CONTENTS

PREFACE 3

INTRODUCTION 5 - 12

STEAM GENERATION PLANT 13 -19

CAPTIVE POWER PLANT 20 - 57

MAIN RECEIVING STATION 58 - 63

AMMONIA PLANT 64 - 75

UREA PLANT 76 - 84

OFFSITES AND UTILITIES 85 - 90

PROJECT STUDY 91 - 98

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ANKUSH SHARMA

INTRODUCTION

NFL Schedule - A & Mini Ratna Category 2004-2005. - I  Company, is a market leader in the fertilizer Industry in India With 17.0% share in Urea production during 2004-2005.

PERCENTAGE SHARE OF NFL IN UREA PRODUCTION

IN THE COUNTRY (2004-2005)     

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NFL was incorporated on 23rd August, 1974 with two manufacturing Units at Bathinda and Panipat.  Subsequently, on the reorganization of Fertilizer group of Companies in 1978, the Nangal Unit of Fertilizer Corporation of India came under the NFL fold. The Company expanded its installed capacity in 1984 by installing and commissioning of its Vijaipur gas based Plant in Madhya Pradesh.

       NFL Corporate office: Noida

The Vijaipur Plant was a land mark achievement in project management in India.  The plant was completed well within time and approved project cost.  In recognition of this achievement, the project was awarded the First Prize in Excellence in Project Management by Govt. of India.  Subsequently the Vijaipur plant doubled its capacity to 14.52 lakh MTs by commissioning Vijaipur Expansion Unit i.e. Vijaipur-II in 1997.  The plant annual capacities have now been re-rated w.e.f. 1.4.2000 from 7.26 lakh MT of Urea to 8.64 lakh MT for Vijaipur-I & Vijaipur-II Plants each. 

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Three of the Units are strategically located in the high consumption areas of Punjab and Haryana.  The Company has an installed capacity of 35.49 lakh MTs of Nitrogenous Fertilizers and has recorded an annual sales turnover of Rs.3,474 crores during 2004-05.  The Company’s strength lies in its sizeable presence, professional marketing and strong distribution network nationwide.

NFL, a profitable public sector undertaking operates under the administrative control of Deptt. of Fertilizers in the Ministry of Chemicals & Fertilizers.

Kisan Urea  and Kisan Khad NFL’s popular brands are sold over a large marketing territory spanning the length and breadth of the country.  The Company also manufactures and markets Biofertilizers and a wide range of industrial products like Methanol, Nitric Acid, Sulfur, Liquid Oxygen, Liquid Nitrogen etc.  The Company has developed Neem coated Urea which on demonstration has improved the crop yield by 4-5%.  The Company is focusing its thrust to widen the marketing operations of Neem coated Urea.

NFL over the years has developed a team of dedicated professionals in the areas of production, maintenance, project management, safety and environment control.  These professionals are sought after in the Industry both in India & abroad for their Specialized Services.

NFL is known in the industry for its work culture; value added human resources, safety, environment, concern for ecology and its commitment to social upliftment.  All NFL plants have been certified for ISO-9002 for conforming to international quality standards and International Environmental Standard i.e. ISO-14001.   With the certification of Corporate Office/Marketing operations under ISO-9001:2000, NFL has become the first Fertilizer Company in the country to have its total business covered under ISO-9001 Certification.

The System of marketing of Urea has undergone a change w.e.f. 1.4.2003 when company has been allowed to market 25% of its produce outside ECA during Kharif 2003.  This

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percentage of sale outside ECA was raised to 50% in Rabi 2003-04, The same portion prevails for 2004-05 and Kharif 2005.

NFL enters into a Memorandum of Understanding (MoU) with the Government for each year under which the Government undertakes to assist NFL with regard to availability of inputs, obtaining ECA allocations commensurate with the availability of fertilizers from NFL plants etc.  NFL on its part undertakes to adhere to its production and movement plans, achieve its ECA allocation and provide regular feed back to the Administrative department. During the past two and half decades, there has been steady increase in fertilizers consumption and to meet this rise in consumption of fertilizers, it was required to create an additional capacity in order to meet the increasing needs. As oil and gas prices has been increasing day by day since 1973 which effected the whole Industrial sector worldwide led to the change in Energy concept in the whole world and so was India forced to increase its nitrogenous Production by switching to new improved Technology which could make use cheaper and economical source of raw material.

The National Fertilizers Limited (Public Undertaking) was thought to plan two modern large capacity single steam nitrogenous fertilizers plant in order to meet the increasing demands. On 23rd August 1974, NFL was formed and registered to set up two modern large capacity Nitrogenous Fertilizers plants. NFL, Bathinda (Punjab)NFL, Panipat (Haryana)

each with the capacity of 5-11 lakh tones /annum. As to set up any plant there are some essential conditions that support the existence and working of plants for years, so Bathinda was basically selected as one of the site of

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Fuel based plant as per consumption point of view since Punjab is mainly agriculture based state. " Feed in " at Bathinda was achieved on 7th Dec. 1984 and from this project ammonia was successfully produced on 28th May 1979 and urea on 2nd June 1979.NFL was incorporated on 23rd August 1974 in order to implement this project contract were entered into with M/s " TOYO ENGINEERING CORPORATION " a well known Japanese Engg. Company and Engg. India Ltd (EIL), a public sector and Engg. Organization .This contract becomes effective on September 26, 1974 with a guaranteed “Feed in” on the Bathinda Fertilizers project to implement within 36 months from the zero date. Due to the power requirements and some other factors, later on it was planned to set up its own power house known as Captive Power Plant (CPP) with 2 turbo generators of 15 MW each. National Fertilizers Limited (N.F.L.) is the largest manufacturer of nitrogenous fertilizers in the Northern India. It is presently operating four large fertilizers plants, two of which are located at Nangal and Bathinda in the Punjab State, one at Panipat in Haryana and one at Guna in M.P. While plants at Nangal, Bathinda and Panipat are fuel-oil based, the one at Guna is gas-oil based. The overall installed capacity of NFL plants is 10.42 lakh MT per annum.

The old plant at Nangal was commissioned in 1961 followed by expansion which was commissioned in 1978. Bathinda and Panipat plants were commissioned in 1979. Guna Plant which is the latest plant of NFL was commissioned in Dec, 1978 and is now in full production.

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Strategically Located - Urea Plants

Leading Producer of Nitrogenous Fertilizers in the Country.

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Capital Cost, Feed  Stock & Plants Capacity

            

Plants Capital Cost(Rs.Crore)

Feed Stock Existing  Capacity    MT/Year

(Lakh MT/Yr.)

Ammonia Urea CAN Bio-Fert.

  Nangal-I 91.26  Naptha

0.66 - 3.181 -

  Nangal-II299.19

  F.Oil/LSHS2.97 4.785** - -

  Panipat338.41

  F.Oil/LSHS2.97 5.115 - -

  Bathinda349.41

  F.Oil/LSHS2.97 5.115 - -

  Vijaipur-I516.00

  Natural Gas5.016* 8.646* - -

  Vijaipur-II1071.00

  Natural Gas5.016* 8.646* - -

  Indore1.42   Strains - - - 100

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  Total2666.55

  19.602 32.307 3.181 100

PRODUCTS OF NFL

National Fertilizers is producing “Kisan Urea, Kisan Khad and Ankur” on commercial scale. NFL is also marketing number of Industrial products produced as By-Products during the formation of “Kisan Urea, Kisan Khad and Ankur”in its plant itself. FERTILIZERS PRODUCTS

Kisan Urea:Kisan Khad:

INDUSTRIAL PRODUCTS (BY PRODUCTS)

Nitric Acid (HNO3)Sulphur (S) Anhydrous ammonia (NH3) Ammonium Nitrate (NH4NO3) Methanol (CH3OH) Nitrogen (N2)Carbon dioxide (CO2) Sodium Nitrate Oxygen (O2) Carbon (C) from slurry

IMPLEMENTATION AND PROJECT COST OF NFL BATHINDA UNIT

As NFL, Bathinda unit was planned to complete in 36 months from the Zero date 26 Sep.1974, so contract for completing this task was given to the well known Japanese

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company “Toyo Engineering corporation limited”and Indian Consultancy Companies as well. The overall approval cost of Bathinda Unit was Rs. 240.47 Crores with a foreign exchange component which was mainly from Japanese Yen.

REQUIRMENTS OF RAW MATERIAL / INPUTS

Fuel Oil /LHLS 850 MT / Day Coal 1680 MT / Day Water 13 MGDPower 28 MW

PROJECT ’s BENEFITS

Increased Food OutputEmployment to nearly 6000 personsBoth Central and State Government has been benefited by way of excise duties and other local taxes on Raw materials and other products.Scope for marketing by-products such as Sulphur , CO2 , Nitrogen , Oxygen , Carbon etc.

NFL won many major awards related to Safety , Productivity , Pollution control , Longest accident free period .

- An OHSAS-18001 certified unit .- An ISO-9002 and ISO-14001 certified unit .

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STEAM GENERATION PLANT

Steam Generation plant is mainly installed for production of steam and then distributed to various parts of the plant.Here this section of plant installed in National Fertilizers Limited, Bathinda unit produces and supplies steam at 100 Kg / cm2 pressure and nearly 480°C temperature to Ammonia Plant.In today’s world steam has gained importance in Industries. It may be used for power processes and heating purposes as well.

BENEFITS OF STEAM

It is colourless, odourless and tasteless .Very economicalNon pollutingCan be used as heat exchanger.It can be easily distributed to various sections of plant.

Steam is generated in Boilers(Water tube boilers mounted on common base fitted with mountings and fittings) and then distributed to other parts of plants . For governing the quantity of fuel to be burned and for maintaining the required pressure their are many automatic fuel feeders, equipments and auxiliaries like pressure gauge etc.

In the Boilers used at National Fertilizers Limited (Bathinda unit); coal, oil natural gas are used as a fuel for production of steam.

NFL , Bathinda is using steam for two purposes ; first and the main reason is for running prime mover and other reason is to exchange heat in the processes taking place their. There are three boilers capable of producing steam at the rate of 150 Tonnes/hr installed in CPP which were supplied

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and erected b BHEL. Generally two boilers are enough to meet the requirements but third boiler is simultaneously running because if steam load consumption increases then the third boiler play its part in order to avoid any faulty condition.

FUELS USED :

Coal : To obtain steam of desired Temperature and pressure, coal is burned to give major source of heat. Initially coal is stored at Coal Handling plant brought from coal sites. It is this section of plant where coal is crushed by crushers in order to make small pieces of coal, then after crushing it the coal pieces rare passed through heavy electromagnet where iron is separated from coal if present. Coal is then sent to Bunkers from where it goes to Grinding mill. Grinding mill is grinding coal into powder form.Conveyor Belts are being used in the whole plant for transportation of Coal. The powder form of coal is sent to the Boilers through pump as pump sucks the coal from grinding mills and throws it into the boiler for combustion. Fuel Oil : As the Boilers are designed to work on both Coal as well as Fuel Oil so fuel oil can also be Pumped to Boiler for combustion.Generally coal alone is not burnt Initially but Fuel Oil(LSHS) is mixed coal and then sent to the furnace for combustion in order to get desired temperature .Flue gases produced which are very hot surrounds the water tubes (Tubes carrying water).When hot flue gases surrounds the water tubes, the temperature of water in tubes starts rising ,as a result Steam is generated.

WHY AND WHERE STEAM IS REQUIRED

As National Fertilizers Ltd, Bathinda unit has its own Steam Generation Plant where steam is produced which is used for driving Turbo Compressors, Heating Purposes, for various reactions taking place in the plant itself.

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Steam is mainly consumed in the Ammonia Plant as nearly 6 to 7 tonnes of steam is required to produce 1 tonne of Ammonia. High Pressure Turbines are being used where high pressure and temperature is to be maintained so SGP section plays a important role for maintaining the said condition. There are three boilers (VU-40 type supplied by M/S BHEL) of 150 tonne/hr capacity .These boilers are Water Tube Boilers i.e water is inside the tubes and hot air surrounds it when coal is burnt ,this makes the water in the tubes boil and steam formation takes place. In the beginning coal is burnt with fuel oil in order to get desired temperature. FIRING SYSTEM : As coal brought from various sites is in form of big pieces of various sizes , so first it is reduced in smaller pieces known as pulverized coal which is then further grinded using BOWL MILLS so that it burns completely in the furnace to give proper combustion. Coal received from material handling plant is stored in coal bunker and is fed to bowl mill through a coal feeder .Hot air is also supplied in the mill for heating the coal and conveying it to furnace through a fan called EXHAUSTER FAN which takes suction from the mill and maintains it under negative pressure. Oversize and un grind able material like stones are thrown out by the mill. Pulverized fuel i.e mixture of coal and air is supplied to Coal Burner through Exhauster. Coal burners are arranged tangentially on all the four corners of the rectangular furnace at three elevation levels. Thus there are total 12 Burners. In between these, three elevations Oil Burners and Start Up Burners/Igniters are arranged at two elevations. Thus there are 8 Oil Burners and 8 Igniters.Igniters use Light Diesel Oil (LDO) .Oil Burners use Heavy Fuel Oil .The Furnace is a cubical suspended enclosure with water tubes forming its four walls. The furnace is designed with sufficient volume to provide for complete and efficient combustion at all loads without flame impingent by the reaction of carbon present in coal and the oxygen present in the air to form Carbon-Di-Oxide.

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C + O2 ▬► CO2 + Heat

WATER AND STEAM SYSTEM As the steam being used should be free from impurities like minerals, silica, oxygen, Iron etc. in order to insure Safe and Efficient working of Steam turbines and Boilers. For this purpose Raw Water is physically and chemically treated and finally supplied to Steam Generation Plant from Ammonia plant. This water is called Boiler Feed water which is further heated to 240º C by the flue Gases and taken to Steam Drum. Steam Drum Acts as storage tank and also separates water from the steam at 315º C and 106 kg/cm2 pressure water then enters the Ring Header formed at on the bottom of outside the furnace and rises by gravity through water wall tubes on the all the four sides ,taken heat from furnace and enters steam drum as a mixture of steam and water.

