ACKNOWLEDGEMENT

The successful completion of any task would be incomplete without

mentioning the people who have made it possible. So it`s with the gratitude

that I acknowledge the help, which crowned my efforts with success.

I would like to express my sincere thanks to the management of NHPC

who gave me the opportunity to work and study in such an esteemed

organization.

It is a matter of pride for me to acknowledge my profound gratitude to

my respected principal MRS.PARVEEN KAUR CHAWLA, who always facilitates

me in gaining practical knowledge.

MS.PRIYA AHUJA & MRS.MEENAKSHI BAJAJ for her valuable

Cooperation Guidance.

Last but not the least, I would like to thank all who supported me in this

study by way of sparing their precious time, providing relevant information and

sharing experience, I needed, without which the project would have been

incomplete.

NITIN KUMAR

MUKESH KUMAR NONIA

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TABLE OF CONTENT

Ch. No. Content

1. INTRODUCTION TO HYDRO POWER

2. TEESTA LOW DAM PROJECT - III

3. COMPONENTS OF A POWER HOUSE

4. FLOORS OF THE TLDP-III POWER HOUSE

5. PROTECTION SCHEME

6. CONCLUTION

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CHAPTER 1

INTRODUCTION TO HYDRO POWER

1.1) HISTORY OF HYDRO POWER

Humans have been harnessing water to perform work for thousands of years. The Greeks used water wheels for grinding wheat into flour more than 2000 years ago. Besides grinding flour, the power of the water was used to saw wood and power textile mills. For more than a century, the technology for using falling water to create hydroelectricity has existed. The evolution of the modern hydropower turbine began in the mid-1700s when a French hydraulic and military engineer, Bernard Forest de Bélidor wrote Architecture Hydraulique. In this four volume work, he described using a vertical-axis versus a horizontal-axis machine. During the 1700s and 1800s, water turbine development continued. In 1880, a brush arc light dynamo driven by a water turbine was used to provide theatre and storefront lighting in Grand Rapids, Michigan; and in 1881, a brush dynamo connected to a turbine in a flour mill provided street lighting at Niagara Falls, New York. These two projects used direct-current technology. Alternating current is used today. That breakthrough came when the electric generator was coupled to the turbine, which resulted in the world’s, and the United States', first hydroelectric plant located in Appleton, Wiscons in 1882.

1.2) HYDROELECTRIC POWER / HYDROELECTRICITY

Hydro means "water". So, hydropower is "water power" and hydroelectric power is electricity generated using water power. Potential energy (or the "stored" energy in a reservoir) becomes kinetic (or moving energy). This is changed to mechanical energy in a power plant, which is then turned into electrical energy. Hydroelectric power is a renewable resource. In an impoundment facility, water is stored behind a dam in a reservoir. In the dam is a water intake. This is a narrow opening to a tunnel called a penstock. Water pressure (from the weight of the water and gravity) forces the water through the penstock and onto the blades of a turbine. A turbine is similar to the blades of a child's pinwheel. But instead of breath making the pinwheel turn, the moving water pushes the blades and turns the turbine. The turbine spins because of the force of the water. The turbine is connected to an electrical generator inside the powerhouse. The generator produces electricity that travels over long-distance power lines to homes and businesses. The entire process is called hydroelectricity.

1.3) TYPES OF HYDRO POWER PLANTS

There are three types of hydropower facilities: impoundment, diversion, and pumped storage. Some hydropower plants use dams and some do not.

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Many dams were built for other purposes and hydropower was added later. In the United States, there are about 80,000 dams of which only 2,400 produce power. The other dams are for recreation, stock/farm ponds, flood control, water supply, and irrigation. Hydropower plants range in size from small systems for a home or village to large projects producing electricity for utilities.

(a) Impoundment

The most common type of hydroelectric power plant is an impoundment facility. An impoundment facility, typically a large hydropower system, uses a dam to store river water in a reservoir. Water released from the reservoir flows through a turbine, spinning it, which in turn activates a generator to produce electricity. The water may be released either to meet changing electricity needs or to maintain a constant reservoir level.

(b) Diversion

A diversion, sometimes called run-of-river, facility channels a portion of a river through a canal or penstock. It may not require the use of a dam.

(c) Pumped Storage

When the demand for electricity is low, a pumped storage facility stores energy by pumping water from a lower reservoir to an upper reservoir. During periods of high electrical demand, the water is released back to the lower reservoir to generate electricity.

Pumped storage hydro-electricity works on a simple principle. Two reservoirs at different altitudes are required. When the water is released, from the upper reservoir, energy is created by the down flow which is directed through high-pressure shafts, linked to turbines.

