PROJECT REPORT Summer Training

BADARPUR THERMAL POWER STATION

Submitted by: Manik Singh B.Tech (E.E.E) GURU TEGH BAHADUR INSTITUTE OF TECHNOLOGY

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This is to certify that Manik Singh, student of Electrical & Electronics Branch IInd Year; Guru Tegh Bahadur Institute Of Technology has successfully completed his industrial training at Badarpur Thermal power station New Delhi for six weeks from 13th June to 23rd July 2011 He has completed the whole training as per the training report submitted by him.

Training Incharge BTPS/NTPC NEW DELHI

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AcknowledgementWith profound respect and gratitude, I take the opportunity to convey my thanks to complete the training here. I do extend my heartfelt thanks to Mrs. Rachna Singh for providing me this opportunity to be a part of this esteemed organization. I am extremely grateful to all the technical staff of BTPS/NTPC for their co-operation and guidance that helped me a lot during the course of training. I have learnt a lot working under them and I will always be indebted of them for this value addition in me. I would also like to thank the training in charge of Skyline Institute of Engineering & Technology Gr. Noida and all the faculty member of Electrical & Electronics department for their effort of constant co-operation. Which have been significant factor in the accomplishment of my industrial training.

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ABOUT THERMAL POWER PLANT

Thermal power plant is a coal based power plant which is based on RANKINE CYCLE (CARNOTS CYCLE)

RANKINE CYCLEThe theoretical basic cycle for the simple steam turbine power plant is the Rankine cycle which is closed one. It include superheating, regenerative feed water heating and reheating. The rankine cycle is a thermodynamic cycle which converts heat into work. The heat is supplied externally to a closed loop, which usually uses water as the working fluid.

DESCRIPTION OF RANKINE CYCLE

A simple layout and processes of the rankine cycle.

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A rankine cycle needs four main parts for operating the cycle i.e. Water feed pump, boiler, turbine and condenser. A rankine cycle describes a model of the operation of steam heat engine which is found in power generation plant. Common heat sources for power plant using the rankine cycle are coal, natural gas, oil, nuclear energy. The rankine cycle is sometimes referred to as a practical Carnot cycle when an efficient turbine is used. The main difference is that a pump is used to pressurize liquid instead of gas. This requires about 100 times less energy than that compressing a gas in a compressor (as in CARNOT CYCLE). The efficiency of a rankine cycle is usually limited by the working fluid. Without the pressure going super critical the temperature range cycle can operate over a quite small, turbine entry temp are typically 565C [the creep limit of stainless steel] and condensor temperature are around 30C. This gives a theoretical Carnot efficiency of around 63% compared with an actual efficiency of 42% for a modern coal-fired power station. This low turbine entry temperature is why the rankine cycle is often used as a bottoming cycle in combined cycle gas turbine power stations. The working fluid in rankine cycle follows a closed loop and is re-used constantly. The water vapor often seen billowing from power station is generated by the cooling system and represents the waste heat that could not be converted to useful work. While many substances could be used in the rankine cycle, water is usually the fluid of choice due to its favorable5

properties such as nontoxic, unreactive chemistry, abundance and low cost as well as its thermodynamic properties.

THE THERMODYNAMIC PROCESSES DEFINED BY THE T-S DIAGRAM

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There are four processes in the Rankine cycle. These states are identified by numbers in the diagram to the left.

Process 1-2: The working fluid is pumped from low to high pressure, asthe fluid is a liquid at this stage the pump requires little input energy.

Process 2-3: The high pressure liquid enters a boiler where it is heatedat constant pressure by an external heat source to become a dry saturated vapor.

Process 3-4: The dry saturated vapor expands through a turbine,generating power. This decreases the temperature and pressure of the vapor, and some condensation may occur.

Process 4-1: The wet vapor then enters a condenser where it iscondensed at a constant temperature to become a saturated liquid.

BRIEF DESCRIPITION OF COAL BASED POWER PLANTA coal based power plant is that in which the coal is supplied from the coal storage to the boiler through the coal handling plant. The atmospheric air is feed to the boiler through an air preheater where air is heated by the flue gases coming out as a waste heat. The heated air enters the boiler and thus increases the efficiency. As a result of combustion of water supplied in the boiler at desired pressure gets converted into steam and ash and flue gases are formed. The ash is removed by ash handling and disposal system whereas the flue gases passes through the preheater, dust collector and finally chimney to the atmosphere. The steam so generated passes through the super heater tubes and gets converted in to superheated steam. This superheated steam enters to the turbine through the steam stop valve (ssv) and governor valve (gv). The stop valve is used for starting and stopping the turbine whereas the governor valves maintain the speed of the

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turbine sensibly constant irrespective of the load. Alternator converts the mechanical energy produced by the turbine into electrical energy produced by the turbine in to electrical energy which is fed to the transformer, circuit breaker and finally to bus bar.

The exhaust steam from the turbine is condensed in the condenser. Due to the exchange of heat with cooling water condenser is equipped with a vacuum pump to extract any air which may be present due to leakage through joints and gases released upon condensation. The condensate is extracted by a condensate extraction pump and lead to L.P. feed heater where feed water is heated with steam bled in the turbine. The heated feed water is pumped back to the boiler through H.P. feed heater.

The cooling water is supplied to the condenser by a circulating water pump through a closed circuit. The heated water is cooled in cooling tower. Some quantity of cooling water in the form of water vapor carried away by the air hence makeup cooling water to the condenser supplied from the river to a filter. If the source of cooling water is an ocean, then there is a need of desalination plant. If the source of cooling water is river then the cooling tower can be dispensed with and the hot water is led to the river as the case may be like an open system. Due to leakage of the steam from the turbine some quantity of steam gets lost. Hence makeup water well treated through a water treatment plant is generally added up in the well of condenser.

BASIC OPERATION OF THERMAL POWER PLANT:As we know ,the thermal power plant basically works on rankine cycle.

COAL CONVEYOR: It is a belt type of arrangement. With this coal istransported from coal storage place in power plant to the place near by boiler.

STOKER: The coal which is brought near by boiler has to put in boiler furnace forcombustion. This stoker is a mechanical device for feeding coal to a furnace.

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PULVERIZER: The coal is put in the boiler after pulverization. For this pulverizer isused. A pulverizer is a device for grinding coal for combustion in a furnace in a power plant.

