Industrial Training Report

1

INDUSTRIAL TRAINING REPORT ( N.T.P.C. BADARPUR, NEW DELHI )

FROM: 11 th JUNE to 21 st JULY, 2012

SUBMITTED TO: SUBMITTED BY:

MRS. RACHANA SINGH BHAL ANKIT SRIVASTAVADGM (HR)N.T.P.C. Badarpur B.Tech 3rd Year Electrical And Electronics

Engineering KIET, Ghaziabad

TABLE OF CONTENT

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Certificate

Acknowledgement

Training at BTPS

1. Introduction ¨ NTPC ¨ Badarpur Thermal Power Station

2. Operation

3. Control & Instrumentation ¨ Manometry Lab ¨ Protection and interlock Lab ¨ Automation Lab ¨ Water Treatment Plant ¨ Furnace Safeguard Supervisory System ¨ Electronic Test Lab

4. Electrical Maintenance Division-I ¨ HT/LT Switch Gear ¨ HT/LT Motors, Turbine & Boilers Side ¨ CHP/NCHP

5. Electrical Maintenance Division-II ¨ Generator ¨ Transformer & Switchyard ¨ Protection ¨ Lighting

CERTIFICATE Page | 2

INDUSTRIAL TRAINING REPORT

This is to certify that ------------------------------------------------- student of Electrical &

Electronics Branch IIIrd Year, Krishna Institute of Engineering & Technology Ghaziabad

has successfully completed his industrial training at Badarpur Thermal Power Station,

New Delhi for six week from 11th June to 21st July 2012.

He has completed the whole training as per the training report submitted by him.

Training Incharge

BTPS/NTPC

NEW DELHI

Page | 3 INDUSTRIAL TRAINING REPORT

ACKNOWLEDGEMENT

With profound respect and gratitude, I take the opportunity to convey my thanks to complete the training here.

I do extend my heartfelt thanks to Mrs. Rachana Singh for providing me this opportunity to be a part of this esteemed organization.

I am extremely grateful to all the technical staff of BTPS/NTPC for their co-operation and guidance that helped me a lot during the course of training. I have learnt a lot working under them and I will always be indebted of them for this value addition in me.

I would also like to thank the training in charge of Krishna Institute of Engineering & Technology Ghaziabad and all the faculty member of Electrical & Electronics department for their effort of constant co-operation. Which have been significant factor in the accomplishment of my industrial training.

TRAINING AT BTPS


I was appointed to do six-week training at this esteemed organization from 11th June to 21st July 2012. In these six weeks I was assigned to visit various division of the plant which were

1. Control and instrumentation (C&I)2. Electrical maintenance division I (EMD-I) 3. Electrical maintenance division II (EMD-II)

This six-week training was a very educational adventure for me. It was really amazing to see the plant by your self and learn how electricity, which is one of our daily requirements of life, is produced.

This report has been made by self-experience at BTPS. The material in this report has been gathered from my textbooks, senior student report, and trainer manual provided by training department. The specification & principles are at learned by me from the employee of each division of BTPS.

INTRODUCTION

ABOUT NTPC

NTPC Limited is the largest thermal power generating company of India. A public sector company, it was incorporated in the year 1975 to accelerate power development in the country as


a wholly owned company of the Government of India. At present, Government of India holds 89.5% of the total equity shares of the company and FIIs, Domestic Banks, Public and others

hold the balance 10.5%. With in a span of 31 years, NTPC has emerged as a truly national power company, with power generating facilities in all the major regions of the country.

A Graphical Overview

POWER GENERATION IN INDIA

NTPC’s core business is engineering, construction and operation of power generating plants. It also provides consultancy in the area of power plant constructions and power generation to companies in India and abroad. As on date the installed capacity of NTPC is 27,904 MW through its 15 coal based (22,895 MW), 7 gas based (3,955 MW) and 4 Joint Venture Projects (1,054 MW). NTPC acquired 50% equity of the SAIL Power Supply Corporation Ltd. (SPSCL). This JV Company operates the captive power plants of Durgapur (120 MW), Rourkela (120 MW) and Bhilai (74 MW). NTPC also has 28.33% stake in Ratnagiri Gas & Power Private Limited (RGPPL) a joint venture company between NTPC, GAIL, Indian Financial Institutions and


MaharashtraSEBCoLtd. NTPC has set new benchmarks for the power industry both in the area of power plant construction and operations. Its providing power at the cheapest average tariff in the country..NTPC is committed to the environment, generating power at minimal environmental cost and preserving the ecology in the vicinity of the plants. NTPC has undertaken massive a forestation in the vicinity of its plants. Plantations have increased forest area and reduced barren land. The massive a forestation by NTPC in and around its Ramagundam Power station (2600 MW) have contributed reducing the temperature in the areas by about 3°c. NTPC has also taken proactive steps for ash utilization. In 1991, it set up Ash Utilization DivisionA "Centre for Power Efficiency and Environment Protection (CENPEEP)" has been established in NTPC with the assistance of United States Agency for International Development. (USAID). Cenpeep is efficiency oriented, eco-friendly and eco-nurturing initiative - a symbol of NTPC's concern towards environmental protection and continued commitment to sustainable power development in India.As a responsible corporate citizen, NTPC is making constant efforts to improve the socio-economic status of the people affected by its projects. Through its Rehabilitation and Resettlement programmes, the company endeavors to improve the overall socio economic status Project Affected Persons. NTPC was among the first Public Sector Enterprises to enter into a Memorandum of Understanding (MOU) with the Government in 1987-88. NTPC has been placed under the 'Excellent category' (the best category) every year since the MOU system became operative.

National Environment Policy:

At the national level, the Ministry of Environment and Forests had prepared a draft Environment Policy (NEP) and the Ministry of Power along with NTPC actively participated in the deliberations of the draft NEP. The NEP 2006 has since been approved by the Union Cabinet in May 2006.

NTPC Environment Policy:

As early as in November 1995, NTPC brought out a comprehensive document entitled "NTPC Environment Policy and Environment Management System". Amongst the guiding principles adopted in the document are company's proactive approach to environment, optimum utilization of equipment, adoption of latest technologies and continual environment improvement. The policy also envisages efficient utilization of resources, thereby minimizing waste, maximizing ash utilization and providing green belt all around the plant for maintaining ecological balance.Environment Management, Occupational Health and Safety Systems: NTPC has actively gone for adoption of best international practices on environment, occupational health and safety areas. The organization has pursued the Environmental Management System (EMS) ISO 14001 and the Occupational Health and Safety Assessment


System OHSAS 18001 at its different establishments. As a result of pursuing these practices, all NTPC power stations have been certified for ISO 14001 & OHSAS 18001 by reputed national and international Certifying Agencies.

Pollution Control systems:

While deciding the appropriate technology for its projects, NTPC integrates many environmental provisions into the plant design. In order to ensure that NTPC comply with all the stipulated environment norms, various state-of-the-art pollution control systems / devices as discussed below have been installed to control air and water pollution.

1. Electrostatic Precipitators: The ash left behind after combustion of coal is arrested in high efficiency Electrostatic Precipitators (ESP’s) and particulate emission is controlled well within the stipulated norms. The ash collected in the ESP’s is disposed to Ash Ponds in slurry form. Flue Gas Stacks: Tall Flue Gas Stacks have been provided for wide dispersion of the gaseous emissions (SOX, NOX etc) into the atmosphere.Low-NOXBurners:In gas based NTPC power stations, NOx emissions are controlled by provision of Low-NOx Burners (dry or wet type) and in coal fired stations, by adopting best combustion practices. Neutralisation Pits: Neutralisation pits have been provided in the Water Treatment Plant (WTP) for pH correction of the effluents before discharge into Effluent Treatment Plant (ETP) for further treatment and use.

2. Coal Settling Pits / Oil Settling Pits: In these Pits, coal dust and oil are removed from the effluents emanating from the Coal Handling Plant (CHP), coal yard and Fuel Oil Handling areas before discharge into ETP.DE & DS Systems: Dust Extraction (DE) and Dust Suppression (DS) systems have been installed in all coal fired power stations in NTPC to contain and extract the fugitive dust released in the Coal Handling Plant (CHP).