FLUE GAS SYSTEM

The products of combustion in the furnace consist of carbon-di-oxide, nitrogen, ash, oxygen and sulphur-di-oxide. After leaving the furnace the heat Of these gases called FLUE GASES, is utilized at various levels.

First the steam from steam drum is heated in two super heaters to get the required temperatures of 4950C and then feed water in BANK TUBES is also heated and the gases leave bank tubes at around 4970C next the heat is utilized to heat feed water in the ECONOMIZER and gases are cooled down to 3200C. These gases are further cooled down to 1500C in ROTARY AIR HEATER where the air is required for combustion and conveying the coal is heated up. Temperature is not reduced further because at lower temperature oxides of sulphur present in flue gases are converted to ACID which damages the down stream equipments. These gases then pass through ELECTRO STATIC PRECIPITATOR (ESP) where ash is removed. From ESP these gases pass on to INDUCED DRAFT FAN which maintains draft in the furnace and finally the gases

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are let off to the atmosphere through a chimney about 80mtr high.

POLLUTION AND THEIR DISPOSAL

Along with optimum utilization of company’s resources to achieve maximum profitability, our unit has always performed its duty to keep the environment clean. We have installed latest available pollution control instruments and equipments. The chief pollutants generated in SGP are ASH and SULPHUR –DI-OXIDE. Their separation and disposal are discussed in brief.

ASH: Ash is the incombustible material contained in raw coal which has about 40% ash. It also consists of heavy metals like vanadium and nickel. If inhaled it can be harmful to human beings. After combustion of coal, ash remains as such. About 20% ash of total ash generated consist of higher wt. particles which fall down to BOTTOM ASH HOPPER provided at the bottom of the furnace. Ash slurry is formed here due to water level maintained in the bottom ash hopper. This is taken out by water ejector once in eight hours and sent for disposal in lagoons.

FLY ASH:

Fly ash is the ash containing light particles. It forms the major portion that is 80% of the ash generated. It is carried away from the furnace along with the flue gases. The ash particles are removed from the gases in electro-static precipitators as shown in block diagram after air-pre heaters.

ELECTRO-STATIC PRECIPITATORS: The electro-static precipitators’ forces to separate out dust particles from the flue gas. High voltage is applied between electrodes arranged in rows alternately. Due to high voltage gas particles are ionized. Most of the ions are negatively charged. They stick to dust particles and carry them to

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positively charged electrodes which are in the form of a rectangular plate. Thus dust particles stick to those plates. These plates are rapped periodically to dislodge the deposited dust which is collected in the hopper below.Ash is ejected from these hoppers by water jet and it forms ash slurry. Fly ash slurry and bottom ash slurry are mixed together and sent to ash slurry disposal ponds outside the factory where the slurry settles down and overflowing clear water is recycled back to the system.

SULPHUR-DI-OXIDE:

Sulphur-di-oxide is formed due the presence of sulphur in coal which varies from 0.1% to 0.5%. For safe disposal of SO2 minimum chimney height has been recommended by pollution boards, depending upon the quantity of sulphur-di-oxide generated per hour. In our case it comes out to be around 75 mts. taking maximum amount of SO2 generated. Chimney height of SGP boiler is 80mtrs.Suitable instrumentation has been provided for monitoring all

the parameters and important analyzers and cutouts of a part or even complete boiler has been provided in case of emergency.

MAIN EQUIPMENT

ECONOMIZER

The main function of Economizer is to preheat the boiler water before it is introduced into the steam drum. It recovers some of the heat from the flue gases leaking out of the boiler. The economizer is located in the second pass of the boiler above the air heater. Each section is composed of number of parallel tubes circuit which is arranged in the horizontal rows. All tubes circuit originated from inlet header and discharge at outlet header.

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Feed water is supplied to inlet water header via free of stop and check valves. The feed water flow is upward through the economizer that is in counter flow to the hot flue gases. Any chance of steam generation within the economizer is eliminated by the upward water flow that is led to the drum via the economizer outlet link.

SUPER-HEATER

The main function of the super-heater is to superheat the steam. Super heater is located at the outlet of the furnace.

OPERATION Before lighting off the unit, open wide inlet and outlet header drains, vents links drains and main steam line drains. Close all the drains prior to lighting off when the headers and links appear free of water drain that senses as a starting drain header drain and is kept open after the unit is on line.

DE SUPER-HEATER

Mainly the function of De super heater is to reduce the temperature of the steam. De super heater are provided in super heater connecting links to permit reduction of steam temp. When necessary and to maintain the temperature at design values within the limits of the nozzle capacity. Reduction in the steam temperature is accomplished by injecting spray water into the path of the steam; the spray water source is the boiler feed water system. It is essential that the spray water should be chemically pure and free of suspended and dissolved solids. Containing only approved volatile organic treatment materials in order to prevent the chemical deposition in the super heater.

DRUM

It is necessary to separate the saturated steam from the steam water mixture for circulation type boiler. This performance is achieved by steam separators arranged in the drum.

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CAPTIVE POWER PLANT

INTRODUCTION:

National Fertilizers Limited has set a Captive Power Plant (CPP) at their complex at BATHINDA, to ensure availability of stable, uninterrupted power and stream to the Ammonia and Urea plant. This will minimize the tripping of the Fertilizer Plant due to transit voltage dips and power cuts.

Since inception, Bathinda unit was drawing electric power from Punjab State Electricity Board (P.S.E.B). Electricity is the main driving force after steam in the plant, being used for moving auxiliary equipments. The unit requires 27MW of power/hr when running at full load. There are two 15 MW turbo-generators to generate power. Under normal running conditions of the plant and healthiness of the P.S.E.B. grid, we generally run in synchronism with the grid merely drawing the power corresponding to the minimum charges to be paid to state electricity board. In case of any disturbance in the grid, our system gets isolated from the grid automatically. With both generators running, we are able to feed power to the whole plant, thus production is not affected. In case only one turbo generator is in line and grid cuts off, urea plant is cut off automatically to balance the load with one generator. As soon as the grid becomes stable, the generators are again synchronized with it. The power generation of each generator can be varied with 2 MW to 15 MW maximum, provision exists to run the generator on 10 % extra load continuously for one hour only.

Operation of C.P.P. is based upon microprocessor based computerized instrumentation which allows automatic operation, start up, shut down of the whole or part of the plant.Latest instrumentation has been used in this plant. It allows controlling process variables like flow, pressure, temperature,

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power factor, voltage, frequency, etc. There is operator interface unit (IOU) LIKE A TV screen on which various parameters can be displayed and controlled. It allows fully automatic start-up, shut-down of boiler, turbine and other auxiliaries.

NEED FOR C.P.P. :

It was thought to install a captive power plant in which electric power for our requirement shall be generated in a COAL FIRED BOILER. The benefits envisaged were:

1. Any disturbance in the PSEB grid used to trip the whole plant. Lot of money was lost due to this as each re-startup costs around 40 to 50 lakhs rupees. Moreover, frequent tripping’s had an ill effect on machines and equipments extending the re-startup period.

2. Three boilers of 150Te/hr steam capacity were initially installed in SGP to keep 25 boilers running and one stand by as designed steam requirement was less than 300Te/hr. but in actual operation steam requirement was more and all three boilers had to be run and there was no breathing time for their maintenance. As new boiler was to be installed for CPP, its capacity was so designed that it could export around 60Te of steam for process requirement so that only 2 boilers of SGP would be run keeping the 3rd as stand by.With these points in mind CPP was installed. The functioning of CPP can be sub-divided into parts:

BOILER AND ITS AUXILIARIES : For generation of high pressure superheated steam.

TURBO-GENERATOR AND ITS AUXILIARIES: To generate power, using steam from the boiler.

Operation of CPP is based upon microprocessor based computerized instrumentation which allows automatic operation, start up, shut down of the whole or the part of the plant.

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BOILER

The basic principle of this boiler is the same as discussed earlier for SGP boiler that is formation of steam by heating boiler feed water inside furnace fired by coal and heavy oil, utilization of heat of the gases and venting these gases at a safe height. Main differences between the two boilers are:

SGP boiler is tangentially fired where as CPP boiler is front fired with 6 coal burners and 6 oil gun fixed inside the coal housing.

SGP boiler can be loaded up to 30% load with oil firing only whereas CPP boiler can be fully loaded with oil alone.Height of combustible zone in CPP boiler is more and it has residence time of 1.5 sec where SGP boiler has 1.0 sec.Mills used for pulverizations of coal in SGP are negative pressure bowl mills whereas in CPP ball tube mill are used which are positive pressure mills.

Due to more residence time and better pulverization the efficiency of CPP boiler is about 4% higher.Boiler feed water required for steam generation can be fully generated in CPP itself.

A part of the steam generated is exported for process use in ammonia plant and rest is utilized for power generation in turbo generators as described below:

DESCRIPTION MITSUI RILEY TYPE BOILER Maximum evaporation 2,30,000kg/hrDesign process for boiler 124kg/cm2GSteam temp at outlet 4950CHeating surface 1250M2

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FUEL COAL SYSTEM

The purpose of fuel coal system is to pulverize coal to dry coal and to convey the pulverized coal from ball tube mill to burners by primary air for coal firing.Fuel coal system consists of three systems:coal supply system.primary air system.seal air system.

COAL SUPPLY SYSTEM

PRIMARY AIR SYSTEM

The primary air system performs two functions. It provides the proper amount of air required to convey the pulverized coal to the burners and the heat necessary to dry coal so it can be pulverized and burned efficiently. The details of primary air fan are:-

Make MEIDENDegree of protection IP 55No of poles 4Frequency 50HzRPM 1475Power factor 0.89Insulation class FRated power 195kWType of construction IEC-34Normal temp rise limit 700C

SEAL AIR SYSTEM

Coal bunkers

Coal feeders

Crushers dryers

Ball tube mill

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The seal air is distributed to the components by the sealing of the mill system by the sealing air fan. The sealing air fan takes suction from silencer and discharges it to a common header. The controller for each mill system provides a constant differential pressure to protect against coal leaking into the bearings and seals. This system should be in service before being placed in operation.

CRUSHER DRYER SYSTEM

Crusher-dryer performs the CRUSHING function. Metered coal from the feeders blends with a properly heated amount of air from the primary air fan and enter the crusher dryer. The non clogging pre crushing flash dryer operates continuously at constant speed. Rotating hammers drive the incoming coal against a breaker plate and adjustable crusher block, increasing the surface area of the coal and mixing it with the incoming preheated air.

BALL TUBE MILL

Grinding the coal to the proper fineness is done by ball tube mill. The crushed coal and air mixture from the crusher dryers enter the mill through the mill inlet boxes on both ends of the mill. The mill barrel rotating at constant speed, contains thousands of kilograms of various sizes of hardened steel balls which cascade down upon the entering coal and pulverize it to talcum powder consistency. The heated primary air, entering with coal, not only completes the drying process, but now conveys the coal dust from the mill through the mill output boxes to the classifiers on both ends of the mill. The specifications of the ball tube mill are as:-

Make MEIDENDegree of protection IP 55Insulation class FNo of poles 4Voltage 3300VFrequency 50Hz

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Current 98APower factor 0.89Type of construction IEC-34Power rating 445kW Connection YTemp. risk limit normal 700CRPM 1430

The pulverized coal from the BTM is fed to the boilers with the help of primary air fans. The coal is burnt in the boiler to generate steam to move the turbines. The forced and induced draft fans are used to assist in the combustion of fuel and steam production. These two major types of fans supporting the units operation.

FORCED DRAFT FAN

The forced draft fans supply the proper amount of secondary air required to support the combustion of the fuel delivered to the boiler. The details of the FD fan are:

Make MEIDENRating ContinuousInsulation class FRated power 320kWVoltage 3300VPower factor 0.85Current 71ARPM 980Poles 6Connection Y

INDUCED DRAFT FAN

The induced draft fans control the furnace draft by drawing the gases of combustion through the boiler, regenerative air heaters, delivering them to the stack. Thus the FD fan provides combustion air for the furnace while the ID fan removes flue

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gases from furnace through chimney. The details of the ID fan are:

Make MEIDENRating continuousInsulation class FRated power 295kWVoltage 3300VPower factor 0.83Current 67.5ARPM 735Poles 8Connection Y

POWER GENERATION:

In C.P.P. two generators of 15MW capacity generate a voltage of 11KV which is fed to the two transformers in the yard. The rating of the transformers is 31.5/25 KVA, these two values depend upon the cooling which we provide, as here 25KVA capacity is when cooling is oil natural air natural and 31.5KVA capacity is when cooling is oil natural air forced. Both these transformers step up the voltage level to 132KV. From the transformers the three phases pass through the lightning arrestors (LA). After this they pass on to the isolator. After this the two lines pass on to the TRANSMISSION pole called DOUBLE CIRCUIT TRANSMISSION. Then these lines go to the M.R.S. i.e. main receiving station.

TURBINE:

The turbine used is supplied by M/S SGP of AUSTRIA. It is condensing cum extraction turbine designed as single casing reaction turbine with single control stage and high pressure (HP), mild pressure (MP) and low pressure (LP) reaction parts. The turbine is fed with high pressure steam at 100kg from boiler and flows through various control valves for normal and emergency operation. It gets high velocity through the nozzle group and then passes over the impellers fixed on to the rotor and fixed diffusers thus rotating the turbine. The enthalpy of

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steam is utilized in steps. Steam is also extracted from various stages. HP1 at 10.4kg/cm2, HP2 at 8.1kg/cm2, feed water bleed at 4.3kg/cm2 and LP bleed at 0.9kg/cm2.