BOILER: Pulverized coal is put in boiler furnace. Boiler is an enclosed vessel inwhich water is heated and circulated until the water is turned in to steam at the required pressure.

SUPERHEATER: Most of the modern boilers are having superheater andreheater arrangement.

REHEATER: Some of the heat of superheated steam is used to rotate theturbine where it loses some of its energy. Reheated is also steam boiler component in which heat is added to this intermediate-pressure steam, which has given up some of its energy in expansion through the high-pressure turbine.

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CONDENSER: Steam after rotating steam turbine comes to condenser.Condenser refers here to the shell and tube heat exchanger (or surface condenser) installed at the outlet of every steam turbine in thermal power stations of utility companies generally.

COOLING TOWER: The condensate (water) formed in the condense aftercondensation is initially at high temperature. This hot water is passed to cooling towers. It is a tower-or building-like device in which atmospheric air (the heat receiver) circulates in direct or indirect contact with warmer water (the heat source) and the water is thereby cooled (see illustration).

ECONOMISER: Flue gases coming out of the boiler carry lot of heat. Functionof economizer is to recover some of heat from the heat carried away in the flue gases up the chimney and utilize for heating the feed water to the boiler. It is placed in passage of flue gases in between the exit from the boiler and the entry to the chimney.

AIR PREHEATER: The remaining heat of flue gases is utilized by air preheater. It is adevice used in steam boilers to transfer heat from the flue gases to the combustion air before the air enters the furnace. Also known as heater; air heating system. It is not shown in the layout. But it is kept at a place near by where the air enters in to the boiler.

ELECTROSTATIC PRECIPITATOR: It is device which removes dust or otherfinely divided particles from flue gases by charging the particles inductively with an electric field, then attracting them to highly charged collector plates. Also known as precipitator.

SMOKE STACK: A chimney is system for venting hot flue gases or smoke froma boiler, stove, furnace or fireplace to the outside atmosphere. They are typically almost vertical to ensure that the hot gases flow smoothly, drawing air into the combustion through the chimney effect (also known as the stack effect).

GENERATOR: An alternator is an electriomechanical device that convertsmechanical energy to alternating current electrical energy. 10

TRANSFORMER: It is a device that transfers electric energy from onealternating-current circuit to one or more other circuits, either increasing (stepping up) or reducing (stepping down) the voltage.

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FUNDAMENTALS PARTS OF THERMAL POWER PLANT

FUNDAMENTAL PARTS:

Boiler Steam turbine Condenser Feed pump

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Training at BTPSI was appointed to do six-week training at this esteemed organization from 13th June to 23rd July 2011. In these six weeks I was assigned to visit various division of the plant which were 1. 2. 3. 4. Operation Control and instrumentation (C&I) Electrical maintenance division I (EMD-I) Electrical maintenance division II (EMD-II)

This six-week training was a very educational adventure for me. It was really amazing to see the plant by myself and learn how electricity, which is one of our daily requirements of life, is produced. This report has been made by self-experience at BTPS. The material in this report has been gathered from my textbooks, senior student report, and trainer manual provided by training department. The specification & principles are at learned by me from the employee of each division of BTPS.

BADARPUR THERMAL POWER STATION(BTPS)INTRODUCTIONNTPC Limited is the largest thermal power generating company of India. A public sector company, it was incorporated in the year 1975 to accelerate power development in the country as a wholly owned company of the Government of India. At present, Government of India holds 89.5% of the total equity shares of the company and FIIs, Domestic Banks, Public and others hold the balance 10.5%. With in a span of 31 years, NTPC has emerged as a truly national power company, with power generating facilities in all the major regions of the country. BTPS is capable of generating 720 MW. The generation of the plant is divided in two phases i.e. PHASE I and PHASE II. The first phase was built up in year 1973, it consists up of 3 unit of 95 MW. The second phase consists of two units of 210 MW. Thus, total capacity of the station becomes 705 MW. The coal is supplied from Jahria Coal Fields (C.C.L) and the Agra Canal is the water source for the various purposes. The corporation is managing the plant since April 15th 1978. At the time of change over of management the installed capacity was 285 MW and under N.T.P.C. two more units of 210 MW , each were erected and commissioned. N.T.P.C. is the front-runner in the power sector. The power is supplied to a 220 KV network that is a13

part of the northern grid. The ten circuits through which the power is evacuated from the plant are : Mehrauli and II Okhla I and IIC Ballabgarh I and II UP(Noida) Jaipur

There are totally five units in BTPS. The details of various units are : 1x95MW in 1973 1x95MW in 1974 1x95MW in 1975 1x210MW in 1978 1x210MW in 1981

The installed capacity of BTPS is 705MW.

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EMD IElectrical maintenance division 1It includes :

OCHP/NCHP HT/LT Switchgear

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COAL HANDLING PLANT

OLD COAL HANDLING PLANT16

It feeds units 1,2,3 (95 MW each). OCHP has two streams from wagon tippler to tippler conveyors in the main power house building via crusher house, each stream contains one wagon tippler, two vibrating feeders below wagon tippler, one vibrating screen, one building conveyors and necessary conveyors. A single telescopic chute reclaim hopper and series conveyors achieve the stacking and reclaiming. Coal unloaded by the wagon tippler is fed to the main conveyor by the vibrating feeders. The main conveyors 1A/1B each of 600 m tones per hour, which is running partly under ground and partly over ground, conveys coal to the crusher house. Coal is fed to the crusher through vibrating screen. The coal after being crushed in the crushers is transported to the bunker conveyor and from the under conveyor coal is fed into the bunker with the help of travelling tipplers with the help of bunker conveyor. Alternatively when the bunkers are full, uncrushed coal is by passed in the crusher house and transported in the stock yard for stacking through the telescopic chutes. However, the provisions also make to stack the coal into the yard after crushing in the crusher house. The motor of 75 HP used in the wagon tippler is fed by three feeders. One main feeder which remain always hold and two other feeders which are operated alternatively, one during one side rotation of the motor and the other during the other side rotation of the motor. There is a limiting switch associated with motor. From wagon tippler the coal falls in the hopper, from hopper it falls on the screen from where the coal of the larger size is separated .When the vibrator vibrates, the coal falls on the conveyor from the screen.

