A

TRAINING REPORT

ON

“THERMAL POWER PLANT”

STUDENT’S NAME: PRATIK GUPTA

COURSE: B.E.

BRANCH: ELECTRICAL & ELECTRONICS

YEAR/ SEM: 2ND/4TH

COLLEGE: DR. C.V. RAMAN INSTITUTE OFSCIENCE & TECHNOLOGY, KOTA

INDUSTRIAL NAME: SIPAT SUPER THERMAL POWERCORP. (NTPC SIPAT)

SUBMITTED BY: SUBMITTED TO:

PRATIK GUPTA MR. PRAVIN PATEL

(EEE 4TH SEM)

CERTIFICATE

This is to certify that the project report entitled asNATIONAL THERMAL POWER PLANT has been doneby PRATIK GUPTA during his vocational training periodfrom 20-06-13 to 20-07-13 at “SIPAT SUPERTHERMAL POWER PROJECT” is a record of studies,site experience and keen interest to the subject andanalysis carried out by him under my supervision andguidance. This is a part of partial fulfilment of theirvocational training programme.

Guided by:-

1. MR. SHALABH SAHRMA2. MR. J.P.Patel 3. MR. Dilip Khalatkar 4. MR. P.K. DAS

DECLARATION

The training work has been carried out and the reportprepared by me during 20th June to 20th July 2013 underthe guidance of faculties ntpc ltd/sipat thermal powerplant and organised by employ development centre,human resource development.

This is the original work carried out by me and not hasbeen taken from any other sources nor been submitted toany institute or organisation as a fulfilment of any othercurriculum.

ACKNOWLEDGEMENT

I hereby convey my deep and sincere gratitude in all humbleness to respected

5. MR. SHALABH SAHRMA6. MR. J.P.Patel 7. MR. Dilip Khalatkar 8. MR. P.K. DAS

Who provided me with an opportunity to learn under their graciousguidance, meticulous care and throughout the training. Their personalsupervision and guidance has enabled me to complete this Project. Ialso thankfully acknowledgement the assistance received from MRPRAVIN PATEL and others for their co-operation during thepreparation of this project report. The project report would not havebeen shaped in this form without their encouragement and guidance.

Contents1. Introduction of NTPC

2. Introduction about Project

3. Production of Electricity

4. Principal of Steam Power Plant

5. Coal Handling Plant

6. Coal Handling Plant Power Distribution

7. Demineral Plant(DM Plant)

8. Coal ,Water and Steam Cycle

9. H.T. Switch gear

10. L.T. Switch gear

11. Generators and Transformers

12. D.C. System

13. Switch Yard

14. Conclusion

INTRODUCTION OF NTPC

India’s largest power company, NTPC was set up in 1975 to accelerate powerdevelopment in India. NTPC is emerging as a diversified power major withpresence in the entire value chain of the power generation business. Apart frompower generation, which is the mainstay of the company, NTPC has alreadyventured into consultancy, power trading, ash utilization and coal mining. NTPCranked 337th in the ‘2012, Forbes Global 2000’ ranking of the World’s biggest

companies. NTPC became a Maharatna company in May, 2010, one of the onlyfour companies to be awarded this status.

The total installed capacity of the company is 41,184 MW (including JVs) with 16coal based and 7 gas based stations, located across the country. In additionunder JVs, 7 stations are coal based & another station uses naptha/LNG as fueland 2 renewable energy projects. The company has set a target to have aninstalled power generating capacity of 1,28,000 MW by the year 2032. Thecapacity will have a diversified fuel mix comprising 56% coal, 16% Gas, 11%Nuclear and 17% Renewable Energy Sources(RES) including hydro. By 2032,non fossil fuel based generation capacity shall make up nearly 28% of NTPC’sportfolio.

NTPC has been operating its plants at high efficiency levels. Although thecompany has 17.75% of the total national capacity, it contributes 27.40% oftotal power generation due to its focus on high efficiency.

