1. INTRODUCTION

Ukai Thermal Power Station is one of the most prestigious power station of Gujarat

Electricity Board Ukai is situated in Surat District and it is one of the few places in the country

where both HYDRO & Thermal Power generating Stations are located. This power Station is

situated near the vallabh Sagar Power Station dam on the river bank of Tapi, is mainly

constructed to meet with the power need of Gujarat State and to improve the voltage condition

of the grid system.

The Main consideration for setting up the Thermal Power Station in this area was easy and

large quantity of water needed for direct cooling of the condensers and for generating steam,

thus elimination the construction of huge cooling towers. The Thermal Power Station is located

almost next to the Broad gauge Railway line making the transportation of fuel (Coal and oil) both

easy and economical. The Thermal Power Station is situated only 3km. away from the main dam.

Thermal Power Station gets its water from the left bank canal in to which it is again discharged to

canal after the cooling process is completed.

This power Station has taken shape in the phases. First stage comprising of 2x1 20 MW

units for which construction work was completed in the year 1976 the cost of project for this unit

was 535 corers. Since these two units of 120 MW each are working continuously without giving

any major trouble. Similarly Stage 11 consisting of 2 units of 200 MW each have also added to the

installed capacity of this TPS from 1979 and are running at full load generation without any

problem. Further one more 5th unit of 210 MW construction was completed in 1985. Its total

installed capacity in 850 MW and total cost of there plant 2308 corers.

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SPECIAL LATEST TECHNOLOGY ADOPTED POWER PLANT

FOR:-

For Providing Uninterrupted power supply to the consumer and for doing so GEB has gone

in for the latest technology available. In Ukai TPS Units have the advanced features the protection

and interlocks systems for automatic sequential start up and Total whose temp.of 549 degree

centi. at 120 Kg/cm.cm entered in to high pressure turbine, from h. p. turbine exhausted steam of

temp.325 degree cent. 2735 Kg/cm.cm is goes to heater from heater. Steam is fed to the

economiesr. An economizer is essentially a feed water heater and derives heat from flue gas for

this purpose. The feed water is fed to the economizer before supplying to the boiler. The

economizer extracts a dart of heat of flue gases to increase the feed water temperature.

From H.P. turbine cold reheat steam goes through reheater heated steam of 26.18

Kg/cm.cm. 537.8 degree centi. Temp. is fed to the I.P. turbine of 14.141 Kg/cm.cm. abd temp

449.3 degree centi. is again to heater no.5 steam from the I.P. turbine is fed to L.P. turbine at a

temp. of 217.6 degree centi. and pressure of 2 Kg/cm.cm Exhausted steam from I.P. fed to

heaters and passed through the economizer. Exhausted steam from L.P. is goes to the condenser.

In order to improve the thermal efficiency of the plant, the steam exhausted from the

turbine is condensed by means of condenser. The circulation water takes up the heat of the

exhausted steam and itself become hot, the hot water coming out from cooling system.

The steam turbine is coupled to an alternator converts Mechanical energy of turbine in to

the electrical energy; the electric output from the alternator is delivered to the bus bars through

transformer, circuit breaker and isolators.

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2. SALIENT FEATURE OF

UKAI TPS

(1) Installed Capacity:

120X2 Units. = 240MW

200X2 Units = 400 MW

210 XI Units. = 210MW

Total Capacity = 850MW

Unit 6 (under construction) = 490MW

(2) The Project Cost:

2 UnitsX120MW = 53.5Crores

1 Unit X 200 MW = 45.9 Corers

1UnitX200MW = 47.4Crores

1 Unit X 210 MW = 84.0 Corers

Total Cost. = 230.8 Corers

(3) All heavy machinery including boiler and turbo generator are indigenous manufactured by

BHARAT HEAVY ELECTRIC LTD. at their various shop viz. THRICHY HARD WAR, BHOPAL and

HYDERABAD.

Instruments are supplied by MIS. I.L.KOTA

(4) A demineralization plant (D.M. Plant) is installed for Preparing Special water for Boiler

which is supplied by MIS. ION Exchange Ltd.

(5) 120 MW units boilers are designed to take'100% load on coal and 100% on C firing of

both, while 200/2 10 MW unit's boilers are designed to take 100% load on co only with oil as

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stabilizing

RATING OF MOTOR :- kw/Equipment

1. I. D.Fan 1000 1700 1200

2. F. D.Fan 630 650 620

3. P. A Fan 320 1250 1250

4. G. R. Fan 125 --- ---

5. Coal Mills. 400 320 335

6. C.W.Pump 315 450 450

7. Condensate Extraction 225 220 250

8. Boiler Feed Pump 1600 4000 4000

9. Ash water Pump 225 500 280

COAL PLANT

SI. NO. Particular. OLD NEW MINE-1 MINI-11

1. Coal crusher capacity 500 500 125 125

(T/Hr)

Thermal power station

A thermal power station is a power plant in which the prime mover is steam driven. Water is

heated, turns into steam and spins a steam turbine which either drives an electrical generator or

does some other work, like ship propulsion. After it passes through the turbine, the steam is

condensed in a condenser and recycled to where it was heated; this is known as a Rankine cycle.

The greatest variation in the design of thermal power stations is due to the different fuel sources.

Some prefer to use the term energy center because such facilities convert forms of heat energy

into electrical energy.

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Introductory overview

Almost all coal, nuclear, geothermal, solar thermal electric, and waste incineration plants, as well

as many natural gas power plants are thermal. Natural gas is frequently combusted in gas

turbines as well as boilers. The waste heat from a gas turbine can be used to raise steam, in a

combined cycle plant that improves overall efficiency. Power plants burning coal, oil, or natural

gas are often referred to collectively as fossil-fuel power plants. Some biomass-fueled thermal

power plants have appeared also. Non-nuclear thermal power plants, particularly fossil-fueled

plants, which do not use cogeneration are sometimes referred to as conventional power plants.

Commercial electric utility power stations are most usually constructed on a very large scale and

designed for continuous operation. Electric power plants typically use three-phase or individual-

phase electrical generators to produce alternating current (AC) electric power at a frequency of

50 Hz or 60 Hz (hertz, which is an AC sine wave per second) depending on its location in the

world. Other large companies or institutions may have their own usually smaller power plants to

supply heating or electricity to their facilities, especially if heat or steam is created anyway for

other purposes. Shipboard steam-driven power plants have been used in various large ships in

the past, but these days are used most often in large naval ships. Such shipboard power plants

are general lower power capacity than full-size electric company plants, but otherwise have many

similarities except that typically the main steam turbines mechanically turn the propulsion

propellers, either through reduction gears or directly by the same shaft. The steam power plants

in such ships also provide steam to separate smaller turbines driving electric generators to supply

electricity in the ship. Shipboard steam power plants can be either conventional or nuclear; the

shipboard nuclear plants are mostly in the navy. There have been perhaps about a dozen turbo-

electric ships in which a steam-driven turbine drives an electric generator which powers an

electric motor for propulsion.

In some industrial, large institutional facilities, or other populated areas, there are combined heat

and power (CHP) plants, often called cogeneration plants, which produce both power and heat

for facility or district heating or industrial applications. AC electrical power can be stepped up to

very high voltages for long distance transmission with minimal loss of power. Steam and hot

water lose energy when piped over substantial distance, so carrying heat or energy by steam or

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hot water is often only worthwhile within a local area or facility, such as steam distribution for a

ship or industrial facility or hot water distribution in a local municipality.

EFFICIENCY :-

Power is energy per time. The power output or capacity of an electric plant can be expressed in

units of megawatts electric (MWe). The electric efficiency of a conventional thermal power

station, considered as saleable energy (in MWe) produced at the plant busbars as a percent of

the heating value of the fuel consumed, is typically 33% to 48% efficient. This efficiency is limited

as all heat engines are governed by the laws of thermodynamics (See: Carnot cycle). The rest of

the energy must leave the plant in the form of heat. This waste heat can go through a condenser

and be disposed of with cooling water or in cooling towers. If the waste heat is instead utilized for

district heating, it is called cogeneration. An important class of thermal power station are

associated with desalination facilities; these are typically found in desert countries with large

supplies of natural gas and in these plants, freshwater production and electricity are equally

important co-products.