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NEW COLD HANDLING PLANTN.C.H.P feeds units 4 and 5(210 MW each). It consists double stream(one working at a time) of conveyors of capacity 600 mtph, which is single. One wagon tippler , four vibrating feeders of 300mtph each below the wagon tippler, two rotator breakers of 600mtph each in breaker house(primary crusher house) reject bin house. Two crushers(ring granular), two vibrating feeders and two belt feeders of 600mtph each in secondary crusher house. One telescopic chute for stacking, two sets of reclaim hoppers, necessary transfer points and new rail tracks for wagon tippler are provided. The wagon tippler is provided with internal weighbridge for recording the gross and true weight of the wagon and located beyond the old marshalling yard. Due to space limitation only one wagon tippler is provided . Car pullers are used for placing loaded wagon on the wagon tippler and removing the empty wagon. The locomotive does marshelling of the load wagon rake for placing it to the inhaul side and for taking the away the empty wagon rake.The marshelling yard ius used for placing the loade rake; the coal from the wagon tippler house( 6 in numbers) is fed to the reclaim conveyor by the vibrating feeders, the reclaim conveyors are partly under the ground and partly over the ground. From reclaim conveyors coal is transported to the bunker house( primary crusher house) and fed into the rotatory breakers. In the rotatory breakers the coal side is reduced to 100mm and the foreign materials like stone shale etc are seperated. The coal is sent to secondary crusher house for secondary crushing or to the old stockyard for stacking through cantelever conveyor with telescopic chute. The reject conveyors conveys the foreign material to the reject bin. Dump trucks are used to carry the reject from the reject bin to reject disposal area. In the secondary crusher house coal is fed to the secondary rusher of ring granulator type (2 in number) through vibrating feeders. The coal after being crushed in the secondary crusher to 20mm in size is transportes to the coalbunker conveyor for unit 4 and 5 finally. Finally coal is fed into the through travelling tipplers. Stacking of the coal in the coal stockyard is done by the cantilever conveyors with telescopic chute, which is conical18

stockpile of 15mm height. The stockpile is spread by means of bulldozers for making a common stockpile for the plant. Normally coal is fed to the bunkers of unit 4 and 5 from N.C.H.P. Necessary dust systems are provided. There is a separate controll room with necessary control panel and MCCS for N.C.H.P.

VARIOUS CONSTITUENTS OF NCHP

1. WAGON TIPPLERThere are 3 wagon tipplers in the BTPS-two for OCHP and one for NCHP

In this unit coal comes from Jawar Mines in Bihar through wagons, so tansportation is done by Indian Railways for BTPS. Each wagon carries about 50-60 tonnes of coal, wt of wagon are about 10-15m tonnes, so wagon tippler is handling about 70-75m tones of coal. During unloading of wagon, wogon is brought to the base of the wagon tippler. This base is operated with the help of the gear system. This gear systen is then operated by motor of 75hp coupled to the gear box, the torque from the motor is then transported to the wagon tippling base, which is then rotated with the help of the rake and pinion arrangement, the complete rotation of the wheel is 151 degree angle. To prevent the full rotation counter weight are provided.

Heat resistant belting is always recommened for handling material at temperature over 60 degree centigrade.

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2. BREAKER HOUSESize of the coal at wagon tippler is about 300mm, which is supposed to be very large. To prevent much load on the crushers, breakers are provided in between which reduces the size of coal to 100mm. Coal is carried to breaker house through conveyor 12A/12B, which is then dropped inside the hopper, from hopper the coal goes to chute. Now the direction of coal is selected.It can either be sent to rotatory breakers or directly to the reversible bulk feeders(RBF 1,2).

There are two rotatory breakers (RB). Each breaker has two rotatory drums.The coal comes in between these drums and broken to smaller pieces. The stone particles which are not crushed by the rotatory drums are thrown out of the breaker sysytem due to rotation of the drum to conveyor belts 18A/18B which take them out to reject bin house.

The whole system is operated with the help of chain drive; an electric motor is to drive the system. Motor is firstly connected to the gearbox, the gearbox is coupled to the chain through teethed wheels.

Two belt wares(BW) are also provided in the breaker house, which are measuring the coal carrying capacity of conveyor belts 12A/12B in m tones/hr.

3. CRUSHER HOUSECoal of 100mm size from transfer point(TP 7) is carried to the crusher house main hopper in the conveyor belts 14A/14B. Before dropping into the main hopper, a magnetic seperator(MS) is provided to remove all ferrous impurities. A conveyor belt is continously used, moving around the MS on which magnetic20

impurities are attached and carry to the iron chute. From main hopper coal goes to vibrating feeders(VF 7,8). From this place it goes to the crusher. There are two crushers in the crusher house; using electric motor operates crusher (CR 1,2). In crusher house there are four rows and each has two shafts there are two types of hammers used

1. Plane hammer 2. Teethed hammer

These are arranged altenatively in each row. The number of hammers in each row follow the sequence 13,14,13,14. Thus total no. of hammers is 54, breaking plates are provided inside the crucher. The coal is bein crushed between the hammers and breaking plates. The crushed coal is passed through a screen or a wire mesh which determines the size of crushed coal. Bigger pieces wont pass through the screen. Capacity of the crusher is 600mtones/hr.

The size of the coal after crushing is 20mm, which is then fed to the belt feeder (BF 1,2) through flap gates(FG 12,13) to conveyor belts 15A/15B. Crushed coal from this conveyor passes through the meatl detector. After detection the metal pieces are removed manually. The coal is then transferred to the TP 8and then to the bunkers. NCHP crushed coal is sent to the boiler unit 4 and 5. The coal to the units 1,2,3 can be fed from this plant. The coal is further pulverised in bowl mill. Belt wares are provided to conveyors 15A/15B.

4. MCC-II

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MCC means motor control centre. MCC II supplies power to conveyor 11A/11B,TP 6,VB 1,2,3,4,5,6 and 25 breakers(440). The supply is coming from UCB IV.

VARIOUS INSTRUMENTS/EQUIPMENTS AT NCHP

MAGNETIC SEPERATORThey are two in numbers and attached to conveyors 14A/14B.There might be possibility that coal has some iron particles in it.It is a box containing impuritys coil wounded over the magnetic material. Electric current is passed after operating it from control unit. A very heavy high magnetic flux density of 700wb/sqm is produced. This flux can attract the iron pieces of 30-40kg.

METAL DETECTORThey are provided near the conveyor 15A/15B to detect metal pieces.It has two plates having constant reluctance between them. Coal and belt are non metallic type, so doesnt affect the reluctance. But as soon as any metal part comes, reluctance is affected so a change in voltage is sensed and motor is tripped. The motor tripping gives current to the solenoid which attracts the metal rod inside it and sand bag marker provided just after MDfalls when metal detected.