In October 2004, NTPC launched its Initial Public Offering (IPO) consisting of5.25% as fresh issue and 5.25% as offer for sale by Government of India. NTPCthus became a listed company in November 2004 with the Government holding89.5% of the equity share capital. In February 2010, the Shareholding ofGovernment of India was reduced from 89.5% to 84.5% through Further PublicOffer. The rest is held by Institutional Investors and the Public.

At NTPC, People before Plant Load Factor is the mantra that guides all HR relatedpolicies. NTPC has been awarded No.1, Best Workplace in India among largeorganizations and the best PSU for the year 2010, by the Great Places to WorkInstitute, India Chapter in collaboration with The Economic Times.

The concept of Corporate Social Responsibility is deeply ingrained in NTPC'sculture. Through its expansive CSR initiatives, NTPC strives to develop mutualtrust with the communities that surround its power stations.

INTRODUCTION ABOUT PROJECT

Sipat Super Thermal Power Station is located at Sipat in Bilaspur district in state of Chhattisgarh.

The power plant is one of the coal based power plants of NTPC. The coal for the power plant is

sourced from Dipika Mines of South Eastern Coalfields Limited.

The project has an installed capacity of 2980 MW consisting of two stages, stage one which got

commissioned late was of 3 units of 660 MW each involving super-critical boilers technology and

stage two consisted of 2 units of 500 MW each.

Stage Unit Number Installed Capacity (MW) Date of Commissioning Status

1st 1 660 2011 June Running

1st 2 660 2011 December Running

1st 3 660 2012 June [1] Running

2nd 4 500 2007 May Running

2nd 5 500 2008 August Running

Total Five 2980

Sipat

Sipat' is a small developing town, approximately 22 kilometers away from Bilaspur, Chhattisgarh, thesecond largest city in Chhattisgarh. It has been in news due to setup of new power plant by NTPCLimited in that area. The project was started on 2001 by Indian former Prime Minister Mr. Atal BihariVajpayee.NTPC Sipat has total installed capacity of 2980 MW.NTPC Sipat has two stages: Stage-Icomprises 3 units of 660MW each and Stage-II comprises 2 units of 500MW each. The thermal powergeneration in NTPC sipat Stage-II is based on "Super Critical Boiler Technology" which is theadvanced technology in thermal power generation. NTPC Limited has helped this town in developingby providing business prospective in that area and by providing education, healthcare facilities.

PRODUCTION OF ELECTRICITY

The means and steps involved in the production of electricity in a coal-fired power station aredescribed below.

The coal, brought to the station by train or other means, travels from the coal handling plant byconveyer belt to the coal bunkers, from where it is fed to the pulverizing mills which grinds it as fineas face powder. The finely powdered coal mixed with pre-heated air is then blown into the boiler byfan called Primary Air Fan where it burns, more like a gas than as a solid in convectional domestic orindustrial grate, with additional amount of air called secondary air supplied by Forced Draft Fan. Asthe coal has been grounded so finely the resultant ash is also a fine powder. Some of this ash bindstogether to form lumps which fall into the ash pits at the bottom of the furnace. The water quenchedash from the bottom of the furnace is conveyed to pits for subsequent disposal or sale. Most of ash,still in fine particles form is carried out of the boiler to the precipitators as dust, where it is trappedby electrodes charged with high voltage electricity. The dust is then conveyed by water to disposalareas or to bunkers for sale while the cleaned flue gases pass on through ID Fan to be discharged upthe chimney.

Meanwhile the heat released from the coal has been absorbed by the many kilometres of tubingwhich line the boiler walls. Inside the tubes is the boiler feed water which is transformed by the heatinto the steam at high pressure and temperature. The steam super-heated in further tubes (SuperHeater) passes to the turbine where it is discharged through the nozzles on the turbine blades. Justthe energy of the wind turns the sail of the wind-mill, so the energy of the steam, striking the blades,makes the turbine rotate.

Coupled to the end of the turbine is the rotor of the generator – a large cylindrical magnet, so thatwhen the turbine rotates the rotor turns with it. The rotor is housed inside the stator having heavycoils of copper bars in which electricity is produced through the movement of the magnetic fieldcreated by the rotor. The electricity passes from the stator winding to the step-up transformer whichincreases its voltage so that it can be transmitted efficiently over the power lines of the grid.

