bushings are made of highly insulating material to insulate and to bring out the terminals of the transformer from the container.

420kV oil-SF6 bushingLV bushing

Tappings: The transformers are usually provided with few tappings 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 NRV.

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.

Water Flow Indicator: It indicates the flow of water through the cooler when the transformer is in operation. The application of this device is same as that of an oil flow indicator.

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: It is a protection device. When the rate of rise of pressure is more than the specified value it operates and gives the tripping command to the breaker.

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GAS INSULATED SWITCH YARD

The term switchgear, used in association with the electric power system, or grid, refers to the combination of electrical disconnects, fuses and/or circuit breakers used to isolate electrical equipment. Switchgear is used both to de-energize equipment to allow work to be done and to clear faults downstream. This type of equipment is important because it is directly linked to the reliability of the electricity supply.

Typically, switchgear in substations is located on both the high voltage and the low voltage side of large power transformers. The switchgear located on the low voltage side of the transformers in distribution type substations, now are typically located in what is called a Power Distribution Center (PDC). Inside this building are typically smaller, medium-voltage (~15kV) circuit breakers feeding the distribution system. Also contained inside these Power Control Centers are various relays, meters, and other communication equipment allowing for intelligent control of the substation.

The transformer hall is also equipped with a GIS. The use of GIS based substation design has made the design of an underground substation possible. Gas insulated switchgear used for transmission-level voltages saves space compared with air-insulated equipment, although it has a higher equipment cost. The space requirement can be as low as 10% of that required by an air insulated switchgear, as all the live parts are metal enclosed and sealed the SF6 GIS is completely immune to atm. conditions. The SF6 GAS INSULATED SWITHGEAR prevents all foreign bodies from coming in contact with the live parts which otherwise can be very dangerous.

At the power house of Nathpa Jhakri HEP, the switching scheme adopted is single breaker double bus type. At POT head yard all the line switchgear is proposed to be placed inside the closed building. In this arrangement only two sets of three-phase CGI bus ducts needs to be extended from the transformer hall to pot head yard. Power cables are required to be extended from transformer hall to pot head yard as that of transmission circuit.

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SYSTEM DETAILS

GIS I includes the following:

• 6 CB bays

• 1 Bus Coupler Bay

• 1 Measuring Bay

• 2 Bus Bar systems

The SF6 gas insulated switchgear are suitable for indoor and outdoor operation with three phase,50Hz, 420kV rated voltage, 2000A, 50kA, short circuit rating, located at an elevation of 1051.5 meter above the sea level. It is located above the Transformer Hall. The rating of the bus bars is 4000A. Double bus bar system comprises of circuit breakers, CTs, PTs, disconnect switches, safety ground switches, high speed grounding switches, lightning arrestors, Oil/SF6

bushing, Transition bus section between gas insulated switch gear and SF6/Oil bushing of the transformers.

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GIS II (Pot Head Yard):

The second 420 KV GIS switchgear is located in such a way that the complete GIS is placed within a building at an elevation of approx. 1173 meter. 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 approx 250 meter.

GIS II

ADVANTAGE OF GIS TECHNOLOGY

1. Reduced static and dynamic operating loads

2. Lesser cost in civil work & building due to reduction in the size and volume of switchgear.

3. Light weight of equipment due to compactness.

4. Insulation not exposed to environment.

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5. High reliability, Availability factor for GIS = 99.57%

6. The arrangement is particularly suitable for extension or modification of switchgear without disruption of services.

DISADVANTAGES OF GIS

1. High Cost comparison to Air insulated switchgear.

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

3. Requirement of cleanliness is very stringent.

4. Dust & Moisture inside the compartment can cause flashovers.

COMPONENTS OF GIS

Circuit BreakerIsolators and Earth SwitchesBus barCurrent & Voltage TransformersSurge ArrestorsBushingsMetallic BellowsLocal Control Cubicles (Panels)Monitoring DevicesDILO Machine

CIRCUIT BREAKERS

The three phase circuit breaker in each bay module is of the single pressure (puffer) type. It is designed for installation in SF6 gas insulated metal clad switchgear and uses SF6 gas insulation and arc quenching.

The circuit breaker is hydraulically operated and designed for single and three pole operation. The horizontal installation of poles allows maximum accessibility for erection and maintenance purpose.

The SF6 gas insulated circuit breaker has the following performance characteristics and ratings.

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Type of breaker : Three phase metal enclosed, SF6 gas insulated hydraulically operated

Line circuit breakers : 2000A

Bus coupler : 4000A

No. of poles : 3

Rated short circuit current : 50kA (1 sec.)

(rms value of ac component)

Rated short circuit making current : 125kA

Auto reclosing (line breakers only) : Single phase and three phase

Operating mechanism : Hydraulic

No. of trip coils : Two per pole

ISOLATORS / DISCONNECTORS

Isolator switches are of 3-phase, single pole group operated type, installed in the switchgear to provide electric isolation of the circuit breakers from the double bus and transmission lines. The disconnector is used to insulate the various parts of the electrical circuits. It can make or break loop currents and capacitive load current during energizing or de-energizing the substation. The isolators are electric motor operated and equipped with manual operating mechanism for use in case of emergency.