In turn, the turbines power the generators to create electricity. Water is pumped back to the upper reservoir by linking a pump shaft to the turbine shaft, using a motor to drive the pump.

1.4) SIZES OF HYDROELECTRIC POWER PLANTS

Facilities range in size from large power plants that supply many consumers with electricity to small and micro plants that individuals operate for their own energy needs or to sell power to utilities.

(a) Large hydropower

Although definitions vary, the U.S. Department of Energy defines large hydropower as facilities that have a capacity of more than 30 megawatts.

(b) Small hydropower

Although definitions vary, DOE defines small hydropower as facilities that have a capacity of 100 kilowatts to 30 megawatts.

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(c) Micro hydropower

A micro hydropower plant has a capacity of up to 100 kilowatts. A small or micro hydro-electric power system can produce enough electricity for a home, farm, ranch, or village.

1.5) LAYOUT OF HYDROELECTRIC POWER PLANTS

Hydroelectric power plants convert the hydraulic potential energy from water into electrical energy. Such plants are suitable were water suitable head are available. The layout covered in this article is just simple one and only cover the important parts of hydroelectric plant. The different parts of a hydroelectric power plant are

(a) Dam

Dams are structures built over rivers to stop the water flow and form a reservoir. The reservoir stores the water flowing down the river. This water is diverted to turbines in power stations. The dams collect water during the rainy season and stores it, thus allowing for a steady flow through the turbines throughout the year. Dams are also used for controlling floods and irrigation. The dams should be water-tight and should be able to withstand the pressure exerted by the water on it. There are different types of dams such as arch dams, gravity dams and buttress dams. The height of water in the dam is called head race.

(b) Spillway

A spillway as the name suggests could be called as a way for spilling of water from dams. It is used to provide for the release of flood water from a dam. It is used to prevent over toping of the dams which could result in damage or failure of dams. Spillways could be controlled type or uncontrolled type. The uncontrolled types start releasing water upon water rising above a particular level. But in case of the controlled type, regulation of flow is possible

(c) Penstock and Tunnel

Penstocks are pipes which carry water from the reservoir to the turbines inside power station. They are usually made of steel and are equipped with gate systems. Water under high pressure flows through the penstock. A tunnel serves the same purpose as a penstock. It is used when an obstruction is present between the dam and power station such as a mountain.

(d) Surge Tank

Surge tanks are tanks connected to the water conductor system. It serves the purpose of reducing water hammering in pipes which can cause damage to pipes. The sudden surges of water in penstock is taken by the surge tank, and when the water requirements increase, it supplies the collected water there by regulating water flow and pressure inside the penstock.

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1.6) SELECTION OF SITE FOR A HYDRO-ELECTRIC POWER PLANT

Some points that should be given importance while selecting a site for hydroelectric power station given below:

Availability of water

Since the primary requirement for a hydroelectric power station, is the availability of huge amount of water such plants should be built at a place (eg. river, canal) where adequate water is available at good head.

Storage of water

There is a wide variation in water supply from a river or canal during the year. This makes its necessary to store water by constructing a dam in order to ensure the generation of power supply throughout the year .The storage helps in equalizing the flow of water so that excess quantity of water at a certain period of the year can be made available during times of low flow in the river .This leads to the conclusion that site selected for hydroelectric plant should provide adequate facilities for erecting a dam and storage of water.

Cost and type of land

The land for the construction of plant should be available at reasonable price. Further the bearing capacity of the soil should be adequate to withstand the installation of heavy equipment.

Transportation facilities

The site selected for the hydro –electric power plant should be accessible by road and rail so that necessary equipment and machinery could be easily transported. It is clear from the above mentioned factors that ideal choice of site for such a plant is near a river in hilly areas where dam can be conveniently built and large reservoirs can be obtained.

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1.7) ADVANTAGES OF HYDRO POWER PLANT

Advantages

1. Renewable source of energy thereby saves scares fuel reserves. 2. Economical source of power. 3. Non-polluting and hence environment friendly. 4. Reliable energy source with approximately 90% availability. 5. Low generation cost compared with other energy sources. 6. Indigenous, inexhaustible, perpetual and renewable energy source. 7. Low operation and maintenance cost. 8. Possible to build power plant of high capacity. 9. Plant equipment is simple. 10. Socio-economic benefits being located usually remote areas. 11. Higher efficiency, 95% to 98%. 12. Fuel is not burned so there is minimal pollution. 13. Water to run the power plant is provided free by nature.

Key facts about hydro power plant

1. World-wide, about 20% of all electricity is generated by hydropower. 2. Hydropower is clean. It prevents the burning of billion gallons of oil or 120 million tons of coal each year. 3. Hydropower does not produce greenhouse gasses or other air pollution. 4. Hydropower leaves behind no waste. 5. Hydropower is the most efficient way to generate electricity. Modern hydro turbines can convert as much as 90% of the available energy into electricity. The best fossil fuel plants are only about 50% efficient. 6. Water is a naturally recurring domestic product and is not subject to the whims of foreign suppliers.