The exhaust steam from the turbine is condensed in a condenser maintained under vaccum to extract maximum steam enthalpy. The output of the turbine depends on flow of steam and heat difference that is on condition of steam at the main steam valve and the pressure at the turbine outlet or condenser pressure. The turbine is connected to the generator through speed reducing gears.

The exhaust steam is condensed in a condenser using cooling water. The resulting condensate can be fed back to LP heater but is normally sent to the polishing water plant.

As shall be clear from the attached block diagram various bleeds from the turbine are utilized for heating purpose. HP1 and HP2 are used for heating boiler feed water in HP1 and HP2 heaters. Feed water bleeds is used for heating the feed water tank and LP bleed is used for heating the polish water make up to the feed water tank.

A lubrication system is also there to lubricate the various bearings of the turbine, gears and generator. Normally the oil pump driven by the turbine shaft supplies oil but auxiliary motor driven pumps are used for start up and during shutdown. A turning gear has been provided for slow cooling of turbine rotor.

Latest instrumentation has been used in this plant. Bailey’s net work-90 microprocessor based instrumentation system is being used. The NETWORK 90 SYSTEM is a distributed process control system. Using a series of integrated control nodes. The network 90 system allows controlling process variables like flow, pressure and temperature according to a control configuration. There is operator interface unit (OIU) like a TV screen on which various parameters can be displayed and controlled. It allows fully automatic start-up/shut-down of boiler, turbine and other auxiliaries.

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DESCRIPTION :-

Make Simmering Graz Panker, AustriaType Multifunction (28 stages)Capacity 65 T/H at 15 MWRPM 6789 at 50 HzCritical speed 3200-3600 RPM

GENERATORS CPP is having two number turbo generators of capacity 15MW each. The generators are type SAT three phase, 50Hz, 11kV, 984amps, at 0.8 power factor rating supplied by M/S JEUMONT SCHNEIDER OF FRANCE. These are totally enclosed self ventilated type with two lateral airs to water coolers for cooling. The alternators are able to bear 10% overload for one hr with an increase in temp. of 100C while maintaining the voltage as near as possible to the rated one. The excitation is compound and brush less with exciter rotor and Rectifier Bridge mounted on the extended main shaft on non driving end. The excitation is controlled automatically with automatic voltage regulator and a PLC controller. All protection relays installed for protection of generator are solid state having high accuracy, quick response and low power consumption.

Under normal running conditions of the plant and healthiness of the PSEB grid, we generally run in synchronism with the grid merely drawing the power corresponding to minimum charges to be paid to state electricity board. In case of any disturbance in the grid measured by higher low frequency, high rate of change of frequency, low voltage etc. our system gets isolated from the grid automatically. With both generators running, we are able to feed power to the whole plant, thus production is not affected. In case only one TG is in line and grid cuts off, urea plant is cut off automatically to balance the load with one generator. As soon as the grid becomes stable, the generators are again synchronized with it. DESCRIPTION:-

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SYNCHRONOUS GENERATOR:

Make Jeumont-Schneider--FranceDegree of protection IP 54Type of excitation Brush lessInsulation class Stator F Rotor FTemp. Rise Stator 70 0K Rotor 70 0KMaximum Inlet temp. Air 50 0C Water 36 0CAltitude 236 mDuty ContinueGenerator weight 44000 kgOutput 18750 KVA Connection star-deltaVoltage 11000 VCurrent 984 AFrequency 50 HzPhases 3Speed 3000 rpm Permissible over speed 3600 rpmTime 2 minute Power factor 0.8 Excitation voltage 163 VExcitation current 580 AMoment of inertia (wr2) 5684 kgm2

DIFFERENT PARTS OF TURBO GENERATOR

STATOR

a) STATOR BODY

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The stator body is totally enclosed structure, suitably ribbed internally to ensure high rigidity. It is designed mechanically to withstand internal pressure of explosion of any type inside.Rigid ends shields close the casing and support the fan shields and shaft seals. The end shields are made in two halves for convenience during erection and inspection.

b) STATOR CORE

The stator core is made up of segmental, vanish-insulated lamination of cold rolled grain oriented silicon steel assembled in an interleaved manner on core bars. The core consists of several packets separated by steel spacers for radial cooling of the core by coolant.

c.) STATOR WINDINGS

The stator has a three phase, double layer short chorded bar type windings having two parallel paths. Each coil side consists of glass insulated solid and hollow conductors with cooling water passing through the latter. The elementary conductors are transposed in the slot portion of winding to minimize eddy losses. An adequate protector is provided to avoid corona and other surface discharges in the slots the coil sides are firmly held in position by fibrous slot wedges, which are mechanically strong and have high dielectric properties.

The overhang portion of the coils is secured and lashed with glass chord to bandage rings and special brackets of non magnetic steel, which in turn fixed to the core press rings. On short circuit, the forces between the conductors tend to open the cone formed by over hang portion of the coil, but the movement is effectively prevented by supports.

ROTOR

a) ROTOR BODY

The rotor is of cylindrical type, the shaft and the body being in one piece and formed from chromium, nickel, molybdenum

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and vanadium steel. Prior to machining, a series of comprehensive ultrasonic examination and other tests are carried out on rotor body and shaft position to ensure that there is not any internal defect. The rotor with all the details assembled is subjected to 20% over speeding for two minutes ensuring mechanical strength.

b) ROTOR WINDINGS

The rotor winding is made from hard drawn silver bearing copper. Rotor winding is held in position against centrifugal forces by duralumin wedges in the slot portion and by non magnetic steel retaining rings in the overhang portion. Gap pick up system is employed for direct air-cooling of windings. Several groups of ventilation holes are milled on the sides of the rotor coil for passage. The rotor slot wedges are of special profile with elliptical holes milled in to match the ventilation ducts (holes) on the winding stack. The main slot insulation in the form of U-trough made of glass cloth impregnated with epoxy resin. The U-profile facilitates easy flow of gas from one side to the other side of the coil stack. The inter turn insulation consists of layers of glass cloth glued to bottom of each conductor and consolidated on required condition of temperature and pressure. The end windings are packed with block of glass laminates to separate and support the coil and to restrict their movement under stress due to thermal and rotational forces. The end windings are insulated from retaining rings with the help of glass epoxy moulded segments. Copper segment type damper winding is provided in the end zones of rotor during asymmetrical and asynchronous operation.

c) ROTOR SHAFT

Shaft end and rotor are integrally forged of high quality steel. The slots receiving the field windings are matched and machined into the rotor body.Space heater

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One space heater is located at the base of the stator to avoid humidity when the generator is not running phase.

SOLE PLATES The slot plates on which the generator is bolted and secured ensure perfect stability without vibrations and permit a very simplified process of erection and contingently of disconnecting of turbo generator.

BEARINGS

Two end shield sleeve bearings with forced oil lubrication are provided. These bearing reduce the friction coming in the way of rotation of the rotor. The oil is continuously circulated to dissipate the heat generated due to the working of bearings.

EXCITER

DESCRIPTION

Totally enclosed, cooled with cold air supplied by the main generator (without bearings)Invented alternator with stationary field and rotating armature.It feed the generator field through a rectifier bridge mounted on the shaft.

ROTATING ARMATURE

The laminations cut in one piece, insulated after the slots, are shrunk on arm that has to be keyed on the shaft. The armature winding is installed in open slots, secured in position and connected to a rotating bridge rectifier.

STATOR

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The frame consists of a laminated magnetic ring on which main pole core is bolted. The field coils are secured on the pole cores.

RECTIFIER BRIDGE

Rectifiers are mounted in Grates Bridge and use two types of cells. Each arm of bridge uses 3 cells in parallel and each elementary rectifier bridge is a protected fuse.

EXITATION AND REGULATION CHANNEL

The main generator excitation system consists of an exciter from the shaft end of the main generator and outputting to its own rotor circuit. The exciter consists of an inverse generator and a bridge of rotating rectifier. An excitation device supplying the exciter field winding.A compound part comprising transformer TS, TSE and diode bridge RD. A shunt part comprising transformer TEX1 + TEX2 and the controller thyristor bridge THY. The diode and Thyristor Bridge are connected in series to supply the exciter inductor.A controller with limiter regulating the excitation of the exciter through the thyristor bridge (AVR).

UNINTERRUPTED POWER SUPPLY : -

The uninterruptible power supply system is connected between a critical load, such as digital drives & automation, distributed digital process control system, telecom equipment, programmable logic controller, mission critical applications, computer and its three phase mains power supply under all rated load and input supply conditions.

The system offers the user with the following advantages: -Increased power supply: -

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The UPS has its own internal voltage and frequency regulator circuits which ensure that its output is maintained within close tolerances independent of voltage and frequency variations on the mains power lines.

INCREASED NOISE REJECTION : -

By rectifying the input A.C. power to D.C. power and then converting it back to A.C., any electrical noise present on the input mains supply line is effectively isolated from the UPS output, therefore the critical load sees only clean power.Power blackout protection: -If the mains power fails, the UPS continues to power the critical load from its battery source, leaving the load immune from power disturbances.

REDUNDANT Vs NON REDUNDABT CONFIGURATIONS:-

In a non-redundant configuration the system is sized such that both UPS modules are required to feed the potential load and if one of the two modules develops a fault or for some reason shut down, the other module also automatically shuts down. In such an event the load is transferred to an unprocessed bypass supply.In a redundant module configuration the system is sized such that the potential load can be provided by just one of the two modules. Under normal circumstances both modules are operational and share the load current equally; but if one module develops a fault, or is shut down, the second module is able to take over the full load demand and continue to provide it with processed, backed-up power. 7400 Module Design:-

The UPS basically operates as an AC- DC-AC converter. The first conversion stage (from AC to DC) uses a 3 phase fully controlled silicon controlled rectifier (SCR) bridge rectifier to convert the incoming mains supply into a regulated 432V DC bus bar.The DC bus bar produced by the rectifier provides both battery charging power and power to the inverter section-which is of a

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transistorized / IGBT based pulse width modulation (PWM) design and provides the second conversion phase i.e. reconverting the DC bus bar voltage back into an AC voltage waveform.During normal operation both the rectifier and inverter sections are active and provides regulated load power whilst simultaneously float charging the battery. In the event of a mains power failure, the rectifier becomes inoperative and the inverter is powered solely from the battery.Critical load power is maintained under these conditions until the battery is fully discharged, whereupon the UPS shuts down. The end of battery discharge is assumed when the battery voltage falls to 320V DC.The period for which the load can be maintained following a mains power failure is known as the system’s ‘Autonomy Time’ and is independent upon both the battery A/Hr capacity and the applied percentage load.

Fig.1 Series 7400 UPS isolator configuration

BYPASS SUPPLIES :- The circuit block annotated ‘Static Switch’ in figure 1 shown above contains an electronically controlled switching circuit which enables the critical load to be connected either to the inverter output or to a bypass power

BATTERY BATTERY

º

º

INVERTER INVERTER

RECTIFIER RECTIFIER

STATIC SWITCH

STATIC SWITCH ºººº

ºº

º

º

º

ºº

BATTERY ISOLATOR

INPUT ISOLATOR

BYPASS ISOLATOR

MAINTAINANCE BYPASS ISOLATOR MAINTAINANCE BYPASS LINE

STATIC BYPASS LINE

MAINS SUPPLY

BYPASSSUPPLY

OUTPUTISOLATOR

UPS OUTPUTSUPPLY

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source via a ‘static bypass line’. Normally the load is connected to the inverter; but in the event of a UPS overload, or inverter failure, it is automatically transferred to the static bypass line due to static switch action. To provide a clean (no-break) load transfer between the inverter and static bypass line, the inverter output and bypass supply must be fully synchronized during normal operating conditions. A second manually controlled, ‘maintenance bypass’ supply is also incorporated into the UPS design. Its purpose is to enable the critical load to be powered from the mains (bypass) supply while the UPS is shut down for maintenance or troubleshooting. The two modules can be used in parallel using a common battery or separate battery for each module. In ammonia plant the modules are used in parallel using a common battery. This is shown in figure . For connecting the two modules in parallel the following thing should be taken care of:-

SYNCHRONIZATION:- as the outputs from both the UPS modules are connected together to provide a single load supply, it is imperative that the inverters are fully synchronized in frequency and phase. This is achieved by digitally locking the two inverters control oscillator. The inverter control oscillators are not only locked together but are also made to track the bypass frequency. This is done so as to provide a clean (no-break) load transfer between inverter and static bypass line.A “common battery” option kit contains a DCDT (DC current transformer) which is fitted to the battery power lines and monitored by the parallel control logic. Each module monitors its battery charge current and compares it with the charge current provided by the other module. This enables a module to match its charge current to that of its partner by effecting the voltage control over the rectifier section.

PROTECTION SYSTEM FOR ELECTRICAL NETWORK IN C.P.P

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With the installation of C.P.P at N.F.L Bathinda, almost all groups of power engineering have been covered. Their main groups are mainly :

Generation TransmissionDistributionUtilization

For handling the quantum of power, intricate protection system is required. Financial reliability for protection is another requirement. It has been seen if all requirements are met with the system can be handled well.