WAGON TIPPLERPower Rated Voltage22

75HP 415V

Rated Current Phase RPM Frequency

102A 3 phase 1480 rpm 50HZ

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

ZERO SPEED SWITCHIt is safety device for motors, i.e., if belt is not moving and the motor is on the motor may burn. So to protect this switch checks the speed of the belt and switches off the motor when speed is zero.

CRUSHER HOUSE

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Power Rated Voltage Phase RPM Frequency

400HP 415V 3 phase 1480 rpm 50 HZ

VENTILLATION DEVICESDust extraction or dust seperation pipes come under this category. Fan is used to blow the dust out pipe, from which it goes to cyclone seperator and where water is spread over it to form slurry and get seperated.

SAFETY DEVICES FOR BELT CONVEYORSSometimes the belt is wet due to any reason, so it may not run due to reduced friction. A switch senses this and prevents the belt from choking.

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Sometime any accident may occur which requires the belt to stop, the pull cords are pulled to stop the conveyor. This system starts again only when the pull cords are rest.

There is a push button in the control room from where the belt can be stopped in case of emergency stoppage.

Other equipments are pulley.Pulleys are made of mild steel, rubber logging is provided to increase the friction factor between the pulley and belt.

MILLING SYSTEM

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

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

3. Ball Mill:The ball mill crushes the raw coal to a certain height and then allows it to fall down. Due to impact of ball on coal and attraction as per the particles move over each other as well as25

over the Armor lines, the coal gets crushed. Large particles are broken by impact and full grinding is done by attraction. The Drying and grinding option takes place simultaneously inside the mill.In ball mill coal is converted to powdered form and due to pneumatic action the powdered form of coal is transferred upwards.Motor specification squirrel cage induction motor Rating340 KW Voltage6600KV Curreen41.7A Speed980 rpm Frequency50 Hz No-load current15-16 A

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Classifier:

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

5. MILL FANFrom ball mill the powdered coal is sucked through mill fan.

6. Cyclone SeparatorsIt separates the pulverized coal from carrying medium. The mixture of pulverized coal vapour caters the cyclone separators.

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The Turnigate

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It serves to transport pulverized coal from cyclone separators to pulverized coal bunker or to worm conveyors. There are 4 turnigates per boiler.

8. WORM CONVEYORIt is equipment used to distribute the pulverized coal from bunker of one system to bunker of other system. It can be operated in both directions.

SWITCH27

GEAR

INTRODUCTIONSwitchgear is one that makes or breaks the electrical circuit.

The equipments that normally fall in this category are :28

1. ISOLATORAn isolator is one that can break the electrical circuit when the circuit is to be switched on no load. These are used in various circuits for isolating the certain portion when required for maintenance etc. An operating mechanism box normally installed at ground level drives the isolator. The box has an operating mechanism in addition to its contactor circuit and auxilliary contacts may be solenoid operated pneumatic three phase motor or DC motor transmitting through a spur gear to the torsion shaft of the isolator.Certain interlocks are also provided with the isolator. These are 1. Isolator cannot operate unless breaker is open. 2. Bus 1 and bus 2 isolators cannot be closed simultaneously. 3. The interlock can be bypass in the event of closing of bus coupler breaker. 4. No isolator can operate when the corresponding earth switch is on

2. SWITCHING ISOLATORSwitching isolator is capable of : 1. Interrupting charging current. 2. Interrupting transformer magnetising current. 3. Load transformer switching.

Its main application is in connection with the transformer feeder as the unit makes it possible to switchgear one transformer while the other is still on load.

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

4. LOAD BREAK SWITCHESThese are those interrupting devices which can make or break circuits. These are normally on same circuit, which are backed by circuit breakers.

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

LT SWITCHGEARIn LT switchgear there is no interlocking.It is classified in following ways:-

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

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

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

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

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

HT SWITCHGEAR31

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Minimum oil Circuit Breaker

These use oil as quenching medium. It comprises of simple dead tank row pursuing projection from it. The moving contracts are carried on an iron arm lifted by a long insulating tension rod and are closed simultaneously pneumatic operating mechanism by means of tensions but throw off spring to be provided at mouth of the control the main current within the controlled device. Type-HKH 12/1000c Rated Voltage-66 KV Normal Current-1250A Frequency-5Hz Breaking Capacity-3.4+KA Symmetrical 3.4+KA Asymmetrical 360 MVA Symmetrical Operating Coils-CC 220 V/DC FC 220V/DC Motor Voltage-220 V/DC

2. Air Circuit BreakerIn this the compressed air pressure around 15 kg per cm^2 is used for extinction of arc caused by flow of air around the moving circuit . The breaker is closed by applying pressure at lower opening and opened by applying pressure at upper opening. When contacts operate, the cold air rushes around the movable contacts and blown the arc. It has the following advantages over OCB:i. Fire hazard due to oil are eliminated. ii. Operation takes place quickly. iii. There is less burning of contacts since the duration is short and consistent. iv. Facility for frequent operation since the cooling medium is replaced constantly. Rated Voltage-6.6 KV Current-630 A Auxiliary current-220 V/DC32

3. SF6 Circuit BreakerThis type of circuit breaker is of construction to dead tank bulk oil to circuit breaker but the principle of current interruption is similar o that of air blast circuit breaker. It simply employs the arc extinguishing medium namely SF6. the performance of gas . When it is broken down under an electrical stress. It will quickly reconstitute itself Circuit Breakers-HPA Standard-1 EC 56 Rated Voltage-12 KV Insulation Level-28/75 KV Rated Frequency-50 Hz Breaking Current-40 KA Rated Current-1600 A Making Capacity-110 KA Rated Short Time Current 1/3s -40 A Mass Approximation-185 KG Auxiliary Voltage Closing Coil-220 V/DC Opening Coil-220 V/DC Motor-220 V/DC SF6 Pressure at 20 Degree Celsius-0.25 KG SF6 Gas Per pole-0.25 KG

4. Vacuum Circuit BreakerIt works on the principle that vacuum is used to save the purpose of insulation and it implies that pr. Of gas at which breakdown voltage independent of pressure. It regards of insulation and strength, vacuum is superior dielectric medium and is better that all other medium except air and sulphur which are generally used at high pressure. Rated frequency-50 Hz Rated making Current-10 Peak KA Rated Voltage-12 KV Supply Voltage Closing-220 V/DC Rated Current-1250 A33