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CHAPTER 2

TEESTA LOW DAM PROJECT - III

Teesta Low Dam Project-III was entrusted to NHPC on 15th Nov, 2000. It stands at 27.00280,88.44098 on River Teesta in Darjeeling district of West Bengal located at 42 km from Siliguri via NH-31. Called the run of the river project as this dam’s function is only to generate electricity and not store water in the reservoir.

Location On river Teesta in Darjeeling dist. (W.B)

Approach Nearest Rail Head - New Jalpaiguri & Nearest Airport - Bagdogra

Capacity (4x33) MW or 132 MW

Annual Generation 594.07 MU (90% dependable year)

Project Cost Rs.768.92 Crores (Net) (Dec 2002 price level)

Year of Commissioning/Completion Schedule February 2011 (Anticipated) (As per MOU 2010-11)

Teesta Low Dam project-III was constructed by the infrastructure company “HINDUSTAN CONSTRUCTION COMPANY LIMITED” and cost 768 crores under NHPC. It has a 32.5 m high, 140 m long concrete barrage and has the capacity to generate 600 MW of power annually. It comprises of four units of 33 mw each. Unit 1 and 2 got commissioned in January 2013, Unit 3 started commercial operations in April 2013 while Unit 4 in May 2013.

The project received the environment ministry nod in July 2003. Due to geological conditions and contractual problems, NHPC had missed the target of commissioning the power plant within the 11th Plan.

The main components of the scheme are:-

1. BARRAGE

2. POWER HOUSE

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2.1) BARRAGE:

A 460 feet long barrage has been constructed across river Teesta at 27 miles(4.5 km from Rambhi).

The height of the barrage gates are 110 feet having 7 openings.

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A barrage is a type of dam which consists of a line of large gates that can be opened or closed to control the amount of water passing the dam. The gates are set between flanking piers which are responsible for supporting the water load. They are often used to control and stabilize water flow of rivers for irrigation systems.

2.2) POWER HOUSE:

TLDP-III consists of a 125x22x56 m surface power house. Power house complex consist of forebay, intake, penstock, bypass and tail race channel.

Further it consists of four units of 33 MW each to generate 594 MWH annually.

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CHAPTER 3

COMPONENTS OF A POWER HOUSE

The power house is mainly used for two tasks: (a) Generation of electricity

(b) Transmission of electricity

Generation: Water conducting system

Cooling system

Compressed air system

Servo oil system

Clean water supply system

Distribution: Transformers

Feeders

Circuit breakers

Protection scheme

Excitation system

3.1) WATER CONDUCTING SYSTEM:-

In water conducting system the process of water is described. The water conducting system contain the following units:

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Power channel

It is the first stage of water conducting system. It is formed by diverting the river in smaller part i.e. Canal/Power Channel. River Ganga is diverted by a barrage into a power channel of 14.3 km length. It connects river and intake.

Intake

It is the place where the water is stored before entering it into penstock

Pen stock

Here the intake water is supplied to the turbine. The process of energy conversion began form here. The potential energy of water is converted into kinetic energy. The water is passed under the effect of gravity from a high of 32.5 m (100 ft.) via a pipe of dia 6 m (20 ft.). The pressure of pan stock is 3.5 kg/cm3.

Draft tube

A draft tube is one important part of a turbine, which is used to transform water into energy. A turbine draft tube is found within the piping system of a turbine. These draft tubes are used in turbines that function in jets, dams, or anywhere else where turbines help do difficult mechanical work.

Turbines need to have a minimum amount of water to propel them in order to produce enough energy. Early versions of turbines, however, did not include draft tubes in their design. Without them, the pressure could drop because of lack of water, and in turn, the entire turbine could fail to work and power could be lost.

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3.2) TURBINE:-

A turbine is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. A turbine is a turbo machine with at least one moving part called a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades so that they move and impart rotational energy to the rotor. There are four type of hydro turbine named as:

Pelton turbine Francis turbine Kaplan turbine Turgo turbine Cross-flow turbine (Banki-Michell turbine or Ossberger turbine)

Kaplan types of turbine are used in TLDP-III. The Kaplan turbine was invented by Prof. Viktor Kaplan of Austria during 1913-1922 and a great development of early 20th century. The Kaplan turbine has some specific properties as

• The Kaplan is of the propeller type, similar to an airplane propeller.

• The difference between the Propeller and Kaplan turbines is that the Propeller turbine has fixed runner blades while the Kaplan turbine has adjustable runner blades angles.