In the C.P.P following fields of electrical engineering can be formed. The general protection provided is:-

GENERATOR

DifferentialOver current (inverse, voltage controlled)Rotor earth faultField failure (protection against asynchronous operation)Stator earth faultInstantaneous over voltageNegative phase sequence (Unbalanced loading)Overload (sustained overloading of machine)Reverse power (protection against protection)Under power

POWER TRANSFORMER

DifferentialOverload IDMTLRestricted earth fault (Winding protection)Backup earth faultBuchholzTemperature (oil & Winding)

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FEEDER TRANSFORMER OR DISTRIBUTION TRANSFORMER

Over current & earth faultRestricted earth faultBackup earth fault BuchholzDifferential

TRANSMISSION LINE

Differential (pilot wire)Over currentEarth fault

HIGH TENSION MOTORS

Over currentPhase imbalanceEarth faultThermal overload (sustained)Locked rotorUnder voltage

LOW TENSION MOTORS

FuseThermal overload

TYPES OF PROTECTION AT VARIOUS POINTS IN C.P.P

L.T MOTOR FEEDERS AND DISTRIBUTION FEEDERS

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Thermal overloadBackup protection as M.C.B (miniature circuit breaker)Fuse protection

Incomers of M.C.C’s (motor controlling current)Current breaker with short circuit protection of M.C.B’s

OUTGOING L.T FEEDERS AT 415V P.C.C (POWER CONTROL CENTRE)

IDMTL over current with high set instantaneous element extreme inverse.

INCOMING OF 415V P.C.C

IDMTL over current relayRestricted earth fault relay for transformerBackup earth fault relay for transformerBuchholz tripping transformerUnder voltageWinding temperature alarm onlyOil temperature

HT MOTOR FEEDERS FOR 3.3KV SWITCH BOARD

Earth fault elementOver current elementNegative sequence elementOverload elementLocked rotor elementIncoming feeders for 3.3KV switch BoardIDMTL over current relayRestricted earth fault relayBackup earth fault relayBuchholz tripping transformerUnder voltageWinding temperature alarm onlyOil temperatureOil level

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OUTGOING FEEDERS FOR 10MVA TRANSFORMER (11/3.3KV)

IDMTL Over current with high set instantaneous protectionDifferential protection inter tripping.

OUTGOING FEEDERS FOR 2 MVA TRANSFORMER (11/415V)

IDMTL Over current with high set instantaneous protectionDifferential protection inter tripping

OPERATIONAL LIMITS OF TURBO GENERATOR

There are five principal electrical design and operational limits and each is discussed shortly below:-

ROTOR CURRENT LIMIT

This limit is set by the type and classification of the rotor windings insulation. Most of the alternators are insulated to class B and this means that the insulating material used will withstand temperatures up to 130C and above this temperature the winding insulation deteriorates with heat leading to a short hand life and ultimate failure.In the turbo generator used in C.P.P insulation material is of class F hence provides the maximum temperature range up to 240C.

STATOR CURRENT LIMIT

As stated for the rotor current limit, the maximum allowable temperature for the type winding insulation material used limits the stator current. The temperature to which windings are subjected will depend mainly on stator current flowing through them assuming that the stator winding coolant inlet temperature and flow rate are reasonably constant.

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The manufacture therefore stipulates the maximum allowable stator current and this will correspond with the maximum allowable temperature for the class of insulation used.If the alternator is operated with the maximum rated current flowing at the rated generator terminal voltage, then the maximum continuous MVA rating will be achieved.

MW LOAD LIMIT

The steam dictates the maximum continuous MW ratings generator capability of the boiler and the horsepower rating of the turbine, rather than the rating of the generator. The alternator in theory is capable of generating output of MW’s that is the same figure as the MVA rating. provided that the stator current is in phase with the voltage i.e. at unity power factor. But generating the true power (MW’s) the alternator has also to be capable of supplying reactive power (MVAR’s) and therefore the alternator is designed to operate at a lagging power factor (typically at 0.85 lag). This mean that when maximum stator current is flowing the rated MVA output is being achieved but as the MW output is equal to the MVA * p.f, then only 85% of the MVA output is MW’s and therefore less steam and smaller turbines are provided to rotation of the turbo generator.

MINIMUM ROTOR CURRENT LIMIT

The power supplied to the alternator at constant speed is proportional to the torque applied to the alternator rotor by the turbine. This power must be counter balanced by an opposing electrical torque from within the alternator else the rotor would accelerate. If the grid system voltage and the frequency conditions are assumed to be constant, then the maximum balancing torque which the alternator can sustain dictated by the level of the magnetic flux which is created by the rotor field current in the air gap providing a magnetic coupling between the stator and

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the rotor. The stronger the magnetic coupling, the more firmly locked is the rotor to the system. If more steam is admitted into the turbine and hence an increase in rotor torque, then the magnetic coupling will be stretched and will ultimately be broken, resulting in the rotor accelerating and the speed rising above that of the system. This will cause a considerable electrical disturbance to the system and may also cause severe overheating of the both stator and the rotor. A reduction in the field current, without any change in steam entering, will have same result. The breaking of the magnetic coupling with the subsequent loss of machine stability cannot normally be altered and therefore the alternator must be operated with sufficient rotor current to ensure that the magnetically coupling is enough.

UNSYMMETRICAL SHORT CIRCUIT PERFORMANCE

The duration of unsymmetrical short circuit should be such that the product of square of negative sequence component of current is expressed in terms of per unit value of stator current and it’s duration in seconds does not exceeds eight.

MOTORING ACTION

Motoring of the turbo generator is allowed within the limitation of turbine.

VARIOUS STATES OF TURBO GENERATOR IN RUNNING

VARIATION IN TERMINAL VOLTAGE

Generator can develop rated power at rated power factor. When the terminal voltage changes with 5% of the rated value, the stator current should accordingly be changed within limits of 5%.

FREQUENCY VARIATION

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The generator can be operated continuously at rated output with a frequency variation of 5% over the rated value. However the performance of the generator with frequency variation is limited by the turbine capability.

OVERLOADING

Under abnormal conditions, the generator can be overloaded for short duration. So the generator must not be made to run beyond the overloading time limit.

OERATION UNDER UNBALANCED LOAD

The turbo generator is capable of operating continuously on an unbalanced system loading provided that conditions such continuous negative phase sequence current during this period shall not exceed 5% of the rated stator current.It implies that maximum difference between lines current is about 100% of the rated value. At the same time current is maximum loaded phase should not exceed the permissible value for given condition of operation of the turbo generator under balanced loads.If the unbalanced load parameters exceed the above permissible limits then measures should taken immediately to eliminate or reduce the extent of unbalance within 3 to 5 minutes. In case it is not possible to achieve this, then the machine has to be run down and tripped.

STATOR CORE HEATING LIMIT

With high values of stator current at leading power factor, heating of the end section of the stator core tend to occur. However, the end heating limit would normally only be reached if the stability limit were exceed and under normal stable operation, the end heating limit is not reached.

OPERATION OF THE TURBO GENERATOR

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CHECKS BEFORE STARTING/INITIALIZING THE SET

Supply the oil to the generator bearing and shaft seals and make sure that the quality, temperature and flow are normal.Fill the generator with inert medium of desired purity and bring it up to rated pressure. Set the different pressure and thrust oil regulator to maintain the desired pressure automatically. Charge the stator winding with distillate of desired quality and ensure normal pressure, flow and temperature.Supply to generator air coolers of desired quality and ensure normal pressure, flow temperature. The generator circuit breakers should be open. The generator field breakers should be open. Select the mode of excitation (auto or manual).

RUNNING UP Only after ensuring the completeness and the availability of all the above the set should be started and taken up gradually up to full rated speed. During the course of running up, bearing vibrations, rubbing if any inside the generator or abnormal noise should be investigated carefully. Also note down the temperature of bearing and seal Babbitt and drain oil.

When the generator comes to the rated speed check the following

Temperature of bearing and seal Babbitt and drain oil.Performance of bush gear.

Phase sequence of generator with the help of residual magnetism.Bearing vibration in all directions.

2. SWITCHING IN OF EXITATION

After ensuring that the mechanically the set is normal switch on field breakers and regulate excitation as per the selected mode (auto or manual).

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SYNCHRONIZATION

The generator should be synchronized with the system only by means of a precise synchronization method after the following conditions are strictly satisfied. The phase sequence of the generator voltage and system voltage is identical. Effective values of both voltages are same.Both the voltages are in phase.Frequencies of both the voltages are same.

LOADING

The rate of loading of the generator is mainly limited to the turbine and the boiler. However the generator should be gradually loaded accordingly to the load requirements. The governor of the turbine is adjusted as necessary for speed and load sharing. The automatic voltage regulator is adjusted for desired value of generated voltage and power factor.

PROTECTIONS INSTALLED FOR TURBO GENERATOR

WINDING TEMPERATURE

Whenever the winding temperature of generator goes beyond 105C then alarm will attract everybody attention and if we are not in a position to control the winding temperature at 120C then generator breaker and excitation system will be tripped.

BEARING TEMPERATURE

In case the bearing temperature goes above 95C first alarm informs then after 100C generator breaker, excitation system and turbine will be tripped.

OVERLOAD

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Continuously overloading increases the temperature to such an extent that generator insulation will be damaged and its useful life reduces. The overloading may be because of over current for remarkable period or cooling system failure. Therefore we have ITG 7231 type of relay. This relay has the setting 9.84in for 1.2secs. Only alarm is there incase of overloading and no tripping.

NEGATIVE SEQUENCE

Alternators, being normally designed to supply balanced three phase currents, coils only support a limited amount of unbalance in the phase currents. Out of balance in these currents, which causes abnormal heating of the rotor of the machine may in fact have a highly damaging effect (Note negative sequence current cause six times heating as compared to normal balance currents). The unbalanced 3phase stator current is induced in rotor. They cause heating of rotor and damage the rotor. Unbalance stator current also cause severe vibrations currents rotates at synchronous speed in a direction opposite to the direction of rotation of rotor. Therefore double frequency currents are induced in the rotor. We have ITI 7621 relay to detect negative sequence current and CT for this relay is of 1000/1A ratings.

LOSS OF EXITATION

Opening of field switch of field circuit breaker can cause loss of excitation. The behavior of generator depends upon whether the generator is connected singly to a load or whether generator is connected in parallel with other units or the system. If it is a single unit supplying a local load, the loss of field caused loss of terminal voltage and subsequently loss of synchronism depending up on the load condition.If the generator is connected in parallel with other units it can draw the magnetizing currents from the bus bar and continuous to run as induction generator. Large magnetizing currents cause heating of generator.

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In fact under normal operation condition an alternator supplies reactive power and its impedance is therefore of a capacitive nature. On the other hand, under synchronous conditions it absorbs reactive power and its impedance becomes inductive. We have YTM 7111 to detect loss of excitation. C.T ratio is 1000/1A and 11KV/1.73KV/110*1.73VP T.

REVERSE POWER

When the input to the turbine is stopped the generator continuous to rotate as a synchronous motor taking power from the bus bars. It then rotates as a synchronous motor and the turbine acts as a load. Power taken by the generator under such condition is very low being about 2% for the turbo generator and 10% for the engine driven set.

UNDER POWER

Whenever there is under power it means there is some fault on the alternator and alarm comes. The relay used for under power is WTGA 7133. it is used for balance or unbalanced network operating on active power, on 3-phase 3-wire system with a definite time characteristics. Relay gets supply from 1000/1A and 11KV/1.73KV/110*1.73V C T and relay setting is 3% of power for 2 seconds.

UNDER VOLTAGE

For under voltage we have signal relay only TTG 7123 used for this purpose with a setting of 0.8Vm. 3 seconds. This relay is two-phase time-delayed relay. Relay gets supply from 11/1.73KV/110/1.73P.T. OVER VOLTAGE

Over voltage are caused by over speeding or due to faulty operation of voltage regulator. This condition leads to insulation breakdown. Relay TTG 7111 is used for this purpose, is a single- phase time delay ED relay having settings.

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UNDER/OVER FREQUENCY

Under frequency means V/f ratio of system changed. This causes more flux drawing, which has an effect of saturation of magnetic core. This causes increase in losses and overheating, which should not be maintained in order to avoid premature aging of insulation. Over frequency cause high speed which is responsible for over voltage, which will ultimately damage the machine insulation. We have relay HD4 7020 to check this situation. Only turbine will trip by this relay.Intentional time lag is provided in the reverse power protection so that the protection does not operate during system disturbance and power swing WTGA 7131 is active reverse power relay for 3-wire, 3-phase unbalanced/balanced network.

ROTAR EARTH FAULT

Normally generator rotor remains insulated from earth. So when a earth fault occurs it is not so serious but second earth fault will damage rotor because single earth fault does cause the flow of current. Since the rotor circuit is underground. When the second earth fault occurs parts of the rotor winding is by passed and the current in the remaining portion may increase. This causes unbalance in rotor and may cause mechanical as well as thermal stresses result in damage to the rotor in some cases vibrations have caused damaged to bearings and bending of rotor shaft. Such failure has caused extensive damage.We have TTE 7015 relay to detect any earth fault. This relay operates on the current injection principle

EQUIPMENTS INSTALLED IN C.P.P SWITCHYARD

TRANSFORMER

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TECHNICAL DATA:-

Type of Cooling ONAF/ONANPhase 3Capacity HV- 31.5/25MVA

LV- 31.5/25MVAFrequency 50 HzRated KV HV – 132KV

LV – 11KV

SV – 11KVConnections Star/Star/DeltaRated Amperes HV - 137 94A

LV – 1655.28

SV – 318.18AOil temperature rise 500CWinding temperature rise 550C

(a) TAP CHANGERS (ON LOAD)

Tapping are provided on the high voltage windings to give a variations of high voltage from +12.5% to –12.5% in 21 steps. Tap position 11 give us 132K.V. Taps position of lower value gives us high voltage and vice-versa. Voltage difference of 1.65 KV i.e. –0.5% is maintained in between two tap positions.

(b) COOLING FANS

We have twelve numbers of cooling fans for our transformers (12 for each). They are divided into four groups, each group comprising of three fans. Each fan has 380mm diameter and rating of 41m3 of air per minute. They get started automatically when the temperature reaches 650C.