Supply Voltage Tripping-220 V/DC Insulation Level-IMP 75 KVP Rated Short Time Current-40 KA (3 SEC) Weight of Breaker-8 K

EMD IIElectrical maintenance division 2

It includes :

GENERATORS SWITCHYARD34

ESP

GENERATORS35

The generator works on the principle of electromagnetic induction. There are two components stator and rotor. The rotor is the moving part and the stator is the stationary part. The rotor, which has a field winding, is given a defence colony excitation through a set of 3000rpm to give the required frequency of HZ. The rotor is cooled by Hydrogen gas, which is locally manufactured by the plant and has high heat carrying capacity of low density. If oxygen and hydrogen get mixed then they will form very high explosive and to prevent their combining in any way there is seal oil system. The stator cooling is done by de-mineralised(DM) water through hollow conductors. Water is fed by one end by Teflon tube. A boiler and a turbine are coupled to electric generators. Steam from the boiler is fed to the turbine through the connecting pipe. Steam drives the turbine rotor. The turbine rotor drives the generator rotor which turns the electromagnet within the coil of wire conductors.

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Carbon dioxide is provided from the top and oil is provided from bottom to the generator.With the help of carbon dioxide the oil is drained out to the oil tank. Hydrogen gas is used to cool down the rotor. Lube oil is used to cool the bearings. DM water is used to cool the stator. Seal oil is used to prevent hydrogen leakage Seal oil coolers are present to cool the seal oil Hydrogen dryer are used which removes the moisture from hydrogen gas and then is supplied to the generator. Clarified water in cooling tower is used to cool down the hydrogen gas.

RATINGS OF THE GENERATORS USED Turbo generator 100MWMAKE BHEL,Haridwar37

CAPACITY 117,500 KVA POWER 100,000 KW STATOR VOLTAGE 10,500 V STATOR CURRENT A SPEED POWER FACTOR FREQUENCY HZ EXCITATION GAS PRESSURE 280 V 2.5 kg/cm2 5 0.85 50 6475

TURBO GENERATOR 210 MWMAKE BHEL,Haridwar CAPACITY 247,000 KVA POWER 210,000 KW STATOR VOLTAGE 15,750 V STATOR CURRENT A SPEED 5000 rpm POWER FACTOR 0.85 9050

38

FREQUENCY HZ EXCITATION GAS PRESSURE kg/cm2 310 V

50

3.5

GENERATOR TRANSFORMER (125 MVA UNIT-I & UNIT-III)RATING 125MVA TYPE OF COOLING TEMP OF OIL 45^C TEMP WINDING KV(no load) 233 KVA LV -10.5 KVA 60^C HVOFB

LINE AMPERES 310 A

HVLV

-6880

PHASE THREE FREQUENCY HZ IMPEDANCE VOLTAGE39

50 15%

VECTOR GROUP DELTA

Y

INSULATION LEVEL 900 KV(peak)

HVLV-

Neutral-38 KV(rms)

CORE AND WINDING WEIGHT Kg WEIGHT OF OIL 37200 Kg TOTAL WEIGHT 188500 Kg OIL QUANTITY 43900 lit

110500

GENERATOR TRANSFORMER(166 MVA UNIT-IV)

RATING 240MVA TYPE OF COOLING ON/OB/OFB TEMP OF OIL 45^C TEMP WINDING KVA 120000/168000/240000 -120000/168000/240000 60^C HVLV

40

VOLTS AT NO LOAD 236000

HVLV-

A5750

LINE AMPERES 587 A

HVLV

-8798

PHASE THREE FREQUENCY HZ IMPEDANCE VOLTAGE 15.55% VECTOR GROUP DELTA CORE AND WINDING WEIGHT Kg WEIGHT OF OIL 37850 Kg TOTAL WEIGHT 234000 Kg OIL QUANTITY 42500 lit OIL CIRCULATION 2*2700 lit/min AIR CIRCULATION M2/min GUARANTEED MAX TEMP RISE IN OIL41

50

Y 138800

30*90 45^C

MAKE TELK DIVISION KERELA YEAR 1977

GENERATOR TRANSFORMER (240 MVA UNIT-V)Electrical generatorAn Electrical generator is a device that converts kinetic energy to electrical energy, generally using electromagnetic induction. The task of converting the electrical energy into mechanical energy is accomplished by using a motor. The source of mechanical energy may be a reciprocating or turbine steam engine, , water falling through the turbine are made in a variety of sizes ranging from small 1 hp (0.75 kW) units (rare) used as mechanical drives for pumps, compressors and other shaft driven equipment , to 2,000,000 hp(1,500,000 kW) turbines used to generate electricity. There are several classifications for modern steam turbines. Steam turbines are used in all of our major coal fired power stations to drive the generators or alternators, which produce electricity. The turbines themselves are driven by steam generated in Boilers or steam generators as they are sometimes called. Electrical power station use large stem turbines driving electric generators to produce most (about 86%) of the worlds electricity. These centralized stations are of two types: fossil fuel power plants and nuclear power plants. The turbines used for electric power generation are most often directly coupled to their-generators .As the generators must rotate at constant synchronous speeds according to the frequency of the electric power system, the most common speeds are 3000 r/min for 50 Hz systems, and 3600 r/min for 60 Hz systems. Most large nuclear sets rotate at half those speeds, and have a 4-pole generator rather than the more common 2-pole one. Energy in the steam after it leaves the boiler is converted into rotational energy as it passes through the turbine. The turbine normally consists of several stage with each stages consisting of a stationary blade (or nozzle)42

and a rotating blade. Stationary blades convert the potential energy of the steam into kinetic energy into forces, caused by pressure drop, which results in the rotation of the turbine shaft. The turbine shaft is connected to a generator, which produces the electrical energy.

Switchyard

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A Switchyard or Substation, consisting of large breakers and towers, is usually located in an area close to the plant. The substation is used as the distribution center where:

electrical power is supplied to the plant from the outside, and electrical power is sent from the plant

Often there are at least 2 main Buses. Very high voltages (typically 220,000 or 345,000 volts) are present. Gas and oil circuit breakers are used. The gas (e.g. sulfur hexaflouride) or oil is used to extinguish the arc caused when a breaker is opened, either by a control switch or due to a fault. Manually or motor operated disconnects are provided on either side of the breaker to allow the breaker to be electrically isolated so that maintenance work can be performed.