The steam which has given up its heat energy is changed back into water in the condenser so that itis ready for re-use. The condenser contains many kilometres of tubing through which the colder isconstantly pumped. The steam passing around the tubes looses the heat and is rapidly changed backto water. But the two lots of water (i.e. boiler feed water & cooling water) must NEVER MIX. Thecooling water is drawn from the river, but the boiler feed water must be absolutely pure, far purerthan the water we drink, if it is not to damage the boiler tubes. Chemistry at the power station islargely the chemistry of water.

To condense the large quantities of steam, huge and continuous volume of cooling water isessential. In most of the power stations the same water is to be used over and over again. So theheat which the water extracts from the steam in the condenser is removed by pumping the waterout to the cooling towers. The cooling towers are simply concrete shells acting as huge chimneyscreating a draught (natural/mechanically assisted by fans) of air. The water is sprayed out at the topof towers and as it falls into the pond beneath it is cooled by the upward draught of air. The coldwater in the pond is then circulated by pumps to the condensers. Inevitably, however, some of thewater is drawn upwards as vapours by the draught and it is this which forms the familiar white cloudswhich emerge from the towers seen sometimes.

Why bother to change steam from the turbine back into water if it has to be heated up againimmediately? The answer lies in the law of physics which states that the boiling point of water isrelated to pressure. The lower the pressure, the lower the temperature at which water boils. Theturbine designer want as low boiling point of water as possible because he can only utilize the energyof the steam – when the steam changes back into water he can get NO more work out of it. So acondenser is built, which by rapidly changing the steam back into water creates a vacuum. Thisvacuum results in a much lower boiling point which, in turns, means he can continue getting workout of the steam well below 100 degree Celsius at which it would normally change into water.

Principle of the Steam Power Plant

The working principle of a steam plant is based upon the Rankine cycle.

Generally steam is taken as the working medium due to its ability to be stable

and that it’s readily stable. The flow of steam in the plant can be very easily be

understood by the flow diagram of the plant. A graph plotted between the

temperature and the entropy would indicate the technical details of the

working by the rankine cycle. The entropy of a system can be understood as an

index of degradation of energy.

PLANT FLOW DIAGRAM

COAL HANDLING PLANT

Introduction: -

NTPC SIPAT gets its coal supply mainly from dipka mines. The coal being filled in the wagons of therail reaches plant. The purpose of this plant is to convey the coal to the bunker in the size not largerthan 20mm.It handles and transports the coal to the bunker from the wagons by passing throughvarious conveyors, transfer points, crusher houses, etc.

Type of unloading the coal: -

1. Manual Unloading: -Previously, manpower was used for unloading the wagons. But it was verytime consuming and more workers were required for the job to be done.

2. Box in (using wagon tippler for unloading): -For this method, Indian Railway grants 10 hours forunloading the 58 wagons. In this method, Wagons are separated and tippled by using wagontippler. The Beetle Feeder is used to move the wagon on wagon tippler. The coal from thewagons gets accumulated in The Track Hopper. At this time; the size of the coal is approximately300mm.

3. BOBR: - Indian Railway grants only 2.5 hours for Unloading 58 BOBR wagons. This is an advancedtechnology in which we use the compressor system.

In Bottom Open Bottom Release (BOBR) technology the wagons are opened from side. Pressureis applied by the compressor to open the bottom gates of the wagon so that the coal getsreleased over the track hopper and wagon get unloaded quickly.

Various equipment used in CHP: -

1. WAGON TIPPLER : - The wagon tippler is a most important device in thermal power project. TheWagon tippler turns back the wagon at 135-degree angle and the structure of the wagon tippleris to be very heavy. Upper side of the wagon is fixed with the many angles for supporting thewagon. When the wagon is fixed on the Platform then whole platform is turned back and thecoal fall down in the wagon tippler hopper. The unloading time of the Rack is 6hours

2. PADDLE FEEDER: - They have been installed on conveyors below the manual unloading trackhopper. There are 6 nos. of paddle feeders, 3 on each conveyer. 3 Paddle Feeders of eachconveyer move to and fro within a limiting range. The rotating part of the paddle feeder is calledas plough wheel. Plough wheel has 6 blades. By the rotation of the plough wheel, the coal of thetrack hopper gets accumulated between the blades and is discharged on the conveyor below it.