3. Cooling Towers: Cooling Towers have been provided for cooling the hot Condenser cooling water in closed cycle Condenser Cooling Water (CCW) Systems. This helps in reduction in thermal pollution and conservation of fresh water. Ash Dykes & Ash Disposal systems: Ash ponds have been provided at all coal based stations except Dadri where Dry Ash


Disposal System has been provided. Ash Ponds have been divided into lagoons and provided with garlanding arrangements for change over of the ash slurry feed points for even filling of the pond and for effective settlement of the ash particles.Ash in slurry form is discharged into the lagoons where ash particles get settled from the slurry and clear effluent water is discharged from the ash pond. The discharged effluents conform to standards specified by CPCB and the same is regularly monitored. At its Dadri Power Station, NTPC has set up a unique system for dry ash collection and disposal facility with Ash Mound formation. This has been envisaged for the first time in Asia which has resulted in progressive development of green belt besides far less requirement of land and less water requirement as compared to the wet ash disposal system.

4. Ash Water Recycling System: Further, in a number of NTPC stations, as a proactive measure, Ash Water Recycling System (AWRS) has been provided. In the AWRS, the effluent from ash pond is circulated back to the station for further ash sluicing to the ash pond. This helps in savings of fresh water requirements for transportation of ash from the plant.The ash water recycling system has already been installed and is in operation at Ramagundam, Simhadri, Rihand, Talcher Kaniha, Talcher Thermal, Kahalgaon, Korba and Vindhyachal. The scheme has helped stations to save huge quantity of fresh water required as make-up water for disposal of ash.

5. Dry Ash Extraction System (DAES): Dry ash has much higher utilization potential in ash-based products (such as bricks, aerated autoclaved concrete blocks, concrete, Portland pozzolana cement, etc.). DAES has been installed at Unchahar, Dadri, Simhadri, Ramagundam, Singrauli, Kahalgaon, Farakka, Talcher Thermal, Korba, Vindhyachal, Talcher Kaniha and BTPS.

Liquid Waste Treatment Plants & Management System: The objective of industrial liquid effluent treatment plant (ETP) is to discharge lesser and cleaner effluent from the power plants to meet environmental regulations. After primary treatment at the source of their generation, the effluents are sent to the ETP for further treatment. The composite liquid effluent treatment plant has been designed to treat all liquid effluents which originate within the power station e.g. Water Treatment Plant (WTP), Condensate Polishing Unit (CPU) effluent, Coal Handling Plant (CHP) effluent, floor washings, service water drains etc. The scheme involves collection of various effluents and their appropriate treatment centrally and re-circulation of the treated effluent for various plant uses.NTPC has implemented such systems in a number of its power stations such as Ramagundam, Simhadri, Kayamkulam, Singrauli, Rihand, Vindhyachal, Korba, Jhanor Gandhar, Faridabad, Farakka, Kahalgaon and Talcher Kaniha. These plants have helped to control quality and quantity of the effluents discharged from the stations.


6. Sewage Treatment Plants & Facilities: Sewage Treatment Plants (STPs) sewage treatment facilities have been provided at all NTPC stations to take care of Sewage Effluent from Plant and township areas. In a number of NTPC projects modern type STPs with Clarifloculators, Mechanical Agitators, sludge drying beds, Gas Collection Chambers etc have been provided to improve the effluent quality. The effluent quality is monitored regularly and treated effluent conforming to the prescribed limit is discharged from the station. At several stations, treated effluents of STPs are being used for horticulture purpose.

7. Environmental Institutional Set-up: Realizing the importance of protection of the environment with speedy development of the power sector, the company has constituted different groups at project, regional and Corporate Centre level to carry out specific environment related functions. The Environment Management Group, Ash Utilisation Group and Centre for Power Efficiency & Environment Protection (CENPEEP) function from the Corporate Centre and initiate measures to mitigate the impact of power project implementation on the environment and preserve ecology in the vicinity of the projects. Environment Management and Ash Utilisation Groups established at each station, look after various environmental issues of the individual station.

8. Environment Reviews: To maintain constant vigil on environmental compliance, Environmental Reviews are carried out at all operating stations and remedial measures have been taken wherever necessary. As a feedback and follow-up of these Environmental Reviews, a number of retrofit and up-gradation measures have been undertaken at different stations.Such periodic Environmental Reviews and extensive monitoring of the facilities carried out at all stations have helped in compliance with the environmental norms and timely renewal of the Air and Water Consents.

9. Up gradation & retrofitting of Pollution Control Systems: Waste ManagementVarious types of wastes such as Municipal or domestic wastes, hazardous wastes, Bio-Medical wastes get generated in power plant areas, plant hospital and the townships of projects. The wastes generated are a number of solid and hazardous wastes like used oils & waste oils, grease, lead acid batteries, other lead bearing wastes (such as garkets etc.), oil & clarifier sludge, used resin, used photo-chemicals, asbestos packing, e-waste, metal scrap, C&I wastes, electricial scrap, empty cylinders (refillable), paper, rubber products, canteen (bio-degradable) wastes, buidling material wastes, silica gel, glass wool, fused lamps & tubes, fire resistant fluids etc. These wastes fall either under hazardous wastes category or non-hazardous wastes category as per classification given in Government of India’s notification on Hazardous Wastes (Management and Handling) Rules 1989 (as


amended on 06.01.2000 & 20.05.2003). Handling and management of these wastes in NTPC stations have been discussed below.

10. Advanced / Eco-friendly Technologies:NTPC has gained expertise in operation and management of 200 MW and 500 MW Units installed at different Stations all over the country and is looking ahead for higher capacity Unit sizes with super critical steam parameters for higher efficiencies and for associated environmental gains. At Sipat, higher capacity Units of size of 660 MW and advanced Steam Generators employing super critical steam parameters have already been implemented as a green field project. Higher efficiency Combined Cycle Gas Power Plants are already under operation at all gas-based power projects in NTPC. Advanced clean coal technologies such as Integrated Gasification Combined Cycle (IGCC) have higher efficiencies of the order of 45% as compared to about 38% for conventional plants. NTPC has initiated a techno-economic study under USDOE / USAID for setting up a commercial scale demonstration power plant by using IGCC technology. These plants can use low-grade coals and have higher efficiency as compared to conventional plants.With the massive expansion of power generation, there is also growing awareness among all concerned to keep the pollution under control and preserve the health and quality of the natural environment in the vicinity of the power stations. NTPC is committed to provide affordable and sustainable power in increasingly larger quantity. NTPC is conscious of its role in the national endeavour of mitigating energy poverty, heralding economic prosperity and thereby contributing towards India’s emergence as a major global economy.

Overall Power Generation

Unit 1997-98 2006-07 % of increase Installed Capacity MW 16,847 26,350 56.40 Generation MUs 97,609 1,88,674 93.29 No. of employees No. 23,585 24,375 3.34 Generation/employee MUs 4.14 7.74 86.95


The table below shows the detailed operational performance of coal based stations over the years. OPERATIONAL PERFORMANCE OF COAL BASED NTPC STATIONS

Unit 97-98 98-99 99-00 00-01 01-02 02-03 03-04 04-05 05-06 06-07 Generation BU 106.2 109.5 118.7 130.1 133.2 140.86 149.16 159.11 170.88 188.67 PLF % 75.20 76.60 80.39 81.8 81.1 83.6 84.4 87.51 87.54 89.43 AvailabilityFactor % 85.03 89.36 90.06 88.54 81.8 88.7 88.8 91.20 89.91 90.09

The energy conservation parameters like specific oil consumption and auxiliary power consumption have also shown considerable improvement over the years.

ELECTRICITY FROM COAL


Coal from the coal wagons is unloaded with the help of wagon tipplers in the C.H.P. this coal is taken to the raw coal bunkers with the help of conveyor belts. Coal is then transported to bowl mills by coal feeders where it is pulverized and ground in the powered form.

This crushed coal is taken away to the furnace through coal pipes with the help of hot and cold mixture P.A fan. This fan takes atmospheric air, a part of which is sent to pre heaters while a part


goes to the mill for temperature control. Atmospheric air from F.D fan in the air heaters and sent to the furnace as combustion air.

Water from boiler feed pump passes through economizer and reaches the boiler drum . Water from the drum passes through the down comers and goes to the bottom ring header. Water from the bottom ring header is divided to all the four sides of the furnace. Due to heat density difference the water rises up in the water wall tubes. This steam and water mixture is again taken to the boiler drum where the steam is sent to super heaters for super heating. The super heaters are located inside the furnace and the steam is super heated (540 degree Celsius) and finally it goes to the turbine.

Fuel gases from the furnace are extracted from the induced draft fan, which maintains balance draft in the furnace with F.D fan. These fuel gases heat energy to the various super heaters and finally through air pre heaters and goes to electrostatic precipitators where the ash particles are extracted. This ash is mixed with the water to from slurry is pumped to ash period.