• It is a pure axial flow turbine uses basic aerofoil theory.

• The Kaplan’s blades are adjustable for pitch and will handle a great variation of flow very efficiently.

• They are 90% or better in efficiency and are used in place of the old Francis types, which is good in many of installations.

• They are very expensive and are used principally in large installations.

• The Kaplan turbine, unlike all other propeller turbines, the runner's blades are movable.

• The application of Kaplan turbines are from a head of 2m to 40m.

• The advantage of the double regulated turbines is that they can be used in a wider field.

• The double regulated Kaplan turbines can work between 15% and 100% of the maximum design discharge.

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3.3) GENERATOR:-

In electricity generation, an electric generator is a device that converts mechanical energy to electrical energy. A generator forces electric charge (usually carried by electrons) to flow through an external electrical circuit. It is analogous to a water pump, which causes water to flow (but does not create water). The source of mechanical energy water falling through a turbine or waterwheel The two main parts of a generator or motor can be described in either mechanical or electrical terms.

Mechanical

Rotor: The rotating part of an electrical machine Stator: The stationary part of an electrical machine

Electrical

Armature: The power-producing component of an electrical machine. In a generator, alternator, or dynamo the armature windings generate the electric current. The armature can be on either the rotor or the stator. Field: The magnetic field component of an electrical machine. The magnetic field of the dynamo or alternator can be provided by either electromagnets or permanent magnets mounted on either the rotor or the stator.

Because power transferred into the field circuit is much less than in the armature circuit, AC generators nearly always have the field winding on the rotor and the stator as the armature winding. Only a small amount of field current must be transferred to the moving rotor, using slip rings. Direct current machines (dynamos) requires a commutator on the rotating shaft to convert the alternating produced by the armature to direct current, so the armature winding is on the rotor of the machine.

Excitation

Generators require direct current to energize its magnetic field. The DC field current is obtained from a separate source called an exciter. Either rotating or static-type exciters are used for AC power generation systems. There are two types of rotating exciters: brush and brushless. The primary difference between brush and brushless exciters is the method used to transfer the DC exciting current to the generator fields.

Static excitation for the generator fields is provided in several forms including field-flash voltage from storage batteries and voltage from a system of solid-state components. DC generators are either separately excited or self-excited.

Excitation systems in current use include direct-connected or gear-connected shaft-driven DC generators, belt-driven or separate prime mover or motor-driven DC generators, and DC supplied through static rectifiers.

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The brush-type exciter can be mounted on the same shaft as the AC generator armature or can be housed separately from, but adjacent to, the generator. When it is housed separately, the exciter is rotated by the AC generator through a drive belt.

The distinguishing feature of the brush-type generator is that stationary brushes are used to transfer the DC exciting current to the rotating generator field. Current transfer is made via rotating slip rings (collector rings) that are in contact with the brushes.

A rotating-rectifier exciter is one example of brushless field excitation. In rotating-rectifier exciters, the brushes and slip rings are replaced by a rotating, solid-state rectifier assembly. The exciter armature, generator rotating assembly, and rectifier assembly are mounted on a common shaft. The rectifier assembly rotates with, but is insulated from, the generator shaft as well as from each winding.

Static exciters contain no moving parts. A portion of the AC from each phase of generator output is fed back to the field windings, as DC excitations, through a system of transformers, rectifiers, and reactors. An external source of DC is necessary for initial excitation of the field windings. On engine driven generators, the initial excitation may be obtained from the storage batteries used to start the engine or from control voltage at the switchgear.

3.4) TRANSFORMER

A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field through these secondary winding. This varying magnetic field induces a varying electromotive force (EMF), or "voltage", in the secondary winding. This effect is called inductive coupling.

If a load is connected to the secondary, current will flow in the secondary winding, and electrical energy will be transferred from the primary circuit through the transformer to the load. In an ideal transformer, the induced voltage in the secondary winding (Vs) is in proportion to the primary voltage (Vp) and is given by the ratio of the number of turns in the secondary (Ns) to the number of turns in the primary (Np) as follows:

By appropriate selection of the ratio of turns, a transformer thus enables an alternating current (AC) voltage to be "stepped up" by making Ns greater than Np, or "stepped down" by making Ns less than Np. The windings are coils wound around a ferromagnetic core, air-core transformers being a notable exception.

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Energy losses

An ideal transformer would have no energy losses, and would be 100% efficient. In practical transformers, energy is dissipated in the windings, core, and surrounding structures. Larger transformers are generally more efficient, and those rated for electricity distribution usually perform better than 98%..Experimental transformers using superconducting windings achieve efficiencies of 99.85%. The increase in efficiency can save considerable energy, and hence money, in a large heavily loaded transformer; the trade-off is in the additional initial and running cost of the superconducting design.