Since the efficiency of the plant is fundamentally limited by the ratio of the absolute

temperatures of the steam at turbine input and output, efficiency improvements require use of

higher temperature, and therefore higher pressure, steam. Historically, other working fluids such

as mercury have been experimentally used in a mercury vapour turbine power plant, since these

can attain higher temperatures than water at lower working pressures. However, the obvious

hazards of toxicity, and poor heat transfer properties, have ruled out mercury as a working fluid.

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3)Diagram of a typical coal-fired thermal power station :-

1. Cooling tower 10. Steam Control valve 19. Superheater

2. Cooling water pump 11. High pressure steam turbine 20. Forced draught (draft) fan

3. transmission line (3-phase) 12. Deaerator 21. Reheater

4. Step-up transformer (3-phase) 13. Feedwater heater 22. Combustion air intake

5. Electrical generator (3-phase) 14. Coal conveyor 23. Economiser

6. Low pressure steam turbine 15. Coal hopper 24. Air preheater

7. Condensate pump 16. Coal pulverizer 25. Precipitator

8. Surface condenser 17. Boiler steam drum 26. Induced draught (draft) fan

9.Intermediate pressure steam turbine

18. Bottom ash hopper 27. Flue gas stack

Steam generator :-

In fossil-fueled power plants, steam generator refers to a furnace that burns the fossil fuel to boil

water to generate steam. In the nuclear plant field, steam generator refers to a specific type of

large heat exchanger used in a pressurized water reactor (PWR) to thermally connect the primary

(reactor plant) and secondary (steam plant) systems, which of course is used to generate steam.

In a nuclear reactor called a boiling water reactor (BWR), water is boiled to generate steam

directly in the reactor itself and there are no units called steam generators. In some industrial

settings, there can also be steam-producing heat exchangers called heat recovery steam

generators (HRSG) which utilize heat from some industrial process. The steam generating boiler

has to produce steam at the high purity, pressure and temperature required for the steam

turbine that drives the electrical generator. A fossil fuel steam generator includes an economizer,

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a steam drum, and the furnace with its steam generating tubes and superheater coils. Necessary

safety valves are located at suitable points to avoid excessive boiler pressure. The air and flue gas

path equipment include: forced draft (FD) fan, air preheater (APH), boiler furnace, induced draft

(ID) fan, fly ash collectors (electrostatic precipitator or baghouse) and the flue gas stack.[1][2][3]

Geothermal plants need no boiler since they use naturally occurring steam sources. Heat

exchangers may be used where the geothermal steam is very corrosive or contains excessive

suspended solids. Nuclear plants also boil water to raise steam, either directly generating steam

from the reactor (BWR) or else using an intermediate heat exchanger (PWR).

For units over about 200 MW capacity, redundancy of key components is provided by installing

duplicates of the FD fan, APH, fly ash collectors and ID fan with isolating dampers. On some units

of about 60 MW, two boilers per unit may instead be provided.

Boiler furnace and steam drum:-

Once water inside the boiler or steam generator, the process of adding the latent heat of

vaporization or enthalpy is underway. The boiler transfers energy to the water by the chemical

reaction of burning some type of fuel.

The water enters the boiler through a section in the convection pass called the economizer. From

the economizer it passes to the steam drum. Once the water enters the steam drum it goes down

the downcomers to the lower inlet waterwall headers. From the inlet headers the water rises

through the waterwalls and is eventually turned into steam due to the heat being generated by

the burners located on the front and rear waterwalls (typically). As the water is turned into

steam/vapor in the waterwalls, the steam/vapor once again enters the steam drum. The

steam/vapor is passed through a series of steam and water separators and then dryers inside the

steam drum. The steam separators and dryers remove water droplets from the steam and the

cycle through the waterwalls is repeated. This process is known as natural circulation.

The boiler furnace auxiliary equipment includes coal feed nozzles and igniter guns, soot blowers,

water lancing and observation ports (in the furnace walls) for observation of the furnace interior.

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Furnace explosions due to any accumulation of combustible gases after a trip-out are avoided by

flushing out such gases from the combustion zone before igniting the coal.

The steam drum (as well as the superheater coils and headers) have air vents and drains needed for

initial startup. The steam drum has internal devices that removes moisture from the wet steam

entering the drum from the steam generating tubes. The dry steam then flows into the superheater

coils.

Super heater :-

Fossil fuel power plants can have a superheater and/or reheater section in the steam

generating furnace. Nuclear-powered steam plants do not have such sections but produce

steam at essentially saturated conditions. In a fossil fuel plant, after the steam is conditioned

by the drying equipment inside the steam drum, it is piped from the upper drum area into

tubes inside an area of the furnace known as the superheater, which has an elaborate set up of

tubing where the steam vapor picks up more energy from hot flue gases outside the tubing and

its temperature is now superheated above the saturation temperature. The superheated steam

is then piped through the main steam lines to the valves before the high pressure turbine.

Reheater :-

Power plant furnaces may have a reheater section containing tubes heated by hot flue gases

outside the tubes. Exhaust steam from the high pressure turbine is rerouted to go inside the

reheater tubes to pickup more energy to go drive intermediate or lower pressure turbines. This

is what is called as thermal power.

Fuel preparation system :-

In coal-fired power stations, the raw feed coal from the coal storage area is first crushed into

small pieces and then conveyed to the coal feed hoppers at the boilers. The coal is next

pulverized into a very fine powder. The pulverizers may be ball mills, rotating drum grinders, or

other types of grinders.

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Some power stations burn fuel oil rather than coal. The oil must kept warm (above its pour point)

in the fuel oil storage tanks to prevent the oil from congealing and becoming unpumpable. The oil

is usually heated to about 100 °C before being pumped through the furnace fuel oil spray nozzles.

Boilers in some power stations use processed natural gas as their main fuel. Other power stations

may use processed natural gas as auxiliary fuel in the event that their main fuel supply (coal or

oil) is interrupted. In such cases, separate gas burners are provided on the boiler furnaces.

Air path :-

External fans are provided to give sufficient air for combustion. The forced draft fan takes air from the atmosphere and, first warming it in the air preheater for better combustion, injects it via the air nozzles on the furnace wall.

The induced draft fan assists the FD fan by drawing out combustible gases from the furnace, maintaining a slightly negative pressure in the furnace to avoid backfiring through any opening.

Fly ash collection :-

Fly ash is captured and removed from the flue gas by electrostatic precipitators or fabric bag filters (or sometimes both) located at the outlet of the furnace and before the induced draft fan. The fly ash is periodically removed from the collection hoppers below the precipitators or bag filters. Generally, the fly ash is pneumatically transported to storage silos for subsequent transport by trucks or railroad cars.

Bottom ash collection and disposal

At the bottom of the furnace, there is a hopper for collection of bottom ash. This hopper is always filled with water to quench the ash and clinkers falling down from the furnace. Some arrangement is included to crush the clinkers and for conveying the crushed clinkers and bottom ash to a storage site.

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Make-up water treatment plant and storage

Since there is continuous withdrawal of steam and continuous return of condensate to the boiler, losses due to blowdown and leakages have to be made up to maintain a desired water level in the boiler steam drum. For this, continuous make-up water is added to the boiler water system. Impurities in the raw water input to the plant generally consist of calcium and magnesium salts which impart hardness to the water. Hardness in the make-up water to the boiler will form deposits on the tube water surfaces which will lead to overheating and failure of the tubes. Thus, the salts have to be removed from the water, and that is done by a water demineralising treatment plant (DM). A DM plant generally consists of cation, anion, and mixed bed exchangers. Any ions in the final water from this process consist essentially of hydrogen ions and hydroxide ions, which recombine to form pure water. Very pure DM water becomes highly corrosive once it absorbs oxygen from the atmosphere because of its very high affinity for oxygen.