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(c) CORE

The magnetic circuit is a three-limbed core type construction, each limb being joined with the tip and bottom yokes by inter leaved metal joints. The laminations are made from high-grade non-aging silicon alloy cold rolled steel. The yokes are clamped by means of end plates with bolts and legs are clamped by means of clamp plates. The clamp plates has a special attachment to connect top and bottom end plates for lifting the core with windings four number of lifting legs are provided.

(d) WINDINGS

Windings are arranged in concentric formation with SV windings next to core, and then LV windings coiled over the SV windings. HV tapping coil is placed to the LV winding coil. HV main coil is placed next to the HV tapping coil.

(e) TERMINAL ARRANGEMENT

The HV line terminal bushings are of the out door, oil impregnated condenser type and the arching norms are fitted with a gap setting of 500 to 800 mm. The neutral terminal bushing for both HV and LV are of porcelain stem type without arching horns. SV windings are also of porcelain stem type. An air insulated cable box is provided on LV line side.The HV line bushings, HV neutral bushings and LV neutral bushing are mounted on turret. The SV bushings are mounted directly on the cover of transformer tank. LV cable box is mounted on tank wall of the transformer.

(f) TANK

The tank is a welded milk steel plate construction. The tank is designed to withstand a vacuum of 5tors absolute of mercury.

(g) OIL TEMPERATURE INDICATOR

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The equipment operating on the principle of liquid expansion provides local indication of the top oil temperature. The temperature is given by a thermometer bulb with is connected by capillary tubing to the local indicator. The pocket of the indicator is to be filled with oil. The indicator is fitted with maximum pointes and two mercury switches. Out of which one is used for alarm and other is for tripping switches are suitable for 5A, 250V AC or D.C. oil alarm temperature is 800C and tripping temperature is 900C.

(h) WINDING TEMPERATURE INDICATOR

This equipment gives continuous indication of the temperature of the windings and initiates alarm when the temperature exceeds a certain limit and tip off the transformer from the circuit when temperature approaches a dangerous level and controls cooling fans. Capillary tubing to the local indicator connects thermometer bulb. The indicator is fitted with a maximum pointer and four mercury switches. Out of the four one contact is for alarm, other for tripping, third one is for controlling fan and fourth is spare switches are suitable for 5A, 250V AC or DC. Winding alarm temperature is 900C and tripping temperature is 1050C.

(h) BUCHHOLZ RELAY

A double float buchholz relay is fitted in the pipe connection between the conservator and the main transformer tank and is provided with two sets of mercury contacts. One mercury contact is in the upper part and the other one is in the lower part. These mercury switches are in aluminum buckets, leads from which are taken to the moulded terminal box.

When a minor fault occurs, heat liberated during arching generates gas in the oil, which is trapped in the relay. As gas accumulates the oil level in the relay falls, leaving the top bucket full of oil and the assembly tilts, closing the mercury switch that initiates the alarm. With a major fault, gas generation is rapid and displaced oil surges through the relay and impinges on the baffle plate, causing the lower assemble to tilt and close the mercury switch to complete the trip circuit.

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Protection is given by both buckets elements against falling oil level, giving first the alarm and then tripping before the danger level is reached. The other faults against which protection is given by the relay are:-

INCIPIENT FAULTS : - Short circuited core lamination, broken down core bolt insulation, local overheating of windings etc.

MAJOR FAULT : - Short circuit between phases and between turns, earth faults, punctures of insulation inside the transformer tank.

Mercury switches will carry 2A at 250V AC or D.C. continuously and will carry 40A at 250V AC or D.C for 0.5secs.

(i) CONSERVATOR

As the temperature of oil increases or decreases there is corresponding rise or fall in oil volume. To account for this, expansion vessel i.e. conservator is connected to the transformer tank. The conservator has got capacity between maximum and minimum oil level equal to 7.5% of total oil level in transformer. The conservator is provided with a magnetic oil level gauge at one of the end covers, which has a low oil level alarm. The dial indicates empty, ¼.350C, ¾ and full. An isolating valve is provided in feed pipe. The conservator is also fitted with filling holes and a drain valve.

(j) DEHYRATING BREATHER

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The conservator is connected to outside atmosphere through a dehydrating breather to make sure that the air in the conservator is dry.

Air entering the breather is first drawn through an oil seal and passes upward through the silica get crystal to the connecting pipe at the top. During the upward passage of air any moisture present is absorbed by the dry silica gel.

The oil seal ensures that the gel absorbs moisture only when the transformer is breathing. When the breather is first installed the crystals have a blue color and after a period of operation, the color of the crystals gradually changes to pink, this indicates that the silica gel is becoming saturated and loosing its absorbent properties when all the silica gel gets pink color then it should be changed or reactivated. Silica gel can be reactivated by heating the gel at a temperature of 1500C to 2000C for two or three hours when the crystals should have regained their original blue color.

(k) RELIEF VENT

In case of severe fault in the transformer the internal pressure may be built up to a very high level, which may result in explosion of tank. To avoid such a contingency, a relief vent is provided on the tank cover. This consists of a 250mm diameter pipe fitted on the cover. It is provided with a Bakelite paper diaphragm at top, which break and relieve pressure in case of excessive pressure build up. To equalize pressure, top of the relief vent is connected to top of conservator by equalizing pipe.

NGR

NGR means Neutral Grounding Resistance. Our transformer is grounded through resistance in the neutral to earth path. The purpose of NGR is to suppress the earth fault current during the earth fault.

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TECHNICAL DATA:-

Resistance 6.35 Voltage 11/1.73KVCurrent 1000A for 15 secondsTemperature 3000C

The transformer is permanently attached to NGR. NGR is also used for providing CTs for the protection of the transformers.Our generators (TG1 and TG2) have NGR of the same rating because both generators and transformers are at same potential so we should have one NGR in line at one voltage level.

LIGHTENING ARRESTERS

Lightening arrestors are wholly connected between phase and ground in distribution system, near the terminals of large medium voltage rotating machines and in HV. EHV sub stations to protect the apparatus insulation from lightening surges and switching surges i.e. impulse voltage wave.

The lightening arrester offers low resistance to high voltage surge and diverts the high voltage surge to ground. Therefore the insulation of protected installation is not subjected to the full impulse wave. Lightening arresters discharge current impulse surge to earth and dissipate energy in the form of heat. After discharging the impulse voltage wave to the earth, the resistor blocks in the surge arrester offers a high resistance to the normal power frequency voltage and acts as open circuit. Surge arresters are not against temporary power frequency over voltages. They provide protection against impulse voltage wave. The normal practice is to locate the L.A as close as possible to the equipment to be protected.

ISOLATOR

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Isolator is a switching device, which can be opened or closed only under no current condition. An isolator disconnects a part of system, from live parts under no load condition.

EARTH SWITCH

Earth switch is a switch that connects a conductor to the earth so as to discharge the charge on the conductor to the earth. Earth switches are generally installed on the frame of the isolator. When isolator is in line earth switch cannot take into the line. Earth switches are connected to the system, only when isolators are disconnected from the system.

BUCHHOLZ RELAY

This relay is generally used for the protection of oil-immersed transformer. All types of faults occurring with oil filled transformer are accompanied by more or less violent generation of gases, which liberates heat from the oil. This phenomenon has been utilized to provide complete internal protection of the transformer. The falling of oil level, which may lead to dangerous situation, is also detected by the relay in time.

CONSTRUCTION

The relay is hydraulic device arranged in the pipeline between the main transformer tank and the conservator tank. It comprised a cast housing which contains two floats-upper and lower. Each float carries a mercury switch; the leads are taken to terminal box. The necessary petcocks for gas release, site testing and a drawing plug on the body of housing are provided. Inspection windows are fitted on both sides of the relay housing to see the level & to ascertain the volume of gas collected on calibrated scale in cubic centimeter. Mercury switch rating is chose 2A at 240 AC or DC.

PRINCIPLE OF OPERATION

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When the transformer is healthy, the entire relay housing remains filled with oil and buoyancy of the respective floats tilts the mercury switch to open position. But when a slight fault occurs, small gas bubbles are generated and these attempting to pass from the tank to the oil conservator.

As this gas accumulates, the oil conservator will be tapped in the upper portion of the relay housing. The oil level in the relay depresses causing the upper float to tilt thus closing their mercury switch. The alarm circuit that is connected to this switch gets energized to ring an alarm bell. With severe internal fault, the gas generation is rapid, causing the displaced oil to surge through the relay. This oil flow impinges on the lower float is thus deflected closing its mercury switch and completing the trip circuit of the circuit breaker. If transformer suffers a loss of oil, causing the oil level drop below the level relay, the buoyancy of both the floats vanishes one after the other, tilting the respective floats. First the alarm and the surge element will operates to close their respective circuits.

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Fig.2 Two modules using a common battery

MAIN RECEIVING STATION

º

STATIC SWITCH

STATIC SWITCH ºººº

ºº

º

º

º

ºº

INPUT ISOLATOR

BYPASS ISOLATOR

MAINTAINANCE BYPASS ISOLATOR MAINTAINANCE BYPASS LINE

STATIC BYPASS LINE

OUTPUTISOLATOR

UPS OUTPUTSUPPY

ºº ºº

º

ºº

ºº

ºº

º﴾

ºº﴾

º

CO

NT

RO

L LO

GICBATTERY

INVERTERRECTIFIER

RECTIFIER INVERTER STATIC SWITCH

BYPASS ISOLATOR

MAINTAINANCE BYPASS ISOLATOR

MAINTAINANCE BYPASS LINE

STATIC BYPASS LINE

1+1 PARALLEL CONTROL

1+1 PARALLEL CONTROL

INPUT ISOLATOR

OUTPUTISOLATOR

COMMON BATTERY KIT

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INTRODUCTION It is clear from the name itself that this section is mainly a receiving end of power from all the sources of power such as CPP and PSEB. The main motive of this station is to collect all the power from the sources and then to synchronize them, resulting into a uniform supply and then to carry on distribution to different plants located in the NFL premises. It may be kept in mind that synchronization actually takes place in MRS. After that MRS steps the in coming common busbar supply of 132KV to 11KV by making use of three transformers of 132/11KV rating, out of which one transformer is spare. Also metering of incoming supply is done so as to record the total energy consumed. The 11KV thus generated is supplied to the various plants such as Urea, Ammonia, CPP etc.

ELECTRICAL EQUIPMENT USED IN MRS YARD

Lightening ArrestorsLightening Arrestors are the devices that are used to protect overhead transmission lines.PTs switchgears.Transformers etc.When they are subjected to over voltage surges due to lightening caused by atmospheric disturbances due to unfavourable conditions or by impulse wave voltages.

NECESSARY REQUIRMENTS

1) It should be able to drain the surge from the line in minimum time.2) It should offer high resistance to the flow of the power current.3) No system disturbance must be introduced by the operator of lightening arrestors 4) Always be in perfect term to perform the function occupied to it.

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CURRENT TRANFORMER

It is used for measuring large alternating currents. The primary windings consists of only one or few turns and is connected in series with load circuit and carries the load current to be measured. The secondary consists of many turns than primary and have the instrument like ammeter, directly connected across it. As the load impedance on the secondary is very small, so CT operates on short circuit condition. Also the current in secondary winding is not governed by load impedance on the secondary but depends upon the main circuit current. CORE

CT is designed with a view to minimize the current ratio and phase angle errors. Core is made from high permeability and low magnetic material such as silicon steel. Losses are also kept down by keeping low values of flux densities. The transformer may be shell type or having a rectangular or ring shaped core. The shell form gives considerable protection to windings but is more difficult to build up. The rectangular forms provide ample space for insulation and are suitable for high voltage work. Ring form is used when the primary current is large.

WINDING

The coils are wound close together in order to reduce the secondary leakage reactance. Copper strips are used for primary winding and No. 14 S.W.G. copper wire is generally used for secondary winding. The winding must be designed with a view that they must withstand the forces experienced by them. The very large forces which develop when a short circuit takes place on the system in which the transformer is connected.

CONSTRUCTION

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It consists of steel tank, porcelain insulator, steel top chamber mounted on the top of the insulator. The C.T. fabricated steel tank on bottom supports the hair pin condenser primary, which passes through the porcelain housing, mounted on the top of tank and terminates in top chamber. The condenser primary posses through the ring type secondary, which are placed in the tank and suitable clamped against any movement in transit or use. The secondary windings are connected to the terminals located in a weatherproof terminal box on the side of the tank. It is important that C.T is always kept in vertical position so that gas forming a cushion at the top remains at top only.

POTENTIAL TRANSFORMER

It consists of core winding, porcelain insulator, steel tank with integral secondary terminal box, top chamber.Core and windings132 KV PT consists of primary winding and secondary winding mounted concentrically on a core carrying mutual flux. The voltage being measured acts across the primary winding that has large number of turns and connected across the circuit. The secondary winding which has a much smaller number of turns is coupled magnetically through the magnetic circuit to primary winding.

TANK

Fabricated from mild steel plates. It houses the core and coil assembly, secondary terminal box form an integral part of tank. The secondary leads and neutral leads of primary windings are taken out through LV bushing in secondary terminal box. Secondary terminal box is fitted with necessary fuses and link connections required. The neutral lead lf HV terminals are solidly earthed inside secondary terminal box.

POWER TRANSFORMER

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In MRS switchyard three power transformers are there which are used to step down 132 KV to 11 KV so as to distribute this supply to various plants such as Ammonia, Urea etc. Two transformers work at a time and the third one is spare one used in case other one develops a fault.