Losses in transformers (excluding associated circuitry) vary with load current, and may be expressed as "no-load" or "full-load" loss. Winding resistance dominates load losses, whereas hysteresis and eddy currents losses contribute to over 99% of the no-load loss. The no-load loss can be significant, so that even an idle transformer constitutes a drain on the electrical supply and a running cost. Designing transformers for lower loss requires a larger core, good-quality silicon steel, or even amorphous steel for the core and thicker wire, increasing initial cost so that there is a trade between initial costs and running cost. Transformer losses are divided into losses in the windings, termed copper loss, and those in the magnetic circuit, termed iron loss. Losses in the transformer arise from:

Winding resistance Hysteresis losses Eddy currents Magnetostriction Mechanical losses Stray losses

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CHAPTER 4

FLOORS OF THE TLDP-III POWER HOUSE:

Like every power house, TLDP-III power house is also divided into two parts:-

1. MACHINE HALL.

2. AUXILLIARY BUILDING.

MACHINE HALL:-

The machine hall consists of the main generation part components. Alternators, turbines and other components associated with generation are present in this part of the power house. In TLDP-III, the machine hall has been divided into 5 floors namely (from top to bottom) :

1. Machine Hall2. Generator floor3. Turbine floor4. Secondary cooling plant5. Primary cooling plant

Various Components:

4.1) PRIMARY COOLING FLOOR:-

This floor is located at an elevation of 176.5 m. The primary cooling floor is associated with the cooling of the generator coolant. This floor employs motors which brings in raw water and pumps it to the secondary cooling floor where the generator coolant is cooled through heat exchangers.

Separate motors are employed for separate units. In TLDP we use 4 motors for this purpose. Also an extra motor is usually kept as standby, which may be required in case of any motor failure.

The pumps shall be centrifugal type directly driven by 3 phase 415V AC squirrel cage induction motors. The pump motor shall be mounted on common base plate. Theimpeller of pumps will be made in stainless steel, pump casing in steel casting andshaft in stainless steel. The discharge capacity of each pumps shall meet the totalrequirement of cooling water of one unit.

4.2) SECONDARY COOLING FLOOR:-

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This floor is located at an elevation of 180.25 m. Due to the presence of large no of conductors and high currents flowing through windings, a large amount of heat is generated. So cooling of generators is very important. The secondary cooling floor generally involves the cooling of the generator. In TLDP-III the generators are cooled by water in a closed pipe. This water is further cooled continuously at the primary cooling floor. From here the cold water is pumped to the various parts of the plant. The secondary cooling floor employs the following components:

Two 3ph 415V AC motorsHeat exchangersDifferential pressure switch

Motors:

The motors used in this floor are simply used for pumping water in and out. One motor brings in the raw water and another motor pumps out the used raw water.

The specifications of the secondary cooling motors are:

1. KW (HP) 45 (60)2. Volt 415 ± 10% V3. IP 554. RPM 14755. Rated Current 80 A6. Connection Diagram 3027. Insulation Class F8. Efficiency 93%9. Duty 8110. Frequency 50 ± 5%11. Ambient Temperature 50ºC

Heat exchangers:

The heat exchanger is used for cooling the generator coolant using the raw water.Pressure and temperature meters are attached to the inlet and outlet pipes of the exchangers which measure the temperature and pressure of the inlet and outlet water.

The specifications of air to water heat exchangers:

1. Heat Load 39 kW2. Volume Of Air Circulated 1.7 m3 /s3. Volume Of Water Circulated 112 LPM4. Weight 375 kg

Differential Pressure Switch:

The differential pressure switch is used check the functioning of the heat exchanger.18

It uses the pressure reading of the meters to determine whether the exchanger is working properly or not.

If the inlet and outlet pressures are different that means the heat exchanger is working properly and if there is no pressure difference ,it indicates some clogging within the heat exchanger. Then the exchanger is cleaned.

The specifications of the differential pressure switch are:

1. Electrical Rating 15 A, 250 VA2. Range 0.4 – 4 kg/cm3

3. Dead Band 0.5 kg/cm2

4. Proof 140 kg/cm2

5. Material Teflon6. Sv. Pr. 33 kg/cm2

4.3) TURBINE FLOOR:-

This floor is located at an elevation of 184.5 m. The turbine floor provides the first step to the generation of electricity. The turbine floor includes the turbine, the runner blades and various other components.

Turbines:

The turbine employed at TLDP – III is a Kaplan Turbine.