The capacity of the DM plant is dictated by the type and quantity of salts in the raw water input. However, some storage is essential as the DM plant may be down for maintenance. For this purpose, a storage tank is installed from which DM water is continuously withdrawn for boiler make-up. The storage tank for DM water is made from materials not affected by corrosive water, such as PVC. The piping and valves are generally of stainless steel. Sometimes, a steam blanketing arrangement or stainless steel doughnut float is provided on top of the water in the tank to avoid contact with air. DM water make-up is generally added at the steam space of the surface condenser (i.e., the vacuum side). This arrangement not only sprays the water but also DM water gets deaerated, with the dissolved gases being removed by an air ejector attached to the condenser.

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Steam turbine-driven electric generator :-

Rotor of a modern steam turbine, used in a power station

The steam turbine-driven generators have auxiliary systems enabling them to work satisfactorily and safely. The steam turbine generator being rotating equipment generally has a heavy, large diameter shaft. The shaft therefore requires not only supports but also has to be kept in position while running. To minimise the frictional resistance to the rotation, the shaft has a number of bearings. The bearing shells, in which the shaft rotates, are lined with a low friction material like Babbitt metal. Oil lubrication is provided to further reduce the friction between shaft and bearing surface and to limit the heat generated.

Barring gear :-

Barring gear (or "turning gear") is the mechanism provided to rotate the turbine generator shaft at a very low speed after unit stoppages. Once the unit is "tripped" (i.e., the steam inlet valve is closed), the turbine coasts down towards standstill. When it stops completely, there is a tendency for the turbine shaft to deflect or bend if allowed to remain in one position too long. This is because the heat inside the turbine casing tends to concentrate in the top half of the casing,

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making the top half portion of the shaft hotter than the bottom half. The shaft therefore could warp or bend by millionths of inches.

This small shaft deflection, only detectable by eccentricity meters, would be enough to cause damaging vibrations to the entire steam turbine generator unit when it is restarted. The shaft is therefore automatically turned at low speed (about one percent rated speed).

Condenser: -

The surface condenser is a shell and tube heat exchanger in which cooling water is circulated through the tubes. The exhaust steam from the low pressure turbine enters the shell where it is cooled and converted to condensate (water) by flowing over the tubes as shown in the adjacent diagram. Such condensers use steam ejectors or rotary motor-driven exhausters for continuous removal of air and gases from the steam side to maintain vacuum.

For best efficiency, the temperature in the condenser must be kept as low as practical in order to achieve the lowest possible pressure in the condensing steam. Since the condenser temperature can almost always be kept significantly below 100 °C where the vapor pressure of water is much less than atmospheric pressure, the condenser generally works under vacuum. Thus leaks of non-condensible air into the closed loop must be prevented. Plants operating in hot climates may have to reduce output if their source of condenser cooling water becomes warmer; unfortunately this usually coincides with periods of high electrical demand for air conditioning.

The condenser generally uses either circulating cooling water from a cooling tower to reject waste heat to the atmosphere, or once-through water from a river, lake or ocean.

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Feed water heater :-

A Rankine cycle with a two-stage steam turbine and a single feedwater heater.

In the case of a conventional steam-electric power plant utilizing a drum boiler, the surface condenser removes the latent heat of vaporization from the steam as it changes states from vapour to liquid. The heat content (joules or Btu) in the steam is referred to as enthalpy. The condensate pump then pumps the condensate water through a feedwater heater. The feedwater heating equipment then raises the temperature of the water by utilizing extraction steam from various stages of the turbine.

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Preheating the feedwater reduces the irreversibilities involved in steam generation and therefore improves the thermodynamic efficiency of the system. This reduces plant operating costs and also helps to avoid thermal shock to the boiler metal when the feedwater is introduced back into the steam cycle. an elaborate set up of tubing in different areas of the boiler. The areas known as

Dearator: -

Diagram of boiler feed water deaerator (with vertical, domed aeration section and horizontal

water storage section

A steam generating boiler requires that the boiler feed water should be devoid of air and other dissolved gases, particularly corrosive ones, in order to avoid corrosion of the metal.

Generally, power stations use a deaerator to provide for the removal of air and other dissolved gases from the boiler feedwater. A deaerator typically includes a vertical, domed deaeration section mounted on top of a horizontal cylindrical vessel which serves as the deaerated boiler feedwater storage tank. There are many different designs for a deaerator and the designs will vary from one manufacturer to another. The adjacent diagram depicts a typical conventional trayed deaeratorIf operated properly, most deaerator manufacturers will guarantee that oxygen in the deaerated water will not exceed 7 ppb by weight (0.005 cm³/L).

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Auxiliary systems :-

Oil system:-

An auxiliary oil system pump is used to supply oil at the start-up of the steam turbine generator. It supplies the hydraulic oil system required for steam turbine's main inlet steam stop valve, the governing control valves, the bearing and seal oil systems, the relevant hydraulic relays and other mechanisms.

At a preset speed of the turbine during start-ups, a pump driven by the turbine main shaft takes over the functions of the auxiliary system.

Generator heat dissipation :-

The electricity generator requires cooling to dissipate the heat that it generates. While small units may be cooled by air drawn through filters at the inlet, larger units generally require special cooling arrangements. Hydrogen gas cooling, in an oil-sealed casing, is used because it has the highest known heat transfer coefficient of any gas and for its low viscosity which reduces windage losses. This system requires special handling during start-up, with air in the chamber first displaced by carbon dioxide before filling with hydrogen. This ensures that the highly flammable hydrogen does not mix with oxygen in the air.

The hydrogen pressure inside the casing is maintained slightly higher than atmospheric pressure to avoid outside air ingress. The hydrogen must be sealed against outward leakage where the shaft emerges from the casing. Mechanical seals around the shaft are installed with a very small annular gap to avoid rubbing between the shaft and the seals. Seal oil is used to prevent the hydrogen gas leakage to atmosphere.

The generator also uses water cooling. Since the generator coils are at a potential of about 22 kV and water is conductive, an insulating barrier such as Teflon is used to interconnect the water line and the generator high voltage windings. Demineralized water of low conductivity is used.

Generator high voltage system

The generator voltage ranges from 11 kV in smaller units to 22 kV in larger units. The generator high voltage leads are normally large aluminum channels because of their high current as compared to the cables used in smaller machines. They are enclosed in well-grounded aluminum bus ducts and are supported on suitable insulators. The generator high voltage channels are

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connected to step-up transformers for connecting to a high voltage electrical substation (of the order of 115 kV to 520 kV) for further transmission by the local power grid.

The necessary protection and metering devices are included for the high voltage leads. Thus, the steam turbine generator and the transformer form one unit. In smaller units, generating at 11 kV, a breaker is provided to connect it to a common 11 kV bus system

4. COAL HANDLING PLANT

GENERAL DESCRIPTION OF COAL UNLOADING SYSTEM :

Coal wagons are unloaded by means of tipplers in the tippler hopper. Coal received in the

tippler hopper is fed to either or both the conveyor 2A & 2B, through rack and pinion operated

gates, electromagnetic vibrating feeders and flap gates.

For manual unloading of coal wagons, one manual unloading hopper is provided. Coal

from this hopper also, is fed to conveyor 2A & 2B through rack and pinion gate electromagnetic

vibrating feeders and flap gates.

Conveyor 2A/2B will feed the coal to the crushers through R & P gates and vibrating

feeders. There are two crushers and coal can be fed either or both the crushers.

The crushed coal can be feed to or both the forward inclined conveyors 4A/4B or to either

or both the slight stock out conveyors 6A/6B. conveyor 4A/4B will feed coal either or both the

tripper conveyors 5A/5B. Conveyor 6A/6B are equipped with belt propelled tripper trolleys to

deliver coal into desired coal bunkers of boiler No. 1 to 4.