The steam from boiler is conveyed to turbine through the steam pipes and through stop valve and control valve that automatically regulate the supply of steam to the turbine. Stop valves and controls valves are located in steam chest and governor driven from main turbine shaft operates the control valves the amount used.

Steam from controlled valves enter high pressure cylinder of turbines, where it passes through the ring of blades fixed to the cylinder wall. These act as nozzles and direct the steam into a second ring of moving blades mounted on the disc secured in the turbine shaft. The second ring turns the shaft as a result of force of steam. The stationary and moving blades together.

MAIN GENERATOR


Maximum continuous KVA rating 24700KVA Maximum continuous KW 210000KW Rated terminal voltage 15750V Rated Stator current 9050 A Rated Power Factor 0.85 lag Excitation current at MCR Condition 2600 A Slip-ring Voltage at MCR Condition 310 V Rated Speed 3000 rpm Rated Frequency 50 Hz Short circuit ratio 0.49 Efficiency at MCR Condition 98.4% Direction of rotation viewed Anti Clockwise Phase Connection Double Star Number of terminals brought out 9( 6 neutral and 3 phase)

MAIN TURBINE DATA

THERMAL POWER PLANT

A Thermal Power Station comprises all of the equipment and a subsystem required to produce electricity by using a steam generating boiler fired with fossil fuels or befouls to drive an electrical generator. Some prefer to use the term ENERGY CENTER because such facilities convert forms of energy, like nuclear energy, gravitational potential energy or heat energy (derived from the combustion of fuel) into electrical energy. However, POWER PLANT is the most common term in the united state; While POWER STATION prevails in many Commonwealth countries and especially in the United Kingdom.Such power stations are most usually constructed on a very large scale and designed for continuous operation.

Typical diagram of a coal fired thermal power station1. Cooling water pump2. Three-phase transmission line 3. Step up transformer4. Electrical Generator5. Low pressure steam6. Boiler feed water pump7. Surface condenser8. Intermediate pressure steam turbine9. Steam control valve10. High pressure steam turbine11. Deaerator Feed water heater12. Coal conveyor13. Coal hopper14. Coal pulverizer15. boiler steam drum 16. Bottom ash hoper


Rated output of Turbine 210 MW Rated speed of turbine 3000 rpm Rated pressure of steam before emergency 130 kg/cm^2 Stop valve rated live steam temperature 535 degree Celsius Rated steam temperature after reheat at inlet to receptor valve 535 degree Celsius Steam flow at valve wide open condition 670 tons/hour Rated quantity of circulating water through condenser 27000 cm/hour 1. For cooling water temperature (degree Celsius) 24,27,30,33 1.Reheated steam pressure at inlet of interceptor valve in kg/cm^2 ABS 23,99,24,21,24,49,24.82

2.Steam flow required for 210 MW in ton/hour 68,645,652,662 3.Rated pressure at exhaust of LP turbine in mm of Hg 19.9,55.5,65.4,67.7

17. Super heater18. Forced draught(draft) fan19. Reheater20. Combustion air intake21. Economizer22. Air preheater23. Precipitator24. Induced draught(draft) fan25. Fuel gas stack

The description of some of the components written above is described as follows:

1. Cooling towers Cooling Towers are evaporative coolers used for cooling water or other working medium to near the ambivalent web-bulb air temperature. Cooling tower use evaporation of water to reject heat from processes such as cooling the circulating water used in oil refineries, Chemical plants, power plants and building cooling, for example. The tower vary in size from small roof-top units to very large hyperboloid structures that can be up to 200 meters tall and 100 meters in diameter, or rectangular structure that can be over 40 meters tall and 80 meters long. Smaller towers are normally factory built, while larger ones are constructed on site.The primary use of large , industrial cooling tower system is to remove the heat absorbed in the circulating cooling water systems used in power plants , petroleum refineries, petrochemical and chemical plants, natural gas processing plants and other industrial facilities . The absorbed heat is rejected to the atmosphere by the evaporation of some of the cooling water in mechanical forced-draft or induced draft towers or in natural draft hyperbolic shaped cooling towers as seen at most nuclear power plants.

2. Three phase transmission lineThree phase electric power is a common method of electric power transmission. It is a type of polyphase system mainly used to power motors and many other devices. A Three phase system uses less conductor material to transmit electric power than equivalent single phase, two phase, or direct current system at the same voltage. In a three phase system, three circuits reach their instantaneous peak values at different times. Taking one conductor as the reference, the other two current are delayed in time by one-third and two-third of one cycle of the electrical current. This delay between “phases” has the effect of giving constant power transfer over each cycle of the current and also makes it possible to produce a rotating magnetic field in an electric motor.At the power station, an electric generator converts mechanical power into a set of electric currents, one from each electromagnetic coil or winding of the generator. The current are sinusoidal functions of time, all at the same frequency but offset in time to give different phases. In a three phase system the phases are spaced equally, giving a phase separation of one-third one cycle. Generators output at a voltage that ranges from hundreds of volts to 30,000 volts. At the power station, transformers: step-up” this voltage to one more suitable for transmission.After numerous further conversions in the transmission and distribution network the power is


finally transformed to the standard mains voltage (i.e. the “household” voltage).The power may already have been split into single phase at this point or it may still be three phase. Where the step-down is 3 phase, the output of this transformer is usually star connected with the standard mains voltage being the phase-neutral voltage. Another system commonly seen in North America is to have a delta connected secondary with a center tap on one of the windings supplying the ground and neutral. This allows for 240 V three phase as well as three different single phase voltages( 120 V between two of the phases and neutral , 208 V between the third phase ( known as a wild leg) and neutral and 240 V between any two phase) to be available from the same supply.

3. Electrical generator An Electrical generator is a device that converts kinetic energy to electrical energy, generally using electromagnetic induction. The task of converting the electrical energy into mechanical energy is accomplished by using a motor. The source of mechanical energy may be a reciprocating or turbine steam engine, , water falling through the turbine are made in a variety of sizes ranging from small 1 hp (0.75 kW) units (rare) used as mechanical drives for pumps, compressors and other shaft driven equipment , to 2,000,000 hp(1,500,000 kW) turbines used to generate electricity. There are several classifications for modern steam turbines.Steam turbines are used in all of our major coal fired power stations to drive the generators or alternators, which produce electricity. The turbines themselves are driven by steam generated in ‘Boilers’ or ‘steam generators’ as they are sometimes called.Electrical power station use large stem turbines driving electric generators to produce most (about 86%) of the world’s electricity. These centralized stations are of two types: fossil fuel power plants and nuclear power plants. The turbines used for electric power generation are most often directly coupled to their-generators .As the generators must rotate at constant synchronous speeds according to the frequency of the electric power system, the most common speeds are 3000 r/min for 50 Hz systems, and 3600 r/min for 60 Hz systems. Most large nuclear sets rotate at half those speeds, and have a 4-pole generator rather than the more common 2-pole one.Energy in the steam after it leaves the boiler is converted into rotational energy as it passes through the turbine. The turbine normally consists of several stage with each stages consisting of a stationary blade (or nozzle) and a rotating blade. Stationary blades convert the potential energy of the steam into kinetic energy into forces, caused by pressure drop, which results in the rotation of the turbine shaft. The turbine shaft is connected to a generator, which produces the electrical energy.4. Boiler feed water pumpA Boiler feed water pump is a specific type of pump used to pump water into a steam boiler. The water may be freshly supplied or retuning condensation of the steam produced by the boiler. These pumps are normally high pressure units that use suction from a condensate return system and can be of the centrifugal pump type or positive displacement type.

Construction and operationFeed water pumps range in size up to many horsepower and the electric motor is usually separated from the pump body by some form of mechanical coupling. Large industrial


condensate pumps may also serve as the feed water pump. In either case, to force the water into the boiler; the pump must generate sufficient pressure to overcome the steam pressure developed by the boiler. This is usually accomplished through the use of a centrifugal pump.Feed water pumps usually run intermittently and are controlled by a float switch or other similar level-sensing device energizing the pump when it detects a lowered liquid level in the boiler is substantially increased. Some pumps contain a two-stage switch. As liquid lowers to the trigger point of the first stage, the pump is activated. I f the liquid continues to drop (perhaps because the pump has failed, its supply has been cut off or exhausted, or its discharge is blocked); the second stage will be triggered. This stage may switch off the boiler equipment (preventing the boiler from running dry and overheating), trigger an alarm, or both.