DISCRIPTION:-

Type OFTR 31500/132 EStandard IS 2026Make NGEFRated KVA OB- 26,500

ON- 20,000Rated voltage at no load HV – 132790V

LV - 11000V

SV – 6600VRated current HV LVOB 115.2 1391.0ON 87.0 1049.8Phases 3 3Frequency 50 HzType of cooling ON/OBImpedance voltage 10.19%(20 MVA Base)Max. Ambient temperature 450CTop oil temperature rise 450CWinding temperature rise 550CYear of manufacture 1976

LIGHTENING TRANSFORMER

DESCRIPTION: -

Make General Electric Co. of India

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KVA 1,000Volts at H.V 11,000No Load L.V 433Amperes H.V 52.48L.V 1333Phases HV LV 3 3Frequency 50 HzImpedance voltage 5.72%Oil volume 200litresWt. of oil 1,044 Kg.Wt. of core and winding 1,640 Kg.Total weight 4,300 Kg.

CABLE

From transformer L.V side to 11 KV bus we have fine cable per Phase of 400 sq.mm is running. These cables are made up of XLPE (Cross linked polythene). We have XLPE cables in our C.P.P Switchyard. XLPE has following properties:

(i) Inherent moisture resistant(ii) High flexibility(iii) Simple accessories(iv) Smaller size(v) Outstanding dielectric properties(vi) High temperature resistant(vii) Mechanically strong

HORN GAP

Horn gap is the simplest protection of line insulators, equipment. The conductive rods are provided between the line terminal and earthed terminal of the bushing of transformers with an adjustable gap. Medium of gap is air. The gap is adjusted to breakdown at about 20% below flash over voltage of bushing

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i.e. 80% of 650 KV 0520 KV. The distance between path and insulator should be more than 1/3 of the gap length i.e. b > 1/3. Precise protection is not possible by rod gap. The advantage of gap is low cost and easy adjustment on site

WORKING OF MRS

Power is drawn from PSEB grid through double circuit 132KV overhead lines at M.R.S. This 132KV transmission lines have toppings with different equipment before stepped down for e.g. lightening arresters, C.Ts, insulators etc. ln MRS a bus bar is made which at 132KV, 800A, 3500 MVA. Now this supply at 132KV is stepped down to 11KV by using step down transformer of 20/26.5 MVA (132/11 KV). There are three such transformers. New bus bar is made at 11KV, 1600A, and 3250MVA. From the MRS the power is supplied to different plants. There are feeders from Ammonia, Urea, CPP, SGP. This supply is further step down to 3.3KV, 415V-using transformers for operating H.T and L.T motors respectively. Different sub stations of various plants receive energy at high voltage and reduce this voltage to a value appropriate for further distribution and provide facilities for utilization of energy.

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AMMONIA PLANT

INTRODUCTION

Ammonia is the key intermediate product for manufacture of urea. Ammonia plant has production capacity to produce 900Te/day of ammonia based on partial oxidation of residual fuel oil by shell gasification process. The plant is laid out in single stream except for the three gasification units. The raw synthesis gas from the gasifier is further processed for H2S removal by low temperature Rectisol Process and then sent to CO shift section to convert CO to H2 and CO2. The process gas is then fed to CO2 removal section where CO2 is removed by low temperature Rectisol Process. The decarbonated gas is sent to Nitrogen wash unit for final purification by scrubbing with liquid nitrogen at -1900C & 37 kg/cm2 pressure. After final purification in nitrogen wash unit, Hydrogen and Nitrogen ratio in synthesis gas is maintained @ 3:1 and is compressed to 190kg/cm2 pressure and ammonia synthesis is carried out.

The oxygen required for partial oxidation and nitrogen requirement for synthesis gas as well as utility nitrogen is produced in the air separation plant.

The plant has been supplied as a package unit by M/S HITACHI and was plagued with constraints during the initial years of operation. These constraints have now been overcome by:Interconnecting the screw refrigeration compressor with the main refrigeration compressor of the synthesis section.Changing the material of construction of the air pre coolers at the upstream of the chilling unit from C.S. tubes to S.S. tubes.Increasing the packed volume of mol. Sieve in the ASU dryers.Modifying the air drier post filtration system of air before entering the cold box.

POWER DISTRIBUTION IN AMMONIA PLANT

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Two feeders from MRS incomer A and incomer B feed the 11kV bus at ammonia control panels for 11kV are provided by L&T. each panel is provided with circuit breaker of 630A, 300MVA which are activated by the relay in case of fault. Panels 1-5 and 12-17 are fed to 415V panel through 11kV/415V, 2MVA transformer and panels 6 and 11 feed the 3.3kV panel through transformer of rating 11/3.3kV, 10MVA. Bus coupling is provided between buses A&B from ammonia there are two feeders to coal handling (1.6MVA), boilers (2MVA), and D.M plant (2MVA). If one of the feeders fails or there is any abnormality then the total load is transferred on the other feeder by using bus coupler. The 11kV supply is then further stepped down to 3.3kV and 415V using step down transformers, 3.3kV is used for H.T. motors and 415V is used for L.T. motors. This plant also has the facility of battery room.

EQUIPMENTS INSTALLED IN AMMONIA PLANT

M.M.G SET Specifications regarding the AC continuous running power supply equipment that is used in ammonia plant.

1. INDUCTION MOTOR

Type Totally enclosed, fan cooledOutput 75 kW/140 kWVolts 415 VFrequency 50 HzSpeed 475 RPMInsulation E classPhases 3Current 1.25/260 APoles 4Ambient temp 45CWeight 825Kg

2. A.C.GENERATOR

Type Guarded drip proof

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Output 75KVA/210KVAVolts 415VFrequency 50HzSpeed 1550RPMPhases 3,4 wireCurrent 97.5/292APoles 4Power factor 0.8

3. D.C.MOTOR(DCM)

Type guarded drip proofOutput 75KVA/210KVAVolts 415VFrequency 50HzSpeed 1500RPMInsulation B classPhases 3Current 370/700APoles 4Ambient temp 45CWeight 880Kg

PRINCIPLE OF OPERATION

STARTING

The 3-phase AC input (415V, 50Hz) received by the input terminals is supplied to the induction motor via the input switch and magnetic switch. To close push button is it is depressed and auxiliary relay becomes energized causing magnet switch to close. When timer times out having measured off the time required for the input current to be reduced to a given level, auxiliary relays becomes energized and IM starting is completed, permitting light to go out. Simultaneously, the initial excitation circuit of the ACG is closed, opening again once ACG voltage has been established, so that the system is then ready for operation.

REGULATION OF ACG OUTPUT VOLTAGE

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An automatic voltage regulator controls the output voltage of the ACG, the input for which is obtained from the ACG output, AVR detects the deviation of ACG voltage from its setting value and feeds its output to fields. With the making of the load, since the output of AVR alone is insufficient to lower generator output in order to compensate, so that always a stable output is supplied to the load.

REGULATION OF ARMATURE VOLTAGE AND SPEED OF DCM

This regulator serves as an automatic voltage regulator (AVR2/ASR), when DCM is driven by IM, senses changes in the voltage of the motor armature and battery to keep the difference in voltage between them at a constant level, and reduces the decline in the AC power failure. AVR2/ASR also serve as an automatic speed regulator , when the motor operates on battery power after an AC power failure and feeds its output to the fields of motor.

BATTERY POWER SLECTION IN AC POWER FALIURE

A power selection circuit is formed when the output voltage of the ACG has been built up. Low voltage relay and low frequency relay connected to the AC input power source or counter electromotive relay becomes energized when the power supply voltage and frequency falls below 85% of rating and 47.5Hz and following operation takes place automatically: BATTERY POWER SLECTION : With relays such as low voltage relays and low frequency relays energized, auxiliary relays are energized causing DC electromagnetic switch to close, hence, power switch is changed over from AC to battery and AC electromagnetic switch is opened simultaneously. When timer has counted 4 sec (0.5 to 5sec), it sends a signal power supply from the commercial AC power source to the ACG.

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OPERATION OF BATTERY POWER : When auxiliary relay is energized. It causes magneto switch to be actuated. As a result, the DCM goes on operating on battery power for about 15 min unless operation is stopped by malfunction. Shunting off power supply to the charger: when magneto switch is closed, a signal is sent to the charger, shunting off power supply to the charger. Signal transmission: relay contacts in the protection circuit are connected in parallel and a signal is transmitted to the instrument panel.

A.C. POWER RESTORATION :

When AC power voltage and frequency are restored to 90% or more of the rated voltage and 47.5Hz or more, detection relays are energized and following operation take place:

AC POWER SELECTION

Power supply to the charger is restored. When recovering charge is completed, a floating charge is automatically starts.

PROTECTION

Following protections are provided which cause immediate and automatic shutting off power supply and giving a warning signal.

(a) DCM over current

(b) DCM over speed (when field current is reduced to zero, speed may become infinite.

(c) Overtime battery drive: equipment operates for about 15min, after an AC power failure, according to the setting on time before it stops automatically and issues a warning signal.

(d) Abnormal battery voltage (voltage drop).

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(e) ACG voltage abnormal: the abnormal ACG voltage is decided by A.C. voltage, relays with H-side set to 45605V and relays on L-side are set to 373.5V and frequency relays set on 45.3Hz on H-side and L-side and timer causes auxiliary to be energized thereby, shunting off the power supply and giving a warning signal.

(f) Abnormal DCG voltage

(g) ACG over current

(h) IM over current

(i) Abnormal power

(j) Abnormal increase in bearing temperature

(k) ACG grounding

(l) Control circuit

TRANSFORMER

Two 10MVA transformers are installed in the ammonia plant which steps incoming the incoming supply of 11kV from MRS to 3.3kV to be used for HT motors.

DESCRIPTION :

Make General Electric Company of IndiaTemperature rise in oil 45CRatings 10,000kVAVolts at H.V 11,000 L.V

3,460Amperes H.V 524

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L.V. 1,669Phase H.V. 3

L.V. 3

Temperature 55CImpedance 9.40Insulation level H.V. 88kV L.V. 16kVQuantity of oil 5,000 litresWeight of oil 4,375 KgWeight of core and windings 9,500 KgTotal weight 21,000 Kg

AUTOMATIC SPEED REGULATOR FOR DC MOTOR

This serves as an AVR for DC motor which is driven by an induction motor, senses a change in the voltage of the motor and battery to reduce the difference in voltage between them to a minimum, reduces the decline in the AC o/p voltage and rush current of the motor to a minimum in an AC power failure and serves as an automatic speed regulator when the motor operates on battery power after AC power failure. This equipment comprises a voltage detection circuit, speed detection circuit and auxiliary relays for voltage & speed selection.

WORKING PRINCIPLE

DETECTION CIRCUIT

This equipment uses two detection circuits; one to detect changes in voltage when DC motor is driven by induction motor, known as voltage detection circuit, And the other to detect changes in speed, when the DC motor operates on battery power, known as speed deviation detection circuit Along with detection circuit, an amplifying circuit is also present. Since the differential voltage is quite small, it is necessary to amplify it to sufficient power to make effective control possible. This is carried out with a magnetic amplifier.

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However, since this is still insufficient power to control the device, this output is further amplified with a magnetic amplifier, thus making a two stage amplifying circuit. This AC output is converted to DC with a selenium rectifier, the control field system added & the output differential reduced to zero.

AUTOMATIC VOLTAGE REGULATOR AC GENERATOR

The output voltage of the AC generator is caused to fluctuate by changes in the speed and load variations. The AVR serves to keep the output of ACG at a constant level so that load is stabilized. The schematic diagram of AVR is shown:

CIRCUIT DIAGRAM OF AVR

OPERATION OF AVR

The output of the reference voltage generator is compared with the feed back voltage by the detector. If the voltage of the

RECTIFIED & VOLTAGE DIVIDER

MAIN SCR CT CKT SCR

SYN C KT &OSCILLATOR

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REFERNCE VOLTAGE

AMPLIFER

ACG

ACG rises, the difference in voltage detected by the detector appears as a positive signal or negative signal at the terminal of operational amplifier. As a result terminal of operational amplifier is negatively charged by this signal causing the transistor to be turned off and the output potential of the amplifier rises. As this potential is applied to the sync generator and oscillator it is applied to the base off transistor so that its collector current decreases. As a result, the charging of capacitor is delayed so that the oscillating cycle of UJT is prolonged, thus delaying the gate signal. In other words the firing angle of thyristor increases causing a decrease. In the field current of the ACG & thus a drop in ACG output voltage if the output voltage of ACG falls the AVR operates in reverse direction, thus maintaining its rated voltage.

DIESEL GENERATOR

IT is uniquely designed self excited compound wound generator.

MAIN FEATURES TYPE KA-70 SERIES

1. Brush exciting system adopted so that elimination of slip rings & brushes that require heavy maintenance is possible.

2. The most important characteristics fro diesel generator is voltage regulation for which new AVR which directly controls the filed current with the thyristor circuit incorporated in the rotor section. By virtue of new AVR, KA-70 series generator can start up cage rotor type motor with the same rotor with conventional brushless type generator can stand up. Voltage regulation under steady operation is within ±1.0%.

The KA-70 series generator has a cylindrical rotor. To obtain uniform distribution of temperature rises in cores and windings in axial direction, both sides of rotor are provided with cooling fans.The standard mountings of the exciter are over hung type on

the bracket of the counter coupling side. The rotary (thyristor &

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silicon’s) and electrical components in the mold package are mounted at the end of the shaft.The tacho-generator used fro speed detection is mounted on

the shaft on counter coupling side.

GENERATOR CONSTRUCTION

The generator frame is constructed of welded steel plates. The basic structure and size are common to those of induction machines. The stator & rotor cores employ Silicon steel laminations. The stator is an armature while rotor is a magnetic field assembled in the cylindrical type structure. Slot for field winding are provided at the same interval along

about 2/3 the entire periphery Cu bars as end rings are used to make up a squirrel cage type damper winding.The armature winding along with the core is put in a vaccum

tank and impregnated with ‘MEW’ resin. After completion of thorough treatment of the winding, the core is installed in the frame. In this arrangement of field winding in the slots, temperature distribution is uniform and effect of cooling is favourable. The field winding is fixed rigidly to the core by use of resin treated glass fiber wedges. Then bearing is of plain type on a single bracket support system for the standard machine.