3. VIBRATING FEEDER: - They have been installed below the track hoppers of wagon tippler.The coal is accumulated over the vibrating feeder so by giving vibrations to the vibrating feederwe discharge the coal from track hopper to the conveyors. Their main purpose is to provideuniform feeding on the conveyors. The vibrating feeders consist of a tray to which vibrator bodyis fixed on the rear end.

4. TRANSFER POINTS: -Transfer Point is provided with flap gate and Conveyer. In transfer Point thecoal is transferred from one conveyer to other conveyer.

5. PRIMARY CRUSHER (ROTARY BREAKER): - In Primary Crusher House, the coal breaks in RotaryBreaker. Here the coal comes from the Transfer point; breaks here and the stone fall down to aseparate place. Coal is converted from 300mm to 150mm size.

Part of the Primary Crusher House – a- Rotary Breaker b- Belt Feeder

6. SECONDARY CRUSHER (RING GRANULATOR): - In Secondary crusher House first themagnetic part separate from the coal and then feed to the Secondary Crusher. This Crusherbreaks the coal in 20mm size and coal is sent to the Flap Gate and then feeded to the conveyer.The Secondary crusher is hammer type. H.T. motor are used for breaking of the coal.Specifications are 700KW 6.6KVMotor.

7. CROSS BELT MAGNETIC SEPRATORS: - They will remove the ferrous particles, which passesalong with the coal. It consists of electromagnet around which a belt is moving. It is suspendedfrom top, perpendicular to the conveyor belt at certain height. Whenever any iron particle

passes below the CBMS, it is attracted by the magnet and stick to the cross belt below it. TheCBMS capacity is of 50kg.

8. METAL DETECTOR: - The purpose of installation is to detect any metallic piece passing throughthe conveyor. Whenever the pieces pass below the search coil of the metal detector, it gives thetrip command to the conveyor. Simultaneously, sand bag marker will fall on the conveyor belt sothat the metal can be searched easily and removed.

9. STACKER/RECLAIMER: -It is a very important device. The whole Structure of it is called SuperStructure. It stacks the excessive coal and reclaims the coal on its requirement. It is a two-waydevice.

10. TRANSFER TOWER: -Here the coal is send to the Tipper. Transfer Tower is provided with a coalsampler.

11. TIPPER: - The Tipper is a three-way device to feed the coal in Bunker. It is moveable device. Itis move on its track.

12. BUNKER: - Here the coal is collected from the tipper and stored. The capacity of the bunker forStage-I is 4800MT & Stage-II is 8700MT

DEMINERAL (DM) PLANT

INTRODUCTION: --

Water is required in plant for many purposes like for formation of steam, for removal of ash, forsafety during fire, etc. But the water required for the formation of steam should be perfectly devoidof minerals because if minerals are present in the steam and the steam strike the blades of theturbine, then due to being high in pressure it produces scars or holes on the turbine blades.

PURIFICATION OF WATER: -

Water is purified in DM plant through a chain of processes as under: --

1. Carbon filter – Water taken from the river is first sent to the carbon filter for the removal ofcarbon contents in the water.

2. Strong acid cation exchanger – After passing through the carbon filter, water is sent to thestrong acid cation exchanger, which is filled with the concentrated HCL. The acid producesanions, which get combined with the cations present in the water.

3. Strong base anion exchanger – After that the water is sent to the strong base anionexchanger, which is filled with the concentrated NaOH.The base produces cations, which getcombined with the anions present in the water.

4. Mixed bed exchanger – And then water is sent to the chamber of mixed bed exchangerwhere the remaining ions are removed. This is the last stage of purification.