5.Steam-powered pumpsSteam locomotives and the steam engines used on ships and stationary applications such as power plants also required feed water pumps. In this situation, though, the pump was often powered using a small steam engine that ran using the steam produced by the boiler. A means had to be provided, of course, to put the initial charge of water into the boiler(before steam power was available to operate the steam-powered feed water pump).the pump was often a positive displacement pump that had steam valves and cylinders at one end and feed water cylinders at the other end; no crankshaft was required.

In thermal plants, the primary purpose of surface condenser is to condense the exhaust steam from a steam turbine to obtain maximum efficiency and also to convert the turbine exhaust steam into pure water so that it may be reused in the steam generator or boiler as boiler feed water. By condensing the exhaust steam of a turbine at a pressure below atmospheric pressure, the steam pressure drop between the inlet and exhaust of the turbine is increased, which increases the amount heat available for conversion to mechanical power. Most of the heat liberated due to condensation of the exhaust steam is carried away by the cooling medium (water or air) used by the surface condenser.

6. Control valvesControl valves are valves used within industrial plants and elsewhere to control operating conditions such as temperature,pressure,flow,and liquid Level by fully partially opening or closing in response to signals received from controllers that compares a “set point” to a “process variable” whose value is provided by sensors that monitor changes in such conditions. The opening or closing of control valves is done by means of electrical, hydraulic or pneumatic systems

7. DeaeratorA Dearator is a device for air removal and used to remove dissolved gases (an alternate would be the use of water treatment chemicals) from boiler feed water to make it non-corrosive. A dearator typically includes a vertical domed deaeration section as the deaeration boiler feed water tank. A Steam generating boiler requires that the circulating steam, condensate, and feed water should be


devoid of dissolved gases, particularly corrosive ones and dissolved or suspended solids. The gases will give rise to corrosion of the metal. The solids will deposit on the heating surfaces giving rise to localized heating and tube ruptures due to overheating. Under some conditions it may give to stress corrosion cracking.Deaerator level and pressure must be controlled by adjusting control valves- the level by regulating condensate flow and the pressure by regulating steam flow. If operated properly, most deaerator vendors will guarantee that oxygen in the deaerated water will not exceed 7 ppb by weight (0.005 cm3/L)

8. Feed water heaterA Feed water heater is a power plant component used to pre-heat water delivered to a steam generating boiler. Preheating the feed water reduces the irreversible involved in steam generation and therefore improves the thermodynamic efficiency of the system.[4] This reduces plant operating costs and also helps to avoid thermal shock to the boiler metal when the feed water is introduces back into the steam cycle.In a steam power (usually modeled as a modified Ranking cycle), feed water heaters allow the feed water to be brought up to the saturation temperature very gradually. This minimizes the inevitable irreversibility’s associated with heat transfer to the working fluid (water). A belt conveyor consists of two pulleys, with a continuous loop of material- the conveyor Belt – that rotates about them. The pulleys are powered, moving the belt and the material on the belt forward. Conveyor belts are extensively used to transport industrial and agricultural material, such as grain, coal, ores etc.

9. PulverizerA pulverizer is a device for grinding coal for combustion in a furnace in a fossil fuel power plant.

10. Boiler Steam DrumSteam Drums are a regular feature of water tube boilers. It is reservoir of water/steam at the top end of the water tubes in the water-tube boiler. They store the steam generated in the water tubes and act as a phase separator for the steam/water mixture. The difference in densities between hot and cold water helps in the accumulation of the “hotter”-water/and saturated –steam into steam drum. Made from high-grade steel (probably stainless) and its working involves temperatures 390’C and pressure well above 350psi (2.4MPa). The separated steam is drawn out from the top section of the drum. Saturated steam is drawn off the top of the drum. The steam will re-enter the furnace in through a super heater, while the saturated water at the bottom of steam drum flows down to the mud-drum /feed water drum by down comer tubes accessories include a safety valve, water level indicator and fuse plug. A steam drum is used in the company of a mud-drum/feed water drum which is located at a lower level. So that it acts as a sump for the sludge or sediments which have a tendency to the bottom.

11. Super HeaterA Super heater is a device in a steam engine that heats the steam generated by the boiler again increasing its thermal energy and decreasing the likelihood that it will condense inside the


engine. Super heaters increase the efficiency of the steam engine, and were widely adopted. Steam which has been superheated is logically known as superheated steam; non-superheated steam is called saturated steam or wet steam; Super heaters were applied to steam locomotives in quantity from the early 20th century, to most steam vehicles, and so stationary steam engines including power stations.

12. EconomizersEconomizer, or in the UK economizer, are mechanical devices intended to reduce energy consumption, or to perform another useful function like preheating a fluid. The term economizer is used for other purposes as well. Boiler, power plant, and heating, ventilating and air conditioning. In boilers, economizer are heat exchange devices that heat fluids , usually water, up to but not normally beyond the boiling point of the fluid. Economizers are so named because they can make use of the enthalpy and improving the boiler’s efficiency. They are a device fitted to a boiler which saves energy by using the exhaust gases from the boiler to preheat the cold water used the fill it (the feed water). Modern day boilers, such as those in cold fired power stations, are still fitted with economizer which is decedents of Green’s original design. In this context they are turbines before it is pumped to the boilers. A common application of economizer is steam power plants is to capture the waste hit from boiler stack gases (flue gas) and transfer thus it to the boiler feed water thus lowering the needed energy input , in turn reducing the firing rates to accomplish the rated boiler output . Economizer lower stack temperatures which may cause condensation of acidic combustion gases and serious equipment corrosion damage if care is not taken in their design and material selection.

13. Air PreheaterAir preheater is a general term to describe any device designed to heat air before another process (for example, combustion in a boiler). The purpose of the air preheater is to recover the heat from the boiler flue gas which increases the thermal efficiency of the boiler by reducing the useful heat lost in the fuel gas. As a consequence, the flue gases are also sent to the flue gas stack (or chimney) at a lower temperature allowing simplified design of the ducting and the flue gas stack. It also allows control over the temperature of gases leaving the stack.

14. PrecipitatorAn Electrostatic precipitator (ESP) or electrostatic air cleaner is a particulate device that removes particles from a flowing gas (such As air) using the force of an induced electrostatic charge. Electrostatic precipitators are highly efficient filtration devices, and can easily remove fine particulate matter such as dust and smoke from the air steam.ESP’s continue to be excellent devices for control of many industrial particulate emissions, including smoke from electricity-generating utilities (coal and oil fired), salt cake collection from black liquor boilers in pump mills, and catalyst collection from fluidized bed catalytic crackers from several hundred thousand ACFM in the largest coal-fired boiler application.

The original parallel plate-Weighted wire design (described above) has evolved as more efficient ( and robust) discharge electrode designs were developed, today focusing on rigid discharge


electrodes to which many sharpened spikes are attached , maximizing corona production. Transformer –rectifier systems apply voltages of 50-100 Kilovolts at relatively high current densities. Modern controls minimize sparking and prevent arcing, avoiding damage to the components. Automatic rapping systems and hopper evacuation systems remove the collected particulate matter while on line allowing ESP’s to stay in operation for years at a time.

15. Fuel gas stackA Fuel gas stack is a type of chimney, a vertical pipe, channel or similar structure through which combustion product gases called fuel gases are exhausted to the outside air. Fuel gases are produced when coal, oil, natural gas, wood or any other large combustion device. Fuel gas is usually composed of carbon dioxide (CO2) and water vapor as well as nitrogen and excess oxygen remaining from the intake combustion air. It also contains a small percentage of pollutants such as particulates matter, carbon mono oxide, nitrogen oxides and sulfur oxides. The flue gas stacks are often quite tall, up to 400 meters (1300 feet) or more, so as to disperse the exhaust pollutants over a greater aria and thereby reduce the concentration of the pollutants to the levels required by governmental environmental policies and regulations.When the fuel gases exhausted from stoves, ovens, fireplaces or other small sources within residential abodes, restaurants , hotels or other stacks are referred to as chimneys.

CONTROL AND INSTRUMENTATION

This division basically calibrates various instruments and takes care of any faults occur in any of the auxiliaries in the plant.

It has following labs:

1. MANOMETRY LAB2. PROTECTION AND INTERLOCK LAB3. AUTOMATION LAB4. WATER TREATEMENT LAB5. FURNACE SAFETY SUPERVISORY SYSTEM(FSSS)6. ELECTRONICS TEST LAB

This department is the brain of the plant because from the relays to transmitters followed by the electronic computation chipsets and recorders and lastly the controlling circuitry, all fall under this.