The isolators have following rating and performance characteristics.

Impulse withstand voltage across open gap : 1665 KVp

Switching impulse withstand voltage : 1245 KVp

Rated normal current : 4000 amp

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Bus bar: It is an element in the main current circuit and is made of aluminium tubing. It can be called a bar fit together in silver-plated multi-finger contacts.

Current Transformers: the current transformers are put to meet the metering and protection purposes. They comprise of an effective magnetic shield to protect against high frequency transients.

Voltage Transformers: the voltage transformers are located inside the independent gas compartment. They are of the inductive type. They cater to the need of protection, metering and synchronization of machines with the grid. They feature an effective magnetic shield to protect against high frequency transients

Surge Arrester: SF6 gas insulated, metal enclosed surge arresters of the gapless metal oxide heavy duty station type are located on HV side of generator transformer. On the other hand, open type gas less metal oxide arrestors are provided at the line end. The following are their ratings and features.

Rated voltage of arrestor : 336Kv (rms)

Maximum continuous voltage capability : 265kV (rms)

Maximum discharge current : 10kA

Energy level : 10kJ/kV

LOCAL CONTROL CUBICLES (LCC): The LCC panel consists of the local control of the isolator and earth switch. This panel is capable of controlling the bay, SF6 density inside the compartment, interface between the GIS and the control room and electrical interlocking between circuit breakers, earth switches, isolators etc.

BATTERY BANK: The pot head yard receives its dc requirement from a 220 V, 1500Ah battery bank and two 48 V, 645Ah battery bank. To the 220V, 1500Ah and 48V, 645 Ah () Battery banks, three identical automatic float cum boost charging equipment, denoted by Charger B1 & Charger B2 and Charger A1 & Charger A2 and Charger B1 & Charger B2 respectively. These are connected with section-1 of dc Distribution board at 995.0 m. There are two dc distribution boards (DCDB) at EL 995 m, one for 220 V and other for 48 V supply.

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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).

GENERAL RATINGS of GIS

Rated voltage - 420kV

Rated normal current- 4000A

Rated frequency – 50Hz

Rated lightning impulse withstand voltage – 1425kV

Rated switching impulse withstand voltage – 1050kV

Rated short time withstand current – 50kA

Rated duration of short circuit – 1sec

Rated power frequency withstand voltage – 520kV

Rated peak withstand current – 125kA

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SF6 density: Normal filling – 48.1kg/m3

Minimum – 42.7kg/m3

SF6 gauge pressure – (1013mbar) at 20°C: Normal filling – 6.3 bar

Minimum – 5.55bar

Ambient temperature: Maximum indoor – 30°C

Minimum outdoor -20°C

Disconnector

Type - SF6

Earthing Switch: Type - MR16-ML16

Operating disconnector and earthing: Switch device

Type - BET-CLT

Circuit breaker ratings: Type - FB16

Rated S.C. breaking current symmetrical – 50kA

Rated S.C. making current – 125 kA

Operating sequence: transformer 0 to 3min-CO-3min-CO

Operating sequence: Bus coupler 0 to 0.3s-CO-3min-CO

Mass of circuit breaker with SF6: 850kg

Circuit breaker operating mechanism: Types CIF 70-40-240

Trip coil dc 220 V

Other equipment: LBB protection and trip circuits – SUPVN

OTHER EQUIPMENTS AT GIS-2:

Synchronization trolley

Local breaker backup

Disturbance recorder

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Wave trapper

Capacitance voltage transformers

Lightning arresters

Triple snow-bird conductors

The sound that one notices (humming) is due to a continuous corona discharge.

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

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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.

HT/LT ROOM:

It is used for the supply of auxiliaries like oil pumps, lifts, cranes, air conditioning plant, battery

charger, lighting and heating floor, UAB, cabling, ventilation etc. There are 2 incoming feeders-

one from Daj and the other from Jhakri (each of 22 kV). Also there is a DG set connected in a

similar fashion as the two feeders, in case the 22kV lines fail to supply. This voltage is then

stepped down to 420V using SST (Sub-Station Transformer). So there is high tension on one side

of the transformer and low tension on the other side of it. The rating of the transformer is as

follows:

KVA : 2500

Vector group : Dyn11

Frequency : 50 Hz

Cooling : ANAN

Weight : 8600 kg

Insulation : F

Winding material : copper

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There is a bus coupler between the two incoming feeders. Vacuum circuit breakers are used on

the HT side. The rating of VCB is as follows:

Rated volts : 33kV

Rated amps : 630 A

Phase : 3

Frequency : 50 Hz

The supply to the auxiliaries is divided into SSB 1, SSB 2 and SSB 3. The supply to these can be

given from one feeder using bus coupler or from separate feeders. SSB 2 is the most crucial of

all. The stepped down 415V from this service substation is connected to all of the generating

units. This provides excitation to the units when supply is to be drawn from HPSEB.