Stock out conveyors 6A/6B will convey crushed coal from crusher house to coal

stockyard.

Automatic belt weights (integration £um recorder) are provided on conveyor 4A/4B for

weighing the coal transported to coal bunkers.

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If there are no coal wagons, then coal can be reclaimed by Bulldozers from the stock yard

and it is fed to the reclaim hopper and then fed to conveyor 8A/8B through R & P gate, vibrating

feeder and flap gate.

COAL PLANT MEASURE EQUIPMENTS ,ITS SIZE AND CAPACITY

1. Wagon tipplers: 21 rakes about 4 Newton tone load one 8 wheeler Box wagon Driven by 80 HP electric

motor.

2. Beetle:(a) Inhaul Beetle : For pulling loaded coal wagons to tipper by steel wire rope

arrangement. It can pull 10 loaded coal wagons at time driven by 60 HP motor.(b) Outhaul Beetle : For pushing empty coal wagons from tipper platform to railway

sidings. Motor capacity 40 HP.

3. Electromagnetic Vibrating Feeders.All electro magnetic V.F. operates on single phase 415V through" AC/DC mixed current

circuit, at 500 vibration per minute.

(a) VF 1A + 18 Capacity 500 Mt. Size 72" x 48"(b) VF3A-3B Capacity 500 MT size 72" x 42"

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5. BOILER

INTRODUCTION:

Today's steam generators are larger in size, have more sophisticated firing systems are

more expensive and are more vital to the power-grid system than earlier generators, these trends

have necessitated a co-ordinate fuel burner management system, the typical system developed

and offered with all BHELL steam generators is popularly called Furnace safeguard Supervisory

system or in short FSSS (F, triple, S)

Generally, furnace oil or any kind of fuel is susceptible to explosion hazards. It has been

established that the majority of explosions occur during start-up, shut- down and low load

operations.

Adequacy of ignition energy is an important factor which should not be left to operator

interpretation. For high capacity boilers where the fuel input rate is also high, major furnace

explosions can result from the ignitions of unburnt fuel accumulated in the first 1 to 2 seconds.

Therefore, it is apparent that human reaction time will be inadequate under circumstances where

there is a need for an instantaneous decision.

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The system design has been developed to offer maximum protection minimum nuisance

trips, minimum power consumption and maximum life for the components used. The system is

basically a relay logic system. The logic is functionally divided into (1) Unit logic (2) Elevation logic

(3) Corner logic.

Unit logic supervises the overall furnace conditions. It monitors all critical parameters of

the fuel firing system and supervises furnace purge. During the operation of the boiler, the Unit

logic continuously monitors critical feedbacks to ensure maximum safety and trips off all fuel, if

dangerous conditions build up.

The elevation logic is an intermediate logic which depends on the operator or unit logic for

initiation of stars or stop actions. In addiction it also provides essential trip commands to the

corner logic. The elevation logic is designed to suit the type of fuel it controls.

The corners logic depends on elevation logic commands for initiation of an action. During

manual operation, the corner logic computer its own permissive based on ignition energy

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availability, status of various corner devices and other factors for sequencing of individual fuel, air

or steam valve operations. In the case of oil firing the logic performs an oil scavenge cycle before

the gun is allowed to retract. However emergency trip signals, originating in Unit logic and

transmitted via elevation logic, will by pass corner logic, permissive and cause immediate closure

of valves.

The Component used in the logic system includes pneumatic timer with on off relay, latch

relays etc.

6. TURBINE

TURBINE DATA :

TYPE : Horizontal, tandem compounded, reheat impulse type. Stop valve

steam condition : 126.55 kg / cm2 and 538˚C temperature.

Steam Turbine Frame TYPE 3 RH 1 B-525

Steam Turbine Serial Number Set No.: 1 -2600011

Set No.: 2-2600012

120 MW AT 3000 RPM

Maximum Continuous rating 11

No. of Stages HP Cy 1 13

No. of Stages IP Cy I 6 Double Flow

No. of Stages LP Cy 1

MAIN STEAM INLET PRESSURE 126.55 Hg / cm2

(At Stop Valve)

MAIN STEAM INLET TEMPERATURE 538 (100 F)

(At Stop Valve)

REHEATED INLET STEAM PRESSURE 26.18 kg / cm2

To interceptor Valve

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REHEATED STEAM INTEL TEMPERATURE 538˚C (91000 F)

To Intereceptor Valve 686 mm Hg.

Condenser vacuum

Each Turbine is of the horizontal, close coupled, tandem compound, reheat, impulse type,

designed for stop valve steam conditions of 126.55 kg/ cm2 at 538˚C (1000.F) Steam exhausting

from the HP cylinder is reheated to 26 kg/ cm2 538˚C be fore it is returned to the intermediate

pressure cylinder. The turbine has a conditions maximum economical rating of 120 MW at the

generator terminals at 3000 RPM steam is extracted from suitable stages' of the expansion to

provide for 6 stages regenerative feed heating with a final feed water temp of 226.23 ˚C (439.82

F)

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The turbine is a single axis machine, suitable compounded so that at expansion of the

steam takes place in three cylinders, one high pressure (HP) one intermediate pressure cylinder

(IP) and one double flow low pressure (LP) Cylinder.

7. Generator & Exciter

THE GENERATOR :

The generator is two cylindrical rotor type driven by a directly coupled steam turbine at

3000R.P.M. It generates three phase alternating current at the standard frequency of 50 cycles

per seconds.

The Kilo volt ampere value specified of the maximum continuous rating of the generator at

rated power factor and corresponds to the maximum continuous rating of the turbine in

Kilowatts.

The stator core consists of high quality silicon iron laminations each comprising a number of

punched segments which' fit between accurately spaced key bars inside the yoke. The individual

segments are insulated one from another to prevent the circulation off of eddy current.

The stator winding is of the involutes type comprising short pitched half coils arranged in

two layers and brazed together at the ends. The half coil comprises a number of parallel stands

transposed along the straight (slot) portion to reduce eddy currents. Each insulated half coils in

vacuum dried and impregnated to exclude voids. Both ends of each phase of the winding are

passed through the generator casing by means of gas tight insulated, terminal busing;

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The rotor winding consists of straps of high conductivity sliver bearing copper, each

slotted of intervals and grooved along one face in straight (slot) part, and grooved along and

across one face in the end winding part. The straps are assembling pair with insulation between

pairs, and performance into half coils. Radial, axial and peripheral ventilation ducts are produced

where slots and grooves in the straight part and grooves in the end winding parts respectively

coincide. The half coils are brazed together and insulated at the ends during assemble in the rotor

to form complete coils of several turns in series.

Cooling is by hydrogen gas which enters each of the rotors through opening in the ends

discs passes into the peripheral, axial, and radial ventilation ducts, and is discharged through

holes in the remaining wedges into the gap between rotor and the stator core.

Two axial flow, one at each of the rotor, circulate cooling gas through generator and

coolers. The Hydrogen in then is cooled by distilled water supplied by distilled water pump. The

distilled water in turn cooled by circulating water in the water/ water coolers.

GENERATOR DATA :-

RATING :

With hydrogen at 2.1 Kg/cm2 120,000 KW

141,176 KVA

0.85. P. F. lag.

13,800 Volt

5906 amp

3000 rpm

50 Cycles per second

With hydrogen at 1.05 Kg/cm2 98600 KW

116, 00 KVA

0.85 P.F. leg

With hydrogen at 0.035 Kg/cm2 58,650 KW

69,000 KVA

0.85 P.F. leg

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With air 30,600 KW

36,000 KVA

0.85 P.F. leg

Excitation at rated load 1730 AMP

446 Volt

772 KW

WEIGHTS :-

Stator (With all attachments) 164,000 Kg

Rotor 29,400 Kg

Heaviest lift 132, 00 Kg

Bearing sizes 38.1 Cm dia. X 25.5 cm long

GENERATER AND TURBINE PROTECTIONS:-

(1) The generator is provided with following protections

a) 220 KV bus differentialb) Generator differentialc) Generator and step up Transformer differential.d) Stator earth faultf) Unit auxiliary transformer differential.g) Generator transformer buchholz.h) Step up and unit auxiliary transformer fire protection. i) Low forward power for 5 -25 sec.j) Generator over voltage trip - 59 G.