5.0 MANOMETRY LAB


5.0.1 TRANSMITTERSIt is used for pressure measurements of gases and liquids, its working principle is that the input pressure is converted into electrostatic capacitance and from there it is conditioned and amplified. It gives an output of 4-20 ma DC. It can be mounted on a pipe or a wall. For liquid or steam measurement transmitters is mounted below main process piping and for gas measurement transmitter is placed above pipe.

5.0.2 MANOMETERIt’s a tube which is bent, in U shape. It is filled with a liquid. This device corresponds to a difference in pressure across the two limbs.

5.0.3 BOURDEN PRESSURE GAUGEIt’s an oval section tube. Its one end is fixed. It is provided with a pointer to indicate the pressure on a calibrated scale. It is of 2 types:

(a) Spiral type: for Low pressure measurement.(b) Helical Type: for High pressure measurement.

5.1 PROTECTION AND INTERLOCK LAB

5.1.1 INTERLOCKINGIt is basically interconnecting two or more equipments so that if one equipments fails other one can perform the tasks. This type of interdependence is also created so that equipments connected together are started and shut down in the specific sequence to avoid damage.For protection of equipments tripping are provided for all the equipments. Tripping can be considered as the series of instructions connected through OR GATE. When a fault occurs and any one of the tripping is satisfied a signal is sent to the relay, which trips the circuit. The main equipments of this lab are relay and circuit breakers. Some of the instrument uses for protection are:

1. RELAY

It is a protective device. It can detect wrong condition in electrical circuits by constantly measuring the electrical quantities flowing under normal and faulty conditions. Some of the electrical quantities are voltage, current, phase angle and velocity.

2. FUSES

It is a short piece of metal inserted in the circuit, which melts when heavy current flows through it and thus breaks the circuit. Usually silver is used as a fuse material because: a) The coefficient of expansion of silver is very small. As a result no critical fatigue occurs and thus the continuous full capacity normal current ratings are assured for the long time.b) The conductivity of the silver is unimpaired by the surges of the current that produces


temperatures just near the melting point. c) Silver fusible elements can be raised from normal operating temperature to vaporization quicker than any other material because of its comparatively low specific heat.

5.1.2 MINIATURE CIRCUIT BREAKER They are used with combination of the control circuits to. a) Enable the staring of plant and distributors. b) Protect the circuit in case of a fault. In consists of current carrying contacts, one movable and other fixed. When a fault occurs the contacts separate and are is stuck between them. There are three types of

- MANUAL TRIP- THERMAL TRIP- SHORT CIRCUIT TRIP

5.1.3 ROTECTION AND INTERLOCK SYSTEM

1. HIGH TENSION CONTROL CIRCUITFor high tension system the control system are excited by separate D.C supply. For starting the circuit conditions should be in series with the starting coil of the equipment to energize it. Because if even a single condition is not true then system will not start.

2. LOW TENSION CONTROL CIRCUITFor low tension system the control circuits are directly excited from the 0.415 KV A.C supply. The same circuit achieves both excitation and tripping. Hence the tripping coil is provided for emergency tripping if the interconnection fails.

5.2 AUTOMATION LABThis lab deals in automating the existing equipment and feeding routes.Earlier, the old technology dealt with only (DAS) Data Acquisition System and came to be known as primary systems. The modern technology or the secondary systems are coupled with (MIS) Management Information System. But this lab universally applies the pressure measuring instruments as the controlling force. However, the relays are also provided but they are used only for protection and interlocks.Once the measured is common i.e. pressure the control circuits can easily be designed with single chips having multiple applications. Another point is the universality of the supply, the laws of electronic state that it can be any where between 12V and 35V in the plant. All the control instruments are excited by 24V supply (4-20mA) because voltage can be mathematically handled with ease therefore all control systems use voltage system for computation. The latest technology is the use of ‘ETHERNET’ for control signals.


5.3 PYROMETER LAB

(1) LIQUID IN GLASS THERMOMETERMercury in the glass thermometer boils at 340 degree Celsius which limits the range of temperature that can be measured. It is L shaped thermometer which is designed to reach all inaccessible places.

(2) ULTRA VIOLET CENSOR This device is used in furnace and it measures the intensity of ultra violet rays there and according to the wave generated which directly indicates the temperature in the furnace.

(3) THERMOCOUPLESThis device is based on SEEBACK and PELTIER effect. It comprises of two junctions at different temperature. Then the emf is induced in the circuit due to the flow of electrons. This is an important part in the plant.

(4) RTD (RESISTANCE TEMPERATURE DETECTOR)It performs the function of thermocouple basically but the difference is of a resistance. In this due to the change in the resistance the temperature difference is measured.In this lab, also the measuring devices can be calibrated in the oil bath or just boiling water (for low range devices) and in small furnace (for high range devices). 5.4 FURNACE SAFETY AND SUPERVISORY SYSTEM LAB This lab has the responsibility of starting fire in the furnace to enable the burning of coal. For first stage coal burners are in the front and rear of the furnace and for the second and third stage corner firing is employed. Unburnt coal is removed using forced draft or induced draft fan. The temperature inside the boiler is 1100 degree Celsius and its height is 18 to 40 m. It is made up of mild steel. An ultra violet sensor is employed in furnace to measure the intensity of ultra violet rays inside the furnace and according to it a signal in the same order of same mV is generated which directly indicates the temperature of the furnace.For firing the furnace a 10 KV spark plug is operated for ten seconds over a spray of diesel fuel and pre-heater air along each of the feeder-mills. The furnace has six feeder mills each separated by warm air pipes fed from forced draft fans. In first stage indirect firing is employed that is feeder mills are not fed directly from coal but are fed from three feeders but are fed from pulverized coalbunkers. The furnace can operate on the minimum feed from three feeders but under not circumstances should any one be left out under operation, to prevent creation of pressure different with in the furnace, which threatens to blast it.

5.4 ELECTRONICS LABThis lab undertakes the calibration and testing of various cards. It houses various types of analytical instruments like oscilloscopes, integrated circuits, cards auto analyzers etc.Various processes undertaken in this lab are:1. Transmitter converts mV to mA.


2. Auto analyzer purifies the sample before it is sent to electrodes. It extracts the magnetic portion.

5.5 ANNUNCIATIN CARDS They are used to keep any parameter like temperature etc. within limits. It gets a signal if parameter goes beyond limit. It has a switching transistor connected to relay that helps in alerting the UCB.

ELECTRICAL MAINTENANCE DIVISION I

It is responsible for maintenance of:

1. Boiler side motors2. Turbine side motors3. Outside motors


4. Switchgear

1. Boiler side motors:

For 1, units 1, 2, 3

1.1D Fans 2 in no. 2.F.D Fans 2 in no. 3.P.A.Fans 2 in no. 4.Mill Fans 3 in no. 5.Ball mill fans 3 in no. 6.RC feeders 3 in no. 7.Slag Crushers 5 in no. 8.DM Make up Pump 2 in no. 9.PC Feeders 4 in no. 10.Worm Conveyor 1 in no. 11.Furnikets 4 in no.

For stage units 1, 2, 3

1.I.D Fans 2 in no. 2.F.D Fans 2 in no. 3.P.A Fans 2 in no. 4.Bowl Mills 6 in no. 5.R.C Feeders 6 in no. 6.Clinker Grinder 2 in no. 7.Scrapper 2 in no. 8.Seal Air Fans 2 in no. 9.Hydrazine and Phosphorous Dozing 2 in no.

2/3 in no.

1. COAL HANDLING PLANT (C.H.P)

2. NEW COAL HANDLING PLANT (N.C.H.P)The old coal handling plant caters to the need of units 2,3,4,5 and 1 whereas the latter supplies coal to units 4 and V.O.C.H.P. supplies coal to second and third stages in the advent coal to usable form to (crushed) form its raw form and send it to bunkers, from where it is send to furnace.

Major Components


1. Wagon Tippler: - Wagons from the coal yard come to the tippler and are emptied here. The process is performed by a slip –ring motor of rating: 55 KW, 415V, 1480 RPM. This motor turns the wagon by 135 degrees and coal falls directly on the conveyor through vibrators. Tippler has raised lower system which enables is to switch off motor when required till is wagon back to its original position. It is titled by weight balancing principle. The motor lowers the hanging balancing weights, which in turn tilts the conveyor. Estimate of the weight of the conveyor is made through hydraulic weighing machine.