The Kaplan turbine is a propeller-type water turbine which has adjustable blades. It was developed in 1913 by the Austrian professor Viktor Kaplan, who combined automatically adjusted propeller blades with automatically adjusted wicket gates to achieve efficiency over a wide range of flow and water level.

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The Kaplan turbine was an evolution of the Francis turbine. Its invention allowed efficient power production in low-head applications that was not possible with Francis turbines. The head ranges from 10–70 meters and the output from 5 to 120 MW. Runner diameters are between 2 and 8 meters. The range of the turbine is from 79 to 429 rpm. Kaplan turbines are now widely used throughout the world in high-flow, low-head power production.Braking and Lifting Plant:

This Plant is associated with the braking of the alternator and also lifting the alternator with help of oil pressure.

The weight of our alternator is 350 tons, so it would be difficult to move such an alternator using water pressure. So, the entire alternator along with the shaft is lifted so that the water through the gates could easily move the turbine which is connected with the alternator.

The specifications of the Braking and Lifting Plant are as follows:

OIL AIRCapacity 1.5 LPM 1500 LPMWork Pressure 240 Bar 7 BarTest Pressure 320 Bar 11 Bar

Other components:

Three transformers namely Excitation Transformer, Unit Auxiliary Transformer and LAVT are also installed in this floor.

Excitation Transformer:

Excitation transformer is nothing but the source or minimum energy given to generator to generate voltage.

We know that the principle of generator is to convert mechanical energy into electrical energy. For this conversion it needs magnetic flux lines which get cut by

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generator coil and produce EMF. To produce this magnetic flux excitation transformer is used.

The secondary is rotating, which is connected to a rectifier bridge comprising of SCRs (thyristors) and freewheeling diodes which regulate the delivered current. In excitation with the brush, the whole arrangement is separate and the dc output is fed through brush to the rotor circuit for DC field.

The rating depends upon the excitation current of the generator.

It is rated as:

11 kV / 225 V415 kVA, 3Ф

Unit Auxiliary Transformers (UAT):

The Unit Auxiliary Transformer is the Power Transformer that provides power to the auxiliary equipment of a power generating station during its normal operation. This transformer is connected directly to the generator out-put by a tap-off of the isolated phase bus duct and thus becomes cheapest source of power to the generating station.

It is generally a three-winding transformer i.e. one primary and two separate secondary windings. Primary winding of UAT is equal to the main generator voltage rating. The secondary windings can have same or different voltages i.e. generally 11KV and or 6.9KV as per plant layout.

It is rated as:

11 kV / 415 V

3Ф, 500 kVA

Lightning Arrester Voltage Transformer (LAVT):

LAVT cubicles are enclosure for housing (i) Lightening Arrester (LA ), (ii) Surge Capacitor (SC), and (iii) Voltage transformers (VT). The cubicles are installed in power generating units:

(i) To protect the generator from High Voltage Surge due to Lightening stroke or electrical fault. LA & SC provide minimum resistance path to the short duration high voltage & high current because of lightening or fault and the complete current flows to ground earth point through the earthed bus bar.

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(ii) For measurement of voltage of a generating unit with the help of VT’s (a) For measurement of power (Metering) (b) Protection circuit and (c) Synchronization of the unit.

VT’s of various accuracies step down the generator voltage of 6.6 KV to 15.75 KV to 110 Volt for the purpose of metering, protection & synchronizing purpose.

The design of LAVT cubicle depends on:-

(a) Voltage level of the generator.(b) Type of bus duct system between generator and step up transformer of the power plant.

Depending upon above mentioned factors LAVT cubicles are designed (a) With or without brushing (b) All the three phases (R,Y,B) sections put together side by side and (c) The three cubicles for R,Y,B phase separated with a air gap of 200 to 400 MM.

Lightning arrestor is a device which is mainly installed across each phase and earth at the entry of the transmission line to the sub – station yard. It can also be seen at HV and LV sides of all power transformer installed at the sub – station.

As the transformer is the costliest equipment installed in the system, for better protection of each transformer is equipped with lightning arrester at its both HV and LV sides.

VT (Voltage Transformer) Cubicle:

These cubicles are similar to LAVT cubicle except provision of LA & SA (Lightening arrestor & Surge capacitor). These cubicles are used when the system requires large no. of voltage transformer for metering, protection and synchronization circuitry of power generating unit.

Neutral Grounding Cubicle (NGC):

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NG cubicle is an enclosure for installation of Neutral grounding transformer (NGT) and Neutral Grounding Resistance (NGR) for grounding/ earthing of Neutral current during unbalanced three-phase load of a generator. This is essentially required for protection of the generator.