Substations generally have switching, protection and control equipment, and transformers. In a large substation, circuit breakers are used to interrupt any short circuits or overload currents that may occur on the network. Smaller distribution stations may use recloser circuit breakers orfuses for protection of distribution circuits. Substations themselves do not usually have generators, although a power plant may have a substation nearby. Other devices such as capacitors and voltage regulators may also be located at a substation. Substations may be on the surface in fenced enclosures, underground, or located in specialpurpose buildings. High-rise buildings may have several indoor substations. Indoor substations are usually found in urban areas to reduce the noise from the transformers, for reasons of appearance, or to protect switchgear from extreme climate or pollution conditions. Where a substation has a metallic fence, it must be properly grounded (UK: earthed) to protect people from high voltages that may occur during a fault in the network. Earth faults at a substation can cause a ground potential rise. Currents flowing in the Earth's surface during a fault can cause metal objects to have a significantly different voltage than the ground under a person's feet; this touch potential presents a hazard of electrocution.

Transmission Yard44

A transmission substation connects two or more transmission lines. The simplest case is where all transmission lines have the same voltage. In such cases, the substation contains high-voltage switches that allow lines to be connected or isolated for fault clearance or maintenance. A transmission station may have transformers to convert between two transmission voltages, voltage control/power factor correction devices such as capacitors, reactors or static VAr compensators and equipment such as phase shifting transformers to control power flow between two adjacent power systems. Transmission substations can range from simple to complex. A small "switching station" may be little more than a bus plus some circuit breakers. The largest transmission substations can cover a large area (several acres/hectares) with multiple voltage levels, many circuit breakers and a large amount of protection and control equipment (voltage and current transformers, relays and SCADA systems). Modern substations may be implemented using International Standards such as IEC61850.

Distribution YardA distribution substation transfers power from the transmission system to the distribution system of an area. It is uneconomical to directly connect electricity consumers to the main transmission network, unless they use large amounts of power, so the distribution station reduces voltage to a value suitable for local distribution. The input for a distribution substation is typically at least two transmission or subtransmission lines. Input voltage may be, for example, 115 kV, or whatever is common in the area. The output is a number of feeders. Distribution voltages are typically medium voltage, between 2.4 and 33 kV depending on the size of the area served and the practices of the local utility. The feeders run along streets overhead (or underground, in some cases) and power the distribution transformers at or near the customer premises. In addition to transforming voltage, distribution substations also isolate faults in either the transmission or distribution systems. Distribution substations are typically the points of voltage regulation, although on long distribution circuits (of several miles/kilometers), voltage regulation equipment may also be installed along the line. The downtown areas of large cities feature complicated distribution substations, with highvoltage switching, and switching and backup systems on the low-voltage side. More typical distribution substations have a switch, one transformer, and minimal facilities on the lowvoltage side.

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Collector YardIn distributed generation projects such as a wind farm, a collector substation may be required. It somewhat resembles a distribution substation although power flow is in the opposite direction, from many wind turbines up into the transmission grid. Usually for economy of construction the collector system operates around 35 kV, and the collector substation steps up voltage to a transmission voltage for the grid. The collector substation can also provide power factor correction if it is needed, metering and control of the wind farm. In some special cases a collector substation can also contain an HVDC static inverter plant. Collector substations also exist where multiple thermal or hydroelectric power plants of comparable output power are in proximity. Examples for such substations are Brauweiler in Germany and Hradecin the Czech Republic, where power is collected from nearby lignitefired power plants. If no transformers are installed for increase of voltage to transmission level, the substation is a switching station.

46

ELECTROSTATI C PRECIPITATOR (ESP)

47

An electrostatic precipitator (ESP), or electrostatic air cleaner is a particulate collection device that removes particles from a flowing gas (such as air) using the force of an induced electrostatic charge. Electrostatic precipitators are highly efficient filtration devices that minimally impede the flow of gases through the device, and can easily remove fine particulate matter such as dust and smoke from the air stream.[1] In contrast to wet scrubbers which apply energy directly to the flowing fluid medium, an ESP applies energy only to the particulate matter being collected and therefore is very efficient in its consumption of energy (in the form of electricity).

The most basic precipitator contains a row of thin vertical wires, and followed by a stack of large flat metal plates oriented vertically, with the plates typically spaced about 1 cm to 18 cm apart, depending on the application. The air or gas stream flows horizontally through the spaces between the wires, and then passes through the stack of plates. A negative voltage of several thousand volts is applied between wire and plate. If the applied voltage is high enough an electric (corona) discharge ionizes the gas around the electrodes. Negative ions flow to the plates and charge the gas-flow particles. The ionized particles, following the negative electric field created by the power supply, move to the grounded plates. Particles build up on the collection plates and form a layer. The layer does not collapse, thanks to electrostatic pressure (given from layer resistivity, electric field, and current flowing in the collected layer).

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C&ICONTROL AND INSTRUMENTATIONThis division basically calibrates various instruments and takes care of any faults occur in any of the auxiliaries in the plant. It has following labs: 1. 2. 3. 4. 5. 6. MANOMETRY LAB PROTECTION AND INTERLOCK LAB AUTOMATION LAB WATER TREATEMENT LAB FURNACE SAFETY SUPERVISORY SYSTEM(FSSS) ELECTRONICS TEST LAB

This department is the brain of the plant because from the relays to transmitters followed by the electronic computation chipsets and recorders and lastly the controlling circuitry, all fall under this. MANOMETRY LAB 1. TRANSMITTERS It is used for pressure measurements of gases and liquids, its working principle is that the input pressure is converted into electrostatic capacitance and from there it is conditioned and amplified. It gives an output of 4-20 ma DC. It can be mounted on a pipe or a wall. For liquid or steam measurement transmitters is mounted below main process piping and for gas measurement transmitter is placed above pipe. 2.MANOMETER Its a tube which is bent, in U shape. It is filled with a liquid. This device corresponds to a difference in pressure across the two limbs.

49

3. BOURDEN PRESSURE GAUGE Its an oval section tube. Its one end is fixed. It is provided with a pointer to indicate the pressure on a calibrated scale. It is of 2 types: (a) Spiral type: for Low pressure measurement. (b) Helical Type: for High pressure measurement.