On LT side, there are 2 bus couplers and air circuit breakers instead of VCBs are used. The

rating is as follows:

Rated voltage : 415V (ac)

Making capacity : 105kA peak

Breaking capacity: 50kA rms

Thermal current : 4000A (for incoming)

1000A (for supply)

Rated frequency : 50Hz

Insulation voltage : 1000V

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Also there is a new HT/LT above GIS-1 which mainly governs the supply of lighting and

dewatering pumps.

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.

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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 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.

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ANNEXUREOPERATION OF MACHINE:

Sequence 1: START

Sequence 2: STOP

Sequence 3: ELD (Electrical Disconnection)

Sequence 4: RSD-1 (Rapid Shutdown)

Sequence 5: RSD-2 (Rapid Showdown)

Sequence 6: ESD (Emergency Shutdown)

Start Sequence (Sequence 1)

Step 1: Start the auxiliaries (cooling water system, oil circulation system, transformer oil system)

Step 2: Open all the braking and jacking systems

Step 3: a) Bypass valve open

b) Service seal open

c) MIV open when pressure becomes equal on the penstock side and the spiral casing

Step 4: rpm > 90 %

Generator voltage > 90%

Step 5: Synchrotact ON

Generator Breaker ON

Step 6: change over process takes place

Step 7: Bypass valve closed

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Stop Sequence (Sequence 2)

Step 1: DTL unload and stop

Step 2: 420kV CB trip, excitation OFF

Step 3: HP oil pump ON

Shaft seal flushing water ON

MIV close

MIV service seal close

Step 4: MIV close

MIV service seal close

Step 5: Speed switch < 20% ON Generator brakes ON

HP oil pump ON Brake dust collector ON

Shaft seal flushing water ON

Step 6: Standstill READY Shaft st. seal ON

HP oil pump OFF

Oil vapour extractor OFF

Governor hydraulic auxiliary OFF

Generator space heater ON

Transformer oil pumps OFF

Step 7: standstill + 1 minute shaft seal flushing water OFF

Cooling water system OFF

Brake dust collector OFF

Step 8: Shaft seal flushing water OFF

Cooling water system OFF

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STARTING CONDITIONS OF UNIT

*intake gates + butterfly valves open + no alarm

*syn. Selector switch off

*syn. Test switch off

*GE MCB ok

*DTL watchdog ok

*DTL ok

*speed signal ok

*guide vane position signal(DTL) ok

*position control(DTL) ok

*isolation network not present

*main C. valve position signal (DTL) ok

*BU-DTL watchdog ok

*BU-DTL ok

*guide vane position signal(BU-DTL ) ok

*position control (BU-DTL) ok

*main C. valve position signal (BU-DTL) ok

*EL. GOV. ready for start

*excitation and AVR ready for start

*rapid shut down 1 ok

*rapid shut down 2 ok

*emergency shut down ok

*auxiliaries on remote

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*unit at stand still

*W.G friction joint ok

*shaft revision seal off

* no RSD1/RSD2/ESD over speed

*MIV BYP.V.1 +2 pos. ok

* MIV AIR.V. valve. pos. ok

*MIV service seal pos. ok

*MIV maint. Seal pos ok

*MIVC MCB ok

*MIV position failure

*MIV pressure equalized

*MIV mech lock released

*GHC MCB ok

*GMC 415v ac supply ok

* GMC 48v dc supply ok

*piston accum. Level ok

*accum. Pressure not high

*accum. Pressure not low

*nitrogen pressure ok

*gen. rotor not lifted

*brake CUB.S . SW on AIR

*T/F – R ac power supply ok

* T/F –Y ac power supply ok

* T/F – B ac power supply ok

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*420Kv gen. CB open

*420 Kv bus A or bus B isol. Close

*420Kv gen M.E . SW. open

*420Kv gen. P.E . SW open

*420Kv common alarm ok

*draft tube gate open ok

*415V feeder to UAB-1 close

* no antivalence

*no reset PB glowing

UNIT ANTIVALENCE

*no main inlet valve antivalence

*no MIV bypass valve 1+2 antivalence

*no guide vane antivalence

*no 420Kv generator CB antivalence

* no 420Kv generator bus A is antivalence

* no 420Kv generator bus B is antivalence

* no 420Kv generator M.E SW. antivalence

*no 420Kv generator P.E SW. antivalence

*no excitation antivalence

*no 52 UT-1 antivalence

*no 52 UA-2 antivalence

UNIT AUXILLIARY REMOTE

*excitation control remote

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*shaft seal system remote

*C.W prime cir. Pump remote

*C.W secondary circular pump remote

*MIVC control remote

* gov. hydraulic control remote

*gen. space heater remote

*oil vapour extraction remote

*HP oil pump remote

*generator breaker remote

*break dust collector remote

*415V switch/over system auto

*T/F - R cooling oil pump remote

* T/F - Y cooling oil pump remote

* T/F - B cooling oil pump remote

*420Kv generator CB remote

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:

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EL rapid shut down 2A. El rapid shut down 2B. Genr. CO2 system operated. Transformer R on fire. 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.

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