COAL, WATER & STEAM CYCLES

COAL CYCLE

C.H.P Plant Bunker R.C Feeder Pulverization mill Boiler section

1. R.C Feeder: It is an induction motor driven device, which determine the Quantity of coal

enter in the pulverize mill.

2. Pulverization mill: Pulverization means exposing a large surface area to the action of

oxygen .Two Types of mill are used in the plant.

3. Ball mail: A ball mill operates normally under suction. A large drum partly filled with steel

balls, is used in this mill .The drum is rotated slowly while coal is fed in to it .The ball pulverize

the coal by crushing.

4. Contact mail: This mill uses impact principle. All the grinding elements and the primary air

fan are mounted on a single shaft. The flow of air carries coal to the primary stage where it is

reduced to a fine granular state by impact with a series of hammers.

WATER CYCLE

D.M Plant Hot well C.E.P Pump Low Pressure Heater 1, 2, 3 DeraterBoiler Feed Pump High Pressure Heater 5, 6 Feed Regulating station EconomizerBoiler Drum

1. DERATER: Feed strong tank of water. To produce sufficient pressure before feeding to B.F.D. .Filterthe harmful chemicals.

2. FEED REGULATING STATIONS: Control the quantity of water in to boiler drum.

3. ECONOMISER: Flux gases coming out of the boilers carry lot of heat. An economizer extracts a part

of this heat from the flue gases and uses it for heating the feed water.

4.DRAFTS SYSTEM: In forced draft system the fan is installed near the base of the boiler furnace. This

fan forces air through the furnace, economizer, air preheater and chimney . In an induced draft

system, the fan is installed near the base of Chimney.

STEAM CYCLE

Boiler Drum Ring Header Boiler Drum (Steam chamber) Super Heater H.PTurbine Repeater I.P Turbine L.P Turbine condenser

1. BOILER: Boiler drum consists two chambers water chamber, steam chamber. Before Enteringin super heater the steam is going in to boiler drum, where the boiler drum filtered themoisture and stored in to water chamber.

2. SUPER HEATER: The function of super heater is to remove the last traces of moisture fromthe saturated steam leaving the tube boiler. The temperature is approx.530 oC.

3. TURBINE: Steam turbine converts the heat energy in to mechanical energy and drives thealternator. The velocity attained during expansions depends on initial and final heat contentof the steam. Turbine having number of stages in which the pressure drops takes place.

H.T.SWITCH GEAR

OPERATIONG VOLTAGE - 6.6KV

For low voltage circuits fuses may be used to isolate the faulty circuit. For voltage higher than 3.3 kVisolation is achieved by circuit breaker.

Requirement of circuit breaker:

1. After occurrence of fault the switchgears must isolate the faulty circuit as quickly as possiblei.e. keeping the delay to minimum.

2. It should not operate when an over current flows under healthy condition.

Basic principal of operation of circuit breaker:

Circuit breaker consists of a fix contact and sliding contact into which moves a moving contact. Theend of moving contact it attached to a handle that can be manually operated or may operateautomatically with the help of mechanism that has a trip coil energized by secondary of CT. Undernormal condition the secondary of CT is not energized sufficiently to trip the coil but under falsecondition the coil is energized fully to operate the trip coil and the circuit breaker is operated.

1. MOCB (Minimum oil circuit breaker)

2. SF6 (Sulphur hexafluoride circuit breaker)

Here oil and SF6 are used to quench the arc.

L.T SWITCH GEAR

OPERATING VOLTAGE- 415VOLT

TYPES OF CIRCUIT BREAKER: - Air break circuit breaker

Air brake circuit breaker:

The arc interruption process of air- based circuit breaker is based on the natural deionization of gasesby cooling action. The arc is resilient and can be stretched, and has a resistance, which can beincreased both by length and confinement. Hence the arc resistance is increased by stretching thearc and as the resistance increases to higher value, the short circuit current drops to zero and arc isextinguished.