PROTECTION AND INTERLOCK LAB 1. INTERLOCKING It is basically interconnecting two or more equipments so that if one equipments fails other one can perform the tasks. This type of interdependence is also created so that equipments connected together are started and shut down in the specific sequence to avoid damage. For protection of equipments tripping are provided for all the equipments. Tripping can be considered as the series of instructions connected through OR GATE. When a fault occurs and any one of the tripping is satisfied a signal is sent to the relay, which trips the circuit. The main equipments of this lab are relay and circuit breakers. Some of the instrument uses for protection are: 2. RELAY It is a protective device. It can detect wrong condition in electrical circuits by constantly measuring the electrical quantities flowing under normal and faulty conditions. Some of the electrical quantities are voltage, current, phase angle and velocity. 3. FUSES It is a short piece of metal inserted in the circuit, which melts when heavy current flows through it and thus breaks the circuit. Usually silver is used as a fuse material because: a) The coefficient of expansion of silver is very small. As a result no critical fatigue occurs and thus the continuous full capacity normal current ratings are assured for the long time. b) The conductivity of the silver is unimpaired by the surges of the current that produces temperatures just near the melting point. c) Silver fusible elements can be raised from normal operating temperature to vaporization quicker than any other material because of its comparatively low specific heat. 4. MINIATURE CIRCUIT BREAKER

50

They are used with combination of the control circuits to. a) Enable the staring of plant and distributors. b) Protect the circuit in case of a fault. In consists of current carrying contacts, one movable and other fixed. When a fault occurs the contacts separate and are is stuck between them. There are three types of - MANUAL TRIP - THERMAL TRIP - SHORT CIRCUIT TRIP 1.3 ROTECTION AND INTERLOCK SYSTEM HIGH TENSION CONTROL CIRCUIT For high tension system the control system are excited by separate D.C supply. For starting the circuit conditions should be in series with the starting coil of the equipment to energize it. Because if even a single condition is not true then system will not start. LOW TENSION CONTROL CIRCUIT For low tension system the control circuits are directly excited from the 0.415 KV A.C supply. The same circuit achieves both excitation and tripping. Hence the tripping coil is provided for emergency tripping if the interconnection fails.

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

51

3. PYROMETER LAB (1) LIQUID IN GLASS THERMOMETER Mercury in the glass thermometer boils at 340 degree Celsius which limits the range of temperature that can be measured. It is L shaped thermometer which is designed to reach all inaccessible places. (2) ULTRA VIOLET CENSOR This device is used in furnace and it measures the intensity of ultra violet rays there and according to the wave generated which directly indicates the temperature in the furnace. (3) THERMOCOUPLES This device is based on SEEBACK and PELTIER effect. It comprises of two junctions at different temperature. Then the emf is induced in the circuit due to the flow of electrons. This is an important part in the plant. (4) RTD (RESISTANCE TEMPERATURE DETECTOR) It performs the function of thermocouple basically but the difference is of a resistance. In this due to the change in the resistance the temperature difference is measured. In this lab, also the measuring devices can be calibrated in the oil bath or just boiling water (for low range devices) and in small furnace (for high range devices). 5.4 FURNACE SAFETY AND SUPERVISORY SYSTEM LAB This lab has the responsibility of starting fire in the furnace to enable the burning of coal. For first stage coal burners are in the front and rear of the furnace and for the second and third stage corner firing is employed. Unburnt coal is removed using forced draft or induced draft fan. The temperature inside the boiler is 1100 degree Celsius and its height is 18 to 40 m. It is made up of mild steel. An ultra violet sensor is employed in furnace to measure the intensity of ultra violet rays inside the furnace and according to it a signal in the same order of same mV is generated which directly indicates the temperature of the furnace. For firing the furnace a 10 KV spark plug is operated for ten seconds over a spray of diesel fuel and pre-heater air along each of the feeder-mills. The furnace has six feeder mills each separated by warm air pipes fed from forced draft fans. In first stage indirect firing is employed that is feeder mills are not fed directly from coal but are fed from three feeders but are fed from pulverized coalbunkers. The furnace can operate on the minimum feed from three feeders but under not circumstances should any one be left out under operation, to prevent creation of pressure different with in the furnace, which threatens to blast it. 4. ELECTRONICS LAB This lab undertakes the calibration and testing of various cards. It houses various types of analytical instruments like oscilloscopes, integrated circuits, cards auto analyzers etc. Various processes undertaken in this lab are: 1. Transmitter converts mV to mA. 2. Auto analyzer purifies the sample before it is sent to electrodes. It extracts52

the magnetic portion. 5. ANNUNCIATIN CARDS They are used to keep any parameter like temperature etc. within limits. It gets a signal if parameter goes beyond limit. It has a switching transistor connected to relay that helps in alerting the UCB. Control and Instrumentation Measuring Instrumentsments In any process the philosophy of instrumentation should provide a comprehensive intelligence feed back on the important parameters viz. Temperature, Pressure, Level and Flow. This Chapter Seeks to provide a basic understanding of the prevalent instruments used for measuring the above parameters. Temperature Measurement The most important parameter in thermal power plant is temperature and its measurement plays a vital role in safe operation of the plant. Rise of temperature in a substance is due to the resultant increase in molecular activity of the substance on application of heat; which increases the internal energy of the material. Therefore there exists some property of the substance, which changes with its energy content. The change may be observed with substance itself or in a subsidiary system in thermodynamic equilibrium, which is called testing body and the system itself is called the hot body. Expansion Thermometer Solid Rod Thermometers a temperature sensing - Controlling device may be designed incorporating in its construction the principle that some metals expand more than others for the same temperature range. Such a device is the thermostat used with water heaters (Refer Fig. 69).