The neutral grounding Transformer (NGT) steps down the voltage of neutral bus from 6.6 KV/ 11KV / 15.75 KV level to 110 Volt or 220 Volt level. This stepped down voltage is connected to a neutral grounding resistance and a Ground earth Terminal for bringing the voltage level of neutral bus as close as possible to Zero voltage level.

4.4) ALTERNATOR FLOOR:-

This floor is located at an elevation of 187.25 m. An alternator is an electromechanical device that converts mechanical energy to electrical energy in the form of alternating current.

Most alternators use a rotating magnetic field with a stationary armature but occasionally, a rotating armature is used with a stationary magnetic field; or a linear alternator is used.

In principle, any AC electrical generator can be called an alternator, but usually the term refers to small rotating machines driven by automotive and other internal combustion engines. An alternator that uses a permanent magnet for its magnetic field is called a magneto.

The specifications of the alternator are:

1. Insulation Class F2. Temperature Rise BP3. Rated Speed 136.36 rpm4. Rated Frequency 50 Hz5. Permissible Overspeed 377 rpm6. Max. Ambient Air

Temperature40ºC

7. Max. Water Coolant Temperature

30ºC

8. Total Mass 346,000 kg9. Degree of protection IP5410. Type of Construction IM8205 (W8)11. Connection Star, 2-fold-parallel12. Duty Type S113. Rated Output 36670 kVA14. Rated Voltage 11000 ± 10% V15. Rated Current 1924.7 A16. Rated Power Factor 0.917. Rated Field Voltage 118

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4.5) MACHINE HALL:-

r

This floor is located at an elevation of 190.5 m. The Machine Hall consists of the OPU set, rectifiers, unit heads and simulation display screens.

OPU set:

It stands for Oil Pumping Unit set. The Oil Pumping Unit set is used to pump oil to move the runner blades. The entire set consists of an accumulator and two motors. The oil is pumped through two big pipes which runs from the unit head to the runner blades through the hollow shaft.

The Oil Pressure Systems are intended for feeding oil under pressure to hydro mechanical section of the governing system and also for control of the shut-off valves and the gate valves of irrigations systems and channels.

The Main Components of Oil Pressure System:

Accumulator tank containing required volume of oil under compressed air.

Oil pumping unit maintaining  effective volume and pressure in the accumulator tank.

Controls of the oil pressure system.

The Oil Pressure Systems are rated from 4 MPa and 6.3 MPa pressure.

The specifications of OPU set are:

1. Changeover Switch 315 A2. Volts 415 A3. Current 320 A

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4. Incomer-1 supply from UAB-2

320 A

5. Incomer-2 supply from UAB-1

320 A

6. OPU Pump-1 110 kW7. OPU Pump-2 110 kW8. Oil Leakage pump guide vane 1.1 kW9. Off line filtration plant 75 kW

Accumulator Tank:

An accumulator tank is a water chamber which has a pre-pressurized internal air bladder. They are designed to be installed downstream of your pump and 'dampen' water pressure spikes, reduce pump cycling, help increase the pump's life and save battery power.

AUXILIARY BUILDING:-

The auxiliary building generally consists of the control room and LT room.

4.6) CONTROL ROOM:-

The Control room is associated with the controlling of the various parameters and conditions of the plant. The whole plant is controlled through SCADA. SCADA (supervisory control and data acquisition) is a type of industrial control system (ICS). Industrial control systems are computer controlled systems that monitor and control industrial processes that exist in the physical world. SCADA systems historically distinguish themselves from other ICS systems by being large scale processes that can include multiple sites, and large distances.

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4.7) L.T. ROOM:-

The LT room is associated with the power distribution for the various primary and auxiliary purposes. The various primary purposes like the lightning of the power house, the elevator supply, protection purpose supplies etc. are fed from the LT Room.

The general Structure of the LT Room is given below:

For auxiliary purposes, two incomers are present. At TLDP-III they have only one incomer i.e. from WBSEB. The power from WBSEB is taken until self-unit

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production starts. As soon as the self-unit production gets underway, the entire load is shifted to the UAT from the SST (incomer from WBSEB). In case neither the incomer nor the self-unit generates power, a Diesel-Generator Set (500 KVA) is employed for this purpose.

The LT room also houses the battery bank and inverters for various purposes like SCADA systems, GPS, etc.

SST:

It stands for Station Service Transformers. These are fed through the incomers from external sources (in this case, WBSEB). These transformers are utilized in the absence of self-generation.

4.8) GIS ROOM:-

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A gas insulated substation is an electrical substation in which the major structures are contained in a sealed environment with sulfur hexafluoride gas as the insulating medium. The main applications for gas insulated substations today are:

- high voltage installations (usually 115kV and above although some manufacturers offer equipment with voltage ratings down to 20kV). The higher the voltage, the more favorable gas insulated technology becomes. The footprint of 765kV conventional substation is enormous, and GIS technology allows a significant size reduction.