Operation of any of these protection relays will operate generator master trip relay TR1 which

will result in:

(a) Opening of generator step up circuit breaker (220 KV)

(b) Auto closing of auxiliary station supply breaker (6.6KV)

(c) Open circuits in winding-

(d) Overheating.

As soon as a stator faults develops, the generator must be disconnected immediately from

25

the system to avoid the faulty machine from being fed by other. The main CKT breaker between

the machine and the busbar most therefore be opened. At the same time it is necessary to

suppress the rotor field to prevent the machine from feeding into the fault itself.

(2) Following protection are provided for generator.(1) Protection against stator phase to phase faults.(2) Protection against Earth faults.(3) Stator Interrupt protection.(4) Negative sequence current protection.(5) Unit differential protection.(6) Over load protection.(7) Generator Transverse Differential protection.(8) Loss of Excitation protection.(9) Pole slipping protection.(10) Generator field failure protection.(11) Generator field failure protection.(12) Reverse power protection.(13) Low forward power Interlock.(14) Back up Impedance protection.(15) Generator Under frequency protection.(16) Generator over frequency protection.(17) Generator Rotor earth fault protection.

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8. Transformer

(A) GENERATING TRANSFORMER :

GENRAL:

The Generator Transformer is oil immersed with mixed rating of 120 MVA under ON

(Natural oil circulation, natural air cooling 168 MVA under OB (Natural oil circulation forced air

cooling) and 240 MVA under OFB (Forced oil circulation, forced air cooling) conditions.

The transformer is provided with two independent 50% banks of radiators, fans, pumps

and associated control equipments. The control equipment is housed in a weather proof

marshalling cubicle. The transformer is also equipped with an off circuit voltage regulating

equipment.

Rating Data:

Outline General Arrangement Drawing G6019858 Combined rating and diagram piato

draeing-English F6129663 Hindi F6129664

The rating data are as follows :

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Class - A

tripping:-

Sr.

No.

Name. Protection zone

1. 100% stator E/F relay This protection covers complete stator winding, and generator bus

duct against any earth fault relay.

2. Generator stator

standby E/F relay

-do-

This is a back up relay of above said relay and covers 5 to 100%

stator winding and bus duct.

3. Overall differential

standy

This relay covers complete generator winding + generator tr. +

H.V. side of UAT’S for any fault.

4. Generator stator

inter winding

differential relay

210 MW generator stator is double star winding, this relay is

connected differentially to protect each part of winding as shown

in Drag.

5. Generator stator

inter winding

differential relay

This relay protects only generator stator winding against any fault.

6. Unit auxiliary Tr. Diff.

Relay.

The said relay is differentia" protection of unit aux. Tr. A / B.

This is "unit" scheme i.e. generator, gen. Tr. And UAT are

connected with bus duct, therefore, any fault on UAT will reflect

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on Generator. Therefore this relay will trip class-A relay and

thereby generator.

7. Minimum forward

power relay

When any of the turbine protection acts it trips class-b relay which

trips the turbine and steam valves get closed (still generator is on

bar) at 1% of rated capacity. Min. forward power relay operates

and trips the generator breaker. The purpose of above operation

is to protect the M/c against over speed and reversal of power in

generator,

8. Generator pole

slippage protection

This relay protects the generator against any instability, i.e.

sudden thrown off load, sudden failure of excitation, sudden

failure of grid or any operation which causes the m/c. out of

stability limit.

9. Generator over

voltage relay

This relay protects the generator and generator tr. Against over

voltage. This is basically attracted armature type voltage operated

relay. The supply to this relay is tapped from generator

P.T.secondary.

10. Generator tr. Over flux relay.

The said relay protects generator tr. Against over flux, i.e. it

operates when V/F ratio exceed 1.1 as flux V/F.

11. Generator tr. Restricted earth fault relay.

This relay protects generator tr. H.V. side against earth fault. It will

also operate in case of failure of lightening arrestor of G.T.

12. AVR. problems Class-A tripping will take place "in case of

1. rotor over current.

2. thyristor failure or problem related with static excitation j

system.

13. S Second rotor E/F relay

First rotor E/F will initiate at alarm, case of second/ rotorE/F the

m/c is required to isolate immediately to protect rotor therefore,

this will operate class-A relays and trips the generator breaker.

14. Generator. Tr.

Buchholz

This relay will give an alarm in case of

1. hot spot on the core due to short circuit of lamination

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insulation.

2. core bolt insulation failure.

3. faulty joints.

4. Interturn faults or other winding faults involving only lower

power feeds.

5. Loss of oil due to leakages.

15. UAT "A" TR. Buchholz

16. UAT "B" tr. Buchholz

Class B- tripping:-

Sr. No. Name. Protection zone

1. Generator field

failure relay

In case of generator field failure i.e. failure of static excitation this

relay will operate class - B relay.

2. Generator

negative phase

protection

Basically this is rotor protection as negative phase sequence

current will heat up rotor. The cause of negative sequence current

may be

1. unbalance loads.

2. loose connections on breaker-isolator or jumper, etc.

3. Generator back up impedance relay

In case of phase to phase fault on line if line breaker fails to clear

the fault, this protection will operate class-B and isolates the

generator from system. This works as a back up protection of line.

The relay operates when V/I ratio falls below pre-set value. 1

4. Generator tr. Back up over current

This is inverse definite minimum time induction type over current

relay, when operates when H.V. side current increases pre-set

value.

5. Unit auxiliary tr. Back up over current relay

This is similar to above with instantaneous operated current unit.

The I.D. M.T. disc unit will operate if the current increases pre-set

value and instantaneous unit will operate in case of dead short on

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L.V. side of the transformer.

6. Generator tr. Back E/F relay

This work s as back up protection of line breaker In case of earth

fault on line side the said relay operates and isolates the

generator from the system if the “main” relay of line fails to

operate.

7. Under frequency protection

This relay operates if the frequency decreases the pre-set value.

8. Excitation system problem

Class-B relay will also operate in case of trouble in excitation

system such as regulation - supply fuse failure - rectifier tr.

Problem etc.

9. Generator tr. winding temperature

In case of GT winding temperature exceeds 95 degrees.

10. Generator tr. oil temperature

In case of GT oil temperature exceeds 90 degrees.

11. UAT-A winding temperature

In case of UAT- A winding temperature exceeds 85 degrees.

12. UAT - A oil temperature

In case of UAT- A oil temperature exceeds 80 degrees.

13. UAT-B winding temperature

In case of UAT-B winding temperature exceeds 85 degrees.

14. Oil level low In case UAT- B oil temperature.

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9. 220KV SWITCH YARD

Main equipment of Switchyard

Transformer

Circuit Breaker (CB)

Isolator

Current Transformer (CT)

Lightning Arrester (LA)

Potential Transformer (PT)

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Capacitor Voltage Transformer (CVT)

Wave Trap

Bus Bar

Bus Coupler

Neutral Grounding Transformer (NGT)

10)

MAX DNA ( DCS SYSTEM ) :-

A distributed control system (DCS) refers to a control system usually of a manufacturing system, process or any kind of dynamic system, in which the controller elements are not central in location (like the brain) but are distributed throughout the system with each component sub-system controlled by one or more controllers. The entire system of controllers is connected by networks for communication and monitoring.

DCS is a very broad term used in a variety of industries, to monitor and control distributed equipment.