Initial flush excitation is required & provided from outside to establish voltage at the time of starting.

In general cases, batteries for controlling may be utilized as power source for this purpose.

AVR OPERATION

The AVR to be mounted on the rotor makes a comparison between the constant setting voltage & the AC output phase voltage. The setting voltage is obtained from ACEX induced voltage through rectifier circuit. The ACG output voltage VAG is obtained from the rotor through rotary transformer RT. This comparison is carried out in the detector circuit. The resultant differential component is amplified at the amplifier comprising IC’S and transistors. The gate signal is obtained at the phase shifter is used for phase control of thyristor output voltages.

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This finally to control the ACG field current to keep the ACG voltage always constant.

EXCITER CONSTRUCTION

This exciter is located on the stator side while the rotor accommodates an armature circuit, arranged in rotary armature system. The exciter cores are made up of punched silicon steel laminations. Both armature and field winding are of class B type insulation. Insulations and resins bands at the ends of the rotor are made on same way as those for generators.

ROTOR RECTIFIERS

For this series is composed of mold packed AVR electronic components together with conventional rectifier elements. The peripheral section is used as a rotary transformer for transferring the detected terminal voltage to the rotary section.

CONDITION FOR AUTO STARTING OR STOPPING

STARTING

When under voltage on one of the tree panel’s emergency diesel engine starts automatically. When the engine start and the generator voltage is established command shall be given to the normal supply breaks in the emergency panel. After a certain confirming times, generator circuit breaks shall be closed automatically and generating will be steady to operate under normal running conditions. Simultaneously, a closing command shall be given to emergency supply breaks in emergency panel.

STOPPING

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1. When restoring the normal power the power supply in the emergency panel shall be changed automatically from emergency to normal power supply.

2. After all normal supply is restored and change over from emergency supply to normal supply is finished, generator B shall be opened and the engine will be stopped automatically.Generator will be started after 8 seconds of power failure and shall be able to supply load corresponding to rated capacity within 3033 seconds after supply.

CONVENTIONAL SELF EXCITED GENERATOR

The exciting circuit of the exciter is provided with compound CT’S to assure the ability of excitation even against large voltage dip due to short circuit failure offers an exact accomplishment of selective separation of faulty loads. The static exciting circuit for the exciter is composed of small components all assembled in a single frame & installed in the generator panel. This system eliminates a special exciter panel often required for self excited compound type.

UREA PLANT

In this plant 1500 metric tons of uncoated pilled urea per stream day are produced by signal train wing

The plant can be divided into four sections

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Synthesis SectionDecomposition SectionRecovery & CrystallizationPrilling section

Different steps being carried out in these sections for urea production can be described as follows

SYNTHESIS SECTION

In this section, urea is synthesized in urea is synthesized in urea reactor (DC-101) under high pressure and temperature from CO2 liquid ammonia and recycle carbonate solution, the temp and pressure in the urea synthesis reactor, and ratio of ammonia to CO2 are so selected that maximum conversion of CO2, to urea is achieved with minimum cost.

DECOMPOSITION SECTION

The gas liquid mixture from urea synthesis section (reactor) flows to the decomposition section, where all the excess ammonia and ammonia carbonate are separated from aqueous urea solution by thermal decomposition in high pressure decomposer (HD) and low pressure decomposer (LD) gas separator (GS)

RECOVERY SECTION

The gases from gas separator go to off gas condenser cool down to 61ºC by C.W. and enter into the bottom off gas absorber. Similarly gases from H.D.L.D are condensed / absorbed in high-pressure absorber, low-pressure absorber is MP loop ammonia is separated in H.A. and it is condensed and recycled back to ammonia reservoir. The inert gases along with

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residual ammonia passes through purge, ammonia condenser, vapour ammonia condensed and recycled back to ammonia reservoir.

In recovery absorbers, ammonia is absorbed in aqueous thus formed about 80% by wt. is with draw from lowest absorber and fed to the top of high absorber.

CRYSTALLIZATION AND PRILLING SECTION

The urea solution coming from gas separator (DA-203) is pumped to the lowest part of the crystallizer, which consists of two parts. The upper part is a vacuum concentrator with vacuum generator in which vacuum is or sated by a two stage steam ejector having barametric condenser and an indirectly cooled interstage condenser the lower part crystallizer where urea crystals are suspended in the solution

The urea slurry is pumped from bottom of the crystallizer to centrifuges. In centrifuges urea crystals are separated from slurry. The urea crystals with about 2.5% moisture are discharged to fluidizing dryer. The separated mother liquid tank and is pumped back to crystallizer and low-pressure absorber.

The drilled crystals from dryers conveyed by a pneumatic pipe to the top of prilling tower and crystals are collected in cyclone and fed to melter. In melter, the crystals are melted and molten urea flows down to head tank through strainer for distributors and from distributors it falls down in prilling tower (IA-301) being cooled and solidified in the process.

The urea dust collecting equipment is provided to minimize air pollution by tower effluent; dust chamber is provided for scrubbing. Then the air is exhausted to atmosphere by induced fan for pt. After water mist from scrubbing section is eliminated by the filters.

The urea slurry is pumped from bottom of the crystallizer to centrifuges. In centrifuges urea crystals are separated from slurry. The urea crystals with about 2.5% moisture are

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discharged to fluidizing dryer. The separated mother liquid tank and is pumped back to crystallizer and low-pressure absorber.

The drilled crystals from dryers conveyed by a pneumatic pipe to the top of prilling tower and crystals are collected in cyclone and fed to melter. In melter, the crystals are melted and molten urea flows down to head tank through strainer for distributors and from distributors it falls down in prilling tower (IA-301) being cooled and solidified in the process.

The urea dust collecting equipment is provided to minimize air pollution by tower effluent; dust chamber is provided for scrubbing. Then the air is exhausted to atmosphere by induced fan for pt. After water mist from scrubbing section is eliminated by the filters.

NFL has been the market leader for manufacturing and marketing of Urea. The capacity utilization during the year 2004-2005 has been 106.2%.

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POWER SUPPLY SYSTEM :

In urea plant, two feeders of 11kV supply are received from MRS in urea substation at 11kV panel. This is further

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stepped down to 3.3kV & 415kV through transformers in urea plant. There are two 11kV/3.3kV 10MVA transformers and four 11kV/415V 1.6MVA transformers. The stepped down voltage i.e. 3.3kV and 415V is further fed to H.T. and L.T. motors. 3.3kV motors are directly fed from motor control centre. Further new buses are made at 415V and hence 415V motors are fed from power control centre.

Normally similar feeders are divided into two groups and fed from alternative sections. It is being done to have availability of partial equipments in case of limitation to some sections. These two feeders are connected together through bus coupler so that when one feeder fails, the bus coupler operates and the load connected to that feeder gets connected to the other feeder automatically.

SYNCHRONOUS MOTOR

DESCRIPTION

Output 2200kW Speed 333.3RPMPoles 18, excited field voltage- 55VVoltage 11kV, excited field voltage-13A Power factor 0.8Current 153AMotor field volts 220V, motor field current-152AArmature insulation class Motor-B, exciter-BField insulation class Motor-B, exciter-BSpace heater 2.5kW, 240VMake TOKYO SHIBAURA ELECTRICAL CO LTD Purpose For CO2 compressor

Synchronous motor is not self starting. The current in a synchronous motor is approximately in phase opposition in phase to the EMF generated current, remains high for longer period to avoid the tripping of motor circuit. The effect of armature reaction is to increase the flux in leading half of each pole. The flux is distorted in the direction of rotation and the

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lines of flux in the gap are skewed in such a direction as to exert a clockwise torque on the rotor. Since the resultant magnetic flux due to stator current rotates at synchronous speed, the rotor must also rotate at the same speed. As in case of induction motor if load is increased, speed slows down but in case of synchronous motor if there is increased in load then there is no change in speed. But in case of synchronous motor if there is increase in load the there is no change in speed. But in case the RPM decreases, the motor will stop running even a point difference in RPM causes the motor to stop running. Varying the field current can control power factor of synchronous motor.

STARTING OF SYNCHRONOUS MOTOR

When the rotor of three phase synchronous motor is stationary, the rotating magnetic field due to stator currents produces an alternating torque on the rotor i.e at once instant the rotor is moved clockwise and other counter clockwise. Since a net torque is zero, a synchronous motor is not self starting. The method to bring the motor up to synchronism is as follows:-

By damping grid in pole shoes:- these grid consist of copper bars short circuited at each end. The rotating magnetic flux induces current in these grids and the machine accelerates. During the starting period the rotor field winding is usually closed through the armature of exciter, normally a DC shunt generator carried on the extension of the shaft and current in the stator is limited to permissible value. When the machine has reached nearly full speed, the rated voltage is applied to stator winding and the exciter voltage will have built up sufficiently to magnetize the rotor poles. The resultant magnetic flux due to stator current is then moving past the rotor poles at a slow speed and produces a slow frequency alternating torque superimposed upon that exerted by the damping grids. Consequently the rotor is accelerated at one instant and retarded at other and the fluctuation of speed is sufficient to bring the rotor up to synchronous speed. Once this speed has been attained the rotor can run in synchronism.

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SYNCHRONOUS MOTOR SELECTION CRITERIA

We are having 2200kW, 11kV synchronous motor for running CO2 compressor UNB102. Why this motor was selected? Why we have not gone for an induction motor or steam turbine?

REASONS : -

LOW SPEED RESIPROCRATING COMPRESSOR

CO2 compressor popularly known as KOBE compressor is a low speed reciprocating compressor. We need very constant speed for this compressor. Normal induction motor has effect of voltage, frequency & mechanical loading on its speed due to said reasons, so this synchronous motor is selected.

POWER FACTOR IMPROVEMENT

In electrical AC system, voltage and current are concurrent. They always deviate with each other by some angle when drawn vertically. Cosine of this angle is known as power factor. LOW POWER FACTOR HAS SUCH DIS ADVANTAGES : -

IT affects the efficiency of generating station. Large electrical equipment such as transformers, motors are inductive in nature and they result in low pf of the system. Resistive loads have limiting pf. Capacitive loads are used to improve pf, which takes care of the motor of the loads. If we would have used an induction motor of 200kW, then capacitor requirement to improve the pf must have increased considerably. To overcome that problem, synchronous motor has been used, which maintains its own pf along with improving the pf of the system.

PROTECTION OF MOTORS

All the equipments are provided with sufficient & efficient protection system. For HV motors, sophisticated relays such as CIM relays,CAU relays etc are provided which monitor the

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current drawn by the motors while running and isolate the individual feeder in case the current exceeds the present values. There is one more relay called 86-P, which must be pf of your interest. Normally when any HV motor is started, 86-P relay is to be got reset. This relay monitors various parameters that are to be fulfilled before the main equipment is started. These parameters are lube oil pressure, seal oil pressure, value positions, dampers position etc. in case the requisite parameters are not fulfilled , the 86-P relay will get reset hence the equipment cannot be started. For LV motors, protection is fuses and thermal overload relay fuses & relay are selected in accordance with size of motor, starting and running conditions for monitoring of process parameters, one interlock contact is given in the starting circuit of the motor, which restricts the starting of the equipment if the parameter is not met. There are some other interlock also depending upon the service of equipment such as conveyors etc thermal overload relay is bimetallic conductor exceeds the limits bimetallic conductor expands in uneven fashion and actuate the trip system, tripping the motor. Fuses are provided as back up protection and for severe faults.

ADVANTAGES OF SYNCHRONOUS MOTOR

The ease with which the pf can be controlled. An overexcited synchronous motor having a leading pf can be operated in parallel with induction motors having lagging pf thereby improving the power factor of the supply.The speed is constant and independent of the load this is mainly used when the motor is required to derive another alternator to generate a supply of different frequency.

DISADVANTAGES OF SYNCHRONOUS MOTOR 1. Cost per kW is higher then induction.2. DC supply is necessary for rotor excitation. Small DC shunt generator carried on the extension of the shaft usually provides this.

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OFFSITES AND UTILITIES PLANTS

D.M. WATER PLANT

Water in its natural form contains no. of dissolved salts such as sulphates, chlorides and nitrates of calcium magnesium and sodium. If water is used as such in the boilers

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for raising steam, these salts will form scale on the tubes, which in addition to heat losses lead to many other many problems. Hence, removal of these salts from the water becomes quite essential. Ion exchange resign are used for this purpose of salt removal.The de mineralizing water plant of NFL Bathinda was supplied by M/s ION exchange (India) ltd Delhi.

It consisted of three units each of cation, anion, mixed bed, four secondary mixed bed and three units of condensate cation. At the time of setting up of a captive power plant, another stream to augment the existing capacity of polish water generation was by M\s BPMEL. It consisted of one unit each of cation, anion, primary mixed bed, two secondary mixed bed and two condensate cations.

Filtered water is received from raw water filtration plant into two filtered water reservoir feed water pumps discharge water from these reservoir tom cation units. These are total five feed pumps each having a capacity 0f 130m3/hr and four cation units. Three of these are charged with 13125L of cation resin and fourth unit is having 11900 0f resins. Cation like Na+, Ca++, and Mg++ present in the water are removed in the cation unit once exhausted, these units are regenerated with the counter current flow of dilute sulphuric acid.

The present day resins are made of cross linked polystyrene and cross linking is done by di vinyl benzene.Cation resins are made of sulphonated polystyrene SO3H can be represented by as RH.anionic resin is similarly made but is chloromethylated and then is animated. The final product is quaternary ammonium compound a strong base and is represented by ROH.