Reducing the phase difference between the system voltage and the short circuit current assure thatwhen the are current is interrupt at its zero value, the recovery voltage has very low value at its notallowed to reach 2-3 times the value of the system peak voltage, a phenomenon that occurs in mostcases, when arc current is interrupted at low power factor.

GENERATORS AND TRANSFORMERS

INTRODUCTION-

The auxiliaries in a plant can be divided into two categories-

1. URGENT AUXILIARIES- the urgent auxiliaries are those, which are associated with running ofunit.

2. SERVICE AUXILIARIES- the service auxiliaries are those whose loss would not affect output.

GENERATOR SPECIFICATIONS-

TURBO GENERATOR (gen1, gen2)

KVA 247000

Pf 0.85

Volts of stator 15750

Amperes of stator 9050

Volts of rotor 310

Amperes of rotor 2600

Rpm 3000

Hz 50

Phase 3

Connection YY

Coolant Water (stator)& hydrogen (rotor)

Gas pressure 3.5kg/cm-sq.

Insulation class B

EXCITATION SYSTEM-

1. STATIC EXCITATION SYSTEM-The generators in stage -1(u-1&u-2) have this excitation system.Static excitation system has slip ring and carbon brush arrangement. It consists of step downtransformer, converter and AVR (automatic voltage regulator).

2. BRUSHLESS EXCITATION SYSTEM –The generators in stage -2(U-3, U-4& &U- 5) have thisexcitation system. It has two exciters, one is main exciter and other is pilot exciter.

GENERATOR PROTECTION-

1. STATOR PROTECTION- The neutral of star connected winding is connected to primary ofneutral grounding transformer, so that earth fault current is limited by over voltage relay.

2. DIFFERENTIAL PROTECTION- In case of phase-to-phase fault generator is protected bylongitudinal differential relay.

3. ROTOR PROTECTION- Rotor winding may be damaged by earth faults or open circuits. Thefield is biased by a dc voltage, which causes current to flow through the relay for an earthfault anywhere on the field system.

4. OVER SPEED PROTECTION – Mechanically over speed device that is usually in the form ofcentrifugally operated rings mounted on the rotor shaft, which fly out and close the stopvalves if the speed of the set increase more than 10%.

5. OVER VOLTAGE PROTECTION – It is provided with an over voltage relay. The relay is usuallyinduction pattern. The relay open the main circuit break and the field switch if the overvoltage persists.

6. SEAL OIL SYSTEM – Hydrogen in the generator is under very high pressure. There is apossibility of this hydrogen to come out of gaps, which is very hazardous. So, seal oil is usedto seal the gaps so that hydrogen doesn’t come out.

7. LUBRICATION OIL SYSTEM –Turbine lubrication-oil system seeks to provide properlubrication of turbo generator bearings and operation of barring gear. Pumps are used tocirculate lubrication-oil inside the generator. The oil of the lubrication and the governingsystem is cooled in the oil coolers. The cooling medium for these coolers is circulating water.

TRANSFORMER

TYPE PF TRANSFORMERS—

1. UNIT AUXILIARY TRANSFORMER: --This is a step down transformer. The primary receivesfrom generator and secondary supplies a 6.6 KV bus. This is oil cooled. These are 8 innumber.

2. NEUTRAL GROUNDED TRANSFORMER: --This transformer is connected with supply comingout of UAT in stage-2. This is used to ground the excess voltage if occurs in the secondary ofUAT in spite of rated voltage.

3. GENRATOR TRANSFORMER: -- This is a step up transformer. This supply gets its primarySupply from generator and its secondary supplies the switchyard from where it is transmittedto grid. This transformer is oil cooled. The primary of this transformer is connected in star.The secondary is connected in delta. These are four in number.

4. STATION TRANSFORMER: --This transformer has almost the same rating as the generatortransformer. Its primary is connected in delta and secondary in star. It is a step downtransformer. These are 4 in number.