2. Conveyor: - There are 14 conveyors in the plant. They are numbered so that their function can be easily demarcated. Conveyors are made of rubber and more with a speed of 250-300m/min. Motors employed for conveyors has a capacity of 150 HP. Conveyors have a capacity of carrying coal at the rate of 400 tons per hour. Few conveyors are double belt, this is done for imp. Conveyors so that if a belt develops any problem the process is not stalled. The conveyor belt has a switch after every 25-30 m on both sides so stop the belt in case of emergency. The conveyors are 1m wide, 3 cm thick and made of chemically treated vulcanized rubber. The max angular elevation of conveyor is designed such as never to exceed half of the angle of response and comes out to be around 20 degrees.

3. Zero Speed Switch:-It is safety device for motors, i.e., if belt is not moving and the motor is on the motor may burn. So to protect this switch checks the speed of the belt and switches off the motor when speed is zero.

4. Metal Separators: - As the belt takes coal to the crusher, No metal pieces should go along with coal. To achieve this objective, we use metal separators. When coal is dropped to the crusher hoots, the separator drops metal pieces ahead of coal. It has a magnet and a belt and the belt is moving, the pieces are thrown away. The capacity of this device is around 50 kg. .The CHP is supposed to transfer 600 tons of coal/hr, but practically only 300-400 tons coal is transfer5. Crusher: - Both the plants use TATA crushers powered by BHEL. Motors. The crusher is of ring type and motor ratings are 400 HP, 606 KV. Crusher is designed to crush the pieces to 20 mm size i.e. practically considered as the optimum size of transfer via conveyor.

6. Rotatory Breaker: - OCHP employs mesh type of filters and allows particles of 20mm size to go directly to RC bunker, larger particles are sent to crushes. This leads to frequent clogging. NCHP uses a technique that crushes the larger of harder substance like metal impurities easing the load on the magnetic separators.


MILLING SYSTEM

1. RC Bunker: - Raw coal is fed directly to these bunkers. These are 3 in no. per boiler. 4 & ½ tons of coal are fed in 1 hr. the depth of bunkers is 10m.

2. RC Feeder: - It transports pre crust coal from raw coal bunker to mill. The quantity of raw coal fed in mill can be controlled by speed control of aviator drive controlling damper and aviator change.

3. Ball Mill: - The ball mill crushes the raw coal to a certain height and then allows it to fall down. Due to impact of ball on coal and attraction as per the particles move over each other as well as over the Armor lines, the coal gets crushed. Large particles are broken by impact and full grinding is done by attraction. The Drying and grinding option takes place simultaneously inside the mill.

4. Classifier:- It is an equipment which serves separation of fine pulverized coal particles medium from coarse medium. The pulverized coal along with the carrying medium strikes the impact plate through the lower part. Large particles are then transferred to the ball mill.

5. Cyclone Separators: - It separates the pulverized coal from carrying medium. The mixture of pulverized coal vapour caters the cyclone separators.

6. The Tturniket: - It serves to transport pulverized coal from cyclone separators to pulverized coal bunker or to worm conveyors. There are 4 turnikets per boiler.

7. Worm Conveyor: - It is equipment used to distribute the pulverized coal from bunker of one system to bunker of other system. It can be operated in both directions.

8. Mills Fans: - It is of 3 types:Six in all and are running condition all the time.(a) ID Fans: - Located between electrostatic precipitator and chimney.Type-radicalSpeed-1490 rpmRating-300 KWVoltage-6.6 KVLubrication-by oil

(b) FD Fans: - Designed to handle secondary air for boiler. 2 in number and provide ignition of coal.Type-axialSpeed-990 rpm


Rating-440 KWVoltage-6.6 KV

(c)Primary Air Fans: - Designed for handling the atmospheric air up to 50 degrees Celsius, 2 in number

And they transfer the powered coal to burners to firing.

Type-Double suction radialRating-300 KWVoltage-6.6 KVLubrication-by oilType of operation-continuous

9. Bowl Mill: - One of the most advanced designs of coal pulverizes presently manufactured.Motor specification –squirrel cage induction motorRating-340 KWVoltage-6600KVCurreen-41.7ASpeed-980 rpmFrequency-50 HzNo-load current-15-16 A

NCHP

1. Wagon Tippler:- Motor Specification(i) H.P 75 HP(ii) Voltage 415, 3 phase(iii) Speed 1480 rpm(iv) Frequency 50 Hz(v) Current rating 102 A

2. Coal feed to plant:- Feeder motor specification (i) Horse power 15 HP(ii) Voltage 415V,3 phase(iii) Speed 1480 rpm(iv) Frequency 50 Hz


3. Conveyors:-10A, 10B11A, 11B12A, 12B13A, 13B14A, 14B15A, 15B16A, 16B17A, 17B18A, 18B

4. Transfer Point 65. Breaker House6. Rejection House7. Reclaim House8. Transfer Point 7


9. Crusher House10. Exit

The coal arrives in wagons via railways and is tippled by the wagon tipplers into the hoppers. If coal is oversized (>400 mm sq) then it is broken manually so that it passes the hopper mesh. From the hopper mesh it is taken to the transfer point TP6 by conveyor 12A ,12B which takes the coal to the breaker house , which renders the coal size to be 100mm sq. the stones which are not able to pass through the 100mm sq of hammer are rejected via conveyors 18A,18B to the rejection house . Extra coal is to sent to the reclaim hopper via conveyor 16. From breaker house coal is taken to the TP7 via Conveyor 13A, 13B. Conveyor 17A, 17B also supplies coal from reclaim hopper, From TP7 coal is taken by conveyors 14A, 14B to crusher house whose function is to render the size of coal to 20mm sq. now the conveyor labors are present whose function is to recognize and remove any stones moving in the conveyors . In crusher before it enters the crusher. After being crushed, if any metal is still present it is taken care of by metal detectors employed in conveyor 10.

SWITCH GEAR-

It makes or breaks an electrical circuit.

1. Isolation: - A device which breaks an electrical circuit when circuit is switched on to no load. Isolation is normally used in various ways for purpose of isolating a certain portion when required for maintenance.

2. Switching Isolation: - It is capable of doing things like interrupting transformer magnetized current, interrupting line charging current and even perform load transfer switching. The main application of switching isolation is in connection with transformer feeders as unit makes it possible to switch out one transformer while other is still on load.

3. Circuit Breakers: - One which can make or break the circuit on load and even on faults is referred to as circuit breakers. This equipment is the most important and is heavy duty equipment mainly utilized for protection of various circuits and operations on load. Normally circuit breakers installed are accompanied by isolators

4. Load Break Switches: - These are those interrupting devices which can make or break circuits. These are normally on same circuit, which are backed by circuit breakers.


5. Earth Switches: - Devices which are used normally to earth a particular system, to avoid any accident happening due to induction on account of live adjoining circuits. These equipments do not handle any appreciable current at all. Apart from this equipment there are a number of relays etc. which are used in switchgear.

LT SWITCHGEAR :-

It is classified in following ways:-

1. Main Switch:- Main switch is control equipment which controls or disconnects the main supply. The main switch for 3 phase supply is available for tha range 32A, 63A, 100A, 200Q, 300A at 500V grade.

2. Fuses: - With Avery high generating capacity of the modern power stations extremely heavy carnets would flow in the fault and the fuse clearing the fault would be required to withstand extremely heavy stress in process.It is used for supplying power to auxiliaries with backup fuse protection. Rotary switch up to 25A. With fuses, quick break, quick make and double break switch fuses for 63A and 100A, switch fuses for 200A, 400A, 600A, 800A and 1000A are used.

3. Contractors: - AC Contractors are 3 poles suitable for D.O.L Starting of motors and protecting the connected motors.

4. Overload Relay: - For overload protection, thermal over relay are best suited for this purpose. They operate due to the action of heat generated by passage of current through relay element.

5. Air Circuit Breakers: - It is seen that use of oil in circuit breaker may cause a fire. So in all circuits breakers at large capacity air at high pressure is used which is maximum at the time of quick tripping of contacts. This reduces the possibility of sparking. The pressure may vary from 50-60 kg/cm^2 for high and medium capacity circuit breakers.

HT SWITCH GEAR:-

1. Minimum oil Circuit Breaker: - These use oil as quenching medium. It comprises of simple dead tank row pursuing projection from it. The moving contracts are carried on an iron arm lifted by a long insulating tension rod and are closed simultaneously pneumatic operating mechanism by means of tensions but throw off spring to be provided at mouth of the control the main current within the controlled device.