- urban installations. Usually, but not always, GIS technology is used for installations in areas where the cost of real estate is a significant consideration

- indoor installations (which are more common in urban areas for aesthetic reasons). It is generally not practical to build an air-insulated substation inside a building, but GIS can easily go inside buildings.

- other environmentally sensitive installations. GIS technology is popular in desert and arctic areas because it can be enclosed in a building with some environmental control. Gas insulated substations also contain the electrical components within a Faraday cage and are therefore totally shielded from lightning.

GIS installations tend to be much more expensive that air-insulated installations with the same rating. The additional capital cost is justified based on the reduced cost of real estate, the ability to provide environmental containment, or the fact that the substation is totally shielded from lightning, something that is not practical with air insulated technology.

In most cases, the circuit breakers in gas insulated substations employ SF6 as the interrupting medium as well as the insulating medium, but there are hybrid installations (especially at lower voltages) in which breakers use vacuum interruption. The gas pressure required for SF6 to serve as an interruption medium is much greater than the pressure required for it to be an insulation medium.

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Transmission:

The power generated at generating station is in low voltage level as low voltage power generation has some economical values. Low voltage power generation is more economical than high voltage power generation. At low voltage level, bot weight and wide of insulation is less in the alternator, this directly reduces the cost and size of alternator. But this low voltage level power cannot be transmitted directly to the consumer end as because this low voltage power transmission is not at all economical. Hence although low voltage power generation is economical but low voltage electrical power transmission is not economical. Electrical power is directly proportional to the product of electrical current and voltage of system. So for transmitting certain electrical power from one place to another, if the voltage of the power is increased then associated electric current of this power is reduced. Reduced current means less I2R loss in the system, less cross sectional area of the conductor means less capital involvement and decreased current causes improvement in voltage regulation of the system and improved voltage regulation indicates quality power. Because of these three reasons electrical power mainly transmitted at high voltage level.

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CHAPTER 5

PROTECTION SCHEME:

5.1) PROTECTION FROM FAULTS

Internal faults are those faults which occur within the circuit due so some special causes like short circuit, overheating, etc. to protect the circuit with these fault a typical circuitry of relay and metering devices is used. The various relays used here are:

Generator Protection:

(i) overvoltage type relays , (ii) overall differential relay , (iii) back impedance relay , (iv) negative phase sequence relay , (v) loss of excitation , (vi) Pole slipping relay , (vii) Under voltage relay , (viii) Auxiliary relay , (ix) Earth fault relay and (x) Over current relay.

Line Protection:

(i) Distance Relay, (ii) Overvoltage Relay, (iii) Definite Earth Fault Relay, (iv) Carrier Aided Relay, (v) Power Swing Protection, (vi) Auto Reclosure Relay, and (vii) Overcurrent Relay

5.2) PROTECTION WITH EXTERNAL FAULTS

External faults are those faults which occur in the circuit by virtue of any external means one of the major cause is the lightening stroke. To protect with this fault lighting arresters are used on the line.

5.2.1) Lightning Arrester A lightning arrester is a device used on systems to protect the insulation and conductors of the system from the damaging effects of lightning. The typical lightning arrester has a high voltage terminal and a ground terminal. When a lightning surge (or switching surge, which is very similar) travels along the power line to the arrester, the current from the surge is diverted through the arrestor, in most cases to earth.

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5.2.2) Circuit Breaker

A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow. Unlike a fuse, which operates once and then must be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to large switchgear designed to protect high voltage circuits feeding an entire city.

Operation Of A Circuit Breaker

A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical

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flow. Unlike a fuse, which operates once and then must be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to large switchgear designed to protect high voltage circuits feeding an entire city.

Operation

The circuit breaker must detect a fault condition; in low-voltage circuit breakers this is usually done within the breaker enclosure. Circuit breakers for large currents or high voltages are usually arranged with pilot devices to sense a fault current and to operate the trip opening mechanism. The trip solenoid that releases the latch is usually energized by a separate battery, although some high-voltage circuit breakers are self-contained with current transformers, protection relays, and an internal control power source.

CHAPTER 6

CONCLUTION:-

NHPC Limited has several units, which are engaged in operation of generating electricity or are under construction stage. Various types of stores inventory need to be maintained to ensure smooth running of these power stations and construction of the units under construction. The purchase and stores accounting procedures shall be subject to NHPC’s policy for procurement of stores, delegation of powers and administrative instructions issued in this regard from time to time. The stores inventory includes inventory for construction (like steel, cement, etc.) as well as for operation purposes. NHPC uses all the procedure and guidelines for the stores management discussed in the report.

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