Electrical power grids and electrical generation plants

Environmental control systems Traffic signals radio signals Water management systems Oil refining plants Chemical plants Pharmaceutical manufacturing Sensor networks Dry cargo and bulk oil carrier ships

A DCS typically uses custom designed processors as controllers and uses both proprietary

interconnections and communications protocol for communication. Input and output modules

33

form component parts of the DCS. The processor receives information from input modules and

sends information to output modules. The input modules receive information from input

instruments in the process (a.k.a. field) and transmit instructions to the output instruments in the

field. Computer buses or electrical buses connect the processor and modules through multiplexer

or demultiplexers. Buses also connect the distributed controllers with the central controller and

finally to the Human-Machine Interface (HMI) or control consoles. See Process Automation

System.

Elements of a distributed control system may directly connect to physical equipment such as

switches, pumps and valves or may work through an intermediate system such as a SCADAsystem.

Distributed Control Systems (DCSs) are dedicated systems used to control manufacturing

processes that are continuous or batch-oriented, such as oil refining, petrochemicals, central

station power generation, pharmaceuticals, food & beverage manufacturing, cement production,

steelmaking, and papermaking. DCSs are connected to sensors and actuators and use setpoint

control to control the flow of material through the plant. The most common example is a

setpoint control loop consisting of a pressure sensor, controller, and control valve. Pressure or

flow measurements are transmitted to the controller, usually through the aid of a signal

conditioning Input/Output (I/O) device. When the measured variable reaches a certain point, the

controller instructs a valve or actuation device to open or close until the fluidic flow process

reaches the desired setpoint. Large oil refineries have many thousands of I/O points and employ

very large DCSs. Processes are not limited to fluidic flow through pipes, however, and can also

include things like paper machines and their associated variable speed drives and motor control

centers, cement kilns, mining operations, ore processing facilities, and many others.

A typical DCS consists of functionally and/or geographically distributed digital controllers capable

of executing from 1 to 256 or more regulatory control loops in one control box. The input/output

devices (I/O) can be integral with the controller or located remotely via a field network. Today’s

controllers have extensive computational capabilities and, in addition to proportional, integral,

and derivative (PID) control, can generally perform logic and sequential control.

DCSs may employ one or several workstations and can be configured at the workstation or by an

off-line personal computer. Local communication is handled by a control network with

transmission over twisted pair, coaxial, or fiber optic cable. A server and/or applications

34

processor may be included in the system for extra computational, data collection, and reporting

capability.

Bharat Heavy Electricals limited (BHEL), Electronics Division, has entered into a Technical

Collaboration Agreement (TCA) for the manufacture and supply of new generation Distributed

Control Systems 'MAX1000+PLUS' , for modern Power Plants & Industries, with MAX Control

Systems (MCS) Inc USA, part of METSO Automation.

The MAX1000+PLUS is now re-named as maxDNA. where-in DNA stands for Dynamic Network of

Applications. maxDNA is a network of applications where diverse hardware and software

solutions co-operate to allow the plant to reach its greatest potential.

BHEL's Electronics Division has established itself in the area of Control & Instrumentation for new

power plants as well as renovation and modernisation of existing power plants. A leader in the

Indian Power Sector market, it has already supplied and commissioned above 200 sets of DCS for

thermal, combined cycle and hydro sets all over the country and overseas.

MCS Inc., USA, former systems division of Leeds and Northrup, USA, is an internationally reputed

technology leader In both Power as well as Industrial process control systems, with 70 years of

rich experience in the field.

This is a description of the maxDNA Interface (formally known as the Max Controls Max1000

Plus+ Interface) to the PI System. The interface can be run on one of the following:

A Windows 2000 or XP PI 3 Server

A Windows 2000 or XP PI Interface node with network access to a PI 2 or PI 3 Server

The interface requires that the maxDNA software be present on the same PC as the interface

and the PC have network access to the SBP.

Migration interfaces are available to connect PI to all generations of MAX systems. The minimum

requirement is that a maxDNA DBM must be present.

35

The customer must contact MCS to run a system analysis to determine available throughput on

older systems.

For proper interface operation, the user must configure points (tags) on a PI 2 or PI 3 home node

(the words "point" and "tag" are used interchangeably in this manual). Tags are used to update

and receive data from maxDNA members. A single interface can collect data from one or more

maxDNA members at a time. Data is received at a given frequency. All values that are written to

the snapshot or archive use the system time from the PI home node.

At startup, the interface scans the PI Point Database for all associated points and builds its own

point list. During runtime, the interface continues to check the PI Point Database for point

updates and modifies its point list accordingly. If the Scan field of any point on the point list is set

to off, the point is removed from the point list. The point is added once again after the Scan field

is turned back on. If a fixed scan rate cannot be found for a given point, the point will be removed

from or will not be added to the point list.

Applications

maxDNA systems are used in many applications throughout the world including electric power

generation, co-generation, cement, glass, ceramics, primary metals, chemicals and petroleum,

water and waste-water treatment and incineration plants.

BHEL offers a variety of solutions for Power Plants ranging from simple control systems to

complex unified automation for Power Plants of any size. The synergy of BHEL's expertise in

Power Plant Controls and cutting-edge technology of maxDNA provides for unified DCS solution

for entire Power Plant comprising of Steam Generator, Steam Turbine Generator and Balance of

Plant C&I. The state-of-the art control system is also configured for complete range of Hydro

Turbine governing and auto sequence controls, SCADA systems and for wide range of industrial

process applications.

TRANSMITTER:-

36

Abstract: The 4-20mA current loop is a common technique for transmitting sensor information in

industrial process-monitoring applications. (Sensors measure physical parameters such as

temperature, pressure, speed, and liquid flowrates.) Current-loop signals are relatively insensitive

to noise, and their power can be derived from a remotely supplied voltage. This makes current

loops particularly useful when the information must travel a long distance to a remote location

Straightforward Loop Operation :-

In a current loop, the output voltage from a sensor is first converted to a proportional current, in

which 4mA normally represents the sensor's zero-level output and 20mA represents the full-scale

output. A receiver at the remote end converts the 4-20mA current back to a voltage, which can be

further processed by a computer or display module. The typical 4-20mA current-loop circuit consists of

four elements: a sensor/transducer, a voltage-to-current converter, a loop power supply, and a

receiver/monitor. In loop-powered applications, the sensor drives the voltage-to-current converter, and

the other three elements are connected in series to form a closed loop (Figure 1).

Figure 1. Diagram of a 4-20mA loop-powered circuit.

The Smart 4-20mAT Transmitter :-

Traditionally, a 4-20mA transmitter included a field-mounted device that sensed a physical

parameter and generated a proportional current in the standard range of 4-20mA. Responding to

industry demand, the second-generation 4-20mA transmitters, called 'smart transmitters', use a

microcontroller (μC) and data converter to condition the signal remotely. Smart transmitters can

normalize gain and offset, linearize the sensor by converting its analog signal to digital (RTD

sensors and thermocouples, for example), process the signals with arithmetic algorithms resident

in the μC, convert back to analog, and transmit the result as a standard current along the loop.

37

The newest third-generation 4-20mA transmitters (Figure 2) are considered 'smart and

intelligent'. They add digital communications which share the twisted-pair line with the 4-20mA

signal. The resulting communication channel can transmit control and diagnostic signals along

with the sensor data.

Basic μC Requisites for a Smart, Intelligent 4-20mA Transmitter :-

There are three specific capabilities that a μC must have to perform this 4-20mA current-loop

application. The μC needs:

1. A serial interface to drive the ADC for data acquisition and the DAC for setting loop current. 2. Low power consumption, as the current budget is 4mA. 3. A multiply-accumulate unit (MAC), which both implements a digital filter applied to the input signal and also encodes and decodes the two frequencies of the Hart Protocol.

THERMOCOPULE:-

What is Thermocouple?