SPECIFICATIONS

Generator transformer (GT-1 & GT-2)

KV 15.75/242

MVA 250

Phase 3

Hz 50

Connections Y-D 11

Type of cooling OFAF/ONAF/ONAN

Rated HV and IV (MVA) 250/150/100

Rated LV (MVA) 250/150/100

No Load Voltage HV (KV) 242

No Load Voltage IV (KV)

No Load Voltage LV (KV) 15.75

Line current HV (Amps) 597.14/358.29/238.86

Line current IV (Amps)

Line current LV (Amps) 9175.15/5505.09/3670.66

Temp rise coil oC 50

Temp rise winding oC 55

Neural grounded transformer (NGT)

KVA 1150

Phase 3

Hz 50

Type of cooling ONAF/ONAN

No load voltage HV (volts) 6600

No load voltage LV (volts) 250

Line current HV (Amps) 105.9

Line current LV (Amps) 2655.8

Temp rise oil oC 50

Temp rise winding 55

Potential Transformer

KVA 1000

Phase 3

Hz 50

Type of Cooling ONAN

No Load Voltage HV (volts) 6600

No Load Voltage LV (volts) 433

Line Current HV (Amps) 87.53

Line Current LV (Amps) 133.5

Temp rise oil oC 50

Temp rise winding oC 55

D.C SYSTEM

INTRODUCTION:

DC system is generally used for control and protection operation, as AC supply is not fullydependable. To maintain constant supply in case of power failure we use DC supply.

DC system consists of a battery charger. These are the mode of energy storage.

CHARGING EQUIPMENTS:

The battery charging equipment comprises of trickle charger, quick charger, battery panel, maindistribution board and switch control and signaling board.

CHARGING EQUATION:

In battery PbO2 used as positive plate and Pb as negative plate.

1. DISCHARGING PROCESS

2. CHARGING PROCESS

BATTERY CHARGER:

Battery charger normally operates in two modes.

1. Float charging: It is constant voltage mode and works as a trickle charger.

2. Boost charging: It is constant current mode and works as a quick charger.

TRICKLE CHARGER:

This charger is fed from three-phase ac supply and gives a dc-stabilized output at rated full loadcurrent. The variation of the dc output voltage is limited to +/- 1% for 0 to 100% load variation andsimultaneously ac voltage variation of +/- 10% of frequency variation of +/- 5% from 50 Hz.

The rectification is obtained through full bridge controlled silicon rectifier. Stack comprising of theseSCR and three diode with the surge suppression RC network connected across each SCR and diode.

SWITCH YARD

As we know that electrical energy can’t be stored like cells, so what we generate should beconsumed instantaneously. But as the load is not constants therefore we generate electricityaccording to need i.e. the generation depends upon load. The yard is the places from where theelectricity is send outside. It has both outdoor and indoor equipments.

SINGLE LINE DIAGRAM OF 220KV SWITCH YARD-

OUTDOOR EQUIPMENTS

1. BUS BAR

2. LIGHTENING ARRESTER

3. WAVE TRAP

4. BREAKER

5. CAPACITOR VOLTAGE TRANSFORMER

6. CORONA RING

7. EARTHING ROD

8. CURRENT TRANSFORMER

INDOOR EQUIPMENTS

1. RELAYS

2. CONTROL PANELS

9. POTENTIAL TRANSFORMER

10. LIGHTENING MASK

11. LIGHTENING MOOSE

CIRCUIT BREAKER:

The code for circuit breaker is 52. An electric power system needs some form of switchgearin order to operate it safely & efficiently under both normal and abnormal conditions.

Circuit breaker is an arrangement by which we can break the circuit or flow of current. A circuitbreaker in station serves the same purpose as switch but it has many added and complex features.The basic construction of any circuit breaker requires the separation of contact in an insulating fluidthat servers two functions:

1. It extinguishes the arc drawn between the contacts when circuit breaker opens.

2. It provides adequate insulation between the contacts and from each contact to earth.

The insulating fluids commonly used in circuit breakers are:

1. Compressed air

2. Oil which produces hydrogen for arc excitation.

3. Ultra high vacuum

4. Sulphur hexafluorides

The Specifications of the circuit breaker used are:

LIGHTING ARRESTER:

It saves the transformer and reactor from over voltage and over currents. We have to use thelightning arrester both in primary and secondary of transformer and in reactors.