Type-HKH 12/1000c Page | 32


· Rated Voltage-66 KV· Normal Current-1250A· Frequency-5Hz· Breaking Capacity-3.4+KA Symmetrical· 3.4+KA Asymmetrical· 360 MVA Symmetrical· Operating Coils-CC 220 V/DC§ FC 220V/DC· Motor Voltage-220 V/DC

2. Air Circuit Breaker: - In this the compressed air pressure around 15 kg per cm^2 is used for extinction of arc caused by flow of air around the moving circuit . The breaker is closed by applying pressure at lower opening and opened by applying pressure at upper opening. When contacts operate, the cold air rushes around the movable contacts and blown the arc.It has the following advantages over OCB:-

i. Fire hazard due to oil are eliminated.ii. Operation takes place quickly.iii. There is less burning of contacts since the duration is short and consistent.iv. Facility for frequent operation since the cooling medium is replaced constantly.Rated Voltage-6.6 KVCurrent-630 AAuxiliary current-220 V/DC

3. SF6 Circuit Breaker: - This type of circuit breaker is of construction to dead tank bulk oil to circuit breaker but the principle of current interruption is similar o that of air blast circuit breaker. It simply employs the arc extinguishing medium namely SF6. the performance of gas . When it is broken down under an electrical stress. It will quickly reconstitute itself

· Circuit Breakers-HPA· Standard-1 EC 56· Rated Voltage-12 KV· Insulation Level-28/75 KV· Rated Frequency-50 Hz· Breaking Current-40 KA· Rated Current-1600 A· Making Capacity-110 KA· Rated Short Time Current 1/3s -40 A· Mass Approximation-185 KG· Auxiliary Voltage§ Closing Coil-220 V/DC§ Opening Coil-220 V/DC· Motor-220 V/DC


· SF6 Pressure at 20 Degree Celsius-0.25 KG· SF6 Gas Per pole-0.25 KG

4. Vacuum Circuit Breaker: - It works on the principle that vacuum is used to save the purpose of insulation and it implies that pr. Of gas at which breakdown voltage independent of pressure. It regards of insulation and strength, vacuum is superior dielectric medium and is better that all other medium except air and sulphur which are generally used at high pressure.· Rated frequency-50 Hz· Rated making Current-10 Peak KA· Rated Voltage-12 KV· Supply Voltage Closing-220 V/DC· Rated Current-1250 A· Supply Voltage Tripping-220 V/DC· Insulation Level-IMP 75 KVP· Rated Short Time Current-40 KA (3 SEC)· Weight of Breaker-8 KG

Electrical Maintenance division II

Generator and Auxiliaries Generator and Auxiliaries Generator Fundamentals The transformation of mechanical energy into electrical energy is carried out by the Generator. This Chapter seeks to provide basic understanding about the working principles and development of Generator.


Working Principle

The A.C. Generator or alternator is based upon the principle of electromagnetic induction and consists generally of a stationary part called stator and a rotating part called rotor. The stator housed the armature windings. The rotor houses the field windings. D.C. voltage is applied to the field windings through slip rings. When the rotor is rotated, the lines of magnetic flux (viz magnetic field) cut through the stator windings. This induces an electromagnetic force (e.m.f.) in the stator windings. The magnitude of this e.m.f. is given by the following expression.

E = 4.44 Ф FN volts

Ф = Strength of magnetic field in Weber’s.F = Frequency in cycles per second or Hertz.N = Number of turns in a coil of stator windingF = Frequency = Pn/120Where P = Number of polesn = revolutions per second of rotor.

From the expression it is clear that for the same frequency, number of poles increases with decrease in speed and vice versa. Therefore, low speed hydro turbine drives generators have 14 to 20 poles where as high speed steam turbine driven generators have generally 2 poles. Pole rotors are used in low speed generators, because the cost advantage as well as easier construction.

Development

The first A.C. Generator concept was enunciated by Michael Faraday in 1831. In 1889 Sir Charles A. Parsons developed the first AC turbo-generator. Although slow speed AC generators have been built for some time, it was not long before that the high-speed generators made its impact. Development contained until, in 1922, the increased use of solid forgings and improved techniques permitted an increase in generator rating to 20MW at 300rpm. Up to the out break of second world war, in 1939, most large generator;- were of the order of 30 to 50 MW at 3000 rpm. During the war, the development and installation of power plants was delayed and in order to catch up with the delay in plant installation, a large number of 30 MW and 60 MW at 3000 rpm units were constructed during the years immediately following the war. The changes in design in this period were relatively small. In any development programme the. Costs of material and labour involved in manufacturing and erection must be a basic consideration. Coupled very closely with these considerations is the restriction is size and weight imposed by transport limitations.

Development of suitable insulating materials for large turbo-generators is one of the Page | 35


most important tasks and need continues watch as size and ratings of machines increase. The present trend is the use only class "B" and higher grade materials and extensive work has gone into compositions of mica; glass and asbestos with appropriate bonding material. An insulation to meet the stresses in generator slots must follow very closely the thermal expansion of the insulated conductor without cracking or any plastic deformation. Insulation for rotor is subjected to lower dielectric stress but must withstand high dynamic stresses and the newly developed epoxy resins, glass and/or asbestos molded in resin and other synthetic resins are finding wide applications.

Generator component

This Chapter deals with the two main components of the Generator viz. Rotor, its winding & balancing and stator, its frame, core & windings.

Rotor

The electrical rotor is the most difficult part of the generator to design. It revolves in most modern generators at a speed of 3,000 revolutions per minute. The problem of guaranteeing the dynamic strength and operating stability of such a rotor is complicated by the fact that a massive non-uniform shaft subjected to a multiplicity of differential stresses must operate in oil lubricated sleeve bearings supported by a structure mounted on foundations all of which possess complex dynamic be behavior peculiar to themselves. It is also an electromagnet and to give it the necessary magnetic strength the windings must carry a fairly high current. The passage of the current through the windings generates heat but the temperature must not be allowed to become so high, otherwise difficulties will be experienced with insulation. To keep the temperature down, the cross section of the conductor could not be increased but this would introduce another problems. In order to make room for the large conductors, body and this would cause mechanical weakness. The problem is really to get the maximum amount of copper into the windings without reducing the mechanical strength. With good design and great care in construction this can be achieved. The rotor is a cast steel ingot, and it is further forged and machined. Very often a hole is bored through the centre of the rotor axially from one end of the other for inspection. Slots are then machined for windings and ventilation.

Rotor winding

Silver bearing copper is used for the winding with mica as the insulation between conductors. A mechanically strong insulator such as micanite is used for lining the slots. Later designs of windings for large rotor incorporate combination of hollow conductors with slots or holes arranged to provide for circulation of the cooling gas through the actual conductors. When rotating at high speed. Centrifugal force tries to lift


the windings out of the slots and they are contained by wedges. The end rings are secured to a turned recess in the rotor body, by shrinking or screwing and supported at the other end by fittings carried by the rotor body. The two ends of windings are connected to slip rings, usually made of forged steel, and mounted on insulated sleeves.

Rotor balancing

When completed the rotor must be tested for mechanical balance, which means that a check is made to see if it will run up to normal speed without vibration. To do this it would have to be uniform about its central axis and it is most unlikely that this will be so to the degree necessary for perfect balance. Arrangements are therefore made in all designs to fix adjustable balance weights around the circumference at each end.

Stator

Stator frame:

The stator is the heaviest load to be transported. The major part of this load is the stator core. This comprises an inner frame and outer frame. The outer frame is a rigid fabricated structure of welded steel plates, within this shell is a fixed cage of girder built circular and axial ribs. The ribs divide the yoke in the compartments through which hydrogen flows into radial ducts in the stator core and circulate through the gas coolers housed in the frame. The inner cage is usually fixed in to the yoke by an arrangement of springs to dampen the double frequency vibrations inherent in 2 pole generators. The end shields of hydrogen cooled generators must be strong enough to carry shaft seals. In large generators the frame is constructed as two separate parts. The fabricated inner cage is inserted in the outer frame after the stator core has been constructed and the winding completed. Stator core: The stator core is built up from a large number of 'punching" or sections of thin steel plates. The use of cold rolled grain-oriented steel can contribute to reduction in the weight of stator core for two main reasons:

a) There is an increase in core stacking factor with improvement in lamination coldRolling and in cold buildings techniques.

b) The advantage can be taken of the high magnetic permeance of grain-oriented steels of work the stator core at comparatively high magnetic saturation without fear or excessive iron loss of two heavy a demand for excitation ampere turns from the generator rotor.