When two dissimilar metal conductors are connected togetherto form a closed circuit and the two junctions are kept indifferent temperatures, thermal electromotive forece (EMF) is generated in the circuit (Seebeck’s effect).Thus, when one end (cold junction) is kept constant at a certaintemperature, normally at 0°C, and the other end (measuringjunction) is exposed to unknown temperature, the temperature at latter end can be determined by measurement of EMF sogenerated. This combination of two dissimilar metal conductors are called “Thermocouple”.

38

Thermocouples are temperature sensors suitable for use with any make of instrument designed or programmed for use with the same type of thermocouple. Thermocouples are based on the principle that when two dissimilar metals are joined a predictable voltage will be generated that relates to the difference in temperature between the measuring junction and the reference junction (connection to the measuring device). The selection of the optimum thermocouple type (metals used in their construction) is based on application temperature, atmosphere, required length of service, accuracy and cost. When a replacement thermocouple is required, it is of the utmost importance that the type of thermocouple type used in the replacement matches that of the measuring instrument. Different thermocouple types have very different voltage output curves. It is also required that thermocouple or thermocouple extension wire, of the proper type, be used all the way from the sensing element to the measuring element. Large errors can develop if this practice is not followed.

39

1. Wire Size of Thermocouple: Selecting the wire size used in the thermocouple sensor depends upon the application. Generally, when longer life is required for the higher temperatures, the larger size wires should be chosen. When sensitivity is the prime concern, the smaller sizes should be used.

2. Length of Thermocouple Probe: Since the effect of conduction of heat from the hot end of the thermocouple must be minimized, the thermocouple probe must have sufficient length. Unless there is sufficient immersion, readings will be low. It is suggested the thermocouple be immersed for a minimum distance equivalent to four times the outside diameter of a protection tube or well.

3. Location of Thermocouple: Thermocouples should always be in a position to have a definite temperature relationship to the work load. Usually, the thermocouple should be located between the work load and the heat source and be located approximately 1/3 the distance from the work load to the heat source.

4. Cold Junction or Reference Junction - The junction generally at the measuring device that is held at a relatively constant temperature.

5. Cold Junction Compensation - Measures the ambient temperature at the connection of the thermocouple wire to the measuring device. This allows for accurate computation of the temperature at the hot junction by the measuring device.

6. Dual Element - Two thermocouple elements housed within one thermocouple hardware assembly.

7. Extension Wire - Wires which connect the thermocouple itself to a reference junction, i.e. controller, receiver, recorder, etc. Extension wire must be of the same type as the thermocouple. Special plugs and jacks made of the same alloys as the thermocouple should be used if a quick disconnect is required for the application.

40

8. Grounded Junction - The internal conductors of this thermocouple are welded directly to the surrounding sheath material, forming a completely sealed integral junction.

9. Ungrounded Junction - Although the internal thermocouple conductors are welded together they are electrically insulated from the external sheath material and are not connected to the sheath in any way. Ungrounded junction thermocouples are ideal for use in conductive solutions or wherever circuit isolation is required. Ungrounded junctions are required where the measuring instrumentation does not provide channel to channel isolation.

10. Exposed Junction - The thermocouple junction or measuring point is exposed without any protection assembly or tube. Exposed junction thermocouples due to their design, offer the user the fastest response time.

11. Hot Junction - The measuring junction.

12. Immersion Length - The portion of the thermocouple which is subject to the temperature which is being measured. Measuring Junction - The junction in a thermocouple which actually measures the temperature of the object. Often referred to as the Hot Junction. Protection Tube - A tube like assembly in which the thermocouple is installed in order to protect the element from harsh environments.

13. RTD - Abbreviation for Resistance Temperature Detector. It is a sensor which operates on the principle that the resistance increases with an increase in temperature at a specific rate. Commonly manufactured using a platinum resistance element. More accurate and more linear than most thermocouples and generally much more costly and slower responding.

14. Thermocouple - A temperature sensor based on the principle that a voltage is produced when two dissimilar metals. The junction produces a voltage in proportion to the difference in temperature between the measuring junction and the reference junction.

PRESSURE SWITCH ;-

A Pressure switch is a form of switch that makes electrical contact when a certain set pressure has been reached on its input. This is used to provide on/off switching from a pneumatic or

41

hydraulic source. The switch may be designed to make contact either on pressure rise or on pressure fall.

FUNCTION :-

Indfos RT Series Pressure switch is produced using technology provided by Danfoss Denmark. These Switches are sturdy, robust and reliable devices meant for Industrial applications. Over one million units have been used in a variety of applications.

RT Series pressure switches utilize a seamless bellows as sensing element. The bellows can be either phosphor bronze or stainless steel to suit various kinds of process medium. The mechanism is enclosed in a weather proof (IP66) enclosure which can be of either DMC or Die Cast Aluminium. Various kinds of switching elements can be provided to meet required electrical load specifications. Both Range and Differential can be independently adjusted. All models feature ± 1% repeatability and device has clearly read setting scale.

RT Series Pressure Switch find applications in :

>>    Power Plants>>    Chemical/Petrochemical Plants>>    Steel rills>>    Pulp & Paper rills>>    Electric & Diesel Locomotive>>    Compressors>>    Machine Tools

SPECIFICATIONS :-

Enclosure : Plastic (Dough Moulded Compound) or Die Cast Aluminium

Enclosure Protection

: Weather proof to IP 66

Sesing Element : Seamless Bellows (Phosphor Bronze or Stainless steel)

Max Process Temp : 90°C

Max Ambient Temp : - 40 to 70°C

Switch Type : 1 SPDT

Switch Rating (Standard)

: 10A resistive 4A inductive 380 VAC, 12 W 220 VDC (Other ratings are also available)

Cable Entry : 1/2" NPT (F) 42

I TO P CONVERTER :-

ABB Electropneumatic signal converters are the link between the control rooms and pneumatic actuators. The type TEIP 11 I/P Converter with various housings is available for cabinet installation, field installation, rail installation and as slide-in type. The signal conversion is based on standard signals. Current signals 0/4 ... 20 mA are converted to pressure signals 0.2...1 bar or 3...15 psi.

Small dimensions; variable mounting position

High immunity to shocks and vibrations with an effect < 1% for loads up to 10 g and frequencies between 20 and 80 Hz

Wide temperature range, - 40°C (optionally – 55°C) … + 85 °C

In compliance with European standard, EMC-guideline 89/336/EWG of May 1989, guideline for CE-conformity marking

Various Ex-certificates, ATEX - FM - CSA, for intrinsically safe and Exd conditions

Convert a current signal to a pneumatic signal so a DCS, PLC, or PC can control a valve or actuator;

or convert pneumatic signals to current signals so remote pneumatic devices can interface with

electronic instruments and computer-based monitoring systems.

43

Swas (steam water analysis system) :

About Power industry and water chemistry and importance of SWAS:-

Today in power industry, high pressure boilers & steam turbines are under constant attack from erosive & corrosive elements

such as Silica, Sodium, Dissolved Oxygen, Calcium, Chloride and Phosphates.Without accurate measurement and monitoring, the plant may suffer heavy mechanical damage that can be caused due to imbalance of turbines, reduced efficiency, deposition on turbine blades, corrosion of steam pipe work & so on.

We have designed our Steam and Water Analysis System (SWAS), to keep you in power. SWAS assures safety of your boiler and turbines, by taking along and analyzing up to a dozen samples from all your water & steam circuits. In today's power industry, sample conditions as high as 560 degree Celsius & 200 bars are quite common. Forbes Marshall SWAS can easily take care of

these samples. To protect your equipment, our SWAS works in two stages:

1. Sample Conditioning

First section of any SWAS is the Sample Conditioning section or Wet Panel:-

Enclosed type W et P anel Open frame free standing W et P anel

44

1) pH : The steam which goes to the turbines has to be ultra pure. The pH value of the feed water gives direct indication of alkalinity or acidity of this water. The ultra pure water has pH value of 7. In steam circuit it is normal practice to keep the pH value of feed water at slightly alkaline levels. This helps in preventing the corrosion of pipe work and other equipment. Typically dedicated pH Analyzers are recommended at following locations in Steam circuit: High pressure heaters, DM Make-up Water, Condensate Extraction Pump Discharge

Dedicated pH analyzer in each line ensures that pH is getting maintained in specified band

Two wire Aquamon 2000 plus model is simplest pH and ORP transmitter. These analyzers are directly loop powered by +24V DC supply from DCS and PLC.