A meter is provided which indicates the surface leakage and internal grading current of arrester.

1. Green – arrester is healthy

2. Red – arrester is defective.

In case of red we first de-energize the arrester and then do the operation.

AIR BREAK EARTHING SWITCH:

The code of earthling switch is 5, 6, 7.The work of this equipment comes into picture when we wantto shut down the supply for maintenance purpose. This help to neutralize the system from inducedvoltage from extra high voltage. This induced power is up to 2KV in case of 400 KV lines.

The specification of earthling switch is:

MAKE S & S POWER

TYPE MADRAS

VOLTAGE 245 KV

CURRENT 10 KA

MOTOR VOLT (AC) 415 VOLTS

CONTROL VOLT (DC) 220 VOLTS

MAKE CROMPTON GREAVES LTD.

TYPE AIR BLAST CIRCUITREAKER

RATED VOLTAGE 245 KV

RATED LIGHTING IMPULSE

WITHSTAND VOLTAGE 1050 KV

RATED SHORT CIRCUIT BREAKINGCURRENT

25 - 40KA

RATED FREQUENCY 50HZ

RATED NORMAL CURRENT 2000 A TO 4000 A

RATED CLOSING VOLTAGE 220 V DC

RATED OPENING VOLTAGE 220 V DC

BUS BAR:

Bus bars generally are of high conductive aluminum conforming to IS-5082 or copper ofadequate cross section .Bus bar located in air –insulated enclosures & segregated from all othercomponents .Bus bar is preferably cover with polyurethane.

1. Current Transformer (CT):

A current transformer is a type of instrument transformer designed to provide a current in itssecondary winding proportional to the alternating current flowing in its primary

.

Current Transformer Diagram

Application:

1. They are commonly used in metering and protective relaying in the electrical power

industry where they facilitate the safe measurement of large currents, often in thepresence of high voltages.

2. The current transformer safely isolates measurement and control circuitry from the

high voltages typically present on the circuit being measured.

3. Current transformers are used extensively for measuring current and monitoring the

operation of the power grid. The CT is typically described by its current ratio fromprimary to secondary. Often, multiple CTs are installed as a "stack" for various uses(for example, protection devices and revenue metering may use separate CTs).Similarly potential transformers are used for measuring voltage and monitoring theoperation of the power grid.

4. Capacitive Voltage Transformer (CVT):

A capacitor voltage transformer (CVT) is a transformer used in power systems to step-down extrahigh voltage signals and provide low voltage signals either for measurement or to operate aprotective relay. In its most basic form the device consists of three parts: two capacitors across whichthe voltage signal is split, an inductive element used to tune the device to the supply frequency and atransformer used to isolate and further step-down the voltage for the instrumentation or protectiverelay as shown in figure below.

The device has at least four terminals, a high-voltage terminal for connection to the high voltagesignal, a ground terminal and at least one set of secondary terminals for connection to theinstrumentation or protective relay. CVTs are typically single-phase devices used for measuringvoltages in excess of one hundred kilovolts where the use of voltage transformers would beuneconomical. In practice the first capacitor, C1, is often replaced by a stack of capacitors connectedin series.This results in a large voltage drop across the stack of capacitors that replaced the firstcapacitor and a comparatively small voltage drop across the second capacitor C2, and hence thesecondary terminals.

Conclusion

On completion of my vocational training at Feroze Gandhi Unchahar ThermalPower Project, Unchahar I have come to know about how the very necessity ofour lives nowadays i.e., electricity is generated. What all processes are neededto generate and run the plant on a 24x7 basis.

NTPC Unchahar is one the plants in India to be under highest load factorfor the maximum duration of time and that to operating at highest plantefficiencies. This plant is an example in terms of working efficiency andmanagement of resources to all other thermal plants in our country. Theoperating plf of the NTPC as compared to the rest of country is the highest with87.54% the highest since its inception.

The training gave me an opportunity to clear my concepts from practical pointof view with the availability of machinery of such large rating.