Stator Windings

Each stator conductor must be capable of carrying the rated current without overheating. The Page | 37


insulation must be sufficient to prevent leakage currents flowing between the phases to earth. Windings for the stator are made up from copper strips wound with insulated tape which is impregnated with varnish, dried under vacuum and hot pressed to form a solid insulation bar. These bars are then place in the stator slots and held in with wedges to form the complete winding which is connected together at each end of the core forming the end turns. These end turns are rigidly braced and packed with blocks of insulation material to withstand the heavy forces which might result from a short circuit or other fault conditions. The generator terminals are usually arranged below the stator. On recent generators (210 MW) the windings are made up from copper tubes instead of strips through which water is circulated for cooling purposes. The water is fed to the windings through plastic tubes.

Generator Cooling System

The 200/210 MW Generator is provided with an efficient cooling system to avoid excessive heating and consequent wear and tear of its main components during operation. This Chapter deals with the rotor-hydrogen cooling system and stator water cooling system along with the shaft sealing and bearing cooling systems.

Rotor Cooling System

The rotor is cooled by means of gap pick-up cooling, wherein the hydrogen gas in the air gap is sucked through the scoops on the rotor wedges and is directed to flow along the ventilating canals milled on the sides of the rotor coil, to the bottom of the slot where it takes a turn and comes out on the similar canal milled on the other side of the rotor coil to the hot zone of the rotor. Due to the rotation of the rotor, a positive suction as well as discharge is created due to which a certain quantity of gas flows and cools the rotor. This method of cooling gives uniform distribution of temperature. Also, this method has an inherent advantage of eliminating the deformation of copper due to varying temperatures.

Hydrogen Cooling System

Hydrogen is used as a cooling medium in large capacity generator in view of its high heat carrying capacity and low density. But in view of its forming an explosive mixture with oxygen, proper arrangement for filling, purging and maintaining its purity inside the generator have to be made. Also, in order to prevent escape of hydrogen from the generator casing, shaft sealing system is used to provide oil sealing.

The hydrogen cooling system mainly comprises of a gas control stand, a drier, an liquid level indicator, hydrogen control panel, gas purity measuring and indicating instruments, The system is capable of performing the following functions :


Filling in and purging of hydrogen safely without bringing in contact with air.Maintaining the gas pressure inside the machine at the desired value at all thetimes. Provide indication to the operator about the condition of the gas inside themachine i.e. its pressure, temperature and purity. Continuous circulation of gas inside the machine through a drier in order to remove any water vapour that may be present in it. Indication of liquid level in the generator and alarm in case of high level

Stator Cooling System

The stator winding is cooled by distillate. Which is fed from one end of the machine by Teflon tube and flows through the upper bar and returns back through the lower bar of another slot? Turbo generators require water cooling arrangement over and above the usual hydrogen cooling arrangement. The stator winding is cooled in this system by circulating demineralised water (DM water) through hollow conductors. The cooling water used for cooling stator winding calls for the use of very high quality of cooling water. For this purpose DM water of proper specific resistance is selected. Generator is to be loaded within a very short period if the specific resistance of the cooling DM water goes beyond certain preset values. The system is designed to maintain a constant rate of cooling water flow to the stator winding at a nominal inlet water temperature of 40 deg.C.

Rating of 95 MW Generator

Manufacture by Bharat heavy electrical Limited (BHEL)

Capacity - 117500 KVAVoltage - 10500VSpeed - 3000 rpmHydrogen - 2.5 Kg/cm2 Power factor - 0.85 (lagging)Stator current - 6475 AFrequency - 50 Hz


Stator wdg connection - 3 phase

Rating of 210 MW Generator

Capacity - 247000 KVAVoltage (stator) - 15750 VCurrent (stator) - 9050 AVoltage (rotor) - 310 VCurrent (rotor) - 2600 VSpeed - 3000 rpmPower factor - 0.85Frequency - 50 HzHydrogen - 3.5 Kg/cm2Stator wdg connection - 3 phase star connectionInsulation class - B

TRANFORMER

A transformer is a device that transfers electrical energy from one circuit to another by magnetic coupling with out requiring relative motion between its parts. It usually comprises two or more coupled windings, and in most cases, a core to concentrate magnetic flux. An alternating voltage applied to one winding creates a time-varying magnetic flux in the core, which includes a voltage in the other windings. Varying the relative number of turns between primary and secondary windings determines the ratio of the input and output voltages, thus transforming the voltage by stepping it up or down between circuits. By transforming electrical power to a high-voltage,_low-current form and back again, the transformer greatly reduces energy losses and so enables the economic transmission of power over long distances. It has thus shape the electricity supply industry, permitting generation to be located remotely from point of demand. All but a fraction of the world’s electrical power has passed trough a series of transformer by the time it reaches the consumer.


Basic principles

The principles of the transformer are illustrated by consideration of ahypothetical ideal transformer consisting of two windings of zero

resistance around a core of negligible reluctance. A voltage applied to the primary winding causes a current, which develops a magneto motive force (MMF) in the core. The current required to create the MMF is termed the magnetizing current; in the ideal transformer it is considered to be negligible, although its presence is still required to drive flux around the magnetic circuit of the core. An electromotive force (MMF) is induced across each winding, an effect known as mutual inductance. In accordance with faraday’s law of induction, the EMFs are proportional to the rate of change of flux. The primary EMF, acting as it does in opposition to the primary voltage, is sometimes termed the back EMF”. Energy losses An ideal transformer would have no energy losses and would have no energy losses, and would therefore be 100% efficient. Despite the transformer being amongst the most efficient of electrical machines with ex the most efficient of electrical machines with experimental models using superconducting windings achieving efficiency of 99.85%, 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 95%. A small transformer such as plug-in “power brick” used for low-power consumer electronics may be less than 85% efficient. Transformer losses are attributable to several causes and may be differentiated between those originated in the windings, some times termed copper loss, and those arising from the magnetic circuit, sometimes termed iron loss. The losses vary with load current, and may furthermore be expressed as “no load” or “full load” loss, or at an intermediate loading. Winding resistance dominates load losses contribute to over 99% of the no-load loss can be significant, meaning that even an idle transformer constitutes a drain on an electrical supply, and lending impetus to development of low-loss transformers. Losses in the transformer arise from: Winding resistance Current flowing trough the windings causes resistive heating of the conductors. At higher frequencies, skin effect and proximity effect create additional winding resistance and losses. Hysteresis losses Each time the magnetic field is reversed, a small amount of energy is lost due to hysteresis within the core. For a given core material, the loss is proportional to the frequency, and is a function of the peak flux density to which it is subjected. Eddy current Ferromagnetic materials are also good conductors, and a solid core made from such a material also constitutes a single short-circuited turn trough out its entire length. Eddy currents therefore circulate with in a core in a plane normal to the flux, and are responsible for resistive heating of the core material. The eddy current loss is a complex function of the square of supply frequency and inverse square of the material thickness. Magnetostriction Magnetic flux in a ferromagnetic material, such as the core, causes it to physically expand and contract slightly with each cycle of the magnetic field, an effect known as magnetostriction. This produces the buzzing sound commonly associated with transformers, and in turn causes losses due to frictional heating in susceptible cores. Mechanical losses In addition to magnetostriction, the alternating magnetic field causes fluctuating electromagnetic


field between primary and secondary windings. These incite vibration with in near by metal work, adding to the buzzing noise, and consuming a small amount of power. Stray losses Leakage inductance is by itself loss less, since energy supplied to its magnetic fields is returned to the supply with the next half-cycle. However, any leakage flux that intercepts nearby conductive material such as the transformers support structure will give rise to eddy currents and be converted to heat. Cooling system Large power transformers may be equipped with cooling fans, oil pumps or water-cooler heat exchangers design to remove heat. Power used to operate the cooling system is typically considered part of the losses of the transformer

Rating of transformer

Manufactured by Bharat heavy electrical limitedNo load voltage (hv) - 229 KVNo load Voltage (lv) -10.5 KVLine current (hv) - 315.2 ALine current (lv) - 873.2 ATemp rise - 45 CelsiusOil quantity -40180 litWeight of oil -34985 KgTotal weight - 147725 KgCore & winding - 84325 KgPhase - 3Frequency - 50 Hz


REFERENCES :-

1. NTPC LECTURE.

2. P.S. BHIMBRA – A BOOK OF ELECTRICAL ENGINEERING.

3. www.google.co.in

4. THEODORE WILDI .

5. www.wikipedia.com

6. www.scribed.com


http://www.scribed.com/

http://www.wikipedia.com/

http://www.google.co.in/

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