Also direct 110-230 V AC powered Aquamon 4000 transmitter is available if Alarm contacts required along with 4-20 mA output. For pH measurement both low and high pH alarm contacts can be used to control dosing for chemicals. Separate PT-100 sensor input can be used for temperature compensation for pH measurement.

2) Conductivity : Conductivity is an impor tant parameter for detecting any contamination of steam in the boiler circuit. Conductivity of pure water is almost zero (1-2 µ Siemens). Even addition of 1 ppm of salt may increase conductivity > 100 µ Siemens. Thus conductivity is an impor tant parameter for the detection of leakages.

45

Typical points in the steam circuit where conductivity should be monitored are . Superheated steam, Drum water, High pressure heaters, Low pressure heaters, Condenser, Plant effluent, D.M. plant, Make-up water to D.M. plant.

Like pH Analyzer, Conductivity is also basic measurement. Both 24V DC loop powered and AC powered option available for this measurement.

These conductivity transmitters can be used with cells with different cell constant. PT-100 temperature sensor in conductivity cell helps to get a compensated reading for conductivity measurement.

3) Silica: The presence of silica in the steam and water circuits of power generation plant is associated with a number of problems both in the super heater and turbine sections. The solubility of silica in stream increases with pressure. The presence of silica in the steam can lead to deposition in superheated tubes and on the turbine blades which may lead to loss of efficiency and turbine blade failure. For proper working of turbines, continuous monitoring of silica is highly recommended. The monitoring of a

nion and mixed bed ion exchanges safeguards and optimizes the operation of demineralization plant. Silica analysis is required at this stage also.

46

Benefits to users :-

To ensure safe operation Silica trend need to be monitored at a multiple location in steam and water circuit. Our multi-channel silica analyzer with inbuilt sequencer is specially designed to take care of this need.

Also Plant chemist is interested in getting graphical trend for each measurement. Silica analyzer is equipped with inbuilt data logger to take care of this need.

We offer smallest cycle time (~9 min) that can help you to know your process better.

We offer Micro-piston Pumping avoiding cross contamination between two different channels.

Automatic two point calibration giving best accuracy.

Locally available reagents and minimum reagent consumption ensures minimum cost of ownership for our analyzer.

There is no need of peristaltic pump tubes/ No need of instrument air.

Auto diagnostic features make our Silica analyzer easy for maintenance

4) Dissolved Oxygen : Within a temperature range of 200...250°C (feed water), dissolved oxygen causes corrosion which may cause puncturing and failures of piping and components respectively. Dissolved oxygen also promotes electrolytic action between dissimilar metals causing corrosion and leakage at joints and gaskets. To minimize corrosion under alkaline operating conditions, mechanical deaeration and chemicals scavenger additives are used to remove the

Dissolved oxygen. An analytical check of process efficiency, therefore, is essential. Dissolved oxygen monitoring is imperative in power stations using neutral or combined operating conditions (pH 7.0-7.5 or 8.0-8.5). The typical points in steam circuit where dissolved oxygen monitoring is required are Deaerator Inlet and outlet

In Boiler & Power Plant dissolved oxygen is removed using deaeration methods. Thus we offer dissolved Oxygen analyzer which:

a) Measures in ppb Range

b) Has better response time.

47

c) Has temperature sensor with NTC for temperature compensation.

d) Has sensors that are directly connected to the transmitter through a detachable cable for an easy removal for main

5) Hydrazine : Hydrazine is used as oxygen scavenger and for maintaining feed water alkalinity to prevent acidic corrosion. It

prevents frothing in the boiler and minimizes deposits on metal surfaces. Hydrazine also helps in

The typical points in steam circuit where hydrazine monitoring is required are. Re-heaters, Economizer inlet and L.P. heaters.

Chiller Package:-

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Chilled water is required where the cooling water available at site is incapable of cooling the sample to the temperature required by the analyzers.

If cooling water temperature exceeds 40 deg.c the sample temperature 45 deg.c which is higher than the temperature of the sample is to be cool at 25 deg.c .we manufacture these in our factors and are the only swas manufactures having this capability.

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RTD( Resistance thermometer detector):-

Resistance thermometers, also called resistance temperature detectors or resistive

thermal devices (RTDs), are temperature sensors that exploit the predictable change inelectrical

resistance of some materials with changing temperature. As they are almost invariably made

of platinum, they are often called platinum resistance thermometers (PRTs). They are slowly

replacing the use of thermocouples in many industrial applications below 600 °C, due to higher

accuracy and repeatability.

General description :-

Carbon resistors are widely available and are very inexpensive. They have very reproducible

results at low temperatures. They are the most reliable form at extremely low temperatures.

They generally do not suffer from hysteresis or strain gauge effects. Carbon resistors have been

employed by researchers for years because of the many advantages associated with them

Film thermometers have a layer of platinum on a substrate; the layer may be extremely thin, perhaps one micrometer. Advantages of this type are relatively low cost and fast response. Such devices have improved performance although the different expansion rates of the substrate There are many categories; carbon resistors, film, and wire-wound types are the most widely used and platinum give "strain gauge" effects and stability problems.

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Wire-wound thermometers can have greater accuracy, especially for wide temperature ranges. The coil diameter provides a compromise between mechanical stability and allowing expansion of the wire to minimize strain and consequential drift.

Coil Elements have largely replaced wire wound elements in the industry. This design allows the wire coil to expand more freely over temperature while still provided the necessary support for the coil. This design is similar to that of a SPRT, the primary standard which ITS-90 is based on, while still providing the durability necessary for an industrial process.

Function:-

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Resistance thermometers are constructed in a number of forms and offer greater

stability, accuracy and repeatability in some cases than thermocouples. While thermocouples use

these beck to generate a voltage, resistance thermometers use electrical resistance and require a

power source to operate. The resistance ideally varies linearly with temperature.

Resistance thermometers are usually made using platinum, because of its linear resistance-

temperature relationship and its chemical inertness. The platinum detecting wire needs to be

kept free of contamination to remain stable. A platinum wire or film is supported on a former in

such a way that it gets minimal differential expansion or other strains from its former, yet is

reasonably resistant to vibration. RTD assemblies made from iron or copper are also used in some

applications.

Commercial platinum grades are produced which exhibit a change of resistance of 0.385 ohms/°C (European Fundamental Interval) The sensor is usually made to have a resistance of 100Ω at 0 °C. This is defined in BS EN 60751:1996 (taken from IEC 60751:1995) . The American Fundamental Interval is 0.392 Ω/°C, based on using a purer grade of platinum than the European standard. The American standard is from the Scientific Apparatus Manufacturers Association (SAMA), who are no longer in this standards field. As a result the "American standard" is hardly the standard even in the US.

Resistance thermometers require a small current to be passed through in order to determine the resistance. This can cause resistive heating, and manufacturers' limits should always be followed along with heat path considerations in design. Care should also be taken to avoid any strains on the resistance thermometer in its application.

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Control valves :-

Control valves are valves used to control conditions such as flow, pressure, temperature, and liquid level by fully or partially opening or closing in response to signals received from controllers that compare a "setpoint" to a "process variable" whose value is provided by sensors that monitor changes in such conditions.[1]

The opening or closing of control valves is done by means of electrical, hydraulic or pneumatic systems. Positoners are used to control the opening or closing of the actuator based on Electric, or Pnuematic Signals. These control signals, traditionally based on 3-15psi (0.2-1.0bar), more common now are 4-20mA signals for industry, 0-10V for HVAC systems, & the introduction of "Smart" systems, HART, Fieldbus Foundation, & Profibus being the more common protocols

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