The mercury will occupy a greater fraction of the volume of the container than it will at a low temperature. Under normal atmospheric conditions mercury normally boils at a temperature of (347C). To extend the range of mercury in glass thermometer beyond this point the top end of a thermometer bore opens into a bulb which is many times larger in capacity than the bore. This bulb plus the bore above the mercury, is then filled with nitrogen or carbon dioxide gas at a sufficiently high pressure to prevent boiling at the highest temperature to which the thermometer may be used. Mercury in Steel the range of liquid in glass thermometers although quite large, does not lend itself to all industrial practices. This fact is obvious by the delicate nature of glass also the position of the measuring element is not always the best position to read the result. Types of Hg in Steel Thermometers are:53

Bourdon Tube Most common and simplest type (Refer Fig. 71) Spiral type More sensitive and used where compactness is necessary Helical Type Most sensitive and compact. Pointer may be mounted direct on end of helix Which rotates, thus eliminating backlash and lost motion? Linkages, which only allow the pointer to operate over a selected range of pressure to either side of the normal steam pressure. (Refer Fig No.77) Dewrance Critical Pressure Gauge Measurement of Level Direct Methods 'Sight Glass' is used for local indication on closed or open vessels. A sight glass is a tube of toughened glass connected at both ends through packed unions and vessel. The liquid level will be the same as that in the vessel. Valves are provided for isolation and blow down. "Float with Gauge Post" is normally used to local indication on closed or open vessels. "Float Operated Dial" is used for small tanks and congested areas. The float arm is connected to a quadrant and pinion which rotates the pointer over a scale. Bourden Pressure Gauge a Bourdon pressure gauge calibrated in any fact head is often connected to a tank at or near the datum level. "Mercury Manometer" is used for remote indication of liquid level. The working principle is the same as that of a manometer one limp of a U-tube is connected to the tank, the other being open to atmosphere. The manometer liquid must not mix with the liquid in the vessel, and where the manometer is at a different level to the vessel, the static head must be allowed in the design of the manometer. 'Diaphragm Type' is used for remote level indication in open tanks or docks etc. A pressure change created by the movement of a diaphragm is proportional to a change in liquid level above the diaphragm. This consists of a cylindrical box with a rubber or plastic diaphragm across its open end as the level increases .the liquid pressure on the diaphragm increases and the air inside is compressed. This pressure is transmitted via a capillary tube to an indicator or recorder incorporating a pressure Measuring element. Sealed Capsule Type The application and principle is the same as for the diaphragm box. In this type, a capsule filled with an inert gas under a slight pressure is exposed to the pressure due to the head of liquid and is connected by a capillary to an indicator. In some cases the capsule is fitted external to the tank and is so arranged that it can be removed whilst the tank is still full, a spring loaded valve automatically shutting off the tapping point.54

Air Purge System This system provides the simplest means of obtaining an indication of level, or volume, at a reasonable distance and above or below, the liquid being measured. The pressure exerted inside an open ended tube below the surface of a liquid is proportional to the depth of the liquid The Measurement of Flow Two principle measurements are made by flow meters viz. quantity of flow and rate of flow. 'Quantity of flow' is the quantity of fluid passing a given point in a given time, i.e. gallons or pounds. Rate of flow' is the speed of. a fluid passing a given point at a given instant and is proportional to quantity passing at a given instant, i.e. gallons per minute or pounds per hour. There are two groups of measuring devices: Positive, or volumetric, which measure flow by transferring a measured quantity of fluid from the inlet to the outlet. Inferential, which measures the velocity of the flow and the volume passed is inferred, it being equal to the velocity times the cross sectional area of the flow. The inferential type is the most widely used. Measurement of Fluid Flow through Pipes: "The Rotating Impeller Type" is a positive type device which is used for medium quantity flow measurement i.e., petroleum and other commercial liquids. It consists of Two fluted rotors mounted in a liquid tight case fluid flow and transmitted to a counter. Rotating Oscillating Piston Type This is also a positive type device and is used for measuring low and medium quantity flows, e.g. domestic water supplies. This consists of a brass meter body into which is fitted a machined brass working chamber and cover, containing a piston made of ebonite. This piston acts as a moving chamber and transfers a definite volume of fluid from the inlet to the outlet for each cycle. Helical Vane Type For larger rates of flow, a helical vane is mounted centrally in the body of the meter. The helix chamber may be vertical or horizontal and is geared to a counter. Usually of pipe sizes 3" to 10" Typical example is the Kent Torrent Meter. Turbine Type this like the helical Vane type is a inference type of device used for large flows with the minimum of pressure drop. This consists of a turbine or drum revolving in upright bearings, retaining at the top by a collar. Water enters the drum from the top and leaves tangentially casings to rotate at a speed dependent upon the quantity of water passed. The cross sectional area of the meter throughout is equal to the area of the inlet and outlet pipes and is commonly used on direct supply water55

mains, Combination Meters this is used for widely fluctuating flows. It consists of a larger meter (helical, turbine or fan) in the main with a small rotary meter or suitable type in a bypass. Flow is directed into either the main or bypass according to the quantity of flow by an automatic valve. By this means flows of 45 to 40,000 gallons per hour can be measured. Measurement of Fluid Flow through Open Channels: The Weir If a fluid is allowed to flow over a square weir of notch, The height of the liquid above the still of the weir, or the bottom of the notch will be a measure of the rate of flow.

A formula relates the rate of flow to the height and is dependent upon the design of the Venturi Flumes The head loss caused by the weir flow meter is considerable and its construction is sometimes complicated, therefore the flume is sometimes used. The principle is same as that of venture except that the rate of flow is proportional to the depth of the liquid in the upstream section. It consists of a local contraction in the cross section of flow through a channel in the shape of a venturi. It is only necessary to measure the depth of the upstream section which is a measure of the rate of flow. This may be done by pressure tapping at the datum point or by a float in an adjacent level chamber. Pressure Difference Flow meters These are the most widely used type of flow meter since they are capable of measuring the flow of all industrial fluids passing through pipes. They consists of a primary element inserted in the pipeline which generates a differential pressure, ^he magnitude of which is proportional to the square of the rate of flow and a secondary element which measures this differential pressure and translates it into terms of flow. (Refer fig. 79).

Primary elements Bernoulli's theorem states that the quantity of fluid or gas flowing is proportional to the square root of the differential pressure. There are four principal types of primary elements (or restrictions) as enumerate below: Venturi; This is generally used for medium and high quantity fluid56

flow and it consists of two hollow truncated cones, the smaller diameters of which are connected together by a short length of parallel pipe, the smallest diameter of the tube formed by this length of parallel pipe is known as the throat section and the lower of the two pressures, (the throat, or downstream pressure) is measured here. Orifice Plate This is the oldest and most common form of pressure differential device. In its simplest form it consists of a thin metal plate with a central hold clamped between two pipe flanges. In the metering of dirty fluids or fluids containing solids the hole is placed so that its lower edge coincides with the inside bottom of the pipe. (Refer Fig.80) It is essential that the leading edge of the hole is absolutely sharp rounding or burring would have a very marked effect on the flow.

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