SULPHUR RECOVERY PLANT

Sulphur recovery plant of NFL Bathinda has been designed and engineered by M/S TOYO ENGINEERING CORPORATION, JAPAN. It was originally designed for processing 1710 Nm3/hr of

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Claus gas for 26.5MT/ of sulphur production but due to switch over to LSHS as ammonia production only 800 to 1000Nm3/hr of Claus gas is generated and 18-20 TPD sulphur is generated. Presently Claus gas contains 30-40% of H2S against 47.5% in original design.

COOLING WATER SYSTEMS

The cooling water systems provided at NFL Bathinda are closed recirculating type supplying cooling water to various consumers in the plant. There are total three systems supplying cooling water to different sections as mentioned below:

Sl no. System Consumer

1. CT-1 Ammonia plant

2. CT-2 Urea plant, boilers, instrument air compressors, service air compressors, caustic dissolving facility and sulphur recovery plant

3. CT-3 Crystallization section of urea plant

4. Emergency pumps ( can be connected with CT-1 or CT-2)

Ammonia storage area, instrument air compressors emergency diesel set

Emergency cooling water pump is in continuous service for ammonia storage area. It takes suction normally from CT -2;

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however, provision is there so that it can take suction from CT-1

DESIGN BASICBarometric pr. = 971 millibarsDry bulb temp. = 390CWet bulb temp = 280CDegree of approach = 50CRelative humidity = 81.1% at 31.40C

Various other design conditions for all three cooling water systems are given below;

COOLING WATER TREATMENT

Cooling water treatment is done to avoid following problems:Corrosion Scaling Fouling Microbiological growth

CORROSION

Corrosion is basically an electrochemical reaction by which metal tends to return to its more stable state of oxide. The main factors responsible for corrosion in cooling water systems are low pH, dissolved gases, conductivity of water, presence of certain corrosive ions such as chlorides and sulphates.Various types of corrosion occurring in cooling water systems

are general corrosion, pitting, galvanic corrosion cracking, stress corrosion cracking erosion and microbiological attack.The approach to protect metal from corroding in cooling water systems involves the formation and maintenance of a sufficiently strong inhibitor film on the cathodic, anodic or both areas.

SCALING

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Scaling is the deposition of sparingly soluble salts. The most common scalants in cooling water systems are carbonates and sulphates of calcium and magnesium and phosphates of calcium, magnesium zinc and iron. The carbonates and sulphates of calcium have inverse solubility with respect to temp. And pH when the solubility of these salts exceed, they tend to precipate out of solution and deposit on metal surface. Scale inhibitors are used which keep the scaling salts in dispersed state and do not allow them to deposit.

FOULING

Fouling is the deposition of suspended matter. The most common foulants in cooling water systems are dust, silt, clay organics like oils and hydrocarbons and the microbiological slime. These foulants are air borne as well as water borne. Fouling does not merely results in drop in heat transfer efficiency but also gives rise to under deposit corrosion leading severe pitting. Fouling is normally enhanced due to low water velocity. Low molecular weight polyanionic compounds are used as anti foulants. These components get absorbed on the surface of the foulest particles and increase the negative charge. Thus when all particles are sufficiently negatively charged they repel each other and thus dispersion is achieved.

MICROBIOLOGICAL GROWTH

Following tree types of microorganisms are responsible from this type of problem:

ALGAE: it is normally observed on the exposed area o cooling tower as it requires sunlight for growth.

FUNGUS: fungus is found on the wooden surface as it requires surface and carbon source.BACTERIA: Three important type of bacteria are:

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A.) NITRIFYING BACTERIA: these bacteria oxidize ammonia to nitrates and nitrites which when dissolved in water reduce the pH of circulating water and cause general corrosion. It is the most severe problem at NFL Bathinda.

B.) SULPHATE REDUCING BACTERIA: these anaerobic bacteria’s reduce sulphate ions to H2S This causes local pH to drop. The hydrogen sulphide thus formed reacts with metal surface to form metal sulphide. These deposits are very hard to remove and lead to severe pitting.

C.) IRON BACTERIA: iron bacteria directly oxidize the metal causing severe pitting. In general most of the species of bacteria present in cooling water secrete slime. This slime acts as a binding medium for the suspended matter and leads to fouling. The fouling deposits in turn give shelter to aerobic bacteria which cause direct corrosion. In addition to chlorine and bromine use of non oxidizing types of biocides is most. Various types of non oxidizing types of biocides are methylene-bis-thiocynate, quaternary ammonium compounds, isothiazoline, dichlorophenes etc. these biocides are normally blended with effective surface and penetrating agents. There by they can penetrate into the deposit layers and can kill anaerobic bacteria.

INSTRUMENT AIR COMPRESSOR HOUSE

There are four compressors of reciprocating type. Air is sucked from atmosphere and fed to L.P. stage. Air is sucked from atmosphere and fed to L.P. stage. Air is compressed at 2.4 Kg & sends to H.P. stage after passing through intercooler where air compressed up to 9Kg. This air is cooled to -15 ˚C. It is oil and dust free.

PERFORMANCE:

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TYPE KIRLOSKAR, HITACHIMODEL TC-BTD-AHCYLINDER BORE X No.FIRST STAGE 487mmSECOND STAGE 267mmSTROKE 200mmSPEED 590RPMCAPACITY:At suction conditions: 1884mc/Hr At 600 RPMSuction pressure 0.99 Kg/cm Sq

PROJECT STUDY OF VARIABLEFREQUENCY DRIVE

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Steam Generation plant is mainly installed for production of steam and then distributed to various parts of the plant.Here this section of plant installed in National Fertilizers Limited, Bathinda unit produces and supplies steam at 100 Kg / cm2 pressure and nearly 480°C temperature to Ammonia Plant.In today’s world steam has gained importance in Industries. It may be used for power processes and heating purposes as well. There are three boilers capable of producing steam at the rate of 150 Tonnes/hr installed in CPP which were supplied and erected b BHEL. Generally two boilers are enough to meet the requirements but third boiler is simultaneously running because if steam load consumption increases then the third boiler play its part in order to avoid any faulty condition.

Each Boiler has 2 ID fans(INDUCED DRAFT FAN) and 2FD fans (FORCED DRAFT FAN).

FORCED DRAFT FAN

The forced draft fans supply the proper amount of secondary air required to support the combustion of the fuel delivered to the boiler. The details of the FD fan are:

Make SEIMENSRating ContinuousInsulation class BRated power 160kWVoltage 415VPower factor 0.85Current 258ARPM 940Poles 6Connection Λ

INDUCED DRAFT FAN

The induced draft fans control the furnace draft by drawing the gases of combustion through the boiler, regenerative air

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heaters, delivering them to the stack. Thus the FD fan provides combustion air for the furnace while the ID fan removes flue gases from furnace through chimney. The details of the ID fan are:

Make SEIMENSRating ContinuousInsulation class BRated power 150kWVoltage 415VPower factor 0.83Current 275ARPM 770Poles 8Connection Λ

Each Boiler of SGP has two Induced draft fan and two Force draft fan. These boilers are Water Tube Boilers i.e water is inside the tubes and hot air surrounds it when coal is burnt ,this makes the water in the tubes boil and steam formation takes place. In the beginning coal is burnt with fuel oil in order to get desired temperature. From above study we come to know that ID fans in the boilers are used to removes flue gases from furnace through chimney and the FD fan provides combustion air for the furnace. In earlier days these ID and FD fans were connected to the 3 phase Squirrel cage Induction Motor through VS coupling (it is just like a mechanical coupling between fan and motor). So when we need less air to force to the boiler from the Forced Draft fan / Induce draft fan we just make this VS coupling so arranged to our requirement that only that much air enters to the boiler i.e. VS coupling can be understood as a dampers which accordingly allows a passage for air to pass as set. When we needed less supply of air from these fans to the boilers, we just close the dampers mechanically to that much extent that only the required air passes but this mechanical Damper system was having severe disadvantages : As the motor connected to the ID /FD fans always was running on full load but we were not utilizing whole energy of

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motor as when air entering from these fans was less or on full capacity, then also the motor was running on same load. So lot of energy was wasted. To overcome this problem VARIABLE FREQUENCY DRIVE (VFD)was installed which not only made the system work efficiently but saved a lot of Energy. As by using VFD we just can vary the frequency accordingly which can be used to vary the speed of the motor connected to ID/FD fans. So by reducing the rpm of the motor by varying frequency ,we was able to take only that much air to the boiler needed for proper combustion and remove flue gases from the Boiler.

INTRODUCTION TO BASIC CONCEPTS TO BE UNDERSTOOD

WHAT IS DRIVE

The power required by the machines for its working is generally provided by electric motors.

The electric motor take electrical energy input and convert it into rotational mechanical energy out put. This mechanical energy drives the machine.

The electric power made available by State Electricity Board ,at times for certain applications need to be modified and controlled in a specific manner before giving it to the motor to get the desired performance from the motor.

So Drive is nothing but the product that takes the available electric power , converts it into the required form and then gives it to the motor and in addition , provides required protection to the motor and the system.

Example 1:

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AC supply --------→ --------→ Variable DCVoltage - Fixed Frequency - Fixed

Example 2: AC supply --------→ --------→ Variable Freq. Voltage - FixedFrequency - Fixed Variable Volt. AC supply

WHAT MOTOR PROVIDES ?

The motor produces torque and this torque makes the motor shaft to rotate. The motor shaft is coupled to the machine shaft and therefore the machine shaft also rotates. Through the coupling mechanical power at the motor shaft gets transferred to the machine. The motor rotates because of mechanical energy produced in the motor.

HOW MOTORS ARE CLASSIFIED ?

There are various ways by which a motor can be classified.One way is to classify motors on the Basis of type of electric supply it needs.

1. DC motors need DC Supply2. AC motors need AC Supply

As most widely used AC motor is 3 phase squirrel Cage Induction Motor. This is because of its few favourable factors such as :

1. Its Robust nature.2. Small size and Weight.

DRIVE

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3. Negligible maintenance.4. Low Cost.

WHAT IS AC DRIVE ?

The electronic product that gives the desired power to AC Motor is called AC Drive. AC Drive takes Fixed Voltage, Fixed Frequency and converts into variable frequency and Variable Voltage AC supply, that is why this Drive is called “ VARIABLE FREQUENCY DRIVE ”.

WHY WE NEED TO GIVE POWER TO AC MOTOR THROUGH AN AC MOTOR ?

The AC motors are normally rated for the rating of State Electricity Board supply which in our case is 3 phase, 415 V, 50 Hz AC supply. When this supply is given to the motor, the motor rotates practically at constant speed i.e. close to its rated speed at all loads. If one needs variable speed at the motor shaft then supply to the motor will have to be given through an AC Drive.

HOW SPEED DEPENDENCE OF AC MOTOR IS DIFFERENT THAT OF DC MOTOR ?

The speed of the DC motor is decided by the voltage applied to its armature/field winding. In the case of AC motor the speed is decided by the frequency of supply given to the motor.

WHAT IS RATED SPEED ?

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The speed of the rotor is determined by the “synchronous speed” of the motor. The synchronous speed is the speed of the rotating magnetic field produced by current in the motor winding.The synchronous speed is determined by the frequency of supply and the number of poles for which the motor is wound.

The formula for synchronous speed (Ns) Ns = 120 f / PWhere f is frequency in Hz.and P is number of Poles for which the motor is wound.

e.g. The synchronous speed (Ns) for 4 pole motor running on 50 Hz is 1500 RPM.

e.g. The synchronous speed (Ns) for 2 pole motor running on 60 Hz is 3600 RPM.

It should always be kept in mind that the Rotor of the motor always rotates at a speed little lower than the synchronous speed. Generally the rotor speed is less around by 4 %.

e.g. The speed of a 4 pole squirrel cage Induction motor running on 50 Hz will therefore be around (1500 - 4 % of 1500) = 1440 RPM.

WHAT IS SLIP ?

As we know now that the Rotor of a squirrel cage Induction motor can never rotate at synchronous speed. The difference in synchronous speed (Ns) and the actual rotor speed (Nr) is called slip.

The slip is always expressed in percentage and is given by the following formula. % Slip = Ns - Nr / Ns * 100

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The percentage slip value depends upon the load on the motor but one can assume it to be around 4 – 5 % at full load.

HOW CAN WE VARY THE SPEED OF AN AC MOTOR, ELECTRICALLY ?

The speed of the rotor is decided by the synchronous speed, which in turn is decided by the frequency of supply and the number of the poles for which the motor is wound.

Thus there are two ways by which we can vary the speed electrically.

1. Vary the frequency of supply given to the motor.2. Change the number of poles for which the motor is

wound.

The first method will provide step less variation whereas the latter will provide variation in steps.

STEP LESS VARIATION STEPPED VARIATION

There is a limitation with regard to the possible number of steps using pole changing method . Generally 2 to 4 speeds are feasible.

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DO WE EXPECT ONLY VARIABLE SPEED FROM AN AC DRIVE ?

Although the primary function of an AC Drive is to get variable speed at motor shaft, the other important parameter that needs to be taken care is to maintain torque producing capability of the motor constant at all speeds. i.e. from minimum to the rated speed of the motor. IF SPEED OF THE MOTOR DEPENDS UPON THE FREQUENCY, THEN TORQUE DEPENDS UPON WHAT ?

The torque in any motor primarily depends upon motor flux and the rotor current. In order to maintain torque producing capability of the motor at rated value at all speeds . The rotor current will then be totally dependent on the torque demanded by the load i.e. more load or load torque requirement less will be the rotor current.

DO WE NEED TO VARY THE VOLTAGE ALSO ?

Along with frequency we need to vary the voltage also in same proportion i.e. if we make the frequency half then voltage given to the motor should therefore control power switching devices in such a manner that we get a supply of whose frequency as well as voltage can be varied. In this variation we should keep the ratio of the voltage to frequency constant.

E = 4.44 × F × Ø × Z

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